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In Reply to: RE: Tube phono preamp DIY suggestions posted by fredtr on November 30, 2015 at 14:44:42
Stephen Robinson in the UK has a great sounding phono design using a D3a and half a 5687 for each channel. The development process is described on his website (see link). Later versions are not necessarily better than early ones though. In particular I would recommend starting with the audio circuit shown as his Mk.15, and you can simplify that by using an output coupling cap instead of the transformer. I started with a version similar to the Mk. 15 some 6 or 7 years ago, and while it's gone through a lot of changes since then I still use a variation of it today. Even the earliest version sounded better than the Artemis PH-1 I was using at the time.
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Thank-you for posting. The description says MC, I have MM cartridge, did I miss something? Is it configurable or switchable MM and MC?
Just leave out the MC stepup transformer (TX 103) and you have a MM phono preamp. In my case, I use an outboard stepup transformer so the preamp itself is MM.
The circuit use battery for grid bias, without the transformer DC will appear at the cartridge, a blocking cap is required.
Or move the battery in series with the grid. No cap needed.
The Artemis PH-1 used battery bias that way---in series with the grid of the input tube (6DJ8).
That's excellent, thank-you. It looks like we both have Shure M65 like preamps, can you compare the sound to that, or maybe some other phono stage preamps? Another preamp I am considering is the World Designs (WAD) phono 3. If you are familiar with it, any comments?
The D3a/5687 is in a different league than the Shure M65. Even a scratch-built M65 like mine which uses pretty much cost-no-object parts has less detail and a smaller soundstage than the D3a/5687. Plus any 12AX7 based phono has noise issues. The SR design is very quiet, actually much quieter than any of the solid state phono preamps I have tried in my system. I have even run my 0.35mv output MC directly into the SR and while no longer super-quiet it had a lot less noise than I expected.
Thank-you for the fast response. Your suggestion has my interest. I hate to bother you, I'm not that familiar with the magnetics, would it be possible to post part numbers?
I am not sure what transformers and choke Stephen used in his build, but there is nothing sacred about his selections. I used standard Hammond power transformers and chokes in my preamp, but my power supply is quite different (simplified) compared to Stephen's. The circuit will operate fine with a B+ ranging from 225 to 285 volts. How you build the power supply to get there is pretty much up to each builder.
OK, thank-you for answering. I think I will try this, thanks again for the recommendation.
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