Will this design work for a basic Discrete Guitar Preamp?? - diyAudio
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Old 30th January 2007, 04:24 AM   #1
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Default Will this design work for a basic Discrete Guitar Preamp??

Hi Guys, I am thinking about makeing a basic Guitar preamp for putting into my next DIY Guitar amp...

My last Guitar amp used Opamps for the Preamp stage and it sounds Pretty good but the sound is a Bit Muddy and there is Too much low end even after eq"ing out the Low end completely so I was thinking a discrete Preamp might have a More dynamic sound and more sustain and Clip more gracefully.....

So I threw together a simple schematic Borrowing some ideas from other designs (as I am not Experienced enough to Design a disrete preamp by myself yet but am pretty good with opamps)...

So could anyone with more experience than me tell me weather this design will work, Or at least has a good chance of working???
and/or tell me how to make it work or point me to one that will work.....

Thanx


PS: I am going to use a Basic 3 band Tone controll after this circuit before the power amp stage.....
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Old 30th January 2007, 02:54 PM   #2
teemuk is offline teemuk  Finland
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Just from top of my head:
- J201 is a bad selection to use in that "Till" FET circuit. Use something like J309 instead.
- You can't just lend a circuit and expect it to work without biasing to adapt the new supply voltages.
- Why have 1k? resistor in parallel with 51 k resistor?
- Why not use dual supply for the first stage as well?
- Why do you use Sziklai PNP stages?
- I simulated the BJT section of the circuit with pspice and it does not work. What were you trying to achieve with that strange configuration?
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Old 30th January 2007, 06:18 PM   #3
Minion is offline Minion  Canada
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Like I said before I don"t know hardly anything about Discrete designs....

If it won"t work then it won"t work ....

Can you point me towards a not to complicated discrete design for a Guitar amp Preamp that will work....I don"t like useing Fets as I have no real Idea of how to properly Bias them, Transistors seem easier to use but they don"t handle the High impedance Input from a guitar very well.....

What design would you suggest??

Thanx
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Old 30th January 2007, 06:47 PM   #4
teemuk is offline teemuk  Finland
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I'm not really keen on telling people what to build, I rather suggest some ideas. If you wish to build discrete stuff why not check out some older amplifier schematics from:
http://acoustic360.homeunix.net/schematics.html and
http://www.standelamps.com/support/s...ics/index.html
Or preamps from http://www.freeinfosociety.com/elect...ew.php?id=1325 or http://www.freeinfosociety.com/elect...ew.php?id=1326
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Old 30th January 2007, 07:10 PM   #5
Minion is offline Minion  Canada
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Thanx for the Reply and the Links....I looked through those designs in the links you posted and most seem too complex and and contain Parts that I don"t have and/Or are very hard to get were I am.....

Thanx anyways...

Maybe someone else will chime in with some other ideas for me to try.....


Cheers
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Old 30th January 2007, 07:35 PM   #6
teemuk is offline teemuk  Finland
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I hope so. Anyway, if you want something simple and discrete why not just scrape up together few common emitter stages and place tone controls in between...
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Old 30th January 2007, 08:04 PM   #7
Minion is offline Minion  Canada
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Well that is Pretty much all I want to do...
Nothing to esoteric or complext But Like I said before I know very little about useing Fets and Transistors so for me to throw together a couple Common emiter stages by myself is Just looking for Problems as I wouldn"t have the Slightest clue as to how to go about it....

Everything I have designed up to this Point have been simple Inverting/Non inverting Opamp Circuits and some Microphones and distortion pedals.....

I do have a Bunch of BC550/560 and some 2N4401/2N4403 and some 2N2222 and some J201 fets and some 2N7000 Mosfets and a Bunch of other Transistors but have absolutly no knowlege on how to use them in a Curcuit......



Cheers


PS: would this curcuit work OK...

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Old 30th January 2007, 09:12 PM   #8
teemuk is offline teemuk  Finland
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Then I guess it's just time to start learning... The circuit you attached is a start and probably works with certain supply voltage values but I suggest you start by creating one simple gain stage that works and then advance from there once you understand the basics of the circuit.

In past history, I found this link especially helpful:
http://users.tpg.com.au/ldbutler/TransisVoltAmp.htm
It shows how to bias simple BJT configurations for single supply voltage and is a nice resource for the basic theory as well. The math works for dual supply circuits as well - just make all calculations on the basis that a dual supply is just a single supply with higher voltage potential. i.e. +-15V dual -> 30 V single.

Also see:
http://www.dself.dsl.pipex.com/ampin...te/singleq.htm and http://www.dself.dsl.pipex.com/ampins/discrete/twoq.htm
For example, the fig. 27 gain stage shown in the last link is "self biasing" and gain set procedure is about as simple as it can get.

For JFET stuff see:
http://www.colorado.edu/physics/phys...FETbiasing.pdf
http://www.borbelyaudio.com/adobe/ae599bor.pdf
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Old 31st January 2007, 01:48 AM   #9
Minion is offline Minion  Canada
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Thanx for the Links ...I will definately read it all , I Probably won"t understand most of it But I will try breadboarding a few things and experiment a bit till I get something that works ok....


Thanx
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Old 18th September 2007, 01:06 AM   #10
billyB is offline billyB  United States
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Minion
Here is the coolest article about tubes and transistors and towards the end is a very simple 2n2222 amp schematic that they used in their comparisons.
I think I am goin to build one myself and see what it does raw and then maybe if it needs taming but a 10k ohm pot across the output . It might make a good thing to plug a guitar into to get more drive from the first stage.
http://www.spectrum.ieee.org/print/1640
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