Rockman Chorus Pedal

[Vivek]

Did you try the before and after filters in the X100 or Nobels schematics ?

[ElectricDruid]

Yes, I learned a lot from doing this. Now, I would like to find the best filters to put at front and end of circuit that will give the past in-colored sound. Does anyone have any ideas to look at?

There is no "best". There is only "the sound you like". Choose some circuits that you like the sound of, and then steal borrow ideas from those to get the sound you're after.

[caspercody]

I got the Rockman chorus to work, but by itself it is dark sounding.

So I see there seems to be (2) different filter designs, one like the CE-1, using 10K resistors in the sallen-key filter and output buffer. The other type uses 47K resistors. I already have a CE-1 (kind of) clone with the Julia, so I went with the 47K filter circuit.

I went with the Zombie chorus since it looked like most of the other 47K types, but has fewer amount of parts. It works, but now I get a noise in the back ground, sort of sounds like bacon frying.. It did not make this noise with the Rockman.

If I remove the cap between pins 6 and 7 on the 4046 chip, the frying noise goes away, but the sound is not good chorus sounding. The chip diagram for the 4046 for pins 6 and 7 says CX.

Any ideas on getting rid of the bacon frying sound? I have a lot of caps between the (-) and (-) battery terminals, if that means anything.

Also, if I connect the out put directly to the first buffer output there is a clean sound coming out. But after pins 7 or 8 on the MN3007, the noise appears.

I tried (2) different LFO's the Rockman one (which has a -voltage on pin 4, and I thought maybe here), and the second LFO was from the Zombie. Both have the noise.

[Vivek]

Does the noise change if you change the setting of the rate pot ?

No cap between pin 6 and 7 of CD4046 should mean no clock oscillation, or extremely high oscillation based on some stray capacitance

[caspercody]

I made a vero board of the Zombie chorus, and it works, and got rid of most of the back ground noise. The noise was probably coming from all the wire I had on the breadboard.

So I added a switch to switch between the Zombie LFO, and the Rockman LFO from pin 9 on the 4046 chip. And I thought it was working, but the chorus effect was not too much on the Rockman side. I went to watch videos of the Rockman, i noticed the LED was flashing. On my build the LED was constantly on. So I built a bread board of the Rockman clock driver. The 4013, and 7555 chips. The 7555 chip when connected does make the LED flash. But the sound does not have any difference.

I then removed the 4013 chip, and came out of the 4046 chip pin 9 (again) but this time with the 7555 installed in the circuit. There is some chorus going on, but I get a oscillating bump in the sound that goes right along with the LED flash.

I am guessing the 4046 clock driver and the 7555 clock are combining and making the louder bump?

I found a Youtube video (https://www.youtube.com/watch?v=s2LcUWQYwjk) showing how to test the 4013, and my 4013 does work. I tried both sides of the 4013 chip and they both work, but I cannot get the Rockman chorus with the 4013 and 7555 combination when hooked up to pins 2 and 6 out of the MN3007.

I also tried using + and - voltage on the 4013 test circuit (just like in the Rockman circuit, no ground reference). This only caused the LED to light up, but would not turn off when I pushed the button.

[john1950]

I have the rockman chorus on the breadboard with 7555 and cd4013. The chorus worked but after playing for a minute the sound disappeared. when I then turned the power off and then on again I could play for another minute until the sound disappeared again. I just can't figure out what's causing it

[ElectricDruid]

I have the rockman chorus on the breadboard with 7555 and cd4013. The chorus worked but after playing for a minute the sound disappeared. when I then turned the power off and then on again I could play for another minute until the sound disappeared again. I just can't figure out what's causing it

If it does that reliably (works when first powered up, but then stops) it's often due to the DC conditions in the circuit not being right. When the circuit is first switched on, it's ok and it works. But then electrolytic caps in the circuit charge up and the bias points get pushed out of the range where it can work. When you turn it off, the caps can discharge and it'll be ok again briefly.

Check any electrolytics in the circuit to make sure they're the correct values and polarity. Check that you have DC blocking caps between stages where you're supposed to, and check that DC voltages around op-amps are what you expect. Something's wrong somewhere.

[PRR]

In tube circuits this can be lack of a working grid-leak (bias) resistor. At turn-on the grid happens to be at a working bias voltage. But with no grid resistor to leak any stray charge, it can drift to a wrong voltage in minutes.

CMOS is liable to this also. No reason other FETs won't.

This will usually show as the plate/drain/output DC voltage being right at first and wrong some later time.

[john1950]

I measured some voltages and at the clock input of the mn3007 pin 2 and 6  I measured a swing between 5 to 11 volts on pin 6 and a swing from 2.9 to 5.6 volts on pin 2. This difference can't be right, can it?

[Vivek]

The two clock pins are supposed to have similar voltage swings.

