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Want help - RCA Tube Manual RIAA Phono Stage

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brucetassin

Member
Joined 2005
Both boards have been stuffed, and tested. They work to my satisfaction.
I have learned from this effort. I replaced some caps as was suggested.
Next project is to build a stereo version of the RH-84 power amp to run
the pre-amp into. I have a PC board for that project also.
Thanks to all who helped.
 

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levelfive

Member
Joined 2008
tweaked RCA setup

Eli Duttman said:
Look at the tweaked RCA setup, with its source follower buffer that can drive a load.
Click to expand...

Hi, Eli
Thanks for sharing!
Here are 3 ground symbols drawn, I hope only one is chassis connected?
What reason is to increase caps values (from 20uF to 30uF)?

+ And why at output two capacitors (0.47 + 5uF) are used? One is ever better (for sound) as two in parallel...
 
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academia50

academia50

Member
Joined 2013
Kevin and Bruce :

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



http://www.diyaudio.com/forums/solid-state/227952-preamp-mc-intosh-ma-6100-diy.html




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 Eli´s with MOSFET, or perhaps would saturate the excessive gain entry .........?

An externally hosted image should be here but it was not working when we last tested it.

Uploaded with ImageShack.us



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 !

Rolando
 
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roline

roline

Member
Joined 2010
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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Jeff Yourison

Member
Joined 2004
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.

Jeff
 
rongon

rongon

Member
Joined 2009
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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Eli Duttman

Member
Joined 2004
PS - Eli's version looks really slick.
Click to expand...

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).
 
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