Ok, so the last remaining hum on my 71A mono amps is bothering me. The filaments have two RC filters after the bridge rectifier, both with 10,000uF of capacitance. Adding 10kuF more actually made the hum worse. It's definitely in the filament supply, since I hooked up a battery and there was no noise whatsoever left.
I want to try a regulated, highly filtered SS supply. Can somebody point me towards a schematic? Or GABE - can you give me part #'s for the supply on your site? It doesn't say what transistors to use, etc. Also, how would I make your supply variable, to adjust the output V?
I need 5V@.75A
Transistors I have on hand are 1N1711, 1N3906, 2N3055, and various diodes.
I want to try a regulated, highly filtered SS supply. Can somebody point me towards a schematic? Or GABE - can you give me part #'s for the supply on your site? It doesn't say what transistors to use, etc. Also, how would I make your supply variable, to adjust the output V?
I need 5V@.75A
Transistors I have on hand are 1N1711, 1N3906, 2N3055, and various diodes.
Attachments
In my opinion these regulated supplies sound disastrous. Especially on a DHT. Not that they don't cure the hum, it's just that they take a whole lot of the music away with it. If you really MUST have dc go for either a choke filtered supply with very high quality caps or a current source.
That's just what i hear.
peter
That's just what i hear.
peter
Most of the time you will need 2.5 to 3 volts minimum for the regulator to work. If you can go a different transformer for the filaments I'd do it if you want to use a regulator. Maybe a 12.3 volt /1 - 2 amp. xformer, bridge, 1000uf and into reg. 22uf on the output and away you go. Bypass with hi dollar parts to taste.
Have fun and let us know what happens.
Later
Bruce
Have fun and let us know what happens.
Later
Bruce
The hum of Joel
Joel,
This evening you posted a reply to Paul about tracing hum, where you said: 120Hz +B, 60Hz filaments.
Now that is generally true, but for DHT there is also a 120Hz component.
I suggest that your increased hum with inceresed smoothing is either:
1) You have just gone past your hum cancellation point.
or
2) You are introducing hum by increasing charging current, either through:
a) Earth current
b) Magnetic field
c) Rectifier overload*
*This is a strange phenomenon I've observed. I think it has someting to do with the instantaneous junction temperature affecting the reverse breakdown on the following half cycle.
Cheers,
Joel,
This evening you posted a reply to Paul about tracing hum, where you said: 120Hz +B, 60Hz filaments.
Now that is generally true, but for DHT there is also a 120Hz component.
I suggest that your increased hum with inceresed smoothing is either:
1) You have just gone past your hum cancellation point.
or
2) You are introducing hum by increasing charging current, either through:
a) Earth current
b) Magnetic field
c) Rectifier overload*
*This is a strange phenomenon I've observed. I think it has someting to do with the instantaneous junction temperature affecting the reverse breakdown on the following half cycle.
Cheers,
I've heard many theories, some more convincing than others. In Idht the capacitance between heater and cathode is what suposedly affects the sound. Not sure if i believe it as the difference from different smoothing capacitors is staggering. In DHT it doesn't seem to be a good idea to make one side of the cathode more biased than the other, hence the approach to use bipolar heater voltage where both sides of cathode are symetrical. Some have reported success with using either very low (<20Hz) or very high (>30kHz) heater supplies. I have no experience with this.
At the level of current models i find it very difficult to draw convincing connections between cause and effect. Empirical observations and auditions are sadly, the only way to improve the way my system sounds. As far as heaters are concerned i find that the quality of heater supply is nearly as important as the quality of plate supply. And valves don't like sharing heater (or plate) supplies because of interstage cross-coupling. In my amps every valve has its own heater and plate transformer. Not commercially viable, but works for me.
cheers
peter
At the level of current models i find it very difficult to draw convincing connections between cause and effect. Empirical observations and auditions are sadly, the only way to improve the way my system sounds. As far as heaters are concerned i find that the quality of heater supply is nearly as important as the quality of plate supply. And valves don't like sharing heater (or plate) supplies because of interstage cross-coupling. In my amps every valve has its own heater and plate transformer. Not commercially viable, but works for me.
cheers
peter
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