Incorporating Cornish Buffer

[jonrhee]

I am trying to add the Cornish Buffer from the Madbean G-2 into a schematic found on FSB for the Light Drive which is essentially the SS-2 without the input buffer, from what I understand.

I've attached the schematics in question and my attempt at it. Could anyone help me understand if I'm doing this right if not how I ought to?

[jonrhee]

My attempt and the FSB schematic of the Light Drive

[stecykmi]

seems okay but you may have some extra components that are unneeded.

R9 and R10 are unnecessary because R7 and R8 do it same job. i don't think these values are too critical, so you can use R7/R8 instead.

and it looks like R24 is extra and unneeded

[RobA]

I must be missing something, but I don't understand the point of putting a a BJT based emitter follower in front of a non-inverting FET based op-amp gain stage. Any ideas why?

[jonrhee]

Thanks, what is the reason for the VA and VD in the Darkside? Aren't VB and VD the same voltage?

According to Cornish the input buffer provides "superior RFI rejecting capability (to eliminate Radio Station interference) and Low Impedance Audio output, allowing the use of extended cable runs from the SS-2™ in bypass mode".

http://www.petecornish.co.uk/SAESS-2.html

[stecykmi]

Thanks, what is the reason for the VA and VD in the Darkside? Aren't VB and VD the same voltage?

According to Cornish the input buffer provides "superior RFI rejecting capability (to eliminate Radio Station interference) and Low Impedance Audio output, allowing the use of extended cable runs from the SS-2™ in bypass mode".

http://www.petecornish.co.uk/SAESS-2.html

Ya, i believe it's to help decouple the power supply, basically provide more power supply filtering. all those small resistors + caps act as low pass filters, so noise won't leak into the circuit through the biasing.

it's legit to stick a buffer in front of almost anything. the tubescreamer has basically the same arrangement except the buffer is simpler.

[RobA]

Well, it obviously does nothing with the output as the buffer isn't on the output. The other claims look to be nonsense too.

The TS has a crap op-amp in it with BJT inputs. It's also not a wired bypass in its original version. So, any kind of buffer in the TS will help.

On the other hand, the circuit here looks to by using a FET input op-amp because of the size of the resistors on the input. A BJT buffer is useful for providing current drive. That's not needed here because the FET inputs don't need/want current. Basically, the buffer is undoing the good that the op-amp does. I'd breadboard it first to see what it actual sounds like.

If you really want a buffer on this circuit, a JFET buffer would make a lot more sense.

Rob

[RobA]

Also, if it's about reducing noise from the PS, then it would make more sense to put some bypass/filtering caps on the PS rails to the op-amp. That's where PS noise is going to show up.