Upgrading Power Supply Caps

M, I'm sure some will say that these are the most-important caps in the amp. I don't agree totally with that, but conrad-johnson seems to believe it--some of their preamps use only film caps instead of electrolytics (els) in the PS. I can remember decades ago when the M75 (?) was upgraded to the M75a; they simply removed els from a decoupling position. I suppose that because the output transistors in a solidstate poweramp are connected directly to the last PS cap, the quality of the caps is MOST important.

I'd look at Michael Percy's el caps, here http://www.percyaudio.com/Catalog.pdf. See what you can afford, and don't forget that you can distribute the PS caps in different places around the amp and that it helps to use smaller values the closer to the output device the power gets. Also, I'd use as much polypropelene capacitance (the Solens are good choices here, as they're good quality, relatively 'small', and relatively inexpensive) as bypasses, with smaller, higher-quality bypasses (TRTs? MultiCap RTXs?), some as close to the transistors as I could get them.

It stands to reason that even though they are not in the signal path that upgrading caps with something better would still help the sound. Unless you don't think upgrading PCs, outlets, and wiring make a difference. If you don't, then it's a waste of time and money.

If you're talking about the large can caps, I renewed the ones in a Threshold S/300 Series II a few years ago. I searched the web for electrical equivalents. Then narrowed it down further to which ones were identical in size. Since my plan was preventative maintenance, finally I chose what was in there to begin with - computer grade Mallorys - only slightly higher in voltage and capacitance; exact replacements were no longer being produced. The Mallory website showed how many of each type were on hand and pointed me to an electrical supplier who could get them.

The switch out was simplicity itself, requiring only a screw driver. Nonethless, keep notes on the postions of the fasteners, the wiring and the orientation of the plus and minus signs marked on the caps.

I hear the rectifier bridge benefits from replacement at the same time but I didn't bother. When it was all done the amp was a maybe a little smoother and more liquid but it could have been my imagination. The main improvement was to my peace of mind.

The caps that you have are probably still within spec on this amp given its' age and the caps used. As such, i would add more to what you already have. Given the size constraints of the amp, you might be better off going with a bank of smaller caps. In turn, you could bypass these with an array of even smaller caps. Using a wider array of values increases the filtering action that is achieved, reducing in a blacker background and less grain. I would also replace the bridge rectifier while doing this. It is your choice as to go with a standard replacement or to go with some other type of "high grade" rectififiers. It it were mine, i'd be using high current Schottky's rather than stock rectifiers. This may lean the sound out a tad due to less ringing, but the increase in clarity and liquidity should easily out-weigh that. The use of snubber's across the rectifiers may / may not be beneficial depending on the quality of your local AC. Some say that these are not necessary with Schottky's, etc... but RF bypasses are always beneficial as far as i'm concerned. Then again, i live in a highly populated area with filthy AC. If your way out in the woods with pretty clean AC, it may not do anything for you. Sean
>