Date   

Re: Tuner alignment procedure causing thermal drift

 

All good points. My procedure is to warm the gear (RF, distortion meter, SG and tuner) up for about an hour before alignment.
The receivers do get warm as they get tested in a closed cabinet with the case on, so it's a worst case.
But the drift is bad after alignment in some units and it seems to be related to the discriminator coil alignment. But not if the service manual is followed. I was curious why my procedure of setting the tuning meter center using the IF signal pattern instead of interstation noise was a problem.

Obviously the solution in this case is to follow the service manual procedure. I'm curious and like to understand how and why things work the way they do.
--
Mike Miller
PA, USA


Re: Denon TU-800

Radu Bogdan Dicher
 

The other thing I'm typically seeing with polypropylene caps is scarce availability of low voltage types (which would obviously make them smaller). Usually, these come at 450V or higher.
The MK2s can be had at 50V, and those are therefore a really good fit for the typical solid state components. 
Radu. 

On Fri, Mar 13, 2020, 5:24 AM Radu Bogdan Dicher via Groups.Io <vondicher=gmail.com@groups.io> wrote:
John,
Fully with you on this one. For me, they've been a revelation for solid state applications, where I didn't think to be possible to use film for coupling. Until I found these ones. And I've tried a ton other other caps, and spent hours on parts databases searches on most suppliers. 

Polypropylene is just too large a type of cap for most anything solid state. I have a small stock of 0.47uF that are relatively tiny, but that's it. 

Radu. 

On Fri, Mar 13, 2020 at 5:17 AM John Ess <jps7216@...> wrote:
For coupling caps, and where space is an issue, the WIMA MKS2 PET film types are an excellent fit. The material is polyethylene terephthalate, which is a step between polypropylene and polyester, and I doubt that most would be able to hear the difference between these and the MKP caps...at least in a tuner anyway. Another bonus with the PET caps is that they have a smaller footprint, allowing space for upsizing of the value if wanted. That's not so easy to do with polypropylene caps. Changing to plastic caps for coupling should give you an increase in clarity and detail. Also look a little further back upstream from the audio section for electrolytics that are coupling. When you change any of these, give them a few days of running time before forming an opinion.


Re: Tuner alignment procedure causing thermal drift

Herb Ward
 

Mike,

Alps made so many versions of the 4 gang , 1 Dual gate FET and 2 bipolar transistor RF packs back in those days. Some had AGC options, some did not. Some had local oscillator buffers for a prescaler, or AFC / reference for digital readouts, and some were barebones. And then there were the slightly more exotic RF packs built for the more expensive Pioneer models. At one point, Alps made many different RF packs covering a wide range of features and performance
 ( or lack of , lol ) Alignment specifics do vary, so being flexible with respect to doing the usual and customary will save time and frustration.

Rick Price brings up an important point. Ambient temp in the shop can be very different than the ambient temp inside the DUT. Often installing the case/cover is an important element in the best alignment practices with some brands/models. With some brands/models, tuner alignment was only performed near the end of the business day after hours of operation, and test equipment warm up. With other brands , alignment could be performed with little consideration to warm up.

HRW


On Fri, Mar 13, 2020 at 9:59 AM Mike Miller <mikeyis43@...> wrote:
Thanks Herb. Those Pioneers don't have AFC. It took me a while to track down the problem because I thought the problem must be in the RF front end, not the IF & detector section. Still puzzling over this.
--
Mike Miller
PA, USA


Re: Tuner alignment procedure causing thermal drift

Rick Price
 


I don't have that problem with Pioneer Tuners or receivers.  But the "swing" of ambient temperatures (not just sample to sample variation, and/or alignment gear/technician variegation) in a given location could make a difference as well.

If your workshop swings 50 degrees in each direction every day (especially in the Winter) then that could make a discernable difference.  

I live in an area (and my two workshops are insulated, although one is far better shielded than the other) where the temperature swings just aren't that "upper midwest" brutal.

But every alignment textbook (or Service Manual) I own has always said you should let both your alignment test gear (I have two Panasonics the VP-8174A and VP-8175a) and the receiver warm-up for about a half-hour before beginning work.  I also have to go through a tuner several times, letting the tuner "settle" for a period of time before going back and retesting.  The first time is the one that usually reveals any significant "drift" from the original alignment and it gets less and less significant with each "retest".  I'm not a career technician, but I have a pretty healthy streak of "nit-picky-ness"/mild OCD.  After a certain point, close enough has to carry the day.  In my experience, all analog tuners will drift if you subject them to a wide enough temperature differential.

On Friday, March 13, 2020, 09:24:18 AM EDT, Mike Miller <mikeyis43@...> wrote:


Hello all,
Another question for the tuner savvy people out there.
For a while I've been bedeviled by thermal drift in the Pioneer SX-780/880 receiver tuners that I've aligned. Since this affected pretty much all the tuners to varying degrees and seemed to show up after alignment, I suspected something was wrong with my alignment procedure although the numbers I was getting (sensitivity, distortion) were fine. This latest SX-790 however was so bad that I had to track it down - enough drift between cold and warm to walk off station (~ +100kHz).

Here is what I found (the WHAT). Perhaps someone can comment on the WHY.
The problem was in the alignment of the discriminator coil T2. At 98MHz I was using the 400Hz modulated IF pattern on the o'scope to set the tuner to center frequency and then adjusting the lower discriminator coil to center the tuning meter, then adjusting the upper coil core to minimize distortion on my HP334A. It seemed to work fine (tuning meter centered and distortion minimized) when the unit was warm, but often resulted in too much thermal drift.

So I went back and followed the service manual exactly which resulted acceptable levels of thermal drift (< 10kHz). Pioneer's procedure has you center the tuning meter using interstation noise and lower core, set the tuner to 98MHz using the tuning meter (not the IF pattern on the o'scope), minimize distortion using upper core, and repeat as necessary til no changes occur in above steps.

