Guitar or bass pre-amp


What I want to say before you read the following:

Sorry for my english. I translated the description directly from a german 
book ("Elektrogitarren" by Helmuth Lemme, Topp Buchreihe Elektronik Bd. 
446) and I'm not a professional. The sentences probably sound terribly 
german! If you have problems, mail me to:

nikik@swissonline.ch


Material list:

1       mainboard for the circuit 
        (coated on one side; 8 x 8 cm, 1 cm = 10mm = 0.394 inch)
1       IC type TL 074 or TL 084
1       IC-socket 14-poles
1       100kOhm trimpotentiometer (please look on the plan for dimensions)
2       3.3kOhm resistors or smaller (min. 1kOhm; see description) 
3       10kOhm resistors
4       22kOhm resistors
2       330kOhm resistors
2       10nF capacitors (2.5mm contact distance)
1       100nF capacitor (2.5mm contact distance)
2       1microF capacitors (5mm contact distance)
2       4.7microF capacitors (5mm contact distance)
3       mini-switches 1-pole (optional)
1       mini-switch 2-poles (optional)
        (if you want to keep the 5-way-switch from Fender, you have to build
        the mini version; if you want to change the switching and build the 
        basic version, be sure that the switches don't reach further to the 
        inside than max. 2.3cm)
1       10kOhm potentiometer with 6mm-shaft 
1       250kOhm potentiometer with 6mm-shaft 
        (because its easier and cheaper to get a potentiometer without split 
        shaft, I got "normal" ones and put original Fender chrome knobs on them. 
        I have to say that this looks much cooler than with the plastic "things" 
        of the Strat)
1       2 x 10kOhm double- or tandem potentiometer with 6mm-shaft
3       chrome knobs  
1       contact for 9V-batery (cable included)
1       9V-batery
1       Stereo jack
some    wood for the placement of the mainboard (8mm thick)
4       screws (2.9 x 9.5mm)
some    2 component adhesive (is that correct english?!?)
200cm   cable (for example thiner loudspeaker cable)


Work you have to do:

Redraw the lines of the print pattern with a black permanent marker (no or 
almost no light should go trough the lines) and take it to a print 
specialist where you will get the mainboard of the circuit. 
Place the electronic parts like on the plans. 
Connect it to the pickup switch/-es, batery, volume/tone potentiometers 
as discribed on the schematic. 
A 9V batery has to be placed somewhere in the guitar (Strat: under the jack 
if you turn the metal holder upside down or better, if you're not afraid 
of further bodywork: create a special batery hole in the backside of the 
guitar (that's how I did with my Strat, I placed it, if you put your guitar 
with the neck upward, right above the 5-way-switch, covered with a small 
plastic board); putting the batery under the regulators is not practical 
(that's how you had to do it with the original Stratoblaster from Alembic, 
I simply don't know if the batery lasts for 5 years).
Paint the inside under the switches with a special electric conducting coat
or take a metal foil instead to shield out disturbing signals (this is 
optional; I had no problems with a TL 084CN without shielding).
 

Description:

The circuit works like the Stratoblaster from Alembic. It's not the original
circuit, but it has further possibilities. It's based on the 
"statevariable filter" priciple.

With the 100kOhm gain regulator, you can set the amplification from 1 to 
10 times. You can adjust the resonance frequency with the tandem- 
(or double-) potentiometer, with 2 x 10kOhm between 1,2 and 4,8 kHz.
For e-guitars, this is just about right. If this is to low (if you want 
thinner, glassier tones), simply change the 3,3kOhm resistors into smaller 
ones, but not smaller than 1kOhm. For an e-bass, you usually want the 
opposite: change the tandem- (or double-) potentiometer to 2 x 25kOhm 
(then you reach down to 560 Hz), to 2 x 50kOhm (300 Hz) or 2 x 100kOhm
(150 Hz).

The resonance top level can be adjusted with the 250kOhm potentiometer 
between 0 and 15 dB; with this, you surpass the resonance of every 
pickup. The variety of tones of this circuit is allmost unbelievable.

For the amplification test, you have to put the guitar together but leave 
the mainboard outside and connect it with addicional cables, or you can 
place the gain regulator under the jack and connect it with a cable (that's 
practical if you want to change the gain later). Adjust the gain or 
increase the voltage (max. 36V) if needed (test this by picking the strings 
very strong). If you want to run the circuit with 36V (I don't know where 
you would place the bateries), be sure that the electronics are able to 
run with 18V.

The tone of the pickup doesn't matter anymore with this circuit, it works
even with low impendence pickups.
There are some cases to change the pickups:
If you want to get rid of the noise from the single coils, use single 
coil - sized humbuckers instead (be sure that the noise doesn't comes from
the cable or the amp!!!).
If your pickups are strongly microfonic.
If your strings don't get the same volume and you can't adjust the height
of the poles.
If the resonance top of the pickup is too weak.


I will send the construction plans, the schematics and the print pattern 
on a foil to your address or P. O. box if you're ready to send me back 
5 $US for it.

All the best!!!

Niki