Since I built my Little Gem MkII with sockets, I might give the 386LM-4/386BD a shot.

I just built a Little Gem Mk II for my son. It is housed in an old school intercom speaker cab along with the 8 inch speaker that came with my Valveking Royal 8. It uses a 9 volt battery right now, but I'll replace that with 8 C or D batteries. There is no volume knob, tone control, or power switch. Just plug in the cable to turn it on. When I have the volume cranked(via knob on the guitar) and I pick hard, the amp sounds like it is cutting out. Perhaps the two lm386's are wanting more current than  a nine volt battery will supply. Even if that isn't the problem, it probably makes sense to use larger batteries. ROG rocks!!!

One thing I did for a nice clean preamp was to setup a few fetzer valve stages(see fetzer valve article at runoffgroove.com). I used an 18v supply. The first two stages use mpf102's and I added a third stage using a j201 for some overdrive. 2n5457's might be better than the mpf102's, but I didn't have any at the time. Two or three 2n5457 stages should give you plenty of gain without preamp overdrive. However, using the mpf102's and the j201 gave me plenty of clean noiseless gain. Then, you can just put whatever tone control you like afterwards. mpf102 or 2n5457 source follower stages might be good for buffering a tone control circuit. Then again, I'm sure you can get suitable results with op-amps. If you want to go with jfets, you should definately check out the fetzer valve article and use jfets with a relatively high cutoff voltage.

Or just do what J M Fahey suggested. He seems to be pretty squared away and knows his stuff.

Another thing, regardless of weather you use jfets, bjts, or op-amps, have a good clean regulated power supply. I went the easy route, and used two 9v batteries, but I'll probably eventually build a decent supply.

Damn. Sounds pretty bad ass, dude.

Quote from: J M Fahey on November 20, 2009, 02:05:01 PM

QuoteEven something like the speakers used in the cheapest giutar amps. I see Fenders, Rogues, etc for $50 or less new. Their speakers sound great with a little 386 amp, but does anyone know where to get them or some like them?

You bet they do, they are *guitar* speakers. But they certainly come from a *massive* OEM factory in China with minimum orders in the thousands, who supplies everybody, just as Eminence does in the US with medium price guitar speakers.

QuoteIf a commercial amp sells for 50 bucks, they must get the speakers for $5 or so, maybe less.

I'm sure of that. Problem is, you won't find them in "regular" audio retailers, who cater to car audio, home theater and other similar big markets.
A Jensen Mod 5" or 6" or similar would be an excellent choice, and much better than what most use , but their $24 or $30 price goes through the roof.
Download their spec sheets and take a hard good look at their pictures, that's what you need: small light voice coils, thin all-paper cones (no foam), reasonable magnets (72mm to 86 mm diameter).
Google "jensen mod guitar speaker" in "Images".
From what you posted, the only reasonable one is what I indicated before, a generic speaker : 6", 3/4inch/19mm voice coil, light cone, unfortunately foam surround and meagre 60mm magnet.
I can buy them in lots of 200 for a very low cost, yet I prefer to roll my own.
Try those and post your results, and even better, some MP3s.

You roll your own speakers? That sounds pretty cool.

I love my Mod 8. Of course, then again, I do not have a tremendous amount of experience with guitar speakers or amps. I was using a general purpose audio woofer to test some of my amp projects. I knew I needed a real guitar amp speaker, so I broke down and bought a Mod 8. There is a world of difference, and it really wasn't that much $$$ (especially for guitar speakers).  However, the old intercom speaker I tried before wasn't too bad. There was a small cone in the middle of the driver that I removed to kill some of the highs. I think the Mac Ruby project(runoffgroove.com) used a Mod 6.

I noticed that the Red Circuits site specifies Q8 as an IRFP240, which has an absolute maximum gate-source voltage of +-20V. With the source follower set-up, the source voltage will closely follow the gate voltage. Perhaps if the gate voltage rises faster than Q8 can react, there will be a short time when the gate-source voltage exceeds 20V. Maybe a zener diode connecting the source to the gate will fix this. Ditto for Q9. Maybe certain bias adjustments affect the likeliness of this condition occurring. In an extreme case of putting the voltage between the gates at 40V, you would reach the maximum GS voltage. In any case, biasing closer towards class A would reduce the quiescent GS voltage.

Perhaps it would be safer to bias more towards class A if we added one or two parallel sets of MOSFETs and reduced the current through each set by increasing R14 and R15. If this all sounds like nonsense, then maybe I need to drink some more coffee. 

