Hello friends,
I am building lm3875 chipamp based guitar amp. currently I am only preparing the power amp section. I had breadboarded it and connected with my computer output. There are some noise issues.
1. There is 'hiss' sound even in the absence of computer input when the amp input pot level above 9 clock... though it is not so loud but still annoying.
2. There is very loud audible click/pop when i press any electrical switches in my home and even worse when changing ceiling fan regulator..
Once i satisfied with the outcome I will make PCB......
Please suggest your views......
thanks
Paku
I am building lm3875 chipamp based guitar amp. currently I am only preparing the power amp section. I had breadboarded it and connected with my computer output. There are some noise issues.
1. There is 'hiss' sound even in the absence of computer input when the amp input pot level above 9 clock... though it is not so loud but still annoying.
2. There is very loud audible click/pop when i press any electrical switches in my home and even worse when changing ceiling fan regulator..
Once i satisfied with the outcome I will make PCB......
Please suggest your views......
thanks
Paku
Thanks WUPS for your reply. Can you suggest any schematic though I have already finished the power supply section.....
You can build up the EMI filtering a little at a time until you get enough filtering to do the job. Start with a snap-on ferrite on the AC power cord, at the amp side (not the wall side). This can be surprisingly effective. You can also add these to devices that you suspect are making a lot of electrical noise. I have many them around my house and have added them to video cables in addition to power cables to reduce RFI that causes visible noise in the video.
Next you can add a X-rated capacitor across the line and neutral of the AC inside the power supply. It must be an X1 or better rated AC safety capacitor, you can't just put any capacitor on there, since failure of this component can be dangerous. You can scavenge such capacitors from old PC power supplies, or an switching power supply from dead consumer electronics. They will be located closer to the AC input, prior to the rectifiers and big filter cap. They are often blue and always have a rectangular plastic shell. They bear the mark "X1", often "X1Y2" (meaning also safe to use as a Y2 capacitor). If you are using a IEC socket, you can solder the cap directly to the legs of the socket. You can also put a AC rated film capacitor (does not need to be safety rated) across each secondary of the transformer.
If that doesn't help, you could try to do more, google EMI RFI AC filtering.
You may also be picking up airborne noise. To help with this, make sure that the amp is in a grounded metal case.
Next you can add a X-rated capacitor across the line and neutral of the AC inside the power supply. It must be an X1 or better rated AC safety capacitor, you can't just put any capacitor on there, since failure of this component can be dangerous. You can scavenge such capacitors from old PC power supplies, or an switching power supply from dead consumer electronics. They will be located closer to the AC input, prior to the rectifiers and big filter cap. They are often blue and always have a rectangular plastic shell. They bear the mark "X1", often "X1Y2" (meaning also safe to use as a Y2 capacitor). If you are using a IEC socket, you can solder the cap directly to the legs of the socket. You can also put a AC rated film capacitor (does not need to be safety rated) across each secondary of the transformer.
If that doesn't help, you could try to do more, google EMI RFI AC filtering.
You may also be picking up airborne noise. To help with this, make sure that the amp is in a grounded metal case.
Paku,
It might be EMI filtering, but a very good possibility is that you haven't put on the "civilizing" parts for the feedback loop and snubber networks. It turns out that the data sheet can be quite misleading about what is really required. Please post your present schematic, and we can see if this is the case. Without these parts, the amp always sits on the edge of oscillation.
All the best...
dan
Akitika GT-101
It might be EMI filtering, but a very good possibility is that you haven't put on the "civilizing" parts for the feedback loop and snubber networks. It turns out that the data sheet can be quite misleading about what is really required. Please post your present schematic, and we can see if this is the case. Without these parts, the amp always sits on the edge of oscillation.
All the best...
dan
Akitika GT-101
hello friends
thank you all for your reply.. I have only done the power amp circuit on the breadboard certainly does not have star ground and other benefits PCB offer. But the annoying thing is the key bouncing sound..
Circuit design: input portion of the power amp taken from Single Chip 25W Amplifier (Project 72) and rest of the circuit components are from lm3875 data sheet.
power supply is regular bridge rectifier with 4700 bypass caps and 0.1 uf filter caps with +-25v in each rail. and pre amp 9v is taken out from lm 317. for relay switching and micro controller I have separate transformer that is rectified and have +5 +12V output from fixed low dropout regulator.
thank you all for your reply.. I have only done the power amp circuit on the breadboard certainly does not have star ground and other benefits PCB offer. But the annoying thing is the key bouncing sound..
Circuit design: input portion of the power amp taken from Single Chip 25W Amplifier (Project 72) and rest of the circuit components are from lm3875 data sheet.
power supply is regular bridge rectifier with 4700 bypass caps and 0.1 uf filter caps with +-25v in each rail. and pre amp 9v is taken out from lm 317. for relay switching and micro controller I have separate transformer that is rectified and have +5 +12V output from fixed low dropout regulator.
a picture would still help us know just what bits and pieces you have adapted to your design.
for example...do you have the RL output network? It's really quite important.
do you have the 220 pF across the input leads (e.g. positive and negative inputs of chip)? It's also quite important.
Akitika GT-101
for example...do you have the RL output network? It's really quite important.
do you have the 220 pF across the input leads (e.g. positive and negative inputs of chip)? It's also quite important.
Akitika GT-101
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I HAVE FEW QUESTIONS TO ASK
1. DO I NEED SEPARATE GROUND WIRE FOR SPEAKER DIRECTLY FROM POWER SUPPLY?
2. I DID NOT ADDED ZOBEL NETWORK AT THE OUTPUT. IS IT NECESSARY?
3. CURRENTLY I AM TESTING WITH MY COMPUTER OUPUT.. WHEN THE COMPUTER IS TURNED OFF OR INPUT IS OPEN, AMP IS PRODUCING GREAT 'HISS'. BUT WHEN COMPUTER IS TURNED ON THEN THE NOISE REDUCED TO 95%..
