New Phono Project

the road not taken.
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julien591
Posts: 10
Joined: Tue May 28, 2019 8:58 am

New Phono Project

Post by julien591 »

Hello Dave,

I contacted Jeffrey for an LR filter few months ago with the WEISS OP-2 AOP.
Finally I decided to work with tubes only.

I like the PTT244 better than the D3A and I would like to use it for the input tube.
I like also the 5687WA and the Telefunken RS242.

It's better to have a low output impedance but I want high gain with two tubes only.

I was thinking about :

STEP-UP/PTT244/1:1/LCR/PTT244/2:1
or :
STEP-UP/PTT244/1:1/LCR/5687/2:1
or :
STEP-UP/PTT244/1:1/LCR/RS242/4:1


But the problem is, what is maximum ratio you can do for a step-up ? (Without sacrificing sound, because, usually, upper 1:20, sound start to be deteriorated)

Or is there any way to make a RIAA filter ? Like high impedance LR filter using a step-up just before it ?

Or how low have to be the output impedance ?


Considering that I am planning to change the cartridge, I have freedom to match everything.
Everything is a matter of compromise, but I don't know all the possibilities to achieve my goal.

Finally, it is not better to have three gain stages to have low output impedance, high gain, and low ratio step-up transformers ?

Overall, I need 1V at the output of the preamp.

Thank you in advance
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Re: New Phono Project

Post by dave slagle »

julien591 wrote:Hello Dave,

It's better to have a low output impedance but I want high gain with two tubes only.
that is no small task.

I was thinking about :

STEP-UP/PTT244/1:1/LCR/PTT244/2:1
or :
STEP-UP/PTT244/1:1/LCR/5687/2:1
or :
STEP-UP/PTT244/1:1/LCR/RS242/4:1

But the problem is, what is maximum ratio you can do for a step-up ? (Without sacrificing sound, because, usually, upper 1:20, sound start to be deteriorated)
depends on the cartridge. I have done 1:100 for the Audio Note Io Ltd.

Or is there any way to make a RIAA filter ? Like high impedance LR filter using a step-up just before it ?
Unlikely because the impedance becomes too high.
Or how low have to be the output impedance ?
that is up to the designer. 9K is about the highest I have been able to do.
Everything is a matter of compromise, but I don't know all the possibilities to achieve my goal.
My guess is you have a long road of experimentation ahead of you. These circuits are not easy even for the experienced builder. I can make you whatever you need as long as you call out the specifications. I cannot however tell you what you need because the design and build process is a very labor intensive one.
Finally, it is not better to have three gain stages to have low output impedance, high gain, and low ratio step-up transformers ?
I can make arguments for both and cannot give you an answer. Unfortunately you need to build listen and learn.

dave
Get Your Fix
www.hifiheroin.com
julien591
Posts: 10
Joined: Tue May 28, 2019 8:58 am

Post by julien591 »

Hello Dave,
Thank you for your reply.

Would you be able to make an LR filter for me ?

For an LR filter, you need to know the tube before, and after the filter because you need to use the parasitic impedance of those tubes to create the filter ?

I was thinking also if it's possible to make a direct coupling between both tubes. For example :

1:10 --> PTT244 --> LR --> PTT244 --> 2:1

If it's possible, I think I would go for that.

Best,
Julien
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

If you tell me the inductor values required for the LR then I can make them for you.

dave
Get Your Fix
www.hifiheroin.com
docali
Posts: 58
Joined: Thu Oct 16, 2008 7:16 am

Post by docali »

*deleted*

Sorry, posted in the wrong thread.
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