eXStata DIY Electrostatic Amp for Intermediate DIYers

[manaox2]

I've been eyeballing the goldpoint mini-v stepped attenuator over the DACt CT-4 quad.

 

[jcx]

the point of my previous post was that there is little reason to want/need 4-channel attn with eXstata - with balanced or se source

Quote:

Originally Posted by jcx /img/forum/go_quote.gif I hate to see so much mental energy and money wasted on balanced input for the exstata - having a high impedance differential front end it can accept single ended signals and still give the same output performance - up to the limitations of its low loop gain and consequent sensitivity to matching just about all of its components it is unlikely that enough have been built that that even one exits (by statistical chance) that actually would give a "better balanced" output with balanced input vs single-ended input given device and component parameter distributions - that are not being measured/matched/trimmed even with balanced source you could save money with dual attenuators with little to worry about in loss of "sound quality"

and earlier:

Quote:

Originally Posted by jcx /img/forum/go_quote.gif Some wrong and misleading info being tossed around this thread re gain and balanced/single ended here The amp is a true differential amp, there is a single gain # applied to Vin difference – it doesn’t matter whether the input is SE or dual polarity/balanced with respect to gnd With 500:1 feedback resistor ratio the differential gain would be 1001 (assuming high enough loop gain - which the circuit doesn't have) There is also a small common mode gain of ~1x With “balanced” input the a,b stator drive signals would be +,-500.5x With SE signal, - input gnded, stator a would see +501x, b –500x The trivial gain imbalance w/SE drive is much smaller than component tolerances – you’d need better than 0.1% tolerance feedback R and > 1e6 open loop gain for these errors to become the same order of magnitude – you could buy or match the feedback resistors but you need more active devices to get the open loop gain Just to spell it out in small words - - this amp doesn’t need/won’t benefit from balanced vs SE input signal -- worrying about balanced input is completely myopic audiophilia nervosa

 

[les_garten]

Heard ya the first time.

No real need to make a post quoting yourself

 

[BoilermakerFan]

So why not just use an SE OptiVol or Nobel in a shunted Pot config? Use nice boutique resistors of your choice, Rikens, Caddocks, Dales, Holcos and you're still under $50 and can get that down to under $30 with Holcos...

Going with a lower R value puts less input impedance variance on the amp and the PVA transformers are optional if you don't want the gain (and we don't need it on the eXStata), but they let the source see a constant load. The catch with the OptiVol is it needs a power source, but it draws 100mA or less. Can't really steal the power form the standard transformers in either eXStata build, but a tiny Hammond or similar would work.

 

[pabbi1]

N/m

 

[jcx]

Quote:

Originally Posted by les_garten /img/forum/go_quote.gif Heard ya the first time. No real need to make a post quoting yourself

3 posters looking for 4 channel atten on the previous page seemed reason enough for me to reiterate and bring to the fore a buried (>1500 posts ago) technical argument

I'm trying to initiate a discussion of the technical issues - how about your not worrying about someone else's posting style, particularly those with less than 0.2% of the thread's post count




when the project goal is a cost effective amp it seems valuable to examine an option that does not appear to have a obvious/predictable (deleterious) effect on sound quality and that does reduce cost, increases builders' options and eases part availability

 

[pabbi1]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif 3 posters looking for 4 channel atten on the previous page seemed reason enough for me to reiterate and bring to the fore a buried technical argument I'm trying to initiate a discussion of the technical issues - how about your not worrying about some else's posting style, particularly those with less than 1% of the thread's post count When the project goal is a cost effective amp it seems valuable to examine an option that does not appear to have a obvious/predictable (deleterious) effect on sound quality and that does reduce cost, increases builders' options and eases part availability

Yawn - open your own thread. And, I don't see anything in your post regarding eXStata that you couldn't tilt in virtually any balanced / differential thread. Your desire to 'initiate' something seems fairly hostile and counterproductive to the 20 or so rather experienced builders here, with a few rookies.