So the question is: What was wrong with my procedure that resulted in such bad levels of thermal drift? How could alignment of the discriminator coil T2 result in this situation?
The Pioneer SX-780/880 uses tuner board AWE-099 with a Pioneer PA-3001A IF chip and quadrature detector.
--
Mike Miller
PA, USA


Re: Tuner alignment procedure causing thermal drift

 

Thanks Herb. Those Pioneers don't have AFC. It took me a while to track down the problem because I thought the problem must be in the RF front end, not the IF & detector section. Still puzzling over this.
--
Mike Miller
PA, USA


Re: Tuner alignment procedure causing thermal drift

Herb Ward
 

Mike,

Some sets have  AFC which in some brands, monitors the detector DC balance and pulls the local oscillator to keep the detector output close to or at 0 volts. There are other ways to do this. In the past I have often found quadrature detectors to be just slightly off. Often the muting or stereo switching suffers as the detector DC balance is monitored by the switching/status logic. With all the different chip sets , and variants within each series, the chip set data sheets are often very useful. Most service manuals simply copy the suggested procedures from the IC data sheets. So, that being said, it is often best to start by doing it their way , before you do it your way. Been there done that...(•‿•)

HRW


On Fri, Mar 13, 2020, 9:24 AM Mike Miller <mikeyis43@...> wrote:
Hello all,
Another question for the tuner savvy people out there.
For a while I've been bedeviled by thermal drift in the Pioneer SX-780/880 receiver tuners that I've aligned. Since this affected pretty much all the tuners to varying degrees and seemed to show up after alignment, I suspected something was wrong with my alignment procedure although the numbers I was getting (sensitivity, distortion) were fine. This latest SX-790 however was so bad that I had to track it down - enough drift between cold and warm to walk off station (~ +100kHz).

Here is what I found (the WHAT). Perhaps someone can comment on the WHY.
The problem was in the alignment of the discriminator coil T2. At 98MHz I was using the 400Hz modulated IF pattern on the o'scope to set the tuner to center frequency and then adjusting the lower discriminator coil to center the tuning meter, then adjusting the upper coil core to minimize distortion on my HP334A. It seemed to work fine (tuning meter centered and distortion minimized) when the unit was warm, but often resulted in too much thermal drift.

So I went back and followed the service manual exactly which resulted acceptable levels of thermal drift (< 10kHz). Pioneer's procedure has you center the tuning meter using interstation noise and lower core, set the tuner to 98MHz using the tuning meter (not the IF pattern on the o'scope), minimize distortion using upper core, and repeat as necessary til no changes occur in above steps.

So the question is: What was wrong with my procedure that resulted in such bad levels of thermal drift? How could alignment of the discriminator coil T2 result in this situation?
The Pioneer SX-780/880 uses tuner board AWE-099 with a Pioneer PA-3001A IF chip and quadrature detector.
--
Mike Miller
PA, USA


Tuner alignment procedure causing thermal drift

 

Hello all,
Another question for the tuner savvy people out there.
For a while I've been bedeviled by thermal drift in the Pioneer SX-780/880 receiver tuners that I've aligned. Since this affected pretty much all the tuners to varying degrees and seemed to show up after alignment, I suspected something was wrong with my alignment procedure although the numbers I was getting (sensitivity, distortion) were fine. This latest SX-790 however was so bad that I had to track it down - enough drift between cold and warm to walk off station (~ +100kHz).

Here is what I found (the WHAT). Perhaps someone can comment on the WHY.
The problem was in the alignment of the discriminator coil T2. At 98MHz I was using the 400Hz modulated IF pattern on the o'scope to set the tuner to center frequency and then adjusting the lower discriminator coil to center the tuning meter, then adjusting the upper coil core to minimize distortion on my HP334A. It seemed to work fine (tuning meter centered and distortion minimized) when the unit was warm, but often resulted in too much thermal drift.

So I went back and followed the service manual exactly which resulted acceptable levels of thermal drift (< 10kHz). Pioneer's procedure has you center the tuning meter using interstation noise and lower core, set the tuner to 98MHz using the tuning meter (not the IF pattern on the o'scope), minimize distortion using upper core, and repeat as necessary til no changes occur in above steps.

So the question is: What was wrong with my procedure that resulted in such bad levels of thermal drift? How could alignment of the discriminator coil T2 result in this situation?
The Pioneer SX-780/880 uses tuner board AWE-099 with a Pioneer PA-3001A IF chip and quadrature detector.
--
Mike Miller
PA, USA


Re: Denon TU-800

Radu Bogdan Dicher
 

John,
Fully with you on this one. For me, they've been a revelation for solid state applications, where I didn't think to be possible to use film for coupling. Until I found these ones. And I've tried a ton other other caps, and spent hours on parts databases searches on most suppliers. 

Polypropylene is just too large a type of cap for most anything solid state. I have a small stock of 0.47uF that are relatively tiny, but that's it. 

Radu. 

On Fri, Mar 13, 2020 at 5:17 AM John Ess <jps7216@...> wrote:
For coupling caps, and where space is an issue, the WIMA MKS2 PET film types are an excellent fit. The material is polyethylene terephthalate, which is a step between polypropylene and polyester, and I doubt that most would be able to hear the difference between these and the MKP caps...at least in a tuner anyway. Another bonus with the PET caps is that they have a smaller footprint, allowing space for upsizing of the value if wanted. That's not so easy to do with polypropylene caps. Changing to plastic caps for coupling should give you an increase in clarity and detail. Also look a little further back upstream from the audio section for electrolytics that are coupling. When you change any of these, give them a few days of running time before forming an opinion.


