So, as i understand, mark in PCB shows direction that increase Offset and Bias, that's right?
Time to desolder transistors from channel B and put them to A 🙂
And try (2), let's make fireworks!!! Yay! 😀
Time to desolder transistors from channel B and put them to A 🙂
And try (2), let's make fireworks!!! Yay! 😀
dunno - I didn't made these pcbs , and always lazy to check traces ....... when faster way is to use ohmmeter and brain
besides that - when working on some aplifier , you don't have always a way to look under pcb (traces) , and most probably you don't have pcb file to look at.
having "just" schematic is usually Bingo! situation
so - show/link to which exact schematic you're using , and I'll show you how to check for starting biasing voltage , for minimal Iq
besides that - when working on some aplifier , you don't have always a way to look under pcb (traces) , and most probably you don't have pcb file to look at.
having "just" schematic is usually Bingo! situation
so - show/link to which exact schematic you're using , and I'll show you how to check for starting biasing voltage , for minimal Iq
I agree, and have already made test ON...
Results - nothing exploded.
Voltage between GND and R2 - around -23 volts.
Seems like that everything works.
Time to set up bias/offset 🙂😱
Transistors Q4 a little heat, i think around 40celsius (104 F) all other are cold.
Addition:
Still do not touch variable resistors, but i touch with screwdriver input cable and hear 50-60 hz hum, it indicates that amplifer WORKS!!!
Last edited:
Another problem. Amplifer works, but change in BIAS do not raise amplifer power. Just nothing.
And i hear that some frequencies do not pass though amplifer, like something part of amplifer works like filter.
Any suggestions?
Voltage between GND and R2 = -23 volts i put all variable resistors to zero and start with bias, and still nothing.
But i hear! I hear that! class A detalization is awesome.
Also output transistors are cold.
And i hear that some frequencies do not pass though amplifer, like something part of amplifer works like filter.
Any suggestions?
Voltage between GND and R2 = -23 volts i put all variable resistors to zero and start with bias, and still nothing.
But i hear! I hear that! class A detalization is awesome.
Also output transistors are cold.
Last edited:
Bias is usually set with Inputs shorted and No Load on Output. You seem to be adjusting bias while playing music.
On my build the bias pots worked backwards.
so be prepared for that.
use a bulb tester to get initial set up and to see which way they adjust.
It can take a lot of turns to get the bias moving.
so be prepared for that.
use a bulb tester to get initial set up and to see which way they adjust.
It can take a lot of turns to get the bias moving.
I desolder R7, R8 replace them by Taiwan metal film oxide resistors 10k 1%.
Then i replace outputs IRFP240 by another pair that i have from F6 transistors kit.
And also i replace zeners to those that i bought from F6 transistors kit.
Test turn ON... and ... good news, output transistors are hot
Thermistor are hot too.
Seems like that amplifer works.
I put bias/offset variable resistors to zero. And output transistors are hot
, that OK?
Also to measure current bias value i need to use these two points GND and another across R2?
P.S Inputs shorted and no load at output.
Thanks!
Then i replace outputs IRFP240 by another pair that i have from F6 transistors kit.
And also i replace zeners to those that i bought from F6 transistors kit.
Test turn ON... and ... good news, output transistors are hot
Thermistor are hot too.
Seems like that amplifer works.
I put bias/offset variable resistors to zero. And output transistors are hot
, that OK?Also to measure current bias value i need to use these two points GND and another across R2?
P.S Inputs shorted and no load at output.
Thanks!
Last edited:
"I put bias/offset variable resistors to zero. And output transistors are hot , that OK?"
65*C norm
65*C norm
you did mount outputs on heatsink , I hope ?
also , you did not touch thermistor , while amp is powered on , I hope ?
also , you did not touch thermistor , while amp is powered on , I hope ?
For bias measurement, just attach clips across the two leads of R2 and
monitor the voltage. Start off with low bias, say around 0.5 across R2 (0.5/0.47
is a little over 1 amp) and adjust using P2.
For offset, use another meter attached to the two terminals of the amp's output
and see the DC voltage. You should be able to get it close to zero or less than
10 mV with a bit of patience by adjusting P1.
I recommend you try to keep the offset low as you adjust the bias (ie, not try
to zero the offset only at the end.)
Another thing to mention is that when you adjust the pots P1 and P2, they can
feel quite 'slow' and it takes a few seconds before you start seeing changes on
your voltmeters. So don't turn the pots too much at a time. Turn just a little
bit and wait for the change and then continue.
