Hi guys. I recently hand-routed the star-ground PCB and built my own LM3886-based PA100 (2 ICs in parallel) mono amps. Work great and sound nice!
Zero noise when used they're used as home home stereo setup. However , my ultimate goal is to use them as the basis for more elaborate car amplifier(s). I already have a prototype SMPS I tested them with. Obviously I am not new to circuit design in general.
Note: I have a 2-amp star grounded car stereo system which normally has ZERO noise. Also the PA100 amp I built has ZERO noise when used as in my home stereo.
Unfortunately, when tested in my car using the front RCA connections from my Alpine DSP, once again ground loop noise (the common "alternator whine") appeared again, as I expected.
Anybody used the chip amps for similiar purposes? Any solutions or practical ideas for eliminating the ground loops? Will I be required to use an op amp circuit on the RCA inputs?
I've tried the usual routes but no relief. I have limited audio amp design experience. Would really appreciate your help! Attached are photos of my hand designed PCB & hand built amp(s).
I would prefer to not have to reverse engineer an existing car amp to find a solution. I know someone on here has gone through the same pains-or has the amp design experience I could learn from...a forum search revealed no directly relevant answer.
Thanks! My schematic is attached (mostly Nat. Semi's example schematic) Please advise if you can!
Zero noise when used they're used as home home stereo setup. However , my ultimate goal is to use them as the basis for more elaborate car amplifier(s). I already have a prototype SMPS I tested them with. Obviously I am not new to circuit design in general.
Note: I have a 2-amp star grounded car stereo system which normally has ZERO noise. Also the PA100 amp I built has ZERO noise when used as in my home stereo.
Unfortunately, when tested in my car using the front RCA connections from my Alpine DSP, once again ground loop noise (the common "alternator whine") appeared again, as I expected.
Anybody used the chip amps for similiar purposes? Any solutions or practical ideas for eliminating the ground loops? Will I be required to use an op amp circuit on the RCA inputs?
I've tried the usual routes but no relief. I have limited audio amp design experience. Would really appreciate your help! Attached are photos of my hand designed PCB & hand built amp(s).
I would prefer to not have to reverse engineer an existing car amp to find a solution. I know someone on here has gone through the same pains-or has the amp design experience I could learn from...a forum search revealed no directly relevant answer.
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.
Thanks! My schematic is attached (mostly Nat. Semi's example schematic) Please advise if you can!
Yes, I realize I could use a transformer based isolator but we all know that's a "patch" and not a real solution. And besides affects frequency response (I've used them years ago and with mediocre audio quality).
The balanced input sounds more reasonable, though I would prefer to keep components out of the audio input "chain."
Hopefully some more ideas will pop up on here also...I'm going to check a few things in the car as well.
The balanced input sounds more reasonable, though I would prefer to keep components out of the audio input "chain."
Hopefully some more ideas will pop up on here also...I'm going to check a few things in the car as well.
Do you have a schematic of your SMPS?
I second the notion to isolate the SMPS and amp grounds.
Does your SMPS use feedback? (opto)isolated,or no? -even if not,it's an easy fix.
In the last amp SMPS I "reworked" for a different use,I Had to add a 1K resistor between the output ground(+/-35V),and the input(+12V) ground to eliminate any ground loop issues.
The feedback didn't seem to mind much at all,and still functions,after a minor adjustment (I replaced the feedback R with a pot,to vary the output voltage,it just needed a slight tweak to compensate for the extra 1Kohms.)
You might be able to get away with as little at 10-100ohms.
Make sure the RCA/interconnect cables are in good shape,and not routed near any power leads,etc.
Maybe also check the RCA outputs of your headunit.. I see alot of issues on here where they've 'opened up'..
Get a DMM/VOM,and set it to the lowest resistance scale,and put one probe on the outside (shield) of the RCA,and one on the case/Ground,there should be ~0-ohms (or very low). If not,you need to fix it/have it fixed.
I second the notion to isolate the SMPS and amp grounds.
Does your SMPS use feedback? (opto)isolated,or no? -even if not,it's an easy fix.
