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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hi Performance Pre amp

Greeting fellow DIYers.
After recently acquiring a LOMC cartridge i am using a battery powered head amp before my SRPP preamp .Thanks to Salas for his assistance. The current preamp is the Elektor project from the early 90's.
I thought it might be time to upgrade. I have seen Allen Wrights designs which look quite good. Are there any other high performance designs i should be considering.
I am looking to build both the phono and linestage into a single enclosure.
I am starting with a blank sheet although it would be nice to recycle the HV ( currently 350 & 310V) regulated power supplies from my existing project. The voltage can be lowered but not increased.
I look forward to your suggestions
 
Allen Wright's hybrid cascode allows the use of a LOMC, without a SUT or "head" amp. AW has worked extensively with the 6922. However, that's not the only type that works in a hybrid cascode, with "sand" "downstairs" and a tube "upstairs". The 6GK5, a type I'm impressed by, is an excellent candidate too.

If you truly like your SS head amp, a tweaked version of RCA's "classic" passively equalized design should do nicely. The RCA circuit offers roughly 45 dB. of gain. I've uploaded the tweaked RCA schematic for your consideration.
 

Attachments

  • Full Tweaked RCA Phono Stage.jpg
    Full Tweaked RCA Phono Stage.jpg
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Thanks Eli. Allens RTP3C looks good if not a little complex. It's on my shortlist along with the current akido/steve bench in another thread. I like the concept of the differential mode of the RTP3 as i'm considering to mate it with the KK 300BPP(P).
Has anybody built the RTP 3 or the KK 300b monos ?
 
Thanks Eli. Allens RTP3C looks good if not a little complex. It's on my shortlist along with the current akido/steve bench in another thread. I like the concept of the differential mode of the RTP3 as i'm considering to mate it with the KK 300BPP(P).
Has anybody built the RTP 3 or the KK 300b monos ?

I have a DIY RTP3 which I built from scratch.

I'm not sure what you mean by "KK 300b monos", but I have built Kevin Kennedy's push-pull 300B monoblocks, if that's any use to you...

Alex
 
Hi Craig,

I would definitely recommend the push-pull 300B amp - it sounds great, it has worked flawlessly (apart from a couple of minor problems due to faulty valves) and its differential operation matches my RTP3 well. The only issue with this combination is gain - the RTP3 has a minimum line stage gain of about 10 (3dB), while the 300B amp has a differential gain of 26dB, which is on the borderline of being too high for my 90dB speakers.

No, the layout was entirely my own design, although I did take Kevin's advice to rotate the output transformers to reduce hum. If you decide to build this amp, I would be happy to give you a rough layout plan and a photo or two if that helps.

Alex
 
No, the layout was entirely my own design, although I did take Kevin's advice to rotate the output transformers to reduce hum. If you decide to build this amp, I would be happy to give you a rough layout plan and a photo or two if that helps.
Alex

Hi, Do you mind posting (or e-mailing me) your layout plan? I am especially interested in the correct orientation of the transformers. Are you using the Citation 2 outputs? I have been planning on building this amp for a long time. I think I would use a CF as the driver though as it would have more strength to drive the 300B's.
Thanks again, Daniel
 
, Do you mind posting (or e-mailing me) your layout plan?

Unless you prefer to keep your design confidential, -this can be understood-, I assume that many people on this forum might be interested by working on a preamp able to surpass the AR SP-11...

If you accept to share your knowledge and skematics, we would be happy !:)
 
I won't post any schematics for the KK 300B amp, since the best way to get them is to order Kevin's excellent article from Lulu.com.

I will put together a layout for the major components, which isn't included in the article, and send it to anyone interested. Apologies for not doing this promptly - shortly after I last posted to this thread, I found out that the one I did put together for my own reference wasn't to scale after all, and then kept putting off updating it.

Alex