DIY/T2 Electrostatic Amp Thread - General

[mulveling]

Thank you. That is an excellent explanation.



If you don't mind, a follow up question about this. For a standard amp, putting it at MAX means maximum gain and usually standard amps produce more distortion at higher gain (correct?). What is it about estat amps volume that causes MAX to mean, if I understand correctly, 0 dB of gain?



I do this because my Benchmark DAC-3b/HPA-4 has a remote and my BHSE is across the room from my listening seat.

A couple additional notes: often amps & preamps with the volume control up front will list "Max input: Infinite" in their specs, because you can always lower the attenuator level to handle any input signal (within reason). Components without a volume control up front will list a finite value for this specification, and you better be careful to heed it!

Downsides to the attenuator-up-front approach? The attenuator cannot attenuate noise produced from the active circuitry. This is only a problem when you have a large surplus of downstream gain + sensitivity. My speaker system, for example, at one time had a high-gain tube preamp (23dB) with a high gain amp (31dB) and high sensitivity speakers (96dB). You could really hear the tube rush noise floor from the preamp, no matter how magically selected the tubes were. The "adjustable input sensitivity" approach of that Meridian 808 allows for the best of both worlds - low noise floor and low distortion, assuming you pick the right level. But really, that was just a bad gain structure. I didn't need anywhere near that much gain.

 

[VandyMan]

Much thanks @mulveling. That clears up for me some things I've been wondering about for years!

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[VandyMan]

Most amps and preamps put their active circuitry *after* the passive volume control. So they're really running at "max gain" all the time!

This makes so much sense and I've been misunderstanding it since, well, forever.

 

[Beefy]

If you don't mind, a follow up question about this. For a standard amp, putting it at MAX means maximum gain and usually standard amps produce more distortion at higher gain (correct?). What is it about estat amps volume that causes MAX to mean, if I understand correctly, 0 dB of gain?

You just need to remember that the volume pot is mostly unrelated to amp gain. The gain of a BHSE is always ~1000x, regardless of the volume pot. The gain of my headphone amp is always 5x, regardless of the volume pot.

The way to look at a volume pot, or digital volume control, is that it 'throws away' (attenuates) some of the signal from your source. If your BHSE is set to maximum, it doesn't change anything, except it isn't throwing away any signal, your source does that job. If your source is at maximum, it doesn't change anything, except it isn't throwing away any signal, your volume pot does that job.

So, complications. Sometimes your source volume control has less distortion than your volume pot. Sometimes your volume pot has less distortion than your source. Sometimes an amp can have different gain settings that change whether you have to throw away more or less signal, and sometimes the different gains sound different.

All things considered, 1000x gain for an e-stat amp is fine. Turning the volume to max and using source volume control is fine.

 

[mbrennwa]

You get distortion from running the signal so high its peaks approach (or even exceed) the output stage's voltage rails (+/-350V to 500V). ... If you're controlling signal level from your source or a preamp and playing at normal levels, that doesn't apply.

I beg to disagree. No matter where you control the volume (at the source output or using the volume pot of the amp input), the voltage levels and non-linear distortion happening in the amplifier circuit is the same for a given amplifier output.

The only difference between controlling the volume at the source or at the amplifier pot I see is with noise. If the source output is at max. and volume is attenuated in the amplifier potentiometer, the noise pickup between the source and the amplifier (i.e., at the cable) will be attenuated by the pot. If the source output is attenuated and the amplifier pot is at max., the noise will not be attenuated.

 

[Beefy]

I beg to disagree. No matter where you control the volume (at the source output or using the volume pot of the amp input), the voltage levels and non-linear distortion happening in the amplifier circuit is the same for a given amplifier output.

The only difference between controlling the volume at the source or at the amplifier pot I see is with noise. If the source output is at max. and volume is attenuated in the amplifier potentiometer, the noise pickup between the source and the amplifier (i.e., at the cable) will be attenuated by the pot. If the source output is attenuated and the amplifier pot is at max., the noise will not be attenuated.

In this day and age, how many sources have problems with noise? Perhaps it might be an issue with analog sources (where you are unlikely to use source attenuation anyway), but I can't see it with digital sources.

