Hey!

Hi all!

Just testing this list out.

Anyway, obviously I'm an ADA MP-1 user. I have one of the old ones
from 1987, with the top-switch. I got it second-hand so it came with
the 2.0 ROM.

I modified mine by replacing the OD1 trimmer pot with a higher
resistance pot, which is mounted on the side of the unit. This way you
can set up the basic overall gain of the device to match the output
level of your pickup without reprogramming all your presets. You can
get tons of gain with any guitar.

Also, I replaced numerous op-amps with NE5532's. Wow, what a
difference!

Another mod I have in place is a current-limiting circuit for the tube
filaments. It is based on a 2SD822 power transistor. What this does is
it prevents any more than 500 mA of current from flowing through the
tube filaments at any time. So when the filaments are cold, they are
not able to pull in a lot of inrush current. This may prolong tube
filament life, and also reduces the transformer load at startup.

I replaced a PNP transistor in the CPU power-on-reset circuit and
changed a capacitor for a longer reset pulse.

Finally, I debugged fixed the flaky startup issue of this unit. It was
caused by the NMI (non-maskable interrupt) circuit. I cut the trace to
the NMI pin on the Z80 CPU and installed a jumper wire (surface
mounted) connecting that pin to +5V, so that NMI is never asserted. The
startup problem is caused by a glitch in that NMI circuit. NMI is edge
triggered and once it latches, the CPU stays in that condition until it
is powered down. The idea behind the NMI circuit was, in the event of a
power loss, to deliver the NMI to the CPU, so that it branches to some
safe loop to avoid trashing data. The problem is that the circuit
sometimes thinks there is a power loss near startup. After spending
time to hunt this down, I discovered on some newer schematics that ADA
put out exactly same fix in 1989! They got rid of that dumb NMI
circuit.