Re: Denon TU-800

John Ess
 

For coupling caps, and where space is an issue, the WIMA MKS2 PET film types are an excellent fit. The material is polyethylene terephthalate, which is a step between polypropylene and polyester, and I doubt that most would be able to hear the difference between these and the MKP caps...at least in a tuner anyway. Another bonus with the PET caps is that they have a smaller footprint, allowing space for upsizing of the value if wanted. That's not so easy to do with polypropylene caps. Changing to plastic caps for coupling should give you an increase in clarity and detail. Also look a little further back upstream from the audio section for electrolytics that are coupling. When you change any of these, give them a few days of running time before forming an opinion.


Re: I have a Sansui 9900 what can I do for mods?

Tim Britt
 

If. you are referring to Ed Hanlon, sadly, his business is closed.

There’s a list of very good tuner techs in the information posted on the TIC home page at www.fmtunerinfo.com


Re: I have a Sansui 9900 what can I do for mods?

RJ L
 

You might want to check these guys out - they are in Eugene


On Thu, Mar 12, 2020, 3:56 PM John L. Reel <johnlreel@...> wrote:
Hello... My Sansui Tu-9900 finally failed and while I used to be a component level tech, medical issue prevent me from now being able to keep track of progress.
I live near Portland, OR and looking for capable contact information to make repairs.. shipping costs can be an issue for me.  I am also thinking on having my AU-9900 serviced since it is the same age.  I appreciate your insight and help.  John Reel


TU-9900 and AU-9900: Service for TU-9900 near me

John L. Reel <johnlreel@...>
 

I need your seat time help...

My TU-9900 just failed and want a very recommend person to mod and repair this.  I have an AU-9900 that is the same age and if you have service info also, this would be appreciated. I can no longer work on my stereo's and tuner's. 

John


Re: I have a Sansui 9900 what can I do for mods?

johnlreel@...
 

where is ed located?


Re: I have a Sansui 9900 what can I do for mods?

johnlreel@...
 

Hello... My Sansui Tu-9900 finally failed and while I used to be a component level tech, medical issue prevent me from now being able to keep track of progress.
I live near Portland, OR and looking for capable contact information to make repairs.. shipping costs can be an issue for me.  I am also thinking on having my AU-9900 serviced since it is the same age.  I appreciate your insight and help.  John Reel


Re: Denon TU-800

Herb Ward
 

John,

One step at a time. Sounds good. Always a good way to evaluate cause and effect as the saying goes.

HRW

On Thu, Mar 12, 2020, 11:50 AM John Boros <jsjb@...> wrote:

Good morning, Herb &

I really enjoyed reading your response, thoughtful and accurate, I'm sure - thank you! 

Regarding my Denon, I did have it aligned and its functionality is flawless, really; but, I do recognize the SQ issue may extend beyond the audio section; but, as you concluded: take it one step at a time! I'm keeping my fingers crossed & my toes, too!

Thank you!

John 


---------- Original Message ----------
From: Herb Ward <hrward82@...>
Date: March 12, 2020 at 8:24 AM

John,

The 4558 op amp is , as so many have
pointed out , old tech. It is entirely possible that there is some slight internal defect ( sometimes old parts just don't work at their best ) in the original op amp that is causing the less than ideal audio presentation. It may very well be that a modern op amp with their improvement in design and manufacturer will improve things.

There are of course, other possibilities.
Alignment, some minor defect in the decoder IC , a detector that is not quite right. And then there are the "radio" issues. Multipath, cross modulation , RF overload. As many members in our forum have observed, a tuner is a collection of many many engineering decisions. Sometimes the bean counters are to blame, sometimes the company making the chipsets don't get it exactly right. Sometimes, too many poor design decisions or compromises by the tuner engineer adds up to a combination of quirks that creates a meh tuner. This is why each of us has our picks and pans. Your radio environment is likely different than mine. The MR78 is a perfect example of a design for a specific need.

For me , one of the really interesting things about Electronics is that there are seemingly a dozen different ways of designing a circuit, that all provide the same function. Each circuit has its pros and cons. Despite what the meter reader says, we have often found that a circuit that measures the same , does not sound the same. I have lots of meters , but at the same time, I know that for every standardized measurement currently used, I wonder if there will be new meters and new measurements in the coming years.

Take it one step at a time and enjoy the discovery of this does that, or that does nothing. If the new parts are installed correctly , you will not need test equipment to evaluate the changes. Just sit down and listen. It's all part of our hobby/careers/pastimes.

HRW

On Wed, Mar 11, 2020, 11:18 PM John Boros < jsjb@...> wrote:
My mistake, MC2105 = 1975

On Mar 11, 2020, at 10:52 PM, John Boros < jsjb@...> wrote:


Herb,

My Denon’s flaws are only in its lack of transparency, while its sound is not smooth, borderline noisy. I say this by comparison with my Sansui tu-9900, which has been upgraded. I have no test equipment, beyond a multimeter and so I decided to start only with the audio section, in the hope of improving SQ. As the resistors are in the signal path and as there are only six, plus the two in the feedback, I had hoped that by changing these, along with the two coupling, two decoupling caps and IC, I’d yield some improvement. It is an educated guess, based also on the guidance of the good people within this group.

As far as the physical condition of these handful of resistors, I don’t see a single issue. Replacement resistors would result in tighter tolerances, but, whether or not I’d hear the difference, is an unknown at this point.

I’m all for just replacing the IC and four caps, if the likelihood of changing the resistors would have little affect! Is it prudent to change them, though, preventative maintenance?

Thanks,

John

P.s. I do have a mint MR67 (1968), married to an MC2105 (1985)



On Mar 11, 2020, at 9:40 PM, Herb Ward < hrward82@...> wrote:


John,

One of the interesting aspects of the TU800 design is that there are very few components in the audio signal path between the output (s) of the stereo decoder IC , and the RCA Jack's. I count 6 resistors in the signal path and the 2 resistors in the op amps feedback loop. I am not including the signal path between the detector and the MPX decoder, but again, the devices in the pre MPX decoder signal path are few, and one wonders what is in the post detection filter box ( T301 ) , and also in the post MPX decoder filter box ( T302, T303 ) So my thinking is change IC303 , C331, and C332. There is also C303 which is a BP, and a good spot for the Green Nichicon BP Muse caps . So I have to ask , what is your objective with the resistor changes?

