John Curl's Blowtorch preamplifier part II

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jan.didden

jan.didden

AX tech editor
Joined 2002
linearaudio.net
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Joshua_G said:
Chris and Scott,
Sometimes there are some correlation between how an amp is measured and how it sounds, but most of the time there isn't such a correlation, at least not a direct and obvious one.

One thing is that the human ear (actually, the ear-brain-mind mechanism) usually doesn't notice harmonic distortion of 0.5% or less in the second harmonic and 0.2% or less in the third harmonic, while it is more sensitive to the higher harmonics and extremely sensitive to the 7th harmonic. So, when one amp measures 0.8% THD and another one measures 0.001% THD, by those numbers alone it's impossible to tell which one of them will sound better.

Another thing is that the measurements which are probably most correlated to the way an amp sounds, that is, TIM and its derivates, are seldom taken and almost never published.

All in all, there is no way to tell how any amp sounds by looking at its' published measurements alone. So, only listening tests can tell how any amp, or any other piece of audio gear, sounds.

The impressions of various individuals of the same audio gear and their evaluations of it are varying to enormous degree. For some a certain audio set sounds great, while to others it sounds mediocre, or bad. If it weren’t like this, all would buy the same amps, speakers and other pieces of audio gear.

Therefore, when I consider purchasing any produced piece of gear for my audio set, whenever it's possible, I listen to it before purchasing, preferably on my own setup. Sometimes it's impossible to do, like in the case of phono cartridges that no merchant will let you try it before you buy. This is also impossible to do on designs which aren't produced. In such cases, I have to rely upon testimonies, or reports of others. Now comes a major question for me: which testimonies or report should I note and which ones should I ignore? As a rule, I don't read reports of audio magazines, whether published, or on-line, for I'm suspicious of possible commercial interests. So I'm left with testimonies and reports of fellow audiophiles. However, there is still the question: which testimonies or report should I note and which ones should I ignore? This question is so much relevant in the light of the enormous differences in appreciations of the same gear. From experience I know that my friends who hear differences between different well engineered cables and me have very similar appreciations of audio gear, while others who don't hear such differences between cables have markedly different appreciations.

Therefore, I'd not consider trying any non-produced design by a designer who confesses that he doesn't hear differences between cables. This is because it's an indication to me that probably his appreciation of the sound of audio gear and mine are most probably markedly different. Of course, not all who claim to hear differences between cables actually hear them. However, I do need a starting point.

I'm absolutely convinced that a designer should have refined listening in order to design and produce great sounding audio gear. A living example for this is my new loudspeakers that came in today. They are Brodmann VC2 (formerly Bosendorfer), designed by Hans Deutsch, who, among other things, was the Tone Master of Herbert von Karajan. These speakers are the best I ever heard and they are ingenious. There is no doubt in my mind that it takes the refined hearing of a man like Hans Deutsch, along with acoustics knowledge and other skills, to design and build such wonderful speakers.

Andre,
Of course the best cables have no influence whatsoever on the sound, in any audio setup, however, such cables are hard to come by.

sawreyrw,
I never measure cables. Moreover, relevant measurements should be done when the cables are hooked to their source and load, something which I'm not sure can be done. Anyhow, this isn't my point at all.

All,
As for MC phone cartridges, many times their recommended load is published.
Click to expand...

Joshua,

There's a lot in your post I agree to fully. I just want to make one comment: You mention 'designers that confess not being able to hear differences between cables'. This may be your interpretation of some posts, just like you seem to think that 'all objectivist only measure and not listen'. This is not really the case, although sometimes it is. Did you really find anybody here to say that he cannot hear differences in cables? Some may have said that audible differences between cables can generally be attributed to measured differences but thta's something else of course.
So I reall ything you should be more carefull to put labels on people which are not existing.

Another thing: I can give you an inside tip to listen to cable differences. Connect a separate preamp with its input *across* the cable you want to check. For instance on a speaker canble, connect the speaker hot side to the preamp hot, with a screened cable, and connect the screen /ground input of the preamp to the power amp output hot. (The preamp should NOT be connected to earth ground or you can damage your power amp). Listen to the preamp signal with headphones, and try to be away from the speaker on that cable to isolate you from that sound.

