Hi, padamiecki.
Your + and - signs are a good way of illustrating what you mean. Indeed, the phase is the same at the plates of both U3 and U6 but there are two resistors in between, 1Meg and 2.2Meg, at the junction of which is the plate of U1, which is the opposite phase. There is NO feedback between the second stage and the output tube.
The way I've drawn the circuit is a bit unconventional, I suppose, and that may cause it to be misleading - sorry!
A more convetional way would be to show the FB loop from plate of 6SN7 to plate of 6SL7 so that it looked completely separate from the larger cross-coupled FB loop. They both meet up at the plate of the 6SL7, in any case.
Your + and - signs are a good way of illustrating what you mean. Indeed, the phase is the same at the plates of both U3 and U6 but there are two resistors in between, 1Meg and 2.2Meg, at the junction of which is the plate of U1, which is the opposite phase. There is NO feedback between the second stage and the output tube.
The way I've drawn the circuit is a bit unconventional, I suppose, and that may cause it to be misleading - sorry!
A more convetional way would be to show the FB loop from plate of 6SN7 to plate of 6SL7 so that it looked completely separate from the larger cross-coupled FB loop. They both meet up at the plate of the 6SL7, in any case.padamiecki said:
I have looked again at your original circuit drawing, and I think that the paraphase arrangement might be one reason you get early distortion.
The second triode part (V1b) is driven both via the common cathode resistor, and via the floating paraphase (R23, R24). This will provide positive feedback and result in a stronger signal from V1b than V1a.
A description of paraphase with a similar arrangement can be found here: http://www.dogstar.dantimax.dk/tubestuf/paraph.htm
Changing the first stage to a straight LTP with CCS seems to be the going opinion.
Svein.
Re: Re: my last project
May be yes, may be no !
I've already built paraphase that way, I mean with a common unbaypassed cathode resistors with no problems.
One may see that as a "LTP / Paraphase Bastard combo" 😉
(I used another word wich was censored: "illegitime son" ) 🙂
Assume the paraphase alone works. Then the cathode currents are equal and opposed. The sum is null, so there is no AC component in the common resistor.
On the other hand, this reaction (or positive feed back) is cancelled by the heavy negative FB around the lower triode.
It just make the summing process more precise (higher open loop gain).
My thoughts !
But you may also bypass the cathode resistor ...
Yves.
Svein_B said:
May be yes, may be no !
I've already built paraphase that way, I mean with a common unbaypassed cathode resistors with no problems.
One may see that as a "LTP / Paraphase Bastard combo" 😉
(I used another word wich was censored: "illegitime son" ) 🙂
Assume the paraphase alone works. Then the cathode currents are equal and opposed. The sum is null, so there is no AC component in the common resistor.
On the other hand, this reaction (or positive feed back) is cancelled by the heavy negative FB around the lower triode.
It just make the summing process more precise (higher open loop gain).
My thoughts !
But you may also bypass the cathode resistor ...
Yves.
Yves - not wanting to thread jack here BUT:
in the schematic of your latest what are the devices shown as R30, R32, R25? - are these zener diodes and the values shown the zener voltage???
I have just about finished the final tune of the conversion of a Chinese Music Angel EL34 PP (Pentode Mode) to your balnced shunt feedback scheme. I will post original and final schematics to the "Baby Huey" thread when complete.
padamiecki and ray_moth may find it interesting as well - I know ray_moth is a big pentode mode EL34 fan.
Cheers,
Ian
in the schematic of your latest what are the devices shown as R30, R32, R25? - are these zener diodes and the values shown the zener voltage???
I have just about finished the final tune of the conversion of a Chinese Music Angel EL34 PP (Pentode Mode) to your balnced shunt feedback scheme. I will post original and final schematics to the "Baby Huey" thread when complete.
padamiecki and ray_moth may find it interesting as well - I know ray_moth is a big pentode mode EL34 fan.
Cheers,
Ian
I plead guilty as charged - right now, that is. Truth is, I waver between triode mode and pentode mode, because both have their positive and negative points.
I find the challenge to design a stable pentode mode PP amp, with low distortion and good damping factor, particularly appealing. There are so many different ways to go about it. I'd love to discuss this subject on this forum, but maybe I should start a new thread on pentode-mode PP, rather than hijacking this thread?
I would certainly be interested to see your schematic, Ian (gingertube). Thank you!
gingertube said:
Yes, more or less !
Just look at here:
http://download.siliconexpert.com/pdfs/2004/0430/index/cs/epco/ds/01590173.pdf
More chat in another thread if you wish 😉
Cheers, Yves.
Re: Re: Re: my last project
You are of course right, Yves! 😱
I have now found this this solution already shown in an old leaflet ""Mullard world series valves for audio equipment": http://www.mif.pg.gda.pl/homepages/frank/other/Mullard/mullard.pdf (bottom of page 5).
Svein.
Yvesm said:
You are of course right, Yves! 😱
I have now found this this solution already shown in an old leaflet ""Mullard world series valves for audio equipment": http://www.mif.pg.gda.pl/homepages/frank/other/Mullard/mullard.pdf (bottom of page 5).
Svein.
Re: Re: Re: Re: my last project
but in general a solution presented by me in the 1st post may be linear (paraphase) or better change it into LTP?
Svein_B said:
but in general a solution presented by me in the 1st post may be linear (paraphase) or better change it into LTP?
This solution looks good to me as is !
Changing for LTP will ask for an additional negative source unless you accept to add two more caps in the signal path
Yves.
Changing for LTP will ask for an additional negative source unless you accept to add two more caps in the signal path
Yves.
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