John Curl's Blowtorch preamplifier part II - Page 3839 - diyAudio
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Old 18th April 2013, 06:13 PM   #38381
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Then why talk about it qusp? Talking 'around' a subject does little to inform.
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Old 18th April 2013, 06:57 PM   #38382
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Quote:
Originally Posted by john curl View Post
Then why talk about it qusp? Talking 'around' a subject does little to inform.
I believe you are quite adept at that technique, John.

jn




ps. Did you really believe that, when handed a blank check, I would not cash it???
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Old 18th April 2013, 07:52 PM   #38383
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Quote:
Originally Posted by john curl View Post
Then why talk about it qusp? Talking 'around' a subject does little to inform.
haha, because you said almost nothing about it, hell even your 'answer' was a bit vague and you think it was specific and informative? I answered with an inferred question mark, perhaps you are unable to see such things, but your post was not there when I formatted the reply. when starting a post with 'I believe' its usually, at least for me, an invitation for others to correct the content as required.

in fact, i'm not even sure what it is you are objecting to me talking about or saying, such is the depth of your arbitrariness; its what you live and breathe. it took you years to post anything worthy of specific technical discussion, preferring to dance around and dodge it as some kind of sport.

pot kettle John, pot kettle. i'm too full of irony to eat another bite

Last edited by qusp; 18th April 2013 at 08:01 PM.
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Old 18th April 2013, 08:25 PM   #38384
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actually it seems I edited the inferred question mark into an actual one.

does the JC2 hold the patent for losing gain from the act of inverting the input? I dont think so, I thought it was normal for some of the gain to be used to invert the input. the +1 for the positive phase gain calc is missing for the negative phase. without using this circuit specifically G = (R2/R1) +1 but we dont have the '+1' for the - input, so some of the gain needs to be used to first copy and invert the signal before adding gain. is that clearer? or if wrong, how?

Last edited by qusp; 18th April 2013 at 08:49 PM.
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Old 18th April 2013, 11:09 PM   #38385
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I didn't say that we could have patented it, only that we had to 'fix' it. We did something similar with the JC-80.
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Old 18th April 2013, 11:14 PM   #38386
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I really don't know, off-hand, quisp, any more than you do. I only know that it is a problem that had to be addressed.
That is why I had hoped that PMA, with his superior education and engineering skills, could explain it in engineering 'baby-talk' so that we could all understand it better.
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Old 19th April 2013, 12:46 AM   #38387
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i'm simply relating the same gain equation that would be used for a simple opamp circuit. treating the JC2 gain stage as an opamp for the purpose of simplification. I didnt think I had to explain where a simple derivation like G = (R2/R1) + 1 came from its so common...

when you run an opamp as a follower with gain (non inverting) you get in simplest terms G = (R2/R1) +1 (the plus 1 is for the input, just the same as many adjustable IC regulators you will use the same calc taking the pre-existing internal +V reference into account) but if you use the same values for an inverting configuration you do not get this free +1 to start with, as you dont have a negative input signal term, the input is opposite in polarity to the desired output.

if you will, some excerpts from your favorite datasheet

notice the inverting gain always lacks the +1 in the suggested values, but the non-inverting gain does, as it has the positive input signal to add to the gain. so if we are lacking the +1 thats added to every calc, no-matter whether its (100Ω/10Ω) +1 = 11, or (4kΩ/200Ω) +1 = 21, as the gain increases, the contribution of the +1 is a smaller amount of the total, thus in inverse proportion to that increase, just as your example.

but the inverting results lack this +1, as it lacks an initial negative input voltage to add to the inverted gain, so it must use some gain of its own, meaning if the values are the same for each side of the circuit ie symmetrical and dont change for balanced vs SE converted, doesnt that make sense? if thats all sound, to equalize there would need to be attenuation on the non-inverting output that was increased in inverse proportion to the gain. ie as the gain was reduced, a larger proportion of the output would need to be attenuated.

i'm sure I could be missing something in your switching and conversion, its not easy to read and I have FAAAAAAAAAR from the experience of most other contributors in this thread and no education bar my self driven learning, the kind help of others and practice, practice practice.


ive gotta tell you, I just had another glance at the schematic of yours for a few minutes, its late and its hurting my head and eyes. Its drawn so convolutedly and seemingly with colours designed to induce an epileptic fit! i'm just about ready for bed and it isnt helping! is that deliberate, like a code? I gave up after a couple of minutes and im not near the bottom of it, i'll havce to print it out in B&W I think.

sorry for verbosity, I hope thats clear on the 3rd time, or at least if i'm confused, the source of my confusion is clearly pointed out.
Attached Images
File Type: jpg AD797 inverting gain table.jpg (45.6 KB, 191 views)
File Type: png AD797 non-inverting follower with gain.png (25.6 KB, 187 views)

Last edited by qusp; 19th April 2013 at 01:09 AM.
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Old 19th April 2013, 12:53 AM   #38388
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Here it is in grayscale for those with epilepsy.

se
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Old 19th April 2013, 12:59 AM   #38389
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I didn't draw the schematic or even do the switching logic. I just oversaw that part. The schematic is made by 'Design Works' and it is one of the best schematic drawing programs available.
This schematic is rather complex due to the fact that the line stage has so many states: Balanced input, unbalanced input, balanced output and unbalanced outputs, also absolute polarity (remote controlled).
It is interesting that the Blowtorch circuit does NOT need so much added correction circuitry, because it doesn't have any global loop feedback.
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Old 19th April 2013, 01:09 AM   #38390
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Hopefully a slightly clearer version:
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