Topic: Radio Design Labs STM-2

[tms]

Hi,

Has anyone ever seen these?  I'm thinking of replacing my SP-SPSB-1 battery box with a pair of these 'stick-on' mic preamps.  The price is right (free) and I'm hoping they will be better than recording with the gain cranked up to +12dB on the JB3 followed by more post amplification in the computer.

My only concern is the low end of the range, 50hz, seems high.  Isn't this number usually ~20hz?  What effect will this have on the sound recorded using this pre-amp?

Right now I'm running a stereo SP gooseneck cardioid mics, battery box, and JB3.  In the past I ran the battery box into a sony MD player at ~+25dB, but the JB3 only goes up to +12

Thanks for any help,
Todd in Buffalo


From the website:
http://www.rdlnet.com/stm-2.htm

STM-2 Adjustable Microphone to Line Level Preamplifier
 
ANYWHERE YOU NEED...

Low-Noise mic preamp
Adjustable output levels
Hi or Lo-Z mic inputs
Mic input to Line Outputs
Two balanced or unbalanced outputs
Internal/External Phantom Capability
RF filtered inputs
You Need The STM-2!

APPLICATION: The STM-2 is a quality low-noise microphone preamplifier designed for use in commercial sound, broadcast, and recording. The STM-2 is very flexible, with gain adjustment from off to +65 dB, two balanced or unbalanced outputs, and available phantom supply input! Its ultra-low distortion and low-noise performance make it the best choice, even when larger preamps could be used! The single-ended supply input range is from 12 to 33 Vdc! Each output drives high or low impedance loads.


Typical Performance
Input Impedance:             150 to 600 ohm balanced; 5 kohm unbalanced
Output Impedance:            150 ohm balanced to drive balanced or
                             unbalanced lines 150 ohm or higher impedance
Gain:                        Adjustable 0 to +65 dB
Frequency Response:          50 Hz to 25,000 Hz +/- 1 dB
THD:                         less than 0.050%
CMRR:                        greater than 60 dB (50 Hz to 30,000 Hz)
Headroom:                    greater than 20 dB (24 Vdc supply);
                             14 dB (12 Vdc supply)
Equiv. Input Noise:          less than 140 dB
Power Requirement:           12 to 33 Vdc @ 25 mA, Ground-referenced

[Scooter]

Cons:

-you still gotta get power to your mics somehow (not sure if those mics require power)
-can't adjust gain easily on the fly
-screw terminals, your cabling will be permanent, no options to change in the field
-gotta lug around a 12v SLA

[tms]

Thanks Scooter,

Those are all good points, they are definitely not ready to plug in and go.  I had to put them in a radioshack project box with some power and audio connectors.

What about the 50hz lower end of the range?  With the quality suffer from this and how will that make it sound?

Lugging around a 12V SLA battery is no problem, I'm using one to power my JB3 anyway and two of these preamps use almost nothing compared to the JB3.  They only use 25mA each. 

The mics get powered by phantom power from these preamps, the screw terminals are all wired inside a box now so the only connections are a 1/8" stereo jack from my mics, a mini-power plug, and two RCA jacks for the line outs.

You're right about the gains not being easily adjustable, there's no easy way to adjust on the fly.  My plan is get them close during sound checks etc. and set them a shade low (hopefully 2-5dB low), then adjust the levels up with the JB3 or later on in the PC.

I tried it last night in front of the stereo and everything seems ok. These are going up on the top of the mic stand, so 12 or 24V will go up and line level signals will come down.

These preamps run on 12-33 VDC (the manual says it will actually run on 9VDC), but with 24-33 VDC operate with >20dB headroom.  What does that mean? Is headroom important?

Thanks for the help,
Todd in Buffalo

Cons:

-you still gotta get power to your mics somehow (not sure if those mics require power)
-can't adjust gain easily on the fly
-screw terminals, your cabling will be permanent, no options to change in the field
-gotta lug around a 12v SLA

[Scooter]

What about the 50hz lower end of the range?  With the quality suffer from this and how will that make it sound?

These preamps run on 12-33 VDC (the manual says it will actually run on 9VDC), but with 24-33 VDC operate with >20dB headroom.  What does that mean? Is headroom important?

I doubt you'll notice any loss down at that level, it's in the sub-bass zone, plus I don't know the specs on your mics, but I doubt they extend that far down anyway...

It's just saying the the headroom of the amp is increased as you increase the voltage that is powering it, you'll prolly have to just deal with the voltage that you have.  Getting 24v power would be a pain...

If the rig works for you, and if it's not a pain to use, and if it sounds good to you, then it's great!  Good luck

[tms]

Ok, I'll try it and see.  The mics are 50-20k, same mics as in sp-cmc-20 just in a gooseneck so I guess it doesn't matter.  Should work better than a battery box and an MD running at +25dB.  If it doesn't can always go back. 

It's just a hobby, pretty far down on the list of priorities, marbe I'll run into sweetheart deal on a UA-5 or else something cheaper and better will come along

Thanks again!


Thanks

What about the 50hz lower end of the range?  With the quality suffer from this and how will that make it sound?

These preamps run on 12-33 VDC (the manual says it will actually run on 9VDC), but with 24-33 VDC operate with >20dB headroom.  What does that mean? Is headroom important?

I doubt you'll notice any loss down at that level, it's in the sub-bass zone, plus I don't know the specs on your mics, but I doubt they extend that far down anyway...

It's just saying the the headroom of the amp is increased as you increase the voltage that is powering it, you'll prolly have to just deal with the voltage that you have.  Getting 24v power would be a pain...

If the rig works for you, and if it's not a pain to use, and if it sounds good to you, then it's great!  Good luck