CF & FX comparison question

[tubenit]

In this thread reply #26 ................. Doug Hoffman has an FX loop that he added to a Plexi 50w style amp.  It looks sort of like just another gain stage after a CF.

http://www.el34world.com/Forum/index.php?topic=10208.0

I got to thinking about this (sort of late to the game),  that maybe if there is a CF then it is essentially functioning the same as the first part of a D'lator style FX loop?

Would it be correct to think that if there is a CF with a tone stack & volume pot that the first half of the D'Lator might not be necessary?
In other words that if there is a Marshallish style CF with a tone stack that the first half of the D'Lator would be redundant?

With respect, Tubenit

[kagliostro]

The CF is a very good output for FXLoop (low impedance and good current, this one especially if an ecc81 tube is used)

The presence of the TS suck the signal and after the TS also if it is preceded by a CF you didn't find an optimal signal for FXLoop output

if you connect between the CF and the TS for your FXLoop output, obviously you loss the effect of the TS and otherwise the signal you find in your FXLoop return is inadequate to drive perfectly the TS

The best solution in absence of a disposable triode I've seen till now, is the use of a Mosfet as source follower as you wisely introduced in your amps  

K

[Willabe]

I think K is right.

If you put a TS after the CF and before the Fx send it will defeat the low Z drive of the CF and you'll get the usual TS losses too.

OTOH, you could try it and see if it works for you.


                  Brad       

[kagliostro]

you could try it and see if it works for you

Jeff uses this kind of architecture in some amps, and I think he is very satisfied by results, although the performance aren't at the maximum possible as FXLoop send circuit

K

[TIMBO]

Hi guy's, T, This is similar to the hiwatt and I kinda like how it sounds and by having a single triode after the TS that would boost the signal if there is TS loss.

I tried the paralleled V1 and it gave me the Fattness I was looking for but it lost the BITEY edge it had. It aslo gave some GHOSTING on some of the notes but that is another story..........

Someone had brought up the subject of an "active tone stack" I think that this could be that.

I have not added a FX loop in this build yet and had planed too. I think that having the jacks before the triode (second half of the FX loop) would boost any signal loss of TS and any FXs in the loop and when nothing in loop acts as a MASTER VOL.

I have not had an active FX LOOP in a build (that work) so I don't know how much added gain it gave but if I could be added as an ENHANCEMENT that would be perfect.

Some ideas.......

[tubenit]

OK, thanks for the replies!  I appreciate your thoughts.

Here is my thinking ........................

I know a passive effects loop works fine with my delay pedals  between the CF tone stack and LTPI.
I know a D'Lator type effects loop works fine with my delay pedals  between the CF tone stack and LTPI.

So, ........... given that Hoffman used a single triode design in his FX loop for the Plexi50 type amps, I was thinking this would work out OK?
I'm not sure about some of the component values?

I was considering this idea on an amp design for a friend & liked the idea since I could use the mosfet for the CF and then use that triode for the FX loop?  It may not be the ideal FX loop, but I would think that it could help using a delay pedal at some level?

This may be one of those "try and see" type ideas?   Any other thoughts on this?

With respect, Tubenit

[kagliostro]

There are particular reasons you can't add a Mosfet source follower after the TS ?

I mean one Mosfet source follower then TS then one other Mosfet source follower

this will give to the FXLoop send full performance

K

[tubenit]

Is this what you are referring to?   Using a mosfet for the first half of an FX loop?

With respect, Tubenit

[kagliostro]

Yes, that is what I'm thinking

one before and one after the TS

K

[tubenit]

That is a novel idea and possibly a great one!

Thanks,  Tubenit

[kagliostro]

Ciao Jeff

I would like to know if you have done further investigations on the matter

and if you have some result to report

Thanks

Franco

[tubenit]

No further investigation at this time.  Maybe more so in mid summer?

With respect, Tubenit

[kagliostro]

Thanks

Franco