John Curl's Blowtorch preamplifier part II

[Joshua_G]

Originally Posted by SY

Have you seen the measurements on my line amp? Will an opamp be significantly better (assuming that 0.004% THD is "good enough")?

Perhaps you should read that article as well.

So, do you design your line amplifier for measurements only?

[SY]

Originally Posted by Joshua_G

So, do you design your line amplifier for measurements only?

No, I use it in my music system. For measurements, I use a BUF03-based system or Pete Millett's excellent interface.

[Joshua_G]

Originally Posted by SY

No, I use it in my music system. For measurements, I use a BUF03-based system or Pete Millett's excellent interface.

Let me rephrase my question:
Do you design your line amplifiers according to how they measure only? By measure I mean measurements relevant to audio amplifiers, like distortion, SNR, output impedance, etc.
To clarify further my question, do you evaluate the quality your line amplifiers also by listening to it, or are you satisfied by it being measured well?

[SY]

If (for example) a hypothetical line amp measured well attached to my signal generator and spectrum analyzer, but played AM radio when I inserted it into my music system, I would not consider that an acceptable design.

I'm confused by your concept of building something, then not using it.

[analog_sa]

Originally Posted by SY

Have you seen the measurements on my line amp?

Have you measured its microphony? Whay about the phone pre? This alone is an issue that no amount of engineering will overcome. Enough about pulling babes - you have a car for that

[john curl]

Good questions, Joshua. I'm as confused as you are. I have 4 of my own preamp designs here, that I can use, yet I only use one, and the others actually have more features. I don't build products just for fun, and if they all sounded essentially the same, I would not bother with any of the newer designs. My Levinson JC-2 had virtually everything and more than I use today, yet it sits on a shelf. This is because I became sensitive to its limitations, as I detected them decades ago, and MEASURED them later.
We did our best, back in 1973, when it was first designed, but we made mistakes that I avoid now. For example, asymmetrical crosstalk, a real image killer.

[SY]

Originally Posted by analog_sa

Have you measured its microphony? Whay about the phone pre? This alone is an issue that no amount of engineering will overcome. Enough about pulling babes - you have a car for that

That is indeed a serious issue for tubes, especially in phono stages. One friend of mine speculates that the popularity of DHTs stems from some artificial forwardness and spatial qualities from the filaments' resonance.

I tested my line amp for microphonics in a rather crude way: tapping on it with a pencil while it was hooked up. No problems. The microphonics in my phono stage were definitely more noticeable, so it required some attention in isolation. That's the disadvantage of tubes in that application.

[Joshua_G]

Originally Posted by SY

If (for example) a hypothetical line amp measured well attached to my signal generator and spectrum analyzer, but played AM radio when I inserted it into my music system, I would not consider that an acceptable design.

I'm confused by your concept of building something, then not using it.

Obviously you avoid direct reply to my questions. My questions are clear, yet you reply to what I didn't ask. One possible reason for this is that you may be an ingenious designer who is reluctant to disclose his trade secrets, thus deterring others from copying them.

Let me tell you this.
Many people post various schematics on the forums here. I intend to build few amps, namely, a power amp, a preamp, a phono stage and a tape head amp.
For some reason, I opted for tube amps for all the above amps.
Since I have neither the time nor the money to build amps according to each and every schematic posted on the forums here, I do my own selection. This selection is very simple and straight forward: reports concerning the sound quality of those amps, based on listening. I don't choose schematics that only measure well, when they aren't supported by listening evaluation testimonies.

Now, according to some things you wrote here, I'm deluded.
May be I am, yet, according to my own experience with various pieces of gear for stereo setup, concerning the sound quality, listening evaluation is far more revealing than the published tests results.

Indeed, there is catch. I know that I can never follow blindly listening evaluations of others, since different people evaluate differently sound reproduction systems. Thus, I know in advance that I cannot take anything for granted before I'll hear it myself, on my own stereo setup. Yet, I will never spend my time and money to build an amp that all I know about it is that it measures well.

Of course, your approach may be just the opposite – and it may not. I have no way of knowing that, since you avoid replying directly me questions, as they were asked. Also, in another thread, I asked you to specify a statement of yours that measurements can predict the sound quality of an amp. You avoided that question by sending me to perform a search, a search which didn't bring about any meaningful results.

So, what I see from you, in various threads, is nullification of the value and use of listening tests, without any clear and substantiated stand on the issue of measurements only, versus combining measurements with listening tests. All I get is that you have something to hide on this issue, though I'm not sure what it is you are hiding and why you are hiding it. You know, attacking and criticizing a certain approach is one thing. Taking a stand and clarifying it is another thing.

As for myself, I cannot prove to others, by scientific means, the inevitable necessity of listening evaluation, on top of any measurements set. But when my limited money is at stake, I cannot and I will not risk it, based on measurements only, without any listening evaluation.

YMMV.

[bear]

could you please be more specific - I read 3-4 pages and found no reference to the comparison between tubes and anything solid state...

thanks

_-_-bear

PS I also use tubes in certain bits of gear... fyi.

[Joshua_G]

Originally Posted by bear

could you please be more specific - I read 3-4 pages and found no reference to the comparison between tubes and anything solid state...

thanks

_-_-bear

PS I also use tubes in certain bits of gear... fyi.

Who did you ask?