The moving-magnet Supra 2.0, especially the one with LT1028's, is an ultrahigh current noise design made by people who don't understand a damn about noise optimization. Replace the LT1028's with low-noise FET op-amps and it becomes a very decent design.
I pointed that out to Elektor right after they published it (but more politely phrased). They even replied that they would publish my comment, but they never did.
I pointed that out to Elektor right after they published it (but more politely phrased). They even replied that they would publish my comment, but they never did.
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Hi all,
Some time ago I also decided to make a Supra 2.0. I had some problems getting this phono preamp up and running. The problem was the LT1028M, not the AM, as the pcb uses a smd package. I had a high DC voltage at the Op Amp output of about 8-12V. The same problem was when I used an AD797B. At that time I didn't use the DC voltage control on the input of the amplifier because I forgot about these elements while making an order in Mouser, even making a short to ground didn't help. After analysis, I found that Op Amp JFETs would work better here because the source (MM cartridge) is 1kohm and the advantages of LT1028, AD797 are not used here. I used ADA4627-1 and all the problems disappeared.
Some time ago I also decided to make a Supra 2.0. I had some problems getting this phono preamp up and running. The problem was the LT1028M, not the AM, as the pcb uses a smd package. I had a high DC voltage at the Op Amp output of about 8-12V. The same problem was when I used an AD797B. At that time I didn't use the DC voltage control on the input of the amplifier because I forgot about these elements while making an order in Mouser, even making a short to ground didn't help. After analysis, I found that Op Amp JFETs would work better here because the source (MM cartridge) is 1kohm and the advantages of LT1028, AD797 are not used here. I used ADA4627-1 and all the problems disappeared.
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Because of its huge inductance, a moving-magnet cartridge is effectively a lot more than 1 kohm. See "Noise and moving-magnet cartridges", Electronics World October 2003, pages 38...43, https://worldradiohistory.com/UK/Wireless-World/00s/Electronics-World-2003-10-S-OCR.pdf Mind you, Electronics World drew one of the sections of the gain switch in the wrong state in figure 5 and I mixed up the terms spectral density and power spectral density.
ADA4627-1 is an excellent choice if you can get it to fit on the PCB. The thread starter's PCB seems to use DIP packages.
ADA4627-1 is an excellent choice if you can get it to fit on the PCB. The thread starter's PCB seems to use DIP packages.
If anyone is interested in my PCB version, I have 3 more pieces, I can send them after covering the shipping costs. When I ordered a PCB board, the minimum quantity was 5 pieces and now the rest of the PCB boards are left. All my documentation is on EasyEDA and I can share it. I think I still have 22nF 1% Wima capacitors, I don't remember the name of the series, but they are for audio.
