Poor sound after recap SAE 2300 power amp

bktheking said:
Caps aside, what is the "health" of the amp, did you check the bias, measure voltages, etc etc?
Click to expand...

This is important, it may seem counter-intuitive but any part for part change can still change an operating point, and these can be cumulative when doing a full recap. Therefore, important to double check and ensure all operating parameters are correct (bias, offset, power supply voltages, etc.)

rswojo said:
My guess is you have polarity reversal somewhere.
Click to expand...

I mentioned that and it wasn't commented on or noted. All OP has to do is double check polarity at all inputs and outputs, or just reverse the polarity on one speaker to know. If it makes a difference, should be better, or even worse than it is. If no difference, then you really have problems.

cdfac said:
one more vote for "clearly something is wrong," as opposed to you just needing to try a different brand of caps or something like that.

this is pretty much a brief summary of the other responses, with my own experience thrown in:

if you have any caps inserted backwards, they'd likely blow within a few minutes. if that doesn't send the amp into protection, then you could have muddy sound like this, although you'd probably have heard the cap blow if you were around the amp or the music was playing. still, look for caps with the top seal shredded. if that's not it, a bad solder joint, an overheated part, or an ESD-damaged part are the likely culprits. the bad part could be tricky to find, but it's possible if you're patient! good luck...

EDIT: the other question i don't think you answered was whether you fully discharged the filter caps before working on the amp. some filter caps discharge slowly on their own, others don't, and in that case they can cause problems to transistors (especially FETs) if you're not careful.
Click to expand...

Omegaman said:
Did you make sure that you provided a ground for the new caps when you replaced the can cap, which used the can itself for ground?
Click to expand...

Both replies are good comments as well.
 
Hello guys,
thanks, I have a lot of good theories to work in, I will go as fast I can.

Here some data:

Pre driver boards had installed Unicon 100uf/10v polar caps and I replaced them by 100uf/25v Nichicon KZ polar caps. I inspected the polarity in the new caps one by one and all of them are installed in the right position.

DC offset was acceptable (I believe) both before and after re-caping. These are CH A: +15mv and CH b: +5mv.

BIAS was adjusted but after that I realized the bad sound. BIAS was adjusted to 11 mv using alternative method measuring voltage drop in 0.2 ohms emisor resistors. These changes in BIAS didnt have effect on poor sound quality occured after re-caping.

Both channels has the same problem, so first thing I will test is reinstall the big can PS´s capacitors.

Thanks a lot again.
 
Last edited:
Hello again guys,

Here some measurements and additional information.

- I am a beginner nevertheles I have recaped some vintage amplifiers before without porblems. I'm not the best welder in the world but not the worst I think.

- I checked and ground cables for channel boards (where new caps are) are well connected.
- Voltages IMHO would be ok.
Outlet: 124VAC.
Toroidal outputs: 52.5 VDC and 5.8VDC.
After rectifier bridge and cans caps: 71.7 VDC.

- I did this interesting rollover, I replaced the new Epcos caps by the original oldest caps, with this the power amp lost its bass punch again but had no effect over the bad performance in mid and high frecuencies, so I think the Nichicon should be the guilty :).
Unfortunatelly, I am so far from Mouser so I must wait one or two weeks for a new Elna Silmic caps shipment.

I will back soon..
Thanks a lot to everybody for your usefull help and please let me know any comment you have.

Edo.
 
Hi Edo, did you measure both the rails? For more reasons can happen that 0V, often not grounded on vintage stuff, is floating.
A reference voltage floating brings to have rails at different potentials, and this make unbalanced a push pull amp.
Just to complete your investigation :)
Good luck
 
Oh yes!
Assemblying my tri-amped system I inverted the phase on one tweeter (and before I inverted the right tweeter with the left one while the mid woofers were ok :D ) and the sound was pretty lifeless.
 
Before ordering caps again, to get the same results, I'd identify the problem first. I'd start restoring the original caps in one channel, one by one and test the performance after each one. I doubt the new nichicon caps are worst than the old caps.
 
Hello,

yes, I have checked signal and speaker cables and no polarity issues. Besides I tried using a second preamp, second pair of speakers and wires and the problem still the same.

Thanks a lot.
 
Hola elnaldo!!,
yes I agree with you, that is a great idea and I thank you very much, nevertheless I would like wait for install the new caps in order to avoid risk and temp that come with one additional soldering on the board. Anyway, probably I will install SILMICs anyway... Thanks a lot.
 
Last edited:
Hello bktheking,
yes, if you wish, you can see values above in this thread. Thanks a lot.
Edo
 
taddeus said:
Hi Edo, did you measure both the rails? For more reasons can happen that 0V, often not grounded on vintage stuff, is floating.
A reference voltage floating brings to have rails at different potentials, and this make unbalanced a push pull amp.
Just to complete your investigation :)
Good luck
Click to expand...

Hello taddeus,

really sorry but I am a beginner and I dont understand that are you talking about.
What are rails? Where are them?
Please explain me a little more.

Thanks.
Edo.
 
Hola elnaldo!!,h
yes I agree with you, that is a great idea and I thank you very much, nevertheless I would like wait for install the new caps in order to avoid risk and temp that come with one additional soldering on the board. Anyway, probably I will install SILMICs anyway... Thanks a lot.
Click to expand...

It shouldn't do that difference installing Elna Silmics or Nichicon. I've replaced all the Philips general pourpose caps inside my Philips amp with Elna Silmic II, and it sounds good, but I don't think that a Nichicon capacitor would sound bad in the way you describe... Even the old Philips capacitors, just general pourpose caps, 30 years old, sounded good too.

I'd keep tracing the problem even if you think to replace the Nichicon with Elna.
 
Dear friends, some days ago I have replaced the suspicious Nichicon capacitors by ELNA Silmic II and after hearing several hours I can tell you that I think that Muse Nichicon capacitors were the responsible for the poor sound.
The amp with the new ELNA capacitors has clearly a better sound, it have regained its brightness and high frecuency´s definition and definitively has much better sound. Guitars and vocals are now more clear and the amp has a good bass too.
I recaped one channel first and I have done hearing comparative tests in consultation with other people to make ensure a more reliable opinion.

I appreciate the support of everyone who helped me find the solution to this strange problem.

A hug to everyone.
 
elara said:
Dear friends, some days ago I have replaced the suspicious Nichicon capacitors by ELNA Silmic II and after hearing several hours I can tell you that I think that Muse Nichicon capacitors were the responsible for the poor sound.
The amp with the new ELNA capacitors has clearly a better sound, it have regained its brightness and high frecuency´s definition and definitively has much better sound. Guitars and vocals are now more clear and the amp has a good bass too.
I recaped one channel first and I have done hearing comparative tests in consultation with other people to make ensure a more reliable opinion.

I appreciate the support of everyone who helped me find the solution to this strange problem.

A hug to everyone.
Click to expand...
KZ need between 100 to 200 hours of burn in and are in the same league with Silmic 2 and they have better high frequency compared to Silmic 2. The only down side of KZ is poor bass compared to caps like Cerafines .Silmic 2 have less clarity and less neutrality compared to KZ.
I replaced some 100uf and 220uf Silmics with KZ and now the amp is much better .
 
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