It's the only well-documented phono-pre DIY project that I know of (please correct me if I'm wrong), but - unfortunately - it does not work. If you compare the schematics with the board layout, you'll notice that ALMOST EVERY electrolytic is oriented wrong. Coincidence, or a deliberate sabotage?
I've built it, and I'm in the process of debugging. Even with the correct orientation of all electrolytics that need to be reoriented, this thing only works as a low-frequency oscillator. I'll tinker with it a bit more, see if I could find some more errors.
Yes, sorry, there was at one time a layout with supply regulators included, and that had a serious error. I removed links to that some time ago. The current layout shown at BUILDING THE MJR Phono Pre-amp Board Layout only has 5 electrolytics but somehow I still got one of those wrong, so sorry again. I will correct that diagram today. My only excuse is old age and a deteriorating brain. Regards, Mike.
That would be great If you correct it, I'll build it and therefore (hopefully) verify it. Again, it's a great project that promises a lot - well documented, relatively easy and cheap to build and well thought. It would be a shame if it wouldn't be in a ready-to-build state...
Thanks Rocket Roll, I've corrected the diagram, but I'm puzzled why you say 'ALMOST EVERY electrolytic is oriented wrong' which is why I thought you must be using an older layout with regulators included, which actually had the wrong supply polarity, so would have damaged almost everything. The current layout had only one reversed capacitor. Let me know if you find any more problems.
Yes, I have been using it - I've had the boards made a year or more ago, actually, and never had the time to start the assembly. But eventually I did, and at first I soldered everything and fired it up without checking... All sorts of wrong things started happening - capacitors exploding, motorboating, etc...
But I had the new boards made, and the result is in the attachment.
Worked from the start. I haven't made any audio measurements, but I did a check the voltages. Vr1 sets the Vx voltage perfectly, down to 0,00V, but that voltage tends to creep up with the passing of time (mind you, during that test the preamp wasn't connected to the amp or to the turntable). After some time, I've made the final adjustments, only to find after a cooldown period, Vx had creeped up to 0,50V. So I've adjusted it again and made a listening test. It sounds great, and that's the bottom line
So far my preamp has played for an hour or two and I love the sound. Coming from the cheaper, integrated phono system, this is a huge improvement. A lot of bass, a lot of pleasant highs... Thank you very much!
Thanks again Rocket Roll, I'm happy to hear it turned out well. The value of Vx is not at all critical, 0.5V is no problem, and some drift is normal as the input jfet changes temperature in use. Even 2 or 3V should have no serious effect. I'm glad to hear you like the sound. I like it also, but my hearing is another deterioration with age, so it's good to have a second opinion.
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