How much ripple on rails?

[90scaraudio]

I've got 2 Soundstream Reference 500s amps. I've gone completely through them with new MOSFETs, full wave bridges, LoESR capacitors, regulators, new FEB and pre driver boards, (new SMD electrolytic caps on all), new emitter resistors.

One of the amps has 60 to 80mv ripple on each rail and the other about 30 to 40.

Now on two of my reference 300 amps the ripple on each rail is about 4 to 6mv.

One thing I noticed is on the schematic for the 500s is C61 and C65 are .1uf and are tied from each rail to signal ground. However on the boards C61 has a marking on the cap of 525 (5.2uf)? and C65 is a .1.

The +/- 16v has about 2mv ripple.

The 300 and 500 amps used 4 1000uf/50v caps and the S series went to 2 1000uf caps, then all the Rubicon series went back to 4 1000uf caps on the rails?

Any suggestions?

 

[90scaraudio]

Here the schematic

 

[Perry Babin]

Did you measure the ripple directly across the rail caps?

Is the ripple at the audio frequency or at the switching frequency?

 

[90scaraudio]

Directly on the caps...I'll check the Freq as I only measured it with a Fluke multi-meter.
So if its the switching freq. would that mean the caps?

 

[90scaraudio]

Thanks Perry for the reply, You make me think .

OK so I replaced C61 and C65 with .1uf 50v Xicon epoxy dipped from mouser.
I also replaced the two 1000uf caps, (nichicon PW(M)), it says they are for switching power supplies , with Xicon 1000uf/50v 105deg caps.
Results...
Neg rail -36.63vdc 1.9mv ripple
Pos rail +36.62vdc 1.9mv ripple
DC Offset Rt ch -6.6mv
Lt ch -6.2mv
Bad caps I guess, they were new within the last 6 months.
Now I have to go through my other amps and pull those nichicon caps out, WTF.

 

[90scaraudio]

OK, so does anyone know the best caps to use. Low ESR, General purpose, Low impedance.....
I cant find very low profile caps that will fit in these soundstreams that are Low ESR. Anyone know where I can buy them, new.

 

[1moreamp]

Try Panasonic FC
PG used those exclusively in their US made gear. I have had fairly good luck with them myself. Only on the 12 volt side do they seem to fall short though....

 

[90scaraudio]

Thanks 1moreamp... Been a while.

I swear the PW caps say there for switching power supplies!

Also, the DC offset was a little high before I switched these...

 

[Perry Babin]

There weren't enough controls in the testing to come to any reliable conclusions. Having your meter leads over a different area of the board could have caused the difference in the ripple voltage readings. If anything, having the long leads on the capacitor would make the ripple worse because it would significantly increase the ESR and ESL of the capacitor.

 

[90scaraudio]

I've ordered a bunch of low ESR Panasonic caps from mouser and will be here today. Now to fix the other 500s and two 405, (one of the 405 is an engineering sample) plus a Zapco that's been giving me fits with high dc offset. We'll see
Will post pics of measurements before and after cap replacement.

An externally hosted image should be here but it was not working when we last tested it.

Scott

 

[90scaraudio]

OK, received all these caps. I needed some .47uf electrolytic SMDs for the clip circuit boards as they were leaking and original.
After replacing the filter caps on one of these 500s I noticed something messed up with my bench powersupply.
The first set of pics is one rail and the next is the other.

After replacing them and testing the amp on my old HP I noticed the ripple was still there. I must have used my other bench supply when the ripple disappeared OOOOPPPPPSSSS

The next set of pics is the ripple on the HP power supply and then the ripple on the newer supply....

Bout pulled my hair out but I did find I need to fix my HP and found a few small problems on the SS 500s. Now she sounds better than it ever has.

THANKS Perry and 1moreamp for the advice on more testing and Panasonic caps.