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 DIY Stick Preamp Prototype Project - Part 1 
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Post DIY Stick Preamp Prototype Project - Part 1
Hi, all.

(Please excuse the length of this post. I wanted to share as much detail as I could. I could also just put this on my blog and link to it but this seems more direct. Let me know if this is too much.)

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:

Image

It has two channels, as you can see. Here's the top showing the knobs:

Image

And here's the insides showing the circuit boards:

Image

And here's one completed circuit board waiting for its box.

Image

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.

The Prototype Project

As you might remember, I'm going to make three prototypes based on three different and popular preamp circuits. Once I have all three done, I will be shipping them all to someone on the forum. I have a list of volunteers and their land-mail addresses. That person (maybe you Rob!) will then try them out for a few days and report back to us. Then they will send them on to the next person on the list. In a few weeks we will have had several experienced musicians and recording artists listen and comment on all the prototypes. I am not sure what will happen after that, but I think this will really be interesting!

My intention is not to make these for sale. I really don't have the time for that. But, I do have time to make a web site to support people making them themselves. I would put up very detailed instructions on how to build them and have all the parts lists ready to order from different vendors. Then, either on this forum, or a dedicated forum just for DIY projects, I and others would help people get theirs made and working. I'm a busy father and teacher so I have to do things one at a time over a fairly long period of time. This is the first step.

I hope this is useful to the Stick community.

-Eric

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Last edited by EricTheGray on Sun Jul 20, 2008 3:29 pm, edited 1 time in total.

Sun Jul 20, 2008 2:19 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
Eric,

This looks promising so far! I look forward to playing through them!

Take care,

Paul

http://www.myspace.com/paulwaltersstick


Sun Jul 20, 2008 2:39 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
Hey Eric,
Nice! That looks awesome. Thanks for doing it and for being willing to share with the community.
Looking forward to it!
-JBA

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Sun Jul 20, 2008 3:48 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
EricTheGray wrote:
That person (maybe you Rob!) will then try them out for a few days and report back to us.

Eric the Gray, wizard of all things electronic and variable impedance, please let it be me!

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Sun Jul 20, 2008 5:13 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
I love the smell of altruism in the morning 8-)

This is fantastic stuff...great pictures too (as usual).

Might I add that it looks funky as hell in that Tupperware(tm)!

:)

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Mon Jul 21, 2008 4:55 am
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Post Re: DIY Stick Preamp Prototype Project - Part 1
Nicely!!

Rob Cathcart


Mon Jul 21, 2008 8:02 am
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Post Re: DIY Stick Preamp Prototype Project - Part 1
Very cool. The clear box is actually really cool. I'm planning on building one myself here soon. I want to be able to turn the preamp on and off to make up the difference of active NS and the Stickup Grand.


Mon Jul 21, 2008 2:38 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
funkyd wrote:
Very cool. The clear box is actually really cool. I'm planning on building one myself here soon. I want to be able to turn the preamp on and off to make up the difference of active NS and the Stickup Grand.

The design actually calls for a bypass foot switch. I didn't bother with it for this prototype. But, it's a true bypass and would be easy to add back in.

-Eric

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Mon Jul 21, 2008 2:42 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
digitalkettle wrote:
I love the smell of altruism in the morning 8-)

Thanks, but I get a lot out of this project, too!

digitalkettle wrote:
This is fantastic stuff...great pictures too (as usual).

The lens I used costs over $500 and my wife gave it to me for xmas one year. I'm always looking for excuses to use it. It's my favorite lens!

digitalkettle wrote:
Might I add that it looks funky as hell in that Tupperware(tm)!

:)

Now that I'm looking at it a few days later I can see that it does look a bit funky! I think I'll start searching for funky plastic boxes. This could be fun.

-Eric

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Mon Jul 21, 2008 3:44 pm
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Post Re: DIY Stick Preamp Prototype Project - Part 1
Nice, I bought a pdf from him a while ago with information on this and a couple other of his circuits but never got around to trying them. this makes me want to get out the iron again.
So might I ask what the part number of the rotary switches is. that's a cool idea to test out the impedance in the circuit.
Mike


Mon Jul 21, 2008 5:15 pm
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