In the last amp SMPS I "reworked" for a different use,I Had to add a 1K resistor between the output ground(+/-35V),and the input(+12V) ground to eliminate any ground loop issues.
The feedback didn't seem to mind much at all,and still functions,after a minor adjustment (I replaced the feedback R with a pot,to vary the output voltage,it just needed a slight tweak to compensate for the extra 1Kohms.)
You might be able to get away with as little at 10-100ohms.
Make sure the RCA/interconnect cables are in good shape,and not routed near any power leads,etc.
Maybe also check the RCA outputs of your headunit.. I see alot of issues on here where they've 'opened up'..
Get a DMM/VOM,and set it to the lowest resistance scale,and put one probe on the outside (shield) of the RCA,and one on the case/Ground,there should be ~0-ohms (or very low). If not,you need to fix it/have it fixed.
If you mount the amp VERY near the head unit and ground both the amp and the head unit to the same point, the ground loop noise should be minimized.
There are good transformers but they're not cheap. Jensen transformers is supposed to have some of the best.
If you don't want additional components in the audio chain, floating the secondary is just about the only option left. It works. Just about every budget brand car audio amp on the market uses it. About the only time it doesn't work well is when you have multiple signal sources. For example, if you had a 4 channel amp powered by a single supply and 2 channels came directly from the head unit (from the sub out, for example) and the other 2 channels passed through an equalizer before being sent to the amplifier. The two different ground points for the head unit and the EQ would cause another ground loop.
There are good transformers but they're not cheap. Jensen transformers is supposed to have some of the best.
If you don't want additional components in the audio chain, floating the secondary is just about the only option left. It works. Just about every budget brand car audio amp on the market uses it. About the only time it doesn't work well is when you have multiple signal sources. For example, if you had a 4 channel amp powered by a single supply and 2 channels came directly from the head unit (from the sub out, for example) and the other 2 channels passed through an equalizer before being sent to the amplifier. The two different ground points for the head unit and the EQ would cause another ground loop.
Hi thanks Perry but my system is not as simple as the average consumer.
Mine goes: head unit -> fiber optic connection & control cable -> digital signal processor -> amplifier(s). There is not a continous analog path between the inputs/outputs to the amp. (It's all in the digital domain). All components are connected to a single junction block leading to the battery via correct copper cabling.
But of course all variables must be checked. The DSP's RCAs do have continuity to system ground.
But at any rate, those are helpful ideas about isolating the power supply's ground. I'll give that and DigitalJunkie's idea a try!
I had a feeling it might be related to that but never found good "do and don't do" info when building the SMPS.
Thanks for the replies I'll post the results A.S.A.P.!
SMPS: +/-35V, 300W (tested max.). My schematic:
Mine goes: head unit -> fiber optic connection & control cable -> digital signal processor -> amplifier(s). There is not a continous analog path between the inputs/outputs to the amp. (It's all in the digital domain). All components are connected to a single junction block leading to the battery via correct copper cabling.
But of course all variables must be checked. The DSP's RCAs do have continuity to system ground.
But at any rate, those are helpful ideas about isolating the power supply's ground. I'll give that and DigitalJunkie's idea a try!
I had a feeling it might be related to that but never found good "do and don't do" info when building the SMPS.
Thanks for the replies I'll post the results A.S.A.P.!
SMPS: +/-35V, 300W (tested max.). My schematic:
Hey guys here are the results!
I tried your first suggestion (before resorting to a balanced input circuit) and isolating the SMPS worked great!
Also I was able to reconnect my SMPS's ground output to the +12V ground using a 10 ohm resistor as you mentioned. No noise then either!
Against my better judgement I originally removed the optional input ground-to-output ground jumper on my PCB I made and had to separate them physically for testing..but not too bad.
It turned that my ground loop was being created while my Planet Audio amplifiers still had there RCA cables (coming from the signal processor) plugged in when I removed one pair for using as an audio source for my homemade PA100 (LM3886) chip amps.
Isolating the SMPS ground worked great!
Thanks so much guys for your practical ideas. The sound quality is excellent too, by the way.
My dream for some time has been to successfully build my own car amplifier as well as get the info organized for others to do the same.
Now it is possible and I haven't been this happy since the first time I took a girl's bra off!
