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Old 14th January 2013, 03:40 PM   #1
limono is offline limono  United States
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Default Valve op-amp pre ?

Is this what I have here? Differential input stage and totem pole (SRPP) output ?
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Old 14th January 2013, 03:52 PM   #2
DF96 is offline DF96  England
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The first two diagrams show a cathode-coupled amplifier (could also be regarded as an unbalanced long tail pair) followed by a cathode follower with active tail.

No differential input. No SRPP output.

The rest is a stabilised power supply. It is unclear to me why this was thought necessary for what is a fairly basic preamp circuit.

I assume you have permission from the copyright holder to reproduce the circuit here.
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Old 14th January 2013, 04:37 PM   #3
limono is offline limono  United States
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Thanks , I need to spend more time on theory of circuits I got the pre and the technical specification sheet states; voltage gain 10 dB , output source 1.5k Ohm Totem pole (that's what fooled me into thinking it's an SRPP )
The circuit doesn't sound bad (like all fairly basic preamp circuits and it uses quality components I just don't want 4 x12AU7 is low level signal path (2x pre and 2x power amp)
and consider a change .

PS. The permission issue will be unresolved . The company is long gone and owner/designer dead. Nobody to ask.
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Old 14th January 2013, 04:46 PM   #4
kevinkr is offline kevinkr  United States
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Concerns about copyright situation noted.
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Old 14th January 2013, 04:56 PM   #5
kevinkr is offline kevinkr  United States
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The design is novel for the time, and actually not all that bad.. The first stage is just a crippled differential amp - all joking aside it is non-inverting amplifier stage, and the output is a current source loaded cathode follower. The overall design is non-inverting. I expect its performance is not a whole lot worse than say an Aikido based on the admittedly mediocre 12AU7A.

This is a unique item, designed and built by a fellow who is no longer with us.. Were it me I would probably keep it as a curiosity and build something else.

What was the company and individual behind this design? Just curiosity..

JMTCW..
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Old 14th January 2013, 05:35 PM   #6
DF96 is offline DF96  England
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It seems a lot of valves for just 10dB gain. It could perhaps be improved by balancing the input stage by adding an anode resistor to VB1a, and converting the output to a White cathode follower. The 12AU7 won't do much harm in this circuit, as signal levels will (presumably) be fairly low. I found in one quick lash-up cathode coupled circuit that the lowest distortion came from an RCA 12AU7; 6CG7 and 6/30L2(ECC804) were worse.
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Old 14th January 2013, 05:48 PM   #7
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On the 12AU7 front, increase heater current capability and install 12BH7s. Other than 2X heater draw, the 12BH7 is a drop in replacement for the 12AU7. Bye/bye linearity issues.
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Old 14th January 2013, 06:08 PM   #8
limono is offline limono  United States
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Thank You ! Will do 12BH7 front . There is plenty of heater current capability .
The company was Antique Sound USA and model of preamp PA4P. I don't think it was that unique but probably didn't get much attention because of Asian connotations so the real value of that pre is low even if the MSRP cost of pre was $1750 in late 90' (quite high) .It uses alps black pot, cerafine caps and is neatly made and quiet. The company sold them as kits too and was sourcing components and chassis for their products from Antique Sound Lab. They look alike but when I contacted ASL for some info they informed me that it was different , now defunct company and they don't have any info available. I bought that preamp from a chap who got it while working for a widow of a company's owner/designer.
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