AU-919 complete restoration

[Overundr1]

One can only imagine what it was like for technicians learning their trade in the 60's and 70's with hands on training and guidance that goes so much farther than textbook learning.

 

[GrisPato]

Thanks for that brief explanation!
As I am not an electrical engineer I always have to find the "evidence" on the web, which is sadly really scarce of real data or maybe just hard to find.
For the reference to manufacturer engineers knowing what they are doing the problem is ofcourse that they also have there different views. Simply said, Sansui engineers did decide not to use LEDs but diode strings, so what does that tell me.
And although I do trust that your friend is an audio technique genius, for myself I would have to know his perspective and maybe even his "soul" to be able to put value on his opinion ( what you do know ofcourse).
I just know from my own profession that at least half of the expert engineers no shlt of what they are doing and just follow common confentions. ( Not making that conclusion about you or you friend )
Interesting that you find enlarging the capacitance on the decoupling capacitors possible detrimental. I do think to that enlarging them to enormous values is not applicable to their function although that is mostly based on a feeling ( not an EE, so little theoretical knowledge).
I do like what you say about a circuit being as a whole a functional unit!
For sure going to try the things you did!
Thanks for sharing your work and thinking!

 

[Dorian]

Thanks for that brief explanation!
As I am not an electrical engineer I always have to find the "evidence" on the web, which is sadly really scarce of real data or maybe just hard to find.
For the reference to manufacturer engineers knowing what they are doing the problem is ofcourse that they also have there different views. Simply said, Sansui engineers did decide not to use LEDs but diode strings.nso what does that tell me.
And although I do trust that your friend is an audio technique genius, for myself I would have to know his perspective and maybe even his "soul" to be able to put value on his opinion ( what you do know ofcourse).
I just know from my own profession that at least half of the expert engineers no shlt of what they are doing and just follow common confentions. ( Not making that conclusion about you or you friend )
Interesting that you find enlarging the capacitance on the decoupling capacitors possible detrimental. I do think to that enlarging them to enormous values is not applicable to their function although that is mostly based on a feeling ( not an EE, so little theoretical knowledge).
I do like what you say about a circuit being as a whole a functional unit!
For sure going to try the things you did!
Thanks for sharing your work and thinking!

Thank you. What you are looking for and the questions you asked are, as I said, a matter of engineering and development. You need to look in books for electronics students and such things are not written in the usual language that is on the web, but very specific terms and loads of equations and graphs, I will look for literature where this is explained just give me a little more time

 

[Dorian]

Really interesting restoration you show here. ( Also the AU-D9 )
It's good to see different approaches to vintage equipment restoration.
First thing that caught my eye is the local decoupling capacitors on the driverboard that are just 330uF. I have heard about the AU-919 having these in some instances. I am just wondering why you didn't bump them up to 470uF?
Second, if I see correctly you also installed the bypass film capacitors for this electrolytics, was wondering if they were installed originally already ( I have an AU-D907 that has them originally.)
Then about the LEDs. I have read before that they are less noisy, at least then zenerdiodes are in a regulated powersupply. I can not find any information if this applies to the function of the MV-103 that Sansui used.
Do you have some measurements available about the noise, and how much less this is.
Of course we want the less noise, but for me, I would not like this LEDs if it is not a proven benefit.
I mean, to they give 2 uV less noise or some value that lowers you S/N with like 0,001 dB or is there a substantial decrease in noise?
Sorry for all the questions, but I really like to learn more.

By the way, to remove any doubts about the quality of what was done, that restoration was done 3 years ago and I know that the owner listens to his 919 every day and there were absolutely no problems during the period of 3 years. Here are some pictures of the position of the owner of the device.

 

[GrisPato]

, to remove any doubts about the quality of what was done, that restoration was done 3 years ago and I know that the owner listens to his 919 every day and there were absolutely no problems during the period of 3 years

No doubts at all about the quality of your work, it's evident your work is high quality and I can only hope to reach the same level!

 

[Dorian]

No doubts at all about the quality of your work, it's evident your work is high quality and I can only hope to reach the same level!

