DI guitar direct input box - increasing gain? - diyAudio
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Old 28th June 2005, 04:40 PM   #1
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Default DI guitar direct input box - increasing gain?

Hi guys I've made the circuit shown here;

http://inet.uni2.dk/home/cosmobiology/preamp27.htm

I'm trying to get the level out of an electric guitar up high enough to record into a line level socket. This preamp has helped somewhat, however I still need more voltage gain (and/or lower output impedance). Any suggestions on circuit mods to increase the voltage gain?

If anyone knows of other diy guitar preamp schematics that can get up to line level, please point me in that direction.


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Old 28th June 2005, 05:00 PM   #2
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If you want to keep the same basic circuit, you could try putting a bypass capacitor across R5. Maybe 100ufd or so. Try also making R5 smaller or R15 larger.
Otherwise a simple opamp non-inverting amplifier may be the way to go.
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Old 28th June 2005, 08:03 PM   #3
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Thanks audiopro. I will try the different values for the components you suggested.

As to the op-amp method, do you know of any good schematics for this purpose? I have a few opa627ap's around that I could use.
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Old 28th June 2005, 08:03 PM   #4
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Audiopro;
I used the bypass capacitor and that certainly gave it more gain (causing distortion), however the voltage swing on the output did not increase and I still can't get a high enough level for proper recording. It looks like I could use more headroom. With 27V input I thought that wouldn't be a problem, but it's probably the transistors limits.
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Old 29th June 2005, 12:15 AM   #5
Enzo is offline Enzo  United States
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Why not go into a mic input on the mixer/recorder?
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Old 29th June 2005, 12:24 AM   #6
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It strikes me that R4 being 15K (by design) limits the output drive of this circuit - if you are running into a nominal 600ohm load there will be substantial attenuation.
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Old 29th June 2005, 06:32 AM   #7
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I don't have a mixer or mic preamp at this stage.
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Old 29th June 2005, 04:57 PM   #8
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You could try one stage of this preamp, or search the entire site. There are quite a number of opamp and discrete designs here.
http://sound.westhost.com/project88.htm
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Old 29th June 2005, 05:03 PM   #9
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RE has a DI box design on his site:

http://sound.westhost.com/project35.htm
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Old 30th June 2005, 12:23 AM   #10
Brion55 is offline Brion55  United States
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Here is a preamp I have built many times over the years for myself and for other guitar players. I designed it to go inside the guitar and use one battery, switched with the output jack. You can set the maximum gain to any value you wish as long as the output doesn't exceed the rail voltage (unless you want lots of distortion). With normal use, the battery lasts about a year.

It could easily be put in a box with a PS, either single or split. If you need plans for the PS, let me know and I'll post one.

If you choose not to use the EQ, ground the two unused opamp inputs to keep it quiet.
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