Electronic phono MC step up transformer

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Hans Polak

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Joined 2005
Sunsun22 said:
As discussed, I am posting the first stage schematic of my phono amp here. This is the 320 phono of Erno Borbely that I have been using it since 2011. A very articulate, quiet and dynamic phono that beats my ASR (old model).

I am thinking if I can use the first stage as MC stage for my tube phono project. Can anyone tell me is it possible to take the output at "TEST" point (Between R27 and R28) and feed it to a 47K MM tube phono amp?
Click to expand...
Without having the component names and values, it will be hard to answer your question.


Hans
 
Onvinyl

Onvinyl

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Joined 2002
Hey sunsun,
I think it is fun to build something and compare to your borbely amp!
You can‘t easily re-use its headamp, though. At the test point, riaa is already provided if i read the circuit correctly.

The first I‘d do is building the pacific prepre to get you going and to give you a feeling where you stand with this simple circuit. You will notice more noise than with the borbeley.

You might parallel up to four fets and cascode it as per post #17 to help the noise.

Edit: or take the first stage from http://www.diyaudio.com/forums/analogue-source/36260-folded-cascode-fet-opamp-mc-phono.html#post419559

I have another idea but would need to search my papers...
 
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Sunsun22

Sunsun22

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Joined 2004
I am interested to use Erno's 320 as MC head amp because it is; to my experience and others' comments, quiet and good. Besides, it is readily available to me since it is a working gear. If I can get a point (TEST point as indicated here) where it is after the first stage gain and connect to my tube phono in progress, it would be the easiest way. I hope connecting from a point in the 320 board would not damage it.

According to the explanation of the circuit from the assembly instruction, the TEST point is before RIAA.

The circuit as mentioned in #17 is easy and I will try it no matter if I can find a output stage from the 320 board. Thanks
 
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Sunsun22

Sunsun22

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Joined 2004
This is what Erno explained:

QUOTE
The amp on the left (the circuit I posted) is a high-gain amp with extremely low noise and FLAT frequency response....... The second amp provides a further amplification of 24 db at 1 KHz and at the same time boost the bass according to RIAA characteristics....

....... R28-C15 (on the right hand side of the circuit that I didn't posted) provides the high frequency roll off of the RIAA equalization.
UNQUOTE

This is what makes me believe that I can take the signal out before R28 by lifting one end of R28 and take the signal out from TEST point. The remaining question is impedance matching at before R28 with a 47K MM tube phono stage. Does it match?
 
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Onvinyl

Onvinyl

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Joined 2002
It doesn‘t need to match as long as it‘s output impednace is reasonably low which i guess is the case. Analog_sa is technically correct you shouldn‘t need cap coupling as long as everything works as expected. Just better be safe than sorry. Personally i wouldn‘t open the box because Ernos circuit is build of now obsolete parts. I wouldn‘t risk it.

And, you can‘t really compare the sound of your different phono amps if you cannot exchange them quickly.
 
Sunsun22

Sunsun22

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Joined 2004
There is a servo in the circuit that, I hope, DC should not be a problem. Besides, I still have few hundreds jfets that I bought from a Japan shop dated back in 2011 therefore parts should not be a problem for me in this project.

I have this drive to build a tube phono because I listened to one of them and found the"coloration" is very good for violin and vocal.
 
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