The Circuit is shown in Figure 1, and has a few interesting characteristics that separate it from the "normal" - assuming that there is such a thing. This is simple but elegant design, that provides excellent tonal range. The gain structure is designed to provide a huge amount of gain, which is ideal for those guitarists who like to get that fully distorted "fat" sound.

However, with a couple of simple changes, the preamp can be tamed to suit just about any style of playing. Likewise, the tone controls as shown have sufficient range to cover almost anything from an electrified violin to a bass guitar - The response can be limited if you wish (by experimenting with the tone control capacitor values), but I suggest that you try it "as is" before making any changes.

the preamp is just as usable for bass or electric piano as for rhythm or lead guitar. A couple of changes that you may consider are ...

* Delete the clipping diodes (unless fuzz bass/piano is something you want, of course). If these are removed, then the output should be taken directly from the Master output pin (M-OUT in Figure 1), so leave out / change the following ...
o Delete R14, and D1-D4
o Delete Q1 and associated components (C14, C15, R15, R16, R17)
o Delete VR5
o Change R13 from 4.7k to 100 ohms

You may also want to experiment with the tone control caps - I shall leave it to the builder to decide what to change, based on listening tests. C3 and C8 may be increased to 4.7uF to provide an extended bass response. If the gain is too high, simply increase R11 (10k would be a good starting point and will halve the gain).

Here is a little audio transistor audio AMP amplifier agnate to what you ability acquisition in a baby transistor radio. The ascribe date is biased so that the accumulation voltage is disconnected appropriately beyond the two adulatory achievement transistors which are hardly biased in advice by the diodes amid the bases. A 3.3 ohm resistor is acclimated in alternation with the emitters of the achievement transistors to balance the bent accepted so it doesn't change abundant with temperature or with altered transistors and diodes. As the bent accepted increases, the voltage amid the emitter and abject decreases, appropriately abbreviation the conduction. Ascribe impedance is about 500 ohms and voltage accretion is about 5 with an 8 ohm apostle attached. The voltage beat on the apostle is about 2 volts after distorting and ability achievement is in the 50 milliwatt range. A college accumulation voltage and the accession of calefaction sinks to the achievement transistors would accommodate added power. Circuit draws about 30 milliamps from a 9 volt supply.

This Guitar Amplifier electronic architecture adopts a able-bodied accustomed ambit cartography for the ability amplifier, application a single-rail accumulation of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the actual simple circuitry, alike for analogously aerial ability outputs, and a assertive congenital amount of loudspeaker protection, due to capacitor C8, preventing the voltage accumulation to be conveyed into loudspeakers in case of achievement transistors' failure. The preamp is powered by the aforementioned 60V balustrade as the ability amplifier, acceptance to apparatus a two-transistors gain-block able of carrying about 20V RMS output. This provides a actual aerial ascribe afflict capability.

Technical data:

Sensitivity:
35mV input for 40W 8 Ohm output
42mV input for 60W 4 Ohm output
Frequency response:
50Hz to 20KHz -0.5dB; -1.5dB @ 40Hz; -3.5dB @ 30Hz
Total harmonic distortion @ 1KHz and 8 Ohm load:
Below 0.1% up to 10W; 0.2% @ 30W
Total harmonic distortion @ 10KHz and 8 Ohm load:
Below 0.15% up to 10W; 0.3% @ 30W
Total harmonic distortion @ 1KHz and 4 Ohm load:
Below 0.18% up to 10W; 0.4% @ 60W
Total harmonic distortion @ 10KHz and 4 Ohm load:
Below 0.3% up to 10W; 0.6% @ 60W
Treble control:
+9 / -16dB @ 1KHz; +12 / -24dB @ 10KHz
Brightness control:
+6.5dB @ 500Hz; +7dB @ 1KHz; +8.5dB @ 10KHz
Bass control:
-17.5dB @ 100Hz; -26dB @ 50Hz; -28dB @ 40Hz

Notes:

* The value listed for C8 is the minimum suggested value. A 3300΅F capacitor or two 2200΅F capacitors wired in parallel would be a better choice.
* The Darlington transistor types listed could be too oversized for such a design. You can substitute them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4).
* T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected.
* D1 and D2 can be any Schottky-barrier diode types. With these devices, the harmonic modifier operation will be hard. Using for D1 and D2 two common 1N4148 silicon diodes, the harmonic modifier operation will be softer.
* In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q2) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
* R9 must be trimmed in order to measure about half the voltage supply from the positive lead of C7 and ground. A better setting can be done using an oscilloscope, in order to obtain a symmetrical clipping of the output waveform at maximum output power.
* To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
* Set the volume control to the minimum and Trimmer R3 to its minimum resistance.
* Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA.
* Wait about 15 minutes, watch if the current is varying and readjust if necessary.

source: free-circuits.com

The circuit must as many or as few input channels as you like and consumes very little energy mix.
The mixer is shown with two inputs, but you can only add as much as you want simply by repeating the “sections” that are clearly visible on the plan.





Electrical Part Component

R1, R3 10K Pot
R2, R4 100K 4.1 W resistor
R5 6.8K 4.1 W resistor
C1, C2, C3 0.1 uF capacitor
Q1 2N3819 Junction FET

MISC Wire, Shielded (Metal) Case, Phono or other connectors for power
Note
1- Many or as few channels needed to be added to the mixer. Do this simply by repeating the command “sections” are clearly indicated on the chart. A version of this mixer I saw had 25 entries!
2- A shielded case is probably necessary to prevent disturbances and vibrations.
3- The circuit can be powered by a 9-volt battery.

Posted in Sound Circuit, audio amplifier.