Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: markmalin on February 18, 2017, 10:56:30 am

Title: where to add effects loop on modified 5E3?
Post by: markmalin on February 18, 2017, 10:56:30 am

Hey gents,


This is a modified 5E3, 1-tube reverb ala Tubenit, and I just re-wired in the "bootstrap" style master volume which works REALLY well, by the way!  I want to add a passive effects loop, but not sure if it should be before the reverb mixer 220k, before the the 0.o22 uf coupling cap (C6), or what.  I'm thinking for sure it needs to be before the 500k bootstrap MV pot.  What seems most reasonable?


humbly,
Mark

Title: Re: where to add effects loop on modified 5E3?
Post by: tubenit on February 18, 2017, 12:22:17 pm

I would install a passive effects loop between the RV2 connection and the 500ka pot.

with respect, Tubenit

Title: Re: where to add effects loop on modified 5E3?
Post by: markmalin on February 18, 2017, 01:07:16 pm

Quote from: tubenit on February 18, 2017, 12:22:17 pm

I would install a passive effects loop between the RV2 connection and the 500ka pot.

with respect, Tubenit

Thanks, Tubenit!  :)

Title: Re: where to add effects loop on modified 5E3?
Post by: sluckey on February 18, 2017, 02:05:02 pm

You'll need to use coupling caps to the FX loop jacks to prevent messing up the bias voltage on the PI tube.

Title: Re: where to add effects loop on modified 5E3?
Post by: markmalin on February 18, 2017, 04:08:26 pm

Quote from: sluckey on February 18, 2017, 02:05:02 pm

You'll need to use coupling caps to the FX loop jacks to prevent messing up the bias voltage on the PI tube.

thanks, Sluckey.

Title: Re: where to add effects loop on modified 5E3?
Post by: markmalin on March 25, 2017, 11:54:42 am

I'm having some troubles with this....  I wired in the effects loop between RV2 and the 500ka pot, and added 0.01 uf coupling caps on each jack (in/out).  I hooked up my Eventide Timefactor delay and when I turn it on, the "peak" light comes on and the sound is overdriven.  Is this circuit just not going to work with a passive effects loop?  Or should I put it before the reverb mixer?


I'd appreciate any input.  I'm tempted to close up the amp and call it a day, but I just ordered a Fulltone Tube Tape Echo with the hopes of running it through this amp via an effects loop   :BangHead:


Mark

Title: Re: where to add effects loop on modified 5E3?
Post by: PRR on March 25, 2017, 12:37:23 pm

Level there is essentially 6V6 grid level, over 10V. Much too high.

Try between the volume pots and the next grid. Should use coupling caps and provide a grid resistor.

Title: Re: where to add effects loop on modified 5E3?
Post by: 2deaf on March 25, 2017, 12:39:53 pm

The Eventide has switches on the rear that allow you to run at line levels.  However, it doesn't use balanced in/out which means it is -10dBV which is .4472V_p.  The Fulltone is strictly guitar level.  Your current setup would have to have the volumes turned WAY down to get the appropriate levels at the effects send. 

What you really need to do is to attenuate the signal going to the effects send then amplify the return, which may not be feasible and/or acceptable with a 5E3.

Title: Re: where to add effects loop on modified 5E3?
Post by: markmalin on March 25, 2017, 02:17:39 pm

Sounds like I should use a different amp for the Fulltone and leave this circuit alone.

PRR, I measured about 35 v there, so yes, way too high.  I'm curious, though, you meant try the effects loop before the grid of V2a?  I may try that, but what would a good grid resistor value be?  And for coupling caps I was using 0.01, I just picked an arbitrary value, but if those aren't good values what would you suggest?

Title: Re: where to add effects loop on modified 5E3?
Post by: HotBluePlates on March 25, 2017, 05:56:30 pm

Quote from: markmalin on March 25, 2017, 02:17:39 pm

Sounds like I should use a different amp for the Fulltone and leave this circuit alone.

Or you use the TTE as-designed, between the guitar and amp input jack.

Title: Re: where to add effects loop on modified 5E3?
Post by: markmalin on March 26, 2017, 08:34:39 am

Quote from: HotBluePlates on March 25, 2017, 05:56:30 pm

Quote from: markmalin on March 25, 2017, 02:17:39 pm

Sounds like I should use a different amp for the Fulltone and leave this circuit alone.

Or you use the TTE as-designed, between the guitar and amp input jack.

Thanks, HotBluePlates.  So the TTE was designed to go between the guitar and amp, not so much used in a effects loop?  I pulled up a manual on-line and the descriptions on how to use it seem to only talk about plugging a "guitar" in, and plugging the TTE into an "amp".  But I don't see anything indicating an effects loop is necessarily bad.  What are your thoughts?  (It's a silly-expensive device and I don't want to mess it up!)

Title: Re: where to add effects loop on modified 5E3?
Post by: HotBluePlates on March 26, 2017, 11:53:17 am

I doubt you're going to hurt the TTE.  But the Echoplex it was based on was produced back in the days when no guitar amps had effects loops (and very few had on-board effects).

If you're wanting to make a loop, PRR probably has the right call:  the loop should go a stage earlier, where signal levels are closer to the guitar-level needed at the TTE input.  Of course, then you might need a make-up gain stage.

Title: Re: where to add effects loop on modified 5E3?
Post by: markmalin on March 27, 2017, 07:56:18 am

Thanks.  For the record, I tried it where PRR suggested and it did work - the Eventide was happy, but seemed to affect the tone.  I used 0.022 uf coupling caps and a 68k grid resistor.  As I said it worked, and the tone change was faint, but it bugged me enough to just pull it and put the circuit back the way it was.  So chalk it up to experience I guess.
Again, thanks everyone for the help.
Mark