Just finished, well mostly, finished my F6 build. Have some odd issues with the left channel. It has an audible humm when idle and a DC spike on the speaker terminal when powering off mainly. It is biased around .6V and idle has .001v offset. It is the closest board to the transformer. Is it possible that I am having issues because of that or should I be taking the board out and reflowing and inspecting everything. It does play music well, the sound stage does lean towards the right channel slightly when compared to other amps. The left channel also pops anytime you adjust volume on preamp or switch sources. Any direction is appreciated.
Congratulations!
The audible hum at idle could be a few things, but the first thing I'd try is to move your primaries away from your left channel board (closest to the transformer). Ideally, when you're done, they'll be twisted, shortened, and routed away. You can just temporarily move them for now to see if the hum reduces/goes away. Next would be to similarly twist and route your secondaries. Next would be to rotate the transformer. There is usually a sweet spot. Last resort / most work would be to get a vertical mount for the transformer and reposition your transformer / PSU or mount the transformer under the PSU board.
Others should chime in re: DC spike. I'd check to see if it happens on the other channel also, and with and without a load resistor.
The audible hum at idle could be a few things, but the first thing I'd try is to move your primaries away from your left channel board (closest to the transformer). Ideally, when you're done, they'll be twisted, shortened, and routed away. You can just temporarily move them for now to see if the hum reduces/goes away. Next would be to similarly twist and route your secondaries. Next would be to rotate the transformer. There is usually a sweet spot. Last resort / most work would be to get a vertical mount for the transformer and reposition your transformer / PSU or mount the transformer under the PSU board.
Others should chime in re: DC spike. I'd check to see if it happens on the other channel also, and with and without a load resistor.
The DC spike is not present on the other channel. From my understanding of DC it seems to be a grounding issue? I could be fighting 2 separate issues. 1. The humm. 2. The dc voltage
Monoblock F6
Sorry to just jump in here but did you ever build the Monoblock F6 ? Due to an interesting set of circumstances I have two working F6 kits and am wondering if I can use the same strategy as with BA3 to get a couple of blaanced input monoblocks. Anyone tried this?
Sorry to just jump in here but did you ever build the Monoblock F6 ? Due to an interesting set of circumstances I have two working F6 kits and am wondering if I can use the same strategy as with BA3 to get a couple of blaanced input monoblocks. Anyone tried this?
My guess is, yes. Two independent issues possibly. I don't know what caps would discharge to output on turn off or if that could be a root cause. Others likely can narrow things down quickly for you.
The hum (or at least a good portion of it) could be b/c you had your primaries sitting right next to or possibly even touching your signal transformer on the left channel if that's the way you tested it. Once you get it all tidied up after testing, it may/should reduce or go away. Hum reduction on F6s is 90% science and half dark art 🙂 The things I mentioned above have worked for me and others. Hope they work for you.
The hum (or at least a good portion of it) could be b/c you had your primaries sitting right next to or possibly even touching your signal transformer on the left channel if that's the way you tested it. Once you get it all tidied up after testing, it may/should reduce or go away. Hum reduction on F6s is 90% science and half dark art 🙂 The things I mentioned above have worked for me and others. Hope they work for you.
I removed the left channel board, re-flowed the entire board, inspected for any solder issues. everything looks good. the primary and secondary wiring is not touching the transformer. that picture was just some mock up. I currently am not going to chase the hum. just the DC spike on left channel output. after reassembly the left channel still goes from a steady .001V offset and spikes all the way to a Volt when you shut the amp down. the right side doesn't do it. I have an 8ohm 100W resistor currently plugged into the left channel output. it still spikes a volt when turning the Amp off. will post some pictures of how the amp currently sits.
Hum is gone, large voltage swing is gone as well. Left channel still “pops” when changing sources on the preamp. I lowered the bias to .55V and let it burn in for awhile.
Great news! What got rid of the voltage spike on turn-off?
Strange that it only pops on the left channel...
If you switch the inputs does it follow to the right channel or stay on the left?
Strange that it only pops on the left channel...
If you switch the inputs does it follow to the right channel or stay on the left?
Black magic? Lol, I reflowed the board, ran new power and ground to it. Set bias at .55V. I hooked up my load box (8ohm 100watt resistors) ran a 1k sine wave at .3V thru it for an hour watching it on a scope. Set offset after that time. Everything just kind of settled in after that.
I haven’t tried seeing if the popping changes if I switch the input cables from right to left. Non of my other equipment does it so it never occurred to try. Had a great listening session with it. Couple hours of mixed music thru a streamer and then on to vinyl. The F6 gives a great deep soundstage when using a tube preamp.
I haven’t tried seeing if the popping changes if I switch the input cables from right to left. Non of my other equipment does it so it never occurred to try. Had a great listening session with it. Couple hours of mixed music thru a streamer and then on to vinyl. The F6 gives a great deep soundstage when using a tube preamp.
Back to share my achievement with you, I had 2 projects at the same time (Headphone amp Noir) and the F6.
The chassis was entirely made of 5 and 6mm aluminum, the heatsinks come from China (not found better in Europe).
The amp works wonderfully, it is as silent as a grave, no "plop" when starting or switching off, no volume noise at full blast without a source, impressive.
Sound side, it is balanced, beautiful deep bass, in the meantime I received a pair of Focal Chora 826, the marriage is magnificent.
A big thank you to Mr Pass for his sharing and his know-how, and to the forum for your help particularly to "2 Picodumbs"
The chassis was entirely made of 5 and 6mm aluminum, the heatsinks come from China (not found better in Europe).
The amp works wonderfully, it is as silent as a grave, no "plop" when starting or switching off, no volume noise at full blast without a source, impressive.
Sound side, it is balanced, beautiful deep bass, in the meantime I received a pair of Focal Chora 826, the marriage is magnificent.
A big thank you to Mr Pass for his sharing and his know-how, and to the forum for your help particularly to "2 Picodumbs"
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Mokaonli, that case looks terrific! Do you mind sharing some information on how how you built it and sourced the parts? I really like the heatsinks and front panel.
Hi everybody,
Today I also replaced the 6.2V zener close to offset adj. trimpot and now all is working well.
Bias is 600mV, both channels offsets are under 10mVs.
No hum, no noise.
So the culprit was both faulty zener and loosening bolt.
Thank you all for help.
Also many thanks to Nelson Pass for his generosity.
PS:I have listened music many years happily with a Nelson Pass designed Threshold CAS 1 power amp.
Today I also replaced the 6.2V zener close to offset adj. trimpot and now all is working well.
Bias is 600mV, both channels offsets are under 10mVs.
No hum, no noise.
So the culprit was both faulty zener and loosening bolt.
Thank you all for help.
Also many thanks to Nelson Pass for his generosity.
PS:I have listened music many years happily with a Nelson Pass designed Threshold CAS 1 power amp.
I could not see posts between 12th January and 24th January, so my posts around January
14th - 16th is absent for me.
Is it only me or others also can not see them?
14th - 16th is absent for me.
Is it only me or others also can not see them?
