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DIY Stompboxes => Building your own stompbox => Topic started by: Peetem on December 02, 2020, 04:01:40 PM

Title: Rockman Chorus Pedal
Post by: Peetem on December 02, 2020, 04:01:40 PM
So, I've adapted the Rockman X100 chorus circuit and modified it for a foot pedal design.  Would love to hear any feedback on the circuit - criticism, concerns, modifications, etc.

I didn't try to recreate the 1/2 rack version yet, so this design doesn't have a "depth" control (e.g., Scholz called it "Long Chorus") or the stereo mix options (Wide, Stereo, etc).  The output would be the "wide" setting using a TRS plug (left side is the chorus/detune and right side is the unaltered guitar) or a 1/2 mix of both using a mono 1/4" plug.  However, if this circuit works out I will modify it for /- 9V with those options (e.g., wide and long). 

The schematic as shown says a bipolar 9VDC is supplied, but as it stands now, everything is optimized for bipolar 6v.  I didn't want to have to change the FET bias (2n4339) and other values for this protocol circuit.

Lastly, I have a PCB layout created and will getting 5 boards made.  If it works without issue, I'll post that as well (Gerber files).

Let me know your thoughts and thanks in advance for the feedback!



(https://i.postimg.cc/mzxtL02r/Schematic-Rockman-Chorus.png) (https://postimg.cc/mzxtL02r)
Title: Re: Rockman Chorus Pedal
Post by: Peetem on December 03, 2020, 03:34:03 PM
I should add that if there is any interest, I can creat a layout using DIY Layout Creator using a perf board.....

Just let me know....
Title: Re: Rockman Chorus Pedal
Post by: antonis on December 03, 2020, 04:02:22 PM
Hi & Welcome.. :icon_wink:

Is there any particular reason for biasing U2A one diode forward voltage drop above GND..??
Title: Re: Rockman Chorus Pedal
Post by: Peetem on December 03, 2020, 06:11:06 PM
Hi & Welcome.. :icon_wink:

Is there any particular reason for biasing U2A one diode forward voltage drop above GND..??

To adjust the gain of the filter before it goes into the BBD - it depends on the gain coming out of the previous stage.  It can be jumped if needed.

Am I thinking about this the wrong way?
Title: Re: Rockman Chorus Pedal
Post by: antonis on December 04, 2020, 08:44:31 AM
Am I thinking about this the wrong way?

I'm trying to figure out the influence of bias level into gain setting..
Title: Re: Rockman Chorus Pedal
Post by: Peetem on December 04, 2020, 11:45:45 AM
See circuit and diagram below. The high impedance input of the op-amp is connected similar in the chorus circuit as a voltage divider. By connecting to the high-Z input, the only current that flows through the resistor will be the input bias current to the op-amp.

In addition, the Re terms on the top and bottom of the gain equation cancel out leaving just a function of N. This removes the impact of end-to-end resistance from the gain equation altogether.
The gain adjustment is non-linear with respect to N, which we want as we're using it as a low-pass filter before the BBD.  However, the diode further reduces the bias to lowering the gain.

The circuit is useful as an audio control or brightness control (if a Vr is used as in the circuit), but in the case of the Chorus, R is not variable and therefore, keeps the gain down as fixed.
(https://i.postimg.cc/R3mSmwQH/864fig02a.gif) (https://postimg.cc/R3mSmwQH)

(https://i.postimg.cc/DWc2wmBY/864fig02b.gif) (https://postimg.cc/DWc2wmBY)
Title: Re: Rockman Chorus Pedal
Post by: antonis on December 04, 2020, 12:49:27 PM
Sorry but I can't follow you..  :-\

The high impedance input of the op-amp is connected similar in the chorus circuit as a voltage divider. By connecting to the high-Z input, the only current that flows through the resistor will be the input bias current to the op-amp.

Through which resistor..??
Title: Re: Rockman Chorus Pedal
Post by: Peetem on December 08, 2020, 02:10:57 PM
Sorry but I can't follow you..  :-\

The high impedance input of the op-amp is connected similar in the chorus circuit as a voltage divider. By connecting to the high-Z input, the only current that flows through the resistor will be the input bias current to the op-amp.

Through which resistor..??

Assume its not there (its been jumped as shown in the schematic).
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 24, 2021, 10:56:27 AM
Hello

Did you get this pedal to work?
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 26, 2021, 01:03:48 AM
I got the Rockman Chorus bread boarded right now. I am using a +9/-9 volt supply. I got the MN3007 from Small Bear. Schematic is basically the same as posted in the first post on this thread.

