09.30.13

Pre-amp for a drum machine.

Putting the drum machine on tape is easy, but not as easy as one might think. Because our drum machine is a consumer- grade piece of equipment, the output voltage of the signal is pretty low. This means that even when the drum machine is playing at top output level, our "pro-level" tape machine still thinks it's kind of quiet and records the signal at well below the optimal level. When we play this back, we'll get more noise and tape hiss than we'd prefer. So we've got to get that drum machine signal louder. How?

We'll use a signal amplifier - either a microphone preamp or an outboard EQ unit. And beyond just boosting the drum machine's output signal to something our tape machine will like, there's a chance that the preamp will add a different color to the sound. Which sounds best? We've got 5 options:

1. Into our Allen and Heath board

2. A Hamptone HFPJ-1 JFET preamp

3. An Orban 6228 parametric EQ

4. An FMR RNP 8380 preamp

5. A dbx 786 preamp

Here they are, one after the other, with a voocal "label". There's a "regular" style of drum machining and a "heavy" version with lots of double bass and cymbals.

Of the five choices, they all sound a little different but it's honestly tough to hear which sounds better. Number 2 (the Hamptone preamp) sounds the most different through the monitors here in the studio - it really emphasizes the bass content and comes off as unbalanced as a result. So that's out.

The others are, frankly, harder to pick from. During the slower part, I'm trying to concentrate on three things - the impact of the bass drum, the clarity of the snare and the coherence of all the cymbal stuff. And boy, it's hard to pick. (This is a good thing - it makes me realize that I've got about 4 choices that are all about the same.) Gun to my head, I think I'd choose the 786, (#5). Part of this may be because I think that it's not smearing the high-end stuff as much as the RNP (#4) does, but retains the snare clarity. And the double bass drum seems to hit in a nice spot.

But the other thing may have to do with EPI, which is also known as Expensive Preamp-Itis. This is a condition where you spend a lot of money on something and then think that it's better because it's new you spent a lot of money on it. (There's also EMI for Microphones, ECI for compressors, etc.) So the final decision is that - other than the Hamptone - they're all pretty good. I guess I'll plug it into the 786 because it's the newest of the bunch.

Two other things about this. First, I'm going to add some low end EQ from the Orban later, so I could use use that and save myself an extra trip back to the EQ when mixing down. The only problem is that I don't know how much I'm going to add without hearing the rest of the instruments, so this will have to be added later.

Second, the drum machine creates a very low level signal when it changes its digital bits into actual analog sound. This tiny little voltage is then amplified onboard (which is why it has a volume knob) and then send to its outputs. So using a preamp to get the signal to tape machine levels is really just putting a second amplifier (the preamp) after a first amplifier (the volume signal onboard the drum machine). Does it sound better to have the 786 doing most of this amplifying work, or the thing onboard the DR-660?

Truth be told, the difference was so slight that I didn't even to through the trouble of creating the comparison file for you to hear. I figure I'll just split the amplification half and half between the two.

So the signal path for the drum machine will be -

- Drum machine (50% volume) into dbx 786 (making up the rest of the gain) onto two channels of the tape machine.

Next, bass mics.

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Here's how the sound samples look in a DAW program. Top line (Sample 1) plays, followed by second line (Sample 2) and so on. This repeats once for the Soundcloud samples.