6SL7 Phono Preamp

denny9167 · 25th January 2008, 11:57 AM

I have several 6SL7's on hand,and want to build a phono preamp,I have posted a link below of a schematic that I like,it's simple,and strait forward,what modifications would need to be made,ex: plate resistors,RIAA curcuitry. Thanks

http://www.bonavolta.ch/hobby/en/audio/dyn_pas2.htm

tubewade · 25th January 2008, 12:30 PM

Hi Denny,

You and I have been thinking along the same lines. As I have researched this subject I have found that higher mu valves like the 6SL7 and 12AX7, especially used in such a simple circuit, do not lend themselves that well to this function. The input capacitance due to miller effect is very high and causes loading of the cartridge which cause a rollercoaster frequency response with many if not most cartridges. Furthermore, with no buffer on the output the amp is only capable of driving high impedance loads, 250k ohms or higher. The best circuit I've found that is basically like the one you are considering is here..

http://www.geocities.com/TimesSquare/1965/phono.html

Best, I say, based on theory and principle rather than on listening tests, though. I have not built that amp yet.

There is a thread with some interesting discussion and some great input from very experienced builders about this very thing here...

Best Sounding Phono Input Tube

Best regards to you,

Wade

25th January 2008, 11:57 AM	#1
denny9167 diyAudio Member Join Date: Nov 2007	6SL7 Phono Preamp I have several 6SL7's on hand,and want to build a phono preamp,I have posted a link below of a schematic that I like,it's simple,and strait forward,what modifications would need to be made,ex: plate resistors,RIAA curcuitry. Thanks http://www.bonavolta.ch/hobby/en/audio/dyn_pas2.htm

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25th January 2008, 12:30 PM	#2
tubewade diyAudio Member Join Date: Jun 2007	Hi Denny, You and I have been thinking along the same lines. As I have researched this subject I have found that higher mu valves like the 6SL7 and 12AX7, especially used in such a simple circuit, do not lend themselves that well to this function. The input capacitance due to miller effect is very high and causes loading of the cartridge which cause a rollercoaster frequency response with many if not most cartridges. Furthermore, with no buffer on the output the amp is only capable of driving high impedance loads, 250k ohms or higher. The best circuit I've found that is basically like the one you are considering is here.. http://www.geocities.com/TimesSquare/1965/phono.html Best, I say, based on theory and principle rather than on listening tests, though. I have not built that amp yet. There is a thread with some interesting discussion and some great input from very experienced builders about this very thing here... Best Sounding Phono Input Tube Best regards to you, Wade

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