and btw funny that the schematic was also posted 4 years ago
you 'forgot' the neat regulators in the original curcuit ?
PCB is already supplied with regulated +/- 12V. No need to double it onboard.
I joined diyaudio 4 years ago when decided to replace my commercial speakers and go for diy. Selected/built PMS by Troels Gravesen (see below). Only 6 months ago i started to play with electronics. Built an F5 and now looking for an adequate preamp for it. This is way i am considering myself a novice.
I joined diyaudio 4 years ago when decided to replace my commercial speakers and go for diy. Selected/built PMS by Troels Gravesen (see below). Only 6 months ago i started to play with electronics. Built an F5 and now looking for an adequate preamp for it. This is way i am considering myself a novice.
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Hello,
I have a current buffer that has ~500k input impedance and I would like to try the preamp described in post 53.
My problem is the sourcing of j74 fets so i thought that I could try this topology with bjt:s at the input.
Is this possible with direct replacemet?
My plan is also to increase the rail voltage a bit in oreder to get more voltage swing.
I have a current buffer that has ~500k input impedance and I would like to try the preamp described in post 53.
My problem is the sourcing of j74 fets so i thought that I could try this topology with bjt:s at the input.
Is this possible with direct replacemet?
My plan is also to increase the rail voltage a bit in oreder to get more voltage swing.
DITTO
I have the same problem with the 2sj74..'they is all gone'!!! I do however have some of the "V" variety which I gather is not a good idea. I also have the 2sk170 in "V".
I need a preamp for my "last" F5 currently sitting near the ungar iron. Should I JBOZ it??or go BJT as shown.Or are the "V" devices workable ??What to do..OH what to do........
I have the same problem with the 2sj74..'they is all gone'!!! I do however have some of the "V" variety which I gather is not a good idea. I also have the 2sk170 in "V".
I need a preamp for my "last" F5 currently sitting near the ungar iron. Should I JBOZ it??or go BJT as shown.Or are the "V" devices workable ??What to do..OH what to do........
Thanks Juma!, I will try this one.
I will keep hunting of those sj74:s still.
Audiosan, Who is this spencer? and how can I contact him?
I have bought a batch from ebay whih turned out to be fakes.
yes
i got a package from him this morning too. a FDA-2 DAC kit.and have earlier ordered a lot of J-fets from him.
Hi!
I built the preamp from post #53 in this thread from juma.
(Now with the correct matched types of jfets)
But I can't get a stable output?
It's always going from -1100mV to 1500mV. If I adjust the 20R pot with a screwdriver, then the output value is changing faster to crazy values like 2.2V, then 0V, then -1.5V, until I put the screwdriver out of the adjusting screw from the pot.
If I blow a little air over the jfets, then everythings running out of control...
The Jfets arent fixed together yet, but very close and there is no air or wind in my room...
I have to say that input and output is open. Would it make sense to short the input (IN+GND bridge) and measure/set again or is there a mistake in my circuit?
Best Regards,
Matthias
I built the preamp from post #53 in this thread from juma.
(Now with the correct matched types of jfets)
But I can't get a stable output?
It's always going from -1100mV to 1500mV. If I adjust the 20R pot with a screwdriver, then the output value is changing faster to crazy values like 2.2V, then 0V, then -1.5V, until I put the screwdriver out of the adjusting screw from the pot.
If I blow a little air over the jfets, then everythings running out of control...
The Jfets arent fixed together yet, but very close and there is no air or wind in my room...
I have to say that input and output is open. Would it make sense to short the input (IN+GND bridge) and measure/set again or is there a mistake in my circuit?
Best Regards,
Matthias
hey zen and juma!
uuups, my bad english... sorry for that.
I think, there is some air in the room.
Sorry I have no pic in the moment... But tomorrow you will get it!
The value is changeing the whole time when its fired up.
Slowly when I do not touch it, but always from about -1100mV to +1500mV (both 12V mains are ok and stable).
Changeing the pots value doesn't show any effekt.
Waiting an half hour changed the output value a little bit to the range from -500mV to about +650mV or so....
Hmm, sometimes I hate me for those things...
@juma:
ooh, I saw your post tooo late...
ok, then I first try to shorten the input!
I didn't check the china fets, cause of christmas stress
I'll give it all a try and write back tomorrow!
THANK YOU!!!
Best Regards,
Matthias
uuups, my bad english... sorry for that.
I think, there is some air in the room.
Sorry I have no pic in the moment... But tomorrow you will get it!
The value is changeing the whole time when its fired up.
Slowly when I do not touch it, but always from about -1100mV to +1500mV (both 12V mains are ok and stable).
Changeing the pots value doesn't show any effekt.
Waiting an half hour changed the output value a little bit to the range from -500mV to about +650mV or so....
Hmm, sometimes I hate me for those things...
@juma:
ooh, I saw your post tooo late...
ok, then I first try to shorten the input!
I didn't check the china fets, cause of christmas stress
I'll give it all a try and write back tomorrow!
THANK YOU!!!
Best Regards,
Matthias
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