Preamp difference : if it's not the frequency, not the slew rate, and not the harmonics, what is it ?

[vintageampfixer]

PermO - I used a passive volume control that was on a very high quality dual rotary switch. Even though I didn't wire it to go to full signal strength (or even very close to it) it still took lots of (very high quality) resistors. In the end, I found the jumps between the click settings of the rotary switch were often just a bit louder or just a bit quieter than what I wanted to hear. So, I suggest that you us a stereo potentiometer to determine the resistor ratios that work for your tastes in your system before wiring up a complex switch system. Make sure you have at least one setting that is very, very quiet, but not completely off. I was surprised how often I wanted that. But in my circuit, the first "on" click was a bit too loud. Best of luck with it.

yup, there's a reason why designers use pots instead of switched attenuators. And it's not cost!

 

[vintageampfixer]

Oh, that sounds kinda cool !

That would not need a control knob in the listening position and that would allow for much shorter wiring.

The approach only works if you don't care - or don't need to care - about impedance matching so generally in applications where cable runs are very short. In a studio situation or a live venue where cables are considerably longer, some form of line driving amplifier will be needed, which to my earlier point would be added because it's needed.

 

[PermO]

PermO - I used a passive volume control that was on a very high quality dual rotary switch. Even though I didn't wire it to go to full signal strength (or even very close to it) it still took lots of (very high quality) resistors. In the end, I found the jumps between the click settings of the rotary switch were often just a bit louder or just a bit quieter than what I wanted to hear. So, I suggest that you us a stereo potentiometer to determine the resistor ratios that work for your tastes in your system before wiring up a complex switch system. Make sure you have at least one setting that is very, very quiet, but not completely off. I was surprised how often I wanted that. But in my circuit, the first "on" click was a bit too loud. Best of luck with it.

Well, exactly this is why I have not build it yet

I have a nice selection of parts from an old (huge) broadcast installation I had to take down and modernize bit by bit.
During my lunchbreaks I took some tools to the dumpsite and stuffed my backpack with transformers and switches, the enigineers there were fine with this as they knew the value of all this stuff going to the scrapyard and started to collect bits for me as well.

I was not planning on buying expensive resistors for this, I've got plenty 1/4W resistors and some high quality 4 deck rotary switches.

Some DC blocking feature might not be a bad idea as this amp will destroy drivers with DC present.
I have some nice 3,3uF filmcaps I could use for this.

Also got some Lundahl 1527 I could use in a 2:1 ratio to drop some volume, and skip the filmcaps.
But adding the transformers will introduce an unknown impedance to react with the stepped attenuator.

So I have got plenty of stuff to solve this, but the reason I have not done it yet is because I have not figured out the best way to do this.


Those ebay attenautors look very tempting, but in the spirit of DIY this should be done with stuff from my collection at no additional cost.

In this situation there will always still be the digital level control at the source, but I don't want to depend on that as it's a sure way to destroy speakers when a loud "surprise !" happens.

 

[rh001]

The exact reason some preamps and other gear sound better has never been revealed via audio measurement as far as I know.

Someone suggested that to identify what "better" actually would require a randomized double-blind test. That kind of reductivist thinking would not work in this matter cuz those kinds of tests assume there is some sameness among the test subjects which there is not. Even with medical tests the subject group is often limited by age or sex etc. A double blind test to answer this question might provide some interesting results if the test were limited to those with proven good taste in music mixing and production...but how would such a selection be made...by song revenue? If any selection is made there will always be cries of unjust from the peanut gallery. In the end the matter is something like those who have good taste simply exercise their good taste and everyone else is of no consideration.

Unfortunately for those who want to develop good taste the entry ticket price is high. Not only is the good, fat, warm, silky, hot, neon sounding gear expensive but one would have to have a budget for making some disappointing purchases. I've been asked as to how one can get started on the path to having really good sounding gear and my simple answer is to start with anything that has discreet opamp or amp, input and output transformer, and no ic's in the signal path...does not have to be the most expensive but if the money is there start with API gear, 312 preamp, 525 compressor and 550A eq. Clones of vintage Neve modules are good if they have the same transformers and tube amp is great but must have output transformer in the plate circuit of the output tube (not after the plate output capacitor) and not in the emmitter circuit.

