HV ss line amps- advantages?

I see people swearing by hv preamps, running rather simple circuits at +/-24v or even +/-48v.

Assuming they are accomodating the same low gain structure, where you need a 2v input at no more than x3 gain, what advantage does the hv line amp have over the run of the mil +/-15v circuit?

And for the sake of the discussion lets say theyre both discrete circuits.

Will the high voltage allow for less distortion with higher bandwidth and linearity?

One advantage i see for hv architecture is if the ccs is passive the pssr could be higher due to higher value resistors.

With low voltage (15v), well, more published circuits to play around with, and stiffer psu is possible because as the voltage goes up the regulator designs gets more expensive/less refined.

What do you guys think?

P.s. the hv circuit i had in mind was bryston doa33
 
Wow, a reply for the man himself. Thank you Mr. Pass.

Now off to figure out how to get the best 24v out of an ic regulator. The 317 at this voltage has a severe performance degradation that begins at 12v, if im not mistaken.

Maybe lm7824 is better here. (Its also what bryston uses)
 
High supply voltages help when you need very low noise bias current sources for some reason.

I once made a preamplifier that used current rather than voltage to represent the signal in some parts of its circuitry. I found out rather late that a disadvantage was that the noise of the bias current sources added directly to the noise floor.

I planned to use +/- 14 V supplies, but after finding out about this noise issue, I added +/- 23 V rails so I could make really low noise bias current sources.
 
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HV line stages risk blowing up the next thing in the chain if something goes wrong (RCA plug loose!!).
That's a good reason to avoid in my book, that and the risk of electrocuting someone when they assume an audio signal is low voltage.

A potential reason to want more headroom might be to implement an EQ section with high Q stages and avoid clipping the intermediate signals, although careful ordering of sections should reduce this problem.

Professional mixing desks often ran everything at circa +/-18V without having to compromize performance.
 
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At +/- 24 V, the risk of electric shocks is still negligible. It's a different matter for valve preamplifiers with 300 V supply voltage. In fact, that's why I put neon lamps across the outputs of a valve preamplifier -their ignition voltage is still a bit high, but it's better than nothing.
 
Heres a circuit i listened to last week and frankly the 'musicality' of it shocked me. Comparing to my home built unit it was clean like a tube preamp, which no doubt is a sign of greater linearity. The company perreaux's subsequent models have not seem deviated much from this design so its something that works for sure.
 

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Looking at a variant of that Hitachi circuit about two feet away from me. Not sure I'd like ±45V on standard RCA connectors. Also the centre hot is typically connected before the ground/shield as the plug is inserted. I've also seen some connectors limit to a max of 25Vac. Personally I think there's safer and better connectors out there for those levels.
 
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Heres a circuit i listened to last week and frankly the 'musicality' of it shocked me. Comparing to my home built unit it was clean like a tube preamp, which no doubt is a sign of greater linearity. The company perreaux's subsequent models have not seem deviated much from this design so its something that works for sure.
If I had those voltages at hand I wouldn't touch transistors...I'd go full tube for safety reasons.There's no smoke comming out of tubes for sure.
 
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This was my circuit from 1994. The input signal is converted to two currents, one with a flat response (marked ongefilterd) over the audio band and a filtered one with almost only bass (marked gefilterd). Those are combined with the potmeters in such a way that you get a loudness control of which you can control the amount of compensation. The signal with flat response passes through two mechanically coupled potmeters, the filtered signal though only one of the two and through a separate potmeter, the one marked referentie, with which you can set the amount of loudness compensation. When you are in the volume range where the compensation is active, reducing the volume by 10 dB only reduces the bass by 5 dB. The noise is dominated by the bias current sources. The supplies are annotated as plus and minus 15 V and 24 V, but my discrete regulated supply was closer to plus and minus 14 V and 23 V.

augurkenblik_fysiologischegeluidssterkteregeling_klein.jpg
 
Thank you for pointing out that its hitachi!

Ive decided to recreate the sm2 circuit at 24v with bjt output, no other changes. I believe a lot of the magic i heard was from its ltp vas and i can recreate it.

As for the hazard of 45v, perreaux solved it by sticking 4uf mkp caps on the output. But with the dc dialed to near 0 along with large output current i bet the distortion contribution of the caps are neglegible.
 
Nothing new under the sun. :cool: Self analysed the circuit in his Audio Power Amplifier Design book, 6th ed. with +/-30V rails and a simple class A output stage. He said levels of distortion above H2 are very low. The dominant H2 comes from a slightly unbalanced LTP and VAS. Trimming the LTP so currents are balanced dramatically reduces H2. Perreaux do this in their amplifiers. A current mirror can help here too. I really like this topology myself and I've owned and really enjoyed several high end amplifiers and preamplifiers that used it. I prefer the use of a proper current source for the LTP to improve PSRR. The basic Hitachi circuit and the Perreaux designs use a simple resistor and save $1 in the process.

Self:

Self.png


Tilbrook:

Tilbrook.png


The phono stage in the Tilbrook preamp used almost the same topology, in two stages, but ran +/-35V rails to improve headroom before the volume control.
 
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