Hi
I built this amp, and yesterday when i play it sounds
wonderful. But today there's a strange sound in the left channel.
It's sounds like the speaker was broken.The sound only appear when there is music on between the song it's completely quit.
Anyone who think he knows whats wrong ??
Please help me !
I built this amp, and yesterday when i play it sounds
wonderful. But today there's a strange sound in the left channel.
It's sounds like the speaker was broken.The sound only appear when there is music on between the song it's completely quit.
Anyone who think he knows whats wrong ??
Please help me !
What do you mean Jan?
Ismannen, how about your rectifier bridge? Way too small.
Have you checked all voltages? You haven't blow any transistor. Bias, do you run in class AB or just B?
I gather that you will mount the transformer better?
The supply wires seem to be _very_ thin.
Your ground and connection of the smoothing caps. It's rather critical the connection between the caps, rectifier, speakers and the signal ground.
The 230 V wires should go loose and on top of other wires. Over longer distances the 230 V wires must have additional insulaltion, or cut the wires and solder in good 230 V wire.
Not smart to place signal input near the transformer. I would also recommend to have the speaker connections well separated from the inputs.
Ismannen, how about your rectifier bridge? Way too small.
Have you checked all voltages? You haven't blow any transistor. Bias, do you run in class AB or just B?
I gather that you will mount the transformer better?
The supply wires seem to be _very_ thin.
Your ground and connection of the smoothing caps. It's rather critical the connection between the caps, rectifier, speakers and the signal ground.
The 230 V wires should go loose and on top of other wires. Over longer distances the 230 V wires must have additional insulaltion, or cut the wires and solder in good 230 V wire.
Not smart to place signal input near the transformer. I would also recommend to have the speaker connections well separated from the inputs.
Peranders
However I go along with you in your reply to iceman.
Bridge rectifier diodes and Supply wiring seems very tiny.
Also check each resistor etc. for correct value (a common error) and the Vbe for all transistors etc.
Just a reflection to the text on the amp website.....
However I go along with you in your reply to iceman.
Bridge rectifier diodes and Supply wiring seems very tiny.
Also check each resistor etc. for correct value (a common error) and the Vbe for all transistors etc.
Let me give an input to this swedish/danish thread. I have encountered similar problem when repairing A-75 amp. One of the mosfet driver transistors was broken and there was a "gap" in music at low levels followed by horrible distortion above "threshold" level.
Iceman,
I have seen the schematics. Was not there :
1) too low quiescent current (cross-over distortion)
and / or
2) thermal runaway in the circuit, resulting in one of the power or driver transistors burnt?
I have seen the schematics. Was not there :
1) too low quiescent current (cross-over distortion)
and / or
2) thermal runaway in the circuit, resulting in one of the power or driver transistors burnt?
That may also be the problem, or that one or more transistors has different pin configuration than the original listed.....
My first statement would be to check your soldering. Often an emitter lead, or base lead will come off and the amp will still work but will be cutting into class B since there's only half conduction.
I have this nice Harman/Kardon amp with PP output stage in CFP and when you leave one power transistor out of the circuit it'll still work and sound fine, but run hot since the design is pecuiliar enough that is biases the single transistor in class A when the other one is missing. I haven't reverse engineered it enough to figure out why this class A thing occurs, however, I find it very interesting. The only problem is, the emitter resistor gets quite hot when this happens because the Q current goes through the roof.
If you're wondering how I discovered this, I was trying some new transistors MJ21193/21194 in there to evaluate their sound (which was very nice.) However, during the changeout, I forgot one of the transistors for some reason. I can't believe I didn't notice that before I turned the amp on. (I'm just happy I didn't find a way to destruct the indestructible amplifier.)😀
I have this nice Harman/Kardon amp with PP output stage in CFP and when you leave one power transistor out of the circuit it'll still work and sound fine, but run hot since the design is pecuiliar enough that is biases the single transistor in class A when the other one is missing. I haven't reverse engineered it enough to figure out why this class A thing occurs, however, I find it very interesting. The only problem is, the emitter resistor gets quite hot when this happens because the Q current goes through the roof.
If you're wondering how I discovered this, I was trying some new transistors MJ21193/21194 in there to evaluate their sound (which was very nice.) However, during the changeout, I forgot one of the transistors for some reason. I can't believe I didn't notice that before I turned the amp on. (I'm just happy I didn't find a way to destruct the indestructible amplifier.)😀
Thanks for replies
Peranders:Yes, all voltages are OK(-+24,2 V). I run it in AB
About the transformer; I will mount it better.
I just dont know yet if i gonna use just this transformer, or if it's overkill to have 500VA 18-0-18 to this amp.
I gonna test the transistor tomorrow.I use TIP35C/36C
The strange thing is that it sound OK yesterday, the only thing i do today was that i fix the cables etc..
About the rectifier;I gonna change it to a new one soon when I put the headphone-amp in the case. The new is built with
MUR2020.
Again: Thanks for all replies
Peranders:Yes, all voltages are OK(-+24,2 V). I run it in AB
About the transformer; I will mount it better.
I just dont know yet if i gonna use just this transformer, or if it's overkill to have 500VA 18-0-18 to this amp.
I gonna test the transistor tomorrow.I use TIP35C/36C
The strange thing is that it sound OK yesterday, the only thing i do today was that i fix the cables etc..
About the rectifier;I gonna change it to a new one soon when I put the headphone-amp in the case. The new is built with
MUR2020.
Again: Thanks for all replies
Well, there you go. Sounds like the bias was very close to the class B threshold!
That's a simple fix eh?
That's a simple fix eh?
Re: more information
Now you are just at the beginning. The strange sound dissapears, but to find and maintain the optimal quiescent current (for minimal THD) - not so easy ..😉
iceman said:
Now you are just at the beginning. The strange sound dissapears, but to find and maintain the optimal quiescent current (for minimal THD) - not so easy ..😉
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