Using a wire from the output jack as a audio probe, I get tone up to pin 3 on the MN3007, and I get a tik, tik sound on pins 2, and 6. But no out put on pins 7, or 8. Voltage reading on the MN30007:

1 - +9.05v
2 - low/high (voltage starts low, then another reading of higher voltage, keeps in beat with the tik, tik sound. The voltage changes with every tik going up).
3 - +.60v
4 - -7.06v
5 - -8.56v
6 - same as pin 2 readings
7 - 5.88 then 5.80
8 - 5.6 then 5.9

Any thoughts on why no sound? If I put my audio probe on either pin 7, or 8 should I hear something?

Thanks
Rob
Title: Re: Rockman Chorus Pedal
Post by: Vivek on June 26, 2021, 04:58:29 AM
Great thread !!

Did you get it to work ? If yes, please ignore all comments below:

I have been spending few hours a day for the last few months, staring at the X100 schematics and it's LTspice simulation.

Eventually, i redesigned the Rockman Chorus to use MN3207 which are more easily available. I also removed 555 LFO and used a PLL instead, then adjusted all parameters to Rockman standards)

I see that you have No summing mixer !!!!


RV2 and RV3 look odd to me

You are running the MN3007 at the absolute max total supply voltage of -18V which might make it more prone to failures. Recommended total supply is -15V.
Title: Re: Rockman Chorus Pedal
Post by: Fender3D on June 26, 2021, 07:28:58 AM
X100 had +6V and -6V power supply not +9V and -9V...
Read stock schematic.

Furthermore, in your schematic there's no BBD's bias regulator, then preceding ICs offset and bias become really important.
Without a proper bias no BBD works...
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 26, 2021, 08:14:34 AM
Thanks for the replies

Vivek, can you please share your schematic

I have both a +/- 6, and 9 volt supply. I tried both to see if any difference.

I am not sure if the full Rockman schematic has a BBD? I do have the full schematic and built my board off of that. Just the chorus portion. But since the OP had an image on the thread that is almost the same, I just referenced it in my post.

Any help is appreciated,
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 26, 2021, 08:18:47 AM
Here is the original schematic. Again, I am just trying to recreate the Chorus portion.





(https://i.postimg.cc/1fQJC1W4/bg2.jpg) (https://postimg.cc/1fQJC1W4)
Title: Re: Rockman Chorus Pedal
Post by: Vivek on June 26, 2021, 08:48:07 AM
Thanks for the replies

Vivek, can you please share your schematic

I have both a +/- 6, and 9 volt supply. I tried both to see if any difference.



There are very few ways to use these BBD in a chorus schematic. Most pedals just use the examples in the Manufacturer's sheet with minor modifications.

So you can refer to the schematics of

LICH CHORUS
ZOMBIE CHORUS
PURPLE CHORUS
HYBRID CHORUS
any other MN3007 or MN3207 chorus

The schematic on my breadboard is really a very minor variation of those. Any of those can work in place of the Rockman Chorus to deliver essentially the same effect (Single delay line chorus effect) . There is no real magic hidden in the Rockman Chorus.



According to my LTSPICE analysis, the power supply voltage makes the most difference in DIST mode, and almost no difference in other modes.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 26, 2021, 09:00:52 AM
I have built the Walrus Audio Julia chorus, but some have talked about how this chorus sounds different and there are no others on the market that sound like this one.

I also have the TC Electronic Corona.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 26, 2021, 09:09:12 AM
Has anyone made this chorus schematic and got it to work as is?
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on June 26, 2021, 01:13:38 PM
some have talked about how this chorus sounds different and there are no others on the market that sound like this one.

I'd say that would be down to the rest of the Rockman circuit around it - the compression, the filtering, and the cab sim. Tom Scholz' tone shaping was pretty detailed and that gives the whole circuit its sound, but there's nothing remarkable in the chorus itself, like Vivek says.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 26, 2021, 07:41:38 PM
I do have the compressor, distortion, clean portion, and filters created and working in a pedal form.

I just hate giving up when I read others have built it and got it to work. I believe I either have a bad MN3007 (but voltages indicate it works), or bad 4013 chip. I swapped out the 7555 for a 555 chip
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on June 27, 2021, 06:32:37 AM
I do have the compressor, distortion, clean portion, and filters created and working in a pedal form.
Well, that should give you the Rockman sound!

