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
New Phono Project
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Re: New Phono Project
that is no small task.julien591 wrote:Hello Dave,
It's better to have a low output impedance but I want high gain with two tubes only.
depends on the cartridge. I have done 1:100 for the Audio Note Io Ltd.
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)
Unlikely because the impedance becomes too high.
Or is there any way to make a RIAA filter ? Like high impedance LR filter using a step-up just before it ?
that is up to the designer. 9K is about the highest I have been able to do.Or how low have to be the output impedance ?
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.Everything is a matter of compromise, but I don't know all the possibilities to achieve my goal.
I can make arguments for both and cannot give you an answer. Unfortunately you need to build listen and learn.Finally, it is not better to have three gain stages to have low output impedance, high gain, and low ratio step-up transformers ?
dave
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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
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
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- Location: NYC
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If you tell me the inductor values required for the LR then I can make them for you.
dave
dave
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