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Re: Mitsubishi DAF76 FM Tuner #photo-notice

newaag
 

I see there are folks selling the DA-F76 service manual, but agree, there is not much info on it otherwise.
If you want to open it up and take some detailed, pictures, it could add to the discussion.
Many of these later "no frills" digital units were mostly an "empty box" with a small board inside.
Bob


Re: IF Alignment Sweep general questions

newaag
 

On Thu, Jul 2, 2020 at 07:07 PM, Mike Miller wrote:
I'll pull the detector smoothing cap another time and see how the IF response looks post limiter coming off the detector diodes.
Yep, now you got it - these look good. Don't worry about the exact IF frequency here - nowhere is it written in stone that it has to be exactly 10.700 MHz. Unlike digital tuners with a crystal time base, analog tuners are fine running a 1% higher or lower than 10.700. 
You may find if you try and change it, it will create a lot of work, and possibly mess up an otherwise already "working fine" unit. That is, for this model, re-aligning the whole tuner to work at 10.70 will not make anything better. The most important thing is that the IF, RF and detector sections are in sync at the exact same IF frequency. 

What EJP is suggesting, I believe, is that you tap the DC from the AGC to drive the scope Y input. So you would likely leave the cap in place, unless it is so big the time constant makes the AGC DC output response too slow for the sweep. If you do this successfully, you will not have an envelope of the waveform, but will show the rectified absolute value of the envelope, which will look more like a typical filter plot. This is what the old sweep generator probes did - rectify the 10.7 MHz, because in the old days (50's-60's)  not many people had scopes that could show 10.7 MHz.
Occasionally, for some tube tuners, I have used the factory service manual, or Sam's recommendation for where to probe, and this sweep filter plot is inverted, so you can get (only) a negative peak amplitude plot as well. 
Bob 
   


Re: MY ACCUPHASE T 100

Victor Dascalescu
 

I understand the importance of that fine adjustment and I don't give up in searching a reliable technician. It wars twice because, if I'll find, I shall adjust also the Fisher MPX 100 that accompany my Leak TL3. I think it will be quite an experience.


Re: IF Alignment Sweep general questions

 

Thanks EJP. I got the IF sweep working.

I input the signal at the input of the IF board (the base of the first amp stage Q 301). I probed Y at the input to the limiter, the base of the first limiter transistor Q304, to avoid the limiter action. Bear in mind that this XY is of the RF signal before the detector diodes, so it is ~10MHz AC signal envelope. X is the ramp in to my RF sweep.
I'll pull the detector smoothing cap another time and see how the IF response looks post limiter coming off the detector diodes.

As I mentioned before, I only use the digital scope for XY patterns to take screenshots Things look much prettier on my analog Tek2235. To work around the limited sweep range of my HP8640B RF generator I manually walked the IF signal through center on the scope at 10.5, 10.6, 10.7. 10.8 & 10.9 MHz.  The sweep width on the scope is set at about 160kHz (+/-80kHz). Tedious, but working with what I have.

The "bad news" is the IF peak looks to be at about 10.63 MHz. Unless my 10x 200MHz scope probe is loading the circuit and pulling it off. I think I'll check for that somehow before I start aligning the IF strip and make more work for myself.
I should probably pick up one of those active RF probes that Bob was talking about earlier.


--
Mike Miller
PA, USA


Mitsubishi DAF76 FM Tuner #photo-notice

cigarband@...
 

Or might be Mitsubishi DA-F76

 I have recently purchased at a good price this tuner on ebay.  I cannot find an owners manual or any documentation
regarding this tuner. It works fine, i have figured out how to program its presets but that's about all. I would be most greatful
if anyone having information about this device could refer me to where i can locate an owners manual PDF  of some kind.

I think it may  possibly been on the market  under other brand names but i can't find any reference to that on the web.


Re: MY ACCUPHASE T 100

Herb Ward
 

Victor,

The T-100 uses the Motorola mc1310 decoder as i recall. The Accuphase implementation of this very common MPX decoder IC is very well done. Past experience has shown that the typical T-100 stereo decoder was very close to being right on even after decades of use  Accuphase used high quality parts in the MPX decoders VCO , and this was a great decision to make. My comment was really about the center tune and distortion adjustments to the detector. If you are finding that ideal center tune ( on a weak signal ) , and max signal strength coincides at the same time, chances are pretty good that the detector in your unit is pretty close to being ideal. 

