ARC Power source+ 12AX7&12AU7 Pre-amplifier - diyAudio
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Old 26th July 2010, 07:03 PM   #1
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Default ARC Power source+ 12AX7&12AU7 Pre-amplifier

Has wanted since to design a perfect vacuum tube Pre-amplifier,This time will make a new attempt.
Will use ARC the power source and 12AX7,12AU7 unifies.
Schematic diagram.
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Old 26th July 2010, 07:11 PM   #2
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Pcb......
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Old 26th July 2010, 07:24 PM   #3
DF96 is offline DF96  England
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What definition of the word "perfect" are you using? This preamp has too much gain for almost all purposes, runs the 12AU7 at too low a current for linearity, is likely to have a fairly high output impedance due to the unbypassed cathode resistor at the output (in spite of global negative feedback which will help), and may have a noisy input due to the high resistor values at the 12AX7 cathode.

With the signal suitably attenuated to avoid overloading it might add some "tube warmth", but if you remove everything after the volume control it will be more accurate and much cheaper.

I think you need to try again, but bear in mind that most systems don't actually need a preamp at all.
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Old 26th July 2010, 08:09 PM   #4
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Quote:
Originally Posted by DF96 View Post
What definition of the word "perfect" are you using?

The perfect way to put someone off tubes for life i guess. I would rather listen to opamps.
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Old 26th July 2010, 08:09 PM   #5
TheGimp is offline TheGimp  United States
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You will need to make changes to your power supply as it only puts out 210V and your desing is based on having 318V for B+ (Measured on a prototype I presume).

You only have 280V out of the rectified and filtered PS before the regulator.
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Old 26th July 2010, 08:53 PM   #6
DougL is offline DougL  United States
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Several thoughts. 12AX7 tubes are very linear,if the cathode is attached to a very high voltage or using a good CSS. This also maximises their gain. Since the gain is already more than required, a lower gain tube may be more attractive.
The power supply is competently designed, if uninspired. As it is already pointed out, it is too low for the design as presented.
Have you considered a shunt power supply? It is certainly more fashionable right now, and has technical advantages (and disadvantages) over conventional regulators.

If it were me, and I needed some gain, I would buy an octal Aikido board and use 6SN7GT tubes. If I did not need gain, a Heretical, a B1, or a TVC are all worthy options.

Just my 2 cents.

Doug
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Old 27th July 2010, 04:56 AM   #7
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Thanks everybody's suggestion very much, But the best vacuum tube amplifier, must have good power. This reminds me of the ARC, as shown below.I want to do with this power, should be able to design a more quiet pre-amplifiers.
I will use 300V DC to supply power, but is not 210V.
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Last edited by gxcnabin; 27th July 2010 at 05:07 AM.
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Old 27th July 2010, 05:09 AM   #8
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Continues to draw….
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Old 27th July 2010, 05:25 AM   #9
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PCB district explanation.
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Old 27th July 2010, 06:18 AM   #10
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Ah, an advertisement. Makes a lot more sense now.
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