Did you measure the Idss of the two jFETs?
That value determines the operating currents & resistances around 50% of the active devices in this amplifier.
Measure before you build.
That value determines the operating currents & resistances around 50% of the active devices in this amplifier.
Measure before you build.
Of course ... not. Not fets. Just resistors.
Just now learning how to measure them. Old ones I took out already, both of them. I found somebody called "AndrewT" written instructions on this forum for this measurement. Let's see how it goes. 😉
Just now learning how to measure them. Old ones I took out already, both of them. I found somebody called "AndrewT" written instructions on this forum for this measurement. Let's see how it goes. 😉
Nah. I must be doing something wrong in the measurement: I'm not able to get any reasonable reading. 😕
G+S together. 100R to D. 9V battery inbetween 100R and G+S, polarity per N or P type jfet. No? Yes? And then...?
G+S together. 100R to D. 9V battery inbetween 100R and G+S, polarity per N or P type jfet. No? Yes? And then...?
Well, new jfets in.
Voltages can reach 0.6V this time. Happy now? No, really not!
Voltages don't stabilize and off-set travels vividly back and forth as well.
Any ideas what should I do next (if I'm not quite ready to trash it and forget all about hi-fi quite yet)?
Voltages can reach 0.6V this time. Happy now? No, really not!
Voltages don't stabilize and off-set travels vividly back and forth as well.
Any ideas what should I do next (if I'm not quite ready to trash it and forget all about hi-fi quite yet)?
Please take some well-lit, in focus photos and post them here. You will be amazed what some people can spot on a photo.
Input shorted or not, same result; off-set going back and forth, with a range of about 60mA. I don't know anything about oscillation in amps, but the word describes to me exactly what I'm seeing.
A couple of resistors, LEDs and a cap. Ok, I guess I can buy those & solder them together per shown. What should I do with it?
I'll try to do that tomorrow.
Can the issue be on PSU side? Even tho one board seemed to bias ok?
you mean 60mV ?
connect across output , whatever orientation ;
if you see Led's lit up , there is oscillation
Yes, of course, 60mV. 😀
Output and ground, i.e. "red and black" spkr terminals? Can do. Once I get the parts.
Well... What if there is oscillation? Some "standard mistakes" I should look into?
Or should I just start from the beginning? I've read there has been multiple successful F5 builds, which is the reason I had the courage to set my hands on this. But... Well... 🙁
Probably not, because you did get one channel to behave.
Don't fret, you will get through this. Everybody here has had a project that didn't behave at one point. It's discouraging, I know, but hang in there!!! 🙂
Btw,
fwiiw,
and maybe some other abbreviation,
there was no any oscillation before I threw in the new jfets: bias was just out of range, but stabile.
fwiiw,
and maybe some other abbreviation,
there was no any oscillation before I threw in the new jfets: bias was just out of range, but stabile.
Didn't think an amp could make me this much depressed, but several months in making and the result being a total bummer... Certainly, I'm on a strange neighbourhood with the electronics, trying to make myself believe I'm not too old to learn new stuff by following a project description with a "plug and play" component package and a ready-made pwb on a project claimed to suit even for beginners... I'm feeling a total idiot! 😡
Before or after the sledge-hammer and throw-away-from-balcony treatment...? 😀
hi Juuso.
You might have just answered part of your problem,you replaced jFet and problem showed up ,a couple of possible things ,maybe that fet is bad,try another one, or the bias resistor is bad or a wrong value,some times you have to add a resistor inline with the pot to get it to into bias area ,And you say one board works fine,You've got a pattern right there ,simply measure the voltages across the resistors and compare them to the board giving you problems,The power supply is a key if it's not stable nothing will be stable so check your voltages there first,That's a good thing about stereo you got 2 channels so you can compare them to one another when things aren't right,Good Luck!!!!!!!!
You might have just answered part of your problem,you replaced jFet and problem showed up ,a couple of possible things ,maybe that fet is bad,try another one, or the bias resistor is bad or a wrong value,some times you have to add a resistor inline with the pot to get it to into bias area ,And you say one board works fine,You've got a pattern right there ,simply measure the voltages across the resistors and compare them to the board giving you problems,The power supply is a key if it's not stable nothing will be stable so check your voltages there first,That's a good thing about stereo you got 2 channels so you can compare them to one another when things aren't right,Good Luck!!!!!!!!
Don't fret...at one point I was ready to swing my F-5 around by the power cord and let it fly out the window....you'll get it working, just hang in there!
Russellc
Lol,
Now if you want to really,I mean sling it hard you can expose it to a airstream at about 700 mph,Let me know and I'll give you my mailing address,lol.
Now if you want to really,I mean sling it hard you can expose it to a airstream at about 700 mph,Let me know and I'll give you my mailing address,lol.
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Hi Russellc,
It's a joke ,,,you put that amp on a AIRPLANE ,get to cruise speed 700 mph in the air,lol.
and ship it to me if you don't want it,lol.
It's a joke ,,,you put that amp on a AIRPLANE ,get to cruise speed 700 mph in the air,lol.
and ship it to me if you don't want it,lol.
this one is going to be made🙂 if i only can find a 100ohm resistor😀 how critical is the value of the cap?
any value can go up or down for 50%
if you don't have proper one , there is always parallellllllll and seriesssssss connnnection
if you don't have proper one , there is always parallellllllll and seriesssssss connnnection
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