I tried your first suggestion (before resorting to a balanced input circuit) and isolating the SMPS worked great!
Also I was able to reconnect my SMPS's ground output to the +12V ground using a 10 ohm resistor as you mentioned. No noise then either!
Against my better judgement I originally removed the optional input ground-to-output ground jumper on my PCB I made and had to separate them physically for testing..but not too bad.
It turned that my ground loop was being created while my Planet Audio amplifiers still had there RCA cables (coming from the signal processor) plugged in when I removed one pair for using as an audio source for my homemade PA100 (LM3886) chip amps.
Isolating the SMPS ground worked great!
Thanks so much guys for your practical ideas. The sound quality is excellent too, by the way.
My dream for some time has been to successfully build my own car amplifier as well as get the info organized for others to do the same.
Now it is possible and I haven't been this happy since the first time I took a girl's bra off!
Instead of a 10 ohm resistor, a better solution is a 10nF to 100nF capacitor (as done in most amplifiers) with an optional damper resistor in parallel (>100 ohms). The purpose of this capacitor in any SMPS is to AC-couple primary and secondary side grounds at RF to prevent common-mode electromagnetic interference due to transformer winding capacitances, but allowing they to float at lower audio frequencies thus breaking the ground loop.
You should also couple the heatsink of the SMPS to the 12V ground (to the same point where input EMI filter capacitors are grounded) with a 100nF capacitor. This will reduce EMI further. A parallel damper resistor may also be added. I don't recommend connecting the main amplifier heatsink to ground directly because this may lead to high currents flowing through unexpected paths...
Have fun
You should also couple the heatsink of the SMPS to the 12V ground (to the same point where input EMI filter capacitors are grounded) with a 100nF capacitor. This will reduce EMI further. A parallel damper resistor may also be added. I don't recommend connecting the main amplifier heatsink to ground directly because this may lead to high currents flowing through unexpected paths...
Have fun
Thanks! I will be adding those options to the SMPS circuit board when I redo the schematic and reduce the PCB size by about 1/2 (or smaller if possible).
My whole point in this is not only to build my own but also to document this properly (BOM, photos, etc.) since information regarding building your own SMPS is generally pretty poor.
My whole point in this is not only to build my own but also to document this properly (BOM, photos, etc.) since information regarding building your own SMPS is generally pretty poor.
Hi there. Yes, that was the case (remove RCA cables = no noise).
But the suggestions by the other two guys resolved it (isolating SMPS output ground or connecting SMPS ground plane to +12V ground with resistor).
So fortunately I have a solution and not only that but I'm more clear on the problem itself-and learned to not ignore my engineer's intuition when creating a design.
But the suggestions by the other two guys resolved it (isolating SMPS output ground or connecting SMPS ground plane to +12V ground with resistor).
So fortunately I have a solution and not only that but I'm more clear on the problem itself-and learned to not ignore my engineer's intuition when creating a design.
I have a lot of interest in this exact subject. I want to use six channels of LM3886 chips in a car amp. I figure i need 4-5amps of +/- 28v(at load) each according to the data sheet. 30 amps total. that seems like a lot for one supply? would it bet better to use 3 supplies? each supply powering a pair of 3886's?
I would love Eva's help with the supply!
I would love Eva's help with the supply!
Ground loop noise
Hi, I built a car amplifier with the LM3886 ics and got fantastic results infact it sounds better than when connected to the mains power supply. Here is what I did:
1) Used a pushpull converter with isolated secondaries which means the amplifier ground and the switching ground are not shared. An isolated topology is highly recommended.
2)I ran my converter at 300KHz which helped to keep the noise away from the audio band.
3)Used chokes for both rails on the output. This is highly recommended as otherwise you will be getting ultrasonic noise such as harmonics of the switching frequencies which you can't hear but waste amplifier power and also degrade signal quality in the audio band e.g. you will get the mushy sound.
3)I used unregulated outputs i.e. no control loop. This ensure excellent dynamic response due to the lack of the loop. The power is always there just like from a transformer used at home amplifiers. If you use a control loop then the power has to catch up to the audio signal, there is lag. Hence we'got thousands of books written on control loop and the associated phase problems.. This delay can cause distortion. If you must use regulated outputs then it better to use regulators (at the outputs of both rails) with an unregulated SMPS for best sound quality.
