What is responsible for soundstage in a preamp design?

[k brown]

Define "sufficient gain".
I suppose you mean voltage gain.
It depends very much on the level issued by the microphone and the destination of signal.
One could imagine a microphone with an output of about -20dBu. A 1:10 xfmr would elevate the signal to 0dBu, which may qualify as line level, but then it would certainly need at least one active stage to present it to the subsequent circuits, e.g. a magnetic head or the input of a A/D converter.
In order to produce -20dBu, the mic would almost certainly need an active stage, or use a very large transducer which wouldmake it impractical and of dubious use.
At least one active stage is needed in the signal chain.

I would say 'sufficient' in the sense of making for a practical commercial product that would have any appeal in the marketplace. The pres in my (now-ancient) Tascam HD-P2 only provide 40dB max, and most reviewers considered it the bare minimum for a commercial product; insufficient with dynamic mics in most cases.

 

[abbey road d enfer]

Magnetic amplifier - Wikipedia In a sense, yes. Not by only using a trafo, but in combination with DC supplies

Can they qualify as "passive"? Actually, although I have no doubt about what qualifies a stage as active or passive, I couldn't find a proper definition of it.
Listed active components are essentially tubes and semiconductors. However, the use of the non-linearities in a magnetic amp xfmr makes it an active element IMO. I believe that the ability of a system to modulate an output under control of an input is what makes it active. Same for Coanda pneumatic amplifiers.

 

[abbey road d enfer]

I would say 'sufficient' in the sense of making for a practical commercial product that would have any appeal in the marketplace. The pres in my (now-ancient) Tascam HD-P2 only provide 40dB max, and most reviewers considered it the bare minimum for a commercial product; insufficient with dynamic mics in most cases.

Clearly, the answer is no. In order to provide 40dB of voltage gain, the xfmr would have a ratio of 1:100, which would result in an output reflected impedance of 1.5-2 Megohm.

 

[k brown]

I don't know how off the rails use of that term has become, but for the first many, many years of it's use it referred to a device that was nothing more that input selector switch and a pot (usually ~10k ohm) between sources and power amp. Obviously how well they worked depended heavily on the input impedance of the pwr amp, and drive capability of the sources.

Sometimes the term was still used (however inaccurately) for devices that placed only a unity gain buffer between the pot and the amp. An example is the First Watt B1 Buffer (though they didn't call it a passive preamp). Since no gain, people started to refer to them as passive preamps. Once this stuff gets started, it's hard to stop.

https://www.firstwatt.com/b1.html

 

[abbey road d enfer]

Yes, another very sloppy word usage; they're passive enough, but 'preamp'? I suppose in the sense that it comes before an amplifier. ; - )

That's interesting. I have been conditioned to think of a preamplifier with emphasis on "amplifier" , with the "pre" indicating its position between a source and a power amp.
But the notion of "pre" apparently has become dominant, something that goes before an amp and after a source, and does not necessarily implies amplification.
I guess the next generation won't give it a thought; who uses a preamp today?

 

[k brown]

The issue got hazy when many home HiFi buyers no longer had any use for phono and/or tape head EQ/amplification, and CD players could produce as much as 2v ouput, making any gain from the 'preamp' unneccesary, but by that time preamp/power amp terminology was so entrenched that the market could get away from it.

 

[abbey road d enfer]

An example is the First Watt B1 Buffer (though they didn't call it a passive preamp). Since no gain, people started to refer to them as passive preamps. Once this stuff gets started, it's hard to stop.

https://www.firstwatt.com/b1.html

They use the word "buffer" in all honesty, and refer to "passive preamp" with the mandatory brackets.
Only the claim of "all without negative feedback" can be debated. A source-follower has almost 100% NFB.

 

[k brown]

: - )

 

[JohnRoberts]

Magnetic amplifier - Wikipedia In a sense, yes. Not by only using a trafo, but in combination with DC supplies

Not to be even more pedantic (I apologize) but my first exposure to a "mag amp" was inside an early DC-DC switching supply, back in the 1960s. The mag amp was used in a power supply current limiting circuit. Mag amps can indeed provide gain as a small current can modulate a much higher current, but they are clearly active (electromagnetic) not passive, or electronic.

Passive transformers do not have power gain****. If anything there will be small internal losses. Primary and secondary turns ratios can step up an AC voltage, but since the transformer output power is roughly equal to the transformer input power, the output will be higher impedance and have much lower drive capability.

Just to make my point if you were to connect a dynamic microphone to a step up transformer and then the output of that step up transformer to a very sensitive loudspeaker it might just make a barely audible sound, but not likely.

Every mic preamplifier I ever designed involved an active electronic amplifier stage.