HRW

On Wed, Mar 11, 2020, 8:11 PM John Boros < jsjb@...> wrote:
Herb & Peter,

Thank you for your sage and experienced advice.

Herb, just to be absolutely clear, are you saying that unless the resistors are running hot, I shouldn’t change them at all? I believe John said the originals are 1/4 watt, carbon film.

Thanks,

John

On Mar 11, 2020, at 7:07 PM, dombro123 via Groups.Io <irote= verizon.net@groups.io> wrote:


Brilliant, thanks! Words to live by...............


-----Original Message-----
From: Herb Ward < hrward82@...>
To: FMtuners < FMtuners@groups.io>
Sent: Wed, Mar 11, 2020 3:42 pm
Subject: Re: [FMtuners] Denon TU-800

John ,

From my perspective, 49 years of audio service now, the only resistors in your tuner that might need to be upsized, are in the power supply. If nothing runs hot then do nothing . As Rick and Radu have suggested, Dale RN55 1% will be more than adequate wattage wise, and in a few places, the tight tolerance resistors may make a measurable difference in gain, noise, and filter response, but I suspect you would have to spend mucho $$$ on test equipment to actually measure the changes that might occurr. The original 1/4 and 1/2 watt 5% carbon films generally hold up well unless run on the hot side. Be thankful you do not have a MR71 where many carbon comp resistors drift up in value , and can often be 30 to 40 percent out of tolerance. I just serviced a pair of McIntosh MC60's that were at a well known " recapper " with a fancy web site. He missed all the out of tolerance carbon comp resistors, and the amps did not meet specs for THD even with all new tubes. He also did not change out the selenium bias rectifier, putting a new set of expensive output tubes at risk. I urge you not to purchase snake oil slathered boutique parts. You have received excellent advise from forum members , and the TU800 is a well designed unit made in the days when RF engineers could and did make improvements to Major Armstrong's
radio.

HRW

On Wed, Mar 11, 2020, 5:44 PM John Boros < jsjb@...> wrote:
Hello John &

Yes, you are correct, this is what I’ve been trying to do, as Panasonic lists a poly with 7.5 mm wide leads, but, no one stocks them.

Thank you for sharing the images, given I can now see how you resolved the issue and have placed my order for all four capacitors with Mouser.

And, thanks for the heads up on the ic socket, ordered as well, along with both opamps, just in case.

Lastly, is it a bad idea to double the wattage of all the resistors - I’ve done this with my headphone amp, without issue, now, for .... years! I’ve always thought the danger was in the other direction, lowering wattage?

Thank you for your help and guidance, for everyone’s guidance, is very much appreciated! Now all I need hope is that I don’t screw it all up! lol

John

On Mar 11, 2020, at 12:04 AM, John Carpanini < jacarp@...> wrote:


[Edited Message Follows]
Hi John, - Correction - Its late & I screwed up the link jc
I get the impression that you are looking for a PolyPro that will drop directly into the existing board board holes. If I'm incorrect, then disregard the rest of this missive. If you are then let me say that It'll never happen, miniature or not. The physical size of a film cap is probably 10X the size of an equivalent lytic. You have to do some lead forming to get them in there. That's why I try to find MPP with straight leads, typically they are longer than the formed lead units and can be formed/bent to fit as needed. A attached a pic of the TU800 audio section. Those big orange things are the film caps and if you look closely you can see where the leads were bent to fit into the board. If this is not acceptable then start looking at the lytics for this application

Digikey has these: Nichicon 2.2 MPP

As for the OpAmp the 2132/34 will absolutely work, the2604 I'm about 90% comfortable with. What I'm suggesting is that a socket be installed and you can swap OpAmps to you hearts content and find one you like. A lot of folks like the LM4562, just another option. Herbs warning/concern re: the newest , fastest ICs is correct, those I've listed are solid performers, running single sided in this circuit.

Regards,
JohnC
<Audio.JPG>

 

 

 

 


 


Re: Denon TU-800

John Boros
 

Good morning, Herb &

I really enjoyed reading your response, thoughtful and accurate, I'm sure - thank you! 

Regarding my Denon, I did have it aligned and its functionality is flawless, really; but, I do recognize the SQ issue may extend beyond the audio section; but, as you concluded: take it one step at a time! I'm keeping my fingers crossed & my toes, too!

Thank you!

John 


---------- Original Message ----------
From: Herb Ward <hrward82@...>
Date: March 12, 2020 at 8:24 AM

John,

The 4558 op amp is , as so many have
pointed out , old tech. It is entirely possible that there is some slight internal defect ( sometimes old parts just don't work at their best ) in the original op amp that is causing the less than ideal audio presentation. It may very well be that a modern op amp with their improvement in design and manufacturer will improve things.

There are of course, other possibilities.
Alignment, some minor defect in the decoder IC , a detector that is not quite right. And then there are the "radio" issues. Multipath, cross modulation , RF overload. As many members in our forum have observed, a tuner is a collection of many many engineering decisions. Sometimes the bean counters are to blame, sometimes the company making the chipsets don't get it exactly right. Sometimes, too many poor design decisions or compromises by the tuner engineer adds up to a combination of quirks that creates a meh tuner. This is why each of us has our picks and pans. Your radio environment is likely different than mine. The MR78 is a perfect example of a design for a specific need.

