vintage Electric Mistress stopped modulating

Started by reflektors, February 09, 2018, 01:25:36 PM

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I sold an original small box mistress to someone on Reverb and he sent it back because it won't modulate. It now operates like it's stuck in filter matrix mode (range and color work). I thought maybe the switch was stuck so I sprayed it out but no luck. any ideas?
I'm not happy it stopped working, but I actually had bad sellers remorse after I sold it LOL


Could be a bad solder joint that reared its head from getting knocked about from shipping so it'd be worth checking them, especially around the rate pot.

Which version is it? The 9V or 18V? Might be a bad cap in the LFO circuitry... you should check the switch with a multimeter for continuity too.


It’s 18v (2 9v battery slots)
I’ll check those two locations thanks


I once fixed up a "broken" MXR flanger that wouldn't modulate. One of the pots had rotated so that a lug was grounded to the enclosure. A few turns with the pliers and a piece of electrical tape later, it worked perfectly. Hopefully you'll find something easy like that, especially since it was working until you shipped it.
"Electrons go where I tell them to go." - wavley


all the solder connections look good to my naked eye.

I need help measuring continuity on the filter matrix switch. it's a Stackpole slide switch. I removed it and on the side it reads (in columns, left to right) 3a 125V AC, 1.5a 250v AC, .5a 125v DC

I can't find any tutorials on measuring continuity for slide switches. I have the mutimeter set to OHMs


It looks like a double-pole switch but only one pole is being used.  Ignore the lugs that have no wires soldered to them.  On the other side, you should get continuity between the middle lug and which ever outside lug corresponds to the position of the slider.

Since you've already cleaned it, I bet it works fine, that's usually all they need.  But if it's not making good contact, check the unused pole, and move the wires over if it's good.

P.S.  Also check the wires themselves for continuity.  If that's solid core, being twisted that tight can easily cause a break inside.


when I switch to the corresponding sides like you mentioned, I'm getting a reading, which as I understand means no continuity. the reading doesn't stay on any number, it just dances around alot



in one row of poles, all poles have wires soldered to them and give a reading. on the other side, there's nothing soldered and I get the same thing.
like you described, I'm keeping one probe on the center pole and reading with the other on the ones next to it.


Sounds like a bad switch then.  I would try contact cleaner one more time before ordering a replacement.  If you do get a new one, look for Switchcraft (they still make them) so the mounting holes line up.  The asian/import types are metric and often have different hole spacing.

Edit:  Actually on second thought, I think some of these slider switches use one of the outside lugs as the "common" rather than the middle.  Check for continuity between all lugs in both slider positions.  Maybe check the unused pole first since it has nothing in parallel, see if you can figure out the pattern, then apply that to the wired pole.

Could still be a bad switch though.

Edit 2:  I think there's some confusion over terminology.  You're saying "poles" for what I call lugs.  Some might say pins in this case, or terminals.  The switch has six lugs, and is a double-pole switch.  "Double-pole" basically means it is two electrically separate switches in one package, but both actuated with the same lever or slider.  One row of three lugs constitutes one pole, and in this case only one pole has wires soldered to it.  The other row of three lugs (the other pole) is unused and has no wires soldered.

It is also a "double-throw" switch, people abbreviate DPDT for double-pole double-throw.  "Double-throw" means that, for each pole, a "common" lug is switching between two different lugs.  Like B connects to A, flip the switch and B connects to C.  The common lug is frequently in the middle, but not always.  A "single-throw" switch is simpler, for each pole it only makes or breaks a single connection, like A connects to B, flip the switch and A does not connect to B.  Does that make sense?

A single-pole, single-throw (SPST) switch only has two lugs, A and B.
A single-pole, double-throw (SPDT) has three lugs, A B and C.
A double-pole, single-throw (DPST) has four lugs, A and B of one pole, A and B of the other pole.
A double-pole, double-throw (DPDT) like yours has six lugs, A B C of one pole, A B C of the other pole.  So it's two SPDT switches, side by side in the same package, actuated by the same slider.

