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  • Author Author: Andy Betts
  • Date Created: 10 Jul 2018 7:53 PM Date Created
  • Views 5492 views
  • Likes 12 likes
  • Comments 12 comments
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Electro Harmonix Electric Mistress v2 - Original PCB Rebuild

Andy Betts
Andy Betts
10 Jul 2018

image

The Electric Mistress....... This effect pedal, along with the Big Muff defined David Gilmours sound through the late 70's and into the 80's and beyond. This pedal, although not used extensively on the album was utilised on nearly all the songs on the Animals "In The Flesh" tour of 1977. Gilmour had found a modulation pedal, that would later add the finishing touches to songs like Mother, Comfortably Numb from the Wall LP, and the Final Cut from the album of the same name. The Electric Mistress was also the pedal of choice for Andy Summers of the Police, who used the effect on a lot of songs such as If The World is Running Down, De Do Do Do De Da Da Da, Don't Stand So Close to me, to name just 3.

 

The history of the Mistress can be dated back to around 1975. In 1968 Mike Matthews founded Electro-Harmonix in New York for producing and distributing guitar effects pedals. The first products had been the LPB-1 booster and the legendary Big Muff PI.

 

Probably 1975 or 1976 David Cockerell developed a flanger for Electro-Harmonix they named Electric Mistress. It was first sold in 1976. It very soon received a change in design of the case printing and the filter matrix switch had been added. Marketing for the Electric Mistress started 1977 with first ads published. The initial list price had been 199 US$.

 

From 1977 to the 1982 the Electric Mistress was produced with only small changes to the schematic, but many different PCBs. In 1978 the Deluxe Electric Mistress had been designed by Howard Davis and introduced to the market. It was produced in parallel with the standard version. The Deluxe featured a larger case with integrated transformer and no battery connectors. The LFO and VCO had been changed to allow a wider range of settings. Further modifications had been added to reduce the noise level and to fix the volume drop. Trouble with labour union led to first bankruptcy of Electro-Harmonix in early 1982. But only a few months later Electro-Harmonix returned to production.

 

The Electric Mistress had been redesigned by Howard Davis working now as a freelancer for Electro-Harmonix with a new LFO and VCO similar to the Deluxe and now ran on 9 V or a single battery instead of 18 V or double batteries like the former versions. In 1984 Electro-Harmonix went bankrupt for the second time which stopped production of the Electric Mistress and Deluxe Electric Mistress. Mike Matthews focused his activities on distributing electronic parts, mainly vacuum tubes, from Russia with his new company New Sensor Corp from 1988 on. Because of the high used marked prices the Electro-Harmonix pedals achieved he started production of some pedals in Russia under his new label Sovtek in 1990. Prototypes of the Electric Mistress had been made in 1994 by Sovtek but were never sold [4]. Matthews bought back the name rights for Electro-Harmonix and started selling so called reissues of his pedals made in USA in 1999. From 1999 on the Deluxe Electric Mistress had been reissued. Although Electro-Harmonix at that time wanted to make the reissues exact copies of the 1980s pedals they had to redesign the Deluxe Electric Mistress because its main integrated circuit, the Reticon SAD1024 BBD, was no longer in production. It's quite remarkable that the design of the reissue already had been made in 1995 by Howard Davis for New Sensor Corp.

 

(Information reproduced from The Mistress Mystery web page. This features all the information you could want about the different iterations of the Electric Mistress)

 

The Electric Mistress has a beautiful sound, like a chorusy type sound. Here's a video showing just how this pedal sounds.... This is a comparison video against one of the recent clone pedals, a Hartman Analog Flanger.

 

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My story starts around 1 year ago, when I was looking at buying an original Electric Mistress. Of all the Mistress pedals out there, the "Holy Grail" appeared to be the v2. I'm not sure why, but it might be something to do with the fact Gilmour used a v2. Looking on the internet at auction sites it was quite apparent that original v2 Mistresses go for a lot of money.... Anything from £500 upwards depending on condition. The SAD1024 IC that are in the old v2 go for £80 and upwards on their own. These are much sought after pedals. I had at that time resigned myself to the fact that I wasn't going to buy an original, and started to look at the various schematics of clones out there.

