Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: markmalin on January 12, 2017, 03:09:07 pm
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I may have gotten in over my head here, and I'm going to be the first to admit it...but I agreed to add a passive effects loop to the latest Bad Dog build I'm doing for a guy (see schematic below). In my head I was thinking, "...no problem...I'll just do it like the Dumble 183 model..." (see schematic below), so after the master volume I add the switched in and out jacks. I haven't tried this yet, but does this make sense? It's a passive loop - that's what i agreed to because it's over my head (and too late) to design/install something with a driver.
Tubenit has several posts on the board with his D'style tweed amp, and it seems like he's done a great deal of research. But the more I read, the more worried I'm getting.
Can someone let me know -- would it work to simply add the jacks after the master like in the 183 D' schematic?
Thanks, fellas. I sure appreciate you all!
Mark
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Mark, I think your idea should work fine. I've tried a Boss delay, Wampler delay and a Carbon Copy delay with passive FX and liked the way they sounded.
I use the same type of jack that you'd use for input jacks on both the send and return jacks .
With respect, Tubenit
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I've done that several times and th funny thing is, the amp's tone changes less than all the active loops I've tried. Unfortunately i've yet to be able to get enough level out of any effect unit even the +4 DSP i use now with a global output level that can be cranked to 200%. So while it sounded quite transparent, the amp wasn't even loud enough to gig with. Plus being after the master every time you turn the master up you have to turn the DSP input down to keep it from clipping.
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Thanks, guys.
Tubenit, I can use typical switched Switchcraft jacks, or do I have to isolate them from the chassis?
Also, I need shielded wire, yes? Where is the best place to terminate it?
Again, thanks for both your responses guys
Mark
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Mark,
Yes use shielded wire if you have a long run. I have not used isolated jacks and they are grounded on the chassis. I grounded the shield of the shielded wire on the jack's ground terminal.
IIRC, I looked up some Dumble layouts to find out how they approached that.
I have not had the problem with volume drop that 12AX7 reported experiencing. Typically for me, a master volume is something of a set and forget and isn't adjusted much at all.
With respect, Tubenit
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Mark,
Yes use shielded wire if you have a long run. I have not used isolated jacks and they are grounded on the chassis. I grounded the shield of the shielded wire on the jack's ground terminal.
IIRC, I looked up some Dumble layouts to find out how they approached that.
I have not had the problem with volume drop that 12AX7 reported experiencing. Typically for me, a master volume is something of a set and forget and isn't adjusted much at all.
With respect, Tubenit
Thanks. Sounds pretty straight forward. I'll give it a try and report back :)
Mark
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Here's a simple passive loop for Fender tweeds using Switchcraft 11 and 12A jacks. The jacks are between the volume control and the second gain stage grid (V2A pin 2):
(https://robrobinette.com/images/Guitar/5E3P_Build/5e3_FX_Loop.png)
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Tubenit, I added the passive effects loop and it works great. Thanks! I ran my Eventide Timefactor through it and it worked like a charm. I wound up wiring it slightly differently, more like the Dumble schematic I attached originally in that on the Send side.
Thanks!