Hi, you all know that kind of background buzz that is present on almost all amps. The low level noice that you can hear if you put your ear to the tweeter, not a ground humm but a buzz like a static sound.
You know what I mean?
I recently put a gainclone with LM3875 to a friend and I get this sound but at a higher level and I would like to know where to look for the solution to the problem.
It is configured as dual mono to the socket and the grounding is as follows:
for each channel there is a signal starground on the groundlug of the RCA-input and a power starground right between the 1500uF capacitors. These are connected with a thin wire (0,4mm). The speakerreturn is connected to the power-star.
The two powerstars are then connected to eachother with a solid wire and fron the center of that is the safetyearth connected.
You know what I mean?
I recently put a gainclone with LM3875 to a friend and I get this sound but at a higher level and I would like to know where to look for the solution to the problem.
It is configured as dual mono to the socket and the grounding is as follows:
for each channel there is a signal starground on the groundlug of the RCA-input and a power starground right between the 1500uF capacitors. These are connected with a thin wire (0,4mm). The speakerreturn is connected to the power-star.
The two powerstars are then connected to eachother with a solid wire and fron the center of that is the safetyearth connected.
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Hi,
I used to have the same problem, but this Forum taught me how to do it properly.
I have just built up 4 monoblocks (two completely different amplifier types) and all of them are completely hum and buzz and noise free.
There is no need to tolerate any buzz from normal sensitivity speakers (mine are 89db/2.83V).
Read some of my grounding posts for extensive advice.
I used to have the same problem, but this Forum taught me how to do it properly.
I have just built up 4 monoblocks (two completely different amplifier types) and all of them are completely hum and buzz and noise free.
There is no need to tolerate any buzz from normal sensitivity speakers (mine are 89db/2.83V).
Read some of my grounding posts for extensive advice.
Ah, so it is the grounding then. I accually thought it was something else since it was more a buzz than a hum. But I'll split the connection chassiground-powerground inte two wires, one for each channel and then lift the signalground with a resistor and see what happens.
Btw, your posts are really informative, you just have to know what to search for
Btw, your posts are really informative, you just have to know what to search for
Hi,
Does the buzz appear when the source of gainclone is shorted, i.e. the input of gainclone is connected together?
If there is then buzzin sound the grounding would effect there, but if there is no buzz in output the noisefloor of source is making the buzz.
If the gainclone itself causes the problem then it might be the chassisground connection to chipground.
Does the buzz appear when the source of gainclone is shorted, i.e. the input of gainclone is connected together?
If there is then buzzin sound the grounding would effect there, but if there is no buzz in output the noisefloor of source is making the buzz.
If the gainclone itself causes the problem then it might be the chassisground connection to chipground.
Hi Fallow, there is no noice at all when I short the input to ground.
(I just put a solid copperwire between the input and signalground)
I have used two sources as of today. A laptop and a portable CD since I don't have a pre-amp ready yet.
Edit:
Theres a buzz on my laptop, stationary computer and portable CD. On my MP3-player there is no buzz.
So I guess that the grounding should be correct then, however, can I get rid of the noice in another way then?
Edit2:
I went through my attic and connected the optical output on my stationary computer to a externad D/A-converter and the noice was back.
(I just put a solid copperwire between the input and signalground)
I have used two sources as of today. A laptop and a portable CD since I don't have a pre-amp ready yet.
Edit:
Theres a buzz on my laptop, stationary computer and portable CD. On my MP3-player there is no buzz.
So I guess that the grounding should be correct then, however, can I get rid of the noice in another way then?
Edit2:
I went through my attic and connected the optical output on my stationary computer to a externad D/A-converter and the noice was back.
Sounds like you need a better sound card in the computers.kmj said:
When the portable CD is battery powered, does the buzz disappear?
If all your mains powered sources are correctly grounded and the power amp is incorrectly grounded, there should be no hum.
However, if one source and the power amp are incorrectly grounded, then you can get a ground loop which will hum.
Attaching only one incorrectly grounded source to a correctly grounded power amp should have no hum.
The result is that a correctly grounded amp can hide upto one incorrectly grounded source.
No, I only use batteries.
I connected the poweramp to a grounded socket in the kitchen and connected the portable cd and the hum was there. I tried the simple thing to turn the powerplug and still there was buzz.
I tried to add a 10ohm resistor between the singal and powerground, it increased the noicelevel so I removed it again.
I fiddled with some of the internal wiring and nothing happend.
I went back to the livingroom and connected the portable and the noice was lower and acceptable, I guess. Audiable at 1m in an otherwise quiet room.
I connected the computers again and the louder noice was back.
So I guess it's a matter of source whick is bad since a computer is my friends primary use.
Hi,
Try to connect signal ground and mains ground with resistor and capasitor parallel, this should be better than single resistor.
