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Old 7th April 2007, 03:27 AM   #1
garydmd is offline garydmd  United States
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Join Date: Dec 2003
Location: west virginia
Default simple guitar preamp with bass treble distortion

Hi there,

Here is just a post of an amp I built. I am posting the results because I am personally very happy with the sound, and I would like comments from anyone who is more experienced. The schematic is shown below. The power amp is simply the 4 resistor amp with gain 33 and 1 uf capacitor on the input and it is not shown here. The preamp is shown below. I disassembled an old defunked gallien krueger amp and got 13 op amps LF353 JFET. Yes I am new, and I have never built anything with an op amp. So I thought I would tinker around with these 8 pin ic's.

When I started, I was going to be happy if I got a half way decent sound. I hooked up the following schematic, and boy, I was surprised. Call me crazy, but I thought this sounded awesome. It really reminded me of an old gibson amp I had as a child when the gain was down(kinks), I felt like I got a decent tube type sound with the gain in the middle (ac/dc), and when cranked, the amp seemed good for old school heavy metal, iron maiden, etc. In fact, to me, I don't feel like I had as good as sounding amp since my tube gibson.

I have been running amp simulators through clean/flat power amps and I think this preamp shown does a better job at simulating an old tube amp.

I ran this preamp into gainclone with gain of 33 and it was suitable and loud for a guitar amp. To me it sounded nearly as loud as my behringer 120 watt head.

The second op amp stage was used because the lf353 is a dual op amp and I wasn't using it for anything else.

I tried to run the circuit into a fender tonestack and marshall tonestack, but I never really got a good sound. I tried the basic high pass, low pass filter for bass and treble and I was able to get good sounds, so I left the configuration alone.

I thought about using the second op amp in the chip for channel switching, which is very common nowadays with guitar amps. You could use diodes/higher gain with input A, and no diodes lower gain with input B, and then use a footswitch.

However, I loved the simplicity of this amp and kept it like it is. The volume pot goes after the circuit shown and then into the capacitor and then the 4 resistor amp.

This amp seems entirely giggable and I am impressed with the sound and volume acheived through 2 12 inch speakers. I have also included the schematics for the tone control section and a wiring diagram which shows how easy the tone controls are to implement. The pictures are borrowed and modified from Adam's Amplifiers (http://amps.zugster.net/articles/tone-stacks)
But the design is my own and are simply high and low pass filters.
I included the picture because it is so easy to hook up, you just wire the components right to the pots. Place this tone control between the preamp and amp section.

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