Long shot and perhaps unrelated, but ensure those nuts on the FE boards are not touching the MOSFET heatsinks. You can also check if lifting the FE off the risers makes a difference or not. Currents in your AC ground flow there. Best kept out of the MOSFET sinks.Correct measuring spots made the difference....adjusted DC offset on the FE board, all good there. Thank you
Still have the tapping noise though....posted on SLB forums, still waiting for a response so I can fix it before I use this beautiful looking amp
perhaps you are hearing the broken engine of your neighbours air conditioner
edit: very nice build!
edit 2: Your PSU boards are unknown to me, but please verify whether you have resistance/NTC or a ground loop breaker between safety and audio gnd/PSU 0v.
regards,
Andy
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Thank you for the nice comments on the build everyone 
The FE board is indeed lifted off the riser with 3/8 vinyl spacers and no metal touches the heatsinks. There is ground loop breaker on the PS boards, but the chassis ground and power switch are the only things connecting both channels. I will check resistance between chassis ground and PS ground and see what that is. I figure maybe I should disconnect one transformer from the PS and the PS from the safety ground and maybe see if the problem is isolated to one channel or the other.
The FE board is indeed lifted off the riser with 3/8 vinyl spacers and no metal touches the heatsinks. There is ground loop breaker on the PS boards, but the chassis ground and power switch are the only things connecting both channels. I will check resistance between chassis ground and PS ground and see what that is. I figure maybe I should disconnect one transformer from the PS and the PS from the safety ground and maybe see if the problem is isolated to one channel or the other.
Hi Soundwavesteve,
I am trying to troublshoot your circuit with the "tapping" noise to see if it is related to the SLB PSU. You say that the tapping is 200Hz and how do you know it is 200Hz? 200Hz is a buzz or hum sound and I would not call "tapping" as I associate tapping with a sound I can hear distinctly sort of sub 10Hz and impulse like in nature. Please measure the AC volts after the SLB and before the amp. It should be under well under 100mV if the SLB is set up correctly. As the LED is meant to show power present in the capacitors (10k series resistor), the only way it doesn't light up is that you have it installed backwards. That should not cause the noise though. If you have an O-scope, please look at the power coming from SLB and signal from amp outputs.
One more thing, are your trafo mounting bolts touching the chasssis front panel at all? If it is, you may have a shorted-turn on the trafo and the noise might be caused by the PSU gettting an unsteady power from the intermittent shorting and recharging cycle of the trafo/PSU combo.
I am trying to troublshoot your circuit with the "tapping" noise to see if it is related to the SLB PSU. You say that the tapping is 200Hz and how do you know it is 200Hz? 200Hz is a buzz or hum sound and I would not call "tapping" as I associate tapping with a sound I can hear distinctly sort of sub 10Hz and impulse like in nature. Please measure the AC volts after the SLB and before the amp. It should be under well under 100mV if the SLB is set up correctly. As the LED is meant to show power present in the capacitors (10k series resistor), the only way it doesn't light up is that you have it installed backwards. That should not cause the noise though. If you have an O-scope, please look at the power coming from SLB and signal from amp outputs.
One more thing, are your trafo mounting bolts touching the chasssis front panel at all? If it is, you may have a shorted-turn on the trafo and the noise might be caused by the PSU gettting an unsteady power from the intermittent shorting and recharging cycle of the trafo/PSU combo.
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aye thx I read that wrongly as Hz too. In that video is an example for "motorboating":
Motorboating
Motorboating
Chede is correct...it is an actual tapping sound with countable beats/taps. I will take a video tonight/tomorrow when time allows. Should I post the video here or on the SLB forum? I do not have an oscilloscope, so I will be taking forum suggestions and trying things. First thing though I think I will probably be taking apart the amp and pulling the boards out to visually inspect the LEDs over the holidays. I do think they are probably backwards too, but I can't imagine how I did that...all four?? We'll find out! ;-P
Hi all,
The pre-amp is playing fine. Only issue, one step turn on the attenuator it is playing at quite high volume. What could be the reason?
