100W Ultimate Fidelity Amplifier

[prasi]

thanks for answer,
I have 4R7 resistor on each rail.
I think the measured value is in phase with the fact that SK1058 snd SJ162 stay cold
I measure +17mv on the 4R7 resistor located at the + rail
and 25mv on the 4R7 resistor located at the - rail
as far I remember the pot R18 is about 100ohm (but not sure)
Turning the screw change the pot resistor value to 177 ohm but not the voltage at the 4R7 resistor
I also checked all the diods and resistors and if I didn't made a wrong reading, all values look fine.

thanks for your comments

Pot as per design should be 1k, or atleast a 500R. I ended up something like 220ohm for 130mA bias (from memory).

 

[camelator]

still4given,
Do you know what is a +/- value for the pot to reach 130mv / 200mv bias?

I am using this layout
http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-651.html#post4641450
I measured the 3 680R that are close together
My linear supply is 300VA
I have +/- 36.2 V DC on each rail

 

[still4given]

You are right. he might not be getting enough feedback to drive the front end.

 

[camelator]

Pot as per design should be 1k, or atleast a 500R. I ended up something like 220ohm for 130mA bias (from memory).

Hi Prasi,
thx for helping,
This is a 1k pot
Not 100% sure, but I think I had around 100ohm for 170 / 200mv... when it worked
Currently, pot looks working, by turning the screw, the resistor value change

 

[camelator]

Pic of my board

 

[camelator]

You are right. he might not be getting enough feedback to drive the front end.

Is it a way to check it?

 

[xrk971]

There's not much to go wrong on that amp. If bias adjust doesn't respond usually it's a bad transistor (BD139/140) or a bad resistor(s) feeding the bias circuit. I would use a multimeter and use diode mode voltage drop check between the base and emitter pins. Should be about 0.6v. If not the transistor may be dead. Use same method and check to make sure none of the 1N4148's are dead. Then check all TO92's with same method. You will need to look up pin outs for each kind of transitor to check.

 

[camelator]

There's not much to go wrong on that amp. If bias adjust doesn't respond usually it's a bad transistor (BD139/140) or a bad resistor(s) feeding the bias circuit. I would use a multimeter and use diode mode voltage drop check between the base and emitter pins. Should be about 0.6v. If not the transistor may be dead. Use same method and check to make sure none of the 1N4148's are dead. Then check all TO92's with same method. You will need to look up pin outs for each kind of transitor to check.

Hi XRK971,
many thanks for your help,
I already checked the resistors and diodes.
I amt very confident about testing transistor while power is up but I'll do that this evening.
If I don't find the wrong one => I'll double check the resistors & diodes.

 

[camelator]

Should be about 0.6v. If not the transistor may be dead. Use same method and check to make sure none of the 1N4148's are dead. Then check all TO92's with same method.

Hi all,
I've checked all transistors (Base-Emitter),
I have around 0.6mv for the smalls...

But for TO92 :

BD140 is 0.7v
and BD139 is 0.25 V??????

I think it should be higher??? If my understanding is correct it should be around 1V for these ones

Do you think it can be my issue?

 

[still4given]

Why not just replace the BD139? Looks like the culprit. Make sure you have an insulator.

 

[prasi]

Hi all,
I've checked all transistors (Base-Emitter),
I have around 0.6mv for the smalls...

But for TO92 :

BD140 is 0.7v
and BD139 is 0.25 V??????

I think it should be higher??? If my understanding is correct it should be around 1V for these ones

Do you think it can be my issue?

Measure on spare BD139 and replace the one on PCB.
After powering, check for overheating of any transistors and also for the 4.7ohm zobel resistor.
If you use a heatsink (small alu. plate on Sonal's PCB) for BD139/140 insulate their backs.

 

[apexaudio]

Pic of my board

Look like you put BC546 instead MPSA92

 

[camelator]

Look like you put BC546 instead MPSA92

Hi apexaudio,
many thanks for your attention,
indeed, I put a A92 instead a MPSA92....
Higher gain, and higer voltage saturation 🙁

Ok hope I have MPSA92 in stock 🙁

many thanks for this comment

 

[camelator]

Measure on spare BD139 and replace the one on PCB.
After powering, check for overheating of any transistors and also for the 4.7ohm zobel resistor.
If you use a heatsink (small alu. plate on Sonal's PCB) for BD139/140 insulate their backs.

Hi prasi ,

thanks for your comments,
I think there is no room for heatsink. Or I have to look for something very thin

 

[Bangla H]

camelator i have used a 2N5401 there, no MPSA in part box, all works fine the second
month now every day with 100mA.

 

[xrk971]

Hi apexaudio,
many thanks for your attention,
indeed, I put a A92 instead a MPSA92....
Higher gain, and higer voltage saturation 🙁

Ok hope I have MPSA92 in stock 🙁

many thanks for this comment

A92 is same as MPSA92. Just double check pins if using 5401.

For BD's you can mount them on bottom and bent 90 deg to use heatsink or a very thin piece of aluminum with two holes drilled. Use insulator as others mention to keep tab of heatsink from touching and shorting.

 

[camelator]

Well not good news...
Changing the BD139 didn't solve the issue.
my bias resistor is measured at 5.0ohm and DC is 24.9mv
without power diodes look good.
=> I decided to check diodes with my PSU connected.
I red few mv on diodes, and very randomly, but the last diode I checked, maybe I touched something wrong, JFET temperature rised, and I blowed a 10R resistor....

🙁 It worked the first day, and now, I think I should change all diodes to be sure. I have 8 PCB left so...

 

[camelator]

I think the wrong diode was D1. But having power off, this diode was ok....

 

[pallab]

replacement

BX22

sir, can I replace all 5 pair output to 2sc2922/2sa1216 sanken? I want to drive 2 ohms speaker for 70 0 70 v dc rails in apex bx 22..

 

[miro1360]

SR150 LtSpice

here is SR150 in LtSpice ... transistors can be changed