What is this Adcom GFA 545 Mod?

M

Markkueh

Active Member
Just picked up this Adcom at local thrift and found this inside. Looks like someone added some capictors and professionally attached them to the bottom with duct tape. All are now loose and one became detached which I'm guessing needs to be re-soldered. Also appears 2 yellow caps were added to the boards.

Excuse my ignorance but what does this mod do? Also, when resoldering do I have to consider polarity, I don't see any markings on the brown capictor.

Before I opened it, I used it for a short time and it worked fine and sounded pretty good
 

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Markkueh said:
Just picked up this Adcom at local thrift and found this inside. Looks like someone added some capictors and professionally attached them to the bottom with duct tape. All are now loose and one became detached which I'm guessing needs to be re-soldered. Also appears 2 yellow caps were added to the boards.

Excuse my ignorance but what does this mod do? Also, when resoldering do I have to consider polarity, I don't see any markings on the brown capictor.

Before I opened it, I used it for a short time and it worked fine and sounded pretty good
Click to expand...
Remove them.
 
My guess is that anyone who uses duct tape to 'secure' capacitors would likely leave a trail of messy work that would be relatively easy to spot. If you don't see any damage perhaps just snip these caps off.
 
yeah, film cap bypasses with poor mounting. There is some amount of mysticism about sticking film capacitors across electrolytics. Supposed to do all kinds of magical things, but at the frequencies that exist in an audio amp I don't really see the point. If you must, use ones that will physically fit between the stock terminals, not some big stupid caps that have to be stuck in with duct tape.
 
OMFG :rflmao:

The whole point of putting bypass caps across electrolytic capacitors, is to provide a lower impedance at high frequencies, where the electrolytics start to lose it. The inductance of those long leads to the capacitors negate any perceived benefit. Also, smaller capacitors tend to do better at high frequencies than these big chonkers.
 
Even better: The inductance of the wires that feed power to the GFA-535/545 board, limits the effectiveness of any bypass cap.

I don't actually install them on the power supply filter caps. Instead, I install 47-100uF local power supply bypass caps, and give them their own ground return wire to the power supply board.

On the underside of these electrolytic local bypass caps, are soldered a pair of 0.1uF polypropylene caps. Sorry I don't have a picture of the bottom, where I tap into the power traces, and where I put attach the common ground wire that goes back to the power supply star-ground.
20170116_021951.jpg
 
C609 and C613 are supposed to be 47uF electrolytic in parallel with a 1uF polyester. This hangs off the negative side of the input LTP, in series with 1K, and AC couples it to ground. Suggest installing your favorite 47uF electrolytic in parallel with a 1uF polypropylene. It's also possible to find a polyester 47uF capacitor that is compact enough to install without resorting to long leads.
 
much more effective if they are as close to where they actually need to provide decoupling anyway.
 
Markkueh said:
Just picked up this Adcom at local thrift and found this inside. Looks like someone added some capictors and professionally attached them to the bottom with duct tape. All are now loose and one became detached which I'm guessing needs to be re-soldered. Also appears 2 yellow caps were added to the boards.

Excuse my ignorance but what does this mod do? Also, when resoldering do I have to consider polarity, I don't see any markings on the brown capictor.

Before I opened it, I used it for a short time and it worked fine and sounded pretty good
Click to expand...


would agree with a few others. Someone added film bypass caps to the stock filter caps and did not mount them in the best method. As long as you don't ship the amp, they should stay in place.

if you remove them you'll get the sound of the electrolytic caps. Adding bypass caps is/was quite common. Many manufacturers now do it as SOP.
 
Was that audiophile duct tape? Need brand, colour, cost, bandwidth , silver or gold rubbed, cryogenically treated? Vibration damping factor.Did music hold together or fall apart post removal.
 
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