Andrew, it would seem the input caps "leak" and my thought was to isolate them from the ground by moving them away. Maybe I am going in the wrong direction here? Are you saying that I need to run the ground closer to the cap. Right now the wire runs are a fair distance away, would you suggest maybe even having the insulated ground connection contact the body of the cap? Thanks
I did some quick tests after work today with pgnd disconnected. I ran the grounds along the caps (taped to them) but had no change. I then split the wires around the cap so the signal ground was not close to the cap, again no change. I am not sure if the k71s have anything to do with the hum. What does the fact that there is no hum with inputs shorted and potentiometer all the way down tell me?
Will,
When you say no hum with the inputs shorted, are you shorting them at the input to the board or at the RCA? If you short them at the board and there is no hum, then I think it means that the noise of the hum is coming in between the RCAs and the board. That would seem to support the short run theory or some other antenna issue.
I have measured the voltage across the speaker outputs with the input shorted at the board and a couple of K71s on longish leads to fastons and measured less than 0.5 mV AC at the output. The actual readings are a flickering 0.1 mV, but the DVOM isn't that accurate that low. That combination also has no hum.
I'm starting to wonder if you have a individual K71 that is in some way contributing to this problem. I bought an 8 pack of K71s, so I have a couple of spare. I couldn't do it right away, but I would be Happy to lend you a pair if you find the source of the problem is the K71s. You might try any other pair of caps that are around 1 uF, just to see if it is K71 related.
Jac
When you say no hum with the inputs shorted, are you shorting them at the input to the board or at the RCA? If you short them at the board and there is no hum, then I think it means that the noise of the hum is coming in between the RCAs and the board. That would seem to support the short run theory or some other antenna issue.
I have measured the voltage across the speaker outputs with the input shorted at the board and a couple of K71s on longish leads to fastons and measured less than 0.5 mV AC at the output. The actual readings are a flickering 0.1 mV, but the DVOM isn't that accurate that low. That combination also has no hum.
I'm starting to wonder if you have a individual K71 that is in some way contributing to this problem. I bought an 8 pack of K71s, so I have a couple of spare. I couldn't do it right away, but I would be Happy to lend you a pair if you find the source of the problem is the K71s. You might try any other pair of caps that are around 1 uF, just to see if it is K71 related.
Jac
cell phone noise?
One question for all of you. I find that my cell phone will make my FE crackle a bit if the FE isn't playing, just on stand-by, and the cell is within about 3 meters of the FE. It could be crackling a bit when playing, but I can't tell. It strikes me as strange since my other electronics seem immune, but then I don't have a very shielded build.
Does anyone else see this noise?
Jac
One question for all of you. I find that my cell phone will make my FE crackle a bit if the FE isn't playing, just on stand-by, and the cell is within about 3 meters of the FE. It could be crackling a bit when playing, but I can't tell. It strikes me as strange since my other electronics seem immune, but then I don't have a very shielded build.
Does anyone else see this noise?
Jac
Jac, I do have a spare set of k71s but thank you for the offer. I have thought about trying different caps for comparison but now it seems that they would be more for troubleshooting. The inputs are shorted at the rcas. It would be nice to be able to narrow down where in the amp I should look, but it could be anywhere. The thing about it is both channels hum so I am hoping the same issue is causing this on each side.
With my 'on the bench' build sure it picks up noise from cell phone.
The problem is in cabling.
Boards (according KSTR's measurements on beta boards) have a fair performance regarding EMI pickup.
My brother's build in metallic case have no pickup problems even if you put the mobile on the chassis.
Will, if you have a pair of RCA sockets please make two 'flying' leads (RCA on one side and molex on the other) and move them arount the chassis (branched, of course...
)You should be able to find what position irradiate.
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If shorted inputs equals no hum at all, then the hum is probably not generated by the amplifier. You most likely have a ground loop somewhere. The orientation of the hot or ground leads to the the input caps or the PCB or each other has nothing to do with it. Connect some other source to the amp to see if the hum goes away. What about taking the pot out of the circuit? Have you tried a different mains circuit? Is all equipment on the same mains outlet? Can you try a cheater plug for testing purposes only? (Do not permanently operate that way.) Have you tried different IC's? Does your previous power amp hum when connected the same way?
This amp, without a metal enclosure, will make ugly noises from mobile devices used nearby. Fully enclosed, no noise. Do you have the cover on the enclosure?
Peace,
Tom E
This amp, without a metal enclosure, will make ugly noises from mobile devices used nearby. Fully enclosed, no noise. Do you have the cover on the enclosure?
Peace,
Tom E
~0.5mVac on the out is a lot of hum.
I expect even a stereo amplifier to have <0.3mVac for "normal" speakers and usually get ~0.1mVac.
In a monoblock there is NO reason to accept even 0.1mVac of hum on the output, I aim for a 0.0mVac reading on every monoblock with a shorted input cable 1m long. That should be an indication of Hum + Noise <0.05mVac as best as a low quality hand held DMM can manage.
Unfortunately my Bench rms reading DMM, switches to show 0.00mVac as soon as the visible reading indicates <100.00mVac
My mobile phone even lying beside, or on top of, my stereo does not cause any audible noises when transmitting to the nearest cell aerial.
RF attenuation at the input of every bit of kit is in my view mandatory.
