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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 18th June 2019, 01:47 AM   #22481
Max Headroom is offline Max Headroom  Australia
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Originally Posted by john curl View Post
Thanks yet again, Markw4. I need to know the problem areas, if I am to address them. Of course, analog is relatively easy to 'improve' but it is not enough. Power supplies can be dealt with, but other digital based problems are a mystery to me.
You can experiment with decoupling cap types around DAC chip, each cap type sounds different as I am sure you know .
IIRC Joe Rasmussen advocated Supercaps across DAC chip supplies.....they can contain carbon in the internal electrodes so this might be what is different in sound to other caps, I have not tried this.
PM me for other info if you like.


Dan.
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Old 18th June 2019, 02:55 AM   #22482
Evenharmonics is offline Evenharmonics  United States
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Originally Posted by syn08 View Post
Thanks for the confirmation, 44 degrees phase margin, a disaster waiting to happen. And that's not even with the output close to the power rails.

For your education, given an N pole compensation schema (you are showing for N=2) there is still not much room to wiggle the ULGF while not affecting the stability margin. This is because audio amplifiers are by their nature minimum phase systems, therefore the magnitude and phase of the loop gain are not independent, you can get the phase(w) by simply applying a Hilbert transform to the gain(w). The only way to pull more loop gain from an audio amplifier, without pushing the ULGF to absurd values, is to use a higher order compensation network, a typical example would be the Cherry NDFL (which was practically used in the PGP amp). Or, in general, to use N poles followed by N-1 zeroes in the loop gain (to bring back the phase) and at the same time taking care of the sensitivity to stay within reasonable limits. I know of a couple of amplifier that are using N=5, one is an amazing small scale commercial class D amp, the other one was designed and build by a former member here (GK) as a proof of concept, but that one had other issues (was going berserk when approaching clipping).

And this is where the free lessons ends. For more, I can send you my hourly rate .

BTW, there's no relationship between the gain/phase plots you are showing, it's like you are pulling rabbits from a hat. I'm sure you have more .
Thanks, syn08 for your latest input. It is just the sort of info that I need.
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Old 18th June 2019, 04:27 AM   #22483
gpapag is offline gpapag  Greece
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John Curl's Blowtorch preamplifier part III
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Originally Posted by scott wurcer View Post
I was surprised how far two people with nerve can get
Tricon MMIC website is still up

("The details contained in the charging documents are allegations. The defendant is presumed innocent unless and until proven guilty beyond a reasonable doubt in a court of law.")

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Old 18th June 2019, 04:37 AM   #22484
Tournesol is online now Tournesol  Belgium
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Originally Posted by Evenharmonics View Post
Thanks, syn08 for your latest input. It is just the sort of info that I need.
This proves your meager knowledge of electronics for having plunged into this fabric of nonsense and conjunctures. Of the same kind as those he has assaulted on the amp of Richard (Read his denial) and the design of Dadod (Who responded as appropriate) .

He claims that it is impossible to make an amp with ULGF> 6MHz? This one goes up to 10.
He claims that the phase margin is 44 °, that he gets out of his hat, while it never goes below 91.4 °.

He makes conjectures about the rail voltage, of which he does not know the level.
He says some stupidity about how to measure the slew rate and do not even understud my answer.
Slew rate have to be measured clipping the amp and calculated between 10 and 90% of the total excusion.

The simple fact that there is no bump of the response curve at the end of the band and no overshoot on square signals should have reassured you about the stability of this amp that gives good and loyal service for more than three years now and supported high capacitive loads on the bench. No need for a Tian simulation of OLG.

Not to mention what he claims on my models, old classic, which are the Cordel ones, the best available for my devices as far as I know. Wrong again.

Funny too his conjunctures about the type of compensation i used, knowing nothing about my schematic.

Fake is fashionable.

This said, my real amp in real life had been more compensated after the tests and measurements, no need for overkill.
And, as appropriate, HF incoming signals are filtered far below its capabilities.


BTW: It sounds very smooth ;-)
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Last edited by Tournesol; 18th June 2019 at 05:03 AM.
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Old 18th June 2019, 05:29 AM   #22485
Joe Rasmussen is offline Joe Rasmussen  Australia
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Originally Posted by Max Headroom View Post
You can experiment with decoupling cap types around DAC chip, each cap type sounds different as I am sure you know .
IIRC Joe Rasmussen advocated Supercaps across DAC chip supplies.....they can contain carbon in the internal electrodes so this might be what is different in sound to other caps, I have not tried this...
Dan, try it.

Seems that supercaps keeps out ultra-LF noise on the DAC that makes them sound more 'digital' and especially with delta-sigma DACs. Having been doing this for about ten years (late noughties), passed it on to some of the DAC designers like clayton Gieseler and also discussed this on the Oppo upgrade thread. Now using supercaps has become a lot more common, they are popping up all over the place.

Also, put one also on the +3.3V to the oscillator where PS is ultra critical.

Above is so easy to do, no reason not to try it.

Joe
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Old 18th June 2019, 05:48 AM   #22486
PMA is offline PMA  Europe
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Originally Posted by Tournesol View Post
"No amp on the market" syn08 seems not to have a lot of experience with CFAs.
PGP Amplifier

Author | Linear Audio
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Old 18th June 2019, 06:36 AM   #22487
Jakob2 is offline Jakob2  Germany
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Originally Posted by Tournesol View Post
<snip>
Slew rate have to be measured clipping the amp and calculated between 10 and 90% of the total excusion.
Usually, the slew rate is measured by a square wave or step input signal that forces the amplifier to slew (a condition we would never like to see during normal operation) and then the maximum rate of change at the output is measured.
Of course, it is a large scale parameter but there is no need to drive the amplifier into clipping.
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Old 18th June 2019, 06:45 AM   #22488
dadod is offline dadod  Croatia
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Originally Posted by syn08 View Post
Yes, I was making an educated guess, and I guess your guess is as good as my guess at this stage. I'm sorry if I upset you Richard and I apologize for the trouble.

P.S. Bob Cordell just posted this today, quite on topic I would think. You may find Bob Cordell more trustful than yours truly.

Bob Cordell's Power amplifier book
I followed your work and I have high esteem of your knowledge, but what bother me is a way you make a comments(attacks?). Why you don't allow that an amp of higher ULGF then used in standard commercial can be very stable. In my opinion Cordell is quite conservative in that respect.
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Old 18th June 2019, 07:08 AM   #22489
PMA is offline PMA  Europe
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I agree dadod, I have an amp with LG as attached and it is stable with no problems.
Attached Images
File Type: png loopgain.png (78.0 KB, 155 views)
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Old 18th June 2019, 07:20 AM   #22490
syn08 is offline syn08  Canada
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Originally Posted by PMA View Post
I agree dadod, I have an amp with LG as attached and it is stable with no problems.
Are my eyes bad, or the ULGF is 700KHz in this example?
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