Hope that helps.


The 18V EM only uses a single pole switch with 2 throws.
One throw gives a steady voltage (for FM mode).
The other throw gives a variable voltage (varying with the sweep for SWEEP mode) that will vary slowly if the sweep rate is low.
The pole reads one of those voltages (according to switch position) and sends it to the clock generator (which sets the delay time).

If your switch is this ...

   Throw1  ---  Pole  ---  Throw2

and you think the Throw1-Pole connection gets made OK, but that the Pole-Throw2 connection does not, then there are two possibilities I can think of...

One is that the switch makes an open circuit in the Throw2 position.  i.e. the pole is not connected to either throw.
The other is that the switch is somehow still connected to Throw2.  i.e.  there is a short circuit between the two throws.

I would not check continuity in the switch in the way you have been (unless you desolder the wires from it first).
Instead measure the voltage levels on the two throws as follows.
Put the -ve lead of your multimeter on ground in the circuit (battery minus) and the positive lead on the throw and measure the voltage there.  Then do the same on the other throw.  Measure the pole voltage too.  Post the voltages please, and say which way the switch was thrown.

EDIT:  Put the rate pot at minimum when doing this and take note of whether you see voltage levels changing while you take measurements on the lugs.  You only need to take measurements on the 3 lugs that have wires soldered to them.  They are the the pole (most probably the middle lug) and two throws on either side.


Thermionix your pole explanation is the missing link I needed. I tried to research the different switches and kept getting confused by the pole thing .

Dralx I’ll check using that method after work tonight
Thank you !!


finally got a chance to measure voltage (restaurant owner here, prepping for valentine's day)

i set the multimeter to V ac
-ve on the -ve snap of the battery clip, rate pot turned down +ve lead on the corresponding lug I've switched to

I have

.016 on the left side (with the switch pushed left)
.006 on the right side (" " " )
.006 in the middle lug


Set your multimeter for DC volts. It will not show much on the AC settings.
With the rate control at minimum you will see a slowly rising and falling DC voltage on one of the slide switch terminals if the LFO is working correctly.


thanks slowpoke

181 mv on both the left and middle lugs,
8.81mv on the right


Need more measurerments.
It looks like you set Range at minimum.
You also did not say if any voltages changed.
Please say how the pots were configured when you post measurements.

You need to take measurements with Range pot set to maximum and the Rate pot set to minimum, and to measure for about 5 seconds so you can see if the reading is changing.
Also take voltages with the switch in the other position.  All that info will be useful.


Sometimes it really would help if I actually read what you wrote. Let's see what's happening.

The multimeter negative (black) lead should go to a ground connection. This unit uses two 9V batteries so follow the lead from one of the clips that connect a terminal on the input connector and connect the negative lead to that terminal.
Install the two 9V batteries and then connect a cable to the input connector. Your usual guitar cable will do. The effect should now be powered.

Follow the lead (red) from one of the batteries that goes to the external power input connector. With the multimeter set to DC volts connect the multimeter's positive (red) lead to the terminal on the input power connector that the battery goes to. You should read about 18 volts. If you do that's good. If you don't make sure that the batteries are good and double check the multimeter's connections.

Leave the multimeter's negative lead attached to the input connector's terminal (this is known as the ring terminal by the way) and then measure what voltages appears on each of the 3 terminals on the slide switch. Have the Rate pot set to minimum and the Range pot set to maximum.

In the picture I have labelled the slide switch terminals 1, 2 & 3. Terminal 1 is for FM mode and will have a steady voltage on it. Terminal 3 is the flange mode and it should have a varying voltage on it that relates to the LFO rate. Terminal 2 is the centre terminal of the switch. What appears here depends on the switch position and if the switch is working properly.

This schematic may not be the exact one but it should help. Your EM only uses three wires at the slide switch which makes it a SPDT (Single Pole Double Throw) type. Latter EMs used a DPDT type slide switch.



"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".