JR

PS; I look forward to seeing schematics of a magnetic amplifier (saturable reactor) mic preamp .

**** it is extremely convenient to think of transformer turns ratios in terms of dB ( a power measure)... it is a bad habit to get into.

 

[user 37518]

Can they qualify as "passive"? Actually, although I have no doubt about what qualifies a stage as active or passive, I couldn't find a proper definition of it.
Listed active components are essentially tubes and semiconductors. However, the use of the non-linearities in a magnetic amp xfmr makes it an active element IMO. I believe that the ability of a system to modulate an output under control of an input is what makes it active. Same for Coanda pneumatic amplifiers.

Yes, you are correct. That is why I found it interesting when I first heard of them around 8 years ago, it is kinda counter-intuitive, since one always thinks of transformers as passive components. Actually there are many definitions for passivity/activity. One definition of passivity is that of a multiport in which the net power or energy delivered at a port is zero, for instance, capacitors can store energy and then return it, the net energy/power transfer is zero (we consider positive power when charging it, negative when discharging back to the source). In that sense, components which many people sometimes classify as active are actually passive, for instance, a diode. But under other definitions a diode can be considered an active component.

A more common perspective that some people use to determine if a component is active or passive, is whether there is a way to control current with the component, in that sense, a transistor is an active component, a tube, and so, the transformer-kinda thing used in the magnetic amplifier is therefore an active component. Yet another definition for passivity, which is very related to the net energy definition I gave before, is whether a component can achieve gain, it is important to be specific and define it as power gain, because if we only say gain (like voltage gain) a transformer could be considered an active component.

Wiki has a good summary of the many definitions: Passivity (engineering) - Wikipedia

 

[user 37518]

Not to be even more pedantic (I apologize) but my first exposure to a "mag amp" was inside an early DC-DC switching supply, back in the 1960s. The mag amp was used in a power supply current limiting circuit. Mag amps can indeed provide gain as a small current can modulate a much higher current, but they are clearly active (electromagnetic) not passive, or electronic.

Passive transformers do not have power gain****. If anything there will be small internal losses. Primary and secondary turns ratios can step up an AC voltage, but since the transformer output power is roughly equal to the transformer input power, the output will be higher impedance and have much lower drive capability.

Just to make my point if you were to connect a dynamic microphone to a step up transformer and then the output of that step up transformer to a very sensitive loudspeaker it might just make a barely audible sound, but not likely.

Every mic preamplifier I ever designed involved an active electronic amplifier stage.

JR

PS; I look forward to seeing schematics of a magnetic amplifier (saturable reactor) mic preamp .

**** it is extremely convenient to think of transformer turns ratios in terms of dB ( a power measure)... it is a bad habit to get into.

Yes, John, not pedantic, you are correct, check my previous post. I used the magnetic amplifier because is what I considered the closest to what might be considered a passive pre (although being active). The only passive pre is what audiophools use to refer to the volume control (a pot) used before a the power amp.

 

[abbey road d enfer]

Yes, you are correct. That is why I found it interesting when I first heard of them around 8 years ago, it is kinda counter-intuitive, since one always thinks of transformers as passive components.

I have been aware of magnetic amplifiers a long time ago, as a student.
One of my physics teacher was ex-army, and he explained how magnetic amplifiers were used in turret control.
He also mentioned pneumatic amplifiers, capable of striking a platoon with 140+ dB of VLF.

Wiki has a good summary of the many definitions: Passivity (engineering) - Wikipedia

Interesting, although it shows there is space for interpretation.

 

[Mr. Moscode]

The term "passive preamp" is hi end hi fi term. There are some step up transformer types with taps for gain positions and there are simply volume controls, both digital and pots with no voltage gain. So the "amp" part of the term is misleading but the market accepted it. Placette makes a digital volume controller. With 2 V out of most CD players and most amplifiers in the 25 -33 db voltage gain range in the hi end hi fi market it worked. it was made expensive military grade low noise resistors, AKA Vishay S102. I bought some from Texas Components which is a military mandated second source to those made by Vishay.

They, to my ears, are very transparent. No haze, virtually no noise.

http://www.placetteaudio.com/passive_line.htm
On the website there is a picture of a woman in deep rapture listening on headphones which is something I have very rarely witnessed. But hey? What do I know about hi fi . . . . or women?

 

[JohnRoberts]

I have been aware of magnetic amplifiers a long time ago, as a student.
One of my physics teacher was ex-army, and he explained how magnetic amplifiers were used in turret control.
He also mentioned pneumatic amplifiers, capable of striking a platoon with 140+ dB of VLF.

