If any one is interested in going though this long and hazards process I can fill in more blanks. The addition of the array across the bridge is to stiffen up the bass. This amp always sounded slappy IMHO. The larger array handles the ripple amps inherent in this grounded collector topology. Which is to say the capacitors form a center tap for the speak output and there by act act as a capacitor coupled amp (every note has to pass through these caps). Adding the caps post bridge makes it more like a convention amp power supply. Now the "off cycle output cap is recharged more consistently.

Any way how does it sound. Well "perfect" is an exaggeration, especially given the audience here and the subjective nature of the thing. But I've been tinkering forever, and know what I like. Clean vocals that don't wander around. Bass that reveal the drums like your doing a sound check. I haven't had a good enough source, or speakers to confirm if the top end is without smearing...But I'm going to check that later today. But so far it is behaving very well. Even into a 4 ohm load. I haven't scoped the output and don't have a dummy load to see when she really clips now, but from listening test so far she has more legs than the meters on the front would have you believe.

I was concern that moving the caps off the PCB would soften the slam, but it plenty stiff. Any way if you have one of these amps and a big bag of caps and load of patience you might be (pleasantly) surprised at what can come of it. I took a couple pictures if any one is interested.

Previous mods included quality volume pots, NL4 connectors, and pure silver output wire

Well to follow up. Did some A/B and brought in some young professional ears...and it's coming up lacking...just not as smooth and creamy with something missing in the middle...maybe a bit harsh. So it's back to the drawing board...or the capacitor store...Solen has a deal on poly caps so I ordered a sac of them. If the dip is around 2-3kHz 20+uF should bolster the transmission. Solen has 30uF/250V for $4.13 so with a little luck these can fill/smooth out the response. I'll cheat and put them on the parking spots of the OEM caps, saving me pulling off the heat sink.

A partial/possible schematic shows up here. If it's correct it does look like a QSC offering

Last follow up...clearly marked on the QSC schematic is ripple null. The power supply is tracked by summing it with the negative feed back and feeding it into the front end...case closed.

http://www.avsforum.com/t/1527237/objective-device-testing-anything-electronic-or-electro-machanical

Happy listening

Cyber1

 RE: Behringer A 500 rebuild revisited - electrovert 15:41:31 05/27/14 (12)
 " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - beppe61 01:20:09 05/30/14 (7)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 04:22:34 05/30/14 (6)

...

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 RE: Behringer A 500 rebuild revisited - electrovert 15:41:31 05/27/14 (12)
 " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - beppe61 01:20:09 05/30/14 (7)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 04:22:34 05/30/14 (6)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - beppe61 10:23:01 05/30/14 (4)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 15:31:57 05/30/14 (3)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 23:28:03 05/31/14 (2)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 18:22:56 06/02/14 (1)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 02:12:24 06/06/14 (0)
 RE: " Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid " - electrovert 04:35:26 05/30/14 (0)
 RE: Behringer A 500 rebuild revisited - electrovert 04:02:20 05/28/14 (3)
 RE: Behringer A 500 rebuild revisited - electrovert 00:26:16 05/30/14 (2)
 RE: Behringer A 500 rebuild revisited - electrovert 00:29:31 05/30/14 (1)
 RE: Behringer A 500 rebuild revisited - electrovert 00:34:57 05/30/14 (0)

What does it sound like. Well better than a Bryston B4...but only 180W into 8. Super tight bottom. No current liming mushy bottom. Stiff and extended. Mids are clean full and revealing. If the program has edge it is present. If it is smooth it is smooth. The noise floor is none existent. If you like running your power amp wide open this is the noise floor for you.

Was it fun to do...not really. Finished cost more than doubled the amps cost. Maybe $800 total including the $230 I originally paid for the amp.

Final result was worth the trip but that's because I can now sit back and forget how much work it was. All connections where quadrupled 22 gauge Teflon insulated pure silver wire. The cap arrays were bussed on stripes of heavy gauge copper sheeting taped together with Kapton tape and then siliconed into place. This takes awhile to strip and solder together. A big old soldering gun is required to build the arrays before you cook the caps.

I have two or three more amps to do now and then I can leave this project forever.

I hope someone find this useful. It takes this marginal device up to where you can actually enjoy it. Ran some NS10M Studio monitors full blast and despite the high SPL nothing sounded strained. Had the golden ears in it passed! Yippy.

Happy listening.

The quick an dirty improvement is a poly across the bridge, and the OEM caps.

Happy listening.

$25 >30uF/250V polys $4.13 Solen On sale hurry before I buy them all

$15 sheet of copper ~12"x 6" as thick as you can solder too (used 350Watt gun)

Now that's $80 sound better

So if you have the rest...that's not so much...as for the pots...well you can do it in software up stream for ~free.

I would recommend pure silver wire...I know it sounds audio pile snobby but using 22 gauge quad wired expanded the sound stage and increase the detail...that's IMHO. Just keep every thing practically short and all the same length. If you have the wire...if not as big as will fit into the OEM CAP holes. Fine stranded copper not tinned 105C preferred.

My way was about 8 hour of labor. If you have never taken this amp apart you may want to consider getting spare lid and side screws as these are sometimes factory striped...

If you have any more questions let me know.

If you can solder try bridging the +/- on the bridge with any cap rated 100V...mind the polarity! Even 30uF will make an audible improvement.

In the photo see where the red and black wires are. Put your cap across there. It can be done without removing the PCB. Just don't have any solder bloopos or you're nuked!

I should put a disclaimer in. Something like no user serviceable parts inside. Contact a reputable technician to risk their life. Dangers of all manners of hazards await those who open Pandora's box. Not excluding a long painful sounding life. The author takes no responsibilities for use or misuse of this information. And what Clint Eastwood said "A man has to know his limitations" but that goes for anyone with a screw driver!

The long term reliability/stability of this mod has not yet been proven.
I'll get back to you in another nine years.

Happy listening

It's time to move on to the next padded cell. I think I hear screaming...

If I understand how the A500 works adding the bridge array allows them to supply current to the output while recharging the off cycle coupling cap array every signal zero crossing. The bridge array still only recharges at 120Hz, and only replaces what the peak rectified signal off the bridge and transformer was doing (OEM) but it does it with a much more constant source of energy. Thus boucey bottom turns to slam and veiled midrange turns to smooth silk.

IMHO I just got the them Y-corded in and bi-wired Bi-amped out. I wish I had done this nine years ago. They are really playing out of there league. again IMHO.

Another observation is that the extra stored charge puts a strain on the power supply during power up...You can hear the power transformer buzz on units without the thermistor. Not a big fan of this form of in rush current limiting but...in this case works just fine. Power cycling before the caps have discharged will put a little thump into your speakers...! So the fancy solution would be a timing relay that step starts with a resistor and shorts or opens the output. But the $210 DigiKey wants for a quality relay is to steep for this project.

Happy listening.