EHX - Octave Multiplexer  [schematic]

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EHX - Octave Multiplexer  [schematic]

Postby reneshelle » 25 Mar 2011, 12:26

I said I would post pictures of my Octave Multiplexer in another threat. I will do so naturally. But I feel a little stupid now that I googled it a bit. It's been traced already - and very well - factory schematic... http://topopiccione.atspace.com/PJ19EHO ... lexer.html

Here are my pictures anyway
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Re: EHX Octave Multiplexer

Postby uncleboko » 25 Mar 2011, 12:37

Excellent photos!!
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Re: EHX Octave Multiplexer

Postby Tonetweaker » 27 Mar 2011, 07:14

+1 :thumbsup

I just bought one of these recently. Not a bad little doodad.


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Re: EHX Octave Multiplexer

Postby Bernardduur » 29 Aug 2012, 09:05

Are there any nice mods for this unit? Better tracking? More volume? Improvements on the circuit?
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Re: EHX - Octave Multiplexer

Postby daemons » 19 Aug 2015, 15:09

reneshelle wrote:I said I would post pictures of my Octave Multiplexer in another threat. I will do so naturally. But I feel a little stupid now that I googled it a bit. It's been traced already - and very well - factory schematic... http://topopiccione.atspace.com/PJ19EHO ... lexer.html

Here are my pictures anyway

Have the part values been checked vs the schematic? I find it hard (almost impossible) to read some of the values on this schematic. :scratch:
That topopiccione BoM has '?' marks in it, which I don't really trust. :!:

If I could validate the values 100%, I would be willing to re-draw this schematic using EagleCAD, and we'd have a readable schematic once and for all. :)

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Re: EHX - Octave Multiplexer

Postby Dirk_Hendrik » 19 Aug 2015, 18:40

R23 is a 15 k.
Leaves that 180k that couls be a 100k as well. That's little experimentation required to find out.
Sorry. Plain out of planes.

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Re: EHX - Octave Multiplexer

Postby armdnrdy1 » 19 Aug 2015, 20:30

daemons wrote:
reneshelle wrote:I said I would post pictures of my Octave Multiplexer in another threat. I will do so naturally. But I feel a little stupid now that I googled it a bit. It's been traced already - and very well - factory schematic... http://topopiccione.atspace.com/PJ19EHO ... lexer.html

Here are my pictures anyway

Have the part values been checked vs the schematic? I find it hard (almost impossible) to read some of the values on this schematic. :scratch:
That topopiccione BoM has '?' marks in it, which I don't really trust. :!:

If I could validate the values 100%, I would be willing to re-draw this schematic using EagleCAD, and we'd have a readable schematic once and for all. :)

Dae.


With the component, trace side pictures and the schematic, you can trace the circuit to verify the values.
Start at the quad op amp and move out from there.
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Re: EHX - Octave Multiplexer

Postby daemons » 19 Aug 2015, 21:47

Dirk_Hendrik wrote:R23 is a 15 k.
Leaves that 180k that couls be a 100k as well. That's little experimentation required to find out.

Yeah, I've also read a few places that some "factory" EH schematic have intentional errors to throw people off.
I think a proper trace, not based on that schematic is in order. It doesn't help that they don't use any part reference on the PCB (R1, R2, etc..).

armdnrdy1 wrote:With the component, trace side pictures and the schematic, you can trace the circuit to verify the values.
Start at the quad op amp and move out from there.

That was my plan. If reneshelle can check the capacitors (as I can't read them) then I can make a proper schematic.

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Re: EHX - Octave Multiplexer

Postby reneshelle » 20 Aug 2015, 22:42

I'm afraid I sold it long time ago. Sorry - no help from me...
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Re: EHX - Octave Multiplexer

Postby daemons » 21 Aug 2015, 06:12

reneshelle wrote:I'm afraid I sold it long time ago. Sorry - no help from me...

Ah rats. I'll look around for another one.

Thanks,

Dirk_Hendrik wrote:R23 is a 15 k.
Leaves that 180k that couls be a 100k as well. That's little experimentation required to find out.

I did find it, and it is in fact 180K. It's the resistor between those two diodes near that huge 470uF cap.

On these photos, I can only identify 5 of what looks like 100nF Mylar caps, but I find 7 on the schematic, so I'll need more photos.

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Re: EHX - Octave Multiplexer

Postby Mig Buff » 22 Aug 2015, 22:47

I just opened mine up - looks a little newer inside then the pictures posted above, but here are all the values. I'll post some pictures as soon as I figure out how...

R1: 10k, C1: 33/16v
R2: 22k, C2: 0.1
R3: 18k, C3: 0.022
R4: 15k, C4: 0.022
R5: 33k, C5: 0.022
R6: 470, C6: 0.1
R7: 180k, C7: 500/10v
R8: 27k, C8: 0.022
R9: 27k, C9: 0.1
R10: 10k, C10: 0.1
R11: 10k, C11: 0.15
R12: 10k, C12: 0.15
R13: 15k, C13: 0.022
R14: 100k, C14: 0.047
R15: 27k, C15: 0.022
R16: 10k, C16: 0.022
R17: 4.7k, C17: 0.022
R18: 22k, C18: 0.1
R19: 18k, C19: 0.1
R20: 47k, C20: 100/10v
R21: 47k
R22: 10k
R23: 15k
R24: 15k
R25: 100k
R26: 680
R27: 100k
R28: 2.2m
R29: 150k
R30: 47
R31: 2.2m
R32: 1k
D1-D3: 1N4148
U1: LM324N
U2/U3: JRC4558D
U4: T04013BP?
All pots: B100k
All caps are green poly except: C1, C7, C20 which are electrolytic

I hope this helps and I'll try to get the pictures posted as soon as possible. All values were printed on the PCB and it doesn't appear this PCB is used for any other layout.

