John Curl's Blowtorch preamplifier part II - Page 3153 - diyAudio
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Old 17th December 2012, 08:18 AM   #31521
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Quote:
Originally Posted by Bonsai View Post
I still need to work on the clipping behaviour
Can't-you bypass the problem by making clipping occurs *before* the input stage or at the input point where you take your input signal to compare ?
May-be you will be amused to look at that ?
An ultimate amp protection circuit ?

Mr Marsh, Error correction works in comparing two signals. I am afraid there is noway to use that kind of thing on an oscillator, where there is nothing to compare.
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Old 17th December 2012, 09:25 AM   #31522
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Yes, I am thinking about clamping the input signal but I want to keep it very simple and consistent with the rss of the circuit.
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Old 17th December 2012, 12:22 PM   #31523
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I am afraid that is no simple solution. When clipping occurs, the error level become enormous. May-be detecting its peak level in normal condition and make-it clip in the comparator if it exceeds this level ? But i do not believe-in it: it seems obvious, looking at your waves, that the OPA itself takes more and more time to recover...
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Last edited by Esperado; 17th December 2012 at 12:30 PM.
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Old 17th December 2012, 12:43 PM   #31524
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by RNMarsh View Post
Nice creative design work, Bonsai. BTW - can you apply your techniques to reducing thd of sine wave oscillators by any chance? Super low distortion oscillators? Thx-RNMarsh
Thanks Richard - unfortunately no, as Esperado says. I think the best approach for that is to use a notch filter.

BTW, I still regularly refer to your capacitor articles - they have certainly stood th test of time!

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Old 17th December 2012, 01:15 PM   #31525
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Originally Posted by scott wurcer View Post
I think I lost it years ago. IIRC you pull the inputs to Vee to disable them and just put a JFET long tailed pair on the comp/offset pins.
I recall making a phono preamp using the LF156 that way, and subbing the inputs with a LM194.

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I question if they have their own fab or are another test and rebrand operation, after all that's how we started.
I don't know. I could ask the rep..

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Originally Posted by john curl View Post
Now that everybody is really confused, the parts linked by JN are modern packages of REALLY OLD PARTS.
Interesting. But as I recall, many here including you, have been lamenting old parts which are discontinued. I linked them so that you guys could decide if they were worth anything.

jn
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Old 17th December 2012, 03:14 PM   #31526
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Not THESE old parts, JN. TOSHIBA, SANYO, SONY, ETC. parts. It is important to 'know when to hold them, and know when to fold them', or in other words, which devices ARE rare and worthwhile to get if possible, and which have been available, but are not so useful, or quiet.
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Old 17th December 2012, 03:30 PM   #31527
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Let us again discuss the significant differences between different families of complementary jfet parts:

1. REALLY OLD PARTS (long gate) >40 years old: Can be fairly quiet, however the extremely low Gm limits mid-range noise to maybe 3nV/rt Hz.

2. OLD PARTS (short gate) >30 years old <40 years old: Higher Gm gives promise of lower midrange noise, some devices can achieve 0.7nV/rt Hz in the midrange.
1/F noise is still dominant and can completely destroy the noise characteristic without selection. Parts have always been available from somebody, but some manufacturers discontinued the parts. Some parts have been made noisy by newer manufacturing methods.

3. JAPAN PARTS (meshed gate) <35 years old till recently: Best overall performance, VERY HIGH Gm, VERY LOW 1/F, a designer's dream. UNTIL discontinued by major Japanese companies. NO REAL REPLACEMENT, until LIS gets their act together, and then at a higher price than previously available.
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Old 17th December 2012, 04:43 PM   #31528
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Quote:
Originally Posted by Bonsai View Post
Thanks Richard - unfortunately no, as Esperado says. I think the best approach for that is to use a notch filter.

After the notch filter, you have the residual... the distortion products/harmonics which can then be used to cancel them in the original waveform. Im sure it would take a whole new approach to impliment. But, then, super low thd from the source wouldnt be needed.
I suspect the ShibaSoku THD instruments might do something similar to get a THD range of .0003% full scale. Putting it out here in case others think of a way to use the isolated harmonics to cancel them in the source. Thx-RNmarsh
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Old 17th December 2012, 05:28 PM   #31529
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Putting it out here in case others think of a way to use the isolated harmonics to cancel them in the source. Thx-RNmarsh
Hi slope pass band around the frequency, followed by trap filters for the nearest frequencies (F2, F3) ?
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Old 17th December 2012, 06:37 PM   #31530
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Quote:
Originally Posted by john curl View Post
Let us again discuss the significant differences between different families of complementary jfet parts:



3. JAPAN PARTS (meshed gate) <35 years old till recently: Best overall performance, VERY HIGH Gm, VERY LOW 1/F, a designer's dream. UNTIL discontinued by major Japanese companies. NO REAL REPLACEMENT, until LIS gets their act together, and then at a higher price than previously available.
Still short channel and its called impact ionization (dramatic gate current increase after 5-8V). LIS has it too. Interesting question is that P-channel FET's are immune to this and still N -channels were prefered. It is well known that in general PNP's can have lower rbb all else being equal. I figure it's a right vs. left hand thing, schematics just look right with N everything.

Half serious here.
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