All the clones and also the new deluxe electric mistress didn't use the SAD1024 chip, Reticon stopped production of these in the early 80's so they are hard to come by. So newer clones normally use the readily available MN3007 chip. And the EHX deluxe Electric Mistress last used the SAD chip in 1981, after that they used an RD5106A IC. However, the holy grail is a flanger with a SAD1024 chip and preferably pre-1978. The SAD1024 chip somehow has a different sound and to date there are no flangers out there that have "That" sound of an early Mistress.

 

Anyway, I digress....... I was scouring the internet 1 year ago and happened across the following post on the EHX forum:

 

image

 

As you can imagine, when I saw that i immediately thought "that's obviously gone....... It's a year old". Also, there was somebody answering the post who was interested, I assumed that i had missed the boat. Whizz forward to 3 weeks ago, and i'm still scouring the internet for that elusive deal on the v2 Electric Mistress, when that same forum post rears its head again. this time I take a punt, and send the guy an instant message hoping that he still has an account on the forum. His post count at the time was just 1 after 2 years so i wasn't holding out any hope. he replied within about 3 hours........

 

 

image

 

You could have knocked me over with a feather. Needless to say, i was speechless and ecstatic. i now had the chance of obtaining a genuine v2 PCB board which i could re-box in a new enclosure. i just hoped it still worked. I already have 2 SAD1024 chips which were given to me by a kind person on Element14 so i didn't want the board with the chip..... I needed to strike a deal for the board minus the chip. Long story short I negotiated a deal for the PCB minus the SAD1024 for £50. A stonking deal, and one of which i'm really proud. The board is old school, hand drawn and tinned... quite messy, but intact and ready to be resurrected.

 

The photos below were taken after I had started to re-solder the wiring, I'd also marked the terminals for the pots and also the voltage input, circuit in and circuit output. I had also inserted the SAD1024 chip into it's new home. Also, for completion below the photos is a copy of the schematic for a v2 Mistress......... Let the fun begin.... Lets bring this thing back to life image Both board photos are very hi-resolution. So if you expand them you get quite good detail, also the schematic is hi-res as well. I may need some help with this if it doesn't work...... The guy I bought it off advised me it was in full working order, so we'll have to see. The SAD1024 is NOS, and never been used, i also have a spare just in case this one's a dud.

 

 

                         imageimage

 

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So, I spent some time wiring the board up, wasn't too hard. And the end result..................... It worked first time. No issues. So my next task is to make a short video to show you it working, and then box it up into an enclosure. I'll get that done in the next day or so. Following this exercise i intend to build another flanger pedal, but a modern clone of the Mistress called a Current lover. This clone pedal uses the more readily available MN3007 chip. I have a pre-fabricated PCB on order and as soon as it arrives I'll get building, it'll be good to do a comparison between the 2 pedals.

 

 

One thing that some of you may be able to help with is on the original pedal, when you engage the effect, you get a significant (10% to 15%) volume drop. This is a common thing with the original Mistresses, and something that a lot of people have tried to solve in many ways. Some people put a clean boost circuit at the output stage to boost the volume back to unity level, others actually use a boost pedal after the Mistress. There are some modifications where people have altered the circuit by soldering into it a 10k resistor and a tantalium capacitor (can't remember the value). I need to find out the cap value and where they're soldered into the circuit, as apparently the modification does stop the volume drop, but it also reduces the amount of flange effect. It sounds like it just boosts the un-effected signal, and leaves the effected signal where it is. Anyhow, it's a simple mod that is reversable so worth a try I suppose. Once I get the board boxed up with an on/off switch you'll be able to judge properly the volume drop issue.... But at this stage I'm a very very happy bunny image

 

You can see a video of the Mistress here. In this video, Graeme has already carried out the modification however I can't workout where in the schematic he has placed the resistor and the cap just from watching the video.... Maybe someone here can work it out? Looking at the video it would appear it's on the Output track of the board.

