John Curl's Blowtorch preamplifier part III

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What I was drawn to about Damir's design was the results I found when testing it. With only moderate over-all NFB the thd with 4 Ohm load and 20Khz is .001x % at 350W. measured.

The distortion does not change much with power or freq or load. Now that is something new. It is also quiet and fast (high slew rate).

IME those are properties, (very important - flat dist vs freq, secondary - , flat dist versus power) that correlate to very good sound.

Sounds like a great amp, I haven't had time to follow all these amp threads
but must obviously be CFB.
 
D'oh, serves me right for writing things in the middle of the night.

687456d1529310332-john-curls-blowtorch-preamplifier-iii-input_noise_isolation-jpg

jneutron, why use the coax shield rather than twisting wires in the same configuration? Is there some special benefit to coax aside from UHF skinning?

When the UHF skins across the outside of the coax, does it not induce any voltage across the signal wires?


I don't see this fixing IR drop from ground currents.
 
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Yeah, try it and let us know what you find.
Oh the joy of moving stuff around, plugging un plugging.

Try just your guitar amp direct into a wall socket or via the filter box.
I have and with different outlets/different circuits. I haven't tried it through the HTTP7000MKII, but I could plug it into once of the amp outlets on it. However, I think your comment

about SPL is most likely the culprit.

Typically, I'll have an amp about 20 feet away...Vol about 3.5 to 4.5. Very efficient speakers, amp completely rebuilt. Axe either ASAT Deluxe, SG, or V-neck Strat, vol set around 7 (to give range when playing...up for more drive/crunch, down for cleaner tone. The set point is right below the edge of distortion/breakup. Sometimes through a pedal, I like a modded blues driver pedal, or modded Ibenez tube screamer with germainium and dialed down.

Sure, and more fun. The vibration caused by guitar amp SPL is causing your gear to reset/misbehave ?. Which gear resets ?
Audio Research SP=10, even with the HTTP 7000MKII.

Other preamp/amp, at times it misses something, not sure what to day, perhaps it's also the laser in CD player(s).

Some of that gear is posted over in the Photo Gallery, search me name.

A lot of things change once you get married and have a kid. Niavely, I told my buddy, Frankie, no problem I can adjust. Frankie: No Sync you don't understand, you're ALWAYS going to be adjusting. Sync: What do you mean?

Frankie: It's not just a one time thing, as I said, you will ALWAYS be adjusting, so you better get used to it.

I'm down to one MI amp in the living room...and minimal music time.

:nownow:

Cheers,
 
If you want a metric for the effectiveness of a topology, divide feedback by THD. So say you have 80db/-100db. The metric is 180db. (my current amp in simulation has 260db at 20KHz, 130db/-130db).

If you want a metric for the simplicity of a topology, divide that by number of solder joints.

I wonder which amps would score the highest?

You could do the same thing with PSRR.
 
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Oh the joy of moving stuff around, plugging un plugging.
and replugging....and discovering new sounds.
I have and with different outlets/different circuits. I haven't tried it through the HTTP7000MKII, but I could plug it into once of the amp outlets on it. However, I think your comment about SPL is most likely the culprit.
I surprised a neighbor by swapping out an old grey 10m 240V extension cord with a modern white one.....his guitar amp clarity and tone changed quite markedly and for the better.
I expect running filtered power to your guitar amp will make a nice difference also.

Typically, I'll have an amp about 20 feet away...Vol about 3.5 to 4.5. Very efficient speakers, amp completely rebuilt. Axe either ASAT Deluxe, SG, or V-neck Strat, vol set around 7 (to give range when playing...up for more drive/crunch, down for cleaner tone. The set point is right below the edge of distortion/breakup.
Sometimes through a pedal, I like a modded blues driver pedal, or modded Ibenez tube screamer with germanium and dialed down.
You should be on Spotify.
Audio Research SP=10, even with the HTTP 7000MKII.
Other preamp/amp, at times it misses something, not sure what to day, perhaps it's also the laser in CD player(s).
Expect a cdp to skip/error with high SPL.
Line level/PA gear should be quite fine, and certainly not 'reset/reboot' !.

Some of that gear is posted over in the Photo Gallery, search me name.
I see you are having some fun.