HRW

On Thu, Jul 2, 2020 at 1:32 PM Victor Dascalescu via groups.io <victordascalescu54=yahoo.com@groups.io> wrote:
Hi Herb,
Nice explanation, a real lesson for me. Unfortunately, there is no one around me to have the gear and knowledge to make the alignment of the decoder. For the beginning, I shall change the Q5/6/7 on each audio board and I shall listen to the tuner as it is. Latter I shall decide if its wars changing one step at the time the capacitors....or not.
Now I just finished a nice session of listening to classical music on a real-time transmission. It was quite an experience, a nice one, with full balanced sound, depth and dynamics...was amazing.


Re: MY ACCUPHASE T 100

Victor Dascalescu
 

Hi Herb,
Nice explanation, a real lesson for me. Unfortunately, there is no one around me to have the gear and knowledge to make the alignment of the decoder. For the beginning, I shall change the Q5/6/7 on each audio board and I shall listen to the tuner as it is. Latter I shall decide if its wars changing one step at the time the capacitors....or not.
Now I just finished a nice session of listening to classical music on a real-time transmission. It was quite an experience, a nice one, with full balanced sound, depth and dynamics...was amazing.


Re: IF Alignment Sweep general questions

 

Any of you fine fellas have any experience with the Wavetek 193 sweep generator? I see one or two on eBay.
Or any suggestions for comparable units of low used cost? As I very seldom encounter tunable IF tuners this would be more for playing/learning with.
--
Mike Miller
PA, USA


Re: MY ACCUPHASE T 100

Herb Ward
 

Hi Victor,

A few comments having modded many tuners for Ed Hanlon and many customers of my own by virtue of owning two hi end audio shops in CT. 

Tantalums were frequently chosen by designers in the seventies for several  reasons. Beaded tantalums are mostly free from the age related issues that typically develop in electrolytic caps. Value stability and almost no leakage are
typical of beaded tantalums. BTW , tantalums used as coupling caps typically do not fail , although I have seen cheapo parts develop internal opens between the part leads and the capacitor element. Small films or audio rated electrolytic’s would be a good choice. 

In the T-100 , there are 3 tantalums in the MPX decoder circuit. A 10 uf at the audio input of the decoder IC, and a pair of 1uf at the audio outputs. Both Wima and Kemit make metalized polyester caps small enough to fit in place of a beaded tantalum. I suggest purchasing the caps supplied for machine insertion as the leads are MUCH longer . The standard Wima or Kemit caps have a lead length of only 5 mm . The axial power supply bypass caps in the T-100 should be replaced with polarized caps. Nichicon HE are wonderful for power supply bypassing having very low ESR even in low values. Finding improved electrolytic caps in a axial lead format is very difficult these days . Vishay does make them but few vendors sell them. Do keep in mind that many manufacturers are slowly abandoning thru hole parts, and many distributors are not restocking thru hole parts as the demand for Surface Mount parts continues to ramp up. Most of the coupling caps on the T-100 audio boards are polyester. Metalized polypropylene in appropriate voltages and sizes are readily available. Boutique parts are of course at your option. I would point out that the Japanese builder of the Almarrow 318 SE amps uses a very standard Panasonic metalized polypropylene in the amps construction. His declaration that boutique parts offer no improvement in the amps sonic presentation makes me wonder about the value of 20 dollar passive parts when a 3 dollar part works the same.  

I would not be the first person to say that an alignment by an experienced tuner tech with a premium FM stereo generator would likely make a substantial improvement in the tuners performance, considerably more than passive part swaps, so I hope you have the option of doing that. I wish you all the best in your project.

HRW

On Tue, Jun 30, 2020 at 4:40 PM Victor Dascalescu via groups.io <victordascalescu54=yahoo.com@groups.io> wrote:
Now I am waiting for the capacitors I ordered at HiFiCollective. Transistors I shall replace only the Q5/6/7 on both modules.
Capacitors I choose only Mundorf, including PSU smoothing and bipolar elco to replace the polar elcos of 100uF and 220uF.
While I am waiting I am listening as it is and the sound is beautiful, much better than Tandberg 3001 which I am comparing in the same room, same setup. And very very quiet, unreal quiet.


Re: IF Alignment Sweep general questions

EJP
 

On Wed, Jul 1, 2020 at 10:57 PM, Mike Miller wrote:
I think I will try backing up before the limiter stage

Try probing the IF from the junction of R327/8. But Scott tuners have critically-coupled IF stages and 1MHz bandwidth at the detector. You're not going to discover anything useful with a sweep of only 200KHz, and the shape of the bottom of the IF oscillogram is irrelevant, as it all gets filtered out.

