Volume problems

Hey guys. I have two units, the CEM3379 and an SM4. After I assembled them and checked them individually, I set out to make a single case with a single power supply for the two units. After “tethering” the two units to one power supply, I’ve noticed that the SM4 is at a significantly lower volume than the CEM3379. I don’t know that it is because of the single power supply, (I can’t remember when the problem started) but that’s what I’m leaning towards. Here’s the setup:

I have a 9V 1000mA DC power supply that plugs into the CEM3379 DC jack. I have 20 or 18 gauge (can’t remember) un-threaded wire soldered to the three pins of the CEM3379 DC jack (bottom of the PCB). Those wires are soldered to the SM4 PCB where the DC jack was located.

I’m not sure if this is related, but the CEM3379 LCD is also brighter than the SM4 LCD. It is important to note, however, that they are different manufacturers and the CEM3379 LCD is green whereas the SM4 is red. It’s not ridiculously dim, but perhaps it’s related. Here is the link to the green LCD I bought:
I got the red LCD module from the mutable shop.

Anyone have any ideas?

I think it’s OK, the CEM3379 board replicates the same circuit as the original Shruti, and the gain stage was different (it’s non-inverting).

LCDs vary in brightness - the brightest parts I’ve seen (those from crystalfontz) suck much more power and require a 500mA or 600mA supply. With 1000mA you’re probably safe.

Scope the +5V pin and check if you see oscillations above 50 or 100mV : if you can see oscillations, you’re underpowered. If, with a meter, you see less than 4.9V there’s probably something wrong. But it wouldn’t turn into a unit being of lower volume than the other… Indeed having an underpowered unit translates into a “motorboating” sound - kind of like a ringmodulator.