R7 & R8 are 47,5 ohms (of course - thanks Botte 😉 )
I'm afraid I didn't listen before taking the amp apart again, since there wasn't much difference in the measurements.
It has worked all along though, but comparing the sound to how it sounded earlyer (when it did bias properly with one LED) is a little difficult since I've been playing around quite a bit testing different output degeneration values. (I seem to much prefer a little negative-phase second harmonic btw. Spikes things up quite a bit to my liking.) Not sure but the center of the soundstage my have shifted a little towards the troblesome channel (left) and maybe a tiny bit of hardness..?
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Oh yes - took it apart again to send the problematic PCB to Generg. He has generously offered to measure the SS and change out the possible broken one.
I must add still that people like this (as many of you others also no doubt - including Nesson of cource) make this place a more hopefull and human place. =)
I must add still that people like this (as many of you others also no doubt - including Nesson of cource) make this place a more hopefull and human place. =)
So each millivolt across the 47 ohms is about 20 uA. You probably want to
stay below 5 mV or so, but if 7 is working for you I would leave it.
😎
stay below 5 mV or so, but if 7 is working for you I would leave it.
😎
Jugi63,
Hm, I just looked at the measurements my friend Oliver and me did on the gate resistors (100R) of our SS when we tried to do a J2 like build.
And there we had with the 100R similar values to yours.....
0.6 and 0.75mV and the other channel 0mV and 0.3mV
But we had also SS with 4.7mV and 2.6mV
So you see your values are not lonely......
🙂
Hm, I just looked at the measurements my friend Oliver and me did on the gate resistors (100R) of our SS when we tried to do a J2 like build.
And there we had with the 100R similar values to yours.....
0.6 and 0.75mV and the other channel 0mV and 0.3mV
But we had also SS with 4.7mV and 2.6mV
So you see your values are not lonely......
🙂
When I combine your values and the explanation of Nelson there seems to be no problem anymore....
🙂
Is there a possibility to have DC-offset to the output if one of the Fets (supposedly the one with "no leakage" (as I suppose that Fet, for some reason, has started to conduct with no gate signal)) is not rock solid any longer and changes its conductivity further?
I might want to change the damaged fet (which ever it is), especially if I happened to have a pretty expensive pair of speakers for the amplifier...
I might want to change the damaged fet (which ever it is), especially if I happened to have a pretty expensive pair of speakers for the amplifier...
it is possible that part is , from some reason , slightly damaged ....... but what's more common is simple and abrupt road to perdition .......
however - if/while you're waiting for nasty surprise , you can place either speaker protection circuit , or simple fuse , between amp and precious spks
and yes - when right , spks are always more precious then amp ........ from simple reason - amp is much easier to bring again in flawless operational condition
that's why I'm having 1A6 fuse , in holder right to pos. terminal , on one of my spks ...... without loosing my sleep regarding relay/fuse/golden preputium debates
however - if/while you're waiting for nasty surprise , you can place either speaker protection circuit , or simple fuse , between amp and precious spks
and yes - when right , spks are always more precious then amp ........ from simple reason - amp is much easier to bring again in flawless operational condition
that's why I'm having 1A6 fuse , in holder right to pos. terminal , on one of my spks ...... without loosing my sleep regarding relay/fuse/golden preputium debates
So, concluding from all your responces, I guess the amp is basically fine but maybe not quite top notch given the change in bias and the somewhat big differance between Gate leakage values. But also one of the jfets might be, like Zen Mod puts it, on the road to perdition...
Well, in some aspects I may be a bit of a perfectionist and I do have somewhat expensive speakers. So I may still want to try changing a jfet... we'll see.
A big thanks everyone! - this has been very educating... 🙂
Well, in some aspects I may be a bit of a perfectionist and I do have somewhat expensive speakers. So I may still want to try changing a jfet... we'll see.
A big thanks everyone! - this has been very educating... 🙂
- post #5742
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You could always buy a few IRFP240s to see if the circuit itself has any issues. I blew a pair of R100 a while ago in a pair of Inducted F2 amps so the next time I tested with an IRFP240 first before I chucked in another R100 =)
you mean #5741 ?
however - if it works , and you are not hearing difference between channels (feed it mono) , then chill ........... (put fuses for tight and cozy sleep ) 😉
if you're happy with sound , buzz Semisouthfan for another 2+2+1 set , to preserve fine old and older wine for rest of time .....
however - if it works , and you are not hearing difference between channels (feed it mono) , then chill ........... (put fuses for tight and cozy sleep ) 😉
if you're happy with sound , buzz Semisouthfan for another 2+2+1 set , to preserve fine old and older wine for rest of time .....
F6 Board Stuffing
Hi Guys,
I'm getting around to stuffing the F6 boards. These are the white Tea-bag boards with the Jensen daughter boards. Looking around for a stuffing guide, but haven't had much luck in searching this thread.
I see that Q3 and Q4 are doubled up, e.g. Q3A/Q3B. Is this just paralleling or cascading for a modified design? I"m building the F6 variable 2nd harmonic version. Using 100A JFets.
Anything else I should be aware of when using these boards? Do the silk screen component numbers match the article as presented at BA 2012?
Thanks,
Vince
Hi Guys,
I'm getting around to stuffing the F6 boards. These are the white Tea-bag boards with the Jensen daughter boards. Looking around for a stuffing guide, but haven't had much luck in searching this thread.
I see that Q3 and Q4 are doubled up, e.g. Q3A/Q3B. Is this just paralleling or cascading for a modified design? I"m building the F6 variable 2nd harmonic version. Using 100A JFets.
Anything else I should be aware of when using these boards? Do the silk screen component numbers match the article as presented at BA 2012?
Thanks,
Vince
Hi Vince,
Those Q3 and Q4A are in case you wanted to use GR types and parallel versus using source degeneration on the JFETs.
If you build full second harmonic, then there is really nothing else to jumper etc.
Those Q3 and Q4A are in case you wanted to use GR types and parallel versus using source degeneration on the JFETs.
If you build full second harmonic, then there is really nothing else to jumper etc.
Is 1000uF and 35v enough for C1 & C2?
I assume it is since the voltage feeding it is only ~2v, but I might be wrong.
I assume it is since the voltage feeding it is only ~2v, but I might be wrong.