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>

 

 

 

 


 

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