Cheers,
Dennis
monitor the voltage. Start off with low bias, say around 0.5 across R2 (0.5/0.47
is a little over 1 amp) and adjust using P2.
For offset, use another meter attached to the two terminals of the amp's output
and see the DC voltage. You should be able to get it close to zero or less than
10 mV with a bit of patience by adjusting P1.
I recommend you try to keep the offset low as you adjust the bias (ie, not try
to zero the offset only at the end.)
Another thing to mention is that when you adjust the pots P1 and P2, they can
feel quite 'slow' and it takes a few seconds before you start seeing changes on
your voltmeters. So don't turn the pots too much at a time. Turn just a little
bit and wait for the change and then continue.
Cheers,
Dennis
It's works!
I set BIAS to .5V (500 millivolts) and OFFSET to .010V (10 millivolts).
Hard to make judgement, but it's sound better than Onkyo A-9050 and Cambridge Audio AZUR 651 that i have listen with my speakers before.
First time i connect it to my iPhone 4s and the first thought was be... what a budget sound, but then i connect it to Lehmann Audio Linear D headphone amplifer with ESS Sabre 192kHz X 24bit DAC and it sound have become much much better.
I put to play "Frank Sinatra - Blue Moon" vinyl rip and Sinatra's voice so real, but i feel that my speakers probably do not reproduce high's good enough, so it's time to get better speakers with ribbon tweeter.
So i can describe sound as powerful, clear, with true tonal balance.
But i do not feel that sound airy enough...
Any suggestions? Finish another channel and try? Or build F5 or M2?
But anyway that best amplifer that i ever have before.
Special thanks to DiyAudio community and Nelson Pass!
Since only one channel works, it's a time to listen Beatles in Mono... huh 😀
Yay! 😉 😱 😀
I set BIAS to .5V (500 millivolts) and OFFSET to .010V (10 millivolts).
Hard to make judgement, but it's sound better than Onkyo A-9050 and Cambridge Audio AZUR 651 that i have listen with my speakers before.
First time i connect it to my iPhone 4s and the first thought was be... what a budget sound, but then i connect it to Lehmann Audio Linear D headphone amplifer with ESS Sabre 192kHz X 24bit DAC and it sound have become much much better.
I put to play "Frank Sinatra - Blue Moon" vinyl rip and Sinatra's voice so real, but i feel that my speakers probably do not reproduce high's good enough, so it's time to get better speakers with ribbon tweeter.
So i can describe sound as powerful, clear, with true tonal balance.
But i do not feel that sound airy enough...
Any suggestions? Finish another channel and try? Or build F5 or M2?
But anyway that best amplifer that i ever have before.
Special thanks to DiyAudio community and Nelson Pass!
Since only one channel works, it's a time to listen Beatles in Mono... huh 😀
Yay! 😉 😱 😀
Last edited:
Finish both channels and let it "run in" for a good period before critiquing the sound.
You can not make big decisions on one channel.
Same.
Yeah, i absolutely agree.
But, i just turned on Asap Rocky (sorry for my Musical choice) huh, and now i can say WOW!
Accuracy, deep bass, silence, tonal balance are awesome! I'am glad!!! Ahahaha 🙂
Last edited:
Great amplifier but very critical. If everything hooked up to it is not as good as it is it will show every flaw. It is that good.
I would definitely concentrate on finishing the other channel and run them
in for a while and up the bias a bit if your heat sinks allow. (Mine were at
around 1.3A, 0.6V/0.47ohm).
The M2 should be fun one to build, another wonderful gift from Papa.
Cheers,
Dennis
in for a while and up the bias a bit if your heat sinks allow. (Mine were at
around 1.3A, 0.6V/0.47ohm).
The M2 should be fun one to build, another wonderful gift from Papa.
Cheers,
Dennis
Another thought.
You have let it warm up fully haven't you?
It will not sound good until it is fully warm. (30min plus.)
You have let it warm up fully haven't you?
It will not sound good until it is fully warm. (30min plus.)
Also, the bias moves up a bit when the amp warms up, so you should check
it when it is warmed up.
Dennis
it when it is warmed up.
Dennis
The F6 is a super amp, no shortcomings on frequency range. I just recently had the chance to audition my F6 and M2 against my favorite 150 wpc AB amp that has been in my main system for many years. I really enjoyed the AB amp, and though it sounded great. But putting the the first watt amps in the same system exposed all of it's flaws, really no contest The AB has been moved to my basement system. Both the F6 & M2 were clearly better in everything.
PJN
PJN