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Old 26th March 2012, 09:27 PM   #1
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Default Acoustic Guitar Pre/Comp/EQ/Blender/DI

First off, this is a great forum! So much knowledge here, it hurts my brain.

I am a complete newb, and will be starting from scratch with simple circuits and kits. However, I have a 2 year plan for a unit I am hoping to build for myself, and I need your help.

You can see from the title of the thread what I hope to build. I'd like to learn by building the easier components as stand alone units first, using components that don't cost an arm and a leg, as they will be practice units and probably built several times over. These would naturally be followed by the more complex units, and eventually, tying them all together.

Where would you suggest I start for each part of the build?
  • Input Stages1
  • Variable HPF
  • Notch Filters (2 per channel)
  • Compressor (optical? VCA?)2
  • Paramtric EQ (3 bands per channel)
  • Phase Switches (location(s) and which circuits)
  • Mono Mixer/Blender (passive or active?)
  • Master Output Volume (for Amp out only)
  • DI Out3
  • Tuner Mute w/LED4

I know this is an ambitious project, but I am a stay-at-home-dad and I need something to keep me sane for a couple years! LOL

I don't care if it is floor bound or rack mounted. In the end, sound quality and transparency is what I am after. When I've built enough cheap versions of each component and figured out how to make them work together, I will go for high end components all around (wherever it will make a difference in audio quality and/or reliability).

1Ultimately, I would like to use a phantom-powered preamp that plugs directly into the guitar, like the preamp module from Pendulum Audio (scroll to bottom). However, I'm looking for something a little simpler. Just recessed input trims. I would like to use a simple LED clip indicators that will start to flicker once the trims have been set to what the first stage on the floor or rack unit wants to see. The reason for the plug in preamp is I am using a passive dual source system and want to run a longer cable and not lose signal. The system consists of a piezo SBT and either a DPA 4060 or Countryman B3 for the mic.

2Compressor is optional as far as being part of the unit. I'm happy with running an insert to a comp, as well. Although, this route would make me go the rack mount route.

3I'd like the DI to be 600Ω and unaffected by master volume. I'm sure there is a way to show the mixer input something resembling unity gain from this output. Right? LOL

4I don't need a tuner output, as I use a Peterson StroboClip on the head stock. This allows me to keep the floor and/or rack clean.

Thanks for any input you may have and feel free to point me to wherever you deem appropriate for anything having to with this project.

Josh
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Old 26th March 2012, 09:40 PM   #2
DF96 is offline DF96  England
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If you are a complete newb, as you say, then you have a lot of reading ahead of you!
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Old 26th March 2012, 10:07 PM   #3
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Originally Posted by DF96 View Post
If you are a complete newb, as you say, then you have a lot of reading ahead of you!
LOL I hope so! I can only read kid's books so many times in a day...
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Old 4th April 2012, 03:41 AM   #4
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I take it you are also a musician/guitar player from the series of project builds you have outlined. Acoustic or electric? It makes a helluva lot of difference in the path you take.
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Old 4th April 2012, 12:06 PM   #5
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Originally Posted by marvinkite View Post
I take it you are also a musician/guitar player from the series of project builds you have outlined. Acoustic or electric? It makes a helluva lot of difference in the path you take.
Strictly an acoustic player. I am learning bass, but it will take a long time to know what I want in that regard.

I'm going to do as much research as possible and figure out what to use for each stage of the unit, then figure out how to marry it all together. If you have any suggestions on what to read or any circuits that may be suitable, I am all ears.

Thanks,

Josh
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Old 5th April 2012, 04:10 AM   #6
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Probably the best (and quickest) road would involve ICs, in particular Op Amps, since they are Integrated Circuit versions of operational amplifiers that suit a lot of audio requirements in neat little packages. Some audio circuits like preamplifiers for headphones for instance can be 'hacked' and upgraded as easily as swapping out the Op Amps that came with the unit, since there are standard pinouts and similar in-circuit specifications that they (mostly) all share. Most audio gear in production today are based on Op Amps of some sort. Signal conditioning circuits (for D/A conversion) and regulated power supplies also use Op Amps. As you probably know in your gleanings from this forum and other sources, the state of solid state audio (even in this mostly digital world) has advanced tremendously thanks to smaller die sizes, and lower power consumption requiring noise floors to be reduced drastically. Modern audio-grade Op Amps are very good indeed. What it all boils down to (because I am in the same boat as you - I am currently prototyping an acoustic guitar with a built-in boundary mic system of my own design) what you are talking about concerning your acoustic music is amplification. Basic class A low-noise Op Amps with special input circuitry like JFETs with very high imput impedance for condenser-type mics and piezo transducer elements that inherently are high impedance devices. Preamps are a good starting point - since they are the first things in the audio chain from the signal source (pickups, microphones, etc.). I am NOT an electrical engineer, so I'm not too far up the path from you. Just an avid musician who wants the very best sound I can come up with on my own. Sounds to me like you are exited. That's good. There's tons out there to learn, now get crackin'.
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Old 5th April 2012, 07:48 AM   #7
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Hi Josh