Tom, I do have everything connected to one circuit. The ground is functional on this circuit. I have used the exact same setup with my integrated with no problems. It is an audiosector LM4780 dual mono build, nearly identical layout inside the enclosure. The audiosector boards do have a connection to ground in the enclosure.
I did use a strip with no ground pin while testing the FE in the shop and if I remember had no hum. Let me verify that.
...With the cheater in place and pgnd disconnected there is still hum.
How exactly does pgnd work? does it capture/redirect the signal at a certain frequency? What would I be gaining by not having it connected, less potential crosstalk between channels?
I did use a strip with no ground pin while testing the FE in the shop and if I remember had no hum. Let me verify that.
...With the cheater in place and pgnd disconnected there is still hum.
How exactly does pgnd work? does it capture/redirect the signal at a certain frequency? What would I be gaining by not having it connected, less potential crosstalk between channels?
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I have been doing a little reading this morning and may have answered my own question. good and bad, I may have been chasing my tail. Anyway I have a question for the builders.
It seems many of you are using a computer as a source, and a DAC and then maybe a pre.
In your hum free setups without a connection to pgnd are you using a component ahead of the FE that is conected to safety earth?
Are any of you using a source component that is double insulated or not connected to safety earth with no other connections to earth in the path? essentially a system with no connection to earth anywhere other than the safety earth from chassis to earth.
Thanks all....
It seems many of you are using a computer as a source, and a DAC and then maybe a pre.
In your hum free setups without a connection to pgnd are you using a component ahead of the FE that is conected to safety earth?
Are any of you using a source component that is double insulated or not connected to safety earth with no other connections to earth in the path? essentially a system with no connection to earth anywhere other than the safety earth from chassis to earth.
Thanks all....
I've been waiting for you to solve all the problems, but I'll jump in again. The only RC version configuration I have that is totally hum free is Computer to Mini2496 DAC to MyRef to speakers. I have tried three pres and two other DACs. They all produce a hum that makes the system unusable. Actually one other setup is hum free and that is a simple battery powered Walkman straight to the FEs. My beta build FEs work with anything.
I tried just about every ground configuration imaginable with no success. I even rewired a DAC to double insulated as well as attempting to use just a bare pot. As I posted earlier, I stopped trying and decided to wait till the final FE version is built, as I suspect either a non-performing part or a soldering/heat related error I might have made.
I have been purposely lagging behind in my build hoping to get some reports on this from the new FFE builders. Meantime, I've been enjoying what I would call perfect operation and top shelf sound with the configuration that has no hum or any other distortion I can detect.
It's interesting that only you and I have reported the hum - which leads me to think it's not a problem produced by a design element. I'll stop waiting and start my final build around mid-week.
The only RC version configuration I have that is totally hum free is Computer to Mini2496 DAC to MyRef to speakers. I have tried three pres and two other DACs. They all produce a hum that makes the system unusable. Actually one other setup is hum free and that is a simple battery powered Walkman straight to the FEs. My beta build FEs work with anything.I tried just about every ground configuration imaginable with no success. I even rewired a DAC to double insulated as well as attempting to use just a bare pot. As I posted earlier, I stopped trying and decided to wait till the final FE version is built, as I suspect either a non-performing part or a soldering/heat related error I might have made.
I have been purposely lagging behind in my build hoping to get some reports on this from the new FFE builders. Meantime, I've been enjoying what I would call perfect operation and top shelf sound with the configuration that has no hum or any other distortion I can detect.
It's interesting that only you and I have reported the hum - which leads me to think it's not a problem produced by a design element. I'll stop waiting and start my final build around mid-week.
In my system all elements have no safety earth connection.
The Sony SACD player has double insulation, the MINI2496 DAC has no safety earth connection, the Sony receiver has double insulation, the DCB1 has no safety earth connection.
Yes I did try that. I had a private dialog with Dario at the time and we tried all the possibilities.
No, not just DC. The setup I'm using now is AC-computer, AC-DAC, AC-FE amp. All are using the three prong plug with earth and chassis ground. This produces no hum as well as the DC Walkman.
The Carver, Dynaco and Sanyo preamps as well as the Weiliang DAC don't have earth ground. The JC-2 pre (no hum when used with the beta amps) does have earth ground.
It was extremely frustrating because any combination of the above is clean on my beta builds.
No, not just DC. The setup I'm using now is AC-computer, AC-DAC, AC-FE amp. All are using the three prong plug with earth and chassis ground. This produces no hum as well as the DC Walkman.
The Carver, Dynaco and Sanyo preamps as well as the Weiliang DAC don't have earth ground. The JC-2 pre (no hum when used with the beta amps) does have earth ground.
It was extremely frustrating because any combination of the above is clean on my beta builds.
It was true (no hum, with PGND connected to safety earth or not) for my 3 My_Ref C builds, FE beta boards, my first FE RC boards (green), my second FE RC boards (blue), one FE RC builder's boards (I've helped him to fix them), FE final boards.
I'm going to build another FE Final couple next week for a partecipant and I expect them to be hum free as well.
I can get hum regularly though... when molex don't give a nice contact, just a little position adjustment on the cable and hum disappear...
Jokes apart, I got hum only when I've had grounding problems or problems with connectors like with my first project, a Chipamp.com Gainclone.
One final essential note: every My_Ref I've ever built have hum with inputs disconnected, it's hum free only when inputs are connected to a pre and/or source.