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Old 28th January 2013, 12:07 AM   #31
kevinkr is offline kevinkr  United States
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If you are going to build the RCA based circuit please have a look at Eli's posts here about a much improved and revised version of the RCA circuit - it will perform a lot better in the real world than the original tube handbook version does.
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Old 28th January 2013, 01:49 AM   #32
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I built one. It was a good experience. See post #21 and #22. If I were to do it over I would build Eli's modified version. If you want to do a PC board version, I will let you use my PC board design. Just let me know if you want it.
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Old 28th January 2013, 03:47 PM   #33
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Kevin and Bruce :

Thanks to both. Currently I am doomed to preamplifier phono SS project, because I want to be controlled tones.


I thought if I am not satisfied with the result but make this design RCA appending the tone control section.
I think there would be disadvantages in using the same above the project of Elis with MOSFET, or perhaps would saturate the excessive gain entry .........?

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Well, anyway, is the next project .....

Bruce :

I think it's time I will have to do the design and tones pre assembled on a single board, thanks anyway. I have done much work. Congratulations again.

Regards !


Last edited by academia50; 28th January 2013 at 03:50 PM.
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Old 28th January 2013, 04:31 PM   #34
roline is offline roline  United States
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I ended up with a smooth plate Ei ECC83 on the first stage of my RIAA amp. I also tried 12BZ7 and 7025. for gain at 100.
I did the groovewatt clone....., toner transfer,
I used a 7062 for a cathode follower for lower output impedance...
SO what is the lowest noise 12AX7 version that is affordable?
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SO many tubes, SO little time!!!
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Old 28th January 2013, 05:41 PM   #35
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roline: I have built Eli's modified circuit and use Sovtek 12AX7-LPS and the Mullard re-issue 12Ax7, both purchased from Jim McShane. Both are quiet, perhaps the Sovtek moreso. I've also tried a couple of random RCA black plates and 12AX7WA gray plates pulled out of other equipment that yielded good results at mid volumes. These last are not too microphonic, but they are not as quiet noise-wise as the first two when you put your ear up close to the speaker.

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Old 29th January 2013, 12:48 AM   #36
rongon is offline rongon  United States
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Years ago, Handmade Electronics in Pennsylvania used to sell a circuit board for the RCA RIAA preamp. I took that, stuffed it, and direct-coupled its output to a 12AT7 (ECC81) cathode follower. My brother wound up with it, and I heard it once, driving his Van Alstine solid-state power amp and a pair of B&W bookshelf speakers. It sounded very good, sort of warm, but not excessively rolled-off in the highs. It just sounded like a nice tube phone stage. Nothing amazing, but very pleasant. FWIW...

Somebody mentioned using a 12BZ7 in place of a 12AX7. Don't do it. The 12BZ7 is a far less linear device. It also has a far lower rp, so will probably change the RIAA EQ. I don't know how drastically, would need to be figured out.


PS - Eli's version looks really slick.
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Old 29th January 2013, 02:54 AM   #37
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PS - Eli's version looks really slick.
Rongon, thank you! The RCA design is fundamentally sound. I shored up a couple of weaknesses. The DC coupled source follower deals with lack of drive capability. A well selected enhancement mode MOSFET "rules" at this buffering job, for several reasons. Even the wimpy 'X7 triode has no problem with the tiny capacitances of the ZVN0545A. Grid leak biasing the 2nd gain block lightly loads the EQ network, which leads to improved bass extension.

As Jeff Yourison said, the Sovtek 12AX7LPS is a terrific choice for RCA phono preamps. The 'LPS is quiet and very well balanced, top to bottom. I'd give it a tumble in the preamp your brother got from you. The "icing on the cake" is the low cost of the 12AX7LPS. Jim McShane charges $29.50 for a PROPERLY matched pair. If top end energy is really lacking, ask Jim to cull a quiet pair of "reissue" TungSol 12AX7s out. That variant has some of the "chime" associated with NJ made NOS (RCA & TungSol).
Eli D.
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Old 21st March 2014, 10:33 PM   #38
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Im happy to find this thread. Normally i did not use pcb for my little self made electronics, but in this case it would be great. Maybe ill use the shown layout of the thread starter, without modification :-). It has to work on a stereo ECL 11 Tube Amp.
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Old 21st February 2015, 01:15 PM   #39
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My congratulations, great project!
But what about the power supply?
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Old 21st February 2015, 10:16 PM   #40
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But what about the power supply?
Contact member Jeff Yourison for the schematic of low cost, high performance, PSU.
Eli D.
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