Masco ME-18

[dunner84]

I have restored two of these amps over the last few years for harmonica players, and I've always kind of wanted one for myself. I made a layout a while back, but never got a round to building it. Another one has fallen into my lap, so it's time for a build. I will be building it stock, and then possibly modding for harmonica after I spend some time with it. From what I remember, I liked the non-modded sound.

This will be my first time using my layout, and I am not sure what to do with the phono input because I don't need it. I am thinking of just running it to a 1/4 inch jack to maybe use for a really hot mic.

I am not sure if the way I have my input jacks on the layout will work, and would really appreciate an experienced set of eyes. Currently the layout shows switched jacks for both inputs, but I am not sure if that will work.

EDIT - Sorry, I originally uploaded the wrong schematic screenshot.. The proper one is now showing.

[DummyLoad]

please see attached.


--pete

[dunner84]

So you think it's more worthwhile to just remove the phono input? I probably will end up removing it, but I'm also kind of curious if it has any use. Could it act as an input for another mic preamp?

[d95err]

The volume for the Phono input will affect the Mic channel. If nothing is plugged in to Phono and the volume is turned up, both channels will be muted.

[d95err]

Another observation - the ”backwards” wired volume control will interact with the 0.01u coupling cap to form a variable high-pass filter. As you turn the volume down, it will cut more and more bass. Since 0.01 is rather low, there will be very little bass left, even at moderate volume settings.

If you are removing the phono input, I suggest changing the volume to conventional voltage divider wiring. Orherwise, you should probably increase the coupling cap to 0.1u or more.

[DummyLoad]

cracking that control open even just a bit will pickup and inject 60Hz hum into v2 pin4. lots of hum. i'd disconnect it. removing it will also boost gain a bit. however, if you like the gain structure of v1 with the two pots in parallel, then replace the phono pot with 470K resistor, or short the wiper of the phono pot to ground. 



--pete