I need a bit more resolution on the pot... any possibility?
Spec gain is high on the BA-3. could you provide a bit more info on downstream equipment? Such as poweramp and speakers.
More resolution is a possibility. But the way to best sound is ensuring proper gain structure (quote Mighty), iow that at max volume on the pot, you have you max happy-for-you volume level. You can adjust gain on the BA-3 FE. Some say not without loss og sound quality. Others (Mighty) say reducing value of R-13 has little to no consequence, other than reducing gain.
I think adjusting values of R10-11 can provide the same effect, but R13 is the easiest route.
Provide info on poweramp gain and speaker sensitivity, and ppl will be able to suggest alternative R13 values for you. With 220R you will reduce gain by approx 1/3rd.
Edit: please confirm value of R13 in your circuit.
Regards,
Andy
I posted a video of the tapping noise on the SLB forum here: https://www.diyaudio.com/community/...x-class-a-power-supply-gb.336479/post-6887645
XRK feels the pulsing noise is coming from the input stage on this BA3 build, you can read more about it if you follow the link in post 1132. When I first turned the amp on, I measured 2+v of bias across R10 and/or R11 (I don't remember which), I had to adjust P1 and/or P2 to bring it back down to 1v. Could that have done any damage to either the Mosfets or the Jfets? It still plays sound without distortion, just has this tapping/pulsing noise with it. Right now it's adjusted for no DC before the output cap and no DC at speaker out, so the noise must be AC.
Since I built parts of this amp 8-12 months ago, I do not remember if I zeroed out P1 and P2 before I installed them. I do remember setting P3 to it's midway point.
Can I set a multimeter to AC and test something somewhere to narrow down the source of the noise?
Since I built parts of this amp 8-12 months ago, I do not remember if I zeroed out P1 and P2 before I installed them. I do remember setting P3 to it's midway point.
Can I set a multimeter to AC and test something somewhere to narrow down the source of the noise?
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DMM to AC at the rails of your PSU. First pos to gnd, the. Neg to gnd. If the value pulsates, problem is in PSU or before it. If not, somewhere after the rails.
If you have a scope, that too can go to the rails. Maybe take some care, heard it can be dangerous. But I am a gremlin, so I connect first and learn after
The initial test for AC was unsuccessful. I hooked up my DMM using the fused 10A input to the V+ on the FE board and to chassis ground. Upon turn on I got static through the speaker and something in the amp started to smoke. For a second or two I was registering 100+ mA on the meter when I turned it off. Unhooking the DMM and turning the amp back on, no smoke and the tapping noise was still there. Did not see where the smoke initially came from. I'm assuming I hooked up the DMM wrong and put some kind of additional load on the amp or gave the V+ a direct path to ground. I should probably read the manual on how to test amperage using the DMM
you attended current measurement***, where you needed to do voltage measurement
if you don't know how and you are not sure how to arrange measurement - just ask
it is not shame not-knowing, shame is not asking and - if you ask - not thinking about replies yo got
**practically - DMM is short circuit between two probes;
example:
if you don't know how and you are not sure how to arrange measurement - just ask
it is not shame not-knowing, shame is not asking and - if you ask - not thinking about replies yo got
**practically - DMM is short circuit between two probes;
example:
- you do not try to measure resistance of your AC wall socket
- you do not try to measure current capability of your AC wall socket
- you can measure AC voltage of your AC wall socket
The initial test for AC was unsuccessful. I hooked up my DMM using the fused 10A input to the V+ on the FE board and to chassis ground. Upon turn on I got static through the speaker and something in the amp started to smoke. For a second or two I was registering 100+ mA on the meter when I turned it off. Unhooking the DMM and turning the amp back on, no smoke and the tapping noise was still there. Did not see where the smoke initially came from. I'm assuming I hooked up the DMM wrong and put some kind of additional load on the amp or gave the V+ a direct path to ground. I should probably read the manual on how to test amperage using the DMM
When I said « DMM to AC at the rails of your PSU», that meant to measure AC voltage @ the rails. Not amperage. Could have been more precise. Sorry