Rotoverb P-100, 1975 large rotary pedal info

[analogmike]

HI,

I have one of these that does not work. All the chips (14 pins) on the board are sanded off, they must have known about the FSB forum even 30 years ago.

it was made in CA, not the smaller Guild rotoverb (though may be similar inside?)
it looks like a 4 switch Leslie control pedal.

Does anyone have the schematic or more info on this old beast?

[theehman]

Hey Mike!  Can you post some gut shots?  I'll bet someone can figure something out from some pics?

[Mark Hammer]

+1

Although the specifics of the chips may not necessarily be decipherable (e.g., is it an LM324 or a TL074?), the connections to power and ground, the pins left unused, and the pins that are obviously used for outputs, can often be readily identified.  This is not just a challenge related to sanded-off part numbers.  I have chips whose markings did not stick particularly well to the surface of the chip, and others with house numbers, whose coding may have been possible at one time with those humungous IC reference books (remember those 1200 page monstrosities on onion-skin paper with the tiny print where the devices were arranged in a bizarre numerical order, regardless of function?).

Honestly, they should have just gooped it.....for posterity.

[analogmike]

I thought it would be easy, as it looked like the SAD1024 evaluation circuit.. but there are no 16 pin chips, so no SAD1024. There are three 14 pin chips, I dont think there were any other BBD chips available back in 1975. It's a very simple circuit but it's not cost feasable to spend more time on it unless we have some info about what chips there are, we already tried mapping them out by pin voltages etc. There is not much info on the web about these at all, was hoping someone might have more info on them or we have to send it back. thanks!!

[BDuguay]

This reminds me of my 'Duet Vocalizer' by 'Lynn'. It looks to have been made around the same time as what you've got.
It has a bunch of 14 pin chips too but they're painted over. I'd be willing to bet though, that they're might be some similarity between these 2 peadls. I'm confident that I could remove the paint with a little M.E.K. and some elbow grease. Would you like me to do that and report my findings?
B.

[Mark Hammer]

As we have discussed here many times, there are a couple of features  or dimensions of rotating speaker sound.  One is certainly the notches created.  Another is the slight amplitude modulation as the rotor points away from you and then approaches you.  Another is the slight pitch modulation.  Still another is the ramp-up/ramp-down action of the motor.

Is a BBD required to perform all of these?  Nah.  People have been using phase shifters to mimic the notch movement of rotating speakers (if somewhat imperfectly) for ages, and the old PAiA Synthespin project (also a 1975-76 vintage) was simply a modulated bandpass filter, for crying out loud.

So if you had 3 14-pin chips, could you produce frequency, amplitude, and phase modulation with "digital switching"?

This means you would have to a) generate moving notches, b) generate ramp-up and ramp down, c) generate some amplitude modulation.

Short answer is "maybe".  One of those chips would provide the "digital switching", which we will assume is a CMOS 4016 or functional equivalent.  That leaves two chips which, for argument's sake, we will assume as being an LM324 or equivalent.  Two op-amps can be used to provide a single notch, or perhaps a pair of bandpass filters (à la Synthespin).  A third op-amp can be used to to achieve some degree of amplitude modulation, although if there are any transistors on the board - specifically FETs - we should probably know about that.  Standard LFO circuits may use two op-amps, but as the P90 illustrates, you can get by with one.  f the unit combines modulated and straight signal, then one needs a splitter and mixer stage, however the splitter can be achieved with a transistor, and the mixer can simply be passive.  That leaves the ramp-up and ramp-down.  There I will plead ignorance; particularly since I have no idea how sophisticated the unit's motor mimicry is.

So, like I say, if it uses a modulated notch filter or bandpass filter, and throws in passive mixing, you may well be able to get away with doing it all in 8 op-amps.  I think key to that guess is simply knowing its vintage.  Best to keep in mind that our expectations for Leslie mimicry were very low in 1975.  VERY low.  One of the reasons why the CE-1 grabbed the world's attention; it was a huge step up in that particular goal.

