I built a nasty little dual chip-dual stage op amp based on the Ruby amp that turned out very good.
Here's a schematic if anyone is interested in building their own.
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nice and simple circuit.. what gain is set on the J-FET input do you know? do you play with a wound pickup or a piezeo? with the 1M5 input resistor i am guessing a piezeo?
No Gain setting on the J-FET, each 386 chip has a 2k Gain pot.
This is a great little amp for Magnetic pickups or piezo's.
The 1M5 resistor in question is just that - a 1/4watt resistor. The J-FET circuit is the same circuit found in the Ruby amp which was my initial inspiration in making this dual chip circuit.
However, lately I made a change to the schematic and thought that I had posted that change here. The new version deletes 1 of the volume pots because both stayed all the way up in all scenarios. I also added a B100k tone pot .
thanks. i will have to look up the circuit for the Ruby amp.
are the two gain pots ganged? that is two pots but one shaft? because if they are different pots i can see asymetric gain possible. because you are using one as an inverting amp and the other as a non inverting amp and stringing the speaker between them you can get a a full 9v swing on both positive and negative parts of the wave.a single amp is internally biased to 1/2 the supply voltage giving a 4.5V swing positive or negative. with this setup you can make the negative part of the wave less gain/quieter ot the positive. or even vice versa.... must have an interesting sound...
2 separate gain pots. When I use it the volume stays all the way up and the 1st gain at about 75%, then I can dial up the 2nd gain for what ever level of nastiness I want.
I prefer using big speakers over the small ones. My current speaker is a 8ohm-15watt WGS 10" Veteran(American Voiced) speaker, but would like to try out a British Voiced speaker some time.
Any updates Erik?
No Problem.
I love my Ruby amp's sound and really wanted something louder with a little more balls. This fit the bill.
I tend to play my acoustic CBG through the regular Ruby most of the time because it just sounds so good through it's 6" speaker The dual chip amp is hooked up to a old Jensen 15" speaker that I pulled from an old Motorola phonograph that was powered by a tube amp. Going to build a Fender Bassman/Tweed circuit out of that when Get around to it.
Also check how the Jfet is positioned. Make sure the correct pins are going where they should.
With flat side pointing up: left pin will be G which connects to input and 1M5 resistor to ground, middle pin S to toggle/input caps circuit and to 3K9 resistor to ground on other side, right pin D to batt+ circuit.
Oh yes, I had the JFET backwards and the circuit just made a clicking sound which went faster when I switched the toggle to use the other capacitor. That was one of a few mistakes. It was such a thrill after fixing the third or fourth goof and hearing it work and get a pretty decent tone! And significantly louder than the single-LM386 circuits I've built.
I'm pretty sure I've got a problem with the pots 'cause when I touch them it makes a buzzing, crackling sound. And the breadboard nature of the whole construction isn't helping. I'm sure when I finalize the whole thing into an enclosure (with everything soldered), it will sound a lot cleaner. I might just jump to that step now that I've proven I can make the circuit work.
Most of my creations run on 9 volts and are encased in wooden cigar boxes. That must do something to the grounding. Would it make sense to fix some hunk of metal in an isolated corner of the box to run a ground to it? Thanks again for all your help!
Yes a piece of metal in the box would be good. Think about big amps, every thing is mounted and grounded to a metal chassis inside the casing and then to the plug ground. The final part is a necessity with large voltage amps for safety, but with 9volts you don't have to worry about that. So a piece of metal to act as a chassis ground would be good.
I would put it in the box with the "chassis" and check it out before replacing any pots.
Thanks again. I really appreciate all your help with this. I'm very excited about this amplifier project. A LM386 amp with guts!
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