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Old 1st August 2008, 09:50 AM   #61
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Quote:
Originally #50 posted by SY
R7 may not be needed. I've seen resistors used in that position to prevent oscillation, so perhaps that was the original function?

R6 adds noise, indeed, but this is a MM preamp, so compared with the equivalent noise resistance of the cartridge... say, wasn't that YOUR argument?
Hello,
the problem isn't that R6 "adds" noise ...

Does anyone know why there is a cascode stage at the input?

The attachment shows the "original" schematic

Kind regards,
Darius
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File Type: zip riaa_funkschau_1964_cascode.zip (28.0 KB, 76 views)
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Old 1st August 2008, 09:57 AM   #62
SY is offline SY  United States
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Quote:
what about the noise caused by R6 ?
Quote:
the problem isn't that R6 "adds" noise ...
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Old 1st August 2008, 01:48 PM   #63
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Quote:
Originally posted by SY



?
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Old 1st August 2008, 03:17 PM   #64
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both quotes are yours and somewhat contradictory. I think that's what Stuart tried to point out.
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Old 1st August 2008, 03:42 PM   #65
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Quote:
Originally posted by dikarner
both quotes are yours and somewhat contradictory. I think that's what Stuart tried to point out.
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Old 1st August 2008, 05:49 PM   #66
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Quote:
Originally posted by dikarner
Then I'm also waiting for oshifis to return and share his insights on the sonical improvements since using these resistors.
Sorry, I was away. I think the contribution of resistors to sonic quality is proportional to their voltage coefficient and to their noise at the particular position. But the major factor is the ratio of output voltage change per resistor value change (i.e. sensitivity). In other words, the larger is the change of the output voltage per resistor value change, the bigger is its influence to the sound. It also depends on whether they are connected to a high impedance or to a low impedance point. This is my theory, not necessarily true.

That said, I think the bigger influence points are R6, R7, then the RIAA resistors R8, R9, R10, and finally R12, R41, R42.

I can imagine a test where the resistors would be changed by 10% one-by-one and the output voltage change would be be precisely measured for each of them. Or use a SPICE simulation in order to determine the sensitivity of the output voltage to each resistor value change. Edit: where the resistance change is caused by the AC voltage on the resistor. The one causing the largest change has the most influence to the sound, and using an audio grade resistor is validated at that position.
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Old 4th August 2008, 01:07 PM   #67
oshifis is offline oshifis  Hungary
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One more thing: you don't need 0.01% tolerance. 1% should be fine. If the prices are prohibitive, consider Mills MRA-5 or MRA-12 wirewound resistors. Low inductance, low noise, audio quality, and relatively small size for the power. They were around 6 Euros over here.
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Old 4th August 2008, 06:33 PM   #68
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I actually decided to go for the VARs (TX2575) - in some places the less expensive variety TX2352 from www.texascomponents.com
I am increasing the size of the coupling Cap(s) to around 180n get away with smaller gird resistors (100K is MUCH cheaper the 400K).
The Mills seem to be a good choice for the Anode-resistors which should be able to handle at a minumum 2 Watt.
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