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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 24th April 2013, 12:01 AM   #38501
buzzforb is offline buzzforb  United States
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Cascodes? What was the advantage of breaking up middle resistor into 4 resistors plu pot. I can see the pot for adjustment of contribution of each half, but why split the others? I like being the only guy that doesnt know.
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Last edited by buzzforb; 24th April 2013 at 12:03 AM.
 
Old 24th April 2013, 12:15 AM   #38502
john curl is offline john curl  United States
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OK, once again, here is the minimum, and then the more versatile version:
Attached Images
File Type: jpg 4Q-min.jpg (205.6 KB, 249 views)
File Type: jpg 4Qnew1.jpg (210.4 KB, 252 views)
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Old 24th April 2013, 12:17 AM   #38503
SY is offline SY  United States
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by buzzforb View Post
Cascodes?
That's one way, but I think that would take more than 4 more parts. I also think there's a better way. Let's see if John has gone there yet.
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Old 24th April 2013, 12:37 AM   #38504
john curl is offline john curl  United States
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Of course there is the 'folded cascode version, which I use with Vendetta and the CTC Blowtorch, but it is actually easier to look at this basic (not primitive) version of the 4Q input stage, and learn what each of the resistor sets do. Here, for example, is a more typical approach that I use with Parasound and Constellation.
First the original, second the typical:
Attached Images
File Type: jpg 4Qnew1.jpg (210.4 KB, 242 views)
File Type: jpg 4Q aka JC-2.jpg (232.1 KB, 234 views)
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Old 24th April 2013, 12:52 AM   #38505
john curl is offline john curl  United States
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Buzzforb, your questions are revealing.
First, some resistors give feedback, others give bias, some do both. The only obvious resistor function on the input is the variable pot.
It can, acting alone, control the total current of the entire 4 devices, forcing the n channel pair current to match the p channel pair current, due to the fact that there is no ground reference, and the only place for the current in all 4 devices to flow, is with the variable pot, YET the bias pot is not really necessary, just a convenience.
(By the way, I will talk about locally connected cascodes later, SY.)
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Old 24th April 2013, 01:06 AM   #38506
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally Posted by john curl View Post
I have never heard the device being criticized at this time. I have no opinion of it, at this time.
You're right. I misread what you wrote. My apologies.

se
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Old 24th April 2013, 01:32 AM   #38507
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Old 24th April 2013, 01:44 AM   #38508
buzzforb is offline buzzforb  United States
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Quote:
Originally Posted by john curl View Post
Here is the 'minimum' version for discussion at the moment:
Does this version contain feedback or is it just another way of loading the output?
Attached Images
File Type: jpg 4Q-min.jpg (205.6 KB, 132 views)
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Old 24th April 2013, 02:14 AM   #38509
john curl is offline john curl  United States
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This version uses the 1K 'load' resistors also as feedback resistors.
What is missing is the BIAS resistors. This simple design runs on the Idss of the input devices and there is NO control their current, so extreme selection would be necessary if we used the design this way, BUT it is the most simple way to show it in full 4 Quadrant symmetry.
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Last edited by john curl; 24th April 2013 at 02:40 AM.
 
Old 24th April 2013, 02:52 AM   #38510
john curl is offline john curl  United States
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Here is the CTC Blowtorch way of input current control:
Attached Images
File Type: jpg 4Q-min.jpg (205.6 KB, 146 views)
File Type: jpg 4Qbasic-with bias r.jpg (218.6 KB, 143 views)
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