4. WHAT IMPROVEMENT CAN BE MADE WITH POWER SUPPLY AND AMP SECTION?
5. A STRANGE CASE-- WHILE THERE IS INPUT ON THE CHIP FROM COMPUTER IF I POWER OFF THE AMP SECTION WITHIN 2 SECONDS THE CAPACITORS COMPLETELY FLUSHED OUT. BUT THEN AFTER 5-6 SECONDS THE AMP MOMENTARILY BECOMES ACTIVE AND PLAY FOR VERY SHORT TIME AND THEN FINALLY STOPS. I CAN'T FIGURE OUT WHAT IS HAPPENING...
CHECK OUT THE ZIP FILE CONTAINING CIRCUIT SCHEMATICS...
1. DO I NEED SEPARATE GROUND WIRE FOR SPEAKER DIRECTLY FROM POWER SUPPLY?
2. I DID NOT ADDED ZOBEL NETWORK AT THE OUTPUT. IS IT NECESSARY?
3. CURRENTLY I AM TESTING WITH MY COMPUTER OUPUT.. WHEN THE COMPUTER IS TURNED OFF OR INPUT IS OPEN, AMP IS PRODUCING GREAT 'HISS'. BUT WHEN COMPUTER IS TURNED ON THEN THE NOISE REDUCED TO 95%..
4. WHAT IMPROVEMENT CAN BE MADE WITH POWER SUPPLY AND AMP SECTION?
5. A STRANGE CASE-- WHILE THERE IS INPUT ON THE CHIP FROM COMPUTER IF I POWER OFF THE AMP SECTION WITHIN 2 SECONDS THE CAPACITORS COMPLETELY FLUSHED OUT. BUT THEN AFTER 5-6 SECONDS THE AMP MOMENTARILY BECOMES ACTIVE AND PLAY FOR VERY SHORT TIME AND THEN FINALLY STOPS. I CAN'T FIGURE OUT WHAT IS HAPPENING...
CHECK OUT THE ZIP FILE CONTAINING CIRCUIT SCHEMATICS...
Attachments
Thanks for the photo update..
I will try to add those extra components and check the performance...
0.7uH is totally rare. is 10E resistance 2W?
do i require any modification on the power supply??
to WUPS
I know that the datasheet avoids electrolytic on C7. But I have checked on many thread that as the current being very small an electrolytic may be an alternative..though not sure about that..
paku
I will try to add those extra components and check the performance...
0.7uH is totally rare. is 10E resistance 2W?
do i require any modification on the power supply??
to WUPS
I know that the datasheet avoids electrolytic on C7. But I have checked on many thread that as the current being very small an electrolytic may be an alternative..though not sure about that..
paku
Did i hear you say the amplifier makes a hissing noise!!. What gain is the amp running ? what sensitivity are the loudspeaker you are testing with. I have constructed a few chipamps using the national chips and the only time i got any hiss was when the amplifier was ocillating. Caused by bad circuit layout and poor local decoupling . Please send some clear pictures of the proto type you have built .
Good luck
Good luck
C7 as an electrolytic is fine. There's essentially no audio or DC across it if the amp is working correctly.
The gain of 22 or 23 is quite typical. That shouldn't be a noise issue. I sell an update kit for the Dynaco Stereo 120 that uses similar values of gain. The amp is pretty well dead quiet with open inputs and your ear up to the speaker.
You might find some useful hints perusing the assembly manuals and schematics, even as it applies to grounding and such. Unfortunately, it won't be a direct comparison, as I use single supply and output capacitor, but I think it still might help.
Here are the links:
Update My Dynaco
Akitika GT-101
The gain of 22 or 23 is quite typical. That shouldn't be a noise issue. I sell an update kit for the Dynaco Stereo 120 that uses similar values of gain. The amp is pretty well dead quiet with open inputs and your ear up to the speaker.
You might find some useful hints perusing the assembly manuals and schematics, even as it applies to grounding and such. Unfortunately, it won't be a direct comparison, as I use single supply and output capacitor, but I think it still might help.
Here are the links:
Update My Dynaco
Akitika GT-101
HI GUYS,
DJOFFE, I have tried your modified circuit but it did not help..There is still noise/Hum.
The noise/Hum is very Louder when the Input is open i.e when disconnected from computer and still has slight noise when attached to the computer.
But when I attached the Ground line with House Earth Line then the noise is almost vanished, as if it were connected to COMP output...
I have even tried different LM3875 and other Transformer but the situation is the same.
I think the ground line is the culprit.
Please verify my PSU PSB if anything wrong and please suggest my next steps...
Paku
DJOFFE, I have tried your modified circuit but it did not help..There is still noise/Hum.
The noise/Hum is very Louder when the Input is open i.e when disconnected from computer and still has slight noise when attached to the computer.
But when I attached the Ground line with House Earth Line then the noise is almost vanished, as if it were connected to COMP output...
I have even tried different LM3875 and other Transformer but the situation is the same.
I think the ground line is the culprit.
Please verify my PSU PSB if anything wrong and please suggest my next steps...
Paku
Paku,
If you've implemented the stability components, then we can probably assume that stability issues aren't causing your problem.
The house ground is a good clue, I think, but I'm not sure yet what it tells us.
I'll think about it some, and see if something comes to mind, even if it is just more questions.
Dan
www.updatemydynaco.com
If you've implemented the stability components, then we can probably assume that stability issues aren't causing your problem.
The house ground is a good clue, I think, but I'm not sure yet what it tells us.
I'll think about it some, and see if something comes to mind, even if it is just more questions.
Dan
www.updatemydynaco.com
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