Mic preamp for SM58

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cboe

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Hi, im a newb and recently got the following karaoke setup:

2 Shure SM58 -> Behringer MDX2600 -> Soundcraft Notepad 8fx -> PA.
Laptop is connected via usb to soundcraft as well.

I set all levels to 0dB. To get the mics to a similar level to the music from usb, I need to crank up the gain for the mics on the soundcraft to almost the full +60dB. My questions:

- is this normal? I get quite a bit of extra noise doing this...
- is it ok to just plug in the mics directly into the mdx2600? Ive heard people say that Id need a preamp here. If yes, what would be suitable?
- People mentioned cloudlifter, could this be inserted before the behringer? It works, but i find the values very sensitive to regulate on the compressor.

Thanks in advance!
 
Maybe that could be an issue ( though its not as quite as extreme as described there). How would i know if the input on the behringer is high or low impedance?
 
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It’s not about impedance. The compressor thing expects line level signals, and the SM58 is nowhere near as loud as it wants. Then, it’s a compressor, so it’s turning the already low level down even more. In the process, the circuit also adds noise. Then you’re trying to turn that all back up afterwards. It would be much better to get as much gain as you need before hitting the compressor, so that you’re not turning up so much noise. That Behringer device has a switch on the back for +4/-10 nominal level calibration. Setting that to the -10 option will get you some of that gain, but it’s still not going to be enough.

In the end, it really is about how much noise you can tolerate, but it would be better with a preamp before the comp. You don’t have to get anything fancy. A decent mic pre is pretty easy nowadays.
 
@ashcat_lt thanks that clears things up and matches what Ive read online ( though I am confused that it says dynamic mics dont need a preamp but I digress). Could you maybe recommend a device? I looked around and Im not even sure what I could use - most Ive seen require phantom power, which I think I dont have at the behringer (though it's available on the mixer). Would really appreciate some advice thx!
 
@cboe - it would help if you explained what you are trying to do with this mismatched equipment chain you've set up.

A PA has a microphone preamp, and almost any PA has enough gain for the SM58, but, yes, you could put a CloudLifter in there, powered by phantom power [directly] from the PA. If your PA has effects send/return, you would put the Behringer piece there, and use the FX-send from the PA to control how much went to the FX.

But you have a computer connected. Why?
 
@keith.rogers

Hi, im a newb and recently got the following karaoke setup:

2 Shure SM58 -> Behringer MDX2600 -> Soundcraft Notepad 8fx -> PA.
Laptop is connected via usb to soundcraft as well.
Click to expand...

It's right there, it's for karaoke. I really don't think its that mismatched, the mixer has everything I needed, even a karaoke effect. The computer plays the music. I just wanted to add the compressor, thus the question.

Please tell me what's mismatched here besides apparently the compressor, I'd love to learn.
 
Yeah, my eyes went right past karaoke. I thought you might be recording...

I'm trying to understand why you need the mixer if there's a PA. But maybe the PA is the house system and you can't get to its board? You're using the computer also for a video feed?

I'd probably have just started with a mixer that has a compressor on the first couple of inputs, and a mic GAIN in addition to volume/level. Send the computer's headphone out to a mixer line in. Keeping it simple.
 
cboe said:
@ashcat_lt thanks that clears things up and matches what Ive read online ( though I am confused that it says dynamic mics dont need a preamp but I digress). Could you maybe recommend a device? I looked around and Im not even sure what I could use - most Ive seen require phantom power, which I think I dont have at the behringer (though it's available on the mixer). Would really appreciate some advice thx!
Click to expand...
Dynamic mics do need a preamp. What they don't need is phantom power.
 
@keith.rogers maybe theres a misunderstanding, with pa i meant my 2 pa active speakers. Sorry if i missled with me not knowing proper terms here. They only have one xlr input so I think I need the mixer. Video is completely seperate!

@RRuskin thanks for the explanation! Could you recommend something thats not overly priced? The mic inputs of the soundcraft 8fx are preamps... Are they just not good enough and noisy? Can i send a previously preamped signal in there? Will a preamp actually result in less noise or will a cheap one be just as noisy?

Btw the compressor did work without the preamp, just had to set threshold etc. very low and I assume thats not ideal...
 
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I'm thinking you need to understand the gear you have now. Your mics should be connected to the mic ins of your Soundcraft before passing the signal on to any other device.
 
Had a quick shufty at the two bits of kit. No, the Behringer is not suitable for mic input, not enough gain* and will be noisy. The Soundcraft should be fine, had one and the mic pres seemed ok.

Then feed the Behrry from the mixer's AUX output and then back to a line input on the mixer then XLR on to the PA. The USB backing track feed 'should' be able to be mixed back in with that signal but that depends on how the mixer routes the signal. However, I am sure there is a way to do it but the mic must go into the mixer.

