Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: toomanyslurpees on May 31, 2010, 03:37:20 am

Title: OD Pedals into DRRI channels question
Post by: toomanyslurpees on May 31, 2010, 03:37:20 am

Ok, so I've noticed that the vibrato channel in my DRRI doesn't take overdrive pedals as well as the normal input, through the vibrato channel the OD is a bit fuzzier and thinner. Not a huge difference but I was wondering if anyone here has noticed this and knows where this difference comes from and whether it's a reissue thing or whether this would also be true in an original. I've swapped tubes around to isolate it and it's not a tube issue.

I have an empty bassman head and I'ld like to put something deluxe reverbish into it, if this tonal difference came from the tremolo I'ld probably just drop it but I'd like to have reverb and if this comes from the reverb circuit I might look into a different way of doing that.

Thanks for any insights. Cheers.

Title: Re: OD Pedals into DRRI channels question
Post by: Geezer on May 31, 2010, 05:10:08 am

Quote

the vibrato channel in my DRRI doesn't take overdrive pedals as well as the normal input

Yes, I think most players find that to be true.

The reason?
Look @ the schematic I have linked below. (Original AB763 or RI, they are both basically the same topology)
The "Normal" channel has 2 gain stages before the PI.
The "Vibe" channel has an extra gain stage for reverb recovery, so it has a bit more gain than the "Norm".
OD pedals generally sound better when run into "clean" preamps.
Therefore, the cleaner Normal channel yields a "better" OD tone.

That's my take on it...$.02

Geezer

http://www.el34world.com/charts/Schematics/fender/DELUXE_REVERB_AB763.pdf

Title: Re: OD Pedals into DRRI channels question
Post by: VMS on May 31, 2010, 06:30:13 am

What Geezer said. And that 47pF bright cap may also have some influence to the brightness (when volume is below noon).

Title: Re: OD Pedals into DRRI channels question
Post by: LooseChange on May 31, 2010, 07:34:12 am

My Super Reverb with the exact same circuit and sounds great with an OD pedal.

Yeah, cut that bright cap out and check the bias.

Title: Re: OD Pedals into DRRI channels question
Post by: toomanyslurpees on May 31, 2010, 06:36:33 pm

Thanks guys, yeh, that reverb bit must be the difference I'm hearing, it's not a huge difference, but the more gain the more noticable it is (not that I use much gain) Is their a more transparent reverb one could think of adding to the normal channel of a Deluxe reverb? Then I could possibly considering removing the entire vibrato channel from that future build I was thinking about, I remember there was someone here looking at doing that a while back.

Title: Re: OD Pedals into DRRI channels question
Post by: OldHouseScott on May 31, 2010, 08:49:44 pm

Clip the 47pF. Fizziness with ODs is usually attributed to that bright cap.