Even when the money is there often the sound is not as good as it could be, for instance as with the Korean guitar baby Sungha Jung or the figure skating music videos of Yuzuru Hanyu both who have high net worths. In the case of Mr. Jung, he should know better...the sonic quality is good but does not match the musical skill...sound lacks some string overtones and neon warmth. In the case of Mr. Hanyu he has mentioned in interest in audio in an interview some years ago, and the well recorded souldtrack is well handled, but it could be better...lacks a little something...probably just needs to have been passed through API 525 and/or Ampex AG-440, in which case the orchestra boomf could be enhanced and some stereo interest could be added by the analog tape.

 

[JohnRoberts]

Has this thread jumped the shark yet?

JR

 

[Cqwet Dbdfte]

Getting a click-free rotary switch, make-before-break, and keeping it clean may not be that great of an idea. I know you can find them on the Bay. https://www.ebay.com/itm/225152465485
https://www.ebay.com/itm/285592463401
My only reservation for the 7-bit "click-free" relay volume control is the curve may not be in dB, but linear. I have to check.

 

[Wavelength]

All,
Just my 2 cents on the subject. I design High End Audio, Custom ProAudio, Guitar amps & pedals, Digital and Analog stuff. Have a Prism dScope III, AverTech and Standford Audio Analyzers and tons of other test sets both analog and digital. Testing with a DAW or even these test sets can be a wash as far as what we have to look for. Again they are all digital and even though they have autoleveling inputs on test sets they still have digital filtering and that can effect what they see. Sometimes just a good scope looking at an analog generated waveform as it passes through the preamp can give you a really good picture of the quality of the design.

I am not a fan of loop feedback, therefore I don't typically use opamps or discrete opamps in anything except control stuff like optical compressors. We found that loop feedback kills space and creates some weird distortion so I try and avoid that as much as possible. Degenerative is not what I would call feedback, it just degrades the amount of the gain in a stage and changes the output Z of that stage.

Preamps are hard to verify, as the designer is faced with a wide range of possible inputs and outputs and without those variables the basic preface of high input Z and low output Z are usually the case. Transformers, Tubes, resistors, capacitors inductors power supplies there is a lot going on here. But in the end it's preference that usually wins out. I had great results with this that or whatever. Remember nobody is wrong here.

In regards to volume controls, my fav is Penny & Giles RF15 have like 20 stereo 10K left. But really where does it belong, before the gain in the middle or at the end. Engineering states putting it at the end would be the most beneficial like a compander that is where the highest signal to noise happens. But what happens to the output Z, well it craps out.

Volume control types like Inductor and transformer work really well on the output as they preserve the Low Z output. But then again the step ratio becomes a bit of a problem and driving these sometimes makes the sonic signature a little bit on the compressor side.

RF is always a problem as some designers feel well it's way out of the 20-20K range so why worry. Well transistors and even tubes can have dramatic effects because of RF. Now with Power over Ethernet, WIFI and Bluetooth this has become a serious problem for some designers and power supply designs. One reason I use tube rectifiers in amps is that they don't pass anything RF, were as solid state does.

Looking back and forward at classic designs the use of some of the simplest transistor and tube designs to me look really elegant and timeless.

 

[vintageampfixer]

Has this thread jumped the shark yet?

JR

just as a diversion, I was given an XR560 yesterday ... !

 

[JohnRoberts]

just as a diversion, I was given an XR560 yesterday ... !

Yup that was one from my mixer engineering group. One of the early ones with a digital efx instead of spring reverb.

JR

 

[Cqwet Dbdfte]

All,
Just my 2 cents on the subject. I design High End Audio, Custom ProAudio, Guitar amps & pedals, Digital and Analog stuff. Have a Prism dScope III, AverTech and Standford Audio Analyzers and tons of other test sets both analog and digital. Testing with a DAW or even these test sets can be a wash as far as what we have to look for. Again they are all digital and even though they have autoleveling inputs on test sets they still have digital filtering and that can effect what they see. Sometimes just a good scope looking at an analog generated waveform as it passes through the preamp can give you a really good picture of the quality of the design.

I am not a fan of loop feedback, therefore I don't typically use opamps or discrete opamps in anything except control stuff like optical compressors. We found that loop feedback kills space and creates some weird distortion so I try and avoid that as much as possible. Degenerative is not what I would call feedback, it just degrades the amount of the gain in a stage and changes the output Z of that stage.

Preamps are hard to verify, as the designer is faced with a wide range of possible inputs and outputs and without those variables the basic preface of high input Z and low output Z are usually the case. Transformers, Tubes, resistors, capacitors inductors power supplies there is a lot going on here. But in the end it's preference that usually wins out. I had great results with this that or whatever. Remember nobody is wrong here.

