John Curl's Blowtorch preamplifier part II - Page 3605 - diyAudio
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Old 28th February 2013, 04:50 PM   #36041
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Vlad, it depends on where you live, I would think. Some places will be almost RF free. Other places, the RF is at annoying levels. This is why we do not strive for SUPER HIGH bandwidth with the Parasound products, we just do NOT know where the product will be used.
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Old 28th February 2013, 04:58 PM   #36042
bcarso is offline bcarso  United States
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Originally Posted by Esperado View Post
the solution i have found, for the moment, is to set a 20K potentiometer between the output and ground, and a 18K serial resistance from the cursor to the - input. It reduce the variation of the Z in acceptable limits, and still feat in the gain range i can accept. Fast'n dirty.
What is your bandwidth requirement? I see schottkies, but you may be using those for their lower forward drop primariliy.
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Old 28th February 2013, 05:04 PM   #36043
bcarso is offline bcarso  United States
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Friends,

Just got word that Ed Dell, the man who started Audio Amateur, Glass Audio, Speaker Builder and later AudioXpress died earlier this week. Ed just turned 90 two weeks ago.
Another loss for the diy community. Ed probably did more for the audio hobby then anybody else.
I had the privelige to meet him a few times, last a few years ago when I interviewed him.

jan
Very sorry to hear. He was amazing for doing as much as he did for so long.
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Old 28th February 2013, 05:44 PM   #36044
Mr. dB is offline Mr. dB  United States
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Originally Posted by jan.didden View Post
Friends,

Just got word that Ed Dell, the man who started Audio Amateur, Glass Audio, Speaker Builder and later AudioXpress died earlier this week. Ed just turned 90 two weeks ago.
Another loss for the diy community. Ed probably did more for the audio hobby then anybody else.
I had the privelige to meet him a few times, last a few years ago when I interviewed him.

jan
Dang.
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Old 28th February 2013, 06:17 PM   #36045
bcarso is offline bcarso  United States
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Originally Posted by bcarso View Post
What is your bandwidth requirement? I see schottkies, but you may be using those for their lower forward drop primariliy.
Actually the more I look at this the more I'd like to know what you are attempting to accomplish. At first I supposed that you wanted a differential input, but perhaps your first inverters just represent independent sources.
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Old 28th February 2013, 06:56 PM   #36046
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Quote:
Originally Posted by Esperado View Post
the solution i have found, for the moment, is to set a 20K potentiometer between the output and ground, and a 18K serial resistance from the cursor to the - input. It reduce the variation of the Z in acceptable limits, and still feat in the gain range i can accept. Fast'n dirty.

I was about to suggest to use a dual gang potmeter with one half used for R and the other for RV. I am wondering, what you are going to use this for?
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Everything is somewhere. Where the @!#$ is it.
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Old 28th February 2013, 08:09 PM   #36047
bcarso is offline bcarso  United States
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Originally Posted by vacuphile View Post
I was about to suggest to use a dual gang potmeter with one half used for R and the other for RV. I am wondering, what you are going to use this for?
I still can't figure out what it is supposed to do. Are there two independent sources to the left? Whatever it does do, I am sure that it could be done more precisely, unless somehow it is using the forward diode drops intentionally (as opposed to putting up with them as a nuisance).

When I first looked at it in the middle of the night I thought some sort of differential front end was intended, but this is not the way the circuit works.
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Old 28th February 2013, 08:29 PM   #36048
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bcarso,
I could be wrong about it but I think it has to do with another thread that Christophe has pertaining to an amplifier protection circuit. It is an external comparator taking a signal from the output and comparing it to the input signal. He can correct me if I am wrong but that must be part of the circuit that he has proposed in his own thread.
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Old 28th February 2013, 09:42 PM   #36049
bcarso is offline bcarso  United States
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Originally Posted by Kindhornman View Post
bcarso,
I could be wrong about it but I think it has to do with another thread that Christophe has pertaining to an amplifier protection circuit. It is an external comparator taking a signal from the output and comparing it to the input signal. He can correct me if I am wrong but that must be part of the circuit that he has proposed in his own thread.
Oh thanks! That would explain a lot! So the two input signals are independent in general, and he's looking for full wave rectification of each. And the reason the other person's suggestion wouldn't work is that the two signals can't be mixed linearly as it were, since in the pathological case of one being the inversion of the other they would cancel.

Thanks again. Now I have an objective, should I choose to pursue it

Brad
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Old 28th February 2013, 11:45 PM   #36050
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First opamp has a diode in the feedback loop. Same for other input. Gain is -2. Now all you have to do is equal sum original input with -2X. The two products can go to the third opamp as either sum or difference.
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