4) Depending on how close the power supply is to the audio section you might need ultrasonic filters at the inputs of audio circuits especially if you switching frequency is low enough to interfere.
Something which I never implemented but have thought of doing is having seperate chassises for the power supply and amplifier section or to implement faraday shields around some of the circuits.
The sound quality I got from the car amplifier can be compared to it being running from batteries absolutely crystal clear.
BTW the alternator whine which you are talking about will not be coming from the alternator as that would be chopped up and attenuated by the switching and inductance. That is likely to be noise from the switching circuitry itself as you won't have sufficient filtering. Chokes and high value electrolytics coupled with 100n ceramics are recommened. You need to have sufficient capacitance after the chokes as the chokes in combination with the capacitors act as low pass filters.
Hi guys. I recently hand-routed the star-ground PCB and built my own LM3886-based PA100 (2 ICs in parallel) mono amps. Work great and sound nice!
Zero noise when used they're used as home home stereo setup. However , my ultimate goal is to use them as the basis for more elaborate car amplifier(s). I already have a prototype SMPS I tested them with. Obviously I am not new to circuit design in general.
Note: I have a 2-amp star grounded car stereo system which normally has ZERO noise. Also the PA100 amp I built has ZERO noise when used as in my home stereo.
Unfortunately, when tested in my car using the front RCA connections from my Alpine DSP, once again ground loop noise (the common "alternator whine") appeared again, as I expected.
Anybody used the chip amps for similiar purposes? Any solutions or practical ideas for eliminating the ground loops? Will I be required to use an op amp circuit on the RCA inputs?
I've tried the usual routes but no relief. I have limited audio amp design experience. Would really appreciate your help! Attached are photos of my hand designed PCB & hand built amp(s).
I would prefer to not have to reverse engineer an existing car amp to find a solution. I know someone on here has gone through the same pains-or has the amp design experience I could learn from...a forum search revealed no directly relevant answer.
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.
Thanks! My schematic is attached (mostly Nat. Semi's example schematic) Please advise if you can!
Hi, I built a car amplifier with the LM3886 ics and got fantastic results infact it sounds better than when connected to the mains power supply. Here is what I did:
1) Used a pushpull converter with isolated secondaries which means the amplifier ground and the switching ground are not shared. An isolated topology is highly recommended.
2)I ran my converter at 300KHz which helped to keep the noise away from the audio band.
3)Used chokes for both rails on the output. This is highly recommended as otherwise you will be getting ultrasonic noise such as harmonics of the switching frequencies which you can't hear but waste amplifier power and also degrade signal quality in the audio band e.g. you will get the mushy sound.
3)I used unregulated outputs i.e. no control loop. This ensure excellent dynamic response due to the lack of the loop. The power is always there just like from a transformer used at home amplifiers. If you use a control loop then the power has to catch up to the audio signal, there is lag. Hence we'got thousands of books written on control loop and the associated phase problems.. This delay can cause distortion. If you must use regulated outputs then it better to use regulators (at the outputs of both rails) with an unregulated SMPS for best sound quality.
4) Depending on how close the power supply is to the audio section you might need ultrasonic filters at the inputs of audio circuits especially if you switching frequency is low enough to interfere.
Something which I never implemented but have thought of doing is having seperate chassises for the power supply and amplifier section or to implement faraday shields around some of the circuits.
The sound quality I got from the car amplifier can be compared to it being running from batteries absolutely crystal clear.
BTW the alternator whine which you are talking about will not be coming from the alternator as that would be chopped up and attenuated by the switching and inductance. That is likely to be noise from the switching circuitry itself as you won't have sufficient filtering. Chokes and high value electrolytics coupled with 100n ceramics are recommened. You need to have sufficient capacitance after the chokes as the chokes in combination with the capacitors act as low pass filters.
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Thanks for following up; good to hear that you had success!
Yes I was using unregulated supplies and additionally I had very little switching noise, although I recall that some was there.