Oh, no worries whatever I can and know, feel free to ask, I'll be happy to share whatever I know

 

[ghamilton]

I respect your principle, but each of us works in a different way, personally I have not noticed any difference either sonically or with the instruments if the polystyrene is replaced with mica or PP, and replacing it with a new one gives me security. I have also repeatedly found that the specifications are far out of tolerance or that the capacity is 0. It is unlikely that anyone takes out the elements and measures the tolerances.

Dorian, You said that you couldn't hear a difference when changing those noble clear plastic caps to mica. Because of your results on this I am going to try ceramic COG.
Some people prefer the COG over mica when using pf values.

 

[Dorian]

Dorian, You said that you couldn't hear a difference when changing those noble clear plastic caps to mica. Because of your results on this I am going to try ceramic COG.
Some people prefer the COG over mica when using pf values.

Yes, C0G is good, it has a great temp coefficient, mostly you don't have to worry about a change in the sound due to the compensation positions, but here is an example that affects the sound in a positive direction. Sansui is in many places due to the fact that in those years bipolar and films with higher capacity values were either unobtainable or extremely expensive. And then ordinary electrolytes were placed in an antiserial connection. Of course Sansui engineers wouldn't have done it that way if they had a choice and that was a big compromise. In those positions, instead of 2 ordinary ones, one quality bipolar or even better foil should be installed, with this a significant shift towards better sound is obtained and the Sansui engineers become happy.

 

[ghamilton]

Yes, C0G is good, it has a great temp coefficient, mostly you don't have to worry about a change in the sound due to the compensation positions, but here is an example that affects the sound in a positive direction. Sansui is in many places due to the fact that in those years bipolar and films with higher capacity values were either unobtainable or extremely expensive. And then ordinary electrolytes were placed in an antiserial connection. Of course Sansui engineers wouldn't have done it that way if they had a choice and that was a big compromise. In those positions, instead of 2 ordinary ones, one quality bipolar or even better foil should be installed, with this a significant shift towards better sound is obtained and the Sansui engineers become happy.

If I understand you correctly there isn't any places on the Amp driver board where I can put a single bipolar in the place of 2 polar caps. That's the board I am redoing right now. I know that the preamp section has some.
Leestereo did that on his 919 restore post (if I understand correctly).

 

[GrisPato]

Oh Dorian, now you're mentioned something I am really confused about.
I do understand that it is better to use a film capacitor for coupling.
The use of bi-polar electrolytic in place of a pair of high quality polar I do not really understand.
First, understand I am not an EE so I miss the knowledge, I look at what Sansui did.
For example, Sansui used bi-polar in cheaper models (AU-417) for coupling pre-amp stage but not in the higher models. And a bi-polar is nothing more then two polar capacitors in one package?
Second, they would go up in capacitance of the RC filter.
And keep doing this into the later alpha models for the bypass of the VBE multiplier. I would think they could have gone with a 1-4,7 uF film but they didn't.
Also for the capacitors shunting the triple diodes on the lpt, instead of going for 1uF film ( used in the head amp of the AU-D907/707) they go with 4,7uF EC with a film capacitor bypass although they use 1uF film in the powersupply.
Talking about the triple diodes ( what is there function in the LTP), in the AU-D907F-G they use 2 bjt transistors in this position and from the x-balanced ( AU-D907X) on they go back to the diode string al the way to the latest alpha from the late '90s. I would think by then they would have known about the lower noise of the LEDs but still choose the diodes.

 

[Dorian]

Oh Dorian, now you're mentioned something I am really confused about.
I do understand that it is better to use a film capacitor for coupling.
The use of bi-polar electrolytic in place of a pair of high quality polar I do not really understand.
First, understand I am not an EE so I miss the knowledge, I look at what Sansui did.
For example, Sansui used bi-polar in cheaper models (AU-417) for coupling pre-amp stage but not in the higher models. And a bi-polar is nothing more then two polar capacitors in one package?
Second, they would go up in capacitance of the RC filter.
And keep doing this into the later alpha models for the bypass of the VBE multiplier. I would think they could have gone with a 1-4,7 uF film but they didn't.
Also for the capacitors shunting the triple diodes on the lpt, instead of going for 1uF film ( used in the head amp of the AU-D907/707) they go with 4,7uF EC with a film capacitor bypass although they use 1uF film in the powersupply.
Talking about the triple diodes ( what is there function in the LTP), in the AU-D907F-G they use 2 bjt transistors in this position and from the x-balanced ( AU-D907X) on they go back to the diode string al the way to the latest alpha from the late '90s. I would think by then they would have known about the lower noise of the LEDs but still choose the diodes.

