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I just tried grounding speaker negative to the chassis and that didn’t make a difference.
It is. I connected the ground planes using a piece of solid #14 underneath the board. You can see the soldered ends in the picture...
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Hmmm... I don’t hear hum from any other component though.
Yes, I hear hum in the speakers without anything plugged into the inputs. I do hear the toroidal transformer hum when I put my ear to it. Also note that I am using 20v secondaries, for whatever that data point might be worth.
I have six Antek transformers in various amplifiers and none of them hum and vibrate.
Perhaps a bad transformer?
Just to rule it out, check that the amplifier ground is approximately 10 ohms above chassis ground (CL60 resistance) to rule out inadvertent short of amplifier ground to chassis.
Another thing to rule out is a bad connection or solder joint of ground. Check the resistance of ground on the power supply board to ground on the amplifier boards and inputs and outputs.
Hi Glen, a really frustrating problem, eh!
I remember someone else had a similar problem awhile back (and with an M2X too?) and ended up routing all the ground wires to a central buss point instead of the string going to the amp board, speakers, etc - this way, the input socket green shield wires, the amplifier ground green wires, the speaker return wires and the central power supply wire(s) all go to one point (a house mains screw terminal brass buss-bar, for example) and from this, the 'ground lift' CL-60 connects to the IEC ground/earth pin along with the chassis connection wire.
You've replaced the input wires with shielded cable - just add the initial green wire at the input socket and connect this to the new central ground - detach the shield for this 'test'
You've eliminated just about everything else and maybe this might 'do the trick'
I remember someone else had a similar problem awhile back (and with an M2X too?) and ended up routing all the ground wires to a central buss point instead of the string going to the amp board, speakers, etc - this way, the input socket green shield wires, the amplifier ground green wires, the speaker return wires and the central power supply wire(s) all go to one point (a house mains screw terminal brass buss-bar, for example) and from this, the 'ground lift' CL-60 connects to the IEC ground/earth pin along with the chassis connection wire.
You've replaced the input wires with shielded cable - just add the initial green wire at the input socket and connect this to the new central ground - detach the shield for this 'test'
You've eliminated just about everything else and maybe this might 'do the trick'
Extremely flexible in that regard.
Depends how you want to slice it up.
Assuming you had a heatsink capable of 100W:
Then you could do 40V rails with 1.25A Bias, 30V with 1.7A etc
If you wanted to do less bias eg 1A you could go to 50V rails.
If you had monoblocks with 200W or more of heatsinking then with the right devices you could go crazy to the limit of the devices.
50W per device is easily doable with ixth64n10l2, I haven't pushed them harder than that but you could try, and they would probably be still ok, they are very robust.
The front end just serves to drop the voltage across the jfets (by the addition of cascode) so you can increase rail voltages, it doesn't change the performance of the amp except maybe some further improvements to psrr.
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If the toroidal transformer is buzzing there is a very good chance you have dc on the mains, or your transformer is faulty, so that's another problem that might need fixing.
You might be able to purchase a cheap device to remove dc and see if the transformer stops buzzing.
It would be nice if that fixed both problems but maybe you have 2 separate issues.
You might be able to purchase a cheap device to remove dc and see if the transformer stops buzzing.
It would be nice if that fixed both problems but maybe you have 2 separate issues.
That’s actually very telling...
You have a bad ground somewhere — something that should be grounded isn’t, or something that should be isolated isn’t, or a combination of the two.
Oh there is one other thing.
It also has the ability to easily add various amounts of degeneration, which the stock pcb doesn’t.
He is hanging out at home, like most people these days
I know because I stopped by his house yesterday to pick up an UltraBiB board. Salas has a new version of the simplistic folded phono. I'm pretty sure he is monitoring that thread.
Hi 6L6 - I will go back and retrace my steps. There isn't much here, I can't imagine where the issue could be.
Question: On the PSU, do all of the pads at ST_IN2 and ST_IN3 need to be tied together? I only tied the two big pads in that area together (with solid core #14 wire).
You're a pilot, correct? I'm a GA pilot for 22 years and fly a Mooney. It with issues like this where the three Cs come in, right? Climb, Confess, Communicate.
Hi picoDumbs - I'm going to run power to this amp from a 20 amp circuit I have isolated to my audio habits in another room to see if that changes anything. And I'll look into a device to remove DC.
BTW, once I fix this issue and the amp is stable I am going to mod my boards using your 3-LED dumb biasing trick.
Hi jameshillj - It is indeed a FRUSTRATING problem!
Thanks for your tips! I will work through this as I inspect for the issues 6L6 suggested.To All:
And in my frustration, I ordered another transformer and a steel cover from Antek to see if that's the issue. I really wanted to do this anyway as they have the AS-4218s back in stock and I really didn't feel comfortable running my F6 differently than most others (I used an AS-4220 for this project).
Additionally if this is of any value in troubleshooting, I have the amp biased modestly to 0.550v and DC offset adjusted to 0.001 on both sides set after warming up for about 4hrs.
My THANKS to everyone helping me on this!!!
As '6L6' mentioned above, it seems you have a ground problem and/or as "the hum turns into a loud buzz at the speakers when I short the inputs..." - maybe there's a problem with the input jfets, resistors or the signal transformer even though the bias and offsets are saying the amp is functioning quite well - I doubt that the extra volts on the transformer secondaries will be problematic
It's quite probably something simple that's just been overlooked and it needs perseverance (and patience) to find it - I once had an isolated diode pin through loss of the via on the pcb after changing them - much agro, that one!
Oh, something you might look at later - maybe try replacing the standard 'block GB bridges' for the Shindengen Schottky bridges, if you can find them - they seem to go well with the Nichicon power supply caps and makes quite a difference to the sound of the amp
It's quite probably something simple that's just been overlooked and it needs perseverance (and patience) to find it - I once had an isolated diode pin through loss of the via on the pcb after changing them - much agro, that one!
Oh, something you might look at later - maybe try replacing the standard 'block GB bridges' for the Shindengen Schottky bridges, if you can find them - they seem to go well with the Nichicon power supply caps and makes quite a difference to the sound of the amp