What is responsible for soundstage in a preamp design?

[ruffrecords]

I have not read all this thread but I will throw in my twopenn'orth. I think it is all to do with second harmonic distortion. 2nd harmonic is a musical octave up so it adds brightness, presence and some might say it enhances the soundstage. The push pull topologies used in just about all op amps these days cancel 2nd harmonic distortion so they lack this effect. Instead they add predominatly third harmonic distortion which is a musical fifth. This adds power and loudness to a note but not depth. All the early single ended class A tube circuits and the well known three transistor class A circuits made back in the 70s by the likes of Neve and Helios, all exhibit primarily second harmonic distortion.

Cheers

Ian

 

[user 37518]

Yes, i think it is but i can’t back that up with actual numbers unfortunately.

So it is just your opinion and you can't prove it, got it.

 

[abbey road d enfer]

I think it is all to do with second harmonic distortion. 2nd harmonic is a musical octave up so it adds brightness, presence

until now, I agree.

and some might say it enhances the soundstage.

I consider it an abuse of language. I agree it "enhances" (or degrades) the perception, but using the word "soundstage" is a metonimy, which, in any scientific discussion is a malapropism.

The push pull topologies used in just about all op amps these days cancel 2nd harmonic distortion so they lack this effect. Instead they add predominatly third harmonic distortion which is a musical fifth.

Actually they do not "add" 3rd harmonics, they cancel out 2nd order, which makes 3rd the proeminent distortion component.

All the early single ended class A tube circuits and the well known three transistor class A circuits made back in the 70s by the likes of Neve and Helios, all exhibit primarily second harmonic distortion.

True, but, unless driven into clipping, the total distortion products were below 0.1%, or 60dB below fundamental, which makes them hard to discern, even more so when mixed with other signals.
I don't deny the fact that different preamps have different sonic signature, but the importance of it is minor compared to the overall processes (balance, EQ, compression, echo/reverb,FX...) involved in mixing.

 

[user 133392]

I have not read all this thread but I will throw in my twopenn'orth. I think it is all to do with second harmonic distortion. 2nd harmonic is a musical octave up so it adds brightness, presence and some might say it enhances the soundstage. The push pull topologies used in just about all op amps these days cancel 2nd harmonic distortion so they lack this effect. Instead they add predominatly third harmonic distortion which is a musical fifth. This adds power and loudness to a note but not depth. All the early single ended class A tube circuits and the well known three transistor class A circuits made back in the 70s by the likes of Neve and Helios, all exhibit primarily second harmonic distortion.

Cheers

Ian

I'm in agreement with you Ian.

I'll add that with any comparative test make sure the signal polarity of the devices are the same. Depending on the source material the differences in perceived brightness can be significant if one is inverted relative to the other. Some years ago I posted a test here using a trumpet solo that were identical only one had inverted polarity. I didn't say what the difference was but asked if they sounded the same or different. Several people posted they could clearly hear a difference. One poster - someone very seasoned and experienced IMHO - asked if they were different takes. If the two files were opened in an editor the differences would have been obvious but I asked that no one peek.

Back to Ian's comments...

I built a distortion-maker which allowed me to control it and find out how various types of distortion sounds.

My thoughts and impressions.

1) Second harmonic adds brightness particularly if its asymmetric with positive pressure at the ear drum. Don't take my word for it. Try it.

2) "Instead they add predominatly third harmonic distortion which is a musical fifth." I think its almost an octave+fifth interval but indeed they do. Op amps, tube amps, saturated transformers etc. can add symmetric odd-order compressive distortion due to non-linearities. I don't understand Abbey's comment "Actually they do not "add" 3rd harmonics, they cancel out 2nd order." Push-pull do both: They cancel second (even) and add third (odd). Third is added due to symmetrical non-linearity.

3) Compressive odd-order distortion in gross amounts can become compressive-sounding. Listen here as the distortion changes from odd-order expansive to odd-order-compressive. Odd-Order Compressive/Expansive Distortion Demo Radical but illustrative of changes made only by adding distortion.

4) HF IM from even order distortion folds down into the midrange where it may not be masked and can vary widely depending upon HF CM rejection in the Demrow/Cohen active input topology. See: Component Matching Minimizes IM Distortion in the Demrow-Cohen Balanced Front End - Pro Audio Design Forum Key jangle test? I work with a manufacturer who will not let a preamp design go into production unless it has passed this test. Odd order forms sidebands which, in the midrange, have a thickening effect. (Listen to the other Waveulator demos.)

5) Feedback. My Class-A (up to about 100 mW) headphone amp's distortion signature changes significantly when its at a power level near the exit point of class A. In Class-A at higher power levels with the output stage open loop it has a simple H2 and H3 structure. Switching to overall FB mode lowers overall THD but spreads it out over a higher-order more-complex harmonic structure. If preamps sound different are their distortion signatures radically different?

