Message 840
From: sasami@hotkey.net.au
Date: Fri Aug 6, 2004 11:49 pm
Subject: Wave Multipliers update.

I have found errors in all variants of the wave multiplier circuit diagrams I have seen. The most significant is the input resistors at "E" and "F". This error is present on the RES18 PCB too, though in a "modified" form.

Both reverse engineered diagrams (you will have seen Dean's) have E and F each feeding through a 1M resistor, then to a 33k pulldown (divider) to earth. If you look at the diagram, these 33k are in parallel, so in their place there is a single 15k resistor on the RES18. Remove it.

These 33k resistors should go directly between Pad E and earth, and pad F and earth. They are on the other side of the 1M resistors to what is shown. Instead of acting like a massive divider, they will now act as a load for the input signal, desirable if the previous module's output is capacitively coupled. The signal getting fed into the wave multiplier will be around 30 times higher once this correction is made. I guess this is why I considered this (the lowest) multiplier to be too subtle on the one I assembled.

There are no capacitors shown across the lower op-amps of each stage of this wave multiplier in Dean's diagram, while in the version I am examining, there cap is across the first stage only, and provision on the board for one on each other stage. Probably this capacitor is added to the stages on an "as needed" basis to stop oscillation, varying between one unit and the next. In the other diagram I have seen, there is one across each stage. These are marked "10n*" on the RES18 PCB. I do not know what value was used on Ollie's board.

There are two 47pF capacitors on the RES18 board that should not be fitted - they are across pins 11 and 12 and across pins 2 and 3 of the LM3900 at the end of the board. There is a capacitor in this position on the first stage, and it DOES belong there.

As already mentioned, the diode marked GE is not a germanium as first expected, but rather a Zener. Dean's diagram shows a reverse biased transistor BE junction, so either do that, or use a zener of around 4 to 5 volts.

These corrections come from my studying of Ollie's photos of his unit.

Ken

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Message 843
From: "Dean Batute"
Date: Sun Aug 8, 2004 6:37 pm
Subject: Re: Wave Multipliers update.

Hello Ken...and All,

I stand corrected on the 33K input resistors. Guess I was a little over zeolous when I did the "TIDY-UP" version of my schematic. To be honest the CORE was my concern so I made sure IT was correct but things like input resistors are so insignificant I guess I rushed by them.

As to the Bypass caps on the Lower circuit, my diagram DOES have one on the first stage as you mentioned it should. As to that topic they are used on a "need to use basis". Though I can't say for sure that this is an example, I DO remember some Serge circuits having extra caps soldered on the foil side of the boards where needed. Their absence or existance constututes neither an error or ommision but just how THAT particular circuit was engineered. Same can be said for the small value caps across pins 11 and 12 of the LM3900's in the upper circuit.

On a side note....just to see who's reading ALL the messages :).... I'm almost finished reverse Engineering the Analog side of the Moog MuRF pedal. I have a friend who got Serial number 11 and he leant it to me for a few days. Should have it done tomorrow night so I'll post it briefly if any one is interested. ??? Pretty basic stuff. Each channel is a single op-amp filter driving a discrete 4 transistor VCA. The enveloping, triggering, and LFO are generated by a Microcontroller (Didn't bother to pull that board out since it's a surface mount IC and I didn't want to MESS the thing up on my friend).

More later..... Off to see "Collateral" with the girlfriend.

T.T.F.N.... Dean.

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Message 844
From: "Steve Ridley"
Date: Sun Aug 8, 2004 8:12 pm
Subject: Re: [resergence] Wave Multipliers update.

Another source of confusion is the panel layout in the late 70s catalogue. It shows two audio inputs to the top section and only one to the bottom stage, but photos of early Wave Multipliers in this style have only one input to the top stage and two to the bottom, and the board only appears to support this arrangement. As it's a 113 board, it's unlikely there was an earlier version, so maybe the catalogue layout was pre production. T.T.F.N....T.T.F.N....

There are no capacitors shown across the lower op-amps of each stage of this wave multiplier in Dean's diagram, while in the version I am examining, there cap is across the first stage only, and provision on the board for one on each other stage. Probably this capacitor is added to the stages on an "as needed" basis to stop oscillation, varying between one unit and the next.

Serge seems to have made provision for stability caps around the opamps in most of his modules as a matter of cautious good practice. He only filled them when necessary.

As already mentioned, the diode marked GE is not a germanium as first expected, but rather a Zener. Dean's diagram shows a reverse biased transistor BE junction, so either do that, or use a zener of around 4 to 5 volts.

He seemed very keen on using the EN5179 transistor reverse biassed as a zener. They're usually across outputs to clamp the maximum vlotage to around 6v, but he uses one as a -6v reference in the PCO. I don't know what's so special about the EN5179 - I can't find any information about it.

I find it odd that Serge used so many different output circuits in the same module. The top section has an output resistor outside the feedback loop, the middle section has an output resistor inside the feedback loop, and the bottom section just has an output cap on the audio out. It makes it difficult to guess what you might find when he doesn't keep to expected patterns.

Will you be posting a definitive schematic?

Moog, Should have it done tomorrow night so I'll post it briefly if any one is interested. ???

Yes please...

More later.....

I wait with baited breath...

Steve

Off to see "Collateral" with the girlfriend.

Off to try and change a nappy without breathing in (-: