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Old 13th January 2003, 08:33 PM   #1
Joel is offline Joel  United States
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Default Solid State DC filament supply

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.
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Old 13th January 2003, 09:07 PM   #2
dhaen is offline dhaen  Europe
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Joel,

You'll get much better hum rejection using an IC regulator like the 317 (variable), or 7805 (fixed).

How much AC voltage have you got to play with?

Cheers,

PS There can be 2 reasons for your increased hum, with incresed smoothing symptom.
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Old 13th January 2003, 09:14 PM   #3
HDTVman is offline HDTVman  United States
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I'd just go with the 7805. Easy, cheep and works, Just follow the app. note.

Just for giggles try small first C ( like 1000uf ) on the input of the supply your using now. If that works I'll tell you why.

Later
Bruce
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Old 13th January 2003, 09:19 PM   #4
dhaen is offline dhaen  Europe
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Quote:
If that works I'll tell you why.
You're not teasing our Joel are you Bruce?

I agree. Once proved, drop it down as far as it'll go.

Cheers,
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Old 13th January 2003, 09:21 PM   #5
HDTVman is offline HDTVman  United States
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Would I do that??????
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Old 13th January 2003, 09:30 PM   #6
dhaen is offline dhaen  Europe
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Quote:
Would I do that??????
Yes.

Seriously Joel, the performance of a discrete component SS regulator is far inferior.

If you really wanted, you could use a FET as series pass, and a valve as error amplifier. Now that would be cool. You'd use up more power heating the error amp, that was output by the reg..

Cheers,
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Old 13th January 2003, 09:31 PM   #7
Joel is offline Joel  United States
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Quote:
Originally posted by dhaen
How much AC voltage have you got to play with?
It's the 6.3V winding from the power transformer. Actually more like 7.2V unloaded.
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Old 13th January 2003, 09:31 PM   #8
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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
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Old 13th January 2003, 09:42 PM   #9
HDTVman is offline HDTVman  United States
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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
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Old 13th January 2003, 09:43 PM   #10
dhaen is offline dhaen  Europe
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Peter,

Have you any idea of the mechanism that causes the "sound disaster"?

Cheers,
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