For me , one of the really interesting things about Electronics is that there are seemingly a dozen different ways of designing a circuit, that all provide the same function. Each circuit has its pros and cons. Despite what the meter reader says, we have often found that a circuit that measures the same , does not sound the same. I have lots of meters , but at the same time, I know that for every standardized measurement currently used, I wonder if there will be new meters and new measurements in the coming years.

Take it one step at a time and enjoy the discovery of this does that, or that does nothing. If the new parts are installed correctly , you will not need test equipment to evaluate the changes. Just sit down and listen. It's all part of our hobby/careers/pastimes.

HRW

On Wed, Mar 11, 2020, 11:18 PM John Boros < jsjb@...> wrote:
My mistake, MC2105 = 1975

On Mar 11, 2020, at 10:52 PM, John Boros < jsjb@...> wrote:


Herb,

My Denon’s flaws are only in its lack of transparency, while its sound is not smooth, borderline noisy. I say this by comparison with my Sansui tu-9900, which has been upgraded. I have no test equipment, beyond a multimeter and so I decided to start only with the audio section, in the hope of improving SQ. As the resistors are in the signal path and as there are only six, plus the two in the feedback, I had hoped that by changing these, along with the two coupling, two decoupling caps and IC, I’d yield some improvement. It is an educated guess, based also on the guidance of the good people within this group.

As far as the physical condition of these handful of resistors, I don’t see a single issue. Replacement resistors would result in tighter tolerances, but, whether or not I’d hear the difference, is an unknown at this point.

I’m all for just replacing the IC and four caps, if the likelihood of changing the resistors would have little affect! Is it prudent to change them, though, preventative maintenance?

Thanks,

John

P.s. I do have a mint MR67 (1968), married to an MC2105 (1985)



On Mar 11, 2020, at 9:40 PM, Herb Ward < hrward82@...> wrote:


John,

One of the interesting aspects of the TU800 design is that there are very few components in the audio signal path between the output (s) of the stereo decoder IC , and the RCA Jack's. I count 6 resistors in the signal path and the 2 resistors in the op amps feedback loop. I am not including the signal path between the detector and the MPX decoder, but again, the devices in the pre MPX decoder signal path are few, and one wonders what is in the post detection filter box ( T301 ) , and also in the post MPX decoder filter box ( T302, T303 ) So my thinking is change IC303 , C331, and C332. There is also C303 which is a BP, and a good spot for the Green Nichicon BP Muse caps . So I have to ask , what is your objective with the resistor changes?

HRW

On Wed, Mar 11, 2020, 8:11 PM John Boros < jsjb@...> wrote:
Herb & Peter,

Thank you for your sage and experienced advice.

Herb, just to be absolutely clear, are you saying that unless the resistors are running hot, I shouldn’t change them at all? I believe John said the originals are 1/4 watt, carbon film.

Thanks,

John

On Mar 11, 2020, at 7:07 PM, dombro123 via Groups.Io <irote= verizon.net@groups.io> wrote:


Brilliant, thanks! Words to live by...............


-----Original Message-----
From: Herb Ward < hrward82@...>
To: FMtuners < FMtuners@groups.io>
Sent: Wed, Mar 11, 2020 3:42 pm
Subject: Re: [FMtuners] Denon TU-800

John ,

From my perspective, 49 years of audio service now, the only resistors in your tuner that might need to be upsized, are in the power supply. If nothing runs hot then do nothing . As Rick and Radu have suggested, Dale RN55 1% will be more than adequate wattage wise, and in a few places, the tight tolerance resistors may make a measurable difference in gain, noise, and filter response, but I suspect you would have to spend mucho $$$ on test equipment to actually measure the changes that might occurr. The original 1/4 and 1/2 watt 5% carbon films generally hold up well unless run on the hot side. Be thankful you do not have a MR71 where many carbon comp resistors drift up in value , and can often be 30 to 40 percent out of tolerance. I just serviced a pair of McIntosh MC60's that were at a well known " recapper " with a fancy web site. He missed all the out of tolerance carbon comp resistors, and the amps did not meet specs for THD even with all new tubes. He also did not change out the selenium bias rectifier, putting a new set of expensive output tubes at risk. I urge you not to purchase snake oil slathered boutique parts. You have received excellent advise from forum members , and the TU800 is a well designed unit made in the days when RF engineers could and did make improvements to Major Armstrong's
radio.

HRW

On Wed, Mar 11, 2020, 5:44 PM John Boros < jsjb@...> wrote:
Hello John &

Yes, you are correct, this is what I’ve been trying to do, as Panasonic lists a poly with 7.5 mm wide leads, but, no one stocks them.

Thank you for sharing the images, given I can now see how you resolved the issue and have placed my order for all four capacitors with Mouser.

And, thanks for the heads up on the ic socket, ordered as well, along with both opamps, just in case.

Lastly, is it a bad idea to double the wattage of all the resistors - I’ve done this with my headphone amp, without issue, now, for .... years! I’ve always thought the danger was in the other direction, lowering wattage?

Thank you for your help and guidance, for everyone’s guidance, is very much appreciated! Now all I need hope is that I don’t screw it all up! lol

John

On Mar 11, 2020, at 12:04 AM, John Carpanini < jacarp@...> wrote:


[Edited Message Follows]
Hi John, - Correction - Its late & I screwed up the link jc
I get the impression that you are looking for a PolyPro that will drop directly into the existing board board holes. If I'm incorrect, then disregard the rest of this missive. If you are then let me say that It'll never happen, miniature or not. The physical size of a film cap is probably 10X the size of an equivalent lytic. You have to do some lead forming to get them in there. That's why I try to find MPP with straight leads, typically they are longer than the formed lead units and can be formed/bent to fit as needed. A attached a pic of the TU800 audio section. Those big orange things are the film caps and if you look closely you can see where the leads were bent to fit into the board. If this is not acceptable then start looking at the lytics for this application

Digikey has these: Nichicon 2.2 MPP

As for the OpAmp the 2132/34 will absolutely work, the2604 I'm about 90% comfortable with. What I'm suggesting is that a socket be installed and you can swap OpAmps to you hearts content and find one you like. A lot of folks like the LM4562, just another option. Herbs warning/concern re: the newest , fastest ICs is correct, those I've listed are solid performers, running single sided in this circuit.