This is mostly a hi-fi forum. The best place to find answers and projects about music production equipment is GroupDIY - We break stuff...and occasionally make stuff.
Some of the best designers in the world are there and they share their knowledge for free.
The only risque is you will like it so much you can't stop building new and interesting studio tools.

chrissugar
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Old 5th April 2012, 10:24 AM   #8
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Quote:
Originally Posted by marvinkite View Post
Probably the best (and quickest) road would involve ICs, in particular Op Amps, since they are Integrated Circuit versions of operational amplifiers that suit a lot of audio requirements in neat little packages. Some audio circuits like preamplifiers for headphones for instance can be 'hacked' and upgraded as easily as swapping out the Op Amps that came with the unit, since there are standard pinouts and similar in-circuit specifications that they (mostly) all share. Most audio gear in production today are based on Op Amps of some sort. Signal conditioning circuits (for D/A conversion) and regulated power supplies also use Op Amps. As you probably know in your gleanings from this forum and other sources, the state of solid state audio (even in this mostly digital world) has advanced tremendously thanks to smaller die sizes, and lower power consumption requiring noise floors to be reduced drastically. Modern audio-grade Op Amps are very good indeed. What it all boils down to (because I am in the same boat as you - I am currently prototyping an acoustic guitar with a built-in boundary mic system of my own design) what you are talking about concerning your acoustic music is amplification. Basic class A low-noise Op Amps with special input circuitry like JFETs with very high imput impedance for condenser-type mics and piezo transducer elements that inherently are high impedance devices. Preamps are a good starting point - since they are the first things in the audio chain from the signal source (pickups, microphones, etc.). I am NOT an electrical engineer, so I'm not too far up the path from you. Just an avid musician who wants the very best sound I can come up with on my own. Sounds to me like you are exited. That's good. There's tons out there to learn, now get crackin'.
Thanks for the great post; that's exactly the kind of thing I needed to hear. The preamp module definitely seems to be the logical first choice. I'll try to update here as I come across things.

Thanks again!

Josh
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Old 5th April 2012, 10:26 AM   #9
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Quote:
Originally Posted by chrissugar View Post
Hi Josh

This is mostly a hi-fi forum. The best place to find answers and projects about music production equipment is GroupDIY - We break stuff...and occasionally make stuff.
Some of the best designers in the world are there and they share their knowledge for free.
The only risque is you will like it so much you can't stop building new and interesting studio tools.

chrissugar
Chris,

I kind of figured this was mostly hi-fi, but had no idea where to start looking for another forum. You've saved me a lot of time, thank you. LOL

I don't mind mind that risk. However, my wife may have a thing or two to say about it.
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Old 26th May 2012, 10:49 AM   #10
teleman is offline teleman  Norway
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Yes, you'd need to think & go stage by stage. I've been that path....but you need to decide whether you want to design/use transistor/JFT/FT based input/buffer stages or IC! I chose the latter & it saved me many tears!

1.Piezo
SBT,UST or Disc?:I've not tried SBT & eleminated UST very early on as it sounds very nasal & quacky! These are constantly under great pressure under the saddle hence the quacky sound! A 20 -27mm piezo disc would suffice.Don't be put off by the price! It's amazing what you can achieve with a well designed buffer/pre. You should be able to source these on the e-Bay for roughly a $1.00 for 5-10 pieces.

Buffer/preamp
A non inverting buffer is a must. You can choose either a charge amp or a non -inverting opamp circuit. The input load impedance should be at least between 4-10 Mohm range.

EQ & gain stage
A good Baxandall 3 way tone circuit.You'd need to scale down the gain of each section. A parametric is not neccessary for this section IMHO.

MIC Pre
I've never come near either of the mics you've mentioned,so couldn't comment on these.
Linkwitz mic modifications would be a good place to start. Yes,a parametric EQ
with mid sweep would be good to tame feedback. Again you'd need to scale the gain down.

Phase Inverter
A simple inverter op amp circuit would do the job & by using a DPDT toggle switch you should be able to change the phase.

Compressor
I personally wouldn't have it ,as it would kill the dynamics of the guitar!

Mixer/summer
A simple virtual earth mixer should do the job. Do not use JFT devices for this stage as they are more prone to "capacitive" effect especially in the out put stages.

Phantom Power/single or dual supply?
You should decide as to how you'd run the unit? 9v,12v or 15v! & whether as a single or dual supply & then adjust the circuit accordingly.

Un-balanced/Balanced out put
This should be easy to implement.There are a lot of schematics floating on the web! An active balanced out put is not neccessary for a guitar pre IMHO;besides,these are not very easy to design & require very precise components. However, you could incorporate a simple passive balanced O/P which would give you +3dB gain!!

Choice of Opamps
Experimenting with these will be the key to achieve the sound you like! You need not go over the board with very expensive devices. One criteria though DO NOT use very high gain opamps! TL07x, NE5532/4, LF35x,OPA2132 are very good yet cheap & cheerful IC devices. Again the choice is yours & the sky is the limit!!

Capacitors
Always aim for the best quality caps you can afford. Avoid polystyrene & ceramic types if possible.Good electrolytics are very important,& always use higher voltage caps than specified.

By all means research & read as much you can. The amount of info available out there is incredible!

Good luck
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