Here are a couple different ideas for guitar preamps.

The tube version is the master volume style preamp circuit from a standard
Marshall amp. Adding a simple op-amp buffer would convert it to a preamp with a normal line out.

For the solid state version shown I would recommend the TLO72 or similar op-amp. It could use a couple additions like a diode to prevent reverse power supply connection and input and out resistors.

 

Thanks! For now, I have two questions:
- if I understood correctly, I need to provide +9V for the solid state preamp and +/- (whatever) V for the power amp, correct?
- because I might not be able to find a transformer that provides 2x(whatever)V, which seems to be required to get both negative and positive voltage for the power amp, can I use a standard transformer and then use some circuit to get +/- voltage?

 

Shucks! That reminds me I really need to get moving on my guitar amp project.

First, I would choose the power amp and decide how you are going to power that amp. It can be a unipolar supply or bipolar supply.

Then I would choose a preamp configuration that uses the same supply, with some decoupling.

This way you do not need a separate supply for the preamp.

 

Good. But all the schematics on the site suggested before ( http://sound.westhost.com/projects-0.htm ) use bipolar supply. How can I power any of them using unipolar one? Take this particular schematic as an example. (it's power is 20W vs. my initial idea of 45W, but that will do too.)

http://sound.westhost.com/project10.htm

 

Here's an example of a single supply power amp circuit:

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000128.pdf

The reason that many power amp circuits require a split or +/- supply is so the at rest voltage at the speaker out is zero.
Many circuits can also be modified by adding adding input biasing and a coupling capacitor to the speaker output.

You can easiliy create a lower voltage preamp DC supply from a higher DC voltage by using a regulator IC or a resistor/zener diode/capacitor circuit.

 

Found It;
http://www.swtpc.com/mholley/PopularElectronics/Apr1968/PE_Apr_1968_pg44.jpg

I built this some years ago. Simple single supply 60 watt amp.
Called the MMM instrument amp.

Couldn't find the schematic, been driving me crazy for the last couple days.

Here's the rest:
http://www.swtpc.com/mholley/PopularElectronics/Apr1968/PE_Apr1968.htm

 

Single supply vs split supply.

If you use a single supply you need to couple output of the amplifier to the speaker with a capacitor of a fairly large value of about 4700μF, especially if you need good bass response.

With a split supply you can eliminate the DC blocking capacitor. However, you have be certain that the output of the amplifier is well balanced, i.e. the output is 0V with no input signal. Installing a fuse with the speaker is highly recommended. You can use thermal resettable fuse or even a small incandescent light bulb.

One of the problems with the DC blocking capacitor is the loud "thump" from the speaker when the power is turned on and off as the capacitor charges/discharges. A solution found in many high powered amps is to install a time delayed relay that switches the speaker in circuit after a short delay.

 

Shucks! That reminds me I really need to get moving on my guitar amp project.

It's got me thinking too... I DO need a new practice amp.

 

Here's an example of a single supply power amp circuit:

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000128.pdf

The reason that many power amp circuits require a split or +/- supply is so the at rest voltage at the speaker out is zero.
Many circuits can also be modified by adding adding input biasing and a coupling capacitor to the speaker output.

You can easiliy create a lower voltage preamp DC supply from a higher DC voltage by using a regulator IC or a resistor/zener diode/capacitor circuit.

The schematic you posted looks promising because it needs 28V at supply and I can only provide a ~27V transformer. BTW, do you know what is the price of that TDA2030 IC?

Found It;
http://www.swtpc.com/mholley/PopularElectronics/Apr1968/PE_Apr_1968_pg44.jpg

I built this some years ago. Simple single supply 60 watt amp.
Called the MMM instrument amp.

Couldn't find the schematic, been driving me crazy for the last couple days.

Here's the rest:
http://www.swtpc.com/mholley/PopularElectronics/Apr1968/PE_Apr1968.htm

Cool, but as mentioned above I can't find a 60V transformer. Can I run it at lower voltage and thus lower power?

 

Yes, the good ol' MMM guitar amplifier. I studied that circuit for a long time. I think I have those pages cut out and saved in my collection as well.

I did end up using the Sinclair Z50 amplifier modules which is based on a similar design.

 

Here are my criteria for a guitar amp project:

• Small, compact, light weight, portable
• Battery powered, 12V sealed lead acid battery
• Good bass response
• 10W - 20W
• bass, mid, treble controls
• might add reverb later

 

The price of a TDA2030 is under 2 bucks from Digi-Key.

Battery's - great idea !
And, two batteries in series @ 24 volts if you need a liittle more wattage would be simple enough.

There are reasonably priced solid-state reverb modules available.
http://www.accutronicsreverb.com/

Here at one of my go-to suppliers:
http://www.tubesandmore.com/

 

Thanks for everything! It seems that I'll do the amp with the TDA2030 + one of the preamps you suggested. One last thing, how can I add distortion effect, do I need a whole new preamp circuit for that or modify this one: http://forum.allaboutcircuits.com/attachment.php?attachmentid=55499&d=1368301625
Also, do I need to connect some kind of capacitor or something between the preamp output and power amp input?

 

You can create distortion by adding two diodes in parallel, one in the opposite direction.

 

Sorry, but I don't see where should I connect those diodes.

 

You can try after the preamp before the main amp.

 

Thanks for everything! It seems that I'll do the amp with the TDA2030 + one of the preamps you suggested. One last thing, how can I add distortion effect, do I need a whole new preamp circuit for that or modify this one: http://forum.allaboutcircuits.com/attachment.php?attachmentid=55499&d=1368301625
Also, do I need to connect some kind of capacitor or something between the preamp output and power amp input?

There is a capacitor from pin 7 on the output, that's all you need.

 

Alright, thanks for everything. I'll start thinking about the PCB & design and will post back if I have any problems or questions.

Thanks again!

 

Hey again. I finished the main amp board, but it doesn't seem to work, so I need your opinion.

I used this schematic here: http://prntscr.com/17ylh2 .. I am confident that the PCB I made is totally correct, so there might be a possibility that the electrical schematic in the link needs some modification. Can you take a look at the schematic and see if there is something (some component) that needs a different value or any other reason because of which the circuit doesn't work?

Something else. The method I used to test the circuit might be incorrect as well. I used the main board only (without a preamp), and used a cellphone for the input signal. I have powered the circuit with a +/- 12V from a PC power supply (not sure if it can provide enough current, on the -12V rail it supplies something like 0.5A).

Any opinions appreciated!

 

The schematic appears to be off the datasheet, and looks Ok.
You have the gnd of the split power supply connected to the circuit gnd correct ?

A quick test would be to check the DC voltages on the IC (referenced to circuit Gnd). The inputs and the output (pins 1,2 and 4) should all be very close to zero volts. Anything else, then check the wiring.

If that checks Ok, then you can test the left half of the amp which is connected directly to the input signal by removing the speaker connection from the right amp chip and connecting that to circuit Gnd