In regards to volume controls, my fav is Penny & Giles RF15 have like 20 stereo 10K left. But really where does it belong, before the gain in the middle or at the end. Engineering states putting it at the end would be the most beneficial like a compander that is where the highest signal to noise happens. But what happens to the output Z, well it craps out.

Volume control types like Inductor and transformer work really well on the output as they preserve the Low Z output. But then again the step ratio becomes a bit of a problem and driving these sometimes makes the sonic signature a little bit on the compressor side.

RF is always a problem as some designers feel well it's way out of the 20-20K range so why worry. Well transistors and even tubes can have dramatic effects because of RF. Now with Power over Ethernet, WIFI and Bluetooth this has become a serious problem for some designers and power supply designs. One reason I use tube rectifiers in amps is that they don't pass anything RF, were as solid state does.

Looking back and forward at classic designs the use of some of the simplest transistor and tube designs to me look really elegant and timeless.

I can understand the reason why tube rectifiers had some charm.
Silicon diodes would not be a point of RF rectification but an inductor in series a diode is used for testing reverse recovery time and generating pulses with a step recovery diode.
A power supply's transformer has parasitic inductance that can interact with rectifiers reverse recovery time.
Newer SiC diodes do not have Trr, and should be used.
Some have analysed the spectral output from power supplies and designed filters to target transformer resonances.
Slow startup is another benefit of indirectly heated tube rectifiers.
This can be accomplished with a MOSFET based regulator
Tube rectifiers have severe drawbacks, low current capacity, large voltage droput,
expensive, added heat load.
I don't miss them.

 

[gyraf]

Someone suggested that to identify what "better" actually would require a randomized double-blind test. That kind of reductivist thinking would not work in this matter cuz those kinds of tests assume there is some sameness among the test subjects which there is not. Even with medical tests the subject group is often limited by age or sex etc.

I respectfully disagree

This is not reductionist, but about statistics - the core of all psychological research, which I worked with for a long time when I was younger

The whole point is that if there is such a thing as "better", then the minimum requirement of proof would be that an average of humans would subjectively qualify it as "better" in a double-blind test. We are not at all interested in sameness, as we are not comparing absolutes, but relative measures - and we don't care about individual preference, but the grand average. We even have the possibility to come up with an effect size, if our sample size is big enough.

So IMO, for any claim of goodsoundingness there is a relevant double-blind test to be done. Complicated and expensive, yes, but it's absolutely possible in this way to extract "hard data" from any subjective experience. If you want to. Hifi don't.

/Jakob E.

 

[vintageampfixer]

I respectfully disagree

This is not reductionist, but about statistics - the core of all psychological research, which I worked with for a long time when I was younger

The whole point is that if there is such a thing as "better", then the minimum requirement of proof would be that an average of humans would subjectively qualify it as "better" in a double-blind test. We are not at all interested in sameness, as we are not comparing absolutes, but relative measures - and we don't care about individual preference, but the grand average. We even have the possibility to come up with an effect size, if our sample size is big enough.

So IMO, for any claim of goodsoundingness there is a relevant double-blind test to be done. Complicated and expensive, yes, but it's absolutely possible in this way to extract "hard data" from any subjective experience. If you want to. Hifi don't.

/Jakob E.

Lots of people thought Marshall guitar amps sounded "good"; they're a very long way from "Hi Fi".

 

[jabe]

Lots of people thought Marshall guitar amps sounded "good"; they're a very long way from "Hi Fi".

But most people's subjective criteria for guitar amps doesn't typically include "hi-fi".

 

[vintageampfixer]

But most people's subjective criteria for guitar amps doesn't typically include "hi-fi".

The OP asked (10,000 years ago) what made things sound good or punchy or ...

 

[JohnRoberts]

The OP asked (10,000 years ago) what made things sound good or punchy or ...

But the OP very specifically asked in the context of "audible differences between preamps".
===
Punch and other subjective descriptions about guitar amps is whole nother can o' worms.

My engineering group used to share lab space with actual guitar amp design engineers. From chewing the fat with them over several years I learned it is a completely different discipline than crafting linear (transparent) audio paths for preamps/mixers.

If you really want to discuss guitar amp design maybe start a different thread, or search we have surely opined about them before.

JR

 

[vintageampfixer]

But the OP very specifically asked in the context of "audible differences between preamps".