Regards,
JohnC
<Audio.JPG>

 

 

 

 


 


Re: Need help with Mitsubishi DA-F20

newaag
 

I will go ahead and order new oscillator parts and install, as I don't consider this job done. Why? 

I removed the adjustable cap for the 10 MHz oscillator, and it measured 10 pf. It is supposed to be 20 pF. 
This is probably right on the edge of even working as an oscillator. It is pulling the crystal about 300 PM higher.

Normally, you can adjust the load cap for a crystal +/- 100 PPM, at best, that is all designers recommend. At some point, it just stops working. At the edge of oscillation / not working, stability and jitter get much worse.

So in this case, it makes sense to simply replace the crystal, and load cap, bring them back to stock values with new parts. For the load cap, it need a 20 pf C0G spec part. For the oscillator crystal, a decent +/- 30 ppm crystal (or better). They are so cheap, it's best to order 10 of each, plus caps +/- 2 pf form 20, to fit the best combination.
The other option is to install a tightly specified TCXO oscillator, and eliminate the on-board one. This is more work, but for those with the chops, not too hard. Most of these are now CMOS running at 3.3V, which means it needs to interface with old tech TTL digital parts. Not sure if this would be a problem or not. So to keep it simple,going with parts replacment as stock. But you can also buy TTL 5V units, but they are either really expensive ($50+) or not TCXO, just can oscillators, and not tightly spec'ed, with no adjustment.

Some may wonder why this problem happened? Was it like this since new?
Probably not. Just like people, these crystals, depending on how they are made, "slowly age" and drift over time. Most data sheets say 5 PPM / year. Well this one is 40 years old!
If it was off +/- 100 PPM to begin with (not unusual), it could be normal aging, and alas, in 2020, off by almost 300 PPM.
Which is why I am documenting all this stuff. There may be other decent tuner units out there (digital tuned) that could use this cheap fix. This sort of instruction (like cleaning gangs) will NOT be in the service manual. :-)
Bob 
To be continued...

 


Re: Denon TU-800

Herb Ward
 

John,

The 4558 op amp is , as so many have
pointed out , old tech. It is entirely possible that there is some slight internal defect ( sometimes old parts just don't work at their best ) in the original op amp that is causing the less than ideal audio presentation. It may very well be that a modern op amp with their improvement in design and manufacturer will improve things. 

There are of course, other possibilities.
Alignment, some minor defect in the decoder IC , a detector that is not quite right. And then there are the "radio" issues. Multipath, cross modulation , RF overload. As many members in our forum have observed, a tuner is a collection of many many engineering decisions. Sometimes the bean counters are to blame, sometimes the company making the chipsets don't get it exactly right. Sometimes, too many poor design decisions or compromises by the tuner engineer adds up to a combination of quirks that creates a meh tuner. This is why each of us has our picks and pans. Your radio environment is likely different than mine. The MR78 is a perfect example of a design for a specific need.

 For me , one of the really interesting things about Electronics is that there are seemingly a dozen different ways of designing a circuit, that all provide the same function. Each circuit has its pros and cons. Despite what the meter reader says, we have often found that a circuit that measures the same , does not sound the same. I have lots of meters , but at the same time, I know that for every standardized measurement currently used, I wonder if there will be new meters and new measurements in the coming years. 

Take it one step at a time and enjoy the discovery of this does that, or that does nothing. If the new parts are installed correctly , you will not need test equipment to evaluate the changes. Just sit down and listen.  It's all part of our hobby/careers/pastimes.

HRW

On Wed, Mar 11, 2020, 11:18 PM John Boros <jsjb@...> wrote:
My mistake, MC2105 = 1975 

On Mar 11, 2020, at 10:52 PM, John Boros <jsjb@...> wrote:


Herb,

My Denon’s flaws are only in its lack of transparency, while its sound is not smooth, borderline noisy. I say this by comparison with my Sansui tu-9900, which has been upgraded. I have no test equipment, beyond a multimeter and so I decided to start only with the audio section, in the hope of improving SQ. As the resistors are in the signal path and as there are only six, plus the two in the feedback, I had hoped that by changing these, along with the two coupling, two decoupling caps and IC, I’d yield some improvement. It is an educated guess, based also on the guidance of the good people within this group.

As far as the physical condition of these handful of resistors, I don’t see a single issue. Replacement resistors would result in tighter tolerances, but, whether or not I’d hear the difference, is an unknown at this point.

I’m all for just replacing the IC and four caps, if the likelihood of changing the resistors would have little affect! Is it prudent to change them, though, preventative maintenance?

Thanks,

John

P.s. I do have a mint MR67 (1968), married to an MC2105 (1985)



On Mar 11, 2020, at 9:40 PM, Herb Ward <hrward82@...> wrote:


John,

One of the interesting aspects of the TU800 design is that there are very few components in the audio signal path between the output (s) of the stereo decoder IC , and the RCA Jack's. I count 6 resistors in the signal path and the 2 resistors in the op amps feedback loop. I am not including the signal path between the detector and the MPX decoder, but again, the devices in the pre MPX decoder signal path are few, and one wonders what is in the post detection filter box ( T301 ) , and also in the post MPX decoder filter box ( T302, T303 )  So my thinking is change IC303 , C331, and C332. There is also C303 which is a BP, and a good spot for the Green Nichicon BP Muse caps . So I have to ask , what is your objective with the resistor changes?

HRW

On Wed, Mar 11, 2020, 8:11 PM John Boros <jsjb@...> wrote:
Herb & Peter,

Thank you for your sage and experienced advice.

