Phono pre, valve or jfet

lndm · 7th March 2006, 05:43 AM

I have spent many hours reducing noise in my phono pre. I use a 12au7 for the first stage as it is supposed to be low in microphonics.

My amp is now quiet but I know I could reduce noise much further if I opted for a jfet. Would anyone recommend this?

SY · 7th March 2006, 10:33 AM

Why not split the difference and use a cascode input stage, jFET on the bottom, tube on the top? I use an NTE458/E88CC combo, but the Toshiba 2SK147 is a popular choice. Very, very quiet.

lndm · 7th March 2006, 11:22 AM

Very interesting. What sort of current/supply rail could I use?

SY · 7th March 2006, 11:29 AM

I used a 200V regulated supply. There are a lot of other options. Allen Wright has some good examples at his Vacuum State site and in his Preamp Cookbook. I've done things rather differently, but Allen's approach has the considerable virtue of being documented.

lndm · 7th March 2006, 11:37 AM

Excellent. I'll go to allens site and do some research. After all, thats part of the fun of DIY

.

Thanks.

Mikewong · 4th April 2006, 10:58 AM

Quote:

Originally posted by SY
Why not split the difference and use a cascode input stage, jFET on the bottom, tube on the top? I use an NTE458/E88CC combo, but the Toshiba 2SK147 is a popular choice. Very, very quiet.

SY,
Do you have the actual schematic?
I saw one from 'borbelyaudio' published in Costruire Hi-Fi some times
ago.

SY · 4th April 2006, 11:25 AM

I built that preamp back in the early 1980s, so the schematic doesn't exist in digital form. I'll see if I can sketch something up. Basically, it's single-ended, the tube has a 180V rail, 45k plate resistor, a 6.9V reference sent to the grid, no resistor between the cathode and the FET drain, and a small source resistor (100 ohm). FETs were selected in-circuit (a lot of tedious plugging in and out).

AW's use of the FET/tube in CC differential is a better approach, I think.

pixpop · 4th April 2006, 02:11 PM

I just finished building a Pearl, which has 4 parallel JFETs on the input. The sound is very beautiful, and very quiet. MM only though. Pass has a different phono stage for MC carts.

7th March 2006, 05:43 AM	#1
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Phono pre, valve or jfet I have spent many hours reducing noise in my phono pre. I use a 12au7 for the first stage as it is supposed to be low in microphonics. My amp is now quiet but I know I could reduce noise much further if I opted for a jfet. Would anyone recommend this?

7th March 2006, 10:33 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Why not split the difference and use a cascode input stage, jFET on the bottom, tube on the top? I use an NTE458/E88CC combo, but the Toshiba 2SK147 is a popular choice. Very, very quiet. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

7th March 2006, 11:29 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	I used a 200V regulated supply. There are a lot of other options. Allen Wright has some good examples at his Vacuum State site and in his Preamp Cookbook. I've done things rather differently, but Allen's approach has the considerable virtue of being documented. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

4th April 2006, 11:25 AM	#7
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	I built that preamp back in the early 1980s, so the schematic doesn't exist in digital form. I'll see if I can sketch something up. Basically, it's single-ended, the tube has a 180V rail, 45k plate resistor, a 6.9V reference sent to the grid, no resistor between the cathode and the FET drain, and a small source resistor (100 ohm). FETs were selected in-circuit (a lot of tedious plugging in and out). AW's use of the FET/tube in CC differential is a better approach, I think. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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7th March 2006, 11:22 AM	#3
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Very interesting. What sort of current/supply rail could I use?

7th March 2006, 11:37 AM	#5
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Excellent. I'll go to allens site and do some research. After all, thats part of the fun of DIY . Thanks.

4th April 2006, 02:11 PM	#8
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	I just finished building a Pearl, which has 4 parallel JFETs on the input. The sound is very beautiful, and very quiet. MM only though. Pass has a different phono stage for MC carts.

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