6) Impedance. I agree that any comparison should present an identical load impedance to the microphone. Otherwise you're not comparing preamps.

7) Why not do a null test with an actual acoustic source? Mult the microphone into both preamps, record a performance and then attempt to null them.

8) (Added.) A phantom-powered mic at high SPLs often produces high-harmonic content common mode (CM) voltage due to signal-induced changes in CM operating current. The phantom source and pick-off resistors (usually 1% tolerance) imbalance the bridge and convert some of that CM voltage to differential at the input which then gets amplified by the preamp's differential gain. It would seem that active preamps with higher differential input impedance would be more likely to see this CM to differential conversion. In addition to conversion to CM at the input, some of the CM passed through the front-end can also get converted to differential due to finite CM rejection downstream. I've seen this effect at the input with a scope but never actually quantified it. One could argue that bench measurements of the effect might be low enough to provide masking but in the real world EQ - sometimes large amounts of it - are applied.

9) (Added.) If one of the preamps being compared has an input transformer, is its core magnetized by a prior phantom fault? That will add H2. I've had clients who de-Gauss'd their input transformers with high level LF tone every once-in-awhile.

 

[Ricardus]

If audio frequency is DC

Ummm, what?

 

[Ricardus]

Direction of cables i don’t think matter even if it can be heard initially, but over time this can change

So over time cable direction matters?

 

[Cranehazard]

I belive the part of the circuit responsible for the effect you speak of is the first active device that the microphone couple's to. for me an instrumentation amp, op amp or differential amp does not sound like a mic pre until there is a discrete active component in front of it. A transformer helps but you still need a discrete fet, Bipolar or tube. To sound right to me. This is after fairly exhaustive experimentation. ( building preamps)

 

[abbey road d enfer]

I don't understand Abbey's comment "Actually they do not "add" 3rd harmonics, they cancel out 2nd order." Push-pull do both: They cancel second (even) and add third (odd). Third is added due to symmetrical non-linearity.

In a push-pull, distortion due to this "symmetrical non-linearity." is usually at a much lower level than distortion due to the Vas amplifier, so the level of 3rd is almost unchanged, but the relative "absence" of 2nd (in the output stage) makes 3rd the dominant harmonic.

HF IM from even order distortion folds down into the midrange

Of course, IM is a very important factor in the sonic signature, if only because its relative amplitude increases quickly with signal level, which allows it to be perceived even in a busy mix.

...overall FB mode lowers overall THD but spreads it out over a higher-order more-complex harmonic structure.

Indeed. Perception of this effect is a big subject, which won't be solved soon, as long as some, blessed with supra-natural hearing, can claim they hear differences others can't.

 

[Somkereki]

Amit itt hallasz, az a Barkhausen kvantálás vagy -torzítás. Ez egyszerűen egy küszöbfüggvény, amely meghatározza a ferromágneses "cella" vagy kristályméret miatt átvihető minimális energiaszintet és az ezek megfordításához szükséges energiatartalmat. Minél jobb a mágneses vezetőképesség, minél kisebbek a kristályok, és minél hosszabbak a természetes szoba visszhangja.

Ha valami extrémet szeretnél hallani ebben az irányban, próbálj ki egy nano-kristályos vagy amorf magos mikrofonlépcsős transzformátort - számomra ez szinte ijesztő élmény volt

/Jakob E.

Good Idea ! have experienced during my many years of work that every transformer has its own sound. I also have a positive experience with the nickel content. As soon as each part has its own sound I am already 68 years old and I started the profession a long time ago. (According to my diploma, I graduated in "Electronic component and device manufacturing") When I was young, I was also an active band sound engineer for many years, now I mainly try to improve recording studio and high-end devices. For example, with a Neumann UM 57 microphone, I can achieve an average of 20 dB signal / noise improvement . This profession is interesting. With my machine, which works on the principle of quantum physics, I can also greatly increase the detail of the sound of cables and speakers. I worked in a special physics research laboratory, where I realized that people's perception of physics will soon change, as from Newtonian physics to Einsteinian physics, now for quantum physics (If the military research labs allow it!) For me, my work is my hobby.

 

[user 37518]

I belive the part of the circuit responsible for the effect you speak of is the first active device that the microphone couple's to. for me an instrumentation amp, op amp or differential amp does not sound like a mic pre until there is a discrete active component in front of it. A transformer helps but you still need a discrete fet, Bipolar or tube. To sound right to me. This is after fairly exhaustive experimentation. ( building preamps)

Normally, you can't connect the mic directly to an op-amp if you intend to achieve the lowest noise figure, so a transformer or a discrete stage is needed, that is the main purpose of these components, not so much to add what people call coloration. However, I see absolutely nothing wrong with the sound of the IA IC's which are meant to be used as a preamp, like the INA217.