 

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I've at last designed and printed my enclosure decal.... I've blatantly copied the name and the logo off a real Electric Mistress as this is after all a REAL Electric Mistress. The filter matrix switch was on the back of the genuine pedal, on mine it's on top between the range and the colour (not color) pots. Yes, I've spelt colour the English way. I've included the flying pig as a Pink Floyd reference (It's also turning into my regular tag on my pedals) and my name is in the original Electro Harmonix font. The decal is a water slide as usual, and the pedal will be sprayed with around 6 to 8 coats of clear coat lacquer to seal it in. Once that's done you can't really see the join or edge of the transfer.

 

    imageimage

 

And here is the finished article. Looks good, and sounds lovely too. I'm in the middle of updating some of the cabling on my rack system, as i now have the mistress I want to run that and my digital effects processor through the effects loop of my pre-amp. As soon as I've rewired that i'll film a demo. It was a tight fit getting it into this enclosure, and had to buy a slightly taller enclosure than I'd normally buy to allow enough room for the pots, and the on/off switch.

 

  imageimage

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Top Comments

  • jc2048
    jc2048 over 6 years ago +4
    I might be wrong, but it looks like the tant is across the 47n and the resistor across the 13k that go from IC1b pin 1 to where the signals get combined at 'SW'. 0.22uF is 220n, so that effectively changes…
  • jomoenginer
    jomoenginer over 6 years ago +3
    Very cool Andy. As a fellow Git-Fiddler myself, I really appreciate you posting about these. It is amazing the design that these had back in the day and more surprising how simple they are. OBTW - Your…
  • jw0752
    jw0752 over 6 years ago +2
    Hi Andy, Great story and I really appreciate the history lesson so we non-aficionados can better understand the importance of these devices. John
  • slyeee
    slyeee over 2 years ago

    heĺlo andy 

    just a little post here to tell my little story

    about 10 years ago, in love with electric mistress i was hearing in the floyd , police and others ,i decided to find this legendary pedal,thegreen one .but i couldn t.too rare,too expensive.

    knowing some little things of electronic ,i decided to make one myself as i at least found a SAD1024 that i bought on ebay.

    i based my pcb and mounting on pictures that i found on the net of a man who had opened it to show i don t remember what.

    toner transfer, buying component , and there i was ,owning a really beautiffuly sounding electric mistress.

    my story was too analog to yours ,i had to tell you

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  • spacekiko
    spacekiko over 6 years ago

    Hi Andy . Great job . I am not a tech but I play guitar and love this unit . I would like to have a new one like yours . Coul you build a new onde for me ? You say how muck would cost and we make it.  Tks and regards .

    Obv: It ´s better to use the SD1024 chip ?. tks..

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  • jc2048
    jc2048 over 6 years ago in reply to Andy Betts

    Yes, they're right. I'd missed the frequency shaping before the delay line and the correction after. To get it right and back to a flat response, you'd have to start changing the capacitor values too and that partly depends on knowing how the delay line behaves as well, so yes, it's a bit messy.

     

    Always worth getting a second opinion.

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  • Andy Betts
    Andy Betts over 6 years ago in reply to jc2048

    Jon, i haven't managed to give this idea a go as of yet, to be honest I'm not too keen on pulling this board around too much as it's quite fragile. But did put it forward as a suggestion on a pedal forum and someone with more electronics knowledge than me has put forward the following issue with your idea:

     

     

    Increasing the resistor will increase the level, true. But your numbers are off, because you are ignoring the 47n capacitor to ground. Its impedance is roughly 3,4k at 1kHz. So the level drop is less than you state, and doubling the resistor won't give double the volume. The problem is by changing the resistor value you also shift the lowpass frequency of the filter that is formed by the three resistors and the capacitor to a higher frequency. You basically get a treble boost. But the output treble filter must match the pre-filter network around IC1B in front of the SAD, or you won't get an even response.

    You can try a small increment, but I doubt you will get it to what you will perceive as unity without making it sound trebly or harsh.

     

    Not sure if there's anything in what he's saying but it certainly looks like there may be other issues to contend with. I've also read a forum post by Howard Davis.... he's the man that designed the Deluxe Electric Mistress and he's said categorically that curing the volume drop is not as simple as one might think. There is a link on that forum post to his volume drop modification but unfortunately it's now a dead link. He does have a website so I might shoot him an email.... www.howardmickdavis.com

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  • Andy Betts
    Andy Betts over 6 years ago in reply to jc2048

    I'll give it a go, and report back

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