Single stage preamp

bigwill · 25th January 2008, 05:11 PM

Quick question - I just ordered the bits required to make a Gary Pimm battery biased CCS, and I was wondering if it's possible to simply use a CCS loaded 6SN7 as a single stage preamp - each half as a channel. Would this arrangement work and be able to drive cables / input stages?

SY · 25th January 2008, 05:34 PM

It depends on the cables and the load. Assuming there's no cathode degeneration in the 6SN7 circuit, the source impedance will equal plate resistance. For usual operating conditions, that will be between 7-10k. That's pretty high. If your power amp has a high input impedance (more than 100k) and the cables are short, you can probably get away with it.

If there is cathode degeneration, that makes things worse; the effective plate resistance will be increased by a factor of 21 times the unbypassed cathode resistance.

bigwill · 25th January 2008, 05:42 PM

I see. I sort of got it into my head it would be able to swing roughly the bias current into the load if needed - if only things were that simple. I guess I'll be using a cathode follower!

dsavitsk · 25th January 2008, 06:14 PM

Or you could just choose a more appropriate tube for the job. Same topology, but with a 5687, will give you roughly the same gain and a Z out of about 2 to 2K5. A 12B4 will give you less gain (which might be a good thing) and an even lower Z out.

bigwill · 25th January 2008, 06:19 PM

Oh neat, it's possible - are there any suitable octals that would also work?

DougL · 25th January 2008, 06:31 PM

6H30 Octal

bigwill · 25th January 2008, 06:43 PM

Hmm, the 6H30 does look awesome but it seems expensive!

ray_moth · 25th January 2008, 06:49 PM

Maybe a mu-follower would be better for your needs? It would use both halves of the 6SN7 (or other double triode), would give practically the same linear performace and gain as a CCS load and would have the low OP impedance of a cathode follower.

The biggest advantage, though, is that you wouldn't need to use the Gary Pimm CCS, so you could save it for another project.

bigwill · 25th January 2008, 06:59 PM

Quote:

Originally posted by ray_moth
Maybe a mu-follower would be better for your needs? It would use both halves of the 6SN7 (or other double triode), would give practically the same linear performace and gain as a CCS load and would have the low OP impedance of a cathode follower.

The biggest advantage, though, is that you wouldn't need to use the Gary Pimm CCS, so you could save it for another project.

Sounds like a good idea to me!

bigwill · 25th January 2008, 07:09 PM

Hold on - If I use the mu-output of Gary Pimm's battery CCS won't that basically achieve the same thing?

25th January 2008, 05:11 PM	#1
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Single stage preamp Quick question - I just ordered the bits required to make a Gary Pimm battery biased CCS, and I was wondering if it's possible to simply use a CCS loaded 6SN7 as a single stage preamp - each half as a channel. Would this arrangement work and be able to drive cables / input stages?

25th January 2008, 05:34 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	It depends on the cables and the load. Assuming there's no cathode degeneration in the 6SN7 circuit, the source impedance will equal plate resistance. For usual operating conditions, that will be between 7-10k. That's pretty high. If your power amp has a high input impedance (more than 100k) and the cables are short, you can probably get away with it. If there is cathode degeneration, that makes things worse; the effective plate resistance will be increased by a factor of 21 times the unbypassed cathode resistance. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

25th January 2008, 06:14 PM	#4
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	Or you could just choose a more appropriate tube for the job. Same topology, but with a 5687, will give you roughly the same gain and a Z out of about 2 to 2K5. A 12B4 will give you less gain (which might be a good thing) and an even lower Z out. __________________ http://www.ecpaudio.com

25th January 2008, 06:31 PM	#6
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 25	6H30 Octal __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

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25th January 2008, 05:42 PM	#3
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	I see. I sort of got it into my head it would be able to swing roughly the bias current into the load if needed - if only things were that simple. I guess I'll be using a cathode follower!

25th January 2008, 06:19 PM	#5
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Oh neat, it's possible - are there any suitable octals that would also work?

25th January 2008, 06:43 PM	#7
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Hmm, the 6H30 does look awesome but it seems expensive!

25th January 2008, 06:49 PM	#8
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	Maybe a mu-follower would be better for your needs? It would use both halves of the 6SN7 (or other double triode), would give practically the same linear performace and gain as a CCS load and would have the low OP impedance of a cathode follower. The biggest advantage, though, is that you wouldn't need to use the Gary Pimm CCS, so you could save it for another project.

25th January 2008, 07:09 PM	#10
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Hold on - If I use the mu-output of Gary Pimm's battery CCS won't that basically achieve the same thing?

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