I play in a contemporary church setup and we’re looking at adding a MIDI synth bass mainly playing sub bass and other to add more power to some songs. However, we dont have an extra amp yet. Will it be okay to play it on the same amp as the bass guitar? Maybe have one on the high and other on the low? Will there be any consequences? Thanks!
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Not really, you can play it on the same Amp. Your bass amp can definitely handle that signal. The most demanding amps are the Bass amp, Keyboard amp, and Drum amp(eDrums) as they have to be able to handle low frequencies Keys and drums amps have to be able to handle all spectrums.
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Can I plug them both directly to the low/high input? Or they have to go through a mixer, then to the amp?
couple problems here. One thing to keep in mind here is the bass sends (and the amp expects) an instrument level signal, while the synth sends line level - much hotter. So I would be very careful with levels in the amp
The synth will also want a stereo out.
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Hey! Thanks for your input here. When you say careful with the levels, will it be fine if we just put all knobs flat on the amp? Would you think it’s best for the bass guitar and (midi keyboard) synth to go through a mixer first before the amp?
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Two issues here. First is making sure the bass amp can take a line level input at all.
Then if it can, you would want to run the instruments in to a mixer because the keys and bass will be at very different levels.
I have run a drum machine (a real one, not a pedalboard one) at line level in to a bass amp before… It worked but that didn’t make it a good idea. Even though the jacks are the same size, Line and Instrument level are very different signal strengths.
You also want to decide what to do with the stereo signal here. The bass amp will be monaural.
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My brother is using the same brand/model bass amp on his midi keyboard > Mac Book Air(DAW)> amp. Does that mean it can take line signal? If it does I think I’ll get a mixer to combine the signals before sending it over to the amp.
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What output is he running from the audio interface to the amp?
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3.5mm to 6.35mm, if I’m understanding your question right 
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I meant what is the actual output? The mac headphone out? Or is this from an audio interface?
I ask because headphone outs are actually hotter than line outs 
Bass amps are designed to take a high impedance, low level instrument signal. Running a low impedance high level signal like Line Out or Headphone Out into their instrument inputs is not ideal.
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Hahaha! Sorry about that I’m new to this tech stuff! And yes that from Macbook’s headphone out to the amp.
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No worrries! All the different levels are confusing.
I have two suggestions then. First, does your amp have an Aux In? If so, running the headphone out in to that would be much better than running it in to your instrument input. Aux In should be able to handle a line or headphone level signal, and also will likely bypass your bass amp’s preamp so the amp tone controls will not affect it, which is what you want for a synth. Plus it’s designed to work while playing your instrument into it at the same time.
For longer term, what I would recommend for both of you is to invest in audio interfaces for your computers, both for recording instruments and also outputting the mac sound (synths, etc) to line outputs for use with mixers and PAs. Decent audio interfaces with the proper options for outputs can be had in the $100 range. This is a popular one:
https://www.sweetwater.com/store/detail/UMC204HD--behringer-u-phoria-umc204hd-usb-audio-interface
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I have an M audio 192 4 at home. Will that work for this setup? Unfortunately this will be played in church and we arent running our instruments on a mixer. We’re only plugging our instruments to the amp.
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Ahh perfect
Audio line out from the macbook through that will be a much better plan than headphone out.
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Ahh bummer. Gimme a sec to try and look up the amp.
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Macbook air is from his setup.
For me, I’ll be going with a Midi keyboard (mvave smk25) to a windows laptop (thinkpad x250) to the amp (high/low)
Then the bass guitar to pedal to amp (high/low).
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I couldn’t find the actual specs but if you were to try this you would want to run a line out in to the Low input. Try the amp at very low levels when you do this as it is a hotter signal than it will expect.
This still isn’t ideal but would be a better idea than trying the high input.
If you want to use the bass and synth at the same time then running them into a mixer would be the best choice so you can control the input levels better, then run one side of the mixer (probably left stereo line out) into the amp. Pan everything to that side. The synth will be a stereo signal most likely (all of mine are, I have to set them to mono manually in the DAW) so you will probably want to set it to output in mono in your DAW.
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Will I still need the audio interface? Or just MIDI - laptop - amp?
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I would use the audio interface, personally. I guess you could use it as a mixer then instead.
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