Quote
I just hate giving up when I read others have built it and got it to work. I believe I either have a bad MN3007 (but voltages indicate it works), or bad 4013 chip. I swapped out the 7555 for a 555 chip
If you've got good clock signals and good biasing, and you still don't get any output, it's possible the MN3007 is bad. But faults in either the clock or the biasing are much more likely. I recently exchanged emails with a chap who could get his Flangelicious to flange - he thought the BBD chip must be dead. I suggested checking the bias and it turned out he'd inadvertently used a 1K instead of a 10K for one of the bias resistors.
Do you have any way to see or measure the clock signals? One way in a pinch is to increase the size of the clock timing cap so the frequencies come down into audio range, and then you can hear if it's working with an audio probe - and can hear if the LFO is modulating it correctly too.
CD4013 isn't too bad to get running, but you need to make sure all the pins are tied to the correct levels, either high or low. That's at least simple to check, going around with a continuity test.
That brings us to the Rockman's unusual BBD input biasing. This would be my chief suspect. Pin 3 needs to be at the right level or no signal will go through the BBD. Often there's a trimmer to adjust this, although it's possible to do it with fixed resistors instead. This schematic basically uses the 0V level as the bias, but shows an (apparently optional) single diode and a 10K resistor to push the bias away from ground by 0.6V. This is the only adjustment you get. I'd be inclined to take those components out and add a trimmer and a cap so the bias is adjustable just to see if that didn't help get it running.
The MN3007 datasheet suggests a pair of 100K resistors and a 3u3 cap to make a midpoint bias supply, but suggests that the lower resistor should be "adjusted for minimum disortion". On a proper bipolar supply, the situation is slightly different, but you can still create a virtual ground for this bias point alone.


Title: Re: Rockman Chorus Pedal
Post by: Vivek on June 28, 2021, 07:18:08 AM

That brings us to the Rockman's unusual BBD input biasing. This would be my chief suspect. Pin 3 needs to be at the right level or no signal will go through the BBD. Often there's a trimmer to adjust this, although it's possible to do it with fixed resistors instead. This schematic basically uses the 0V level as the bias, but shows an (apparently optional) single diode and a 10K resistor to push the bias away from ground by 0.6V.


I feel :

For a very large range, the DC bias on Pin 3 only determines THD. It does not determine work/no work unless you really go out of your way to apply seriously wrong DC there.


If the MN3007 gets +6 and -6 supplies, Pin 3 should be maybe roughly between -1.5 to +.6 V, at point where THD is lowest for that particular MN3007. But yet, there will be chorus (with higher distortion) if you bias anywhere from -2.5 to +1.5

In the Rockman schematic, the DC on pin 3 is either 0 or +0.6V. That's fair enough and both should work but at slightly different THD. One has to choose between these 2 settings. If one chooses wrongly, it still works, but at slightly more THD.

Both bias options are not so wrong a DC on pin 3 as to prevent operation of the BBD.
Title: Re: Rockman Chorus Pedal
Post by: Vivek on June 28, 2021, 07:33:44 AM
I got the Rockman Chorus bread boarded right now. I am using a +9/-9 volt supply.

1 - +9.05v
3 - +.60v
4 - -7.06v
5 - -8.56v

Thanks
Rob


Brother Rob,

A) I see that your supply has slightly unbalanced outputs on each side. I dont know if that is the cause of the problem. Is your supply adjustable ?

B) Normally pin 4 should be 1V more than pin 5.
You could try to adjust R150 2.2K so that pin 4 is 1 volt more positive than pin 5. Try 1.5K or 1.2K there.

C) You could try to remove R164 temporarily and see if you get a delay type of sound after mixing Chorus out with 6mainsig.

Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on June 28, 2021, 08:39:05 AM
Both bias options are not so wrong a DC on pin 3 as to prevent operation of the BBD.

No, true, as long as they're working correctly, it should be ok. I was proposing to test whether they are working correctly, but a voltmeter might be enough. I've just recently seen a case of the bias stopping the BBD from running, as I mentioned, so perhaps I've got it on the brain!

There's only a few things it can be: bad clock, bad bias, bad chip. Otherwise signals of some sort should go through the BBD.
Title: Re: Rockman Chorus Pedal
Post by: Fender3D on June 28, 2021, 11:38:43 AM
B) Normally pin 4 should be 1V more than pin 5.

