ECC88 mu-follower

[ruffrecords]

Interesting circuit! The pot varies both open-loop and closed-loop gain - I assume that helps maintain stability?

Spot on!!! It is inspired by the Telefunken V76 which does much the same thing with pentodes. My improvement is to ensure stability also at the LF end of the spectrum by dc coupling the NFB. The NFB lies between 20 and 30dB at all values of closed loop gain from 6 to 40dB.

This technique of altering open loop gain at the same time as closed loop gain seems to be endlessly rediscovered. It was used in a discrete op-amp design a couple or three decades ago:

http://www.technicalaudio.com/pdf/Valley_People/Valley_People_Trans-Amp_LZ.pdf

and is very useful in virtual earth mixers as an aid to stability.

Cheers

Ian

 

[tinitus]

This circuit here will do that:

Ian

cool 🙂 and saved well 😛

can I ask how much gain ?....ah, I see its been answered while I posted

 

[ruffrecords]

cool 🙂 and saved well 😛

can I ask how much gain ?....ah, I see its been answered while I posted

I can supply a PCB with two of these circuits on it for stereo. It also has a mod so you can use an ECC99 instead of an ECC88. PCBs are 15GBP plus shipping.

Cheers

Ian

 

[merlin el mago]

Yes, DIY is supposed to be the basis of this site. We help, but we don't do it for you.

Hi!



Yes that is putting in nicer words what I wanted to say. Didn't want to appear harsh. Remember that the answers you get will probably not be better than the questions you ask. You need to get over that first step to be able to ask good questions, only then you can make progress

Thomas

Hey guys, I do not want that you make nothing for me, I only ask to do it myself following the people that wants to help.