ARC Power source+ 12AX7&12AU7 Pre-amplifier

gxcnabin · 26th July 2010, 07:03 PM

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.

gxcnabin · 26th July 2010, 07:11 PM

Pcb......

DF96 · 26th July 2010, 07:24 PM

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.

analog_sa · 26th July 2010, 08:09 PM

Quote:

Originally Posted by DF96

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.

TheGimp · 26th July 2010, 08:09 PM

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.

DougL · 26th July 2010, 08:53 PM

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

gxcnabin · 05:07 AM

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.

gxcnabin · 27th July 2010, 05:09 AM

Continues to draw….

gxcnabin · 27th July 2010, 05:25 AM

PCB district explanation.

analog_sa · 27th July 2010, 06:18 AM

Ah, an advertisement. Makes a lot more sense now.

26th July 2010, 08:53 PM	#6
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 25	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 __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

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26th July 2010, 07:24 PM	#3
DF96 diyAudio Member Join Date: May 2007	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.

26th July 2010, 08:09 PM	#5
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	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.

27th July 2010, 06:18 AM	#10
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Ah, an advertisement. Makes a lot more sense now.

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