Thursday, September 16, 2010

New Guitar Preamp Project - NE5532 Based Buffer + Booster

Today I would like to show you my new design. It's a guitar preamp (buffer + booster). It's based on the same technology like MXR MicroAmp or CMOY.
The heart of the circuit is an operational amplifier: NE5532. I was testing also popular TL071, TL072, like in MicroAmp, but it was a little bit colder and less full than the NE5532.
The NE5532 has got much higher power consumption than the TL072/071, so it should work with some stomp-box power supply.

My preamp is working with the one volume potentiometer and two DPDT on-on switches.

One of the switches is used to switch the circuit from the buffer (almost no gain) to the booster mode and inversely. The second swich is used to turn on and off the volume control.

When the pedal will be working as a buffer, the volume control will be able only to decrease the signal. In the booster mode, the volume control can be used to manipulate the boost. This way of switching will allow you to switch your stomp-box from low gain to high gain by a one click. You will be able also to decrease guitar volume with no losses in the frequency characteristic. It is a very useful thing, if you want to have some more clean tone from your tube amp.

Volume control pot is on 50%.
When the pedal is working in the buffer mode, the natural guitar volume is decreased to ca 50%. In the effect, I have really clean, bright tone and my tube amp is not making a crunch.
When I will swich my pedal to the booster mode, it will start working in ca 50% of the maximum boost.
When I will swich it from the buffer to the booster mode by pushing both switches, my box will start working on the maximum boost.

The circuit is quite simple, so can be done on a multipurpose PCB (Printed Circuit Board).

List of parts:
1. op-amp: NE5532
2. potentiometer: logarithmic, 100 – 200 kOhm recommended (any value will work to some degree)
3. switches: 2x DPDT on-on
4. electrolytic capacitors:
      C1, C3, C5: 10 uF
5. film capacitors:
     C2: 0,1 uF
     C4: 600 pF (0,0006uF)
6: resistors:
     R1, R2: 100 kOhm
     R3: 1 Mohm
     R4: 1 kOhm
    R5: 10 kOhm (gain 11x), or 20 kOhm (21x), or higher value, up to 40 kOhm – You can try to use even some higher values than 40 kOhm, for more gain and really big crunch, but it can make some unwanted distortion effect.
Personally, I like to using boosters only for a little signal warm-up or a little bit of crunch tone, so 10 kOhm is enough for me.
     R6: 250 Ohm

In some next post, I will show you the 'easy to read' schematic of this circuit - here it is.