John Curl's Blowtorch preamplifier part II

[janneman]

Originally Posted by Joshua_G

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.

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

[Allen Wright]

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/fileuploa...protractor.pdf

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

Regards, Allen (Vacuum State)

[SY]

Originally Posted by Allen Wright

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!

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?

[Allen Wright]

SY,
Hoe do you make such a calculation?

No, I never bothered making any measurements - it sounded great and that was the task done.

Yes, it was with my RTP3D preamp, with a bipolar/tube cascode (differential) input stage.

Regards, Allen (Vacuum State)

[SY]

Originally Posted by Allen Wright

SY,
Hoe do you make such a calculation?

The cartridge has a Thevenin equivalent of a voltage generator in series with a 3R (according to the maker's specs). This forms a voltage divider with the load impedance. 20 log (68/71).

[Joshua_G]

Jan,
What you wrote may apply to some people while what I wrote may apply to some others.

Allen,
Thank you. Once the speakers will be broke in and once the amplification will be finalized I'll check again the VTA.

SY,
There may be differences between simulation and actual measurements.

[janneman]

Originally Posted by Joshua_G

Jan,
What you wrote may apply to some people while what I wrote may apply to some others.

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]

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.

[SY]

Originally Posted by john curl

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.

Originally Posted by SY

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.

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]

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 ;-) )