Pass Design Adcom - Filter Cap Problem

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
PreCD

PreCD

Member
Joined 2011
I have been studying for a couple of days the variety of PS Filter caps to use in my Pass design Adcom GFA-555 amplifier. For one it seems there are not a huge variety of 15000uf 100v caps out there to be had. I have scoured the earth and am leaning toward a Vishay PHR-ST type. $38 a pop.

Max ESR 16 Mohm @ 100hz.
Rated ripple current @ 100hz = 12.3

What have others used for this amp design?
 
PreCD

PreCD

Member
Joined 2011
Done and done. Ordered the Vishays from Digikey along with 3.9kOhm 3W Metal Film resistors which reside on the filter caps at this time. Might as well replace those too. I would like to know why those resistors are there as bleeders though..............
 
PreCD

PreCD

Member
Joined 2011
Ok. The filter caps are in but I have a few questions. The old filter caps look to be wired in series with no polarity showing on the caps. How do I complete the installation of the new caps observing correct polarity? The amp also has one wire, left channel side, which goes to the power on led. Two others on the right side go to the distortion lights. Do these go on the negative or positive terminals of the new caps?

Again if the old caps had polarity markings on them I would replace with no problems. I am just confused how the new caps should go in.

Thanks and Happy Holidays.
 
eyoung

eyoung

Member
Joined 2007
AFAIK all polarized caps have polarity marked on them one way or another ... a stripe or a dot square lead or something. if all else fails remove rail fuses and ck for polarity on board with out caps installed. dim bulb and variac can be your friend if all else fails.

good luck my friend,

Elwood
 
PreCD

PreCD

Member
Joined 2011
I would imagine the polarity designations on these caps were hidden by a custom wrap put on them by Adcom. Really nothing there.View the attachment to see how I have them wired at this time which I think is wrong. I believe I need to flip the first cap up in the front of the unit 180 degrees and wire them in series.

I thought my work was correct. I pulled the rail fuses and hit the on switch which blowed the main 10amp fuse. Hopefully nothing has been hit hard and the fuse + pulling the rail fuses saved any damage.

eyoung said:
AFAIK all polarized caps have polarity marked on them one way or another ... a stripe or a dot square lead or something. if all else fails remove rail fuses and ck for polarity on board with out caps installed. dim bulb and variac can be your friend if all else fails.

good luck my friend,

Elwood
Click to expand...
 

Attachments

  • new_caps.jpg
    new_caps.jpg
    150.8 KB · Views: 154
PreCD

PreCD

Member
Joined 2011
Ok so now I have the power caps wired properly in series and read 80v at each rail. I have yet to replace the rail fuses as I would like to hear back from anyone who might have advice on what to check next before I do that.

My concern is that I have damaged something in the process of having the caps wired incorrectly.

Should I get an accurate offset voltage reading at this time with rail fuses pulled?
 
Last edited:
PreCD

PreCD

Member
Joined 2011
Thank you for responding. That is a schematic for the 555II which was a later version and much different. I have a schematic but am not adept at reading it as I should be.

I got the amp running now. The offset voltages are all good and everything is sounding nice. I will run it for the next few days and see what changes replacing the 25 year old filter capacitors make.

One day I will hit this forum with a amp build rather than a trouble question. All in time. Thank you for your help.

Zen Mod said:
will this help ?
Click to expand...
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom