EM3207 (v1.1) - MN3207 based EHX Electric Mistress (9V) clone

[Pdr]

Hi there,

I don't have a lot of experience in electronic projects so some doubts appeared in my head.

First of all, I'd find a Deluxe EM project verified on GGG (http://www.generalguitargadgets.com/projects/20-modulationecho/123-deluxe-electric-mistress) and I saw the opportunity of build one for myself, but first I need some informations. I'd like some help to understand the main differences between the deluxe and non-deluxe version because the deluxe version is seriously more complicated, and I don't know if it's worth the effort.
Next, if i decided to build the deluxe, I was considering replacing the sad1024 (and here's the reason why I'm posting here) by MN3207 using the circuit showed in this page - http://img220.imageshack.us/i/sad1024retrofitmn3207lo.jpg/. Here's the source of this link: http://www.diystompboxes.com/smfforum/index.php?topic=78270.60 [page 4, 3rd post].
Is that replacement even possible?

Thanks for everything, this forum is amazing. Sorry for my bad English.

1st post! Hope I didn't break all the rules at once.

[Thomeeque]

 Hi Pdr,

main difference is different audio path, second (minor) difference is AC/DC (rectifier + filter + 15V regulator) block on-board (in case of DEM). Rest is pretty much same. I would not even say that DEM is "seriously more complicated", what makes it *little* more complicated is this AC/DC block (which you may even omit if you have external 15VDC PSU) and need of use of some kind of retrofit instead of SAD1024 (I would choose MN3007 based retrofit in this case - MN3207 based is not very convenient here as the 15VDC exceeds MN3207 limits).

So you should IMO choose one you like better from other points of view (sound character, dimensions, ..).

Note that both EM3x07 and DEM with MN3007 based retrofit will suffer by the same "doubled delay time at same clock frequency" issue, elaborated here a lot.

Btw. DEMs audio path makes it easier to use TDA1022 based retrofit (which would not suffer by the "doubled delay time at same clock frequency" issue as it is 512 cell BBD) - are you able to get TDA1022 in your area?

T.

[Pdr]

Hi T,

When I said that I didn't really know the differences between them, I was talking about the sound character. There are a lot of DEM videos out there, but not EMs (specially clones) . Can someone help me by sending a sound clip of EM clone (preferentially with MN3207)  with some abusive settings? I really wanna see how wacky the sound can get. Or video links that you think that might be useful.

I'm 99% sure that I'll go for the EM because of resources I have to spend on this project. Also, TDA1022 is not available in my area and I believe a 230v-18v transformer inside the pedal would make it much heavier then a stompbox is supposed to be.
The cons list of building the DEM is getting big, and the pcb for the EM with MN3207 is somewhere ready-to-print in this forum so...

Thanks for everything. I'll let you know about my decision and progress in a few days. Any question or problem, I'll ask for help.

Pdr

[Thomeeque]

..and the pcb for the EM with MN3207 is somewhere ready-to-print in this forum so...

No kidding!

[Thomeeque]

 Actually there is (or will be soon, I have not found project documentation but I may be just badly looking for it) another MN3x07 based EM project:

madbean's Current Lover

Damn strong competitor, I'd say, cool

T.

[kranja]

I have finally finished my EM MN3207 build  and to my surprise I got a tone (I'm a complete amateur in electronics). The tone that I'm getting isn't quite the tone that I heard on the youtube clips, and I hope the main reason for this is that I need to do the alignment procedure.
I read all the thread and tried to follow the suggestions about the alignment, but somehow find it difficult to follow for someone who have little knowledge about electronics.
I even installed a great software called Visual Analyser, and I generated a wave and passed it to the EM and back to the soundcard, got the visualization of the wave and got stocked with what to do with the trimpots.
Could someone describe an detailed alignment procedure for complete idiots, eventually with the software I mentioned and some pics or video?

Another problem I'm having is the color pot, which I think is not working at all, because when I turn it it happens absolutely nothing. I tried to play with the RT1 trim but the sound doesn't change at all. The other two knobs work OK, and I'm getting the flange sound. Any suggestions?

[Thomeeque]

I have finally finished my EM MN3207 build  and to my surprise I got a tone (I'm a complete amateur in electronics). The tone that I'm getting isn't quite the tone that I heard on the youtube clips, and I hope the main reason for this is that I need to do the alignment procedure.
I read all the thread and tried to follow the suggestions about the alignment, but somehow find it difficult to follow for someone who have little knowledge about electronics.
I even installed a great software called Visual Analyser, and I generated a wave and passed it to the EM and back to the soundcard, got the visualization of the wave and got stocked with what to do with the trimpots.
Could someone describe an detailed alignment procedure for complete idiots, eventually with the software I mentioned and some pics or video?

Another problem I'm having is the color pot, which I think is not working at all, because when I turn it it happens absolutely nothing. I tried to play with the RT1 trim but the sound doesn't change at all. The other two knobs work OK, and I'm getting the flange sound. Any suggestions?

Hello kranja,

the fact that you are getting the flange sound means that most parts (LFO, clock, clock buffer, BBD, most of the audio path..) of your unit work correctly and that your RT2 and RT3 are adjusted good enough to get full functionality from 100% healthy build.

So at this moment don't touch RT2 and RT3 and focus on the COLOR pot issue which indicates that there is something wrong in the audio path (RT1 adjustment does not have fatal influence on this functionality, it's there just for fine-tuning). What comes to my mind first is: did you wire feedback jumper? Then check visually all connections around COLOR pot (pot itself, RT1, C4..). If you don't see nothing obvious make yourself an audioprobe, set RT1 and COLOR pot to the middle and check signals at top and middle pot lugs and then at pin 5 of the IC1, you should get wet signal there.

If it does not help, post hi-res pictures of you build (top and bottom of the PCB from few different angles) and maybe sound sample here, we'll see..

Good luck, T.

[mr_deadmaxxx]

the video has four pots. your design only has three. what's the pot no.4?

[morales72]

Hi to all!

I wasn't sure about posting here or in the MN3007 retrofit since I built this 3207 smaller PCB version adapted to the 3007.
So far it sounds great, swirly, metallic and CLEAN (I build the "bigger" version but was really noisy).
The main issue here is the volume drop when I engage it. I tried changing R5 (3K6) and both R16 and R18 to 8K2. I even put a FET based buffer both at the beginning and the end with no luck.
I use it consistently with my band so it gets annoying when I stomp on it and can't cut through. Any suggestions?

Thanks in advance.

Cheers,

Fernando.

[Thomeeque]

the video has four pots. your design only has three. what's the pot no.4?

Current Lover has an additional volume pot (could be handy actually - to get simply similar pot on EM3x07 I would advice to replace R5 by 10~25k pot working as a "gain").

Btw. there is already CL project file (including schematic) on-line, I hope madbean will not mind direct link here: http://www.madbeanpedals.com/projects/CurrentLover/CurrentLover.pdf

T.

[mr_deadmaxxx]

so how do I connect it? as a variable resistor? should I short the middle and one of the outer lugs? Linear or Audio pot?

thanks..

[Thomeeque]

The main issue here is the volume drop when I engage it. I tried changing R5 (3K6) and both R16 and R18 to 8K2.

Hi Fernando,

first: lowering of R16/R18 won't help! These form passive mixer and 1/2 divider for both dry and wet at the same time, at lower value they will still divide the same (not exactly of course as it is complex passive RC network, but principially yes).

Actually, I would say that replacing R18 by 12k gives better dry/wet ratio (wet path gets boosted by BBD) and may help little bit with volume too.

Adjusting R5 should help - even with my build I'm considering to add little more gain to the input stage, but drop in my case is really small. Try to replace R5 be 10k trimmer and find the match. If it still won't be enough there is something wrong in your build I would say.

Another possibility to gain volume is to use output booster as is used in the Current Lover (find link in my previous post) - maybe just use bigger value for C23 (like 1uF), 100n seems little small to me.

Good luck, T.

so how do I connect it? as a variable resistor?

Yes, excactly - bigger value = bigger gain.

should I short the middle and one of the outer lugs?

Well, it won't hurt and you are safer against audible pops caused by wiper momentary loosing contact with the taper.

Linear or Audio pot?

Experiment. Audio is probably better choice but linear may be OK here as well, range is small (11dB in case of 25k).

thanks..

You're welcome - just please post your results and remember: pictures and sound samples of finished builds make me happy

Good luck, T.

[morales72]

Thanks for the prompt answer T!

I will try those mods. I even checked out the Lover and try the final boost stage too. I'm also considering changing to the MN3207 since I have a couple of them lying around. Maybe it's a voltage related problem? I'll try with 15v to see if it boosts up the volume.
I'm sticking with it though. I love the sound. To me it's even better than the DEM reissue I also have.

Regards,

Fernando.

[mr_deadmaxxx]

1. Actually, I would say that replacing R18 by 12k gives better dry/wet ratio (wet path gets boosted by BBD) and may help little bit with volume too.

2. Adjusting R5 should help - even with my build I'm considering to add little more gain to the input stage, but drop in my case is really small. Try to replace R5 be 10k trimmer and find the match. If it still won't be enough there is something wrong in your build I would say.

3. Another possibility to gain volume is to use output booster as is used in the Current Lover (find link in the previous post) - maybe just use bigger value for C23 (like 1uF), 100n seems little small to me.

Ok so among these three, which do you think would give the best gain or should I say a good boost for this pedal?
Will replacing R5 with a pot be better than that one in No. 3?

Hmmmm...

[Thomeeque]

 Start with 1. - better dry/wet ratio is worth trying even if it won't solve volume drop issue.

Then it depends:

Increasing gain (2.)

• is simpler,
• it gives better SNR (signal/noise ratio) but
• it lowers dynamic range of the effect (signal gets distorted sooner).

Booster at the output (3.)

• is little more complicated mod,
• it makes S/N ratio little worse (it does not increase SNR of the effect and adds it's own noise) but on the other hand
• it does not alter (and even allows to simply increase) dynamic range,
• it makes effect less vulnerable to the influence of the load at the output (makes passive output network buffered) and
• in this case it fixes phase of the passing signal (one of "built-in" EM issues - passing signal is inverted at the output)

To make some conclusion:

If you want to just slightly boost the fx signal to compensate volume drop, you don't get unpleasant distortion and you use simple monophonic signal path (guitar -> pedals -> amp in one simple chain), where phase error does not metter, go for 2.

In other cases go for booster.

T.

[kranja]

I checked all the stuff you mentioned and I found two traces on the pcb touching itself and making a short circuit. After I solved this, everything started to work, the sound is absolutely fantastic!
I would recommend this build to everyone!
Now I still have to figure out the alignment procedure and see if the sound gets even better.
TNX Thomeeque!!!

[mr_deadmaxxx]

Okay. I was thinking of no. 3..
Anyways, if I use no. 3, why use 1uF instead of 100nF? Can 1uF be polarized?

BTW, can I use electrolytic capacitors instead of tantal/tantalum capacitors specified on your builds? What would be the difference?

Thanks..

[mr_deadmaxxx]

What's the alignment procedure?

[morales72]

Hi to all!

I had a late night Mistress session after rehearsal and I tried the first two options.

1 - 12K R18: Matched bypass volume but to my ears was too dry and had to crank feedback badly to hear the effect.

2 - 10K trim: did the job all the way up so I replaced with a 12K (don't have 10Ks lying around) and did the trick. Again I can hear the watery effect and with matched volume to bypass.

I will try next Friday with the band to see if it cuts through!

Here are some pics of the building. Forgive my "Back to the future" Dymo style, I was a teenager in the 80's...



Uploaded with ImageShack.us



Uploaded with ImageShack.us



Uploaded with ImageShack.us

I'm usually not this messy but it got out of control at some point.

Cheers!

Fernando.

[Thomeeque]

I checked all the stuff you mentioned and I found two traces on the pcb touching itself and making a short circuit. After I solved this, everything started to work, the sound is absolutely fantastic!
I would recommend this build to everyone!
Now I still have to figure out the alignment procedure and see if the sound gets even better.
TNX Thomeeque!!!

Hey kranja, that's great news - congratulations!

I'll try to write proper alignment procedure later, you may wait or try to do your own research meanwhile, there's lot of info on-line

Okay. I was thinking of no. 3..
Anyways, if I use no. 3, why use 1uF instead of 100nF?

100nF may cut low frequencies too much (exact behavior will depend on the volume pot position and load at the output; if you want to know more learn how to use LTSpice, there are tutorials on-line like http://gaussmarkov.net/wordpress/tools/software/ltspice/ltspice-ac-analysis-with-the-bmp-tone-stack/). But maybe that's the point, you can simply try both options.

Can 1uF be polarized?

Yes, plus at the Q3 collector.

BTW, can I use electrolytic capacitors instead of tantal/tantalum capacitors specified on your builds?

Yes, no problem, original uses electrolytics IIRC..

What would be the difference?

I prefer to use tantalum mainly in LFOs and "around" LFOs as they should be more stable, should have lower parasitic resistance and they should last longer. But it's nothing critical, if sourcing was problem I'd calmly go with electrolytics. More about electrolytic vs. tantalum e.g. here.

Hi to all!

I had a late night Mistress session after rehearsal and I tried the first two options.

1 - 12K R18: Matched bypass volume but to my ears was too dry and had to crank feedback badly to hear the effect.

2 - 10K trim: did the job all the way up so I replaced with a 12K (don't have 10Ks lying around) and did the trick. Again I can hear the watery effect and with matched volume to bypass.

Hm, it makes me wonder if the MN3007 does not make the difference here - I had never used it in my EM3207, all my experiences and measurements are based on the use of MN3207.

Nevertheless I'd check whole audio path by measuring dry and wet signals:

• set filter-matrix mode,
• maximal RANGE,
• zero COLOR,
• put e.g. 0.2V 200Hz sinus at the input and
• measure AC voltages at IC1@1, IC1@7, IC2@7, IC2@8 and Q1@E

all measured AC voltages should be at least 0.2V * R3/(R2+R3) * (1 + R5/R4).

I will try next Friday with the band to see if it cuts through!

Please, let us know then.

Here are some pics of the building. Forgive my "Back to the future" Dymo style, I was a teenager in the 80's...

Thanks! I love it (maybe because I was a teenager in the 80's too )!

I'm usually not this messy but it got out of control at some point.

No problem, it gives it cool organic feel T.