Another quasi-complementary design

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#521
Very low voltage ,donatel. If you could post high resolution
pictures of your board.

Many burnt mosfet's I've read about lately, wish I had them all.
😀 😀

Also , I do the Idle bias right at the emitter resistor (R29/30-.22 ohm) = 22mv for 100ma / 11mv for 50ma
bad Hf performance/burnt OP stages sounds like severe
oscillations.🙄
 
#524
ostripper said:
Very low voltage ,donatel. If you could post high resolution
pictures of your board.

Many burnt mosfet's I've read about lately, wish I had them all.
😀 😀

Also , I do the Idle bias right at the emitter resistor (R29/30-.22 ohm) = 22mv for 100ma / 11mv for 50ma
bad Hf performance/burnt OP stages sounds like severe
oscillations.🙄
Click to expand...


Thanks for the answer, therefore do you believe that the motive for my breakups is due to the fact that my tension is too much low? Are R29 and R30 already from 0,22 ohms, only that have not understood still the setup of this amplifier, if I set to 0,3 or to 0,4 voltses??? I think that the greatest error is this...
 
#525
Hi Ravslanka,

I've examined the voltages you have posted and they are close to what they should be but not quite, so you could have a genuine fault. Using DC rails of 43 volts means you must change R7 otherwise T2 will not work. Change this to 18k before you continue and check if this fixes your problem.

Now lets have a look at the circuit in this order.

The constant current source in the first stage sets a voltage across R4 and across R9 of about 3 volts. This voltage appears on the bases of T6 and T8. If you allow for the b-e junction of these transistors you must have about 2.4 volts between the emitters of T6 and T8 and the positive rail on R15 / D5 etc. Allowing for voltage drops across R18/R16 VR2 and R15 you should have about 1.5 volts across the c-e of T5.

But you do not have this so pull out T5 and check it. If it tests ok make sure that it is connected correctly. Then check T4 and D5.

Now back to the first stage. If you do not have about 3 volts across R4 and across R5 check that the constant current source is working. The easiest way to check this is to measure the voltage across R7 (now 18k). The differential here should be about 32 volts.

Lets make the above checks first and let me know how you get on.

Note, when setting the bias for the out put stage do it very slowly. Allow the amp to warm up with the bias set to half what it should be and watch it closely as it rises slowly to a much higher value. Gradually back it off if you need to and set it finally after 15 minutes or so.

Cheers
Q
Cheers
Q
 
#526
quasi said:
Hi Ravslanka,

I've examined the voltages you have posted and they are close to what they should be but not quite, so you could have a genuine fault. Using DC rails of 43 volts means you must change R7 otherwise T2 will not work. Change this to 18k before you continue and check if this fixes your problem.

Now lets have a look at the circuit in this order.

The constant current source in the first stage sets a voltage across R4 and across R9 of about 3 volts. This voltage appears on the bases of T6 and T8. If you allow for the b-e junction of these transistors you must have about 2.4 volts between the emitters of T6 and T8 and the positive rail on R15 / D5 etc. Allowing for voltage drops across R18/R16 VR2 and R15 you should have about 1.5 volts across the c-e of T5.


But you do not have this so pull out T5 and check it. If it tests ok make sure that it is connected correctly. Then check T4 and D5.

Now back to the first stage. If you do not have about 3 volts across R4 and across R5 check that the constant current source is working. The easiest way to check this is to measure the voltage across R7 (now 18k). The differential here should be about 32 volts.

Lets make the above checks first and let me know how you get on.

Note, when setting the bias for the out put stage do it very slowly. Allow the amp to warm up with the bias set to half what it should be and watch it closely as it rises slowly to a much higher value. Gradually back it off if you need to and set it finally after 15 minutes or so.

Cheers
Q
Cheers
Q
Click to expand...

hi quasi

thanks for your reply

here are my measurements

with biasing off 0.60 volts for 2 pair mosfets and 42.3 volts dc rail and 10 ohm resistors in both rail

across r4=2.83 volts

r9=2.66 volts

the same voltages on bases of t6 and t8

from positive rail to emimiter of t8 its 1.94 volts and for t6 its 2.04
from positive rail to base of t8 its 2.80 volts and for t6 its 2.64 volts

across c-e of t5 its 1.30 volts

voltage across r7 its 32.5 volts
so i think constant current source is working

voltage across

r17=3.5 volts
r19=3.4 volts

voltage on positive fet with one meter lead connected to ground
g=3.5 volts
d=41.6volts
0.083mv
and negative fet

g=-39 volts
d=0.056mv
s=-41.3 volts

for t8
e=40.3 volts
c=3.5 volts
b=39.6 volts

t6
e=40.3
c= -1.1 volts
b=39.5 volts

t7
e= -1 volt
c= -39 volts
b=0.10 mv

t5
c=40.8 volts
b=41.7
e=42.3

t4
cb=42 volt
e=40.9 volts

t3
c=39.4 volts
b= -0.076mv
e= -575mv

t2
c= -33.2 volts
b= -41 volts
e= -41.6

giving clear buzz when connected to a speaker
not tested with one fuse and one 10 ohm resistor yet

so quasi is it working ok is it ready to play yet
 
#527
quasi said:
Hi Ravslanka,

I've examined the voltages you have posted and they are close to what they should be but not quite, so you could have a genuine fault. Using DC rails of 43 volts means you must change R7 otherwise T2 will not work. Change this to 18k before you continue and check if this fixes your problem.

