Corrrral Chorus (CE2) problem

[col]

I just built this on stripboard using the schematic at Tonepad (big layout)! I have built it over a couple of weeks as I've been struggling for time lately but I have double checked everything. I have the output through IC1a and b but there is nothing coming through the modulation path. I have subbed the MN3007 for a MN3207 and the MN3101 for a MN3102 which look compatiable from the data sheets. I have adapted the power supply for the 5v MN3207 as Mr Chatwin does in one of the Babani books by increasing the R52 on the tonepad layout to 150R from 33R and adding a 5.1 Zener diode.
Voltages around the ICs are;
MN3207 1 5.1v, 2 2.49v, 3 2.16, 4 4.77v, 5 0v, 6 2.47v, 7 6.17v, 8 6.17v
MN3102 1 5.1v, 2 2.47v, 3 0v, 4 2.49v, 5  0.14v, 6 4.9v, 7 1.3v,  8 4.77v

The stand outs are pin 7 and 8 of the MN3207 which are above the 5.1v of pin 1. Should these be different?

I have used an audi probe and I have a signal to pin 3 of the MN3207 but no output from pins 7 and 8 which are linked. When I turn the volume up full I can hear an oscillation so I think that the oscillator around IC2 is functioning. (LF353 instead of the TL022). I also used BC549C transistors as I didn't have any 2N5088s but they are nominally the sane Hfe.

Any help would be appreciated,

Col

[CGDARK]

From my experience the MN3007 and MN3101 are not interchangeable with the MN3207 and MN3201 as you may think. I don't know what it is, but they don't work in the same way.

CG

[Fuzzy-Train]

I would just try using the original ICs (if you have them) I had some trouble getting this one to work... turns out I had a lifted pad. Once it was working though all the trouble was worth it... this thing sounds great.

Here are the voltages I used for reference that might help you out.

[col]

I finally got it working with the ICs I used. they are interchangeable of a sort but the pinouts are differnt, especially the + and ground pins of the MN3207. There are jumpers all over the board at the moment but at least i know it'll work,

thanks for the info

[Fp-www.Tonepad.com]

Just to get this straight, you got the circuit to work using the MN3207 and MN3102 by just changing the pinout?

If you search the forum you'll find a few suggestions that this isn't quite possible, that's why I'm asking.

Fp

[CGDARK]

Just to get this straight, you got the circuit to work using the MN3207 and MN3102 by just changing the pinout?

If you search the forum you'll find a few suggestions that this isn't quite possible, that's why I'm asking.

Fp

That's what I told him four posts back. I'm asking myself too.

CG

[col]

Finally finally finally I got a couple of hours to sort this out and it WAS working fine. Changes are
1. + and earth swap on MN3207.
2. pin 2 of MN3207 to pin 2 of MN3102
3. Pin 6 of MN3207 to pin 4 of MN3102
4. R14 on tonepad schematic to earth
5. increase of R52 on tonepad schematic to 150R
6. addition of 5.1v zener parallel with C30
7. C7 is 1 3n3 and 1 4n7 in paralell rather than 1 8n2
8. C12 is 10n as above.
9. Vibrato mod
10. Chorus intensity switch mod. DPDT with 33p cap actoss middle lugs and a 10p on one side with a 47p on the other, making 33p, 43p and 80p options.
I think that's it!

The effect is superb, it is a really rich strong chorus and the vibrato mod I put in as per the tonepad directions is superb, seasick inducing almost. With the 80p option there is some hiss and ticking, albe it at VERY low levels in headphones. I don't think it'd be noticable live.
Now the bad bit! I had been testing it with a duracell battery. No problems. Plug it into my muli powere point and nothing! Lower power batteries, nothing! Duracell perfect. I suspect it's drawing a lot of current. that's beyond the limit of my multipoint. Something I will have to test later.

