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Old 13th May 2008, 06:05 PM   #1
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Default Tube Phono stage dilema

HI, having recently redescovered the delights of vinyl I am looking to build a moving coil compatible tube phono stage, for a low to medium output mc cartridge, 0.3mV output.

Previously i have used the first version of the Curcio Daniel, set up in the higher gain option, this comprised a single ECC88 cascode with 100R cathode, and 20K plate load, Passive eq and a further Parallel ECC88 Common Cathode with 392R on each sections cathode and a
20K plate load.

Great sounding, but I found the noise levels not really acceptable for a 0.3mv output moving coil. Not in the long term anyway.

So what to build?

I would prefer a zero feedback topology, all tube if possible. with minimum number off stages

I have considered a hybrid similar to the Daniel, only with a Jfet as the first input device aka Allen Wright, Erno Borbelly amongst others. I guess this would solve the noise and gain issues, but i would still prefer an all tube design

Or perhaps a parrallel input tube like the Steve Bench or Toccata Loesch preamp, or the later Curcio Sarah would just be quiet enough.

Would it be better to build a 2 stage low gain moving magnet RIAA equaliser and build an extra moving coil stage such as the Hampton or MC Hammer , trouble is 3 stages off amplification.

Has anyone tried a cascode with multiple tubes on the bottom section, operating with near zero grid bias?

Any sugestions or ideas welcome
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Old 13th May 2008, 06:14 PM   #2
cerrem is offline cerrem  United States
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Try using a Step-Up transformer then into a traditional MM Phono stage.... A well designed transformer will have low distortion and wide bandwidth.... A mediocre design will mess up the audio and colorize it...

Chris
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Old 13th May 2008, 07:23 PM   #3
Sheldon is offline Sheldon  United States
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Default Re: Tube Phono stage dilema

Quote:
Originally posted by velvetsunrise

I have considered a hybrid similar to the Daniel, only with a Jfet as the first input device aka Allen Wright, Erno Borbelly amongst others. I guess this would solve the noise and gain issues, but i would still prefer an all tube design

Or perhaps a parrallel input tube like the Steve Bench or Toccata Loesch preamp, or the later Curcio Sarah would just be quiet enough.
It's going to be tough to get reasonable noise performance without a step up transformer or jfet input. You could the replace the input tube with a jfet in the Bench design. I built a variation of his design, but used a transformer step up. If you use one of the Jensen transformers, you can get more than 25-30dB of gain, depending on how you load it: http://www.jensen-transformers.com/datashts/34kdx.pdf

Sheldon
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Old 13th May 2008, 07:24 PM   #4
SY is offline SY  United States
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I'd second that. You have a nice, low input capacitance, just perfect for a good step-up transformer. A nice 1:10 from someone like Jensen or Sowter, and you're good to go. The step-up also allows you to run your cartridge and interconnect balanced, which can be a big advantage with regards to noise pickup.
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Old 13th May 2008, 07:52 PM   #5
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Hi, Chris

Thanks for your suggestion.

I have tried a couple off vintage transformers from neve and utu, nice, but sounded a just a tiny bit bandwidth limited at the low end. I guess the modern ones now available have greater bandwidth.

I was hoping to avoid transformers if at all possible, just to create something a little bit different i suppose.

Though, if it sounds good, it is good.

Thanks Chris.
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Old 13th May 2008, 08:18 PM   #6
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The only two options i know that will work well and give low noise are the hybrid cascode or step up transformers.
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Old 13th May 2008, 08:18 PM   #7
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Hi, Sheldon.

Hi, Sy.

I have enjoyed reading all you posts. You obviously have a lot off experience of RIAA preamps.

Seems the Transformers have it. Unanimously!

I guess it would be easier and cheaper to just add a transformer than build a new phono preamp from scratch, though i was looking forward to starting a new project. I have been collecting a few choice parts for a while.

I will investigate your transformer options.

Thanks.
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Old 13th May 2008, 08:22 PM   #8
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Have a look at the phono stage kit available at K and K audio.
www.kandkaudio.com It has all the features you are looking for.
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Old 13th May 2008, 08:27 PM   #9
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Hi Brett,

I have read your posts regarding the Allen Wright preamp with great interest, how does the fet/tube input stage compare to a good step up transformer?

Thanks in advance.
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Old 13th May 2008, 08:57 PM   #10
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Different flavours. I would use different topologies in a JFET hybrid to a Tx input, so I cannot give a comparison. I will be building a hybrid from end when I get back to playing vinyl if that says anything.
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