MK114 versus MK186

The descriptions and specs are insufficient to really tell exactly what you get without schematics. What’s the difference between the MK114 and MK186 (assuming I use some other interface instead of the built-in microphone)? I see the MK186 handles 5A, and the MK114 about 4.16 on 12V. The input sensitivity spec of the MK114 is in watts, which is obviously blatantly wrong, as surely this thing doesn’t consume 60 watts; I assume this actually has some high impedance input meant to go across a speaker line and is actually sensitive to volts. The panel & knob seem nice on the MK186.

I am particularly interested in determining any isolation requirements for using other inputs to the MK186 instead of the built-in mic, the input impedances and level of the signal input to each, and converting either to run on a 6V supply.

Can I please get the schematic for an MK114 and MK186, and then I can probably figure out what I want to do, and maybe some referral to any preferred place to purchase (it seems some of my favorite vendors don’t carry them all, or at least don’t list all the Velleman kits in their online catalogs).

It looks like what I want to start with is an MK114.

I’m a little bit concerned about putting a diode (and load) across my speaker. At first I assumed that was a limiting zener or something to protect the opto-isolator/coupler but it looks like it’s just a crude half-wave rectifier for DC to power the LED in the opto-isolator. There really should be a limiter zener to protect the LED in the opto-isolator. Assuming a normal damping factor from the amp, it shouldn’t matter, but I’m inclined to double the value of the input resistor to increase the input impedance, and use four of the input diodes as a bridge to still get enough voltage to drive the opto-isolator.

Then I might want to mess with the gain and output of the back-end, but I’m more inclined to try it on the 6VDC supply first, and measure what happens; it looks like it might work down to 6V as-is. I want to rectify and filter an existing 6.3VAC filament supply to supply the MK114.