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Old 27th October 2010, 09:11 PM   #5111
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Quote:
Are your parts having the description ''GR'' on them?
Yes, they are K170 GR 8K.
Thanks Salas, punctual as ever!!!
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Old 27th October 2010, 09:27 PM   #5112
Salas is online now Salas  Greece
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Just remind me your cartridge and I will see what we can do with them. Did you fix your Bench tube phono?
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Old 27th October 2010, 09:52 PM   #5113
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Wow Salas, you're so sharp!! I fixed the Steve Bench but haven't inserted the fet source follower. Just increasing the output cap to .68uF I got a marked improvement in bass and I like the sound as it is: full, detailed and a slight increase in soundstage and depth.

The cartridge I use is the Nagaoka MP-20 on a 301. However, talking of cartridges I was tempted by the discussion of various TT/cart combos on this thread to try a Sansui SR-22 with a Grado FT+ (bought in the 80s) and the sound is excellent too - which I describe as sweet, though not lacking in punch. I know you recommend the Grado Black, so maybe I'm biased, but to me the combo is a challenger to 301/Nagaoka.

I have already populated the riaa boards with components except the FETs and large capacitors, so I wouldn't like to make drastic changes. I'm building the 36dB gain version which I think is enough for my MM cart needs. Don't you think so?

BTW you haven't said anything else about the GR designation on the fets. I'm curious. Bought them from a UK supplier.

JA
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Old 27th October 2010, 10:06 PM   #5114
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BTW, forgot to tell you I ordered a matched quad SK170 from Spencer on this Forum anyway, thinking I would use them in the gain stages of your NJFET RIAA. They are even cheaper than the ones I bought from UK. I asked him to match them 7-8mA as per your circuit note. Now I'm worried the ones I have (GR) are way out to be used in the buffer and Zener CCS position.

Regards.
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Old 27th October 2010, 10:14 PM   #5115
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The 36dB is fine for those carts. Keeps gain adequate and noise too. GR are the ''green'' lower Idss Toshiba selection. They have GReen, BLue, Violet. Increasing Idss range. By having the boards populated, I have to look in to the 36dB and see if we can tweak some resistor values for the buffer output only so to fit the GRs there. You said you got 10pcs, so we can spare a couple to make it constant current like B1. I will be back with it very soon. No Zener, you will use resistor in the reg voltage reference, and leds in the phono. Nice you got your SB from Kof's thread up n' running again.
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Old 27th October 2010, 10:23 PM   #5116
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Thanks Salas, no particular hurry as I still have to make the Shunt regulator from scratch. Yes, of all the phono preamps I made or have, I like the Steve Bench phono best. I got interested in this because it is not a complex circuit, a pcb has already been posted and is cheap enough to tackle it just for fun, sort of.
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Old 27th October 2010, 10:27 PM   #5117
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Just to be sure, what you make is from PSGR's PDF? So I know what to look for the tweak.
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Old 28th October 2010, 06:36 AM   #5118
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OK, here we go. Use your GRs for 1st and 2nd stage, also in the reg, and put the matched BL in the 2 buffer Jfets positions. More mA for output. The slightly lesser in Idss from each pair will be Q4. For Q1 and Q3 use your best 2 pairs of GR near in Idss per position per channel. Use a 10K trimmer in the reg instead of a Zener, wired as your phono input trimmer. I saw that 38dB is better for 4mV cart like the Nagaoka, 36dB is better for 5mV carts. With such low gain and low R2 your noise at output will be negligible. Turn the input trimmer load for finding your best preferred tonality. Good luck.
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Old 28th October 2010, 08:37 AM   #5119
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Quote:
Use a 10K trimmer in the reg instead of a Zener, wired as your phono input trimmer. I saw that 38dB is better for 4mV cart like the Nagaoka, 36dB is better for 5mV carts. With such low gain and low R2 your noise at output will be negligible. Turn the input trimmer load for finding your best preferred tonality. Good luck.
Thanks Salas. Im not sure I understand you correctly when you talk about the trimmer. Are we saying well have two trimmers:

a) 100K trimmer across the cartridge input (replacing the input resistor (47K) and capacitor (~ 100 pf));
and
b) a 10K trimmer in the regulator instead of the Zener. Here, are you referring to the 20-22V Zener between the Source of the IRFP9240 and Drain of the SK170 in your Shunt Regulator?

Regards,
JA
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Old 28th October 2010, 09:05 AM   #5120
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a) Yes. Its in the one I posted above as for variable input load. Replacing. Influences your cart's response much, tunes easily.

b) Yes. Do the attached schematic. W1,W2 sense wires that meet W3,W4 main current force wires at the DCin,GND same points on the phono (remote load). All Leds red BTW.
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