Home › Forums › Vintage EHX › Bad Stone Mummy Version 1 oddity?
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November 25, 2013 at 10:18 pm #83238TheGrokeMember
Hi everyone,
I recently purchased a non-functional Bad Stone version 1. Opening it up, it looks quite different from any Bad Stone I have seen online. It uses transistors, like the mummy version, but it also has a section with two op amps in a section that is unpopulated on normal mummy boards.
Does anyone have any info on this version or know the function of this extra part of the circuit? Even if not… I figured others might be interested in at least seeing this version, since it hasn’t shown up online before.
The images might looked cropped off in a browser window – it seems to work better if you right click and open them in a new tab – or just drag to the desktop to view.
http://www.umich.edu/~damont/BadStone1.JPG
http://www.umich.edu/~damont/BadStone2.JPG
http://www.umich.edu/~damont/BadStone3.JPGbest – D
November 25, 2013 at 10:55 pm #119519The EH ManModeratorPics no workee
November 26, 2013 at 8:52 am #119522TheGrokeMemberHi. I fixed the pics. They might looked cropped off, but if you right click and open them in a new tab (or just download them to your computer) then you will see the full view.
best – D
November 26, 2013 at 12:56 pm #119524The EH ManModeratorAre you talking about the 2 big ICs or the 2 small ones?
November 26, 2013 at 1:09 pm #119525TheGrokeMemberHi Ron.
I am mostly curious about the 741s and the surrounding circuitry.
I believe the other two big ICs are just LM324s, which I believe are the A and B ICs in the original circuit, as seen here:
htp://www.freeinfosociety.com/electronics/schemview.php?id=380
I’m guessing EH just scratched them off to protect their circuit from being copied?
But there are no 741 op amps on the original, not from what I have seen from Googling at least.
Some members of one of the popular online stompbox forums made a clone of the mummy board. It looked similar to mine, but omitted the section with the 741s.
Mine also has a different configuration of trim pots (I have one – others seem to have three or so).
best – D
November 26, 2013 at 1:13 pm #119526The EH ManModeratorHard telling knowing EH at that point in time. I have a couple of those Bad Stones as well but I haven’t opened them up . I’ll have to dig them out and check.
November 26, 2013 at 1:15 pm #119527TheGrokeMemberThanks Ron – that would be great! Let me know if you need a link to the forum with the cloned schematic for comparison. I’m not sure I can post that here.
If you do open one and find that it is the same, could you please take a picture of the wiring. I’m not 100 percent sure that mine is correct, and it’s hard for me to figure out without a schematic.
best – D
November 26, 2013 at 1:16 pm #119528The EH ManModeratorWill do. I have access to the forum and I also have some of the PCBs they were offering there.
November 30, 2013 at 6:33 pm #119542The EH ManModeratorChecked both of mine and neither of them have the extra ICs or even a place for them.
November 30, 2013 at 7:10 pm #119543TheGrokeMemberHm… the plot thickens. Well, thanks so much for checking yours – much appreciated. Some more info, if anyone is curious:
The circuitry around what I am assuming is a scratched off LM324s certainly seems similar to Version 1. The four surrounding transistors (maybe 2N4302s, but marked with only “SCOTT” on mine) also make sense with this part of the schematic.
The two similar looking transistors in the middle are also marked with only “SCOTT”. Those might be Q1-6, the 2N4302s from Version 1.
There are also two more transistors on the component side marked FS37000 327. Not sure what those are. I found some posts on this forum claiming that they are PNPs. Could those be functional equivalents to Q8, the 2N5087?
The transistor on the trace side is marked 2N5363. I guess that is Q7.
I suppose I’ll need to attempt to draw something up for this if I am ever going to get it to work. Kind of cool to have this weird anomaly though
Does anyone else out there have one that looks like this?
Thanks again – D
December 3, 2013 at 11:14 pm #119551TheGrokeMemberLo and behold… this thing suddenly works. Cleaning up the boards, I found one loose capacitor. The ground connection was also a bit flakey.
I have to say, the vibrato setting on this (via the color switch, oddly enough) yields a really pleasantly, messed up sound. I didn’t look at the wave, but it can’t just be a sine – seems much more complex – almost random. Gives everything you play has a real sea sick quality. Nothing like any other vibrato I have heard.
The only issue is that I am getting some clock noise bleed. On the slow settings, it’s just a quiet occasional tick in the background, but when I put it on the fast settings, the clicks are close together and create a constant buzz when I am not playing.
Assuming that the original V1 schematic is at least partially relevant – can anyone suggest which components might have gone south?
Thanks – D
December 4, 2013 at 12:14 am #119552ScruffieMemberVery interesting
I have a theory… I have seen a mummy face with the 4049 and vibrato toggle before it went to having the manual control and perhaps this is earlier and using the audio path of the 4049 bad stone (which used 3 OpAmps ignoring the phase shift stages or as here, 2 x 741s and a transistor working as the buffer OpAmp) but they hadn’t developed the way of biasing the 4049 they did later maybe.
The 2N3563 on the schematic is to do with the bias, yes the SCOTT transistors in the dot package were 2N4302s (I might be wrong but isn’t SCOTT Mike Matthews son?) perhaps one transistor is to produce a hyper triangle LFO wave like the later models…
Doesn’t quite add up but it’s a start.
Very odd! I may have to draw up a schematic if you can get some more photos as the Bad Stones are one of my favourite phasers.
December 4, 2013 at 8:53 am #119554TheGrokeMemberHey Scruffle,
Thanks for your input. It seems plausible that this is something between the standard mummy face and the mummy face enclosure with 4049. I will dismantle it again and try to get some better shots for both sides, especially near that extra circuit.
Any thoughts on the noise I’m getting at fast rates? There is one trim pot, and I can change the frequency of the noise by adjusting it (the buzz has more low frequencies in it than I previously indicated – so perhaps it is a hum and buzz), but doing so also cuts out a lot of the effect.
best – D
December 7, 2013 at 10:37 pm #119559TheGrokeMemberI took some more pictures. A lot of them are sort of bad – I was trying to get shots that covered components nested under components, etc. Didn’t work so well. I think the X-rays and the original set should be useful though. The others might come in handy when looking at individual component values.
The ground wire for one of the batteries broke off in the second set (“after cleaning”), but it is quite easy to see where it should go in the first set (“before cleaning”) or on the original pictures that I posted.
Here is a link to a zip of the pics:
umich.edu/~damont/BadStoneVersion1.5.zip
best – D
December 12, 2013 at 5:26 pm #119567ScruffieMemberThanks for the photos!
Not sure when i’m going to find time to trace through at this time of year but i’ll be interested to see what’s going on and report back when I know.
I also suggest you post the photos at freestompboxes.org as someone there may very well trace them faster than I.
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