Herb, just to be absolutely clear, are you saying that unless the resistors are running hot, I shouldn’t change them at all? I believe John said the originals are 1/4 watt, carbon film. 

Thanks,

John

On Mar 11, 2020, at 7:07 PM, dombro123 via Groups.Io <irote=verizon.net@groups.io> wrote:


Brilliant, thanks!  Words to live by...............


-----Original Message-----
From: Herb Ward <hrward82@...>
To: FMtuners <FMtuners@groups.io>
Sent: Wed, Mar 11, 2020 3:42 pm
Subject: Re: [FMtuners] Denon TU-800

John ,

From my perspective, 49 years of audio service now, the only resistors in your tuner that might need to be upsized, are in the power supply. If nothing runs hot then do nothing .  As Rick and Radu have suggested, Dale RN55 1% will be more than adequate wattage wise, and in a few places, the tight tolerance resistors may make a measurable difference in gain, noise, and filter response, but I suspect you would have to spend mucho $$$ on test equipment to actually measure the changes that might occurr. The original 1/4 and 1/2 watt 5% carbon films generally hold up well unless run on the hot side. Be thankful you do not have a MR71 where many carbon comp resistors drift up in value , and can often be 30 to 40 percent out of tolerance. I just serviced a pair of McIntosh MC60's that were at a well known " recapper " with a fancy web site. He missed all the out of tolerance carbon comp resistors, and the amps did not meet specs for THD even with all new tubes. He also did not change out the selenium bias rectifier, putting a new set of expensive output tubes at risk. I urge you not to purchase snake oil slathered boutique parts. You have received excellent advise from forum members , and the TU800 is a well designed unit made in the days when RF engineers could and did make improvements to Major Armstrong's
radio.

HRW

On Wed, Mar 11, 2020, 5:44 PM John Boros <jsjb@...> wrote:
Hello John &

Yes, you are correct, this is what I’ve been trying to do, as Panasonic lists a poly with 7.5 mm wide leads, but, no one stocks them. 

Thank you for sharing the images, given I can now see how you resolved the issue and have placed my order for all four capacitors with Mouser.

And, thanks for the heads up on the ic socket, ordered as well, along with both opamps, just in case.

Lastly, is it a bad idea to double the wattage of all the resistors  - I’ve done this with my headphone amp, without issue, now, for .... years! I’ve always thought the danger was in the other direction, lowering wattage?

Thank you for your help and guidance, for everyone’s guidance, is very much appreciated! Now all I need hope is that I don’t screw it all up! lol

John

On Mar 11, 2020, at 12:04 AM, John Carpanini <jacarp@...> wrote:


[Edited Message Follows]
Hi John, - Correction - Its late & I screwed up the link  jc
I get the impression that you are looking for a PolyPro that will drop directly into the existing board board holes. If I'm incorrect, then disregard the rest of this missive.  If you are then let me say that It'll never happen, miniature or not.  The physical size of a film cap is probably 10X the size of an equivalent lytic.  You have to do some lead forming to get them in there.  That's why I try to find MPP with straight leads, typically they are longer than the formed lead units and can be formed/bent to fit as needed.  A attached a pic of the TU800 audio section.  Those big orange things are the film caps and if you look closely you can see where the leads were bent to fit into the board.  If this is not acceptable then start looking at the lytics for this application 

Digikey has these: Nichicon 2.2 MPP

As for the OpAmp the 2132/34 will absolutely work, the2604 I'm about 90% comfortable with.  What I'm suggesting is that a socket be installed and you can swap OpAmps to you hearts content and find one you like. A lot of folks like the LM4562, just another option. Herbs warning/concern re: the newest , fastest ICs is correct, those I've listed are solid performers, running single sided in this circuit.

Regards,
JohnC
<Audio.JPG>


Re: Nikko Preamps, etc.

Radu Bogdan Dicher
 

Thank you both.

Interestingly enough, it mirrors part of the modification I've made to the Triode Electronics board I have in my Dynaco MKIII monoblocks - namely, in my case, a cascode MOSFET CCS far more linearly loading the long tail pair pre-driver to the PP finals. It's been so long since I put this together it completely slipped my mind (in all honesty, I need to spend more time reading the schematic to get all this - thank you Bob for expanding on the details of the circuit). I enclose the schematic  for my monoblocks for reference. 

If anyone can point to (a source of) Marsh' article in AA, I'd love to see it. I'll try to locate it too. 

I guess then the pot is to be adjusted to null the DC balance on the PP as seen at the output of the stage - thank you Herb for clarity. I'll measure what DC I see on there first, to calibrate the effort.

Thank you,
Radu. 

On Wed, Mar 11, 2020 at 2:49 PM newaag via Groups.Io <newaag=yahoo.com@groups.io> wrote:
Yes, Herb is right, that is a common amplifier adjustment as well for 0 DC at the output.
Those pots are for adjusting current from the current source, to balance the long tailed pair, but also correct for other circuit imbalance from downstream stages. The long tailed pair circuit itself should already be pretty balanced, as it uses matched-pair-in-one-die JFETS (2SK68A) and cascode transistors (2SC1775).

