This Week on the Breadboard: The Bloody Germanium Overdrive

[DDad]

Old thread but want to ask - I see several versions of the amplifier LM386 at DigiKey for different wattages, 325mw, 700mw, and 1W. Does it matter for this circuit? Since it wasn't specified, guessing not. Can an approximate wattage be calculated without using something like LT Spice?

 

[Chuck D. Bones]

We can do a quick cocktail napkin calculation to get into the ballpark.

Maximum output swing is around 8Vp-p. Assuming a square wave, that works out to 4Vrms. There is a 560Ω series resistor (R15). Output power is Pout = 4^2/560 = 29mW delivered to R15. This is pretty much the worst case situation: output shorted. If we look at the datasheet device dissipation vs. output power, the 9V curve indicated that at 29mW output, the device dissipation is around 350mW and most of that is quiescent dissipation (the power dissipated when the output power is zero). The DIP packages (N suffix) are all rated for 1.25W dissipation. We have plenty of margin and this was a pessimistic calculation. The only time we care about the part no. suffix is when we want to run on a higher rail voltage (N-4 suffix). The SMD parts have a lower max dissipation limit, but they would still have positive margin.

 

[bluedmc777]

Supposed nobody made this it seems interesting!

 

[z2amiller]

I put together a layout for this over the weekend - I'll probably have it in my hands in a couple weeks when I get my next batch of stuff from JLC. If it sounds good, I'll share the gerbers with @Chuck D. Bones 's blessing.

 

[DDad]

We can do a quick cocktail napkin calculation to get into the ballpark.

Maximum output swing is around 8Vp-p. Assuming a square wave, that works out to 4Vrms. There is a 560Ω series resistor (R15). Output power is Pout = 4^2/560 = 29mW delivered to R15. This is pretty much the worst case situation: output shorted. If we look at the datasheet device dissipation vs. output power, the 9V curve indicated that at 29mW output, the device dissipation is around 350mW and most of that is quiescent dissipation (the power dissipated when the output power is zero). The DIP packages (N suffix) are all rated for 1.25W dissipation. We have plenty of margin and this was a pessimistic calculation. The only time we care about the part no. suffix is when we want to run on a higher rail voltage (N-4 suffix). The SMD parts have a lower max dissipation limit, but they would still have positive margin.

Crazy cool. Arthritis (old age) and carpal tunnel (computer programming career) makes it hard to play guitar. The electronics of pedals is saving me in my partial retirement (and is a redux of my early Heathkit and 50-in-1 days). Thank you for the time to explain, much appreciated. Rock on.

 

[cooder]

Yes, very nice grind box, strong essence of Marshall goodness.
Here's my boxed up version, sounds great already and I still have to spend some time tweaking the trimmers to where they tickle my setup the sweetest. Germanium diodes are Mullard OA6.
Nice. Thanks to @Chuck D. Bones and @HamishR for the inspiration and design.

Photo festivities:

 

[bluedmc777]

Yes, very nice grind box, strong essence of Marshall goodness.
Here's my boxed up version, sounds great already and I still have to spend some time tweaking the trimmers to where they tickle my setup the sweetest. Germanium diodes are Mullard OA6.
Nice. Thanks to @Chuck D. Bones and @HamishR for the inspiration and design.

Photo festivities:

I’m gonna speak for the whole community and say you should sale pcbs.

 

[gtt]

Yes, very nice grind box, strong essence of Marshall goodness.
Here's my boxed up version, sounds great already and I still have to spend some time tweaking the trimmers to where they tickle my setup the sweetest. Germanium diodes are Mullard OA6.
Nice. Thanks to @Chuck D. Bones and @HamishR for the inspiration and design.

Photo festivities:

Question. I'm not sure who makes your circuit boards -- do you solder all the parts yourself or do you do like JLCPCB and let them pick and place, wave-solder, etc.?

 

[cooder]

I’m gonna speak for the whole community and say you should sale pcbs.

Thanks but I don't want to step on anyone's toes and leave that to @Robert and @szukalski / sheepylove to get around doing the pcb sales, they also do the usual ppcb layout I/O etc.
Apart from that I live in a far away land downunder (not OZ, that's the West Island) that has shipping prices tougher than prohibiton even before orange dudes tariffs kick in. So yeah...

Question. I'm not sure who makes your circuit boards -- do you solder all the parts yourself or do you do like JLCPCB and let them pick and place, wave-solder, etc.?

On the circuit boards I solder all parts myself, the I/O relay board has some smd pick and place parts done by JLCPCB and then some added parts that I solder myself (like relay, jacks, non standard pick and place parts).