I'll answer later in a bit more detail, I'm pressed for time right now. I see that you have made a lot of effort to study the entire series of service manuals. We will never know the answer to many questions unless one of the Sansui engineers from that time gets involved. A lot of things are still unclear, but I'm afraid that the answers would be trivial. What could be obtained at that moment and what was available was installed. I see things in a completely different way. It doesn't matter at all when looking at the topology and the schematic diagram, who is in the signature, but how it works and accordingly I determine what can or makes sense to do. The AU-D907f is virtually identical to the AU-D11 and is just one of the possible iterations of the input differential. As for LED's and why they aren't there is no answer to that, one of the possibilities when doing large run production of GaAs is a very expensive diode and it is a very large item in high volume production. And it is by no means the same as 2 polar or one bipolar, you forgot about the asymmetry of 2 polar, longer signal path and 100 other things. As for the alpha series and these days I will post the @907XR restoration and quote what the owner said later. It used to sound like Rotel, now it's truly hi-end

 

[GrisPato]

Thanks Dorian for the fast reply, although not necessary.
I can wait but am really happy already to get a more detailed explanation then : it is better.
Of course I am limited to you just look what other engineers decided to do because I can not make educated decisions myself.
One thing I would like to know what is the use of those diode strings in the input differential, no hurry at all, but if and when you can find time.

 

[ghamilton]

Dorian, although I didn't put a bipolar cap in the place of those 2 polar caps (in the phono and preamp sections) I did at least put a high quality bypass wima cap with them. Because of this I don't think I want to go back in there to make that change.

 

[Dorian]

To je u redu, ali opet bih dodao bilješku, ako idete na staru verziju, antiserijski polari koliko vidim su Panasonic FC, osobno bih izbjegao FC na signalnom putu, jer su ispravljači FC u redu

 

[AUD101]

From Google Translate ^^

That's fine, but again I would add a note, if you are going for the old version, the anti-serial polars as far as I can see are Panasonic FC, personally I would avoid FC in the signal path, as FC rectifiers are fine

 

[ghamilton]

I may make that change sometime.
I am using Elna Selmic ll on the preamp board bypassed by a wima.
Also, on the preamp (flat amp) board C 19 20 21 22 are 100uf caps and Leestereo used a 47uf cap to replace the two 100uf caps. Why not a 200uf instead of one 47uf cap? Strange.

 

[Leestereo]

...Also, on the preamp (flat amp) board C 19 20 21 22 are 100uf caps and Leestereo used a 47uf cap to replace the two 100uf caps. Why not a 200uf instead of one 47uf cap? Strange.

When two identical capacitors are connected in series, the total capacitance is half of their single rating, e.g., two 100uF polarized capacitors in series are equivalent to a single 50uF bi-polar capacitor.

 

[ghamilton]

When two identical capacitors are connected in series, the total capacitance is half of their single rating, e.g., two 100uF polarized capacitors in series are equivalent to a single 50uF bi-polar capacitor.

And there is the answer!
Thanks!

 

[ghamilton]

To je u redu, ali opet bih dodao bilješku, ako idete na staru verziju, antiserijski polari koliko vidim su Panasonic FC, osobno bih izbjegao FC na signalnom putu, jer su ispravljači FC u redu

Thanks Dorian. I was wondering why you think FC is not a good choice when compared to other standard caps or what was in there from the factory (if the factory caps measured fine) if I wish to keep it as original?
Please reply in English.

 

[ghamilton]

Oh well, Dorian is a busy man.
I will simply replace those 2 polar caps with 1 bipolar cap on the flat (pre) amp and phono boards. Parts ordered.
I am going to keep those bypass caps at stock values unless someone thinks its a bad idea.