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Old 28th September 2005, 01:40 PM   #21
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Lumanauw

"This fact of having a "background" noisefloor can "boost" the details"

I read a little article published in Electronics World which said it has been scientifically proved. But instead of designing a power amp with difficultly modifiable noise, hiss, etc... it is just easier to introduce nicely sounding clarifying defaults at will using a "magic box" at the input of the amplifier.

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Old 28th September 2005, 01:48 PM   #22
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tlf9999

"People should have the right to be irrational."

Sure. belgian singer Jacques Brel even said :
"The right to be stupid shold be written in the constitution"

Yes, I agree. What I less agree, and contest using polite but hard words, is when people try to convince others to adher to their irrationnality.

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Old 28th September 2005, 02:25 PM   #23
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I've also gone down the Doug Self road of very low distortion and built several very low distortion amps that I've been ultimately dissatisfied with. The words sterile, cold, uninvolving go some way to describing the end result. More recently though I managed to bridge that 'low THD > musically involving' gap. My main tools are a 24 bit audio analyser and 200MHz CRO but they were unable to measure any change. Me thinks there is more to it than just THD signature. The project was a class A preamp / headphone amp. THD at 6KHz was below -118 which is the limits of my analyser as were IMD tests. It's a generic DS design but the EF VAS config favoured by DS has been substituted with a CFP, still with single pole Cdom compensation. Initially the extra VAS gain caused a 70MHz parasitic but I was able to remove it with VAS degeneration. The sound however was still cold and sterile and that character was actually made slightly worse after VAS degeneration. I used an F14 ferrite coil former as a bead on the VAS emitter and hey presto not only did the parasic vanish (as expected) but the treble became delishiously sweet and involving. At this stage I have no way of measuring the settling time or indeed the real world transient behaviour but it's worth investigating further. My design philosophy was ultra high speed and there are other aspects of the design that are a little unique such as special thermal tracking of current mirror collector voltages and DC offset.

I'm not sure to what extent these cct highlights are contributing but for for the time being I'm just enjoying the result.
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Old 28th September 2005, 03:35 PM   #24
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The explanation is supersimple: following non-linear solid state devices will detect and intermodulate. This is nothing good, a kind of alchemy. Yes, distortion emphasizes details. This kind of emphasizing should be strongly avoided.

That's not it. Since the oscillation was at 15MHz, all the IMD will be centered around 15MHz, and I highly doubt that it makes any sonic difference. What's actually happening is that the superimposed 15MHz voltage is shifting the operating point of the finals to a more non-linear condition, and that's what is causing the apparant improvement in the sonics.

This kind of emphasizing should be strongly avoided.

This goes to personal preference. Obviously, the customer who wanted the amp to oscillate did not agree. Yes, it does "offend" one's sense of technical excellence to be producing amps with more distortion than you know you can achieve. However, in the final analysis, amps are for entertaining people with music, not distortion and spectrum analyzers. So who's ultimately "right"?
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Old 28th September 2005, 03:48 PM   #25
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Hi, Forr,

You can make money here Why don't make a "black box" preamp, that actually rides the original music with Mhz background? Those who doesn't know electronic will praise it as a "magic detail enhancher". It is not "bass" it is not "treble" it is not "BBE" it is not "loudness", it is something else. Revealing detail on every frequency. Oh no.... On the other hand, PMA wouldn't buy it
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Old 28th September 2005, 03:58 PM   #26
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You can make money here Why don't make a "black box" preamp, that actually rides the original music with Mhz background? Those who doesn't know electronic will praise it as a "magic detail enhancher". It is not "bass" it is not "treble" it is not "BBE" it is not "loudness", it is something else. Revealing detail on every frequency.

Yannow, I just might do that. I've seen way wierder stuff being sold for some surprising $$$$$.
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Old 28th September 2005, 04:53 PM   #27
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Quote:
Originally posted by Miles Prower
[B

That's not it. Since the oscillation was at 15MHz, all the IMD will be centered around 15MHz, and I highly doubt that it makes any sonic difference. What's actually happening is that the superimposed 15MHz voltage is shifting the operating point of the finals to a more non-linear condition, and that's what is causing the apparant improvement in the sonics.
I was playing with that. Adding sinus waves in MHz range to an audio band signal. Depending on circuit non-linearities, new components in audio band were created. It is about multiplication and subtraction, so one cannot refuse possibility of new frequency components in audio band.

15MHz - my CD has similar noise at the output. When filtered by audio buffer circuit, the sound has much better resolution. I do not agree with the idea that HF noise/interference brings anything audibly good.
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Old 28th September 2005, 05:21 PM   #28
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I don't really know what happens, but I suspect it is far more than just "adding". It has to do with intermodulation, but I don't know what kind.

If you just "adding" Mhz sinusoidal to the music, maybe the result will be different than what I experienced. It is because the oscilating one is the output stage, and it has feedback to the differential. So must be more than just "adding". More like Intermodulation. But Miles Prower makes sense. It is too far from 15Mhz to 20khz. So what is actually happening?

One other strange thing. When the amp is set to not-oscilating, the threshold point of bias pot (VBE multiplier) is around 12 O'clock. Setting the bias less than 12 O'clock, the output is distorted.

But when the setting is in oscilating mode, even when I put the bias pot at minimal, the output is not distorted.

Is that oscilating amps needs less VBE bias than proper one?
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Old 28th September 2005, 05:53 PM   #29
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Hi LUMANAUW

Make money with a "magic box" ? Well I am not in the business and France is a so clever nation that a lot of things is done to dissuade you to enter it.

The magic box I planned to built (one day...) will not add high frequency components to the signal. It may include a noise adder but it is mainly based on an attenuator made of a resistor and a biased diode followed by a buffer, after a Ian Hickman's design . This will give better graded components of distorsion than any mythic tube la 300. The generated distorsion will be added to the initial signal at will and sent to the power amplifier. Then funny experiements will start.

I think Mr Cheever, the one of the famous thesis, should have play with such a box before writing all his stuff about the harmonic content of amplifers.

Anybody with ultra-subjective claims should be submitted to blind tests with magic boxes of different kinds.

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Old 28th September 2005, 07:19 PM   #30
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I do not agree with the idea that HF noise/interference brings anything audibly good.

I don't get it myself. However, we're not talking about you or me. We're discussing
lumanauw's customer:

Quote:
When I finished modification (I eliminate the oscilation fully, thanks to Mr. Pass and Jocko Homo), I return the amp to him.

The next day, he return the amp to me and said, "I don't like the sound, it is different than when I heard in your house..."

HAAAAH.....I tough myself. He likes the sound of oscilating amp??? To test it, I change back only the oscilating modification, putting it back to where it oscilates. When he hear it, he said "Yes, you are good. I like this very much".
How do you account for that?

Sure, in one sense, you give the customer what he wants, even if you think it's "wrong" or utterly ridiculous. He's the guy who's paying your bills, after all.

I'd like to see the matter resolved. However, even if we knew exactly what was going on, you'd still have personal preference to deal with.
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