You now can actually listen to the sound that the cable takes away from the amp output. You can hear: almost nothing, or a softer version of the music but undistorted, or a softer version but distorted. Each case has different implications. If you do this, you really get great insight to what a cable actually does to your sound. Very illuminating!

jd
 
A

Allen Wright

R.I.P.
Joined 2001
vacuumstate.com
John,
You ask: "Allen, what are you trying to say? Why 68 ohms?"

The IKEDA sounded exceesivly bright on 47k, so I just kept lowering the loading until I had killed the life in the thing alltogether, and then came back up again until I had found a happy medium where it was alive, dynamic but sounding "right". One of the best cartridges I have ever heard, with this 68 ohms loading!

Josuha:
Step up transformers are a different ball game to resitive loading of an MC cart, and I can not offer any suggestions - except try running without the traffo.

And if you haven't done any VTA adjustments for a while - my experience says you may be well off optimium - I don't know what "by the book" means but if it means having the arm tube parallel with the record surface - you will be WELL off optimum.

I suggest you, and all vinyl fans, try my Guru Alignment method:

http://www.vacuumstate.com/fileupload/GuruSetUp.pdf

with the protractor at:

http://www.vacuumstate.com/fileupload/Guru_protractor.pdf

It may take you some time, but I assure you the results will be well worth it!

Regards, Allen (Vacuum State)
 
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
Allen Wright said:
John,

The IKEDA sounded exceesivly bright on 47k, so I just kept lowering the loading until I had killed the life in the thing alltogether, and then came back up again until I had found a happy medium where it was alive, dynamic but sounding "right". One of the best cartridges I have ever heard, with this 68 ohms loading!
Click to expand...

I calculate a 0.4dB loss at that lower loading for your cartridge. Certainly measurable, with all due respect to John. Did you do a frequency response or impulse response (square wave?) measurement with 47k and 68R and your cartridge? I assume you were using one of your preamps so that the input C was quite low?
 
jan.didden

jan.didden

AX tech editor
Joined 2002
linearaudio.net
Paid Member
Joshua_G said:
Jan,
What you wrote may apply to some people while what I wrote may apply to some others.
Click to expand...

Yes, agree, generalisation is often dangerous. But you would be hard pressed to find anyone on this forum who flatly denies that no cable audible differences exists, and that objectivists never judge amps by sound.
What I say applies to almost all people here, with maybe a few exceptions. Have you found the exceptions? If not, I would ask to stop using those labels.

jd
 
john curl

john curl

Member
Joined 2003
OK, let's cut the parsing (on my part, this time). SY I have you 'by the short hair' and you should well know it. Who are YOU to decide what is 'obvious' from listening and what is NOT? i.e. what you call 'extraordinary claims' is just your CHOICE of when you believe enough in something, to trust your ears. Sometimes MEASUREMENTS don't show much. IF ANYTHING.
Your rationalization that the slight gain change is important is bogus too, because I ALREADY said that this could be easily compensated for. After all, why not just change the gain slightly, to get the optimum sound, rather than change the loading?
What we have here is something that virtually everyone, from both sides accepts as a real change, YET it is difficult if not impossible to measure under real playback conditions comparable to how it was detected in the first place. Look at the evidence, or even better, many of you should get off your 'duffs' and TRY to measure a few things, before you rely EXCLUSIVELY on measurements to form your opinions about what can sound different from something else.
Allen, you were probably 'dead on' with your 68 ohms. I was trying to get you to more closely clarify what you had done to find this. You just can't make a statement like that, in this environment, without being dismissed as a 'crank'.
With the VENDETTA RESEARCH, we have continuous variable loading, from 10 ohms to 47K. It is generally most useful to about 300 ohms. After that, just 47K. We have done this for more than 25 years. Customers of mine, like Dave Wilson and Brian Cheney (VMPS) have given me numbers like 167 ohms or 84 ohms for a particular high quality MC cartridge. Why do we do it, why do we add such a control? BECAUSE WE CAN HEAR THE DIFFERENCE, THAT'S WHY!
Yet, it is almost impossible to measure. It is simply lost in the rest of the distortion, noise, etc. OF COURSE, something is happening, it is not magic, it is just hard to measure.
 