 

[abbey road d enfer]

What you hear here is the Barkhausen quantisazion or -distortion. It's simply a threshold function determining the minimum-energy-level transferable because of ferromagnetic "cell" or crystal size, and the related energy content required to flip these. The better magnetic conductivity, the smaller crystals and the longer the "tails" of natural-room reverb..

If you want to hear something extreme in this direction, try a nano-crystalline or amorf-core mic stepup transformer - to me that was an almost scary experience

/Jakob E.

Jakob, you've been warned, quantic cables are coming!
Actually, I've heard (1st day of last month) Neutrik are working on their Quantik line of connectors.

 

[Lampie519]

So over time cable direction matters?

The oposite as the direction of a cable can be heard at a first comparison but later it settles so the direction doesn’t matter after all (not sure how to phrase that differently as it does sound silly). Maybe to be compared to transformers that need time in case a dc voltage had been applied, this is beyond me but has been proven many times especially on unballanced systems.
As many things “the proof is in pudfing” and can’t be expressed in numbers as for me the equipment to measure it is not available. Also even small difference can be heard it is not always implemented as the implementation takes too much effort for such a small difference.
That is why high end stuff costs so much more not only for build quality and marketing.

 

[Lampie519]

Jakob, you've been warned, quantic cables are coming!

There are already available for who is interested,
Look up spintronics and magnonics.
It is nothing new and used in many aplications like hard discs (old stuff) but that is beyond this thread and this forum i guess.

 

[Newmarket]

this is beyond me but has been proven many times especially on unballanced systems.

Has it though ? References for that ?

 

[Lampie519]

I have worked in the audio business for many years before changing to the pro world. In the pro world this is something not to discuss but in the high end audio this is possible. Now i know of many so called audiophools ( mentioned already here) as these mainly are people without a technical background. As i am very sceptical ( maybe this looks strange to you) i need to be convinced personally, so i do invite sometimes people who claims to have something interesting to show or they send me a product to test. This because it is known to people arrond me that my setup is all revealing (even though it is never finished) and minute changes can be heard. So this for me is prove (1st hand / ears ) not any numbers or stories/reviews presented.

One of the products i was asked to test was this cable (some years ago already) at first nothing interesting but a few days later it was very audible that it does work as advertised ( i use the power cables not speaker cables as i don’t use low impedance loudspeakers).

 

[abbey road d enfer]

Look up spintronics and magnonics.

How do they relate to analog audio performance?

 

[Lampie519]

How do they relate to analog audio performance?

https://patents.google.com/patent/EP3639280A1/zh
Yes, quantic cables are already here !
Actually they have always been from the moments cables have been made. It is up to you to wanting to dive into this or not.

 

[abbey road d enfer]

https://patents.google.com/patent/EP3639280A1/zh

It just shows that a patent has been filed and it's pending. There is no detail about the purpose of the invention.
Links to Spindeco pertain to MRAM, which is a totally different subject than analog audio.
Apparently, the company is not in business anymore, which I tend to think as a sign that the concept was not particularly viable.

Actually they have always been from the moments cables have been made.

Of course, quantics (just like Maxwell equations or relativity) are at work in all aspects of our life, but their distinct effects are in most cases irrelevant, as long as we don't try to launch rockets or try to put the Higgs boson in evidence. That's why Newtonian physics, Ohm/Kirchoff laws and the good old chronometer are still useful and relevant to the common man's life.

 

[Lampie519]

Not sure if the company has been sold or not but it states in the document that it actually enhances the audio signal.
Maybe it can still be found here and there or someone else will pick it up eventually.
https://myhifihouse.com/en/collections/spinx-cables
https://patents.google.com/patent/US11462674B2/en?inventor=Petteri+Koljonen

 

[user 133392]

In a push-pull, distortion due to this "symmetrical non-linearity." is usually at a much lower level than distortion due to the Vas amplifier, so the level of 3rd is almost unchanged, but the relative "absence" of 2nd (in the output stage) makes 3rd the dominant harmonic.

Of course, IM is a very important factor in the sonic signature, if only because its relative amplitude increases quickly with signal level, which allows it to be perceived even in a busy mix.

Indeed. Perception of this effect is a big subject, which won't be solved soon, as long as some, blessed with supra-natural hearing, can claim they hear differences others can't.

WRT to H3/odd I wasn't thinking just about power amps but op amp output stage loading, class-A push-pull running out of steam during current peaks, transformer saturation, symmetrical diode limiters, supply sag etc, that bend the I-V curve identically in both quadrants I and III. These examples are all compressive odd-order.

I'm hard-pressed to think of expansive odd-order examples that we normally see (*) but when it's added synthetically it can sure put a point on a transient. (*Maybe severely underbiased tape or class-B?)

For the record I've never used the word "soundstage" except to describe a building where film and video are recorded and I've never heard a difference in cable direction.