I built a DC heater supply and tested it. It's little heatsink can't keep up though. I hollered out a string of colorful adjectives and verbs after touching it.
In any case the hum is still there. I think the AC heaters weren't a problem at all. I'm suspicious of the wiring to the 6AS7 cathode resistors on the back of the amp. They're unshielded and flank the choke. The right channel wire is closer to the choke than the left and also produces more hum. I'm guessing with all the current going through the choke, a strong enough EMF is generated. Dunno. So those wires are gonna get shielded for my next test.
If only I could get the old Tek 531 running. The dual trace plugin isn't happy.
In any case the hum is still there. I think the AC heaters weren't a problem at all. I'm suspicious of the wiring to the 6AS7 cathode resistors on the back of the amp. They're unshielded and flank the choke. The right channel wire is closer to the choke than the left and also produces more hum. I'm guessing with all the current going through the choke, a strong enough EMF is generated. Dunno. So those wires are gonna get shielded for my next test.
If only I could get the old Tek 531 running. The dual trace plugin isn't happy.
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OK. Gyrator on the back burner. I've still got enough parts to fry... ehem... try it three more times and get it right.
In the meantime I've been looking over the The Menace's schematics . Two stage choke
I have an identical 6H choke that I can borrow from another amplifier. So I'll try:
5AR4 --> 40uF --> 6H 150ohm --> 120uF --> 6H 150ohm --> 707uF
I don't think I'll have too much of a voltage drop with this set up. Should be an easy experiment.
If each channel uses no more than 90ma then I could use two cheap 10H Triad C-7X's. One for each channel.
In the meantime I've been looking over the The Menace's schematics . Two stage choke
I have an identical 6H choke that I can borrow from another amplifier. So I'll try:
5AR4 --> 40uF --> 6H 150ohm --> 120uF --> 6H 150ohm --> 707uF
I don't think I'll have too much of a voltage drop with this set up. Should be an easy experiment.
If each channel uses no more than 90ma then I could use two cheap 10H Triad C-7X's. One for each channel.
Tried out the extra 6H choke. Hum was down a good bit, but the voltage also dropped to 275v. So I don't know if the hum dropped because of the voltage drop or if it was the extra choke. Gain is down too and there is still enough hum to be discouraging.
Working out the gyrator will be important I think.
Working out the gyrator will be important I think.
I suspect I goofed up something in the point-to-point wiring. That or the B+ was too much for one of the components. I haven't gotten around to doing an autopsy on it yet. Stay tuned...
I did a bit more sniffing about today and I think I'm dealing with a grounding issue. I tinkered with some of the grounding and have notice cetain combiations are more or less awful. For example if I disconnect the source the hum gets very strong.
The saga continues...
I swapped out the 270HX transformer for a 370HX I got cheap for another project. It seems like most hum is gone but I can't tell where I had the 270HX doing work for the heaters and it was buzzing like mad. I thinks the power tranny is the source of the noise. What now? I'm feeling a Antek AN-3T275 when I can scrounge up the bucks. Or the 370HX may just get stuck on there... 🙂
I swapped out the 270HX transformer for a 370HX I got cheap for another project. It seems like most hum is gone but I can't tell where I had the 270HX doing work for the heaters and it was buzzing like mad. I thinks the power tranny is the source of the noise. What now? I'm feeling a Antek AN-3T275 when I can scrounge up the bucks. Or the 370HX may just get stuck on there... 🙂
Hi
Did you ever sort out the hum issue? I have just had a friend build me a similar amp, and it hums like crazy. Removing the ground wire on the AC supply helped a little, but it's bad. We have no ideas of where to look.
Thank you.
Did you ever sort out the hum issue? I have just had a friend build me a similar amp, and it hums like crazy. Removing the ground wire on the AC supply helped a little, but it's bad. We have no ideas of where to look.
Thank you.
The first thing that I would try to do would be to isolate the source of the hum. Is it at the input and in any way related to pot position (volume level)? Does it change if you touch the chassis? Either of those might point to a ground loop which would mean that you've got a few ways to try to address that. From your description of removing the ground wire I'm guessing that at least part of you problem is ground-loop related. Are your inputs isolated or tied to the chassis?
One other thing that you could look into would be floating the filaments above ground with a resistor divider. I did this on one of my builds and it certainly helped the noise floor.
The hum level is constant - totally independant of volume pot setting. I think the inputs are insulated - will have to check this evening. Touching the chassis has no effect.
The transformer is also quite noisy, mechanically.
The transformer is also quite noisy, mechanically.
The guy that built the amp, winds his own transformers, so it's one of his. I certainly seems big enough. I don't have the details at this stage, but I'll try and get some specs.
I'm in South Africa, so it's 230volt / 50hz
I'm in South Africa, so it's 230volt / 50hz
Did the guy ever build an amplifier before?
Sorry for asking, but an amplifier built by someone who knows his stuff shouldn't hum like crazy...
I never did find the source of hum, but my feeling was a power supply problem in one of the channels. Only one channel had hum, the other was dead silent. I plan to do a rebuild at some day.
I pillaged the iron, so I'll have to remind myself where I put the power transformer. I think I sold it off. If so I'll probably use something similar, but not a 200 series from Hammond.
I pillaged the iron, so I'll have to remind myself where I put the power transformer. I think I sold it off. If so I'll probably use something similar, but not a 200 series from Hammond.
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This is the first headamp he's built. I'm sure he'll sort it out. I was in a hurry to start listening, so took the amp before it was 100% sorted.
I'm hoping the input from you guys will assist in getting the hum issue eliminated.
The transformer mechanical hum is troubling. The filament supply of the output tube coupled with the HV current requirement certainly presents a pretty unique spec for a transformer and as whitelabrat experienced even the correctly spec'd Hammond 270 wasn't really up for the task.
Here's how I biased the filament supplies for The Menace.
Here's how I biased the filament supplies for The Menace.
HA-2 Re-dux
Anybody out there working on the HA-2 type headphone amp? I am. It runs hot, real hot the two 2K resistors need a significant heatsink, and the Hammond 270HX is hot and over loaded.
I will probably install a separate filament xformer that i have. I could use some advice on the heater circuit, I'd like to run the center tap of the 6.3 secondary for the 6sN7 to a voltage divider across the B+ and run some positive DC, but i don't know the appropriate values. Transformer has 3 separate 6.3v secondaries so I am planning to run a to the 6as7G heater which can take 300v between its heater and cathode. But maybe the voltage divider makes some sense here too. Given what i've gathered from the web, this circuit is tough on tubes, maybe this will help?
Despite these things the sound is fantastic!
Anybody out there working on the HA-2 type headphone amp? I am. It runs hot, real hot the two 2K resistors need a significant heatsink, and the Hammond 270HX is hot and over loaded.
I will probably install a separate filament xformer that i have. I could use some advice on the heater circuit, I'd like to run the center tap of the 6.3 secondary for the 6sN7 to a voltage divider across the B+ and run some positive DC, but i don't know the appropriate values. Transformer has 3 separate 6.3v secondaries so I am planning to run a to the 6as7G heater which can take 300v between its heater and cathode. But maybe the voltage divider makes some sense here too. Given what i've gathered from the web, this circuit is tough on tubes, maybe this will help?
Despite these things the sound is fantastic!
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