Valve Wiz Buffer Loop

[gary sanders]

In no way questioning it but was wondering if anyone knows first hand how it does in an amp.It has its similarities to the D lator but less parts and thats what I need cause I only have room for a point to point assembly in my chassis.

And where would I tap off an ODS power supply for this or should I add another filter cap in between the screen and PI filters

http://www.freewebs.com/valvewizard/accf.html

[ampdoc1]

I don't think it will matter a whole lot if you take it off any of preamp PS nodes. Definitely run a dropping/isolation resistor and an additional filter cap.

I have a dumbleator circuit in my hybrid TW/Dumble amp, right before the PI, and it works well @ about 210VDC supply.

a'doc

[Structo]

That schematic is fairly close to the D'lator but for me, since HAD designed the D'lator as a companion buffered loop for his ODS amps, I trust his design to work and sound better than just about any other design.
If you want to build the loop inside an existing amp, shouldn't be a problem as long as you have room for another tube.
Just wire it point to point.
Grab the B+ off of the PI node for the right approximate voltage then drop it down from there.

[Merlinb]

In no way questioning it but was wondering if anyone knows first hand how it does in an amp.It has its similarities to the D lator but less parts

The only real difference between the Dumblator loop and mine is that the D'lator has the 44Meg local feedback loop, which has precisely no effect on tone or performance at all (and my loop has less Johnson noise).

[Structo]

Hi Merlin,
How would the Johnson noise present itself in the D loop?

Would that sound like tube hiss.

As I understand it Johnson noise is thermal noise usually associated with resistors which is the worst in carbon composition resistors.

On your loop you have no way to control the recovery or output which I find useful in my D loop as a way to control the gain and recovery of the effects signal back to the amp.

[Merlinb]

As I understand it Johnson noise is thermal noise usually associated with resistors which is the worst in carbon composition resistors.

Yes it is just hiss. Not necessarily audible, but there nonetheless.

On your loop you have no way to control the recovery or output which I find useful in my D loop as a way to control the gain and recovery of the effects signal back to the amp.

Most effects have their own output levels controls. But in any case it's just a pot. Easy to stick a pot in place of the grid leak. (That's not really a difference between the two circuits, since both have a resistor in the same position. Whether that resistor is made variable is up to the user; it does not make it a completely new circuit.)

[Structo]

OK, thanks!

[gary sanders]

Hey cool!THe man is on here .I did it just like n the page and it sounds great.a little cramped up for space but its in there!Had a slight hum but moved the cathode ground to share with where the v2 cathode grounds are and its awesome now.Hope I get your books for fathers day,Merlin! (hint if anyone that knows my kids are reading this....)

Thanks for your posts and your entire pages.Theyve been most helpful and educating

[Gaz]

So, Gary, did you make the grid loop variable, or did you just do it like the schem? I'm looking for loop myself, and wonder if the pot is really necessary.

[dcribbs1412]

Sounds like a cool project
I need to figure out a layout for this
Gary any pics of this in your build?

Darin

[gary sanders]

I did it just like Merlins schematic,had to use a different pot because i didnt have a 22k but it works great.Lovin the tone the stage gave the amp.

dcribbs1412,you dont want to do it the way I did if you have room in your chassis.it is CRAMMED in to a 6 post terminal strip,point to point.Ive already got it back in the cab but will put up a pic if i pull it out again.gonna tie stuff together and make it EL34-ish later

I threw this together real quick while the soldering iron was heating.I think its right.This is what i went by.see attchmnt

[gary sanders]

and thats just a rough draft,i had to change the grounds around,there was a slight hum,didnt get louder when you turned it up,but it was there.maybe that can give you an idea.Im probably one of the last guys on this forum youd want advice from.this is the first amp ive ever done,not counting the two times ive started from scratch

[dcribbs1412]

Thanks Gary
I guess I'm a visual guy and this will get me going.
Don't sell yourself short ...you have experience

Experience is a great teacher.
John Legend

[gary sanders]

man ive built a thousand stomp boxes but this amp stuff is new.more dangerous,makes it interesting.Its like that Operation game but if you touch the sides YOUR nose lights up.

Hope you try it out,it made such a great difference in my rig.I run an old analog delay,a boss ch1 chorus and a demeter tremulator in my fx loop.they sound like they should now.im going to build a loop bypass instead of putting a relay on the in and out.much simpler than all that extra wiring in the amp.my chassis is totally stuffed

[rsalinger]

...this amp stuff is new... more dangerous, makes it interesting. Its like that Operation game... but if you touch the sides YOUR nose lights up.

Thank you for that, Gary. I had a good long chuckle... Got my day off to a good start.

Rob