to mr perry babin and anyone who can answer this question on repair

[russdeanlee]

on the 1996-97 soundstream picasso Class A 4 channel amp can you explain the role those 8 big yellow metallized polypropelyne caps (marked, 4.7k 100v, mpa ch) plays in the amplifier and would it be okay to replace with a different value? due to availability. if they are leaky will replacing them with solen 4.0uf 250v metalized poplypropelyne caps be ok or would it cause problems. what if i was to replace them with a solen 4.7uf 400v metallized polypropelyne capacitor would this be ok. would i need to replace them in pairs or should just replace all 8 of them. would it make a difference if i was to replace with elec. caps instead? thanks to all for ready and many thanks to whom is able to answer my question.

[Perry Babin]

What is the circuit board designation for the capacitors?

Can you post a photo of them?

[1moreamp]

they are used on the main amp input diff pairs as DC blocking caps and they are bypassed with 470 ufd @ 6.3 volt electrolytic's to improve full bandwidth reproduction of complex waveforms. Hope this helps some, Yes I have the print..

Merry Christmas everyone


PS PPI used similar 4.7ufd value PP caps also in all of their Art series, PC series and PCX series. Failure of these is very rare...hope this helps some

[russdeanlee]

i'm refering to the yellow ones with the axial leads marked with 4.7k 100v. I'm trying to find replacements for them but due to availability would it be okay to replace with 4.0uf 250v or 4.7uf 400v. or is the value 470uf???

[1moreamp]

The circuit was designed for a 4.7 ufd device and you might end up altering the frequency response curve of the amp if you deviate from original spec. It may or may not be critical but unless you have the gear to SPICE model it or test it real world I would not change the values.
As I described the 4,7ufd caps are bypassed by a electrolytic cap of 470 ufd at 6.3 volts these two caps form the inter-stage decoupling from the IC frontend to the main amp channels. They provide DC blocking and were picked to provide the SQ your getting from the amp. These RARELY fail. I would be more worried about the 470@6.3 electrolytic cap having issues. And since the 470@6.3 sits right across the 4.7 PP cap it more then likely will cause the deviations your mentioning.

This amp like most is based on the standard op-amp internal designs which means there is a plus and a minus input to the main amp and both of these inputs have the same set of caps on them < hence why you see two large yellow caps on each channel >. On bridgeable channels the input switches to the opposite transistor in the input pair for inversion so the signal is 180 out of phase and thus bridgeable with its partner channel right beside it. Its done this way in just about any amp you might mention. So nothing new here.

If your determined to replace them I would replace them with the original value of 4.7 ufd, voltage ratings may not cause any impairment as these rarely see 8 to 14 volts AC peak to peak across them...

I can reach Jaime directly PM me if you like and I will message him for you if you like...hope this helps some

PS I sent him a email asking him to check your posts.

[Perry Babin]

There is virtually no chance that those capacitors are defective.

[russdeanlee]

i suspected that it is faulty due to me swapping out 2 from the left rear channel with the left front channel and nothing else just the pair with the other pair and the fault moved channels correcting the one that was faulty. fault being obvious difference in level and reduced low frequencies.

[Perry Babin]

These amps (all SS amps with this type of switches) have intermittent problems that can cause all sorts of problems. Something as simple as flexing the board can make the switch contacts make or break their internal connections). I'd suspect the switches are the reason that the signal level changed.

If one has failed, it will be the first one in 25+ years of doing repair work that I've seen fail (of that type).

[russdeanlee]

do you think it would be a good idea to take of the switches and just jump the pins to permanently set them the way i want, would this fix the switches problem?

[Perry Babin]

If you know how you want them set, it would solve the problem. Replacing them may be a better option if you can get them from Jaime. For testing, it sure would eliminat them as a possible problem.