Actually pin 4 IS 1V more positive than pin 5 (pin 4 - -7.06v pin 5 - -8.56v)

Opamp output offset voltage adds up to bias voltage.
Definitely wrong BBD bias voltage CAN prevent it from functioning, as Tom correctly said.
Title: Re: Rockman Chorus Pedal
Post by: Vivek on June 28, 2021, 03:41:45 PM
I calculated pin 4 to be 1.5V more than pin 5,

Spec sheet days the difference should be 1 V

The bias network for pin 4 has been calculated for +6/-6 but Rob is using +9/-9.



Yes wrong bias voltages can screw up everything, that is a general truth that cannot be denied

However, do you see any BBD bias error in the Rockman design or the voltages Rob posted ?
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 28, 2021, 04:43:08 PM
Thanks everyone for your input! I am new to understanding BBD, and clock circuits. I found the following image to test a MN3007, but I do not have a 4047 chip. I ordered one from Mouser should be here in (2) days. But, could I use the Vbias going into Pin 3 on the tester image as ElectricDruid mentions in post #19? Would this replace the 10K and diode on IC106A? Or the 6.8K and  2.7nf connected to pin 3 of MN3007?

Is the 15PF the clock timing cap?

As for this statement: The MN3007 datasheet suggests a pair of 100K resistors and a 3u3 cap to make a midpoint bias supply, but suggests that the lower resistor should be "adjusted for minimum distortion". On a proper bipolar supply, the situation is slightly different, but you can still create a virtual ground for this bias point alone. I do not understand this statement? Is the "lower" resistor referring to the 2.2K?

I also found this block diagram of a chorus that helped me understand where the clock, LFO were in the circuit.

(https://i.postimg.cc/zLhtGXv1/MN3007-tester-quick-Fixed.gif) (https://postimg.cc/zLhtGXv1)

(https://i.postimg.cc/ppDKrhYC/Lich-King-Chorus-18.png) (https://postimg.cc/ppDKrhYC)
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on June 29, 2021, 09:59:04 AM
But, could I use the Vbias going into Pin 3 on the tester image as ElectricDruid mentions in post #19?
You could.

Quote
Would this replace the 10K and diode on IC106A?
Yes

Quote
Or the 6.8K and  2.7nf connected to pin 3 of MN3007?
No, this is additional single RC filtering stage, following on from the active filter around U2A.

Quote
Is the 15PF the clock timing cap?
Yes, the 15pF on the 7555 is the clock timing cap.

Quote
As for this statement: The MN3007 datasheet suggests a pair of 100K resistors and a 3u3 cap to make a midpoint bias supply, but suggests that the lower resistor should be "adjusted for minimum distortion". On a proper bipolar supply, the situation is slightly different, but you can still create a virtual ground for this bias point alone. I do not understand this statement? Is the "lower" resistor referring to the 2.2K?
The lower resistor would be the lower of the pair of 100Ks used to make a bias voltage.
With a bipolar supply (say +/-6V) we actually have a genuine midpoint ground voltage, so there isn't usually any *need* to create a "virtual ground" on a bipolar circuit like we would on a single-supply circuit. However, in this case, we would like to be able to tweak that voltage a bit, so it makes sense to create a "virtual ground" rather than using the genuine one.

Quote
I also found this block diagram of a chorus that helped me understand where the clock, LFO were in the circuit.
Yeah, that's a good diagram to get your head around the building blocks we need for a chorus. The Rockman design is basically the same thing except that it uses a 7555+4013 flip-flop to provide the clock.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on June 29, 2021, 05:09:08 PM
What does the 4013 do in the circuit?
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on June 29, 2021, 05:51:45 PM
What does the 4013 do in the circuit?

It provides the biphase clock signal that the BBD needs by dividing the clock frequency in half and providing both positive "Q" and negative "~Q" outputs.
The 4046 PLL includes this function already and has both outputs, so it doesn't need the extra chip. The 4047 astable is another chip you see used for this job (EH Small Clone, for example) since it also includes positive and negative outputs.
Title: Re: Rockman Chorus Pedal
Post by: Peetem on June 30, 2021, 09:29:14 AM
The question was asked in a PM, but I thought it relevant to the discussion....

The Rockman chorus pedal has a unique sound from the Compressor, CLN2 and EQ2 aspects of the circuit (we can debate if the CLN1, EQ1 and other aspects are important to the Rockman sound later   ;) ).  Therefore, those elements were included in the posted schematic. 

Without them, the rest of the chorus isn't a whole lot different from any other chorus unit.

Title: Re: Rockman Chorus Pedal - ERROR on Schematic
Post by: Peetem on June 30, 2021, 04:07:55 PM
Hey -

Another poster noted it - there is an error on the schematic.