There are also fluidic amplifiers, where low power fluid signals can control higher power fluid flows.

I see a theme there.

JR

 

[user 37518]

I don't know how off the rails use of that term has become, but for the first many, many years of it's use it referred to a device that was nothing more that input selector switch and a pot (usually ~10k ohm) between sources and power amp. Obviously how well they worked depended heavily on the input impedance of the pwr amp, and drive capability of the sources.

Sometimes the term was still used (however inaccurately) for devices that placed only a unity gain buffer between the pot and the amp. An example is the First Watt B1 Buffer (though they didn't call it a passive preamp). Since no gain, people started to refer to them as passive preamps. Once this stuff gets started, it's hard to stop.

https://www.firstwatt.com/b1.html

Nelson Pass is in my book both as a genius and as a quack. He will do some awesome designs, bu sometimes I just think he knows that whatever he does will be praised by the Hi-Fi crowd, so I think he sometimes just makes ridiculous stuff just to mess with them and have a laugh, or because he is bored and wants to make stupid stuff (exhibit A).

 

[Mr. Moscode]

Nelson Pass is in my book both as a genius and as a quack. He will do some awesome designs, bu sometimes I just think he knows that whatever he does will be praised by the Hi-Fi crowd, so I think he sometimes just makes ridiculous stuff just to mess with them and have a laugh, or because he is bored and wants to make stupid stuff (exhibit A).

Your guess is better than mine. I've met him at trade shows but never got to know him well. He has lots of dedicated customers.
We can't expect the non-technical audio hobbyist to really know what's under the hood like this DIY crowd of veteran audio engineers does. I've been to a lot of Stereo Wars starting in NYC when I was 12, then in Chicago when I joined NYAL, Rocky Mtn Audio Fest, NYC again then Vegas. I've also had to argue with some reviewers that thought they knew more than I about my product. They are the fans in the stand, the press in the press box. We're (were, are?) the players on the field. We build, they buy. Then they sell or trade for the next shiny toy.

I never got that until I started riding a motorcycle and started buying and selling to see what I would like. Hi Fi is a hobby to many, a status symbol to some and musical ecstasy to the rest.

 

[mustik]

I just want to respond exclusively to @nano_lee, if he hasn't already lost interest in the forum. I think he already knows the answers to his questions. We just need to do some reverse engineering. First, the very concept of soundstage comes from sound engineering. That is, sound is localized from bottom to top depending on its frequency, from left to right depending on panning in stereo, and from front to back depending on reverb and harmonics. Stopping at the last aspect, when a sound engineer wants a certain sound to get right in the face and cut through the mix, he adds saturation or noise modulation. The sound loses depth in doing so; moreover, saturation expands the signal left and right. This is from psycho-acoustics. In the hardware selection aspect, we're talking about the difference in nonlinear distortion and noise between -90dB and -120dB. Many people will say that they can't hear such levels and they will be right, but after processing with compressors and equalizers a lot becomes noticeable. Or on the other hand, to make the audio signal lose depth, it is enough to add harmonics and noise. Also any periodic signal, as you know, has a lot of natural harmonics, called overtones, which form the timbre of the sound. In psycho-acoustics we noticed a pattern that if you cut out the lowest harmonics in a vocal signal, our brain reconstructs them, because we all know how a bass or alto or soprano should sound. If in the Pro-q equalizer we apply a high-pass filter to the recorded vocals at 5kHz, from a "scientific" point of view we should hear only sibilants like "s", "ch" and "sh". But you can also clearly hear the difference between the signal recorded on a professional interface and a budget one. With high probability you will also hear higher harmonics in the middle frequencies, and your brain will reconstruct the middle frequencies, which should not be there. And the more harmonics added by the microphone and amplifier, the more midrange frequencies will be heard.

 

[Newmarket]

How's this for fuel on the fire... I argue that specs are meaningless, in making music recordings to sell to the general public ...

Specs' are not meaningful to the consumer / general public. But they are meaningful to engineers, system designers etc in designing and building systems that deliver audio to that public.

 

[abbey road d enfer]

Specs' are not meaningful to the consumer / general public. But they are meaningful to engineers, system designers etc in designing and building systems that deliver audio to that public.

Indeed! A recurrent argument is that measurements and specs are unrelated to the subjective experience, but until now, I believe that any electronic device worth of its name has been designed by someone who has a good grasp of the science behind it (I would exclude Magic Alex )
Designing a product cannot be done by throwing parts on a bench and soldering them in random manner until it is capable of producing whatever it is supposed to produce; a design brief (as succinct as it were) has to be at the start of a design.

 

[gyraf]

user mustik​

..playing with ChatGPT?

/Jakob E.