I'll let y'all guess why phono preamps need that much headroom.

Y'all don't need that much headroom.

Do you want us audiophiles to take our business elsewhere?

If you going to have a crappy attitude, than perhaps you should.
Audiophiles, with there "golden ears", often have reasons for doing things that defy engineering/technical logic (oxygen-free copper, anyone?), which is what is used here.

 

Phono preamps often have that much voltage headroom or higher.

I'll let y'all guess why phono preamps need that much headroom.

As a cheap way to reduce the input stage harmonic distortion caused by a non-flat transconductance function and poor design? Or because that's just the transformer they "always use"?

Also, #18 might be the best "audiophile" power supply I've ever seen, exactly what I would expect from such an esteemed source.

Also, I see that the circuit is assured of having frequency-dependent crosstalk between the two channels. Is there a graph in the spec sheet?

Free medical opinion: "Oxygen-free" might be OK for copper, but not so much for humans.

Do you want us audiophiles to take our business elsewhere?

You are presenting a unipolar circuit with *six* capacitors in the signal path (not counting the two in the equalization network), three of them electrolytic, one resistor labeled as a capacitor, a half-wave rectified, unregulated power supply with zero noise filtering and/or transient suppression (and no fuse!), zero power decoupling, very poor power supply rejection, an asymmetrical (and reactive) input impedance, an asymmetrical and not-very-low output impedance (and source impedance for the equalization network) as an example of your "audiophile"-ness. No great loss.

I recommend Stackex; they loooooove people like you. https://electronics.stackexchange.com/

ak

 

Well that's an excuse outta directly answering the headroom query if I've ever heard one. But maybe you're excused because AAC is not really an audio-specific community. Do you want us audiophiles to take our business elsewhere?

Do you understand what headroom means?
What is the output voltage of the phono preamp?
What is the noise threshold?
40 dB is 100 : 1 voltage ratio.
60 dB is 1000 : 1 voltage ratio.
80 dB is 10000 : 1 voltage ratio.
How much headroom do you need?

 

Let't try this again ...

23 V is a strange number. Plus, that is a *lot* of headroom for a phono preamp, no matter what the circuit is.

Explain what you mean by "headroom". And if that's related to 23V

 

Explain what you mean by "headroom". And if that's related to 23V

Speaking only for myself - the simple description is power supply voltage minus the peak signal voltage. That does not translate well to the current discussion because your example circuit (and its unbelievably bad power system) does not have bipolar power with the circuit's reference potential ("GND") midway between the two and not influenced by either. So a better-fitting description is (power supply voltage minus the maximum peak-to-peak signal voltage) / 2.

I mucked around with unipolar audio circuits like that back in the 60's and early 70's, then moved to opamps. They weren't great, but could be beaten into submission. What worked better was a "discrete opamp", a 6- or 7-transistor class-A circuit that mimicked the common opamp topology with way better GBW, noise, and high-frequency performance. Then the 5532/33/34 came out and the world shifted. "Harsh" sounding, TIM, blah blah blah - Yes, the 2134 is better in almost every parameter except noise, but it came along 21 *years* later. For two decades, the 553x just plain r.u.l.e.d.

ak

And - back then, many many many analog circuits ran on 6, 9, 12, and 24 V. It didn't matter that the device was not portable; people thought in terms of batteries. In that context, 23 V is curious.

 

And - back then, many many many analog circuits ran on 6, 9, 12, and 24 V. It didn't matter that the device was not portable; people thought in terms of batteries. In that context, 23 V is curious.

Yes, you can run an opamp based phono preamp on, say, two 9v batts. The decent Hagerman Bugle is an example.
https://www.hagtech.com/pdf/bugle.pdf
But, with phono, you can do better. So higher-voltage power circuits are an option. One reason for higher headroom is that when you get loud pops and clicks, you still retain some linearity.
Some more reasons:

 

Yes, you can run an opamp based phono preamp on, say, two 9v batts. The decent Hagerman Bugle is an example.
https://www.hagtech.com/pdf/bugle.pdf
But, with phono, you can do better. So higher-voltage power circuits are an option. One reason for higher headroom is that when you get loud pops and clicks, you still retain some linearity.
Some more reasons:

The real question is what does the phono pre-amp NEED -- and there are some nuances to this.

What is the minimum voltage that it needs to function at all? Will it work at 20V, or do the bias and/or other portions end up so out of whack that it effectively doesn't function.

Then there is the question of what the minimum voltage is at which it will operate acceptably well. Whether this is a need or a want depends on the specifics of the application and who gets to decide.

With that in mind, you are then in a position to consider the implications for your power supply and the viability of the options available to address the problem you are trying to solve (the excessive heating). Some of those options that might be most attractive might have the disadvantage of slightly lowering the output voltage. Whether or not they do so to a point that is unacceptable can only be answered if you know what you actually need.

 

Paul has a ton of cred, but this video is disappointing. Lotsa hand-waving, unsupported statements of "fact", and colorful opinions, but zero technical discussion about how increasing the electric field gradient *inside* a transistor might make its GBW, F(t), transconductance flatness, etc. "better", and what any of these have to do with its "sound". Yes, higher operating voltages can be a cheap way to improve linearity a small amount, but better circuit design is better.

BTW I still use the MPS8099 and 8599. OK for a power amplifier front end, but a bit noisy for a preamp input. The transistors in your Radio Shack circuit are better.

P1: I like the way tube circuits "sound".
P2: Tube circuits need high operating voltages.
Q: Therefore: The more transistor circuit voltages approach tube circuit voltages, the more transistor circuits will "sound" like tube circuits (that I already know I like).

No. The blazing problem here is that vacuum tube physics and bipolar transistor physics a.r.e. n.o.t. t.h.e. s.a.m.e.

ak

ps. In the 80's I spent a few years designing and maintaining equipment in a psycho-acoustics research lab. Back in my TV days I worked with a true "golden-eared wonder", but the lab quantified that while some of those people are real, they are few and far between.

 

Some more reasons:

At 2:49 he describes the same circuit i described in #25. My guess is that thousands of designers worked up the same circuit (or variations) independently.

Here is one of the earliest publications: https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1972-07.pdf

ak

 

What I have not seen mentioned is on the cover of that blue power transformer: Looking carefully it looks like there are two 115 volt primaries, connected IN PARALLEL for 115 volt operation OR CONNECTED IN SERIES for 230 volt operation.

The "cheap trick" would be to change the connections to put the two primaries in series. This would immediately cut the secondary voltages in half, from 36 volts to 18 volts. resulting in also reducing the DC output voltage by half. Simple, cheap, and probably easy.

IS THERE any information about the modules with the blue transformers???