Does this FET buffer circuit look familiar?

homemade · 12th January 2008, 04:44 PM

I just got this completed board off ebay. $15 with shipping from China. Wondering if it looks familiar to anyone. Also curious if the design is any good. I'm hoping to use it as an output buffer for my cd player.

homemade · 12th January 2008, 04:45 PM

pic of board. each is 2 channel

juma · 12th January 2008, 05:10 PM

Hi homemade,
that is cascoded complementary buffer, well known/used and nice performing circuit. Usually, it's made with 2sk170/2sj74.
2sk246/2sj103 are a bit different jfets (less transconductance).
Try it and tell us how does it sound

poynton · 17th January 2008, 04:30 PM

Hi.

I've seen this advertised too.

Have you tried it yet ??

Andy

formula 22 · 26th April 2012, 03:58 AM

Quote:

Originally Posted by juma

Hi homemade,
that is cascoded complementary buffer, well known/used and nice performing circuit. Usually, it's made with 2sk170/2sj74.
2sk246/2sj103 are a bit different jfets (less transconductance).
Try it and tell us how does it sound

Hi
Is this buffer can work on Ucc=+/-9V or need something changed?
What needs to change the schematic to its input resistance is 1Mohm?
thank you

Itsmee · 09:32 PM

Quote:

Originally Posted by formula 22

Hi
Is this buffer can work on Ucc=+/-9V or need something changed?

Remove R1, R2, R7, R8, Q4 & Q8, fit links on the PCB in the Q4 & Q8 collector/emitter position.

Quote:

What needs to change the schematic to its input resistance is 1Mohm?

Make R6 1M.

Take a look at the input of the F4 amplifier buffer in the Pass Labs forum, also have a look at the DCB1 buffer as an alternative.

Itsmee · 27th April 2012, 06:21 AM

Quote:

Originally Posted by Itsmee

Remove R1, R2, R7, R8, Q4 & Q8, fit links on the PCB in the Q4 & Q8 collector/emitter position.

Quote:

What needs to change the schematic to its input resistance is 1Mohm?

Quote:

Make R6 1M.

Forgot to mention, remove C2, otherwise you will have a bandwith of 1.6KHz.

forr · 27th April 2012, 07:32 AM

Strange cascode.
In Juma's circuit, the base voltage of each common base bipolars is half way between the output and the rail.
In Homemade's circuit, R2 and R7 are in series and not connected to the output.
Using this connection, a fet associated with its bipolar do make not cascode at all.

CBS240 · 27th April 2012, 07:45 AM

Post 1 is a true cascode. Post 3 results in a constant Vds for the fets, sort of like a bootstrap. I think for a common drain circuit (source follower), constant Vds may be more advantageous.

27th April 2012, 07:45 AM	#9
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Post 1 is a true cascode. Post 3 results in a constant Vds for the fets, sort of like a bootstrap. I think for a common drain circuit (source follower), constant Vds may be more advantageous. __________________ All the trouble I've ever been in started out as fun......

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17th January 2008, 04:30 PM	#4
poynton Magneto the Gravity Man diyAudio Member Join Date: Mar 2005 Location: A life on the ocean waves when I'm not at home in N. Wales (but I'm not Welsh so no sheep jokes!)	Hi. I've seen this advertised too. Have you tried it yet ?? Andy

27th April 2012, 07:32 AM	#8
forr diyAudio Member Join Date: Dec 2004 Location: Next door	Strange cascode. In Juma's circuit, the base voltage of each common base bipolars is half way between the output and the rail. In Homemade's circuit, R2 and R7 are in series and not connected to the output. Using this connection, a fet associated with its bipolar do make not cascode at all.

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