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SY

SY

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Joined 2002
SYclotron.com
john curl said:
Who are YOU to decide what is 'obvious' from listening and what is NOT? i.e. what you call 'extraordinary claims' is just your CHOICE of when you believe enough in something, to trust your ears...
Your rationalization that the slight gain change is important is bogus too, because I ALREADY said that this could be easily compensated for. After all, why not just change the gain slightly, to get the optimum sound, rather than change the loading?
What we have here is something that virtually everyone, from both sides accepts as a real change, YET it is difficult if not impossible to measure under real playback conditions comparable to how it was detected in the first place...
Yet, it is almost impossible to measure. It is simply lost in the rest of the distortion, noise, etc. OF COURSE, something is happening, it is not magic, it is just hard to measure.
Click to expand...

SY said:
In my own preamp, I saw a large difference between loading with 68R versus 680R for my 15R source impedance MC, but maybe THAT is the special case, not the sort of preamps that you or syn08 design.
Click to expand...

I didn't say anything about "audible." I'm responding to the assertion you made about measurable. I saw measurable changes in level and measurable changes in transient response. That's not exactly extraordinary. Are they audible? I don't know but if they were, it wouldn't surprise me a bit. But they are easily measurable, at least for my MC and preamp- I don't have Allen's or yours to compare.
 
john curl

john curl

Member
Joined 2003
Please show proof of measurable change. Without measurements, then I have to take your word for it. I have never seen or measured it, so I have to doubt your observations too, if they are not backed up by hard measurement. ;_)
(looks like I just missed, congratulations ;-) )
 
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syn08

syn08

Banned
Joined 2005
synaesthesia.ca
john curl said:
Please show proof of measurable change. Without measurements, then I have to take your word for it. I have never seen or measured it, so I have to doubt your observations too, if they are not backed up by hard measurement. ;_)
Click to expand...

John,

You are in no position to ask anybody to produce any proof, at least no more than anybody can ask you to produce evidence of what you say you hear (cables or whatever).

Though, because I'm a nice guy enjoying helping others: I can do such measurements in about an hour; in fact I already did some (that's the reason why the HPS 3.1 has such a wide range of input loads, to allow testing). I can do 0.01 dB level calibration @1KHz and look at the response with about the same error. You can take a look at my web site and see the HPS series RIAA response error to estimate the resolution of my setup.

Unfortunately, while investigating the response of a cartridge as a function of frequency, with the loading as a parameter, I realised it is impossible to compare the results. The random errors are orders of magnitude larger than the possible loading effects. That is, repeating the same experiment, with the same cartridge, test record, loading, etc... renders results that are spread over more than 0.1dB. I have tried filtering, analyzing distributions, I tried to eliminate gross errors by using a chi test, to no avail.

I can speculate about a few reasons why this happens (in particular related to my VPI turntable) but that would not bring any extra clarity.

My conclusion is that if there are any loading effects, they are one order of magnitude lower than the experimental errors.

It is possible, by using an (e.g.) Clearaudio Statement Reference ($150,000), to get some significant results. On such a system it is also possible to hear the differences. However, nobody can persuade me to believe that such differences are audible in my system, where measurements are buried in random errors.

Send me that turntable and I'll be happy to repeat the measurements :D
 
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
john curl said:
5 mH moving coil? Is that the one you use, SY?
Click to expand...

Nope. Using the calculator on that page, I plugged in a WAG for mine (I'm nervous about hooking it up to an inductance bridge) of 60uH, then varied the loading. Dropping it to 30R, the bandwidth (I assume it's an f3) drops to 80kHz, pretty close to the tip resonance and possibly enough to cause a potentially audible phase shift. At 68R, the bandwidth is 180k, well away from the audio band. For a 47k load, the rolloff is somewhere around the 2 meter band.

I can see these bandwidth changes interacting with the preamp, so again, your claims of sonic changes with resistive loading are certainly plausible.
 
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