Keep in mind that the frequency response of computer speakers will be very different than guitar speakers.

Are you going to post any sound clips?

The schematic for the power amp is at the top, and you can get the schematic for the preamp here: http://www.ssguitar.com/index.php?topic=1121.0. I don't have a combined schematic for both, and I might experiment with different preamps before I build a finished amp, though I might just build the power amp separately for a more modular approach. If you decide to build this setup, let me know how it works out for you.

Here are some the sound clips I promised. Keep in mind that my recording setup is VERY CHEAP. On top of that, I'm using a crappy car stereo speaker. Hopefully soon, I'll get around to modifying my Combo amp to allow me to plug in different heads into the speakers. Also, I'm no Joe Satriani, so please excuse the guitar playing.

As I mentioned on my site, this circuit is a power amp, and needs a preamp. I used a MOSFET booster as a preamp. There are no tone controls, other than the tone knob on the guitars (Though there needs to be). On one clip, I'm using my Jackson 7 String ( I think a DR-7). On the other clips, I'm using my Ibanez RG5EX1.

I think playing this through real guitar speakers would improve the sound the most. If I had a tone control pedal, I would put it between the preamp and the CMOS Power Inverter amp. Maybe I'll build a ROG Tonemender for this.

I when playing clean, I was surprised how clear the sound was. The cheap mic didn't do it justice. Maybe I'll gut the mic housing and build a condenser mic.

http://www.riemer.us/sound/CMOS_Power_Inverter_12V/CMOS%20Power%20Inverter%20Demo%20-%20Jackson%207%20String%20-%20Mostly%20Clean.mp3
http://www.riemer.us/sound/CMOS_Power_Inverter_12V/CMOS%20Power%20Inverter%20Demo%20-%20RG5EX1%20-%20Bridge%20Psudosingle%20-%20clean.mp3
http://www.riemer.us/sound/CMOS_Power_Inverter_12V/CMOS%20Power%20Inverter%20Demo%20-%20RG5EX1%20-%20Neck%20Humbucker%20-%20Overdrive%20-%20Simple%20Chording.mp3
http://www.riemer.us/sound/CMOS_Power_Inverter_12V/CMOS%20Power%20Inverter%20Demo%20-%20RG5EX1%20-%20Neck%20Humbucker%20-%20Overdrive.mp3

Here are some pics. Obviously I don't have this finished yet. The first pic shows the amp as it currently exists, just some components connected on a solder-less breaboard. The speaker is just some crappy 20W car stereo woofer. In the lower left corner, you can kinda see my preamp. There's obviously some stuff in the photo that has nothing to do with this project. My work area is quite cluttered. Maybe one day I'll clean it up.

The second shot is a close up of the amp on the bread board. Due to clutter, there's some non-related stuff on the breadboard. You can see the input buffer near the blue pot, which is used for biasing the MOSFET in the buffer stage. The two power MOSFET's are on a heat sink that I scavenged from an old atx power supply. The very large cap at the top of the board is just for killing power supply noise.

The third pic shows the inside of my preamp. This is the MOSFET Booster circuit that I posted about here: http://www.ssguitar.com/index.php?topic=1121.0 . It's breadboarded in my ProtoBox. I just got an aluminum enclosure and small breadboard from RadioShack. I mounted the breadboard inside, and drilled holes for various pots and jacks. When I eventually do a permanent build of this circuit, I'll use this ProtoBox for something else.

The last pic shows the front of the protobox.

I'm sure this isn't the finished product you were wanting to see. Hopefully I'll get this permanently built soon.

I'll have to get back to you on that. I'll try to get some sound clips soon. Right now, I've only got it breadboarded. I plan on doing a permanent build, but I'd like to configure it for a 24V supply first. It sounds plenty loud enough for my purposes at 12V, but I'd like a little more headroom for clean tones. Based on Multisim calculations, which of course will differ some from the real thing, it probably puts out about 1.5W clean and around 5 or 6 W dirty. If I had a function generator, I'd tell you how it works out with my current setup. I'll be out of town for a little more than a week, but when I get back, I'll work on the sound clips if everyone can excuse my guitar playing. Before I leave, I might have my wife bang away on my guitar while I measure the Vpp on my little oscilloscope. That might give a better idea about the real world power output.

Here's another intentionally simple idea I've been playing around with. Hope you like it. See here for a detailed explaination: http://www.riemer.us/cmos-power-amp

Here's a link about this circuit on my site . http://www.riemer.us/yambo-booster