That MG15 pre-amp looks similar to the Guv'nor pedal also produced by Marshall. Guess the sound could be similar. But a believe there are two important differences that could make the distortion sound different;

- Guv'nor uses two red LEDs to produce (symmetrical) clipping, with one green an one red LED, which the MG15 pre-amp uses, the clipping should be asymmetrical if I get this right?

- Instead of connecting the diodes to the ground like the Guv'nor, the diodes is at the feedback (not sure about the thermology here so feel free to correct me if I'm wrong) of the op-amp. This usually produce a softer clipping than putting them between the signal and ground. But the MJ4558 use in the MG15 is described as an "high gain op-amp" in the data-sheet (Guv'nor uses the old familiar TL072). So I don't know, I guess it can clip quite hard anyway.

I'm also looking for a good metal pre-amp and this one really looks interesting. One that sounds like the ProCo Rat (best metal distortion ever IMO) would probably be better, but maybe this one can work.

Thanks, and congratulations to you too!

Quote from: rowdy_riemer on January 20, 2010, 05:05:18 PM
No prob. That works much better now. BTW, you're amp looks pretty cool.  :tu:

Thanks, your amp looks good, really vintage using a such intercom box, not a bad idea. Just wonder if the back i open as in the picture, or if put something to cover the back then you play?

Yes, it totally does! Therefore I put all the pics and soundclips at google instead. Thanks for the tip, and hope it will work better for you now.

Hi, I've built two battery powered amps actually, one for guitar and another one for bass guitar. But I'll only mention the one for guitar because it turned out to be the most successful one so far. (Maybe I can post it later if anyone wants to know).

It's a Little Gem amp mounted in a open back cabinet with two fullrange speakers. For you how aren't familiar with the Little Gem amp it's a really simple (but sounds quite good anyway) cicuit based on the LM386 1/2 W audioamplifier chip. The Schematic can be found at http://runoffgroove.com/littlegem.html I use a 9 v battery to power the amp, or an DC adapter. It can also be run at 12 V DC, a little more output is available then.

I use the schematic (and perfboard layout actually) found at RunOffGroove and didn't made any changes, except that I added a headphone socket (how to wired this is only found on that site I think), a DC jacket, a socket for external speaker and LED power indicator.

The speakers are some cheap fullrange speakers I bought at my local hardware store. Haven't found much data about them. All I know is the power rating and the impedance (8 ohm). I wired them in series then, to get the total impedance higher.

The cabinet is made of 8 mm plywood and covered with fabric. The dimension of the cabinet is approx. 270 X 200 X 180 mm. The plate for the controls and jackets is a piece of galvanized sheet metal.

The sound of this simple amp is pretty amazing. Well there are a lot of downsides also, of course. A EQ would probably be a good idea and maybe a buffer before the amp. But it still is possible to get some really nice tunes out of it. Really loud too for only ½ W amp. And some how it sounds like a MUCH bigger amp.

I recorded some sound clips using only the microphone on my iBook and no external speaker, only the two in the cabinet, which you can see in the pics I've attached. The guitar I played was a "modified" HSS strat-copy manufacture by J&D Brothers. No pedals or anything before the amp was used. Gain was to 3 o'clock then recorder using the humbucker pickup (bridge) and no or a little gain then playing with the singlecoil pickup (neck I think). Master was set at max or almost max.

Can't think of more to tell about this little project now, so feel free to ask if I forgotten something or so. And I really hope my langue is not being judge in this contest...

And by the way, if you're using a single coil pickup, put the gain 12 o'clock or so and direct your guitar in the right position, you can pickup the local FM-station with the amp. Just enough loud to be able to hear it with the master volume at max.


Pics

Overview
Back
Top
Inside
Inside 2
Speakers
Front

Soundclips

Humbucker 1
Humbucker 2
Humbucker 3
Singlecoil

Yes, what I need is of course a high Z BUFFER circuit, don't know why I was taking about boosters. Your circuit (thanks btw) looks good to me, I'm thinking of building it actually, just need to know a few more things before a start....

I can fix a bias supply for the op amp, just a simple voltage divider you was thinikng of or? But that 10 v connection at your schematic makes me a bit confused. Why, and what op amp runs on 10 volts? Don't know what op amp I'm going to use yet, but at least some that runs on 9 v, since the mixer circuit also runs at 9 v. There's a lot of op amp that runs at 9 v, so which one should I choose? Is there any special features needed, or will the TL072 do the job? (the one used in the buffer circuit at generalsguitargadgets.com)

Ok, I know there was I hatch. But if using to pedals with the guitars could solve the problem, wouldn't it be enough to use a cleean booster/buffer circuit like the MXR microamp or  AMZ MOSFET booster (found on tonepad.com I think) in line with the guitar before the mixer? A such circuit could easily be built in the mixer, at the input of every channel, just skipping the volume control for the buffer circuit using the pots in the mixer-circuit for volume instead*. Maybe it was something like this that cicuit you thought about was designed. This way you'ld have a mixer ciruit this insultated high Z inputs or? (yeah my english maybe sucks but I hope you'll understand that i mean anyway)

* Just checked the schematics, Ithought the level controll at the booster only was an regular log pot at the and as in most stompbox design, but it's not. Looks more like an gain control or I don't really know. Maybe it's better to remove the pots at the input of the mixer instead or maybe both is needed, cause I it looks like they're actually doing to different things. Anyone got an Idé?

Hi, I'm thinking of a way to use two guitars in the same amp. Of course a simple 2 mono to 1 mono cable splitter can be use, there are some donwsides with this solution I've heard though. Sometimes some tones from one of guitarist totaly takes over the signal and playing with heavy distortion may also sound weird then a Y-cable is used.

But why not use a simple mixer cicrcuit like "Mini-Mixer" at generalguitargadgets.com? A better solution in my opinion, coluden't siounds worse than the Y-cable solution anyway. However I don't know if it will solve the problems mention before, I'll have to try I guess.

So, have anyone else done something similiar and want to share their experience before I start maybe? If there's a better mixer-circuit for guitar, please post.