My somewhat clumsily made point was intended to allude to that oft-arising disparity between the market's view and performance measurements!

And I'll chuck in that the answer to the OP's question may well be in his second paragraph "If we run the preamps too hot" so I wonder if the missing element is actually headroom?

 

[Wavelength]

All,
First off one problem with tubes is your taking the mains and increasing them for the HV section no matter if it's guitar or audio amplifier. I have one in front of me at 600V.
Marshall was a smart guy and look at the quality of transformers used.
That said HiFi and Guitar Amps are 2 different animals. HiFi and Preamps though are not far off. Quality parts makes a big difference and design.
Plus talking guitar amps vs HiFi is also polar opposite.
I have a 500 series dual tube preamp that is half done that I hope to have ready at some point.
Thanks,
Gordon

 

[terry setter]

Yes, headroom can be an important fact (and I have found this to be particularly true in recording consoles, where the input signals contain such vastly different, uncompressed levels). But, relative to this thread, here is something to consider. Decades ago, I was involved in writing the review of a Hi-Fi audio preamp from a well known manufacturer (not a microphone preamp). The magazine that commissioned the review had a policy of letting the gear maker pre-read reviews in case there was anything they wanted to address, or even correct in production models. To create this review, measurements were taken, extensive listening tests were done, and the review was drafted. It mentioned one or two less-than-stellar aspects of the sound of that preamplifier. When the manufacturer read the review they took great exception to our findings and challenged the primary author and me to do a blind A/B/C test. They had only two conditions: any circuits being compared to theirs had to be set within 1/2 dB of playback volume at 1KHZ, and the frequency response of any circuit we wanted to include had to fall within 1/2 dB of their circuit (which measured very flat from very low to very high). My friend and I took up the challenge with great swagger, and we were ready to "set them straight".

Too bad for us. When we met their criteria, no one who heard the tests could distinguish between any of the several circuits we ended up testing on that day. We spent hours and tried various topologies, tube/SS, P-to -P- wiring vs circuit boards; we pretty much covered it all. WHEN THE FREQUENCY RESPONSES AND PLAYBACK VOLUME WERE MATCHED WITHIN 1/2 dB, NO ONE COULD DISTINGUISH THE CIRCUITS. By the way, I don't mean that we EQ'd frequency responses to be within 1/2 dB, I mean that we only used circuits that, by design, were that close in frequency response right out-of-the-box (20-20K).

We then focused on some listening that considered noise/distortion content. What we found was that we had to add so much noise/distortion in order to come up with repeatable differentiations between the units that we knew no one would ever even try to sell such a noisy/distorted circuit.

I have never fully gotten over the impact of participating in these tests. I owned exotic great sounding gear. I had ears that could tell the difference between subtle changes in circuits and systems. I had done many tests previously and the results consistently supported my belief that the sonic differences between circuits were palpable. One last detail: We measured some units that had frequency responses that were only slightly farther off from the test preamplifier than 1/2dB. Guess what, we could tell the difference, and we had preferences.

Nowdays, I STILL buy gear that is highly rated and glowingly reviewed. The difference is that since the day of that test, I realize that at least THE PRIMARY differences in PREAMPLIFIERS (to address the topic of the OP) are locateable in frequency response. Do I have a playback system that I think sounds "wide", and has fantastic dynamics, etc., etc. I sure do. But when it comes to PREAMPLIFIERS, I think the differences are far smaller than amps, and vastly smaller than they are between speakers, microphones, and phoro cartridges. Very careful measurement of FR will tell you a great deal about "Quickness", "Slam", and other audiophile categories of performance.

If you have a modicum of test gear, try the comparison test for yourself. But remember, you only get to have plus-or-minus 1/4 dB in frequency response and playback volume (at 1KHZ) between the examples you are trying to compare. Let me know if you hear a difference. Maybe it's time for me to learn something new - again!

 

[Mworthin]

Yes, headroom can be an important fact (and I have found this to be particularly true in recording consoles, where the input signals contain such vastly different, uncompressed levels). But, relative to this thread, here is something to consider. Decades ago, I was involved in writing the review of a Hi-Fi audio preamp from a well known manufacturer (not a microphone preamp). The magazine that commissioned the review had a policy of letting the gear maker pre-read reviews in case there was anything they wanted to address, or even correct in production models. To create this review, measurements were taken, extensive listening tests were done, and the review was drafted. It mentioned one or two less-than-stellar aspects of the sound of that preamplifier. When the manufacturer read the review they took great exception to our findings and challenged the primary author and me to do a blind A/B/C test. They had only two conditions: any circuits being compared to theirs had to be set within 1/2 dB of playback volume at 1KHZ, and the frequency response of any circuit we wanted to include had to fall within 1/2 dB of their circuit (which measured very flat from very low to very high). My friend and I took up the challenge with great swagger, and we were ready to "set them straight".