Or try to put thinner or longer wire(to offer weaker path from power ground to signal ground) connecting between signal ground and power ground, because there should not be any current flowing from power ground to signal ground.
Have you tried to put 220nF capasitors parallel of the 1500uF capacitors? Or maybe move the starground connection away from capacitors, because those big caps tend to produxe noise when those are used. (Just some ideas which might work, dunno)
I'm fighting with same problem with my own preamp, there is buzzing sound at the vlme controller of my source, when I connect my gainclone to commercial source, i.e. The EMU 0404 or CD-player, the buzzing sound dissappears or it is significantly lowered. There is one trick which might help to lower the buzzing noise when the machine is on, but nothing going in (this trick does not help on silent part's of the music). You can put a resistor division to input of your amplifier, this lower's the volume, but at the same time it lowers the noisefloor, when the noise of resistor's is not greater than the noisefloor.
then back to the original problem:
Do you have a way to measure the output inpedance of your source and input impedance of your gainclone, then put similar load to your source and measure it's noisefloor.
And check the impedance matching of your source and gainclone,
this might also be the problem for generating the high frequency noise to your system.
Good luck of hunting the source of noise.
Try to connect signal ground and mains ground with resistor and capasitor parallel, this should be better than single resistor.
Or try to put thinner or longer wire(to offer weaker path from power ground to signal ground) connecting between signal ground and power ground, because there should not be any current flowing from power ground to signal ground.
Have you tried to put 220nF capasitors parallel of the 1500uF capacitors? Or maybe move the starground connection away from capacitors, because those big caps tend to produxe noise when those are used. (Just some ideas which might work, dunno)
I'm fighting with same problem with my own preamp, there is buzzing sound at the vlme controller of my source, when I connect my gainclone to commercial source, i.e. The EMU 0404 or CD-player, the buzzing sound dissappears or it is significantly lowered. There is one trick which might help to lower the buzzing noise when the machine is on, but nothing going in (this trick does not help on silent part's of the music). You can put a resistor division to input of your amplifier, this lower's the volume, but at the same time it lowers the noisefloor, when the noise of resistor's is not greater than the noisefloor.
then back to the original problem:
Do you have a way to measure the output inpedance of your source and input impedance of your gainclone, then put similar load to your source and measure it's noisefloor.
And check the impedance matching of your source and gainclone,
this might also be the problem for generating the high frequency noise to your system.
Good luck of hunting the source of noise.
yet another consideration...
on one channel for trial, put 2 bigger caps, say >= 4700 . then use 2 x 100uf instead of the 1500uf... in some of my own experiments, notice use of bigger, > 470, near chip amp can be touchy and sensitive to grounding issues(not always). it would seem the all or significant power supply filtering near the chip amp can be problematic but i haven't confirmed across all builds to make that an absolute. i had one board layout that was lucky and immune to ground noise pickup breaking that rule. i had caps located together in opposing layout (not having stripes same direction).
or if resources limited, borrow the other 2 1500's, put those 4 further away from chip and find some 33-100's to place on the rails closer to chip. should be a quick little experiment (curious myself if theory, errr, observation holds any water)
on one channel for trial, put 2 bigger caps, say >= 4700 . then use 2 x 100uf instead of the 1500uf... in some of my own experiments, notice use of bigger, > 470, near chip amp can be touchy and sensitive to grounding issues(not always). it would seem the all or significant power supply filtering near the chip amp can be problematic but i haven't confirmed across all builds to make that an absolute. i had one board layout that was lucky and immune to ground noise pickup breaking that rule. i had caps located together in opposing layout (not having stripes same direction).
or if resources limited, borrow the other 2 1500's, put those 4 further away from chip and find some 33-100's to place on the rails closer to chip. should be a quick little experiment (curious myself if theory, errr, observation holds any water)
oh yeah... along similar lines. what happens if only one input plugged in? I'd had buzzes where dead silent with nothing plugged in. hook up, buzz. remove on jack, buzz subsides. once used hack ignorantly placing link between 2 grounds of rcas directly, uh, creating a loop, and squashed it. but don't like that as not right.
Hi Mike,
I would make two changes to your layout.
1. The on board decoupling (often used in discrete) taken straight to main system ground.
2. The reference to chassis removed from the input ground.
To clarify the need for safety, I would add a note about wiring in a safety ground directly to and permanantly attached to the chassis. This removes any ambiguity the builder may have about the safety ground location. Then a note on the various ways to interconnect the safety ground to the main system ground using the optional components to form a disconnecting network.
I would make two changes to your layout.
