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As Mark pointed out, you've got a lot of gain here, so there may be a number of issues outside of the BA-3 that could be contributing to this. If you can't hear it when you are sitting down, it might not be worth a lot of time and effort. But if it truly bothers you, I have a few observations from your build image:
- You've twisted the wrong set of wires: You have twisted your regulated DC supply (unnecessary) and you have left your AC wires from the trafo to the regulator straight (problematic). Twisting the AC wires may help to eliminate some RFI, and potentially some hum.
- Make the AC wires to your regulator shorter and the DC wires from the regulator longer.
- Tie ALL AC wires as tightly to the metal of the chassis as you can. You've done this reasonably well with the AC mains into your power switch, but the AC wires on the primary side of your transformer seem to be flying high in open space.
- Ditto on your AC signal wires, keep them close to the metal chassis to help them reject RFI. You've done this well on the left side of the image where you've tied them down, but they are flying high by your input select and your volume control, then back to the BA-3 circuit.
- It also looks like you might be able to stand your transformer on its end, instead of flat. Make or buy an L-bracket ( or just pick it up with your hand and move it around). Orient the transformer so that the "axis" of the "wheel" points forward and backward in your chassis. Don't "point" it at your regulator or the BA-3 circuit.
- You've twisted the wrong set of wires: You have twisted your regulated DC supply (unnecessary) and you have left your AC wires from the trafo to the regulator straight (problematic). Twisting the AC wires may help to eliminate some RFI, and potentially some hum.
- Make the AC wires to your regulator shorter and the DC wires from the regulator longer.
- Tie ALL AC wires as tightly to the metal of the chassis as you can. You've done this reasonably well with the AC mains into your power switch, but the AC wires on the primary side of your transformer seem to be flying high in open space.
- Ditto on your AC signal wires, keep them close to the metal chassis to help them reject RFI. You've done this well on the left side of the image where you've tied them down, but they are flying high by your input select and your volume control, then back to the BA-3 circuit.
- It also looks like you might be able to stand your transformer on its end, instead of flat. Make or buy an L-bracket ( or just pick it up with your hand and move it around). Orient the transformer so that the "axis" of the "wheel" points forward and backward in your chassis. Don't "point" it at your regulator or the BA-3 circuit.
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getting visually fancy now...
Here's the story:
I had the occasion to melt a little bit of solder, so I started to source parts for the BA-3. (My next excuse not to start my F4 which scares me don't know why...)
Stumbled on those PRP-resistors...
Hei, red resistors on a red PCB!
Checked the available values, which seem to be "strange" (there's a name for certain groups of values), some don't fit the BOM.
Piggybacking 2 resistors could be an option to come close.
But that's just stupid, I won't do it...
Finally, here's the question:
The BOM requires 10r, PRP has 11r... that's a 10% deviation. Would this work?
Here's the story:
I had the occasion to melt a little bit of solder, so I started to source parts for the BA-3. (My next excuse not to start my F4 which scares me don't know why...)
Stumbled on those PRP-resistors...
Hei, red resistors on a red PCB!
Checked the available values, which seem to be "strange" (there's a name for certain groups of values), some don't fit the BOM.
Piggybacking 2 resistors could be an option to come close.
But that's just stupid, I won't do it...
Finally, here's the question:
The BOM requires 10r, PRP has 11r... that's a 10% deviation. Would this work?
Any of the order-it-yourself-from-Gerber-CAD-files power supply units, can be purchased in RED. For example, here is a set of price quotes for the PSU designed by member "iamwhoiam" , Gerber files found attached to this message
I used the comparison shopping website
PCBShopper – A Price Comparison Site for Printed Circuit Boards
to obtain these quotes on Friday morning, 28 Aug 2020. Click on the white "X" in the lower left hand corner, to see the images full size and undistorted.
_
I used the comparison shopping website
PCBShopper – A Price Comparison Site for Printed Circuit Boards
to obtain these quotes on Friday morning, 28 Aug 2020. Click on the white "X" in the lower left hand corner, to see the images full size and undistorted.
_
Attachments
G‘day Mark!
You are very helpful! And even more thorough! (Triple times, actually)...
(I have to admit that sometimes, when you reply in this quality, I myself turn red as those PCBs [emoji15]...)[emoji846]
I was hoping somebody would‘ve pointed me to a prefab pcb, of such a quality as say VRDN... but why not take that step of a project too?
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Tranformer, PSU…
6L6, I put the option of a "configured" red VRDN aside (but haven't ditched it!) because I don't get the math to adapt it to 24V, so looked further and found this old post of yours.
PS-19 seems to be expired, there's this Dual/Bipolar LV-Reg or this PS-22 Bipolar Power Supply Kit... Good news is both seem to be fancy RED pcb
… care to comment?
A 20 - 30 VA would be sufficient to have BA-3 flying/singing even if the MOSFETS would be fed with ~100mA, correct? (And a 24V secondary would be good to go, too?)
Thank you!
david
6L6, I put the option of a "configured" red VRDN aside (but haven't ditched it!) because I don't get the math to adapt it to 24V, so looked further and found this old post of yours.
PS-19 seems to be expired, there's this Dual/Bipolar LV-Reg or this PS-22 Bipolar Power Supply Kit... Good news is both seem to be fancy RED pcb
… care to comment?And according to this post above, there seems to be a very reasonable transformation-requirement.
A 20 - 30 VA would be sufficient to have BA-3 flying/singing even if the MOSFETS would be fed with ~100mA, correct? (And a 24V secondary would be good to go, too?)
Thank you!
david
I’m not sure if you’re being serious or not with the requirement for the color red...?
Comments -
PS-22 appears to be a simple and nice PCB holding a 317/337 regulator set. Will work well.
Dual/Bipolar LV-Reg was actually made at my specific request (after a great dinner at a Thai food restaurant) to be a PSU intended for this very project and similar (the BA2018 linestage)
Needless to say, it works beautifully.
20VA is for all practical purposes 20 watts.
100mA is 2.4W
It’s bipolar, so double that.
...I.E., 20VA will work perfectly, the transformer will be loafing along at a fraction of it’s ability, and that’s usually good for noise performance.
Comments -
PS-22 appears to be a simple and nice PCB holding a 317/337 regulator set. Will work well.
Dual/Bipolar LV-Reg was actually made at my specific request (after a great dinner at a Thai food restaurant) to be a PSU intended for this very project and similar (the BA2018 linestage)
Needless to say, it works beautifully.
20VA is for all practical purposes 20 watts.
100mA is 2.4W
It’s bipolar, so double that.
...I.E., 20VA will work perfectly, the transformer will be loafing along at a fraction of it’s ability, and that’s usually good for noise performance.
Thanks 6L6!
Actually, red is not mandatory. I'm trying to include it into my part-selection's criteria as far as it still makes sense. If it's not possible (good parts aren't red), fine. If there's a viable alternative in red, I'll go for them. I now it's silly, but silliness is, well, part of me
Now, the VRDN as PSU really starts to make sense (I misunderstood it as possible but not-so-ideal...). I'll try to understand what has to be done to get there... and get them in red