Got it (I think... I’ll have to look closer at your second point). I put a Q3X that measured 4.1mA Idss and could then get above 36Vdc. I reduced it to get 3.5V TP1-TP2. Is the goal to have approximately the same TP1-TP2 voltage?
Other board shunt also fires up fine, but I’ll have to put a higher Idss Q3X in it as well. The only other one I have above 4mA is 5.xmA.
Other board shunt also fires up fine, but I’ll have to put a higher Idss Q3X in it as well. The only other one I have above 4mA is 5.xmA.
I've got another question. I have been enjoying the preamp but have just replaced my second fuse in the last few weeks. These are the ones I am using:
5TT 600-R Bel Fuse Inc. | Circuit Protection | DigiKey
Did I miss something when I was picking this out? I tried to get the one recommended in the PDF. Thanks!
5TT 600-R Bel Fuse Inc. | Circuit Protection | DigiKey
Did I miss something when I was picking this out? I tried to get the one recommended in the PDF. Thanks!
It's a general recommendation. Specific depends on the transformer model. Does it have a published primary current spec?
It says the secondary current is 3.57A but nothing about primary current.
Y236654 is the part number: Transformers and Power Converters From Avel Lindberg, Inc.
Just an update. Board #2 was acting the same as #1 with a 3.5-ish mA Idss Q3X in it. The highest one I had was 5.56mA, so I put that in. Bad move... I was having a hard time getting the shunt voltage into the RIAA stage below 40V. I replaced it with a 3.87mA... much better. Shunt voltage now easily held at 34.5V, which seems to be the sweet spot for easily obtainable 3.6V TP1-TP2.
I haven't built up the raw PSU yet (this week), and once I decide on a final transformer spec for it, I my replace the shunt pots with precision fixed resistors. We'll see.
Might actually have to get my turntable out of storage and listen to it this weekend 🙂
Good progress. But don't replace the trimmers with fixed resistors because you may need to readjust in the future. When you will box it for instance. The input JFETs in MC mode are sensitive to ambient temperature changes.
Got the raw PSU done and got the Antek AS-0532 2x32V transformer.
With 1 ohm RDLInks in, I am getting 41.2Vdc out (at the last 10K resistors) loaded. No problems getting the shunt output to ~34.5Vdc and stable 3.6V on TP1-TP2 with adjustment range remaining on both pots.
I still haven't tried listening to it yet.
With 1 ohm RDLInks in, I am getting 41.2Vdc out (at the last 10K resistors) loaded. No problems getting the shunt output to ~34.5Vdc and stable 3.6V on TP1-TP2 with adjustment range remaining on both pots.
I still haven't tried listening to it yet.
Looks like its electrically correct. Is it configured with 1X2SK369 per channel (MM) or with 2X (MC)?
I compared the Salas Step Up run off of batteries with a 1:16 Shure Mic Transformer I bought for cheap on ebay. MM Stage is Salas folded, Cart is Ortofon Quintet Blue.
I have never used transformers before. And it will take a better transformer than this to beat the jfet step up. The transformer sounded very veiled compared to the jfet step up. I tried different loading on the secondary, always sounded dull in comparison.
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Many people seem to prefer transformers. Can good Cinemag, Lundahl, etc. really be that much better than these Shure transformers?
Anyways, JFET mc pre will stay for now. I will concentrate my efforts on power supply and maybe try the Hiraga BJT mc pre for comparison.