Humm from heaters is zero if You use 2A3 RCA /only RCA/ with AC heating.
I'd like to say again....Forget 21 C. filter...hummm will go out with iron chock more 10 Hn for every channel /it will give You best dynamic, IMO every SS filter press it and is break for fast current/. Humm is proportional to the +B current. If you have possibility to build two filter channels, current will be 2 time less for every channel and it will be better for the class of HiEnd. Choice is Yours....
I don't like transistor like load in plate of prestage....good linearity doesn't mean good dynamic sound, IMO...
I'd like to say again....Forget 21 C. filter...hummm will go out with iron chock more 10 Hn for every channel /it will give You best dynamic, IMO every SS filter press it and is break for fast current/. Humm is proportional to the +B current. If you have possibility to build two filter channels, current will be 2 time less for every channel and it will be better for the class of HiEnd. Choice is Yours....
I don't like transistor like load in plate of prestage....good linearity doesn't mean good dynamic sound, IMO...
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wow, I somehow didn't realize he was using DC. I would never even think to use DC with 2a3...
Just try AC with a hum-buck circuit if the filament transformer isn't center tapped. Center tapped 2.5v transformers can be had pretty cheap these days...
Also - is the 2.5V on the HT mains transformer? I would avoid that if possible.
Just try AC with a hum-buck circuit if the filament transformer isn't center tapped. Center tapped 2.5v transformers can be had pretty cheap these days...
Also - is the 2.5V on the HT mains transformer? I would avoid that if possible.
Regulators reduce ripple from where it is, but they are not perfect and work better with a clean signal.
In a headphone amp where 1mW of hum results in 98dB noise this is unlikely to work.
So on my todo list:
Mess with Regulator grounds to see if they are the issue
Test AC filaments
Add filtering before the regulator.
Anything else I should try before reporting back?
You are all truly awesome.
Good point (I don't build headphone amps). But its pretty easy to go to AC and just test it.
Has he posted his DC regulation circuit? I don't see it anywhere...
Tube 2A3 from RCA works with AC heating, You don't need DC.
My PSU for my SE 2A3 works with rec. GZ34 Siemens and iron chock 6 sq. cm /for about 65 ma/ for every channel /two parallel filters channels - two chocks/ and hummm is 000 in my 96 dB speakers.
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I tried AC Heating (I have a 5V CT, so I heated 2 tubes) and I got enormous hum. I tried adding an RC filter before the regulator, nothing worked.
When I paralleled a 15ohm resistor with the headphones, the hum went away but I didn't get any amplification (sound was pretty quiet), when I remove the resistor, I get full amplification, but the hum comes back.
I can't measure any ripple on the PSU or the DC heaters
When I paralleled a 15ohm resistor with the headphones, the hum went away but I didn't get any amplification (sound was pretty quiet), when I remove the resistor, I get full amplification, but the hum comes back.
I can't measure any ripple on the PSU or the DC heaters
Two tubes? Series???
If you connect one independent channel's direct heated tube heater to another channel"s ones (using common AC or only one DC heater supply), practically shorted left and right channels!!!
Do you have two independent DC heater raw supply, and two regulator?
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no. not if you're getting hum.
I use everything from cheapest chinese and russian to expensive NOS. Its all in the implementation.
You will have to check your DC regulators with someone who knows. sorry I can't help much here. I don't build headphone amps.
Ian
Yeah, we need a proper circuit diagram of what is on the ground.
You can't heat BOTH 2a3's off the same winding in series. that won't work. Clearly some basic things to address with this amplifier circuit.
Please draw it like it actually is and post it. I'm pretty sure nobody will be critical, since you are new here and just starting out.. We will just try to help.
I meant I paralleled the tubes to get the right voltage, I didn't have the second tube connected the amp.
I added a bypass cap, BAM, no hum.
so that issue is resolved.But now, even with a regulated DC heater, and then trying with CT AC, I am getting him with the input tube connected. So now I have both tubes in place and am getting hum, when before it occurred even with no input tube. I think that counts as progress
I'll post a ground scheme asap
Ignore the alligator clips, they are for the 6SN7 supply and the cathode bypass caps.
Here are ground pics
Here are ground pics
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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