RE: It can, but

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RE: It can, but

Posted by JKT (A) on February 10, 2017 at 11:13:18

In Reply to: RE: It can, but posted by Eric Chan on February 10, 2017 at 03:24:38:

"Second thought is to swap in a 6H6n tube to replace the 6H30, this move may need to change the valuse of 1st stage resistor values because the 1st and 2nd stages are direct coupled"

Without seeing the schematic this is only a guess. If the 1st and 2nd stages are differential and direct coupled check to see if there is a voltage differential between the two grids of the 2nd stage. Any voltage difference there will "eat" into the voltage headroom of the second stage. If this condition were found to be worse at start-up that could explain the problem. If this is the case changing to 6N6Ps would make it worse. At the same plate voltage and bias current the grid bias voltage of the 6N6P is about half that of the 6N30 (less headroom).

I have a fully differential phono pre where the first and second stages are direct coupled. The first stage is a MOSFET/tube cascode with CCS plate loads (very high output impedance). Some of the plate load current source current is shunted to ground across a resistor (part of the RIAA network). This sets the plate voltage of the 1st tube and the grid voltage of the second. Matching this voltage for the two halves is very important. When they are not matched this does result in a hard sounding distortion. The second stage of this preamp is a 6N30 (150Vp/k, 25mA/side). Originally I used a 6N6P. In this application the 6N6P was more prone to brittle sounding highs and harsh transients. Your milage may vary

"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln

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Follow Ups Full Thread

Topic - Would Volt regulator IC contribute harsh sound(IMD) ? - Eric Chan 19:45:30 02/08/17 (14)

RE: Would Volt regulator IC contribute harsh sound(IMD) ? - Michael Samra 15:30:17 02/09/17 (0)

It can, but - Ralph 11:30:50 02/09/17 (7)

RE: It can, but - Eric Chan 03:24:38 02/10/17 (6)

One of the problems with this design - Ralph 11:35:33 02/10/17 (4)

RE: One of the problems with this design - Eric Chan 08:47:58 02/11/17 (2)

RE: One of the problems with this design - Ralph 14:39:41 02/13/17 (0)

RE: One of the problems with this design - JKT 10:44:28 02/11/17 (0)

RE: One of the problems with this design - JKT 12:58:32 02/10/17 (0)

RE: It can, but - JKT 11:13:18 02/10/17 (0)

RE: Would Volt regulator IC contribute harsh sound(IMD) ? - Triode_Kingdom 09:40:47 02/09/17 (1)

RE: Would Volt regulator IC contribute harsh sound(IMD) ? - Eric Chan 03:18:57 02/10/17 (0)

RE: Would Volt regulator IC contribute harsh sound(IMD) ? - Stuben 04:25:49 02/09/17 (1)

RE: Would Volt regulator IC contribute harsh sound(IMD) ? - Stuben 14:12:09 02/09/17 (0)

RE: Would Volt regulator IC contribute harsh sound(IMD) ? - drsx 22:39:54 02/08/17 (0)

Follow Ups

RE: It can, but - JKT 11:13:18 02/10/17 (0)

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