Little Gem and Ruby mini SS amps...Mods?

[John Lyons]

These amps seem really neat! I've poured over the info and I'm excited to make some of these.

http://www.runoffgroove.com/littlegem.html

In the Little Gem MKII the wattage is doubled but there is not as much control, at least in the schematic on line. Can pots for gain and master volume be added as in the Regular Little Gem? I assume they can but it would seem to get messy with the two 386 amps.  Values for the pots the same? Dual pots needed?

Any ideas about this?

John

[Peter Snowberg]

For a master volume, try adding a 500 ohm pot in series with one of the speaker leads. That works great.

For a gain control, you could go about it in (at least) two ways...

(1) Add a 50K (or so) pot right after the .22uF coupling cap with the CCW lug grounded, the CW lug attached to the coupling cap, and the wiper attached to the 386 inputs.

(2) Use a dual-ganged 10K pot with one element in series with each of the gain caps between pins 1 and 8.

If you haven't built a Gem or even better a JFET buffered Gem (or Ruby), or any other 386 amp, you're going to love it!

As always, I think we should all collectively take our hats off in respect to the 'Groove.

Take care,
-Peter

[B Tremblay]

You're right, adding a gain control would probably require a dual pot for best results.  As far adding a volume control to the LGMkII, I'd suggest using a pot as shown in the Ruby schematic since a master volume would be difficult to implement given the bridged output setup.

[B Tremblay]

Thank you for your kind words, Peter.  The DIY-FX community, with Aron's forum as the hub, has provided me with a wealth of knowledge and an equally valuable partnership with Gary Burchett.  It's very rewarding to reciprocate by sharing circuits and ideas at the 'Groove.

Getting back to the topic, I have yet to try the 500 ohm series pot.  I thought about suggesting it here, but was unsure of its effectiveness in the MkII bridged output.