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plugging a preamp into a bass head's effects return
- Thread starter mrpackerguy
- Start date
You can send from your preamp's Main Out to either amp's input or FX return...depending on whether it's instrument or line level. I send to my amp's input from my EBS MicroBass II Output.
Usually, it's better to feed the FOH from your preamp's DI out...
Usually, it's better to feed the FOH from your preamp's DI out...
Last edited:
My Tech 21 DI does have a volume and I turned it up to max. However, with inquiry, in the last 24 hours I have realized my 30 year old DI only provides instrument level signal and it does not provide the effects return with enough line evel signal to produce enough volume.
Thanks for your help.
- Feb 12, 2006
- 61,047
- 5
- 220,998
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Many effects returns will work with instrument level from a pedal (bass instrument level is typically about 10dB higher than guitar level) but the master volume control on the amp will need to be turned all the way up.
This is generally true for all of the amps I have designed, and common in others as well.
This is generally true for all of the amps I have designed, and common in others as well.
The Level knob on my Fender Rumble does nothing when I plug the Tech 21 into the effects return of the amp. Apparently, this application disables all controls on the Fender Rumble.
The explanation is simple: the FX loop is placed after all controls, according to Block Diagram in Rumble's manual.
https://www.fmicassets.com/Damroot/Original/10002/237060_bamp_manual_all_revA.pdf
Do it all the time with my SWR SM-400.
However, much depends on the amp and the way it’s configured.
If the amp has a series effect loop, which gets between the signal path between the built in preamp and the power amp stages, plugging into the effects return breaks the connection and removes the built-in preamp from the signal path. That effectively turns your amp into a straight ahead power amp.
Whether or not your pedal has enough grunt to drive the effrcts return is a different matter. If it doesn’t, putting a very clean boost like an MXR Micro Amp into the effects return first, and then plugging your preamp into that, will usually get you there.
With my SWR it’s not an issue. I just plug any one of a half dozen preamps I have into the effects return and have at it. Like getting a new amp to play for each day in the week. (Yay!)
How the XLR direct out will work also depends on the amp. On most amps you can select between direct and line (or pre/post) settings. “Direct” bypasses everything in the amp and just boosts the signal on the amp’s input jack to line level, which it then sends straight through to the line out. On the “line” setting, the signal that is coming off the preamp stage gets boosted to line level, and from there gets sent to the line out XLR connector.
So if you’re using an outboard preamp that’s plugged into a series effects return - and you want to go to the FOH - there’s a channel the amp’s direct XLR jack isn’t going to work at all since there’s no signal going into the built-in preamp, or coming off the back of it. So unless the direct out is getting its signal after the effects loop, it isn’t going to have any signal to work with. That’s because you bypassed all the circuitry that came before the effects loop by plugging into the effects return jack. Again, this is a possible issue if you have a series type effects loop. So to get a direct out you may still need to use a DI box in some cases
If you have a parallel effects loop, the XLR line out should work in line mode regardless since the preamp and the effects loop get mixed together before going to the power amp stage. But how well it will work for you depends on the design of the amp and how the preamp and effects loop signal chains get mixed, and where in the chain the direct out is getting its signal. Check your amp’s block diagram (if there is one available) to see where the signal paths are.
Luck!
However, much depends on the amp and the way it’s configured.
If the amp has a series effect loop, which gets between the signal path between the built in preamp and the power amp stages, plugging into the effects return breaks the connection and removes the built-in preamp from the signal path. That effectively turns your amp into a straight ahead power amp.
Whether or not your pedal has enough grunt to drive the effrcts return is a different matter. If it doesn’t, putting a very clean boost like an MXR Micro Amp into the effects return first, and then plugging your preamp into that, will usually get you there.
With my SWR it’s not an issue. I just plug any one of a half dozen preamps I have into the effects return and have at it. Like getting a new amp to play for each day in the week. (Yay!)
How the XLR direct out will work also depends on the amp. On most amps you can select between direct and line (or pre/post) settings. “Direct” bypasses everything in the amp and just boosts the signal on the amp’s input jack to line level, which it then sends straight through to the line out. On the “line” setting, the signal that is coming off the preamp stage gets boosted to line level, and from there gets sent to the line out XLR connector.
So if you’re using an outboard preamp that’s plugged into a series effects return - and you want to go to the FOH - there’s a channel the amp’s direct XLR jack isn’t going to work at all since there’s no signal going into the built-in preamp, or coming off the back of it. So unless the direct out is getting its signal after the effects loop, it isn’t going to have any signal to work with. That’s because you bypassed all the circuitry that came before the effects loop by plugging into the effects return jack. Again, this is a possible issue if you have a series type effects loop. So to get a direct out you may still need to use a DI box in some cases
If you have a parallel effects loop, the XLR line out should work in line mode regardless since the preamp and the effects loop get mixed together before going to the power amp stage. But how well it will work for you depends on the design of the amp and how the preamp and effects loop signal chains get mixed, and where in the chain the direct out is getting its signal. Check your amp’s block diagram (if there is one available) to see where the signal paths are.
Luck!
It's available here (page 10):
https://www.fmicassets.com/Damroot/Original/10002/237060_bamp_manual_all_revA.pdf
If my reading of the diagram is correct, the DI out is after the FX loop. I am not sure whether the loop is series or parallel though...
Looks to be series.
Easiest way to check is to plug your preamp output into the effects return and see if you get signal to the speaker and off the XLR jack. If you do, you’re golden.
Alternatively you can plug into the front like usual - but with a plug also inserted in just the effects return jack. If you don’t hear your bass, it’s a serial effects loop.
I was only able to take a quick glance at the diagram. But it seems Fender is throwing a speaker emulation circuit into the direct out, so that’s different than on my amp. Nice feature though since it lets you use the amp as a direct box in the studio without sounding too squeaky clean and electronic.