 

[VandyMan]

In this day and age, how many sources have problems with noise? Perhaps it might be an issue with analog sources (where you are unlikely to use source attenuation anyway), but I can't see it with digital sources.

Maybe with a tube pre-amp? I'm using a Benchmark HPA4 which is as clean as they come.

 

[mbrennwa]

In this day and age, how many sources have problems with noise?

As I wrote, it's about the noise pickup between the source output and the amplifier input. And I never said that's a problem.

 

[Beefy]

As I wrote, it's about the noise pickup between the source output and the amplifier input.

Ok, so how many of us have *that* crappy cables?

And I never said that's a problem.

So why..... oh, never mind.

 

[oneguy]

I received my T2 back from Kerry last week but didn’t have a chance to hook it up until today due to a move. It’s sounding much better now.

The problem ended up being a cracked resistor.

 

[kevin gilmore]

so this whole voltage gain thing is a real mess now that some dac outputs are 10 volts or more.

the way it used to be done going back 60+ years is that the amp (or preamp) had the pot at the front of everything. with tube input things, no big deal, input saturation was 15 volts or more, and the standard signal was 1 volt. (rms)

there are now many items, most are tubes that put the volume control after the first amplifier and before the output stage. so if you turn the knob to zero, it is way more quiet than it would be at normal listening levels. so pretending to have a higher signal/noise ratio. but put it at normal playback levels and pause the source, and then there is noise. in fact there is a portable dac out there that when you put it into pause, it mutes the output.

there are some things now, like the audio-gd and the ayre kx-r-20 that now have 2 volume controls. 1 at the front end to prevent the front end from clipping, and the second one in the middle after the gain stage and before the output buffer (or amplifier)

in fact just about all solid state input circuits (differential, and dual differential) will clip somewhere around 5 to 6 volts input unless you put an attenuator up front.

the various versions of the cfa3 do the same thing. in fact its easy to clip the front end before the output of the first stage clips if you pick a lower overall output gain.
This is REALLY BAD for tweeters.

and most of this is due to our good friend amir whose one and only test is thd+noise.

noise is largely proportional to overall loop gain. and the noise of the input stage is fixed and significantly caused by the temperature of the input device.
so an electrostatic amp with a gain of 500 to 1000 will always measure about .01% thd + noise. no matter what you do. but if you just measure thd, then .001% or better.

so i have been messing around with dual peltier elements and cooling the input stage down to -60C. yep the noise goes down. a bunch. like 10db or so.
turns out you actually need a dual stage system with water cooling. so i'm not sure people are going to want to pay $4k for the peltier system for a $1k amplifier.

or put the whole amplifier et all in a insulated styrofoam box and keep the box stuffed with dry ice.
(and hope that the bias does not drift out of range)

just because you can make a dac with a 10v output does not mean you should.

 

[number1sixerfan]

I received my T2 back from Kerry last week but didn’t have a chance to hook it up until today due to a move. It’s sounding much better now.

The problem ended up being a cracked resistor.

Glad it was finally sorted for you! I know it's tough when an issue persists like that. Hopefully it's just happy listening from here.

 

[mbrennwa]

some dac outputs are 10 volts or more.

Really? Is this a peak-to-peak, peak-to-zero or sine-RMS number? Single ended or balanced? Can you provide an example of such a DAC?

 

[VandyMan]

and most of this is due to our good friend amir whose one and only test is thd+noise.

Very interesting post and perhaps to some degree Amir is to blame for bringing attention to that measurement, but hasn't that test been widely done for decades? Hasn't Stereophile done that test since like forever? And it is just not true that it is the only test he does. Just check any of his amplifier reviews. For example: https://www.audiosciencereview.com/...onic-m3a-600m-class-d-amplifier-review.56104/

 

[SolarCetacean]

Really? Is this a peak-to-peak, peak-to-zero or sine-RMS number? Single ended or balanced? Can you provide an example of such a DAC?

Ferrum Wandla outputs nearly 10V RMS from its XLR outputs. Not sure about which DACs Kevin was thinking of, but they exist.