Listen to this hum with a NEVE EZ1290 almost all the way up. Normal?

[777funk]

I did some critical listening (not sure if I did proper or lab worthy testing) but I plugged a 57 in and turned the gain almost all the way up (2 clicks from it). Here's what I was getting:
http://www.rocketfireguitars.com/forums/other/1-4-13%20Neve%20Hum.mp3

Is this ok?

Beyond the obvious hiss and background noise there's a low volume sound that almost sounds like an electric motor (similar tone to a clothes dryer motor). This is the hum I'm talking about. Maybe 120Hz?

It's pretty quiet otherwise. I moved transformers and cabling around with no change so I don't think it's picking it up from the power transformer or supply circuit.

The SM57 was stuffed into a gig bag and the gain is so loud you can still hear background noise.
Again Note that this is CRANKED; If someone actually sang at a normal level into the mic it'd be hard clipping.



All the way up on the gain (last two clicks) and I get oscillation by the way.

 

[3nity]

2 clicks away from the last position?
Its about to pick anything on the field.

how far its the transformer from preamp and mic?
However i wouldnt move more than 4 position on the switch!

 

[777funk]

The low hum is what I'm a little concerned with but... realistically I don't think it's going to make or break my recordings (or even a pro recording for that matter)... more just electronics nit picking.

Maybe better filtering would fix it.

I still wonder if oscillation with the gain all the way up is normal with the EZ1290.

 

[Brian Roth]

That sounds like what I'd expect with a bazillion dB of gain and a mic plugged in.  What I heard sounded like acoustic noise rather than electronic.

Try soldering a 200-ish Ohm (actual value not hugely important) film resistor between pins 2 and 3 of a male "cable mount" XLR and then put the connector's metal cover on.  Plug that in instead of the mic.

Bri

 

[ruairioflaherty]

777Funk,

Offtopic question - sorry!  Are you the owner/builder of Rocketfire Guitars?

Cheers,
Ruairi

 

[radardoug]

The SM57 hum cancelling winding is not quite accurate, and an SM57 will pick up hum. Use a 200 ohm resistor in a connector instead.
If you are getting so interested in what your gear is doing, buy some decent test gear and measure it. Good old test gear can be had for peanuts on Evilbay.

 

[777funk]

That makes sense, that way I have just the load and no actual sound pickup. This was more just a quick and dirty test. I honestly think I hear power supply hum in there but I could be wrong and it could be just a noisy 57 microphone. The shielded resistor would be a much better way to go. Maybe I'll just unsolder the mic element itself and use the 57's case as the shield.

Thanks for the tip on test equipment. I have a scope for my basic troubleshooting and biasing things, but I have NO experience in signal to noise ratio testing etc. I'll have a look into that.

And to Ruairi, yes that's me (rocketfire).