I think the 10 ohm at the Source is 22 ohms if voltage is dropped to 16v.
just found there is a jfet BOZ thread with this
curcuit
several mods are suggested to try a lower distortion
one suggests 1k drain, and 5ohm source
maybe I will try something in between
but I better take it there if I have further questions
Hello,
I am building a Juma's pre (post 53 schematics).
Question about DC offset .... which is the acceptable value ??? I am able to adjust ch right to 0,0mV, but not able to go under 87,2 mV on Ch left. RGDS
0mV is what we aim for, but couple of mV up or down due to thermal drift is OK.
87mv is not acceptable - you have wrong value resistor soldered or, more probably, input JFETs are badly mismatched...
Resistor value is fine.
Yesterday I forgot to say that BC560 is B (not C). Is the BC560B/BC550C couple an issue ?
After several JFET/transistors swap (tried many combination i am actually at:
- CH left drifting from -8mV to +6mV (pot P1 is in the middle of the run)
- CH right drifting from +1mV to +18mV (pot P1 is at the end of the run)
............... better but not good enough i think
Yesterday I forgot to say that BC560 is B (not C). Is the BC560B/BC550C couple an issue ?
After several JFET/transistors swap (tried many combination i am actually at:
- CH left drifting from -8mV to +6mV (pot P1 is in the middle of the run)
- CH right drifting from +1mV to +18mV (pot P1 is at the end of the run)
............... better but not good enough i think
- CH right drifting from +1mV to +18mV (pot P1 is at the end of the run)
I guess you should be able to change that with a resistor on the adjust pot
wouldn't +/-10mV be ok ?
Fit the DC blocker at the input of the Power Amp.
There you have the Rin value and thus can sensibly select an appropriate cap value that gives the bandwidth that you want/need.
If you decide to fit an extra DC blocker in the Source, then at least make it optional, so that you can choose whether the power amp or the source has the more appropriate blocker. Remember you do not need dual DC blockers.
There you have the Rin value and thus can sensibly select an appropriate cap value that gives the bandwidth that you want/need.
If you decide to fit an extra DC blocker in the Source, then at least make it optional, so that you can choose whether the power amp or the source has the more appropriate blocker. Remember you do not need dual DC blockers.
So, apart of "cap / no cap" (the never ending story) .....
never ending story ? not sure what you are saying
your F5 have no input cap, right ?
ok, I always thought only alternative to no cap would be a servo curcuit dealing with DC
never considered no DC protection at all could be an option
well then, I guess you have to trust your curcuit 100% not to drift or fail and possibly pass DC
does not seem like that right now then
never considered no DC protection at all could be an option
well then, I guess you have to trust your curcuit 100% not to drift or fail and possibly pass DC
does not seem like that right now then
It explains the thermal drift......This is a picture of my current layout
You have pictures of good working layout in posts #54, #82 and #90. I suppose that you know why did you choose to ignore it ...
You have been a Member for 4 years.............As i am a novice i didn't know/considered that FETs need to be thermally coupled. ..........
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
- Home
- Amplifiers
- Pass Labs
- Preamp ideas for F5