1. The on board decoupling (often used in discrete) taken straight to main system ground.
2. The reference to chassis removed from the input ground.
To clarify the need for safety, I would add a note about wiring in a safety ground directly to and permanantly attached to the chassis. This removes any ambiguity the builder may have about the safety ground location. Then a note on the various ways to interconnect the safety ground to the main system ground using the optional components to form a disconnecting network.
AndrewT said:
Hi Andrew,
First one note: the input jacks need to be next to each other. In this case drill two more holes 3/4" to 1" apart in the wood and run the ground wire as shown; using twisted pair wiring back to the amp circuits and single lo-Z back to the central ground.
2.) The input grounds need to be implemented as shown. There is a good reason for this but, until it's been tried, common knowledge has most designs (that I see published) doing it differently and the proof is in the manual simulation.
1.) The board decoupling caps are still part of the power supply filter loop and should be returned back to the filter caps. I actually haven't used/needed these but most applications guides call for them. If there is a chassis, then connect them to the chassis and use that as a low-z return (prefered).
My thought here is that there is no chassis ground; most of the chip amps I've seen here appear to use wood or have most of the circuitry floating (wood chassis' seem to be popular).
The circuit ground to the chassis (if there is one) should be connected wherever the two power supply grounds (because of the two transformers and filter pairs) come together, which is, as I noted, as close to the tranformers as possible. By this I intend that the center ground from the secondaries be as short as possible. (I have experimented with this approach extensively)
As for the safety ground (if there is a chassis) it should connect directly to the chassis where it enters. With no chassis, take it directly to the central ground (I've tried this and unless there is a short there is no noise circulating through any of the functional loops (it's quiet).
Thanks for your comments, but experimenting with the layout as shown is what my intention is. There's a noise voltage being developed in the grounds, this approach controls this.
Regards, Mike.
AndrewT said:
Hi again Andrew,
I just realized I mis-read the above to think you were refering to the decoupling caps at the output stage, not that you were making reference to any decoupling located on the drive board. Sorry bout that. I agree, actually either the main ground or filter grounds will work on drive circuit bypassing. Most of what's being returned through that path is pretty weak.
I should probably slow down when I read, but then the speed reading course I took would be a waste on money; although, it gets me into more trouble than it was worth...
The input grounding is correct from my experience.
Regards, Mike.
Hi Mike,
bypassing is a different issue again.
By bypassing I mean the tiny fast caps used to attenuate voltage glitches due to current changes in high current devices.
These bypass caps should be inserted into the circuit to bypass the current spike back into the device and do not need to be returned to the ground.
bypassing is a different issue again.
By bypassing I mean the tiny fast caps used to attenuate voltage glitches due to current changes in high current devices.
These bypass caps should be inserted into the circuit to bypass the current spike back into the device and do not need to be returned to the ground.
Hi,
Do you have a Central Ground?
How many capacitance you have on the filters? For Chip-Amps, you like to use 10.000uf PER VOLTAGE LINE!!! If you use 1000uf, 2200uf, 3300uf, 470uf, you will have HMMMMM and BUZZZZZZZZZ
Can you put your POWER SUPPLY on a PCB? This is very dangerus use a Power Supply, how you are using in this moment.
Do you have coupling on the input? You REALY NEED a high pass filter on inputs. You can test, a Non-Inverted operation and using 2.2uf and 100k resistor. To make a high-pass.
Can you post in here your schematic.
Best Regards.
Do you have a Central Ground?
How many capacitance you have on the filters? For Chip-Amps, you like to use 10.000uf PER VOLTAGE LINE!!! If you use 1000uf, 2200uf, 3300uf, 470uf, you will have HMMMMM and BUZZZZZZZZZ
Can you put your POWER SUPPLY on a PCB? This is very dangerus use a Power Supply, how you are using in this moment.
Do you have coupling on the input? You REALY NEED a high pass filter on inputs. You can test, a Non-Inverted operation and using 2.2uf and 100k resistor. To make a high-pass.
Can you post in here your schematic.
Best Regards.
Hi MOD!
I currently have the supplied caps from Peter Daniels KITs (1500uF, 50V) so 3000uF per channel.
No PCB, it might be more dangerous this way but he whos going to use it will never even open it.
I don't have a filter on the input but I could add one on the Pre-amp if it is needed. The pre is the Freebird designed by Russ White here at the forum.
The shematic is the one used in the chipamp.com LM3875-manual and the groundingschematis is the same as MikeF used here
I currently have the supplied caps from Peter Daniels KITs (1500uF, 50V) so 3000uF per channel.
No PCB, it might be more dangerous this way but he whos going to use it will never even open it.
I don't have a filter on the input but I could add one on the Pre-amp if it is needed. The pre is the Freebird designed by Russ White here at the forum.
The shematic is the one used in the chipamp.com LM3875-manual and the groundingschematis is the same as MikeF used here
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