oh I forgot,
I have mure hum. Is it possible that the two 2SK170 have less hum rejection than the Zener-IRF9610 combination to feed the sources of the J-FETs?
I have mure hum. Is it possible that the two 2SK170 have less hum rejection than the Zener-IRF9610 combination to feed the sources of the J-FETs?
The voltage across R11 and R14 will tell you almost exactly what value R14 needs to be for equal current sharing through the differential pair. If you are passing 18ma through the front end then in order to be equal R14 needs to be the voltage drop across R14 divided by 9ma. If the voltage drop is 1.2 volts then R14 should be 133.3 ohms, simple math. Use a 500 ohm trimmer to fine tune it.
Bill did you mean the voltage drop over R114 or R111?
divided by 9mA?
Because there is no voltage over R114, I suppose C10 makes it impossible.
or should I take AC 50 Hz?
divided by 9mA?
Because there is no voltage over R114, I suppose C10 makes it impossible.
or should I take AC 50 Hz?
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I'm lost in nomenclature - mixed schematics ;
boyz - first agree which one you're using for nomenclature
😉
Generg - hum doesn't have anything with equal current through input LTP - try to find culprit somewhere else
put gate stopper resistor in LTP CCS - say that 1K is good enough
boyz - first agree which one you're using for nomenclature
😉
Generg - hum doesn't have anything with equal current through input LTP - try to find culprit somewhere else
put gate stopper resistor in LTP CCS - say that 1K is good enough
I am speaking of R11 as the resistor above the front end CS being 1Kohms. As you have measured, you have a total current of 18ma determined by the voltage drop across R11.
R14 is in one leg of the front end and should pass exactly half of the total current, which will be 9ma.
Because of the feedback supplied from the output section, Q2 will attempt to eliminate any output offset by passing more or less current through its leg.
Within reason, the amp will self adjust to keep the output offset low with no regard for maintaining the current balance between the halves of the front end, but it will tell you what voltage the R100s need on their gates to maintain the minimal output offset.
So now you know the voltage needed across R14, and you also know the proper current required to maintain current balance in the front end. So in the case of using your measurements, simply divide the voltage across R14 by the required current of 9ma and you have your answer.
R14 is in one leg of the front end and should pass exactly half of the total current, which will be 9ma.
Because of the feedback supplied from the output section, Q2 will attempt to eliminate any output offset by passing more or less current through its leg.
Within reason, the amp will self adjust to keep the output offset low with no regard for maintaining the current balance between the halves of the front end, but it will tell you what voltage the R100s need on their gates to maintain the minimal output offset.
So now you know the voltage needed across R14, and you also know the proper current required to maintain current balance in the front end. So in the case of using your measurements, simply divide the voltage across R14 by the required current of 9ma and you have your answer.
I think R111 and R114 were typos, I'm going by his posted schematic.
Posted at same time.
Posted at same time.
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I think - it's best to leave him alone for 24h , to enjoy in new amp
then - he'll sort 50% of things needed to sort , and we'll have just another 50%
then - he'll sort 50% of things needed to sort , and we'll have just another 50%
O.K. Bill I measured 1,9 V over R14, so 211 Ohm could be right....🙂
I thank you both for the time shared.....😀😀
the irritation was my fault I switched between the schematics of Aleph 3 and 5, and they have different numbers.
I thank you both for the time shared.....😀😀
the irritation was my fault I switched between the schematics of Aleph 3 and 5, and they have different numbers.
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That is correct, but double check your offset to be sure it is close to minimum.
Happy listening!
Happy listening!
Hi,
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Generg - I'm not sure now what was a call regarding value of R14 ;
Bill told you just to check voltage across it - to determine current through left side of LTP and compare is it 50% of overall LTP current
value of R14 is dependable of needed (Ugs+Urs) for desired output Iq and don't have anything with proper current share in LTP itself
varying LTP current and R14 value will vary OLG and feedback ........ but that's another part of story
Bill told you just to check voltage across it - to determine current through left side of LTP and compare is it 50% of overall LTP current
value of R14 is dependable of needed (Ugs+Urs) for desired output Iq and don't have anything with proper current share in LTP itself
varying LTP current and R14 value will vary OLG and feedback ........ but that's another part of story
hm, hm.... 🙂🙂
you both know to much for me to discuss your thoughts, but I can do what you suggest and hear the sound and get more feeling for theory reading your comments .....😀
I will try different values in the range opened by the discussion and given by Nelson. 😀
In A3 the current through the differential pair is also around 20mA ....if I read the SM correct, in A3 and A5 the values he suggested are 750 and 450 Ohm.
next days I will measure with a 60Hz tone the voltages Nelson described in Zen Variations 2, just for fun, learning something new....and never giving up....🙂
you both know to much for me to discuss your thoughts, but I can do what you suggest and hear the sound and get more feeling for theory reading your comments .....😀
I will try different values in the range opened by the discussion and given by Nelson. 😀
In A3 the current through the differential pair is also around 20mA ....if I read the SM correct, in A3 and A5 the values he suggested are 750 and 450 Ohm.
next days I will measure with a 60Hz tone the voltages Nelson described in Zen Variations 2, just for fun, learning something new....and never giving up....🙂
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I believe there is a slight language barrier. Please read my post again. I have taken into account all the points that you mention. The Vgs of the R100s determines the voltage needed across R14. If the offset is minimal then it is in the correct range, and then the voltage drop divided by the proper current determine the proper resistance. If the amp is operating with high offset, the voltage range for the R100s will be incorrect and will throw the current sharing off in the front end.
there is sometimes just too much for typing .......
NB that 5mA per input jfet is good
also - 10mA - as in FW J2 is good for driving one output gate
two input Jfets have x transconductance
that combining with y value of needed drain resistor at 10mA of current will give exactly Ugs+Urs for Iq of ~1A5 to 2A ...... and that will give z OLG , which - combining with feedback net set at 10x will give xx db- of feedback , giving yy output impedance ...........
rise time , blahblah ......
so - conclusion - whatever stage you think of ......... just let it bleed
NB that 5mA per input jfet is good
also - 10mA - as in FW J2 is good for driving one output gate
two input Jfets have x transconductance
that combining with y value of needed drain resistor at 10mA of current will give exactly Ugs+Urs for Iq of ~1A5 to 2A ...... and that will give z OLG , which - combining with feedback net set at 10x will give xx db- of feedback , giving yy output impedance ...........
rise time , blahblah ......
so - conclusion - whatever stage you think of ......... just let it bleed
there are 3 of us here , in this moment .....
I wasn't sure that Generg is following you - at least in moment when he started to write resistor values , instead of currents/voltages through LTP and each half of it
so - I think that I know what you were saying ....... but wasn't sure what Generg is measuring
one more thing - Generg - voltage accross drain resistor in input LTP seems little off - decreased at least for value across output Jfet source resistor ?
This ain't rocket science. I think Generg gets it. If he works through a couple of NPs previous Aleph front ends he will get it.
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yup 😉
for sure ; Generg is ..... Generg !
seems that little confusion started in multilateral chat
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