This is a really premium preamp phono gain stage design, as it uses both a current source on the tail (versus a resistor) and cascode circuit on top. It may look like a current mirror on first glance, frequently used there, but it's cascode, some feel the best architecture you can have there for audio stages used w/ feedback.
Marsh detailed the cascode circuit advantages in Audio Amateur way back in the old days, with plenty of
example circuits and measurements.    
More background here
https://www.electronics-notes.com/articles/analogue_circuits/transistor/long-tailed-pair-circuit.php
https://en.wikipedia.org/wiki/Cascode

from the wiki on cascode
"The major advantage of this circuit arrangement ... the upper transistor permits the lower FET to operate with minimal negative (Miller) feedback, improving its bandwidth."
Bob


Re: Denon TU-800

John Boros
 

My mistake, MC2105 = 1975 

On Mar 11, 2020, at 10:52 PM, John Boros <jsjb@...> wrote:


Herb,

My Denon’s flaws are only in its lack of transparency, while its sound is not smooth, borderline noisy. I say this by comparison with my Sansui tu-9900, which has been upgraded. I have no test equipment, beyond a multimeter and so I decided to start only with the audio section, in the hope of improving SQ. As the resistors are in the signal path and as there are only six, plus the two in the feedback, I had hoped that by changing these, along with the two coupling, two decoupling caps and IC, I’d yield some improvement. It is an educated guess, based also on the guidance of the good people within this group.

As far as the physical condition of these handful of resistors, I don’t see a single issue. Replacement resistors would result in tighter tolerances, but, whether or not I’d hear the difference, is an unknown at this point.

I’m all for just replacing the IC and four caps, if the likelihood of changing the resistors would have little affect! Is it prudent to change them, though, preventative maintenance?

Thanks,

John

P.s. I do have a mint MR67 (1968), married to an MC2105 (1985)



On Mar 11, 2020, at 9:40 PM, Herb Ward <hrward82@...> wrote:


John,

One of the interesting aspects of the TU800 design is that there are very few components in the audio signal path between the output (s) of the stereo decoder IC , and the RCA Jack's. I count 6 resistors in the signal path and the 2 resistors in the op amps feedback loop. I am not including the signal path between the detector and the MPX decoder, but again, the devices in the pre MPX decoder signal path are few, and one wonders what is in the post detection filter box ( T301 ) , and also in the post MPX decoder filter box ( T302, T303 )  So my thinking is change IC303 , C331, and C332. There is also C303 which is a BP, and a good spot for the Green Nichicon BP Muse caps . So I have to ask , what is your objective with the resistor changes?

HRW

On Wed, Mar 11, 2020, 8:11 PM John Boros <jsjb@...> wrote:
Herb & Peter,

Thank you for your sage and experienced advice.

Herb, just to be absolutely clear, are you saying that unless the resistors are running hot, I shouldn’t change them at all? I believe John said the originals are 1/4 watt, carbon film. 

Thanks,

John

On Mar 11, 2020, at 7:07 PM, dombro123 via Groups.Io <irote=verizon.net@groups.io> wrote:


Brilliant, thanks!  Words to live by...............


-----Original Message-----
From: Herb Ward <hrward82@...>
To: FMtuners <FMtuners@groups.io>
Sent: Wed, Mar 11, 2020 3:42 pm
Subject: Re: [FMtuners] Denon TU-800

John ,

From my perspective, 49 years of audio service now, the only resistors in your tuner that might need to be upsized, are in the power supply. If nothing runs hot then do nothing .  As Rick and Radu have suggested, Dale RN55 1% will be more than adequate wattage wise, and in a few places, the tight tolerance resistors may make a measurable difference in gain, noise, and filter response, but I suspect you would have to spend mucho $$$ on test equipment to actually measure the changes that might occurr. The original 1/4 and 1/2 watt 5% carbon films generally hold up well unless run on the hot side. Be thankful you do not have a MR71 where many carbon comp resistors drift up in value , and can often be 30 to 40 percent out of tolerance. I just serviced a pair of McIntosh MC60's that were at a well known " recapper " with a fancy web site. He missed all the out of tolerance carbon comp resistors, and the amps did not meet specs for THD even with all new tubes. He also did not change out the selenium bias rectifier, putting a new set of expensive output tubes at risk. I urge you not to purchase snake oil slathered boutique parts. You have received excellent advise from forum members , and the TU800 is a well designed unit made in the days when RF engineers could and did make improvements to Major Armstrong's
radio.

HRW

On Wed, Mar 11, 2020, 5:44 PM John Boros <jsjb@...> wrote:
Hello John &

Yes, you are correct, this is what I’ve been trying to do, as Panasonic lists a poly with 7.5 mm wide leads, but, no one stocks them. 

Thank you for sharing the images, given I can now see how you resolved the issue and have placed my order for all four capacitors with Mouser.

And, thanks for the heads up on the ic socket, ordered as well, along with both opamps, just in case.

Lastly, is it a bad idea to double the wattage of all the resistors  - I’ve done this with my headphone amp, without issue, now, for .... years! I’ve always thought the danger was in the other direction, lowering wattage?

Thank you for your help and guidance, for everyone’s guidance, is very much appreciated! Now all I need hope is that I don’t screw it all up! lol

John

On Mar 11, 2020, at 12:04 AM, John Carpanini <jacarp@...> wrote:


[Edited Message Follows]
Hi John, - Correction - Its late & I screwed up the link  jc
I get the impression that you are looking for a PolyPro that will drop directly into the existing board board holes. If I'm incorrect, then disregard the rest of this missive.  If you are then let me say that It'll never happen, miniature or not.  The physical size of a film cap is probably 10X the size of an equivalent lytic.  You have to do some lead forming to get them in there.  That's why I try to find MPP with straight leads, typically they are longer than the formed lead units and can be formed/bent to fit as needed.  A attached a pic of the TU800 audio section.  Those big orange things are the film caps and if you look closely you can see where the leads were bent to fit into the board.  If this is not acceptable then start looking at the lytics for this application 

Digikey has these: Nichicon 2.2 MPP

As for the OpAmp the 2132/34 will absolutely work, the2604 I'm about 90% comfortable with.  What I'm suggesting is that a socket be installed and you can swap OpAmps to you hearts content and find one you like. A lot of folks like the LM4562, just another option. Herbs warning/concern re: the newest , fastest ICs is correct, those I've listed are solid performers, running single sided in this circuit.

Regards,
JohnC
<Audio.JPG>

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