[ElectricDruid]

I measured some voltages and at the clock input of the mn3007 pin 2 and 6  I measured a swing between 5 to 11 volts on pin 6 and a swing from 2.9 to 5.6 volts on pin 2. This difference can't be right, can it?

Unfortunately, I'd say that's pretty normal. Those two pins are the clock signal, so you're trying to measure a high frequency square wave with a DC voltage setting - it's not a Dc voltage at all, so the DC reading has not much contact with reality. Even an AC voltage setting wouldn't be much better, since those assume a sine wave and would over-read heavily for a square. You can work out by how much and adjust and stuff, but it's far from obvious and not a "set it and see" thing at all.

What voltages have you got around the rest of the circuit? If you post the schematic and the voltages, we might eb able to spot something wrong. Just voltages around the ICs and any transistors will do for starters - we don't need both ends of every single resistor or anything.

[Vivek]

Oops, I assumed John measured these high frequency clock signals with an oscilloscope


But even if he measured any other way, I feel he should have got similar readings on pin 6 and 2

[john1950]

I was only able to measure the voltages of the mn3007- because the multineter's battery ran out. mn3007 pin1 +6v pin2 3.3 to 3.5v pin3 0v pin4 4.9v pin5 -6v pin6 6.8-7v pin7 0.3v and pin8 0.2v I am using the rockman soloist scheme of boston guitarist Tom scholz.

https://dokumen.tips/documents/rockman-x100-and-soloist-schematics.html

[Vivek]

When I was working on the Rockman Chorus around Dec 2020, I found

there were some errors in the schematics on the net.

We received a bum lot of BBD/clocks and broke our heads on them. Then we got a new lot from another source and everything started to work.

I had checked some points with ELECTRICDRUID, and he guided me regarding biasing the BBD, especially since the new MN3207 BBD cannot accept 12Volts total supply, so I had decided to use 6V total supply to the BBD, and that needed rebias.

[john1950]

The rockman chorus runs on +6/0/-6 volts bipolair power, so that's going to be 12 volts. You mean I can try running the mn3007 on 6 volts?

[Vivek]

The MN3007 do work in the Rockman schematic

They were getting harder to find

So I redesigned with MN3207

But those accept 10V max. We can't give +6/-6 to MN3207

So I decided to feed 6V unipolar to the MN3207

In the end, all configurations worked in the Rockman schematic

MN3007 with 555
MN3207 with 555 and unipolar supply
MN3007 with Lich LFO
MN3207 with Lich LFO and unipolar supply

[john1950]

I've found the error, I accidentally connected the gnd of the guitar cord to the -6v and not to the 0. The chorus no longer cuts off and works fine now.

[Vivek]

Congratulations !

[ElectricDruid]

Congratulations indeed! Nice work.

Isn't it nice when you find it?!?

[caspercody]

John, congratulations!!!

Can I ask you, did you build it just like the schematic? Or did you change anything around?

I know my MN3007chip is working, because I  built a Zombie chorus (using this schematic  https://pcbguitarmania.com/wp-content/uploads/2020/02/Zombie-Choir-Building-Docs.pdf)  I then made a vero board of the Rockman LFO and connected it to my Zombie through a switch. I also added a 390pf to the clock on the 4046 per something Vivek mentioned in another tread. Please see attached.

For this build I connected the Rockman LFO as I drew up voltage wise, and it works. I also connected it with a bipolar power supply (just like in the Rockman schematic) and that way also worked. I just felt it was easier to use the voltages provided on the Zombie and not include a bipolar charge board.

I also tested my 4013 chip, with a Youtube tester I found (https://www.youtube.com/watch?v=s2LcUWQYwjk&t=157s   schematic at 2:39). And it appears that my 4013 works.

Now going back to my Rockman chorus bread board (that does not work). I ran a jumper from the first filer output (R148) to the input of the output filter (R153) and I have sound. So it appears my filters work.

I replaced the 10K bias resistor (R171) with a pot, and I was able to get sound out after adjusting the pot, but no chorus sound, and when I added the 10K resistor for the clean sound, I got no sound at all (basically the chorus/vibe switch on the attached Zombie chorus). When I disconnected the pins 2, and 6 from MN3007 to the 4013 chip, I still get sound. Which I should not be getting sound (the reason I saw this is when I disconnect these from my working Zombie, i get no sound).

I also tried a 4046, and 4047 chip with the Rockman filters, and I still could not get it to work. So, I feel I am not biasing the MN3007 correctly with the Rockman input filter. Why, because every other way I have tried worked with the MN3007, 4046, and 4047 chips I have. But as soon as I go back to the Rockman filters, nothing.

I just found another circuit that uses an inverting op amp input (https://stompville.co.uk/?p=236), so I will try to bread board this later this weekend.