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Old 23rd August 2004, 01:00 PM   #1
ebijma is offline ebijma  Netherlands
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Question regulated valve buffer with lm317 and lm337

Regulated valve buffer with lm317 and lm337.

I want to regulated a valve buffer of a gainclone.
I know i can do this with the lm317 and lm337.
Have them laying around.
The transformer i want to use is 30 volts.
So that would be 40 volts DC on each rail.
Thats the max input voltage of these regulators.
And i want a output of 35 volts.
I don't want to run them that high.

My question is can i lift the adjust pin with a zener diode?
Lets say i put in a 10 volt zener, so that the input to adjust pin on
the lm3xx would be 30 volts.
Is this possible?
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Old 23rd August 2004, 01:15 PM   #2
Nuuk is offline Nuuk  United Kingdom
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But the power supply for a valve buffer is around 6 volts!

I presume that you want to regulate the PSU for the chip rather than the buffer. In which case, use the LM338s.
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Old 23rd August 2004, 01:24 PM   #3
ebijma is offline ebijma  Netherlands
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Thanks for the reply nuuk.
i ment the +- 35 volts rails.

So not the 6.3 volt villament.
i know the lm317 and the lm337 can handle the ampers.
So if i just lift them up with a zener.......
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Old 23rd August 2004, 01:33 PM   #4
moamps is offline moamps  Croatia
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Hi,
you don't need zeners for LM317/337 output voltage seting.
Just use two resistors...R1=ca 220ohms,
Vout=1,25*(1+R2/R1)
Regards
Milan
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Old 23rd August 2004, 02:21 PM   #5
Franz G is offline Franz G  Switzerland
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I would be interested in a comparison with and without regulator, for the tube buffer.

Do you have both solutions?

I think, because the tube buffer is running completely in class A, there is a constant current, wich make regulators in this case workless.

Maybe I am wrong?

Franz
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Old 23rd August 2004, 03:18 PM   #6
ebijma is offline ebijma  Netherlands
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Hallo Franz G,

Im not trying to regulate the current.
Im want to regulate the rail voltage of +- rails.

So............
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Old 23rd August 2004, 03:23 PM   #7
Franz G is offline Franz G  Switzerland
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I think I understood you right: you want to regulate the anode voltage of the tube.

And there is a constant current, imho.

Franz
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Old 23rd August 2004, 03:45 PM   #8
ebijma is offline ebijma  Netherlands
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I know there's a constant current.

I don't think i understand you Franz.

As i see it the voltage of the +- rails of about 35 volts can drop or rise when the mains is not stable.
So with regulation this will be stable.

So my question was how to let the lm317 and the lm 337 work with an input voltage of 40 volt.
I don't want to run them on there maximum input voltage.
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Old 23rd August 2004, 03:47 PM   #9
moamps is offline moamps  Croatia
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Quote:
Originally posted by Franz G
I think, because the tube buffer is running completely in class A, there is a constant current, wich make regulators in this case workless.
Hi,
Regulators are used to suppress ripple from bridge stage. Tube buffer has poor PSRR and needs very clean rails. But, regulators can insert HF noise in rails also, etc. CLC network is the best solution, IMO. Or maybe using Didden's regulators.
Quote:
Maybe I am wrong?
Yes, You are wrong. Regulators are normally used in constant current applications. Three pin regulators are usually poor performers in power amps applications.

Regards
Milan
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Old 23rd August 2004, 09:24 PM   #10
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CLC network is not regulator ( stabiliser ). " ... constant current application.. " - realy ? " ... three pin... " - realy ? Why ? Summary : Franz, do all like in year '26, 'cos all past this year is wrong .
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