Unity Gain Tube Buffer

AKSA · 29th December 2003, 06:10 AM

I wish to make a unity gain tube buffer, preferably cascaded two stage, which will handle up to 100Vpp input/output.

To keep input impedance high, it would be better to use feedback injection from the output of the second stage to the cathode of the first stage .

If OLG of the two stages were around 100 (40dB), then a feedback ratio of this size would give vanishingly low Zout and distortion. However, devising an input stage which will handle 100Vpp is no slouch.

My thinking would be that a differential input using medium mu tubes followed by a larger tube running say 15mA for output might be best.

Does anyone have any experience/thoughts on this topology?

Cheers,

Hugh

fdegrove · 29th December 2003, 06:34 AM

Hi,

It's been ages but I once used something similar as you describe using a 6DJ8 cascaded into a 6BX7 to drive a 211....

Details of which must be somewhere at the end of my little tape but it worked nicely.

Cheers,

Sch3mat1c · 29th December 2003, 07:32 AM

Err... wth you need 100V for... in any case... what you need two stages for, this screams CATHODE FOLLOWER.

Tim

Will · 29th December 2003, 07:45 AM

Hi,
I'd be interested if someone can post a schematic on a 6922 tube buffer with constant current source.

AKSA · 29th December 2003, 09:56 AM

Thanks Guys,

Frank, thank you for your thoughts. But a 6DJ8/6BX7 would not handle feedback down to unity gain, I don't believe so anyway.

Tim, no, I don't want a Cathode Follower, because the feedback is local, and I need something with interstage feedback, unless....

Could an anode follower do it? Anyone know how it might be configured with say a 300V B+ to input and output 100V with feedback around the stage?

Of course, this might mean a pentode like the 12GN7, but it might just be possible if it could be configured to avoid input overload. That's the tough one; input overload.

Cheers,

Hugh

Sch3mat1c · 29th December 2003, 10:03 AM

wtf everyone got against local FB anyways

dhaen · 29th December 2003, 10:18 AM

Try English Tim...

fscarpa58 · 29th December 2003, 10:59 AM

why do not try
a 6DJ8 White Follower ?

low distortion, low output impedance
high Vpp

Federico

Sch3mat1c · 29th December 2003, 10:54 PM

Quote:

Originally posted by dhaen
Try English Tim...

No need. Point being a CF is the ideal circuit element to use here, I don't see any reason to add more distortion or complication by using two stages. Nor the 100V requirement.

Here's some

back at 'ya.

Tim

SY · 29th December 2003, 11:01 PM

Tim, Tim, Tim. It's much cooler if you use a complicated circuit with a fancy name, preferably one originally developed for a 1942 vintage table radio. Why do something simple when there's a hard way to do it? Besides which, a fancier circuit will have a few extra poles in it, which can lead to many happy hours trying to stabilize it. A CF is just no fun.

29th December 2003, 06:10 AM	#1
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Unity Gain Tube Buffer I wish to make a unity gain tube buffer, preferably cascaded two stage, which will handle up to 100Vpp input/output. To keep input impedance high, it would be better to use feedback injection from the output of the second stage to the cathode of the first stage . If OLG of the two stages were around 100 (40dB), then a feedback ratio of this size would give vanishingly low Zout and distortion. However, devising an input stage which will handle 100Vpp is no slouch. My thinking would be that a differential input using medium mu tubes followed by a larger tube running say 15mA for output might be best. Does anyone have any experience/thoughts on this topology? Cheers, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

29th December 2003, 06:34 AM	#2
fdegrove diyAudio Senior Member Join Date: Aug 2002 Location: Belgium	Hi, It's been ages but I once used something similar as you describe using a 6DJ8 cascaded into a 6BX7 to drive a 211.... Details of which must be somewhere at the end of my little tape but it worked nicely. Cheers, __________________ Frank

29th December 2003, 07:32 AM	#3
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Err... wth you need 100V for... in any case... what you need two stages for, this screams CATHODE FOLLOWER. Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

29th December 2003, 09:56 AM	#5
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Thanks Guys, Frank, thank you for your thoughts. But a 6DJ8/6BX7 would not handle feedback down to unity gain, I don't believe so anyway. Tim, no, I don't want a Cathode Follower, because the feedback is local, and I need something with interstage feedback, unless.... Could an anode follower do it? Anyone know how it might be configured with say a 300V B+ to input and output 100V with feedback around the stage? Of course, this might mean a pentode like the 12GN7, but it might just be possible if it could be configured to avoid input overload. That's the tough one; input overload. Cheers, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

29th December 2003, 10:03 AM	#6
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	wtf everyone got against local FB anyways __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

29th December 2003, 07:45 AM	#4
Will diyAudio Member Join Date: Sep 2001 Location: Kuala Lumpur	Hi, I'd be interested if someone can post a schematic on a 6922 tube buffer with constant current source.

29th December 2003, 10:18 AM	#7
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Try English Tim...

29th December 2003, 10:59 AM	#8
fscarpa58 diyAudio Member Join Date: Nov 2003 Location: Genova, Italy	why do not try a 6DJ8 White Follower ? low distortion, low output impedance high Vpp Federico

29th December 2003, 11:01 PM	#10
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Tim, Tim, Tim. It's much cooler if you use a complicated circuit with a fancy name, preferably one originally developed for a 1942 vintage table radio. Why do something simple when there's a hard way to do it? Besides which, a fancier circuit will have a few extra poles in it, which can lead to many happy hours trying to stabilize it. A CF is just no fun. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

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