C16 should go to +V and -V.

I'll correct and repost the schematic.
Title: Re: Rockman Chorus Pedal
Post by: Peetem on June 30, 2021, 04:39:17 PM

(https://i.postimg.cc/3WHDBMcQ/Rockman-Chorus-ver-1-5.png) (https://postimg.cc/3WHDBMcQ)
Title: Re: Rockman Chorus Pedal
Post by: caspercody on July 22, 2021, 05:39:17 PM
I finally got some time to bread board the below MN3007 tester. By adjusting the 50K to about half way I get sound out of the board, anyway in either direction and no sound. So that must be it's bias point.

But adjusting the 25K pot (delay) there is no difference in the sound, maybe some less or more low level noise. Should I be hearing a delay sound?


(https://i.postimg.cc/Whyfkvb4/MN3007-tester-quick-Fixed.gif) (https://postimg.cc/Whyfkvb4)
Title: Re: Rockman Chorus Pedal
Post by: PRR on July 22, 2021, 09:50:32 PM
> adjusting the 25K pot (delay) there is no difference

You can't hear short delays directly. One way to may delay apparent is to mix the raw and the delayed of a complex signal and listen for pasing and combing.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on July 22, 2021, 10:36:22 PM
I am not sure how to add clean signal on this circuit?
Title: Re: Rockman Chorus Pedal
Post by: Fender3D on July 24, 2021, 03:50:59 PM
Should I be hearing a delay sound?

If you hear sound, that will be enough... the chip works!
Of course you have to set up bias correctly.

The Delay pot is useless, if BBD works (you do hear sound) it does not matter the delay it's working at
Title: Re: Rockman Chorus Pedal
Post by: caspercody on July 26, 2021, 11:25:04 PM
Thanks for all your help, tonight I got a circuit working. Bias is a bitch on these chips.....
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on July 28, 2021, 05:48:26 PM
Bias is a bitch on these chips.....

It's like anything. The first time is difficult. After that, you know what you're aiming for and you've got more experience of how it behaves, so it gets much easier.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on July 28, 2021, 11:28:55 PM
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?
Title: Re: Rockman Chorus Pedal
Post by: caspercody on July 29, 2021, 02:57:55 PM
I found some good information on Electro Smash about the before and after filters.
Title: Re: Rockman Chorus Pedal
Post by: Vivek on July 29, 2021, 03:17:00 PM
Did you try the before and after filters in the X100 or Nobels schematics ?
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on July 29, 2021, 06:30:34 PM
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.
Title: Re: Rockman Chorus Pedal
Post by: caspercody on August 09, 2021, 10:28:33 PM
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.
Title: Re: Rockman Chorus Pedal
Post by: Vivek on August 10, 2021, 09:40:29 AM
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
Title: Re: Rockman Chorus Pedal
Post by: caspercody on September 05, 2021, 02:19:44 AM
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.
Title: Re: Rockman Chorus Pedal
Post by: john1950 on September 12, 2021, 03:48:34 AM
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
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on September 12, 2021, 07:14:33 AM
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.

Title: Re: Rockman Chorus Pedal
Post by: PRR on September 12, 2021, 12:44:02 PM
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.
Title: Re: Rockman Chorus Pedal
Post by: john1950 on September 12, 2021, 01:18:48 PM
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?
Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 12, 2021, 07:15:49 PM
The two clock pins are supposed to have similar voltage swings.
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on September 12, 2021, 07:21:02 PM
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.
Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 13, 2021, 02:14:44 AM
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
Title: Re: Rockman Chorus Pedal
Post by: john1950 on September 13, 2021, 11:46:14 AM
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





Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 13, 2021, 01:36:55 PM
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.
Title: Re: Rockman Chorus Pedal
Post by: john1950 on September 13, 2021, 02:56:18 PM
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?
Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 13, 2021, 03:58:45 PM
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


Title: Re: Rockman Chorus Pedal
Post by: john1950 on September 14, 2021, 03:16:19 PM
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.
Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 14, 2021, 04:14:15 PM
Congratulations !
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on September 16, 2021, 05:03:18 PM
Congratulations indeed! Nice work.

Isn't it nice when you find it?!? ;)
Title: Re: Rockman Chorus Pedal
Post by: caspercody on September 16, 2021, 08:13:07 PM
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.