A lot of things change once you get married and have a kid. Niavely,
I told my buddy, Frankie, no problem I can adjust.
Frankie: No Sync you don't understand, you're ALWAYS going to be adjusting.
Sync: What do you mean?
Frankie: It's not just a one time thing, as I said, you will ALWAYS be adjusting, so you better get used to it. I'm down to one MI amp in the living room...and minimal music time. :nownow:
Yes, it's called being owned....'so you better get used to it.' :eek:


Dan.
 
http://www.diyaudio.com/forums/atta...ch-preamplifier-iii-input_noise_isolation-jpg

Recipe for disaster in my experience, and EMC giants like H.W.Ott would certainly agree. To work it needs the small signal part fully shielded because the whole inside of the outer chassis is polluted with radiated RF from the incoming cable shield. Relying on some distance as indicated in the drawing isn't enough with today's levels of GHz-ish RF.
 
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Get your ducks in a row, guys :rofl:.

You missed the memo Waly. The great debate over what is and isn't high. low and medium nfb.

What are you doing with your time? pay attention. -10 demerits. My point was that you can get extremely low distortion with low amounts of over-all neg feedback. With simple circuitry. Why the need for the complexity of creating high to very high OLG?

For me 30-60 is medium for solid state.

-RNM
 
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Synctronx -- you have a voltage regulation issue. Line voltage drops too much at high volume --- causes some gear to reset etc.

An electrician would probably go around removing all the wall sockets and tightening all the connection screws, same for going through all the of the breaker panel connections. Also, look for loose neutrals in the panel, which all connect to a bus bar inside the back of the panel.

That is standard maintenance work for electricians. Also, look for warm or hot breakers. Electricians now have infrared cameras to look at a whole panel very quickly.

If nothing obvious then probably appropriate to troubleshoot by watching a voltmeter while varying the load. Presumably the voltage is dropping somewhere and it may be necessary to trace it back to the source of the problem. Should also be able to measure whether hot voltage is dropping, neutral is rising, or hot voltage is shifting depending on loads on other phases which may indicate a floating or loose neutral problem. None of those things is too uncommon.

If not competent as an electrician, best to call one to work on it. Loose connections can get hot and occasionally cause fires. Best to be safe.
 
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IME those are properties, (very important - flat dist vs freq, secondary - , flat dist versus power) that correlate to very good sound.

.
But why should flat distortion vs frequency matter as long as worst case is low enough? If you feel happier with that I have no issues, but peel back the marketing cruft and leftover FUD from the 70s and there doesn't seem to be a good reason for it, just an interesting technical challenge.
 
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But why should flat distortion vs frequency matter as long as worst case is low enough? If you feel happier with that I have no issues, but peel back the marketing cruft and leftover FUD from the 70s and there doesn't seem to be a good reason for it, just an interesting technical challenge.

That's the key phrase. yes... If it is low enough. And, when it is not?


-RNM
 
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An electrician would probably go around removing all the wall sockets and tightening all the connection screws, same for going through all the of the breaker panel connections. Also, look for loose neutrals in the panel, which all connect to a bus bar inside the back of the panel.......
I was getting around to this advice.....my questions were to diagnose if an AC connection somewhere is microphonic due to loose screw connection etc, or duff AC GPO switch. A guitar amp is not a big load and shouldn't cause serious voltage sag on it's own.

Dan.
 
My point was that you can get extremely low distortion with low amounts of over-all neg feedback. With simple circuitry. Why the need for the complexity of creating high to very high OLG? For me 30-60 is medium for solid state.
Sorry, you still need to

GSGDucks.jpg


- 60dB loop gain @ 20KHz is unusually high for an audio power amplifier. The double pole allowing this (even if it has some downsides) is one of Damir's sales pitches.

- Damir's amp is anything you want (low distortions, fast, etc...) but simple, this is the latest schematic, I believe http://www.diyaudio.com/forums/solid-state/243481-200w-mosfet-cfa-amp-123.html#post5311565

Please note that I'm not invoking here any technical reasons why I'm not a fan of Damir's amp, this is besides the point and off topic (which I admit is funny to say in this thread, though).
 
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