Questions about Little Gem I

[David]

Gary, et al.:

Could the Little Gem I be adapted for use with those little ear bud headphones?  If so, how?  If I were to put the JFET front end from the model II on it, could I use it with low-impedance inputs - not just with guitar?

I'm trying to build a simple headphone amp, and I'm beating my head against the wall because everything I try either sounds distorted or oscillates!  Is it possible that I'm just having problems because of the internal capacitance of the breadboard?

[Gary]

Brian, aka B Tremblay has built a headphone amp from a 386.  He'll see this and point you to a link.  Hang loose.

[B Tremblay]

I used this project from Headwize.

I made a couple mods, but nothing major.  I put a switch in for the treble cut/bass boost.  I built the circuit as mono and included two outputs: a 1/4" for a speaker and an 1/8" for headphones (with the left and right channel lugs connected).

It works beautifully with my iPod earbuds as well as with a speaker.

I built it in a tape measure enclosure, which allows me to clip it on the guitar strap.

[David]

Brian:

I tried that one (at least, I think I did!)  Aren't you the one that had a posting indicating that you removed the feedback loop and set up a switching mechanism to put the "guitar" components in and out?  The post mentioned using a SPST switch to do this, but I couldn't for the life of me figure out how.  I thought it would at least require a SPDT.

Did you breadboard yours first before you built it?  Every 386-based circuit I've tried so far seems to overload when I feed a guitar into it!  I'm using a LM386 model 3 chip being powered by 1 flatpack 9V battery.  I've got my breadboard set up currently so that I can parallel another 9V for additional current.

If you could help me sort this out, I sure would appreciate it.  Then I could get back to pedals...  which I seem to do a little better with!

[David]

Brian:

I tried that one (at least, I think I did!)  Aren't you the one that had a posting indicating that you removed the feedback loop and set up a switching mechanism to put the "guitar" components in and out?  The post mentioned using a SPST switch to do this, but I couldn't for the life of me figure out how.  I thought it would at least require a SPDT.

Did you breadboard yours first before you built it?  Every 386-based circuit I've tried so far seems to overload when I feed a guitar into it!  I'm using a LM386 model 3 chip being powered by 1 flatpack 9V battery.  I've got my breadboard set up currently so that I can parallel another 9V for additional current.

If you could help me sort this out, I sure would appreciate it.  Then I could get back to pedals...  which I seem to do a little better with!

[Oliver]

I used this project from Headwize.

I made a couple mods, but nothing major.  I put a switch in for the treble cut/bass boost.  I built the circuit as mono and included two outputs: a 1/4" for a speaker and an 1/8" for headphones (with the left and right channel lugs connected).

It works beautifully with my iPod earbuds as well as with a speaker.

I built it in a tape measure enclosure, which allows me to clip it on the guitar strap.

Hi,

that looks cool !!!

i thought about a HeadphonePlug in my LittleGem.

It well be added soon  

bye
Oliver

[B Tremblay]

The SPST is placed between Pin 5 and C5.  The C6-R5 network is left as-is; no switching there.

Have you used a volume control in front of the 386 amp in your other attempts?

Also, I can't take credit for the tape measure idea, Joe Gagan's Tape Measure Boost (which is actually the AMZ Muffer sans feedback cap and diodes) inspired me.

[David]

Brian:

As a matter of fact, I DID use a volume pot in some previous attempts.  I had tried to build a minimalist version of the "Pocket Rockit".  I used a 5534 in a configuration similar to the preamp stage of Smalley's Simple Octave Up, but I changed the resistors to give unity gain.  When it wasn't oscillating, it was distorting.  I thought that maybe the 5534 was too hot for the 386, so I swapped the 5534 for a LF353, and grounded out the inputs of the unused op-amp.  Same thing.  I tried again with a resistor combo that would give LESS than unity gain.  Distortion again.  So far, the only thing I've gotten to work reliably is the headphone amp from the old SmokinPot 50 megs site.  This uses a 386 and 3 capacitors.  No pots.  It works "OK", but I have to turn the guitar volume down or I overload that too.  I'm using a 386-3 and running it with a single 9V battery -- which is good.

[David]

Brian:

As a matter of fact, I DID use a volume pot in some previous attempts.  I had tried to build a minimalist version of the "Pocket Rockit".  I used a 5534 in a configuration similar to the preamp stage of Smalley's Simple Octave Up, but I changed the resistors to give unity gain.  When it wasn't oscillating, it was distorting.  I thought that maybe the 5534 was too hot for the 386, so I swapped the 5534 for a LF353, and grounded out the inputs of the unused op-amp.  Same thing.  I tried again with a resistor combo that would give LESS than unity gain.  Distortion again.  So far, the only thing I've gotten to work reliably is the headphone amp from the old SmokinPot 50 megs site.  This uses a 386 and 3 capacitors.  No pots.  It works "OK", but I have to turn the guitar volume down or I overload that too.  I'm using a 386-3 and running it with a single 9V battery -- which is good.

[B Tremblay]

So far, the only thing I've gotten to work reliably is the headphone amp from the old SmokinPot 50 megs site.  This uses a 386 and 3 capacitors.

That's the first 386 amp I built.  I've built three in total: the Smokin' Pot one, the "gain of 20" datasheet version, and the Headwize project I linked above.

The Headwize one's gain setup keeps it a bit cleaner than with pins 1 and 8 unconnected.