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Old 3rd June 2012, 12:21 AM   #11
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by Salas View Post
Why burning a huge drop? Utilizing an existing Tx reason?
Pass tube requires a minimum of 200V for proper operation, it is a series pass after all. I actually get transformers built to spec for most of my designs. Based on ongoing listening experience I still find I prefer this design sonically to some more recent designs. I have not tried the shunt yet..
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Old 3rd June 2012, 12:21 AM   #12
Salas is offline Salas  Greece
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Quote:
Originally Posted by kevinkr View Post
SY is correct, the noise contribution of that 100 ohm resistor is negligible compared to the noise resistance of the cartridge/transformer combo.
What kind of DCR your SUT secondary has?
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Old 3rd June 2012, 12:25 AM   #13
kevinkr is offline kevinkr  United States
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Quote:
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SPU is extremely low DCR I thought.
My SPU is a Classic GM E II with a DCR of six ohms, primary SUT dcr is 0.4 ohms through a 16X step up transformer so 1638 ohms equivalent noise resistance (16^2 x 6.4 ohms) for the cartridge and SUT primary.

The transformer secondary DCR is 53 ohms, small enough so that the transformed cartridge and primary DCR is the dominant noise source as it should be.

Nominal output with this transformer at 5cm/sec is about 3.2mV..

Cartridge noise is equivalent to 5.26nVrtHz or 0.74uV over 20K BW which calculates to an SNR of almost -73dB referenced to 3.2mV which is several dB beyond what the medium can do under the very best circumstances.. (And more than 10dB better than most good recordings) - the pre-amp is around -80dB (ref 3.2mV)...
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Old 3rd June 2012, 12:26 AM   #14
SY is offline SY  United States
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I hate when I'm off by a factor of ten.

Salas, I think this is for MM, not for the SPU.
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Old 3rd June 2012, 12:37 AM   #15
kevinkr is offline kevinkr  United States
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Quote:
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I hate when I'm off by a factor of ten.

Salas, I think this is for MM, not for the SPU.
No, this is for the SPU with SUT, but not just SPU, works fine with MM and HO MC, it was designed to be pretty compatible with anything, highish overload margin and low input capacitance.. (It's been tested with several other cartridges including a MM)
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Old 3rd June 2012, 12:53 AM   #16
Salas is offline Salas  Greece
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56dB gain I thought of MC input. Many with that gain are classified MC. Including an SUT is another ein calc of course.
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Old 3rd June 2012, 12:59 AM   #17
kevinkr is offline kevinkr  United States
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Quote:
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56dB gain I thought of MC input. Many with that gain are classified MC. Including an SUT is another ein calc of course.
In my system another 20dB - 26dB of gain would be required for an MC, plus I like the noise margins better this way as you can see from the calculations referenced in a previous post. I like my electronics to be as close to silent as possible.
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Old 3rd June 2012, 10:38 AM   #18
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The 6S3P-EV specs show a mu spread of 35-65, which seems rather large. In practice, have you seen that much variation?
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Old 3rd June 2012, 03:50 PM   #19
kevinkr is offline kevinkr  United States
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Actually I haven't, and the 5842 also has a pretty large spread which also has not proved to be an issue in practice. (I have 32 pieces of the 6S3P-EV, but have only looked at 10) I suspect in the case of the 6S3P it depends on what part of the plate curve you operate as well - in this case obviously the range is extremely limited. (And towards the left hand side of the plate curves where mu is pretty consistent)

The two channels are very closely matched (0.1dB) with randomly selected tubes. I was concerned about this issue, but since the tubes are dirt cheap I figured I would just match a bunch if necessary, it hasn't proved to be so far. The interesting thing will be to see how things progress as the tubes age and transconductance falls and grid current possibly increases.

The old D3A/5842 based design this replaced actually had worse channel to channel matching than this one does, at ~0.2dB.
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Old 3rd June 2012, 09:23 PM   #20
kevinkr is offline kevinkr  United States
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Some interesting information on the 6S3P-EV from the Russian Klausmobile site - the comments and the nice looking curves are what intrigued me in the first place about this tube, the bargain prices clinched the deal. This site is worth a good look in general.

Here: Tube Tester Files - 6S3PEV
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