Hum problem with jfet Aleph 3 (babbelfish)
I thought it would be better to start a new thread with my problem. Perhaps I'm not the only one struggling with hum.
I have built a different version of Zen Mod's babbelfish, with two pairs of output transistors. It sounds very good (I had it working without noise for some reason), but now I have problems removing the noise and adjusting the bias.
I have tried to connect all ground wires the same place, but that didn't fix my problem. I have also swapped all bjt's and tried removing c102.
My supply is a crc with 2x15mF->0.2R->4x15mF and my ripple is +/- 25mV with one channel running, but I want to use it to power both channels. The output ripple is 10mV
I have attached my schematics with measured values and I have some pictures of my setup here:
Please tell me if I need to supply more information. I have a 60MHz scope.
How much ripple should it be able to reject?
Is my supply simply too tiny? (I do however have 90mF per rail while aleph 3 has 88mF)
Do I have any fundamental errors in my schematics?
How do I fix it?
Re: Hum problem with jfet Aleph 3 (babbelfish)
adjusting the bias?
if you have problems with that-just decrease slightly R124 in your schematic
I see that you now have similar currents per mosfet ; what was issue? mosfet or resistor?
you must tell us now how you made supply .
mebbe diode bridges are tiny....... or you need to rearrange CRCs
technical details for my normal A3 with irf9610
-one transfo for both channels + 2 x 35A bridge +2 x 68000uF
-after separate LC sections for right and left
-total cap 408000uF +4 x 1.2mH
-25 v rail and 2A bias
-power supply ripple is 25mV
-hum is very low on output
-oversize heatsink for around 40C to 45C after 3 hrs
-exactly 50% ac gain
-just to check your power supply my supply ripple for both
channels 4A is also 25mv ac and just a small hum on
(92db speaker) no problem so your supply seem ok
-maybe a ground loop so if you remove all input what
happend to hum on speaker and also ground input
-maybe transfo magnetic induction so ?? try
to isolate with metal sheet
-when you said "problem to adjust bias" same problem
for me my aleph ccs was unstable but with 1nF cap
on base and collector q103 (mpsa18 in normal A3)
it s ok now
Re: Re: Hum problem with jfet Aleph 3 (babbelfish)
capacitors are in total 12x15000uF
I just tried to see if a metal plate between psu and amp changed anything, but nothing changed on the scope.
Re: Re: Re: Hum problem with jfet Aleph 3 (babbelfish)
Is the rated VA of trafos sufficient? Seems some tinny.
seems irrelevant - if I conclude OK-that you have hum even in breadboard variant,where toroid was miles away from main pcb
if then you haven't hum.......there is a culprit
I think I might have found the error - or at least I have found something which is wrong. The CCS regulation seems to be oscillating insanely. I took a picture (with my left hand - sorry!) of the scope output. I'm looking at the node connected to basis of Q103 and R133,R125 and R123.
The scope is set to 5V and 2us
did you try 1nF on base and collector
the official aleph 30 design has 1nF
and it s work in my aleph 3
Can I use 10nF?
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