Rack preamplifier for acoustic guitar - diyAudio
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Old 13th January 2013, 09:48 PM   #1
diyAudio Member
Join Date: Oct 2009
Default Rack preamplifier for acoustic guitar

Hello everybody!

Few months ago me and my friends bought rack effect - TC Electronic M300. It was a gift for our friend, who plays acoustic - rhythm guitar in our band. We bought it, because I own one and I know it is great with acoustic guitar. So, since we all love rack equipment, we started searching for some rack preamplifier for acoustic guitar. Something simple and transparent sounding preamplifier in rack case. BUT, we found nothing. Except Pendulum SPS-1 which is hard-to-get stuff and also, it is really expensive. This sucks that we acoustic players don't have some good preamplifier for resonable price. So, last few months I spend designing electronic circuit of such preamplifier.

What this preamplifier contains, what are the goodies of this preamp?:
- discrete input stage, pad switch(-15dB)
- Gain, Bass, parametric mid control(frequency and level), treble, bright switch
- boost function(footswitchable)
- effect loop: mono send / stereo return(*)

- balanced MIC preamplifier. No phantom power. Gain knob, phase switch(**)

- aux input(***)

- stereo vu meter, Master knob
- Mute function(footswitchable)
- headphones out

- post master line out, balanced out(stereo/mono), ground switch
- footswitch(boost & mute)

What means(*****):
(*), (***): The circuit itself is designed that way that parts of it can be left outside. For instance, if someone need just basic mono preamp we can left outside aux input, mic input, headphones out, make it mono or stereo... So circuit and final preamp can be modified by wish/need.

(**): Microphone preamplifier is mixed with direct signal AFTER fx-return. Mix between direct and microphone signal is made with gain knobs, since they are transparent sounding(so, not like tubes).

Scheme is designed carefully and parts of scheme was already tested in other projects, so this thing should work. Everything will be packed in one rack unit(1U, standard 19'' rack).

So, why am writing this up here? Why I don't make 1239851 pieces and became the richest bastard on the planet?

I'm curious what is the demand for this kind of product. In case that there IS demand or let me say, if you are interested in this preamp, I may invest my further time and money to make prototype. With that kind of prototype I could tweeak it, test the circuit and finally, make some sample sounds which you could have for reference. The point is, that I don't want to invest money in something that doesn't have future at all or even there is no need for that kind of thing.

"What do you actually want from us up here?" Nothing but some feedback if you would be interested in that kind of preamplifier, which would cost you around 230EUR. The price of course is a matter of final "mass" production.

What I can promise is, that I am not going to sell any crap products. Meaning, I will make sure that preamp will have good specifications and of course, great sound. But, as you can see, this preamp is just preamp without any effects and other "useless" stuff. At the end, this thing should be usable in live as in studio.

I hope I gave you enough informations that you could make a decision. That doesn't mean I am collecting orders for a preamp, that nobody ever heard. That just mean I'm curious about how many of us are interested in that kind of preamp with that price.
This is it! I wait for comments, questions, crucifixion and spitting. Wait with orders.

Greetings, sch

p.s.: This picture presents the right-now state of circuit board. The controls&in&outs:
INPUT, pad switch, gain, bass, mid frequency, mid level, treble, bright switch; BOOST, boost switch; MIC IN, mic gain, phase switch; VU meter, mute switch, master, headphones out, aux.
On the back: fx send, stereo fx return, stereo line out(balanced&unbalanced), gnd switch, footswitch.
Some things can't be seen, because they are connected to the board with wires.Click the image to open in full size.
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Old 14th January 2013, 12:35 AM   #2
DUG is offline DUG  Canada
diyAudio Member
Join Date: Jan 2003
Location: mississauga ontario canada
Sounds like a guitar amp without the amp section for two guitars. (stereo)

If you want to accommodate an acoustic why not build a good mic system that can feed any guitar amp the player wishes to use?

Good luck on your project.
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
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Old 14th January 2013, 08:32 AM   #3
diyAudio Member
Join Date: Oct 2009
Originally Posted by DUG View Post
Sounds like a guitar amp without the amp section for two guitars. (stereo)

If you want to accommodate an acoustic why not build a good mic system that can feed any guitar amp the player wishes to use?
I don't think I understand what you tried to tell me. I will try to respond as best as I can:
This is acoustic guitar preamplifier. Output signal can be feed into any audio equipment like mixing desk, power amplifier, effects, guitar amplifiers,... So, almost anything except speaker, since it is only preamp not power amp.

About microphone preamplifier. As we all know, acoustic guitar is usually recorded with direct signal from pickup and external microphone. Sound from pickup is sharp, clean and pounchy, sound from microphone is soft and warm. Best sound is mix between both of them, this is what this preamplifier can do.

Well, I hope I unswered your question. You've probably know this things anyway.

Let me know, if there are any more questions.
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Old 14th January 2013, 10:12 AM   #4
Tesla88 is offline Tesla88  Italy
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Join Date: Dec 2011
Location: Italy
I worked in some recording mastering studios and the trick to get a good sounding acoustig guitar is a good audio compressor .
My suggest is to add a compressor , try with an optical or OTA...
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