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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nice, and very impressive for a first speaker
and excellent experienced choices as well
my good man, you have passed the novice level a long time ago
and excellent experienced choices as well
my good man, you have passed the novice level a long time ago
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.
BJTs as direct replacement - no way !
But if BJT is your weapon of choice, this can fit the bill (Zin is about 300k, gain about 3.5 V/V, Zout less than 300 Ohms):
But if BJT is your weapon of choice, this can fit the bill (Zin is about 300k, gain about 3.5 V/V, Zout less than 300 Ohms):
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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.
Spencer supplies well matched devices and gives good service with tracking number in fact some arrived this morning.Only one week from dispatch to delivered.
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
GentryBa,
did you measure the new JFETs that you got from China?
Did you thermally couple them ?
When setting the DC offset shortcircuiting the input is a must.
BTW, please let some the air into the room, you risk suffocation ... 😉
did you measure the new JFETs that you got from China?
Did you thermally couple them ?
When setting the DC offset shortcircuiting the input is a must.
BTW, please let some the air into the room, you risk suffocation ... 😉
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