looking for easy, low cost guitar amp project

[jmillerdoc]

Hello,
I have built several stereo tube amps to date and a close friend of mine was at the house the other day admiring them. He is a guitarist and it dawned on him that I might be able to make him a guitar amp.

Well, I am sure I can but I haven't the first idea of what to look for in a guitar amp. To be honest, I don't think he does either. Until now he has only played acoustic, non- amplified guitars but is getting ready to buy an electric (if I will build him an amp).

I have looked at many different schematics on the web and there is a huge variety of implementation out there.

I guess what I am looking for needs to meet a few basic criteria.
1) all in one (preamp with ability to overdrive or distort and treble/bass control)
2) I think push/pull will be the way to go for power's sake
3) simple schematic
4) low cost parts

I plan to use Edcor Iron and will build my own cabinet.

Any help leading me to a project that meets these criteria would be greatly appreciated. I am definitely open to suggestions about my criteria too. Maybe I should even have more criteria but I simply am ignorant when it comes to guitar amps and what one looks for in a good performing set-up.

Thanks again, this forum always proves to be the most helpful and you guys are great!
Jeff

[kavermei]

I would say start small. Two or three common-cathode preamp stages, a phase inverter, and two EL34, 6L6 or EL84 in push-pull. Drop in a tone stack. This will already offer huge tone-shaping possibilities e.g. by tweaking bias points, cathode capacitors, etc. Also, it will produce ample volume for practice and small gigs.

A push-pull stage creates mainly odd harmonics so you need to complement this with 2nd harmonic distortion in the phase inverter and preamp stages.

Later on you could add stuff like reverb or tremolo. Also, keep in mind higher gain ("lead") amps, with more preamp stages, may be more difficult due to proneness to hum and oscillations.

Have fun!

[speleo]

To keep it simple and cheap ... look at the AX84 project.

[Bandersnatch]

hey-Hey!!!,
My only SE amp I ever designed was for guitar amp service. One KT66, an EF184 and a twin triode( 6GU7 to 6BQ7 in gain ). Two grounded cathode stages feeding the EF184/KT66 E-Linear stage. The OPT is a custom Heyboer unit with a 10% tap to feed the E-Linear EF184 connection and a 40% tap for the Ultra-Linear connection to the KT66's screen. It is driving an open baffle EV Wolverine LS8 and is remarakbly loud.

I suspect the even-order harmonics generated by SE operation are quite desireable for instrument amp service, so I stuck with SE design. Power can be increased to ~15W if a properly loaded KT88 is used( see Pete Millett's E-Linear amp write up on his site for the power stage part of the amp).
cheers,
Douglas

[Eli Duttman]

How about something tried and true, like a Fender Deluxe? You'll have add some gain to deal with tone stack losses. Locktal 7F7s can sub for both the 6SC7 and 6SL7.

[Francis_Vaughan]

+1 on looking at AX84. It is a very nice and friendly forum, and there are some very good designs that are well sorted. In particular the designers are players and they understand the tweaking of the designs for sound. Guitar amps are a glorious thing, since there is no preconception about accuracy in sound, only the sound you want. So undersized iron, saggy power supplies, off the wall voltages and biasing are all part of the toolchest. That and a lot of experience in voicing an amp.

Guitar amps stride a wide variety in tones, from clean and warm (for say jazz players) through to high gain monsters that are essentially only capable of producing a hard edged square wave with any input. On the AX84 forums the original AX84 P1 remains a standard, and the P1eX a sold rock and roll voiced design.

Don't underestimate the criticalness of the speaker. Again, the choice has a significant bearing on the final tone. There is much good advice to be had on choices here.

[jmillerdoc]

I found the AX84 series of kits at Doberman's website, not too much info on the variety of amp kits. Where can I fond out more detailed info about these kits? The price is pretty descent but I don't know what features these kits carry.

OK, now for a real howler of a question.....what EXACTLY is a tone stack?
Jeff

[moonshine]

Originally Posted by jmillerdoc

OK, now for a real howler of a question.....what EXACTLY is a tone stack?

A tone stack is for tone control, in guitar amps there are usually bass, middle and treble controls. Check any old Fender or Marshall schematic to see the ubiquitous tonestack suitable for a guitar amp. You can also download Tone Stack Calculator TSC to compare different tone stacks with different component values easily.

Edit about the kits: check their schematics if you haven't done so already, they are the most exact reference there is. You haven't specified if you need a lot of distortion or only some. P1ex is easy to build and to get working and there is quite a lot of distortion with volume dimed. Hi-Octane has lots of distortion available from the preamp, but for that reason it might oscillate easily if not done right. If you (buy a kit and) follow the layout closely that should not be a problem though.

[Geek]

Originally Posted by speleo

To keep it simple and cheap ... look at the AX84 project.

Great site for beginners.

Cheers!