EJP


Re: Tantalum capacitors

 

There certainly would be no harm in replacing those three tantalum caps with good quality caps of the same value and same or higher voltage rating. I have found that WIMA MK film caps are usually small enough to replace tantalums and are of good "sonic quality". There are other options, but that is a possibility. The problem with using polyester caps is often  their large size.

Again, the issue I often find replacing tantalums in the signal path is size - the little blue or yellow teardrops tend to be quite compact and the PCB layout might not allow for a appreciably larger capacitor.

--
Mike Miller
PA, USA


Re: Tantalum capacitors

Victor Dascalescu
 

Thanks Herb,
The capacitors in question are on the signal path from the decoder de-emphasis to the audio board input. What is strange to me that they used on the audio board polyester metalized films all around but on this particular part which is also audio those tantaluses, which to tell you the truce I don't trust very much.


Re: IF Alignment Sweep general questions

newaag
 

this is my analog sweep setup - it is shown for testing ceramic filters, but can also sweep tuners. You use the counter to measure the filter frequency center point and bandwidth.

https://groups.io/g/FMtuners/files/Murata%20Ceramic%20Filter%20Information/FilterSweep.pdf

I have attached two plots made with this sweep setup, posted here a while ago, showing plots of Murata ceramic filters, a 150, and 280.
But I now use the nanoVNA for ceramic filter sweeps. So far it is mixed for measuring tuner IF response, still playing with that. 

Bob


Re: IF Alignment Sweep general questions

newaag
 

On Tue, Jun 30, 2020 at 01:26 PM, Mike Miller wrote:
That active probe looks like a very tempting little tool that might be handy to have around. Have you gotten one yourself to check out?
Yes, I bought the version with the AD8307 on it. It is an incredible deal, even if you put it in a box and don't use it as a probe. It has both the detector and log amp built in, so you get great looking X Y plots on your analog scope.
I already had an HP 1144A active probe, bought to use with my HP54522A digital scope. This is the exact setup I used in the 90's to measure audio jitter on digital DAC projects. At the time, the scope and probe rig sold for over $10K. I worked for HP and was borrowing it from the demo pool, so grew very attached to the scope's capabilities. You can get it now for under $500, which is what paid many years later for both. I later picked up the HP 1142A power supply to power the probe without the scope on. It works great with the nanoVNA, but I assume the recommended active probe from Ebay would be just as good. 

Just make sure you understand the differences - the probe with AD8307 gives a DC output, the other one has a wideband AC output. You want the DC output to drive the Y input when doing IF sweeps with an analog scope. That DC output can also be used to detect RF levels in both the RF and IF sections with great accuracy, and is likely more sensitive that a typical scope with a 10:1 probe. 
Bob

 


Re: Tantalum capacitors

Herb Ward
 

Mac,

LOL  !   very good !   I needed a good chuckle this morning.

Cheers, 

HRW

On Tue, Jun 30, 2020 at 11:59 PM Mac <macbradley@...> wrote:
On Tue, Jun 30, 2020 at 01:19 PM, Herb Ward wrote:
Marc, {Mac}
 
I bought a Pioneer SK-31 boom box for myself in 1973. It's been on every weekend in the garage, and it has not been recapped 
 
HRW
I still have a Schwinn World Voyager I bought new in 1974 and it definitely needs re-capping actually there's not enough tire left to be recapped it needs to be re-tired LOL sorry about that.
I've been in enough audio forums to know that capacitor management is a polarizing topic.  Having said that, I estimate your boom box has about 40,000 running hours on it don't you think it's time to refresh those bad boys?


Re: Tantalum capacitors

Herb Ward
 

Mike,

YES !  Exactly. My comments are not meant to discourage enthusiasts from recapping, but rather to educate them. As a few others have pointed out, many of the electrolytic caps of the early and mid seventies are really of very good quality, and unless they are well cooked by a close by heat source, they often measure as well as new premium caps. ( and they function properly for decades )  What is unfortunate, is that many products of the late eighties and nineties were modified by the bean counters to lower unit manufacturing cost. In particular, electrolytic cap quality really suffered. And then, there was the flawed electrolyte formula which is well documented on a number of sites. For those of you familiar with the Adcom amp driver board issues, the leaky cap problem
 ( the chemically defective electrolyte rotted the rubber plugs and the PCB's became soaked with juice ) only started after an alternate supplier was used for the small bypass caps.

