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Q. Why don’t my mixer inserts work when using the mic input?

By Hugh Robjohns

Soundcraft EFX12 mixer.

My Soundcraft EFX12 mixer is pretty new and hasn’t given me any problems until now. I hope it’s just ‘operator error’, but when I try and use a channel with a microphone (an SM57 or AT-2030), and an insert cable running to an effects loop with various Moog pedals, I get almost no level from the mic — it’s like it’s running it pre-everything into the pedals. If I crank the gain up to almost full I get a small amount of signal, with nasty distortion. If I remove the insert, the channel behaves as normal. And if I use a line input with the insert, that works as expected. I can’t work it out. It’s my understanding that the insert is post-gain but pre-fader/EQ, so I just can’t see why I’m not getting a normal level. I’ve tried various channels and get the same result. Can you help?

SOS Forum post

SOS Technical Editor Hugh Robjohns replies: The insert point is indeed after the input-stage preamp, which handles both mic and line signals, so the signal appearing at the insert point will be the same regardless of the actual type of channel source. This assumes you set the channel gain structure for mic and line sources to provide the same signal levels on the meter when you PFL the channel(s).

So, when you say the inserts work with line sources but not mics, there must either be some level of ‘user error’ going on, or you’re talking about different channels connected with different insert cables and different effects pedals. In other words, something must be significantly different in the insert signal path but you’re overlooking that difference for some reason!

The way to resolve a problem like this is to simplify things as much as possible, then work logically through the signal path. With that in mind, the likely possible errors/faults are:

1. You have a defective insert Y-cable.

2. You’ve plugged the split ends of the Y-cable into the pedals the wrong way around (the send is connected to a pedal output and the return to the pedal input —it’s easily done!).

3. The pedals can’t handle the line-level input signal or are unable to operate at unity gain, and are therefore returning too low a signal level into the insert return.

You can test the cable by setting the mic channel up as normal without the insert cable plugged in. Next, plug in the insert cable: at this point the channel should go quiet because the send/return plugs aren’t connected to anything, and so the send signal is not getting back into the return path. If you now touch the tips of the two send/return jack plugs together the channel should burst back into life. If it does the cable is good... if not, it ain’t!

If you find you have a good insert cable, the next thing is to confirm the correct send/return connections. Although most desks use the tip=send / ring=return connection format, some wire unbalanced inserts up the other way around. In the same way, some insert cables are labelled for the uncommon/incorrect arrangement! To check whether you have a reversed send/return configuration, plug the insert return lead into the output of an effects pedal that you know works, and plug a guitar (or some other suitable device) into the input of said pedal to serve as an independent sound source. You should then hear the guitar (or other source) passing through the pedal and straight back into the mixer channel via the insert return connection. If necessary, adjust the output level of the effects pedal (assuming it has one) to achieve a similar volume through the mixer to that achieved previously during the mic channel test.

If it won’t go loud enough, the pedal isn’t suitable for use as an insert effect on its own — you’ll need something else in-line to boost its output signal level. And if you get nothing at all, you probably have the reversed send/return scenario, so try swapping to the other side of the insert Y-cable and see if that works. If it does, the insert cable is labelled the wrong way around for you, so re-label it!

Having proven that the return side of the insert connection is working properly with the pedal, you can check the send side. Disconnect the guitar (or other source) and plug the send side of the insert cable into the pedal input instead. You’ll probably need to adjust the pedal’s input level downwards at this point, because the insert send level will probably be louder than the guitar used previously. And hopefully, everything will now be working as required!

Published April 2018