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Old 17th January 2008, 07:50 PM   #11
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have you already exhausted fixing the hum by troubleshooting the heater wiring and grounding scheme? Those are much more likely sources of hum in a tube circuit.
I tried over 5 different grounding schemes, including different star grounding positions and grounding connected / disconnected to the chassis, without a single change in hum.

When I disconnect the tube and connect the inputs directly to the LM3886s, the output is pretty clean without a single bit of hum or buzz.

I also tried different things with the filament (It's powered from 6.3V DC using an LM317) like connecting one of the wires to the ground rather than leaving the regulator outputs floating (The 6.3V regulator is powered from a rectified 8VAC winding on the transformer), no differences here as well. I tried different RCA connectors insulated from the chassis, no difference. I think I just got the grounding scheme worse with all the experimentation, it started buzzing a bit when I don't use the tube with all the changes brought.

Note that there's no hum while the capacitors are discharging when I turn off the amp (but there's still sound), is this a good indication that it could be caused by the power lines?

Also, I tried a few different voltages(The amp has two 25-0-25 + 8VAC transformers with the 25-0-25 in series and the 8VACs in parallel to give 50-0-50 for the amp and tube and 8VAC for the tube filament PSU)

When the transformers were wired in parallel(About 25-0-25 before rectification), there was half the hum.

The only way I found to reduce the hum and keep higher voltage lines was to put different resistors between the 3886s and the tube, but I have less gain at the same time.
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Old 18th January 2008, 07:26 PM   #12
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So far the only solution seems to be Martin's the TL783 doesn't have a negative voltage version. Actually, TI doesn't make adjustable negative voltage regulators. Will I have to get HV parts?
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Old 18th January 2008, 09:39 PM   #13
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Quote:
Originally posted by DragonMaster
So far the only solution seems to be Martin's the TL783 doesn't have a negative voltage version. Actually, TI doesn't make adjustable negative voltage regulators. Will I have to get HV parts?
I have been running my LM317 non-HV with no protection diodes at all providing 160VDC for a tube preamp for a few years now. KISS.
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Old 18th January 2008, 09:47 PM   #14
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So the datasheet's not all I should look at!
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Old 18th January 2008, 10:25 PM   #15
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Quote:
Originally posted by DragonMaster
So the datasheet's not all I should look at!
Not sure if that's sarcastic or not. Whatever you decide, at least consider adding an extra loading resistor to the schematic you drew. As I said, if you have a small small load, the current will just flow through the zener and bypass the regulator entirely. That is what will happen if you are just feeding a single tube with the regulator.
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Old 20th January 2008, 11:56 PM   #16
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K...
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Old 22nd January 2008, 11:21 PM   #17
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Guess what I just got, 10 years after using a soldering iron for the first time : A breadboard !

Now I'll be able to experiment w/o veroboard and point to point wiring betwen floating components. (i.e. Testing the new PSU.)

My old method was to make sure everything works before building anything. Then build, then find the errors if there are any, exactly what happened with my gainclone. I built the minimum circuits and now need to add tons of stuff.
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Old 20th April 2012, 06:56 AM   #18
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Default the input voltage size

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Originally Posted by DragonMaster View Post
Thanks for the replies!

So this would work?
the input voltage size?? about 45v?
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Old 20th April 2012, 07:05 AM   #19
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Default 45v

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Originally Posted by DragonMaster View Post
Hi,

I need a 45V regulator, but I can't find any "simple" ways of doing it except by using LM317/LM337 HV parts. The problem is that I can't find these anywhere, even Mouser doesn't have them. Anyone knows how I could get 45V off the standard parts?

I found this:
http://www.national.com/ms/LB/LB-47.pdf

The regulator sees a 5V difference, but I don't know how which resistance I should give to R6 and if the circuit is possible to build for the LM337.


hello ,I need a 45V regulator,too.have you finished? can you give me a schematic diagram
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