What Should I Consider in Vocal Pedal Designs?

jdduffield

jdduffield

Active member
I’m thinking about building a reverb pedal for vocals. (FV1)
This means I would be working with XLR instead of 1/4” mono guitar jacks. What are some things I need to consider when designing a circuit with XLR jacks? For example, I imagine I will need to keep power negative and earth separated. I imagine I will need to handle the possibility of 48V phantom power making its way up the output cable. Any thoughts or advice is welcome.
 
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This could serve as some inspiration for your input stage.
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CP5 Colour Mic Preamp

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What exactly you should do depends on what your signal chain will be. Are you expecting this to receive a raw microphone signal? If so, it will have to serve as a pre-amp as well as an fx pedal. In that case, you don't necessarily need a THAT1512, a 5532 will also do a decent job. However you need a way to unbalance the signal, the benefit of the 1512 is that the device serves as a balanced input, pre-amplifier, and unbalanced output.

As usual, Rod at ESP also has some inspiration for you https://sound-au.com/project122.htm (though no phantom power in this case).

I would personally use isolated DC-DC converters for power in this project, aim for 9-12v DC in, then use an isolated converter for either +/- 12 or 15v, a separate converter for 48v, and a regulator for the FV-1 which I think needs 5v.
 
Maybe the $5 Mic Pre would be enough? Very similar to the above. If it's a dynamic mic for a live setting, it could even be simplified a little more. Powering it cheaply has always been its Achilles heel. I haven't tried it with a DC-DC converter. With 4 batteries it's fine.
 
Define if you need a preamp for the microphone. If the microphone first goes to a preamp, then the reverb pedal input will be line level.

Is different to guitar pedals, since usually for microphones you have first a preamp to amplify up to 50-70dB the signal while keeping a good signal to noise ratio. After the preamp, you insert processors that use line level signal. Both use XLR connectors, but the signal is different (voltage and impedance).
 
CR0SSBL4DE said:
Define if you need a preamp for the microphone.
Click to expand...
I don't think so. What I want is very similar to the TC Helicon Mic Mechanic. I think it is unity gain without a preamp. I know it doesn’t have a volume knob on it. I suppose I could look at the schematic. With the Mic Mechanic, the preamp stage still happens at the mixing board.
 
What I envision is a pedal with the left side being delay and the right side being reverb. Then, inside, 2 FV1 chips, one for the delay section that then goes into the second one for the reverb section. I was just wondering about the circuit and how I would handle XLR as it has 3 connecting pieces (positive, negative, and ground). It seems there is talk of unbalancing the signal. Is that truly necessary or is there a way to maintain the XLR balanced aspect/integrity. I was also wondering if I need to add something to prevent 48V phantom from damaging the circuit, or what safety measures if any are needing to be considered in the event that phantom power is turned on at the mixing board.
 
jdduffield said:
I don't think so. What I want is very similar to the TC Helicon Mic Mechanic. I think it is unity gain without a preamp. I know it doesn’t have a volume knob on it. I suppose I could look at the schematic. With the Mic Mechanic, the preamp stage still happens at the mixing board.
Click to expand...
Mic always goes first into the preamp.
 
Yeah, I think I was wrong about the Mic Mechanic not having a preamp. Apparently it does. I got confused because the volume is roughly the same if you bypass it even with a dynamic mic.

So, it seems like my effect with need a preamp first within the circuit.
 
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