What do you think?

[BDuguay]

I think Mike still needs to respond to my offer. Oh yeah, and what you said Mark 
Seriously though, I think we're on the same track as far not over thinking a circuit that was made back when Happy Days was a decent show.
B.

[notchboy]

I've got one that doesn't work, either, also with sanded chips.  I've never been able to find schematics for it.

[theehman]

I've got one that doesn't work, either, also with sanded chips.  I've never been able to find schematics for it.

Post some good gut shots (both sides) and we'll see if we can figure it out.

[analogmike]

This reminds me of my 'Duet Vocalizer' by 'Lynn'. It looks to have been made around the same time as what you've got.
It has a bunch of 14 pin chips too but they're painted over. I'd be willing to bet though, that they're might be some similarity between these 2 peadls. I'm confident that I could remove the paint with a little M.E.K. and some elbow grease. Would you like me to do that and report my findings?
B.

yes please!!!!

Since I am not the only one who needs to fix one of these, it's worth figuring out.

Here is the board, really nice how it plugs right into the motherboard. The motherboard is mostly power supply stuff, but also two 4013 chips and 4 or 5 transistors. The chip that's not sanded off is an NE5532



here is the other side of the board:

[notchboy]

And this is just a wild guess, but I always wondered if the "3001" on the board had anything to do with an MN3001...

[analogguru]

Boaahh.... is this boring without the surrounding wiring guts:
http://analogguru.an.ohost.de/temp/rotoverbcomponents_c.jpg

With the surrounding wiring a schematic could be created - anyway, maybe this could be helpful to make it run.

enjoy,
analogguru

[grizzlytone]

I'm new to this forum but I've been in the electronics business for a long time, I'm also a collector of select effect pedals that I think I might be able to use when making music. I'm pretty confident that I could repair a broken Rotoverb regardless of sanded chips so if anyone reading this thread is up to selling his/her non functional Rotoverb I'd be most interested in buying, I'm thinking in the region of $120 + shipping depending on the overall condition of the unit. You can contact me privately through email or if you like you can just reply in this thread. Thanks/ M.B.
...and if I do get a chance to crack this nut I promise to post my findings on this forum to the benefit of all.

[analogmike]

Thanks for the identification info. We still have had no luck, my guys tried all the chips labelled above and a few more on the motherboard which had markings on them. But still no leslie sounds.

Any luck removing the paint on those chips? We looked very hard at our chips but they were too well scratched off.

We can't guess the unlabelled chip at the top left. Here is some info on it:

pins not connected : 3, 9, 13, 14
7 and 8 are tied together

+15V on pin6
-15V on pin11

No audio signal is getting to this chip (possibly due to another problem but I guess this
is not an audio chip).

thanks again!

[analogguru]

Again:
Hows about a picture from the off-board wiring (which leads to that chip) ?
This would be helpful to identify it.

No audio signal is getting to this chip

It is not in the signal path.... it appears to be for the speed (ramp) control.
Is the orientation of this chip according to the screen printing on the pcb ?
Is pin 1 of this chip connected to somewhere ?
If you take this chip out of the socket, can you see any code on the bottom of the chip ?

analogguru

[analogmike]

There was one on ebay, the seller kindly sent me pictures.

A little photoshopping and i can see the chip!



Will get one of these ICL8038CCPD waveform generator chips asap.

Thanks!

[jmasciswannabe]

If I recall correctly that is the same chip that is in the Roger Mayer Voodoo Vibe.

[analogmike]

I finally found some of the chips and it works!

Thanks!!!

[newperson]

How does it sound? 

[analogmike]

It sounds interesting, sort of dark and swirly. Chorus switch adds dry to change the vibrato into a better sounding chorus, as on a Uni-Vibe.

There is a DELAY switch so the speed ramps like a real Leslie. Slow speed is very subtle.

Not a great effect compared to what we have now, but pretty cool and innovative in it's day.