If I attempt this again (I never got the ground loop issues resolved no matter what I tried) I would be taking a different approach for sure.
Regarding what you said, following the example of commercially produced car amplifiers, the output side of the switching supplies aren't isolated.
I believe that I did not design input stages as I should have to remove the "alternator whine" (ground loop noise) as other amps to.
I had gotten my hands on some JBL and Alpine car amp schematics and I looked at what they did. As I recall there may have been noise removal stages in the amps (don't have the schematics here to check right now).
The next time around, I would be spending less time on my SMPS as I've found some available on eBay and could use 2 for the required supply. All I would need then is LM3886 modules and then deal with the noise issues rather than have to chase problems with everything if they are homemade.
So, almost all the parts are all available off-the-shelf to build my own car amp if I try again, which is great. I spent too much money & time on DIY parts & etc.
Also I made my LM3886 boards too small and it was hard to change part values and/or modify them to deal with the noise. Lesson learned!
Yes I was using unregulated supplies and additionally I had very little switching noise, although I recall that some was there.
If I attempt this again (I never got the ground loop issues resolved no matter what I tried) I would be taking a different approach for sure.
Regarding what you said, following the example of commercially produced car amplifiers, the output side of the switching supplies aren't isolated.
I believe that I did not design input stages as I should have to remove the "alternator whine" (ground loop noise) as other amps to.
I had gotten my hands on some JBL and Alpine car amp schematics and I looked at what they did. As I recall there may have been noise removal stages in the amps (don't have the schematics here to check right now).
The next time around, I would be spending less time on my SMPS as I've found some available on eBay and could use 2 for the required supply. All I would need then is LM3886 modules and then deal with the noise issues rather than have to chase problems with everything if they are homemade.
So, almost all the parts are all available off-the-shelf to build my own car amp if I try again, which is great. I spent too much money & time on DIY parts & etc.
Also I made my LM3886 boards too small and it was hard to change part values and/or modify them to deal with the noise. Lesson learned!
You wouldn't need any kind of filtering to stop noise from the alternator etc. as any noise would get chopped up by the switching and the final noise on the outputs will be the switching frequency noise and its harmonics. The only way to effectively deal with this is with chokes before the output capacitors on both rails. You need to measure the output noise with an oscilloscope a multimeter would be too slow and would not pick it up unless it is a very high end one. You need to get the noise coming out of the outputs to a very low level just a few tens of millivolts. The LM3886 has poor power supply rejection ratio at high frequencies especially on the negative rail. Any noise getting in from the power supply will be amplified by the gain of your amplifier.
You can limit the frequency response of your amplifier circuit so it is well below the switching frequency. You need to add a 50p capacitor in parallel with the feedback resistor. This will limit the frequency response to around 100KHz @-3db. BTW you will find most car amplifiers are using an unregulated isolated topology. They also have steep ultrasonic filters at the inputs. If you look at the LM833N datasheet you will see an ultrasonic filter circuit there. However it is better you deal with the source of the noise than try to fix the problems which it causes i.e. sort the power supply out. I used no filters except the 50pf capacitors.
Which switch topology are u using? Which core? How many turns? Whats the output capacitance?
The ground loop noise is not related to the power supply. It's in the audio path and I didn't remove it on the input side as I should have originally.
I installed car audio equipment before I got out of college and had to deal with this many times, win or lose.
I'll revisit this project probably some day with off-the-shelf parts and better filtering on the input side. I disassembled the old amplifier and sold the parts because I knew I could rebuild it faster, cheaper, and better next time but mostly wanted to do so another way next time to resolve this.
Thanks.
I installed car audio equipment before I got out of college and had to deal with this many times, win or lose.
I'll revisit this project probably some day with off-the-shelf parts and better filtering on the input side. I disassembled the old amplifier and sold the parts because I knew I could rebuild it faster, cheaper, and better next time but mostly wanted to do so another way next time to resolve this.
Thanks.
You need to try to implement the star grounding technique in a more abstract way as obviously you can not modify the circuitry inside the head unit. The grounds from all equipment including your amp should return to a common point. Breaking the shielding on one end of the RCA cables might also help.
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