Avoiding big caps on solid state preamp inputs

[Lampie519]

Mono preamps and poweramps (the preamp is still under construction).
The poweramps are a Zotl design and the preamps have integrated D/A converters (also mono). This way i can get 192Khz over S/Pdif per channel.

 

[k brown]

What happened to the OP?

 

[Lampie519]

It is still on topic (sort of) as it shows that electrolytics are used as coupling capacitors (actually used and not just talk about it) in these amps (D/A converters mainly) with good results (at least for me and the person who is using them).

Interesting to know is that some sought after vintage gear is full of electrolytics (tantalum mainly) in the signal path and nobody seems to mind.

 

[gyraf]

don't underestimate the sound of modestly-dimensioned tantalum capacitors as a significant part of e.g. the Sontec sound

 

[k brown]

don't underestimate the sound of modestly-dimensioned tantalum capacitors as a significant part of e.g. the Sontec sound

'70s Neve gear also had a lot of signal-path tants, but it seems since then tants have gotten worse, while electros have gotten better.

 

[Lampie519]

Electrolytic capacitors have definitely gotten better but i wouldn't know if tantalum caps have gotten worse as i don't use them much (only mil grade and Polymer tantalum i use occasionally but they are not as transparent as the Os-Con's in my opinion).

 

[soapfoot]

it seems since then tants have gotten worse, while electros have gotten better.

Interesting, this is the first I’ve heard this alleged.

Is this just a subjective impression, or are tantalums now objectively measuring differently in some way?

 

[Mr. Moscode]

Tants don't seem to have long term reliability is my experience and going film where possible is to my ears always an improvement.

 

[Henke]

Through-hole tants have generally become way less reliable lately in my experience, while SMD tants are just fine

 

[soapfoot]

Interesting. Does operating at more conservative voltage (e.g. using a 25v part in place of a 16v part) seem to help?

 

[JohnRoberts]

This is an old anecdote (of mine), I generally avoided tantalums during recent decades. Back in the old days, tantalums were popular for their density (high capacitance for small size), but notorious as fire-starters when they short circuited across PS rails. Tantalums were notorious for poor dielectric absorption (DA), another specification blown out of proportion by the audiophile crowd. BUT back in the 70s I offered to do a kit article for Popular Electronics, in return for a cover story (you can't buy that kind of advertising). The design they wanted was a CX record decoder. A now obscure encode/decode vinyl noise reduction system. This technology was developed by CBS Records and I was provided a free license with full support package.

This was not very difficult, a simple 1:2 downward expander to complement the encoder 2:1 compression used to master the vinyl. As part of the licensee documentation I received a copy of the circuit design of the mastering 2:1 encoder designed by Urie (well respected for signal processing). To my unpleasant surprise I found a tantalum capacitor in their side chain primary time constant. In my experience DA is pretty innocuous in dc blocking audio paths, when used in a side chain, however the DA can actually make a difference. I arguably over engineered my decoder. I used a tantalum capacitor in my decoder side chain so any DA errors introduced to the encode control voltage would be symmetrically cancelled out in the decoder.

In the process of dialing in the time constants I found a mistake in the pro-forma decoder schematics that CBS provided (about a 10% error to the time constant). I made my decoder accurate to the published CX standard time constant, and notified CBS of the error in their published recommended circuits.

I delivered my finished article to popular electronics in time for the Christmas issue. Shortly thereafter while I was attending the AES show in NYC I wandered into the Urie booth and introduced myself to them. They responded "so you're the guy who found the mistake" . Then they shared that because multiple consumer companies had already manufactured a few 10k playback decoders using the wrong time constants, CBS decided to change the encode time constant to agree with the mistake.... making me the odd man out, because I did it right. As soon as I caught my breath I called the editor of Popular Electronics and tweaked my side chain (one resistor value) to agree with the new wrong time constant. Of course CBS never notified me of the change, I only found out by my chance meeting with the Urie design engineers.

JR

 

[Mr. Moscode]

Interesting. Does operating at more conservative voltage (e.g. using a 25v part in place of a 16v part) seem to help?

I don't remember the failure mode, whether they short, open or leak, but not using them in my designs made them 100% reliable. . . you dig? There are better choices.

 

[soapfoot]

I don't remember the failure mode, whether they short, open or leak, but not using them in my designs made them 100% reliable. . . you dig? There are better choices.

Understood, but they do seem to “do something” to the sound in certain applications (Bateman demonstrated very large contributions of second harmonic in some use cases)

I once removed all of the tantalums from the record and repro electronics of an Ampex AG-440-B, replacing with film or aluminum electrolytic. The difference was truly not subtle (I don’t use “not subtle” like an audiophile would… I mean it was actually really obvious).

If replicating or repairing a vintage unit known for color I can imagine wanting to retain them.

 

[Lampie519]

That is indeed a danger when “updating” vintage gear. First off all we don’t know how it sounded when new and second we change the sound if we want it or not. In some cases the magic is lost after replacing components and it is hard to find what component is responsable for this loss as most of the time multiple components have been replaced in an overhaul.

 

[Mr. Moscode]

Mono preamps and poweramps (the preamp is still under construction).
The poweramps are a Zotl design and the preamps have integrated D/A converters (also mono). This way i can get 192Khz over S/Pdif per channel.

Cool. Tube outputs? Watts?

 

[Lampie519]

PL508, about 10 watt.

 

[Mr. Moscode]

PL508, about 10 watt.

How's the sound? Specifically the top 2 octaves? Imaging?

Thanks

 

[Lampie519]

Similar to OTL but more dynamic. Holographic and free of artifacts. No listening fatigue ever yet bright and airy by nature.
(maybe start a new thread?) ZOTL and ferrites

To keep on topic: I recapped my old and trusty TNT-200 (Acoustat) and it became a different beast .... more detail as it sounds less compressed, all very subjective naturally as when you invest time and money into a project you expect it to be better....

An audiophile friend of mine claims that the audio set sounds better after a rainy day as the grounding is better because of wet soil, who can can say...

 

[Mr. Moscode]

I have a pair of Futtermans I went to town on. 10 output tubes 200 W/8/ch. I came up with an enhanced triode circuit for the outputs. It's airy and holographic and I pair it with Quad 63s (modded). Still the best I've ever heard. It also drives up the electric bill.

So the Zotl is David Berning's idea, right? Using output tubes as a digital switcher amp?

 

[Lampie519]

Yes, David Berning's invention. Not digital, this is a misconception. Futtermans are great as well (i had a phone call once with Harvey about my problems with oscillation he helped me solving it).

I guess this is way off topic... sorry about this. Please start a new thread.