Teac A-1d amplifier

[gabe75]

Hello everyone! i am trying to replace all the electrolytic caps in 12 year old amplifier, and there are a lot of coupling 10uf np(not polarized).
I am sure i could find very inexpensive nichicon es muse, but I am curious if I could use polyester caps instead of the muse caps. And what I mean is what value of the polyester should be enough to replace a 10uf electrolytic?

 

[JonSnell Electronic]

10uF 50V as per the circuit diagramme.
They will be too large physically! 12 years is not old enough to require replacements especially as they are mainly signal coupling.

 

[gabe75]

thank you for the answer.
I am not trying to replace the 10uf electrolytics with 10uf polyester , I need lower value for the new ones , as you said they would be to large and to expensive too.
I was thinking more like 2.2-4.7uf . i am talking about c20, 127, 38, 40 and 44.
Would that be good?
And yes and no, 12 years may not be so long but this is my project for right now.

 

[Mooly]

Reducing the value of the caps will move the low frequency turnover point.

In other words the overall effect will be that the response of the amp doesn't go as low as it does now. Is that what you want ? Poor low frequency performance.

If you intend replacing the caps then get suitable like for like replacements.

 

[gabe75]

thank you for the answer!
No , i dont want poor low frequency performance.
But i am confused now.
Most of the chip amps(lm3886/4780) that i put together had an 1-2uf coupling film capacitor, and that preamp has 10uf caps starting with the input till the exits to phone amp and the power amp. The coupling cap(c72-73) for the power amplifier is actually 47uf!

 

[gabe75]

this is the schematic for the power amp.

 

[Mooly]

You need to understand how the capacitors 'reactance' works in conjunction with the parts around it to see how changing the value will affect the performance.

OK, so you mention the input coupling cap on the preamp. Out of all the ones you mention, that is the one that could be reduced with no practical impact. 10uf working into 1meg gives a cut off point of around 0.02Hz. You could safely fit a 0.47uf film here but not for the others.

Take C44. That is currently giving a 3.4Hz -3db point for that stage. Fitting a 0.47uf would raise that to a massive 72Hz. That's not what you want.

 

[gabe75]

thanks Mooly, you are right about understanding how electronics work, I don’t.
So in other words I should replace these caps with new electrolitics with the same values.
This sucks , I always thought electrolytic caps are not as good as the film ones.

Can anybody tell me about the c42-c43, 10uf/50 volts , is that a critical value ? or I could replace it with a 22uf or even 47uf?
These were elna cerafines and I have problems finding them in that value , but I have some of those 47/50.

 

[Mooly]

C42 and C43 are simple bypass caps across the vbe multiplier. 22 or 47uf would work OK.

 

[gabe75]

Thank you again!
now i am going back to the preamp , c129-130 are 330nf , they are very close to the bass potentiometer...
Is that a critical value? Can it be replaced with 390 nf?

 

[Mooly]

You will change the overall response of the tone circuit slightly if you alter those.

 

[gabe75]

Ok , thanks Mooly