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Old 22nd February 2013, 05:04 PM   #1121
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What's the output voltage of your Audioquest Onyx LOMC? I suspect can be enough with your 1:10 SUT & Itch.
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Old 22nd February 2013, 05:26 PM   #1122
Salas is offline Salas  Greece
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Quote:
Originally Posted by cygnus x1 View Post
I'm using an Audioquest Onyx LOMC, and currently running it through a set of vintage Shure SUT 1:10 (which I like a lot). Arm is a Sumiko Premier MMT on a modified VPI HW 19 MKIII w/outboard motor. So far I have been happy with a Siren Song, SB cascode 12AY7, and a Salas NJFet RIAA w/SSHV reg (thanks Salas for the great designs). Both the Siren Song and NJFet are really quiet.
The Itch along the 1:10 SUT should suffice for gain even if your cart is 0.2mV to 0.3mV. Already having a line preamp with some gain presumed.
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Old 22nd February 2013, 05:29 PM   #1123
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My cart is 0.25mV togheter my SUT is 1:6 are enough for Itch.
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Old 22nd February 2013, 06:00 PM   #1124
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I had a hard time finding any info on it. All I know it is close to a Audioquest AQB100MH, which is listed as 1.6mv (was built by Scantech and rebranded and labeled for the US). I do think that the rated output is correct for the Onyx. It's no more that 2mv. Yes I do have a line stage, a 26 5:1 xfmr coupled.
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Old 22nd February 2013, 06:07 PM   #1125
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You will see how it best matches when you will have it built then.
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Old 22nd February 2013, 06:07 PM   #1126
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I didn't find any info of your cart, AQB100MH have load impedance 47K is the same like your Onix?
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Old 24th February 2013, 05:12 PM   #1127
RCruz is offline RCruz  Switzerland
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Hi Salas

I am now studying the Itch and allready have some basic questions:

In the first stage you use a rather highish plate resistor for the lower triode (R2 = 82k) and I believe you do so because you do not need a large voltage swing on the output of that mu stage.

Anyway, the dynamic impedance of that resistor should be around R2 / (1 - Avcf)

What value should I consider for Avcf (Voltage gain of the CF on top?)

Around 0.9 ?
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Old 24th February 2013, 05:16 PM   #1128
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Second question:
I see you ground V1 V2 filament heater supply but you bias V3 V4 filament supply at half B+... why ?
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Old 24th February 2013, 05:18 PM   #1129
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I think so, that's the way I have it loaded through my SUT.
BTW, I did a search through all my schematics I've archived over the years, and found a very similar circuit to the itch. I was by the late great N. Shishido, published in MJ mag in the 80's and later republished in Sound Practices. Dual 6DJ8 with a passive Tango LCR riaa between stages and 1:10/20/40 Tango SUT input. The 6N1p input and the SSHV should really make this itch circuit sing (very clever Salas).
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File Type: bmp Shishido LCR Phono.bmp (163.6 KB, 65 views)
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Old 24th February 2013, 05:41 PM   #1130
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What you may learn...Shishido had done alike is pretty nice. I would never use same amount gain stages, the BGs, the high bias commanded for driving the LCR, and the stoppers though. I am confident the Itch is 10dB better for noise by implementing the head amp concept and possibly has more accurate EQ.
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