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4CM advice pls 2 active preamps sharing 1 effects loop


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Hello, I have a two channel Frenzel amp head. Each channel has it's own inputs and full controls and can operate simultaneously. It has an effects loop on the back with 1 send and 1 return.


I would like to use the expression pedal on my Helix floor unit to fade between one Frenzel channel and the other. I would also like to have my delay effects between my preamps and Amp section of my Frenzel.


I imagine I will use the 4 cable method, using 2 Helix effects loops. Do I just use a Y adapter on the effects loop send of the Frenzel to get two returns back to the Helix? 


Thank you.

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If the amp only has 1 send, then you only have 1 signal to choose from, meaning you can't blend between the 2 outputs at all - splitting it into 2 won't help you as both signals will be identical. So you only need 1 return.


However, you may be able to blend in some way between the 2 channels by having the expression pedal alter the send level to the 2 channels - but that is likely to sound quite different from blending the return (which you can't do). For example, if one channel is higher gain than the other, a 50/50 split of output is likely to have a lot more signal from the high gain channel in the return. You might be able to ameliorate this a bit by adding a volume block in there controlled by the same pedal, but I've not tried anything like that.


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You need two sends, and one return on the Helix...

You would have to experiment with a loop and a separate send if you want to minimize the blocks used, but if you set this up as three blocks it would be fairly easy. 


Send A - Send to channel 1  (set the expression volume from "unity level - all the way down")

Send B - Send to channel 2 (set the expression volume from "all the way down - unity level")

Return A - this is a common return for both channels... from the loop in the amp. 

Output from Helix would return to the loop IN on the amp. 


The expression is now controlling the send volumes to each channel. Heel down it goes to channel 1, toe down goes to channel 2. 


Everything in between will be a blend - but there is no guarantee how the blend will work out. If the 2nd channel is a "gain channel" then you won't be hitting it with enough gain to work until it is full so I don't think blending into it will work as you think it might. 


IMO - I would put the two sends on a toggle switch. You will get "full channel one", or "full channel 2"... just like a 2 channel amp with channel switching. 



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