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Re: EHX - Octave Multiplexer

Postby Andy2No » 04 Oct 2015, 22:05

I've just opened mine up, and it looks nothing like that. It's an XO series, I guess. I bought it new, a couple of years ago.

I was hoping to tap into the pure square wave outputs of the 4013 - there's the one that's actually used, and the one an octave above that, that just feeds the second one. Only the NOT Q outputs are in use, according to the schematic, so there should also be the option of using the Q outputs - 180 degrees out of phase.

Unfortunately, it looks like I can't get it apart without damaging the three knobs, and the side of the PCB I can see, only has connections for the pots, jacks and switches, some capacitors, a diode and what appears to be a transistor (K30A GR0H), and some via points.

Possibly all I can realistically do is poke around with an oscilloscope, to see if I can pick up the second NOT Q signal from the 4013, or something close to it, before it feeds into the rest of the circuit. I won't be able to get to the first stage, or the unused Q output pins, unless I can get it apart.

The alloy case has Made In China moulded into the inside.

The PCB has "EC-D19rB" marked on it, near the Direct Out socket.

Behind the High Filter pot, there are pads labelled GS1 Ground Spring, with holes that the spring presumably should fit into, to connect those pads to the metal case - there is no spring. Maybe I should make one?

You have to take the back off to change the battery, of course. I've removed the one that was in there because it's been there for a while now, and might start to rot. It could easily never get another one.

The pots, jacks and switches, are all mounted on the PCB. The PCB shows no indication of 0.1" spaced chip legs, so it's presumably all surface mount, on the other side.

I can't get the PCB out without removing the knobs, which may well be glued on (after unscrewing the bits that secure the jacks) . I can't pull them off and they are hollow moulded plastic, so I'd damage them trying to lever them off.
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Re: EHX - Octave Multiplexer

Postby Andy2No » 05 Oct 2015, 03:42

Hmm... Maybe "XO" means a bigger box. Mine appears to be the same one that's currently shown on the EHX website:

http://www.ehx.com/products/octave-multiplexer
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Re: EHX - Octave Multiplexer

Postby daemons » 05 Oct 2015, 03:50

I haven't posted in a while. Life has been getting in the way.. annoying how it does that. :) That said, I've started tracing a more recent (est. 1980s) version that Mig Buff posted the parts list earlier. As soon as I'm done, I'll be posting a full schematic that will be confirmed, and easy to follow.

Andy2No wrote:I've just opened mine up, and it looks nothing like that. It's an XO series, I guess. I bought it new, a couple of years ago.

That being an XO and currently being produced, I wont be tracing it. It's probably close to the older model anyways, aside from the direct out and lots of SMD parts.

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Re: EHX - Octave Multiplexer

Postby Andy2No » 05 Oct 2015, 04:12

Yep, it may well be the same circuit, Dae. I was hoping it was constructed in the same way - with parts I could get to, on a scale I have some chance of soldering. Sadly, no.

I'll have a look at the signals at the pins of that transistor, or FET soon. If it's doing the same thing as Q1 in that schematic, maybe the signal at the gate / base will be roughly what I was looking for.

The mixing done by a 100k pot, that then connects to the output, seems a little odd. I thought pedals had lower impedance outputs than that.

I was also under the impression that the Sub switch was for a sub octave - i.e. one further down, but it seems to be just a choice of filters, going by that diagram.
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Re: EHX - Octave Multiplexer

Postby Bernardduur » 24 Nov 2015, 22:48

I've got a nice vintage unit. Different outlay compared to all other units I've seen.

DSCF8257.JPG


2x LM324N
It was bolted on the other side of the box.
DSCF8259.jpg
DSCF8261.jpg


I thought it was a DIY version; then I found some other pics of the exact same circuit (2x LM324)
eh-octave-1975.jpg
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Re: EHX - Octave Multiplexer

Postby Bernardduur » 24 Nov 2015, 22:53

Octave Multiplexer vintage.JPG
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Re: EHX - Octave Multiplexer

Postby Andy2No » 25 Nov 2015, 02:08

Interesting, Bernardduur.

I did get the knobs off mine, in the end - the XO version. It seemed to be the same circuit apart from the sides of the 4013 being swapped over, for the pin numbers. I should check if the output circuit is still the same - tapping off a 100k pot, unbuffered, giving a horribly high output impedance.

I meant to try feeding the square wave via another pot, to add another sound. It's all very small to work on, of course. I got side tracked, but I may get back to it soon.

I took pictures, which I haven't posted yet. I'll dig them out tomorrow, if I remember.
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Re: EHX - Octave Multiplexer

Postby daemons » 01 Dec 2015, 00:14

Nice one Bernardduur. I guess I should finish my trace of the one I started. It uses 1x 324 and 2x 4558

Some of the values are different, and some connections aren't exactly the same. It'll be interesting to compare.

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Re: EHX - Octave Multiplexer

Postby johnk » 01 Dec 2015, 03:36

I built one about a year ago (I etched a PCB and the enclosure for it) and I love it. I found that it could use a bit more output so I added a Jfet boost to the output with a volume control:

Image

Image
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