John Curl's Blowtorch preamplifier part II

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Depends. If one uses a panel of listeners and collects rankings along various "subjective" quality axes (e.g., "brightness," "clarity," "image specificity," that sort of thing), objective conclusions can be drawn about subjective impressions. These data are often presented in "radar charts." ANOVA is your friend here.

That's not very practical for low volume items made for niche markets, unfortunately.

Yes, I agree the best way to 'objectivize' a subjective issue like listener perception is to use some sort of numerical scoring method. Works in things like staff appraisals on the soft issues as well.

(I was also just trying be a bit of a smart *** :D)
 
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George

So far I have only measured flux leakage. Still to be done is line noise pass through and AC balance.


The loser is the flatpak. The best may be r core and tortoid.

There is more than 2 millivolts across the chassis for the flatpak.

That's second from left in your pic? I would have thought the split bobbin would give quite a good result.
 
You mean a controlled listening test with experienced listeners?
I believe John is against that.
jan

Jan, sorry for the late response. Yes I mean that. Getting some opinion from outside can open your sensitivity. As designer you have some blinders (that's normal)and therefore this can be helpful.

Listeners must not be audiophiles, it could be musicians - and best women (they listen more critical).

Think you're right John is not a friend of this.
 
Can you describe the test setup a little better? Some sketch of the different setups would help a lot. I'm not sure I understand what you are measuring.

If you look at the bench photo you can see the test leads connected to the chassis. They are on the same side of the transformer as the sheet metal. What is being measured is the voltage across the length of the chassis.

The transformer is measured 3 ways. First unplugged, then with AC but no load and finally with a load.

The load is shown. It is two diodes going to a 50 ohm resistor filtered with a 2200 uF capacitor. In the ground leg is a .1 ohm resistor that has a transformer load on the secondary by 72 ohms.
 
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Jan, sorry for the late response. Yes I mean that. Getting some opinion from outside can open your sensitivity. As designer you have some blinders (that's normal)and therefore this can be helpful.

Listeners must not be audiophiles, it could be musicians - and best women (they listen more critical).

Think you're right John is not a friend of this.

Agree. Actually, arguably EVERYBODY has his blinders, not just the designers.
But I do not agree listeners must be musicians. It has been argued elsewehre that they pay far to much attention to the musical interpretation and not the actual reproduction, and I agree. Musicians, unless they are trained listeners to sound reproduction, are not advised for such a test.
Same argument goes for women - if they are traned listeners, fine, if not, not.
Judging sound reproduction isn't about the last half octave above 18kHz.

jan
 
Joao, I would appreciate it if you understood me better. OF COURSE, experienced musicians LISTEN and EVALUATE my products. They don't do it in the design process, how could they? But after the design is done, or even if the design is still a prototype, we will send a component out to music schools and such for evaluation. In fact, I am soon getting for my own use, a newly designed power amp that has been evaluated in just this way, and not only with other designer/audiophiles. We just sent another amp to Germany for independent evaluation.
However, personal approval from a symphony conductor or such will not cut much weight with this audience who think that virtually all good amps sound the same. ALL my amps and preamps measure very well, so many here think that they should sound the same as any other component that measures very well. It isn't my experience, but many here discredit my experience, as propaganda or hallucination. '-)
 
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If you look at the bench photo you can see the test leads connected to the chassis. They are on the same side of the transformer as the sheet metal. What is being measured is the voltage across the length of the chassis.

The transformer is measured 3 ways. First unplugged, then with AC but no load and finally with a load.

The load is shown. It is two diodes going to a 50 ohm resistor filtered with a 2200 uF capacitor. In the ground leg is a .1 ohm resistor that has a transformer load on the secondary by 72 ohms.

This is a good beginning to learn that there really IS leakage and induced currents from transformers. The size of the transformers, the current draw/load and location from the audio circuitry, impedances involved, all impact the results in practice.
Next is to take the cheapest one and make it better than the others.... isolated from direct contact with chassis, shielding et al. Or, maybe just remote mount the supply for preamps and others.
Oh. And compare to UL leakage acceptance levels for safety. as well.

Thx-RNMarsh
 
John,
I think in an ideal world that all amplifiers would sound the same but I think we all realize that is far from the truth. What it is that makes us like one over the other is a better question than saying they should all be as transparent as a straight wire, which I have never heard.

I think that is really the reason that people are asking you why you chose one way of doing something over another. What makes you select certain components and how you arraigned them to get to your end result. If I thought all amplifiers did sound alike I would just go to the local Fry's and buy the cheapest sample that had the power output I wanted and move on. We still seem to be far from that ideal.
 
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This is a good beginning to learn that there really IS leakage and induced currents from transformers. The size of the transformers, the current draw/load and location from the audio circuitry, impedances involved, all impact the results in practice.
Next is to take the cheapest one and make it better than the others.... isolated from direct contact with chassis, shielding et al. Or, maybe just remote mount the supply for preamps and others.
Oh. And compare to UL leakage acceptance levels for safety. as well.

Thx-RNMarsh


JC tried to point out why his products have to cost what they do.... I would like to add on to that in another way.... UL safety and parts costs related to it.

In anything I do for others, i insist, or I dont work for them, that parts which touch ac line volatges must be a UL approved part.... every inch of it. I dont want to get sued, later. The cords, switches, fuses, fuse holders, capacitors, inductors, pcb trace size and materials and spacings -- everything pertaining to safe construction for sale to the public. Well, wouldnt you guess that each part that has VDE, UL et al stamped on them cost several times more than the same value without such testing and approved part? Several times as much. then it has to be constructed with similar care and standards applied. Then the whole package/finished product has to get approved ... more $$$ and many distroyed products later, you get to sell it to the public. I am not saying any brand is or isnt -- just that a good, proper and safe design cost a lot more.... and buyer beware! of what you get for your $. Specify it also be UL approved or dont use the transformer or cap etc.

Thx-RNMarsh

One of the test equip used for low power products -- test junky that i am -- attached;
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Richard,
Is every part really marked with a UL approval stamp or is that a little beyond the requirement? Does an inductor even have a label many times or would a circuit board have to be checked before you could use it? Isn't it the product in its entirety that is tested by a licensed inspection lab to UL standards? And what about TUV or any European inspection requirements?
 
This is a good beginning to learn that there really IS leakage and induced currents from transformers. The size of the transformers, the current draw/load and location from the audio circuitry, impedances involved, all impact the results in practice.
Next is to take the cheapest one and make it better than the others.... isolated from direct contact with chassis, shielding et al. Or, maybe just remote mount the supply for preamps and others.
Oh. And compare to UL leakage acceptance levels for safety. as well.

Thx-RNMarsh

Thanks,

It was nagging at me I forgot one test. Leakage current and how swapping the primary leads affects it. Will try to post a bit after lunch and do a few more tests.
 
Jan,

There was a reason why I mentioned the bit about testing the tester,

Let us assume I have a setup where two identical turntables with identical recordings, completely in sync, drive two different preamplifiers, that in turn drive identical amplifiers going to a single switch to a single loudspeaker in a well balanced room. The listener sit on axis and has an ABX switch. What does it prove if no listener can tell what x is? What if only one of the panel can tell? What if they all can tell?

Now if none of the listeners can tell, but the power amplifier is changed and the results change, what does that mean?

ES
 
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