Tube phono preamplifier by 12ax7

[roline]

Don't for get the groovewatt RIAA, very similar to the WAD, a couple of 12AX7 SRPP stages with the RIAA comp between them. Then a 12AT7 follower output. I'm currently fabbing one to try it out, design looks solid, but I added the 50k cutting head 3.18us comp components. Heaters need a raised 12 V due to the SRPP design, I decided on about 70V based on the B+ that I'l have available.

[formula 22]

Originally Posted by siliconray

Planning to design a low cost tube phono preamplifier. After searching on the web I realized a phono preamplifier should have the following features:
1. High gain. Normally 40 to 45dB
2. A RIAA circuit is necessary
3. High input impedance is needed for piezeo phono head
4. Low input impedance is needed for magnetic phono head

I found a very simple circuit designed by 7025 (12ax7), attached below. Is ther anybody had tried this circuit? How about the performance?

THe output impedance is 220kOhm, maybe too high for some power amplifiers. I think a cathod follower should be added.

What changes should by made to the schematic instead of Tube/Valve 12AX7 to PCC88 use?
thanks you!

[Dinkers]

Hi, all records of WAD can be sent to your mailbox. File too big to post on the Forum. Dinkers

[formula 22]

Originally Posted by Dinkers

Hi, all records of WAD can be sent to your mailbox. File too big to post on the Forum. Dinkers

Hello Dinkers!
Send documents to my e-mail. And if you have a schematic with a buffer for tube/valve PCC88 send.
Thanks you!

[Dinkers]

Hi, I scanned all records of WAD. It was a supplement in the British journal Hi-Fi World - November 2000. Formula 22, PCC88 - I think that is the worst tube for audio ... Greetings Dinkers

[riccoryder]

Originally Posted by siliconray

BTW, what do you think can be 'different' from the other 1 million companies products?

Maybe you should try building the RCA design and others here. It fun and you may enjoy it. Search the forum and try various things. Listen critically. Compare with other commercial preamps at high-end audio stores. Build an inverse RIAA network. See if sound quality is altered running through preamps you test and that network. (it does the opposite of what the preamp does, the overall result of the two combined should be neutral and not alter a clean source heard through it.) Something others are not doing? A tubed phono section with circuitry to remove pops and clicks could certainly be a complex undertaking.

[formula 22]

Originally Posted by Dinkers

Hi, I scanned all records of WAD. It was a supplement in the British journal Hi-Fi World - November 2000. Formula 22, PCC88 - I think that is the worst tube for audio ... Greetings Dinkers

Thank you Dinkers for your cooperation.