I have my newly completed BA-3 playing sound, but I am getting a tapping noise on the outputs, both channels, not volume dependent. Sound will cover the tapping noise.
Tapping noise is not related to AC Hz or a multiple of it....its about 200 beats per minute. Tapping noise is present whether there is a preamp connected or not.
My BA-3 is dual mono, one plug. I am using matched transistors from the DIYA Store. Power supplies are dual XRK SLBs running at 32volts. (Actually 34.5v because the Antek transformers under load are not sagging as much as expected). Everything is separate once power leaves the power switch, though all Neutrals are tied together, and of course there is chassis/earth ground. Speaker ground goes to power supply ground.
There is no measurable DC on the outputs, the tapping noise was present both before and after I biased the amp and did not change in level. I do have a cheap LED 120v-12v driver for the power switch light that is wired to incoming AC - I have not tried disconnecting it yet.
Maybe an odd behavior I noticed when biasing the amp was no DC offset was ever observed from the BA-3 voltage driver board.
Suggestions/thoughts/troubleshooting steps?
Tapping noise is not related to AC Hz or a multiple of it....its about 200 beats per minute. Tapping noise is present whether there is a preamp connected or not.
My BA-3 is dual mono, one plug. I am using matched transistors from the DIYA Store. Power supplies are dual XRK SLBs running at 32volts. (Actually 34.5v because the Antek transformers under load are not sagging as much as expected). Everything is separate once power leaves the power switch, though all Neutrals are tied together, and of course there is chassis/earth ground. Speaker ground goes to power supply ground.
There is no measurable DC on the outputs, the tapping noise was present both before and after I biased the amp and did not change in level. I do have a cheap LED 120v-12v driver for the power switch light that is wired to incoming AC - I have not tried disconnecting it yet.
Maybe an odd behavior I noticed when biasing the amp was no DC offset was ever observed from the BA-3 voltage driver board.
Suggestions/thoughts/troubleshooting steps?
I would try removing that. I don't know much about much, but that sounds sus to me.
I had that/similar issues when I was getting started. How are you measuring offset? From what pin to what pin?
I measured DC offset on the voltage board across R12, I believe, according to the build guide.
Beautiful build! I love your front-end placement!
Try measuring from the top of R12/C3 to ground.
Try measuring from the top of R12/C3 to ground.
Attachments
give us pic of that LED driver
DC Offset - more precisely - voltage level of output node of FE is measured before FE output cap
because of that coupling cap, there can't be DC output offset
DC Offset - more precisely - voltage level of output node of FE is measured before FE output cap
because of that coupling cap, there can't be DC output offset
I’m running my front panel LED off the +V power supply with a 10k resistor. I’d eliminate that converter and just run it off your existing DC.
Yeah, that switcher could be injecting something.
Beautiful build, BTW. (Though I am a bit disturbed by the neatness of the bench... 😀 )
Beautiful build, BTW. (Though I am a bit disturbed by the neatness of the bench... 😀 )
Thanks for the comments 🙂
No change to output noise with LED driver disconnected. Tapping sound remains.
No change to output noise with LED driver disconnected. Tapping sound remains.
in that case, see with XRK for "dual XRK SLBs running at 32volts"
same problem in both channels ...... means same omission/mistake in PSUs of both channels
same problem in both channels ...... means same omission/mistake in PSUs of both channels
Will do, thanks for the input 👍. Also, still no DC whatsoever before output cap on voltage board. I did have DC on the speaker outputs that I had to adjust offset for, so I doubt the tapping noise is related. I am not terribly worried about it, just thought it was odd.
When measuring the DC offset on the front end board, what two points are you measuring between?
Also, how is your DMM set?
I'm not asking to question/challenge your results. I only ask because having "no" DC offset "whatsoever" on the front-end board would be rare. A few mV would be a very good result at temp equilibrium. Watching it wander into the 10s of mV or more as it reaches equilibrium is the norm among many builders.
Love your FE board on the mezzanine!
Also, how is your DMM set?
I'm not asking to question/challenge your results. I only ask because having "no" DC offset "whatsoever" on the front-end board would be rare. A few mV would be a very good result at temp equilibrium. Watching it wander into the 10s of mV or more as it reaches equilibrium is the norm among many builders.
Love your FE board on the mezzanine!
Hello soundwavesteve,
I fully agreee with ItsAllInMyHead - I have built 4 BA-3 frontendboards and each one was fluctuating some mV around.
DMM set to meaasure mV - red probe at R12 (measure at correct side) or C3 (input) and black to ground on BA-3 -frontendboard.
Cheers
Dirk 😉
I fully agreee with ItsAllInMyHead - I have built 4 BA-3 frontendboards and each one was fluctuating some mV around.
DMM set to meaasure mV - red probe at R12 (measure at correct side) or C3 (input) and black to ground on BA-3 -frontendboard.
Cheers
Dirk 😉
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I will definitely try the measurement locations suggested....that could be the difference....makes sense to reference to ground...was just following the original instructions. This is my second BA3 FE board and I had some DC offset on the first one, and I remember putting the positive probe on the cap but don't remember where I stuck the negative probe at. My meter is a Fluke and it was set at DC mV. The most I ever got across R12 was .01mV, but 99% of the time it was 0.00mV DC. I will report back....
You will get none measuring across R12, that is a mistake in the guide. You should be measuring BEFORE the cap and to ground.
Whoops, I see someone already caught that one.
Russellc
You are not the first one to run into that mistake. It has been caught numerous times during this threads life. If you think about it, it is impossible to measure offset across a resister....its coming from the output, so yes the other lead to ground....
Russellc