Preamp power supply capacitor upgrade

I recently purchased a used Backert Labs Rhumba Extreme 1.3 preamplifier. Although it sounds excellent, I’m on a quest to get it to sound as close to the Backert Labs Rhythm as I can on the cheap. I’ve already sent it back for the 1.4 circuit upgrade and I upgraded the coupling caps to V-Cap ODAM’s. I’ve also upgraded the tubes to Amperex 7316’s from several recommendations here. For reference, my amplifier is Coincident Frankenstein 300B MkII and speakers are Reference 3A Reflectors.

The Rhythm power supply uses four 0.33uf V-Cap CuTF caps which gets rather costly at $218 each. However, the TFTF caps are discounted at $104 each.

My question is, since these would be used in the power supply, would the price differential justify going with the CuTF vs the TFTF?

Ag insider logo xs@2xyowser

I would have a very difficult time justifying a high-end bypass cap there.  My suggestion is to get a Cornell-Dubilier of that value and see if you hear any difference at all.  CD makes excellent bypass caps by the way, so if you like them, leave them in and send me the difference.  :D

@yowser I've worked with the V-Caps a lot. The Copper foil series is audibly superior (and measure better as well). Given how you're going about this the cost differential seems irrelevant.  I do feel compelled to point out however that as coupling caps the copper foil caps are better than the ODAM parts (which are quite good). You might want to rethink this.

I forgot to mention, the V-Caps would replace Jantzen Audio Silver Z-caps which retail for $23.

@atmasphere Thanks for chiming in!  I did consider the CuTF's for the coupling caps but they are not available in 2.7uf.  I wanted to retain the specification of the existing circuit.

@erik_squires I understand what you're saying and is partially why I posed the question.  Below is Backert Labs justification for the V-Caps in the power supply:

"At Backert Labs, all of our preamplifiers use the new GreenForce™ power supply.  Because GreenForce is totally unlike previous power supplies, Bob Backert was granted a patent on GreenForce in 2013.

For those who are familiar with electronics, an example of the surprising quality of GreenForce is that the capacitors used to power our Rhumba preamp total less than 1 uF (one microfarad). Most power supplies for a similar preamp would use hundreds, or 1000’s of microfarads.

Because so little capacitance is needed, GreenForce is the only power supply in the world that can run a stereo component entirely on PTFE capacitors such as V-Cap™ capacitors, which we feel are the finest type of capacitor for a power supply available today."

And another excerpt:

"The heart of any power supply is its capacitors.  Similar to batteries, capacitors provide the power for your equipment to operate.

The GreenForce power supply employed in all preamps by Backert Labs is unique, in that it allows the use of extremely high quality capacitors to run the power supply.

In our Rhumba and Rhumba Extreme models, the GreenForce power supply uses very high quality polypropylene capacitors for extremely linear and nimble response.

In our Rhythm models, the GreenForce power supply uses the costly V-Caps™ copper/PTFE capacitors. Online capacitor comparisons such as The Great Capacitor Shoot-Out tend to rank V-Caps in first place (and that is with the tin version of V-Caps, rather than the upgraded copper version that we employ).

The Rhythm 1.3 preamplifier is the only audio component in the world with an all-V-Caps or all-PTFE power supply.

The results:   Incredibly fast transients.  Tight, accurate bass with visceral texture and punch. Extremely accurate timing.  Incredibly fast dynamic changes — dynamics that really tell the story of what is on your source material."

I just went over to DIYaudio to read about this power supply and the patent.  I can't say I would not absolutely use a great big cap right around the outputs and solve all my problems!! 🤣

So, I'm stepping back from this discussion as I'm not only not familiar with the thinking behind it but also have a number of questions that I don't have time for.

Miflex makes an excellent copper cap.  Mundorf also makes a nice sounding cap for a lot less.  Not sure of the specs you require though.

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Thanks for the suggestions!

@bigkidz The Miflex copper foil/polypropylene oil and Mundorf Supreme silver gold series are certainly within budget and worthy of consideration.

@alan60 The "vertical" configuration of the leads of Duelund would may pose a problem, so I’d like to stick with the "horozontal" configuration.

I would be interested if anyone has any thoughts on the Audyn true copper max or silver series metalized silver polypropylene.

I think I’m beginning to over think this, so might just stick with the discounted V-Cap TFTF since it’s going in the power supply.

@mark200mph The cap supply store I use is partsconnexion.

@yowser Your goal here is, I assume, to improve performance.

To that end, by bypassing the power supply, what you want is uniform output impedance of the power supply at all frequencies. So the correct dielectric may not be the one that is also the most expensive!

I'd stay away from oil and paper parts as they have a way of developing electrical leakage and may also leak physically. We stored a bag of such parts for about 10 years and upon retrieval, found that the bag smelled of oil. So for reliability I would not use such parts if DC voltages are involved.

@yowser I used thr Audyn True Copper Max caps in a recent phono stage build. The enameled leads were cumbersome, but they sound fantastic. My impression of them is they're a little more present and less euphonic than Miflex but still that big soundstage and smooth copper foil sound. Very nice caps. 😁 They're not small caps though so make sure you have some space.



If you go 'on the cheap' now, you will always be questioning whether you should have bought the better capacitors. Audiophilia is all about seeking that elusive 'Perfection' - usually at any cost! If you don't upgrade now, you probably will further down the road. Go for it...

I'd reach out to Chris VenHaus at VH Audio (supplier for V-Caps), he's busy but very helpful when he gets back to you....I'd get his input here if it were me.

Also I believe his prices are lower than what you mentioned, and he offers a 20% quantity discount 

@atmasphere Yes, I was somewhat concerned about leakage over time but wasn't sure if it was a legitimate concern.  So, I guess that would point toward the V-Caps or Audyns as being more appropriate in the power supply.  I must say that I'm leaning towards the V-Caps as that's what Backert Labs had chosen for their Rhythm.  I understand what you previously said about the cost difference between the CuTF and TFTF being irrelevant (although $450 difference when using four is somewhat relevant to me), I just wasn't sure there would be a noticeable sonic difference when used in the power supply.

I just exchanged a few emails with Chris VenHaus and explained my dilemma.  In a nutshell, he said go with the TFTF's in the power supply which was what I wanted to hear but not confident enough in my knowledge of circuits and capacitors to decide for myself.  So I guess I'm good to go and thanks for all the replies!

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