Do I need a direct box before a compressor?

David Mason · Post by **David Mason** » 28 Feb 2005 9:42 am

I am putting together some rack gear for recording purposes only. I am planning to (at least initially) set it up with a stereo compressor to a stereo graphic equalizer to a Lexicon 110. The compresser I am leaning towards is the Alesis 3630. I want to be able to feed it a steel guitar signal, a regular guitar signal, and signals from a fairly ridiculous variety of stompboxes. The Alesis 3630 claims to have an input impedance of greater than 100k ohms, unbalanced (as do the Presonus Comp16 and Bluemax). Is there any reason to put a direct box first, when a steel pickup only puts out 16K ohms or so?

Dave Grafe · Post by **Dave Grafe** » 28 Feb 2005 10:35 am

Try putting the comp AFTER the EQ. Also check eBay for an Ashly CL52 stereo compressor, it is a much higher grade of device and still shouldn't cost you much used.

James Quackenbush · Post by **James Quackenbush** » 28 Feb 2005 6:34 pm

You might also want to check out a company FMR....They have a RNC ( really nice compressor ) ( that's REALLY what it stands for ) ......GREAT sounding compressor ......Very inexpensive, and MUCH better than the Alesis ....Jim

basilh · Post by **basilh** » 28 Feb 2005 7:37 pm

I think you might have a problem matching the output level of the steel if you go direct ..you say

when a steel pickup only puts out 16K ohms or so

Puts out 16K etc implies that you think 16k is it's output VOLTAGE ..and not its IMPEDANCE..

The steel's output voltage will only be millivolts whilst the compressor will require upwards of 220 millivolts to drive it..
Check the INPUT sensitivity and compare that with the OUTPUT voltage of your guitar.. The pick-up manufacturer can tell you what the OUTPUT VOLTAGE is..
Baz

------------------

Steel players do it without fretting

http://www.waikiki-islanders.com

Jerry Gleason · Post by **Jerry Gleason** » 1 Mar 2005 11:13 am

Ditto on the RNC compressor. It's a great sounding unit. It can be transparent and unobtrusive, or it can slam like the old Armstrong "Orange Squeezer" that Buddy E. used on some of those early '80's recordings.

Like most any other device that's designed for line level, you would need to buffer the input with some type of preamp first, the steel pickup won't drive it well.

It works well for me from the output of my Hilton pedal, and gives the sound and response I prefer. Some may choose to place the compressor ahead of the volume pedal for a "hot" pickup sound with full volume pedal range.

Post by **Dave Mudgett** » 1 Mar 2005 3:15 pm

If the input impedance of the signal receiving device is not a lot larger than the output impedance of the signal generating device, you will tend to lose something. For a typical guitar/steel pickup, I think an input impedance of around 1 MegOhm should work fine. I think an input impedance of 100 KOhm (which is 10 times lower than 1 MegOhm) is too low for a 16 KOhm pickup. I suggest either 1. get a better compressor with a higher input impedance, or 2. get a DI box with a high input impedance, and low output impedance (this is the buffer that Jerry speaks of). It's the ratio of receiving input impedance to generating output impedance that should be high.

Post by **Dave Mudgett** » 1 Mar 2005 3:52 pm

Shoulda said this too. basilh is correct, you should be sure that whatever compressor you get, that the input voltage levels it can accept are appropriate to the output voltage level of the steel-pickups/guitar-pickups/stompboxes you use. This is completely separate from the input-to-output impedance ratio issue. Generally, guitar/mic output voltages are much smaller than line-level outputs. I took a quick look at the Alesis 3630 online manual, it looks like it can handle a wide range of input levels (although it said some low-voltage guitar ouput signals may need a preamp). I say all this because a lot of rack-mount compressors are designed for line-level operation. I suggest you shop carefully here.

One other point: There are various schools of thought on this, but I generally prefer to place any device that can generate noise after compression in the signal chain. EQs and effects normally add some noise to the signal. The problem is that compression, by definition, amplifies more when the input signal is small, hence tends to bring up the quiescent noise floor (i.e., when you're not playing, the noise level increases). So I prefer to give compressors the quietest possible signal.

David Mason · Post by **David Mason** » 1 Mar 2005 4:55 pm

Thanks for the replies! I am leaning towards starting the signal with either an ART XDirect active DI Box, or an ART ZDirect passive DI Box - it sounds as though the active boxes tend to "color" the sound less and can handle different signal levels better? I have a fair amount of control over the level of signal I'll be feeding the beast with my various little stompboxes - MXR Dynacomp, Boss 7-band EQ, and Rolls minimixer among them - but I'd like a DI that I can feed a variety of stuff to. I can already get a good sound going from my boxes right to the Lexicon 110, but I want to work the 2X15-band rack EQ and a stereo compressor in there too. For sure, compressor->EQ->Lexicon to start, and I'll fiddle with patching effects into one side of the stereo rig and leaving one side clean.

Is there maybe a single good book that explains this stuff clearly? All this inductance-impedance-millivolt-microvolt-microdot talk is making me dizzy. I don't need something on the level of "An Idiot's Guide for Dummies", but I'm not trying to become a recording engineer either, just trying to get after that joyful noise a little more competently.[This message was edited by David Mason on 02 March 2005 at 03:12 AM.]