Now lets have a look at the circuit in this order.

The constant current source in the first stage sets a voltage across R4 and across R9 of about 3 volts. This voltage appears on the bases of T6 and T8. If you allow for the b-e junction of these transistors you must have about 2.4 volts between the emitters of T6 and T8 and the positive rail on R15 / D5 etc. Allowing for voltage drops across R18/R16 VR2 and R15 you should have about 1.5 volts across the c-e of T5.


But you do not have this so pull out T5 and check it. If it tests ok make sure that it is connected correctly. Then check T4 and D5.

Now back to the first stage. If you do not have about 3 volts across R4 and across R5 check that the constant current source is working. The easiest way to check this is to measure the voltage across R7 (now 18k). The differential here should be about 32 volts.

Lets make the above checks first and let me know how you get on.

Note, when setting the bias for the out put stage do it very slowly. Allow the amp to warm up with the bias set to half what it should be and watch it closely as it rises slowly to a much higher value. Gradually back it off if you need to and set it finally after 15 minutes or so.

Cheers
Q
Cheers
Q
Click to expand...

hi quasi

thanks for your reply

here are my measurements

with biasing off 0.60 volts for 2 pair mosfets and 42.3 volts dc rail and 10 ohm resistors in both rail

across r4=2.83 volts

r9=2.66 volts

the same voltages on bases of t6 and t8

from positive rail to emimiter of t8 its 1.94 volts and for t6 its 2.04
from positive rail to base of t8 its 2.80 volts and for t6 its 2.64 volts

across c-e of t5 its 1.30 volts

voltage across r7 its 32.5 volts
so i think constant current source is working

voltage across

r17=3.5 volts
r19=3.4 volts

voltage on positive fet with one meter lead connected to ground
g=3.5 volts
d=41.6volts
0.083mv
and negative fet

g=-39 volts
d=0.056mv
s=-41.3 volts

for t8
e=40.3 volts
c=3.5 volts
b=39.6 volts

t6
e=40.3
c= -1.1 volts
b=39.5 volts

t7
e= -1 volt
c= -39 volts
b=0.10 mv

t5
c=40.8 volts
b=41.7
e=42.3

t4
cb=42 volt
e=40.9 volts

t3
c=39.4 volts
b= -0.076mv
e= -575mv

t2
c= -33.2 volts
b= -41 volts
e= -41.6

giving clear buzz when connected to a speaker
not tested with one fuse and one 10 ohm resistor yet

so quasi is it working ok is it ready to play yet

please do comment soon

thanks in advance
ravs
 
#531
Re: Go for it

quasi said:
.
Hi Ravslanka

Things seem ok so go ahead and replace the fuse and connect your speaker.

Enjoy, but remember you are only running 2 pair of FETs. If you increase the rails then you will need more FETs.

Cheers
Q
Click to expand...


thanks quasi

after warm up time of about 20 minutes with fuse and resistor
biasing of 0.60 volt and dc offset of 0.3mv.after that i replaced them with fuse everything is fine.i connect the speaker feeding the amp with computer output the sound is not clean it is breaking.

the i switched it with bigger supply with same biasing and dc offet
and dc rails of 76-0-76 and aux 86 volts with two pairs only for testing purpose .fuses in both rails rhe situation is the same. broken sound. what iam doing wrong.

voltage across

r4=3.24 volts
r9=3 v0lts
r7(27k)=53.3 volts
r19=3.32 volts
r17=3.61 volts

voltage across c-e of t5 1.48 volts

r16,r18=0.22 volts
please do reply soon

regards
ravs
 
#533
ravs.
All those voltage are normal.
Looks to me like your power amplifier works just great.

Question1:
What is voltage across R32 and R33 (0R33)?
Is alright if is 0.010 Volt - 0.020 Volt (30-60 mA in each MOS)

Question2:
You have one CD-player?
With some volume control.

Maybe this can give better sound.
If maybe your PC output is not perfect good for Power Amp input.
 
#534
lineup said:
ravs.
All those voltage are normal.
Looks to me like your power amplifier works just great.

Question1:
What is voltage across R32 and R33 (0R33)?
Is alright if is 0.010 Volt - 0.020 Volt (30-60 mA in each MOS)

Question2:
You have one CD-player?
With some volume control.

Maybe this can give better sound.
If maybe your PC output is not perfect good for Power Amp input.
Click to expand...


hi lineup

i have checked it already with a cd player and a pre amp from (esp)
i think only one side mosfets are working
voltage across

r32=31.4 mv
r33=0 volts
 
#540
quasi said:
Yup, that sounds like a problem to me.

Check to see that you the FET gates are actually connected to the gate drive resistor. Do you have access to a CRO? This will let you look at the audio signal at the various stages of the circuit.

Anyway you will need to check the output FETs for both a short cct and open cct condition.

Good to hear Nmos200 working.

Cheers
Q
Click to expand...


hi quasi

as you said i removed my fets and checked them they were were all ok. but i replaced them with new one .only one pair. the problem still remains.then i increased the biasing current to 1.20 volt the sound is clear now.with rails of 43 volts no auxilary.the amp is running for an hour with only one pair.the driver heat sink is cool main heatsink is a bit warm.is it ok to allow this much current to fets.iam planning to further increase the current to 1.30 volts.after that i will put all fets back to the board.suggest the voltage should go te resistor for 3 and 6 pair versions.

thanks in advance
ravs
 
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