Power supply upgrades

Elizabeth, have you heard equipment with power supply upgrades? I only ask because I have heard of folks who did power supply upgrades and claim to have heard positive changes. I suspect this to be truthful as some manufacturers and modders offer upgrades to power supplies that contain premium parts.

At one time an outboard (separate chassis) set of additional electrolytic capacitors was a popular mod. Easy to do. It was helpful if the amp's power supply was undersized.

I'm not familiar with the Nichicon electrolytics, but assuming they are of at least decent quality I don't think you'll gain anything by replacing them. You might realize some small benefits by paralleling ("bypassing") them with good quality film caps, of lower value, although I agree with Elizabeth that capacitors in the signal path are much more critical.

Electrolytics provide filtering of ac ripple, and energy storage. They almost invariably provide poor performance at high frequencies, so bypassing them with a polypropylene or other good film capacitor will potentially help filter out noise or other garbage before it reaches the components that are in the signal path (where power supply decoupling/bypass capacitors are presumably incorporated as well, but cleaning up the dc voltages as much as possible before they enter those areas can't hurt and might help).

The capacitance values you listed for the electrolytics strike me as adequate for the relatively low and fairly constant current draw of a 3 x 12AX7 phono stage, so I don't think there is anything to be gained by increasing their values. Adding the film bypass capacitors will, of course, provide a bit of added capacitance as an incidental benefit.

Regards,
-- Al

Thanks Al, the film bypass caps have been my first inclination from the start. What value bypass caps should those electrolytics be bypassed with? I've heard various percentages discussed in various forums, or is simply bypassing with .1uf caps good enough?

Also, any suggestions as to best axial resistors for the signal path in the Cayin? The Vishays and Texas Instuments are impossible to fit here.

Thanks again, Scott

Increase your filter capacitance, and replace your rectifiers with FREDs. I've done the former in the past(in tube amps) with excellent results. That's one of the first things most tube amp modders address, as it will improve the amp's bottom end performance and, overall, make everything sound more effortless. I just did the latter in both my SS woofer amp, and two Cary monoblocks. The results/improvements are too numerous to list, but the dynamics, slam and resolution you are seeking will be presented "in spades". I used a pair of IXYS VBE 17-06NO7 in my SS amp, and six IXYS DSEI 12-10A each in my Carys. Those are easily obtained from Digi-Key. How I wish that Black Gate was still manufacturing their large filter caps, or that Sanyo had OS-CONs big enough for amplifier power supplies. Al's filter cap/film cap bypass suggestion will also yield improvments. OOPS- I also recently upgraded the power supply in my TacT pre-amp, using FREDs and OS-CONs. Made a whole new beast out of it. I got carried away, talking about the power amp mods. SORRY! =8^) The tubes you choose will make a dramatic difference in your presentation also. Regarding the resistors: See if any of Caddock's will work in your app: (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeMK.pdf) Read the bottom of the data sheet.

What value bypass caps should those electrolytics be bypassed with?

I don't think it's particularly critical, as long as the bypass caps are of good quality. Anything from 0.1 to several uf strikes me as reasonable. If you find indications of particular values that worked well for people, in the forums you spoke of, go with those, but quality is probably more important than value.

Rodman -- As I think you indicated towards the end of your post, I'm not sure that the improvements you cited, which were mostly with power amps, would be relevant to a phono stage's power supply, where the current load is much more stable as well as much lower.

Regards,
-- Al

If he could find some Black Gates to directly replace the caps he has, there would definitely be an improvement with regards to dynamics. Some of their old suppliers still have the smaller values in stock, although at a premium. Upgrading to Black Gates, or Sanyo OS-CONs will improve dynamics installed in any circuit that provides gain. I believe he could easily find them for his phono pre. If the pre has rectifiers, replacing them with soft recovery FREDs will yield even greater benefits. These things just hold true, regardless of the power supply's application.

Rodman, my problem in replacing caps with Black Gates is firstly their size, the size of the circuit board is seriously limited. My old Cary monoblocks were all point to point wiring, much easier to swap out ps caps. Secondly, Black Gates are mostly lower voltage, 160v highest for 100uf, 350v for .22uf (I suspect enough here). Is the 160v rating high enough in this application?

I have investigated swapping out rectifiers, the problem is severe space limitations. I have two bridge rectifiers, RS804 and BR310, building my own from FREDs looks impossible to fit.

Caddocks are on my list of possible resistor upgrades.

Al, I'm willing to try premium electrolytics, at this point I'm leaning towards trying the bypass solution to begin with, if that works, fine, if not, try the upgrade electrolytics route. At the very least it would be an interesting experiment. What do you think about the 160v rating on 22uf caps, enough?

I've been doing a bit of investigating on the new Takman 'ultra premium' resistors. Sound very promising considering the few who have tried them. These would go in the signal path. Anyone have experience with these?

What do you think about the 160v rating on 22uf caps, enough?

I don't know what voltage the power supply is outputting to the plate circuits of the 12AX7's, but I suspect you should go with a considerably higher rating on the caps than 160V. Perhaps the 12AX7's are being run somewhat lower than 160, but probably not much if anything below 120 or 130V. And the 12AX7 and 12AX7A have rated plate voltage maximum's of 330V, so in the absence of further information it could very well be that they are even being run a bit above 160V.

Good derating practice in my experience as an electronics design engineer (although it was in defense avionics, not audio!) was considered to be a factor of 2 or more. Meaning use capacitors with voltage ratings of 2 or more times the actual voltages that are likely to be encountered; otherwise long-term reliability is degraded.

And, finally, the 450V rating of the existing electrolytics was probably chosen for a reason!

Regards,
-- Al

Sns- I agree completely with Al about not replacing caps with anything of a lower voltage rating. Your RS804 can be replaced with an IXYS FBE 22-06N1. The Phono One seems to have a spacious chassis. I would think you'd be able to accomodate four IXYS DSEI 12's(TO-220 package) or one VBE 26-12NO7 without a problem, to replace the BR310, and run wires. I promise: The benefits will far outweight the effort.

Thanks guys, think I'll go with film bypass caps on ps caps. Rodman, thanks for the specific replacements for the bridge rectifiers, something I've been searching for!

Enjoy your music!!