Not sure why you want the Behringer in the path? Compressors always limit the 'gain before feedback' in PA systems and always worsen noise levels. Use good mic technique to control levels.

*a "600 Ohm to 50k" mic transformer MIGHT get you enough gain but I doubt it.

Dave
 
@RRuskin @ecc83 thanks for the input! It makes sense that the mic input has to go in the mic ins obviously...

Since for our karaoke we have singers of all kinds of skill, I wanted the compressor to lift up the whisperers and push down the yellers a bit. Plus the tube and enhance of the behringer might give some extra quality but thats not that important.

Would this work, basically as @ecc83 described: send the 2 mics through aux to the compressor and back again with jacks to the line ins? Can I still use the notepad's effects then? Aux/fx is controlled by the same knobs...

This quickstart guide has a graphic with the routing. I also found this in the manual:

Notepad 8FX
Aux/FX Sends control input channel contributions to both the FX processor and the Aux output via the Aux master control. The processed signal is returned from the Lexicon FX processor at unity gain to the master mix, so the Aux master acts as the overall wet/dry control
Click to expand...

If i turn up the aux/fx knobs of the mics + aux master + effects, in my mind i should get the original mics on my aux, plus the effects on my master. However, the effects would be based on the "uncompressed" signal. Is this viable? Id test it but dont have the cables now...
 
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You bought a mixer without the channels having the very common insert jack where the compressor connects to. You dont really have yet the skills to bodge it in a way it will work successfully. Rule number one. Mixers need operators. If you want a set and forget, using the limiter to try to level things out, that rarely works, and feedback city is the usual result. Scrap the compressor and just plug the 58 and the computer in and it works fine, using a person to set the music to voice balance, and job is done. For what it is worth, karaoke also usually needs reverb, so you are sorted there. Just forget the compressor. The 58 works perfectly directly into that mixer, your active speakers will be happy, so job done. Setting up compressors is a bit of an art, and on cheaper systems, adding one is rarely positive. Often, you end up with an unstable system when yo7 hand mics to untrained people.
 
Heed Mr Aylestone! You cannot solve the repro' problems of untrained, inexperienced performers* with technology well, not unless it is very expensive 'AI' stuff with a top bloke or gal driving it.

K.I.S.Sir and try to get the others to get their act together.

*I "did my time" in theatres with AmDrams and Gang Shows!

Dave.
 
Thanks yall Ill probably do just that and drop the compressor. I didnt expect to fix singers (and our standards arent that high so this is already overkill ?), was just hoping for a bit of extra quality and convenience. Thanks for the input and explanations! What you mean with K.I.S.?
 
cboe said:
Thanks yall Ill probably do just that and drop the compressor. I didnt expect to fix singers (and our standards arent that high so this is already overkill ?), was just hoping for a bit of extra quality and convenience. Thanks for the input and explanations! What you mean with K.I.S.?
Click to expand...
I was being polite! "Keep It Simple Sir" (I have assumed? Could be "Sisi"? )

Dave.
 
Microphones need to see a microphone preamplifier.
Your mixer has two, behind its XLR inputs.

The compressor and PA speakers expect line level so plugging a microphone directly into either is no good.

Taking the inputs 1 and 2 (your microphones) out Aux and back into channels 3+4 is an option, assuming you aren't using those already.
If Aux is stereo then that should work perfectly.
You'd need a 1/4" TRS to 2x 1/4" TS cable to achieve this.
Yes, the compressor has XLR inputs too but that's probably a more common cable to get ^.


You'd want channels one and two hard panned left and right, so that they are kept separate from each other,
and the compressor can work on them separately.

You'd then set the pan on 3+4 to centre (or whatever your preference) so that both singers hit both speakers.


Personally I'd leave out the compressor and just plugin two mics into 1+2 with XLR to XLR,
and the two main outputs into your PA speakers with XLR to XLR.

While it'll work, to some extent, a compressor isn't really for handling the differences between a loud singer and a quiet singer.
You'd be much better off having someone there to adjust the gain knob between singers, if needed.



A cloudlifter or similar, for additional info, is better described as a booster.
Yes, technically it's a kind of preamp but with a microphone preamp we generally think of mic level input and line level output.
A CL1 or similar raises the mic level somewhat but wants to go in front of a proper mic-to-line preamp.

Running your 58s into the XLR microphone inputs of the mixer, you shouldn't need additional boosters. (y)
 
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Thanks a lot, ive learned a lot ? Ive heard a lot of people say that a compressor is great to have for karaoke... Is that false? Also seen videos of podcasters doing this and sounds great. How would you do a proper setup for this? Could I do the setup @Steenamaroo described better with a bigger mixer? Not planning to do anything just curious.
 
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