Some Musings on a MC Preamp Stage - Page 2 - diyAudio
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Old 6th January 2012, 09:11 AM   #11
h_a is offline h_a  Europe
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Hi wrenchone,

I only had a rough look at circuit #1, but I love your circuits They may have their practical drawbacks (a helper CCS, additional negative rail), but are refreshingly different.

I hope you'll build a prototype and present a full phono stage at some point.

Hannes
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Old 29th August 2014, 07:59 PM   #12
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This thread may start to wake up again, as I just bought my first LOMC cartridge.
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Old 31st August 2014, 09:33 PM   #13
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This MC input stage looks promising - it's a variant of the Pass Pearl. The difference is that this one allows a gain of 200X in one go, taking the place of the normal first stage of a passively equalized phono preamp. After the EQ, a gain of 30 stage would follow. FYI, that also was the purpose of the circuits previously shown here. I like this one better than some of the earlier offerings, as the high order harmonic content is pushed down more.

I may try this one with my new low output MC cartridge (once I get it set up). With some tweaking, this one might also work well using the BF862 instead of the 2SK170. In that case, I may need a drain resistor on each of the BF862s to prevent them from singing to each other...
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Old 31st August 2014, 10:20 PM   #14
sreten is offline sreten  United Kingdom
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Hi,

MC stepup design is dominated by noise considerations
not distortion usually, and usually its linear as an input
into a MM stage, for practical commercial success.

However with DIY you can build it as a complete RIAA
stage or replace the first stage of a 2 stage MM circuit.

YMMV but I equate low noise and impedance with BJT's.

rgds, sreten.
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Old 31st August 2014, 10:29 PM   #15
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I'm gunning for both low noise and low distortion, especially as I'm going for a lot of gain with one stage. This probably won't be as low noise as a BJT stage, but the biasing is less problematic, and I'm getting all this with a single-ended stage, compatible with my current setup. My cartridge (in the mail) is good for 0.4 mV, so I could probably tone down the gain on this stage (100X instead of 200X).

Since I have a lot of experimental MM preamps floating around from previous efforts, I'll likely try one of the step-up transformers I have first, and do some mix and match.

Last edited by wrenchone; 31st August 2014 at 10:35 PM.
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Old 2nd September 2014, 07:42 AM   #16
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I'm looking at something similar to this for the output stage. Gain is 30X, and as can be seen, the distortion is pretty low driven for 900mV output. I may or may not include the input cascode - the circuit is easier to compensate without it.

This stage is non-inverting, so I'll have to reverse the cartridge leads to make all my inputs have the same phase since the input stage is inverting.
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Old 14th September 2014, 02:34 AM   #17
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I've laid out a preamp for use when I finally have a stable TT setup, using versions of the gain cells shown in posts 13 and 16. I decided on a passive RIAA network between stages using 100nF and 34 nF. Caps are 100nF K-71 Russian polystyrene and 33nF Roederstein 1840 series + 1nF Roederstein 1830 series polypropylene caps.
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Old 14th September 2014, 11:48 PM   #18
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For a rainy day - a day when it's raining MC cartridges (though to be honest, just one would suffice).
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Old 15th September 2014, 03:15 AM   #19
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I may populate this amp with BF862s on little self-ginned surf boards with integral stopper resistor as a tip o' the hat to what seems to be the future, even though I have enough 2SK170s to get this SOB going if I was to insist on through -hole purity.
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