SM57 on amp is distorting the preamp input

[DanR]

I have been trying to record a guitar amp (Ampeg Jet-about 15 watts) with a Shure SM57 running through a M-Audio DMP3 preamp. Even though the amp is less than half way up and non distorted, I keep getting distortion, particularly on the highs from the preamp. I'm recording into an old Boss BR-8 recorder. If I just use the BR-8's pre, I still get distortion. I purchased a 30dB mic pad and although the level is attenuated considerably, I still get distortion when I get enough level to record. I substituted a cheap Radio Shack mic and also an EV dynamic mic that I use for vocals with my band, and I still have the same problem. I dug out an old Yamaha MM30 mixer (I'm pretty sure they're Hi-Z inputs) and if I use the mic pad and use a low to high impedence transformer, I don't get distortion.

So what gives? Surely someone else out there uses a SM57 through the DMP3 to record guitar amps. I thought I could isolate the guilty piece of equipment by trying out different mics, and even using the preamp of the BR-8, but I still keep getting the distortion.

DanR

[zed32]

how close are you putting the mic? and how much gain are you using?

[DanR]

Originally Posted by zed32

how close are you putting the mic? and how much gain are you using?

I've tried different mic positions from right on the grill cloth to about 15 inches away and I definitely still get the distortion even 15 inches away, especially without the 30dB mic pad . The distortion is a lot less with the pad, but it is still present.

The gain needs to be up (90%) to make the VU meters barely move (nowhere near in the red), yet it still distorts. When I used the same mic and preamp on vocals and acoustic guitar (it's all I have except for my band mic and the cheap Radio Shack mic) I have no distortion problems at all.

DanR

[BrentDomann]

This might sound like a stupidly simple question/suggestion, but where is your channel fader set? It sounds like you are getting (too much) input, but low output and low VU readings. I think some recorders have the VUs, even individual track or channel VUs, set post-fader. If your fader is down and you are cranking the preamp to compensate, you're clipping before you lose all that volume to the VUs.

Also remember that a clean guitar has a lot more dynamic range that a guitar that is clipping.

[DanR]

Originally Posted by BrentDomann

This might sound like a stupidly simple question/suggestion, but where is your channel fader set? It sounds like you are getting (too much) input, but low output and low VU readings. I think some recorders have the VUs, even individual track or channel VUs, set post-fader. If your fader is down and you are cranking the preamp to compensate, you're clipping before you lose all that volume to the VUs.

Also remember that a clean guitar has a lot more dynamic range that a guitar that is clipping.

On the BR-8, the channel faders don't affect the incoming signal. There's an input trim and a mic trim if you're using the onboard mic pre. When using the DMP3 and using the line input, the onboard preamp is bypassed. Even if every channel fader is down, there will still be distortion at the input. And yes, you're right about the clean guitar and the dynamic range. The distortion is less prevalent if I am using an overdrive pedal before the amp.

DanR

[Lectric_Lab]

sounds like an impedence mismatch too me or faulty channel, with all you've tried you probably have tried a different channel....right? A microphone wont usually cause distortion, its at the receiving end, going back to the old Tascam decks, I remember easily distorting the channel at the trim level...but it had xlr connects, 1/4" connects would be a high ....no problems using high-imp adapters? theres your culprit.

[Micter]

Originally Posted by Lectric_Lab

sounds like an impedence mismatch too me or faulty channel, with all you've tried you probably have tried a different channel....right? A microphone wont usually cause distortion, its at the receiving end, going back to the old Tascam decks, I remember easily distorting the channel at the trim level...but it had xlr connects, 1/4" connects would be a high ....no problems using high-imp adapters? theres your culprit.

Ya that's what I was thinking. Good call.

[jonnyc]

Is the ampeg jet a tube amp? If so you might want to try rolling off the volume even more. Low wattage tube amps can still distort on clean channels at higher volumes(even half way). I had an ac30 for a while that just loved to distort at even moderate volumes using the clean channel. However just rolling the volume down even lower and even trimming the guitar volume knob a little really solved the problem and gave me the nice sparkling cleans I expected out of the amp. If you really have tried everything else then go back to the begining of the chain and tweak the amp.

[DanR]

Originally Posted by jonnyc

Is the ampeg jet a tube amp?

Yep, it's a 1960 Jet with 6V6 output and 6SL7 preamp tubes.

DanR

[Lectric_Lab]

Originally Posted by DanR

Yep, it's a 1960 Jet with 6V6 output and 6SL7 preamp tubes.

DanR

Hey DanR...you wanna sell that ol' Jet?

[DanR]

Originally Posted by Lectric_Lab

Hey DanR...you wanna sell that ol' Jet?

Nope, don't want to sell it. I got it on Ebay about 4 years ago for $275. It's a great sounding amp. I use it a lot at home and it's just loud enough for band rehearsals. It's also light, which makes it an easy job transporting it to the rehearsals.

DanR

[Jimbo Jones]

Don't forget to rule out a faulty mic cable.

[tom18222]

how high is the gain on the amp? i've always heard to record with lower gain, because through the signal chain after its recorded, it can become too overdriven, not to mention for note clarity.

[DanR]

Back to the original subject of the distortion.....

I later ran the SM57 through the DMP3 into the line ins of the Yamaha mixer and had no distortion. So it appears that there may be an impedance problem between the DMP3 and the BR-8. Also, I found that if I ran the DMP3 into a FMR RNC and THEN into the BR-8, the distortion is easier to eliminate by backing down the BR-8's input levels a bit.

I had done vocals and acoustic guitar (with the SM57) with the RNC in the chain and had no problems there. I began the recording of the electric guitar not planning on using the compression and that's when the distortion manifested itself.

DanR

You need 2 mics to record an electric guitar through an amp.

You will drive yourself crazy using one mic.

Use the 57 in front of the amp make sure the signal is not driving any point of the chain.

Use another mic in the middle of the room or further away or even behind the amp.

Again make sure no part of the chain is being over driven.

Blend both signals until you get the right balance. You might have to reverse phase of one of the mics.