Too bad for us. When we met their criteria, no one who heard the tests could distinguish between any of the several circuits we ended up testing on that day. We spent hours and tried various topologies, tube/SS, P-to -P- wiring vs circuit boards; we pretty much covered it all. WHEN THE FREQUENCY RESPONSES AND PLAYBACK VOLUME WERE MATCHED WITHIN 1/2 dB, NO ONE COULD DISTINGUISH THE CIRCUITS. By the way, I don't mean that we EQ'd frequency responses to be within 1/2 dB, I mean that we only used circuits that, by design, were that close in frequency response right out-of-the-box (20-20K).

We then focused on some listening that considered noise/distortion content. What we found was that we had to add so much noise/distortion in order to come up with repeatable differentiations between the units that we knew no one would ever even try to sell such a noisy/distorted circuit.

I have never fully gotten over the impact of participating in these tests. I owned exotic great sounding gear. I had ears that could tell the difference between subtle changes in circuits and systems. I had done many tests previously and the results consistently supported my belief that the sonic differences between circuits were palpable. One last detail: We measured some units that had frequency responses that were only slightly farther off from the test preamplifier than 1/2dB. Guess what, we could tell the difference, and we had preferences.

Nowdays, I STILL buy gear that is highly rated and glowingly reviewed. The difference is that since the day of that test, I realize that at least THE PRIMARY differences in PREAMPLIFIERS (to address the topic of the OP) are locateable in frequency response. Do I have a playback system that I think sounds "wide", and has fantastic dynamics, etc., etc. I sure do. But when it comes to PREAMPLIFIERS, I think the differences are far smaller than amps, and vastly smaller than they are between speakers, microphones, and phoro cartridges. Very careful measurement of FR will tell you a great deal about "Quickness", "Slam", and other audiophile categories of performance.

If you have a modicum of test gear, try the comparison test for yourself. But remember, you only get to have plus-or-minus 1/4 dB in frequency response and playback volume (at 1KHZ) between the examples you are trying to compare. Let me know if you hear a difference. Maybe it's time for me to learn something new - again!

Your experience reminds me of the experiment that they did with tone capacitors for guitars. Once they matched the capacitors is perfectly for capacitance, there was no difference in sound between paper-in-oil, orange drop, etc.

 

[Mihobro]

Capacitors and transformers have some very interesting frequency dependent characteristics especially at the high and low extremes. Phase shifting, harmonic reactance and other distortion too. And since even a plain wire can have capacitance and reactive elements, we may not be able to measure it but it is still going to be there. We used to spend a lot of time overdriving circuits with sine waves at different frequencies, and also response to square waves to measure slewing rates. The hope is to exceed the ability of the hearer, which varies a lot also according to ear structure, and ability of the brain to process audio etc. We are fortunate to live in a time where components have improved a lot,. For example, new "music" caps are so much better than the ones from days past. I have found recapping old tuners from the 70's with modern caps, can be like night and day. Also the oversizing of caps, in signal pass circuits an octave below the originals can help to really open up the bottom end.
On another note: RF filtering requirements vary from location to location. I lived down the street from the Empire State Building's transmitters and had all kind of RF bleed into a Neve console from stock Neumann, Audio Technica and to a lesser degree AKG mics. oddly enough and counterintuitively, they responded to the removal of the small silver and ceramic caps across each of the legs of the mic outputs and the ground, what I guess is a RF shunt in theory. sometimes filters setup a better antenna. Of course, just down the block and in the studios that had chickewire faraday shields built into the walls, these mics had no problem with RF. As far as preamps are concerned, most mixers being being manufacturered today use similar two stage discrete fet design and sound better than most of the famous console mic preamps with the exception of Avalons, Jensens and a few other legends, largely because of improved components and computer aided designs. If you are not ready to spend a fortune though, the latest preamps like Mackie VLZ4 and others, may work for you. Keep on trying new stuff, We all may eventually get to recording something meaningful..eventually.