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Old 1st December 2012, 07:33 PM   #3131
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Update 2

First of all resistance measurements I gave in previous post were high - forgot to subtract lead resistance.

Took out the pots and R13, R14 to calibrate my ears with zero resistance on SSs

Listened for a couple hours and then did R13 =0 and R14 = .05 ohms. After that I reversed R13 and R14. To my ears with R13 =0 and R14 = .05 soundstage was forward. Reversing the resistors moved it back. When Nelson said a small amount of resistance added to SSs I think he meant it. It doesn't take much to change things.

I'm back to no degeneration - it sounds best to my ears and with the other amps in my tri-amp.The voices sound really natural - there is good slam and detail. I would love to hear F6 with a 100dB system like LaScala

Again thanks to all that have helped - may learn how to take some measurements with the Mac.

buzzforb - If no boards become available I will hand wire the Jensens.

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Old 1st December 2012, 07:45 PM   #3132
generg is offline generg  Germany
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Happy you had succes...!
Yes measuring the channels to see if they have a very different distortion spectra is a good idea.
I repeat, my left channel had k3 and k2 on the same level, right channel had k2 clearly higher. Seems to depend on on the SS pairs...
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Old 1st December 2012, 07:49 PM   #3133
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Thank you for everything - measurements are up next - resurrected my Waveterminal U24 and I will go from there.
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Old 1st December 2012, 07:57 PM   #3134
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Quote:
Originally Posted by flocchini View Post
Update 2

First of all resistance measurements I gave in previous post were high - forgot to subtract lead resistance.

Took out the pots and R13, R14 to calibrate my ears with zero resistance on SSs

Listened for a couple hours and then did R13 =0 and R14 = .05 ohms. After that I reversed R13 and R14. To my ears with R13 =0 and R14 = .05 soundstage was forward. Reversing the resistors moved it back. When Nelson said a small amount of resistance added to SSs I think he meant it. It doesn't take much to change things.

I'm back to no degeneration - it sounds best to my ears and with the other amps in my tri-amp.The voices sound really natural - there is good slam and detail. I would love to hear F6 with a 100dB system like LaScala

Again thanks to all that have helped - may learn how to take some measurements with the Mac.

buzzforb - If no boards become available I will hand wire the Jensens.

Best
Mine will be played on my ALtec system which should come in at about 98dB@1W
AS for degerneration. It is interesting to me that such a small amout of degernation could have so much affect, but I agree with you. THere is something that is truly freed in the music wthout it, but youe must really work to find the balance considering overall distortion as well. I wonder if this is a situation where reall y high quality source resistors would be in order. My question is the difference in sound a result of performance parameters chaging, ie more global feedback or does this circuit really reveal parts? Did you go without degeneration on the FE?
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Old 1st December 2012, 07:57 PM   #3135
lhquam is offline lhquam  United States
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I think you are missing the point. The primary source of distortion in any FET amplifier is due to the square law nonlinearity of the devices. Any feedback, whether a global loop or local source degeneration introduces higher order distortion components.

The figure below shows a mathematical derivation of the harmonic components of a single ended FET common source amplifier with degeneration. The coefficients a[i] powers of v, v^i correspond to the magnitudes of the corresponding harmonics. In a push-pull amplifier, the even harmonics tend to cancel if the device parameters and Rs are properly matches and/or adjusted. The important point of this derivation is that the odd harmonics can be reduced by minimizing Rs.

Quote:
Originally Posted by Antoinel View Post
The 1978 article by Mr. Pass which is entitled "Cascode Amp design" is a must read to understand and characterize the distortion of then a power NPN bjt. In our case, cascoding locks Vds to a constant value during operation but allows for current variations.

A possible idealized output amplifying device in a theoretical diyF6 maybe an NPN-STASIS (TM). It is made up of a power NPN transistor operating in Class A driving 4 or more PNPs. One set is needed for the upper and another identical set for the lower power output positions. However, the input impedance of each NPN is low compared to that of JFET. Nonetheless, this arrangement locks the variation of the current flowing through the input NPN in charge of defining net distortion to a constant.

I can envision replacing each on the NPNs operating in constant current mode with IRFP240s doing the same in a "clone STASIS (TM)"; clearly bending backwards to accomodate the diyF6 JENSEN.
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Old 1st December 2012, 08:00 PM   #3136
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Quote:
Originally Posted by lhquam View Post
The important point of this derivation is that the odd harmonics can be reduced by minimizing Rs.
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Old 1st December 2012, 08:33 PM   #3137
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Quote:
Originally Posted by buzzforb View Post
Mine will be played on my ALtec system which should come in at about 98dB@1W
AS for degerneration. It is interesting to me that such a small amout of degernation could have so much affect, but I agree with you. THere is something that is truly freed in the music wthout it, but youe must really work to find the balance considering overall distortion as well. I wonder if this is a situation where reall y high quality source resistors would be in order. My question is the difference in sound a result of performance parameters chaging, ie more global feedback or does this circuit really reveal parts? Did you go without degeneration on the FE?
No degeneration on the front end - the Idss is 8.5

I just used the 5% Stacpole Metal oxides I had here - paralleled .1 ohm resistors

jameshillj has commented on resistors in the F3 thread I believe - He used Isabellenhuette as I remember.
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Old 1st December 2012, 08:52 PM   #3138
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Quote:
Originally Posted by lhquam View Post
I think you are missing the point. The primary source of distortion in any FET amplifier is due to the square law nonlinearity of the devices. Any feedback, whether a global loop or local source degeneration introduces higher order distortion components.

The figure below shows a mathematical derivation of the harmonic components of a single ended FET common source amplifier with degeneration. The coefficients a[i] powers of v, v^i correspond to the magnitudes of the corresponding harmonics. In a push-pull amplifier, the even harmonics tend to cancel if the device parameters and Rs are properly matches and/or adjusted. The important point of this derivation is that the odd harmonics can be reduced by minimizing Rs.
Thanks lhquam, you have the gift of such skills I can only wish and imagine to have. Please strike off the above clone STASIS (TM) idea with MOSFETs.
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Old 1st December 2012, 10:59 PM   #3139
Tea-Bag is offline Tea-Bag  United States
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So, with Nelson's approval, I will try to post something close to the following for sale after a prototype is made and built.

It will use a daughter card concept to add in a Onetics or Jensen transformer, or allow a Perfboard to be mounted on the 2x10 2.54 Male pins to roll your own transformer onto it.

It will have all four pots and will be based on the F6 Second Harmonic. If one wants a simpler versions than jumpers need to be put in place for it. It may not be for everyone, but it will reach market, pending approval and I don't get hit with a snowplow or something.
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Old 1st December 2012, 11:16 PM   #3140
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Looks great !!!
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