Instead of starting a new thread, I would rather prefer to bring back alive this long dead thread.
I have built this amp working fine without any measure issues, the only issue i have is, when i start the amp i can hear the thump sound. How do i solve this issue can some one help me out.
Below is the Protection Schematic.
Regards,
Sadik
I have built this amp working fine without any measure issues, the only issue i have is, when i start the amp i can hear the thump sound. How do i solve this issue can some one help me out.
Below is the Protection Schematic.
An externally hosted image should be here but it was not working when we last tested it.
Regards,
Sadik
Thank u for ur reply Nikosokey. I have Matched all the transistors except the MJE's. Do i have to match them also?
Disconnect your speakers, pull out the servo OP77 tsip ,fire up the amp , measure the the output in mv lets say 10mv-30mv , if you measure volts the input transistors no mached good..
You are right, thank you for pointing out. After removing the IC i found 2.4Volts in output. Secondly I have used OP07 ic instead of OP77 Because OP77 is not available here.
Can you point out which are the transistors that should be perfectly matched? Because i am a learner. In this Process I had wasted 4 sets of PCB's just to make this Amp run. After trial and error and going on with this thread i managed to Run my Amp.
This is my Amp.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Sadik
How you can hear the thump when ralay not contact yet?
Do you mean that it isn't any delay time?
Yes, there is a delay of about 8 to 10 Seconds, I can hear the thump sound after the relays are in contact.
Seems if you hear a thump when the relays close (8~10 secs after power-up if if I understand correctly) then its because you have an offset on the amplifier output.
Measure the output of the amp wrt 0V. It should be close to 0V - i.e. 50-100mV max - within 2-4 seconds after you apply power to the amplifier. If not, then this is what you need to focus on to fix the thump.
If you have any appreciable offset on you amp, the speaker mute relays should not be engaging in the first place though.
IIRC, the Crescendo has servo that should be removing the offset - maybe you can post up a circuit of the amp so we can look into it.
Measure the output of the amp wrt 0V. It should be close to 0V - i.e. 50-100mV max - within 2-4 seconds after you apply power to the amplifier. If not, then this is what you need to focus on to fix the thump.
If you have any appreciable offset on you amp, the speaker mute relays should not be engaging in the first place though.
IIRC, the Crescendo has servo that should be removing the offset - maybe you can post up a circuit of the amp so we can look into it.
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Hi Andrew this protection circuit don't act when d.c is precent on output.
I will try to find the max d.c allowed on out.
Oh, dc protection +4.7v/-4.3v !
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Hi Bonsai,
There is no offset on amp. The Offset is set to 47mv on Both Channels as suggested in Elektor magazine. When the relays turn on at that time the measured DC voltage at speaker out is 700 mV which after 30 Sec drops down between 0 V to 5 mV which is constant.
Below is the Photo of PCB & Circuit Diagram
There is no offset on amp. The Offset is set to 47mv on Both Channels as suggested in Elektor magazine. When the relays turn on at that time the measured DC voltage at speaker out is 700 mV which after 30 Sec drops down between 0 V to 5 mV which is constant.
Below is the Photo of PCB & Circuit Diagram
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
May be i am not that lucky to get rid of that tump sound.
I did a lot of work to make this Amp run. Imagine wasting 4 sets of PCB's, the Itching, Drilling, Soldering all work done by myself. And after so much efforts the amp is running good and i am happy with it & can carry on with that thump sound if it is not solved.
Sadik,
The voltage at the amplifier output should be a few mV BEFORE the speaker relay closes. 700 mV will give you a noise.
How long after you apply power does it take for the relay to close?
The voltage at the amplifier output should be a few mV BEFORE the speaker relay closes. 700 mV will give you a noise.
How long after you apply power does it take for the relay to close?
It takes about 8 to 10 Sec time for relays to close. I hear the Thump Sound when the relays close even after delay of 10 Sec, At this time the Voltage is 700 mV on speaker output, which gradually drops down to 0-5mV within time span of 35 to 40 Seconds. After that the voltage is constant which is between 0-5mV.
Thank you for your kind reply and taking the time to compare my problem with your amp, I am in no hurry take your time. Once again thank you.
Sadik
That seems like its a bit too long - I would expect the amp to settle to under 100mV within 2-3 seconds.
Are you sure you have the correct values for R16, R19, R24 and R26? if any of these values was out by a factor of 10 then you might get long settling times.
If you disconnect the servo, does the amp settle quickly to its final value (it will have a big offset, but the question is about how quickly it settles - does it stilltake 35-40 seconds?
Are you sure you have the correct values for R16, R19, R24 and R26? if any of these values was out by a factor of 10 then you might get long settling times.
If you disconnect the servo, does the amp settle quickly to its final value (it will have a big offset, but the question is about how quickly it settles - does it stilltake 35-40 seconds?
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