Circuit mods by means of changes in the parts quality ( no value change ) of passive parts often do not produce audible or measurable changes. There is of course the perceived changes which are a psychological response to installing $200 of boutique parts in your set. The use ( and benefits ) of placebo pills in the field of medicine is well documented. I do appreciate the likelihood that there may very well be elements of hearing that do not have an objective parallel, or that a suitable measure has not as yet been determined.  For many, passive component circuit mods are a means of personalizing your equipment and is just one of the many ways to enjoy this hobby.

HRW

  

On Wed, Jul 1, 2020 at 8:54 AM Mike Miller <mikeyis43@...> wrote:
Thanks for saying what I was thinking Herb. Sometimes old caps do have to be replaced. I've pulled my share of old power supply electrolytics that were cooked by being run too close to their voltage rating and/or too hot. And capacitor technology has advanced so much in 50 years that replacing a polarized 1uF electrolytic in the signal path, or perhaps a tantalum, with a new WIMA film cap probably MIGHT make a measurable difference, if that difference is not obscured by other distortion mechanisms left in place. As far as caps needing to be broken in, I have never seen a scientific explanation of what physical or chemical change could be produced in a capacitor that would improve its "sonic qualities".

Of course if it makes someone happy to spend time doing such, then there are worse things to spend time and money on I suppose.
--
Mike Miller
PA, USA


Re: Tantalum capacitors

James Callahan
 

I’m not a tech or do I have any background in electronics . I’m a hobbyist who likes to restore vintage audio gear. My slant on “break in”  is that it’s our brains more than the equipment . The equipment needs to warm some sure but it’s our “music memory “(MM) that needs to be reset /cleared . Then with your MM  is cleared you will hear how your setups sounds . Just as you can read and understand a paragraph missing  words ,because your noodle (brain) fills them in for you . It’s the same with music your brain knows the songs and how they sound. I occupy my mind with something else when testing gear for sound quality . The differences better or worse will stand out. Also while I’m rambling ,listen to your setup at 2am or 3am (winter months better)  volume at 8 or 9 o’clock  just loud enough to it hear well. How does it sound?  

 

From: FMtuners@groups.io [mailto:FMtuners@groups.io] On Behalf Of Mike Miller
Sent: Wednesday, July 1, 2020 8:54 AM
To: FMtuners@groups.io
Subject: Re: [FMtuners] Tantalum capacitors

 

Thanks for saying what I was thinking Herb. Sometimes old caps do have to be replaced. I've pulled my share of old power supply electrolytics that were cooked by being run too close to their voltage rating and/or too hot. And capacitor technology has advanced so much in 50 years that replacing a polarized 1uF electrolytic in the signal path, or perhaps a tantalum, with a new WIMA film cap probably MIGHT make a measurable difference, if that difference is not obscured by other distortion mechanisms left in place. As far as caps needing to be broken in, I have never seen a scientific explanation of what physical or chemical change could be produced in a capacitor that would improve its "sonic qualities".

Of course if it makes someone happy to spend time doing such, then there are worse things to spend time and money on I suppose.
--
Mike Miller
PA, USA


Re: Scott LT-112B distortion

@feathed
 

The unit does seem to have slightly but audibly less distortion in mono. It is most evident in spoken word sibilance. Also the  center tune meter is off to right 1/2 to almost two black rectangles. There is a chance this unit was previously aligned and it seems not too far off so I will only try to adjust T304 (detector can) slightly. I will mark the starting point so I can always go back if things get worse. I bought this unit as it was cheap and just to have something while my main tuner is in the shop for alignment and mods but I've grown quite found of it. It is cosmetically in very good condition, sounds quite good and I think rather cute. Thanks to all for the advice.


Re: IF Alignment Sweep general questions

 

Thank you Joe. The info about probing sensitive circuitry is invaluable.
And I think I do really need to investigate a way to expand my IF sweep range if I want to do any amount of IF alignment down the road. Either a used sweep generator or a higher frequency digital synthesis function generator than the 10MHz one I have now. I wish I had purchased a 30MHz function generator when I bought the 10MHz one I have now. Live and learn.
--
Mike Miller
PA, USA


Re: IF Alignment Sweep general questions

 

Yes, I ran into that. I could not find a location on the secondary side of the detector that did not exhibit S-curve behavior. I think I will try backing up before the limiter stage and see if I can get a more typical IF curve Y output (more bell shaped).
--
Mike Miller
PA, USA

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