(https://i.postimg.cc/SXyb4KNZ/zombie.jpg) (https://postimg.cc/SXyb4KNZ)
Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 17, 2021, 12:22:38 AM
Rob, what is the voltage at pin 3 of MN3007 in the chorus that works and the chorus that does not work ?
Title: Re: Rockman Chorus Pedal
Post by: caspercody on September 17, 2021, 09:47:42 PM
Here are voltage readings with it bread boarded just like the schematic (Rockman X100 Rev .10). The voltage supply reads +6.04/-6.04.

IC106A - TL062
1 - 0.58
2 - 0.58
3 - 0.58
4 - -5.60
5 - 0
6 - 0
7 - 0
8 - 6.04
IC110 - MN3007
1 - 6.04
2 - 6.04
3 - 0.58
4 - -4.47
5 - -5.70
6 - -5.6
7 - 2.88
8 - 2.60

IC109 - 4013
1 - -5.60
2 - 6.05
3 - 6.03
4 - -5.6
5 - -5.6
6 - -5.6
7 - -5.6
14 - 6.04

When I remove the (-) voltage connection to the 4013 chip, my (1) voltage jumps up to -6.01. When chip 4013 is connected the (-) voltage drops to -5.60?
Title: Re: Rockman Chorus Pedal
Post by: caspercody on September 18, 2021, 01:31:06 AM
I do believe I got it to work!!!

Thanks!!!!
Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 18, 2021, 03:03:59 AM
Congratulations Rob !
Title: Re: Rockman Chorus Pedal
Post by: caspercody on September 18, 2021, 04:19:47 PM
I got the Rockman filters to work, but I changed the circuit to just use positive, and ground power. I removed the negative power supply. I got the circuit to work with a 4046 chip. I think I have a bad 4013.

Can anyone please show how to wire up the 4013 chip with out using the negative  voltage supply?
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on September 18, 2021, 07:47:54 PM
I got the Rockman filters to work, but I changed the circuit to just use positive, and ground power. I removed the negative power supply. I got the circuit to work with a 4046 chip. I think I have a bad 4013.

Can anyone please show how to wire up the 4013 chip with out using the negative  voltage supply?

Honestly, I think your time would be better spent finding out what's wrong with your negative supply rather than trying to redesign the circuit to avoid it. If the 4013 is bad and affecting the -v supply, it might be that simple.

The 4013 should work at 6V. It only uses Vdd and Vss, so connect 6V to Vdd, and Ground to Vss and off it goes. But 4000 series logic is fine up to 18V or so (IIRC) so +6/-6 works fine too (12V across the chip).

At some point you'Re going to need the full 12V because the 3007 won't run at 6V. And that means your clock signals need to be 12V too, because if the 3007 is at 12V, it'll need clocks of the same level (or some additional levl shifting - don't let's go there!)

HTH
Title: Re: Rockman Chorus Pedal
Post by: caspercody on September 18, 2021, 08:53:40 PM
The MN3007 does not work at 6v? That might be my problem the whole time. I will remove the 6v regulator from my bi polar power supply. I left the bread board intact with the in and out filters.

When I did have the 4013 connected with the 6v bi polar power supply, I was getting 6v out of pin 1, but nothing out of pin 2/5. It was connected per the schematic, should I have the same voltage out of pin 2/5? Can anyone please provide voltage readings of IC106 A and B, MN3007, and 4013?
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on September 19, 2021, 12:13:24 PM
The MN3007 does not work at 6v?

No. Check the datasheet:

https://www.experimentalistsanonymous.com/diy/Datasheets/MN3007.pdf (https://www.experimentalistsanonymous.com/diy/Datasheets/MN3007.pdf)

In fact, according to the datasheet, it won't work within the given specs below 14V, but we know it does work below that (it probably just degrades some of the other figures a bit - distortion, S/N, etc).


Title: Re: Rockman Chorus Pedal
Post by: Vivek on September 19, 2021, 01:24:49 PM
I did get the MN3207 to work with 6V though

It does perform better with higher voltages
Title: Re: Rockman Chorus Pedal
Post by: ElectricDruid on September 22, 2021, 03:47:52 PM
I did get the MN3207 to work with 6V though

It does perform better with higher voltages

The MN3207 is a completely different story. It was specifically designed as the low voltage variant, and works fine at 5V, with the reduction in headroom that you'd expect (about 1.2Vpp, iirc). This headroom difference probably explains the slightly worse noise figures of the 3207 versus the 3007. Some people think that the 3007 is less noisy, but actually I think it'd be more accurate to say that that the signal is louder. I suppose ultimately it amounts to the same thing - that's why we have S/N as a measure.