The Next DIY Stick Preamp
This was originally posted on the forum on stickist.com. I want it here too.
This is my second Stick preamp project. This one has more to it than my first one.
I have finished the first of three prototype DIY Stick Preamps. This one is based on this circuit from Jack Orman. I bought two Printed Circuit Boards from him:
http://www.muzique.com/schem/mosfet.htm
This is a prototype and I wanted to save money on the box so I used a cheap plastic storage box. Once I have finalized my plans based on the prototypes, I’ll use a high-quality box. Here’s the first picture of it:
It has two channels, as you can see. Here’s the top showing the knobs:
And here’s the insides showing the circuit boards:
And here’s one completed circuit board waiting for its box.
Operation:
- It is two mono channels that are completely separate, they even have separate batteries.
- The Gain control varies from about a 4db boost to a hefty 30db. This is a lot of gain and you can overdrive most amps with it.
- The Input Impedance is a really interesting feature I decided to add. We talk about what the best input impedance is for Sticks a lot on the forum. I wanted to be able to hear the difference on the same preamp. So, I added these rotary switches that can vary the impedance in discrete jumps. This will let you know exactly which one you prefer. The different values, all in MOhms, are 1, 2.2, 3.3, 4.7, 7.5 and 10. I was worried that there would be a pop when the switch was changed but it is dead quiet.
How’s it sound?
I have one of the original simple little preamps like Curtis and Japhlet have made. I don’t have a StepABout to compare it with, though. I was delighted with my first little JFET preamp and I thought it would be hard to beat. But, this mosfet pre is better, and I think it is much better. First, it has gain, lots of gain. This is great even when you don’t turn it up much. When you play a little harder it really gives you the gain. You have the feeling that it won’t quit, it will just keep getting louder as you play harder.
Next, the frequency response is basically straight flat. There is no coloration of tone at all. The JFET circuit is known to add a pleasing coloration to the sound of guitar-like pickups. Pleasing to most people, that is. This mosfet circuit adds nothing, it just gives you all the sound from the pickups.
The input impedance switch gave me a big surprise. The difference in tone and highs from 1 to 10 MOhms was actually fairly subtle. It is quite noticeable but it is not as dramatic as I thought it would be. The other surprise is that I am tending to like the bass side to have a lower input impedance than the melody side. Right now I’m at 2.2 for bass and 4.7 for melody. I think this is a really nice feature. I had originally just planned on this being a prototype feature. Once I found my preference I was going to just hard-wire that in the final version. However, now I’m going to keep the switch. If you are going after a rounder, more jazzy tone, then 1 or 2.2 might be better. If you are going for an acoustic sound 7.5 or 10 might be just the thing.
And then there is the tone. The tone is just wonderful. It is clear and transparent with no nasty edge to it. The highs are crystal clear and there is more bass than I was ever used to. This is a sweet circuit, I can now see why it is one of the most popular ones in the guitar and bass DIY communities. And Jack has been very helpful. I asked him a bunch of questions and he answered them all in good detail. The boards are very high-quality and building them was a joy.
How about noise? The circuit uses a single mosfet transistor. This results in an extremely quiet circuit. You can hear lots of noise if you turn the gain up all the way. But, that would be expected at 30db of gain! At normal levels you need a completely quiet rig and be listening with headphones to hear any noise from the preamp if you turned it up a bit.
Next, I’m making another prototype based on JFETs with more gain than my last one. This is getting interesting!
Take care.