 

[les_garten]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif 3 posters looking for 4 channel atten on the previous page seemed reason enough for me to reiterate and bring to the fore a buried (>1500 posts ago) technical argument I'm trying to initiate a discussion of the technical issues - how about your not worrying about someone else's posting style, particularly those with less than 0.2% of the thread's post count when the project goal is a cost effective amp it seems valuable to examine an option that does not appear to have a obvious/predictable (deleterious) effect on sound quality and that does reduce cost, increases builders' options and eases part availability

You made your point the first time. Sorry you were ignored. That's no reason to bring it up again. Starting your own thread seems like a great idea. You've made your point twice now.

 

[Beefy]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif 3 posters looking for 4 channel atten on the previous page seemed reason enough for me to reiterate and bring to the fore a buried (>1500 posts ago) technical argument I'm trying to initiate a discussion of the technical issues - how about your not worrying about someone else's posting style, particularly those with less than 0.2% of the thread's post count

The solution to the problem isn't to just give up on balanced attenuation, but to find a better option for balanced attenuation.

And the assumption that everybody is just going after balanced for some audio-peen is silly. My DAC has 1 set of balanced and 1 set of unbalanced outputs. The unbalanced outputs feed my M3, the balanced outputs remain unused...... why would I not use these for the Exstata?

*

So back the to the original discussion.

For my money - less than $50 - a dual PGA2320 controller is just perfect. Excellent channel matching, no drift over time, no mechanical connections. Some people would be afraid of the fact that it is essentially an OPAMP in the signal path...... but considering everything of mine is solid state, I couldn't care less

 

[cfcubed]

We should leave this, but as one of the attenuator "tangentors" I side w/jcx here. Certainly attenuators were more OT than the points he's trying to make, even if other threads may be best for both. Can see how it seemed the topic/value of his recent posts was lost in a largely OT tangent. There's detailed, relevant info in those posts.

Having tried to keep CTH threads on-topic; it's a difficult & worth-while thing to do.
I'll exit here as I've no eXStata-specific stuff to discuss

 

[pabbi1]

Moving way on, anyone else have observations OR, mod ideas?

 

[minivan]

is dual mono power supply possible? can the amp handle that much power?

 

[digger945]

Quote:

Originally Posted by BoilermakerFan /img/forum/go_quote.gif So why not just use an SE OptiVol or Nobel in a shunted Pot config? Use nice boutique resistors of your choice, Rikens, Caddocks, Dales, Holcos and you're still under $50 and can get that down to under $30 with Holcos... Going with a lower R value puts less input impedance variance on the amp and the PVA transformers are optional if you don't want the gain (and we don't need it on the eXStata), but they let the source see a constant load. The catch with the OptiVol is it needs a power source, but it draws 100mA or less. Can't really steal the power form the standard transformers in either eXStata build, but a tiny Hammond or similar would work.

Could I trouble you for a link to those PVA transformers you are referring to, please sir?
I'm interested. Thanks kindly.

 

[luvdunhill]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif Could I trouble you for a link to those PVA transformers you are referring to, please sir? I'm interested. Thanks kindly.

Don't you have another attenuator to be building

Anyways, I'll take a shot:

Electra-Print.com PVA Passive Audio Pre-Amplifier

but, there are others out there:

intact audio

My favorite are bifilar wound TVC for use in balanced applications. Basically two of the above on a single core. But as far as I know, the only real options are customs, which is the route I went.

 

[digger945]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Don't you have another attenuator to be building

Um, yea, I need to get cracking on that don't I.

Quote:

Anyways, I'll take a shot: Electra-Print.com PVA Passive Audio Pre-Amplifier

Oh, yea. That's the one that is mentioned earlier in the thread I believe. Thought it was something new.

Quote:

but, there are others out there: intact audio

Yea, I go there and eyeball those every so often.
The pics of the Slagleformers have been removed from the bentaudio site, so I need some pron from time to time. You know.
Quote:

My favorite are bifilar wound TVC for use in balanced applications. Basically two of the above on a single core. But as far as I know, the only real options are customs, which is the route I went.

I've seen these somewhere else before. hmm.