[col]

I tested this and it's only drawing 25mA (varies between 24.7 and 25.3mA) so it's not that! What I have noticed is that these chips have an operating voltage of 4 to 10v and the protection diode is an 11v zener. I strongly suspect that my regulated power supply is putting out between 12 and 15v but don't have it to test at the moment. I will replace the 11v zener with an 8 or 9v one and see if it makes a difference. I found some other batteries it works with, it seems OK with battery voltages between 7.5 and 9.5v.
With a new battery and 80pF selected the vibrato is SICK! It sounds like a record player with a constantly variable speed control. I can't think of any way I'd use that live so I might reduce the 33pF to 15 or 18pF and see if I can get some more flange like sounds from it. I tried connecting the oscillator direct to pin 7 of the MN3102 but it resulted in clicking and other strange noises.
Chatwin's book "Advanced projects for the Electric Guitar" uses this pair of chips for an analogue delay and an oscillator to produce flanging and chorus sounds.
The spec sheet for the MN3207 that I downloaded off the internet has a delay circuit on the last page with suggested values for components for operating between 4 and 10v. Indeed, that's where I took the pin connection data from.

[Mark Hammer]

I'm assuming "sick" means good, but let's talk about vibrato for a moment.  When the chorus is being used in chorus mode, there is always an on-pitch version of the signal present to serve as one's "pitch anchor".  With an anchor to hold one's sense of what the true pitch is in place, more wobble is tolerable (though past a certain point it is every bit as disconcerting).  When the anchor is lifted, however, the same amount of pitch wobble becomes less tolerable.

I will suggest that the "solution" to this is to use a toggle to simultaneously reduce depth/wobble at the same time as breaking the clean/dry path in order to achieve vibrato.  If one looks at the CE-2 schematic over at Tonepad, you can set that sweep depth (i.e., the output amplitude of the LFO) is set by VR2, a 100k pot.  If a fixed resistor is placed in series between pin 7 of IC2b and lug 3 of the pot, then the pot will behave as if it has been turned down.  Moreover, the reduced range of wobble that the pot now controls will be spread over the entire rotation of the pot, making it easier to dial in subtler shades of vibrato. 

We don't want this to be too severe, so lets make the added series resistor something modest, like 33k-39k.  That will reduce the maximum depth to about 2/3 of the original maximum.  Restoring maximum depth is as simple as shunting the added resistor.  Since vibrato is created by breaking the path between R21 and its signal source, we can achieve a more controlled "tasteful" vibrato by simultaneously breaking that path and un-shunting the added depth resistor with a DPDT toggle.  Flick the switch the other way and the added 33k-39k resistor is shunted and essentially out of circuit, at the same time that the clean path is restored to produce chorus.

The "deluxe" version of this would take into accont the fact that the speed range used for vibrato is also different than that for chorus.  Where slow chorus speed lend a nice swirl, slow vibrato rates are often almost inaudible.  Of course if one is reducing the depth of sweep, audibility is reduced again.  So, an optimized switchover from chorus to vibrato would also change the speed range at the same time.  There are a couple of ways to do that.  One is to change the value of the 0.1uf cap that sets the LFO range (C19 in the Tonepad drawing), however that can result in audible popping.  Since the LFO rate depends on the joint function of that cap and the input resistor (R32 = 1M) and how fast the cap can charge up, given the current-limiting of the input resistance and voltage attenuation of the Rate control, the simplest fix would seem to be dropping the value of that input resistor.

That, in turn, seems to have a few different approaches to take.  The resistance can either be dropped by placing a second selected resistance in parallel, or it can be achieved by having one resistance for vibrato and s econd series resistance added to it to slow things down in chorus mode.  Let's take the first one. 

I'm not touting these values as necessary, but off the top of my head I will suggest that we can try replacing the 1M resistor with a 680k and 330k in series.  That gets us close enough to a 1M 5% tolerance total.  When you factor in that the 0.1uf cap is probably not exactly 0.1uf either, you'll see that being finicky about the resistance is largely wasted effort.  If you're fussy you can measure and select the resistors in question, or you can go completely crazy and use a 220k+250kpot+510k and adjust for proportional changeover (where the pot wiper subs for the 330k/680k junction; I'll leave that to the advanced class).  In principle, R32=680k when in vibrato mode, and if the 330k series resistor is shunted, that's what we'll have.  Unshunt the 330k and we're back to the stock 1M value.

This can all be situated in a 3PDT stompswitch that will now do all of these things at once:
1) open the connection to R21, cancelling the dry signal
2) unshunt the resistor in series with VR2, dropping the sweep depth/width/amount
3) shunt  the 330k series resistance in the LFO integrator, bumping the speed range up a bit.

...two breaks and 1 make.

Hit the switch again, and it restores the dry signal, adds a bit more sweep depth, and slows the LFO down a bit; Two makes and one break.

Do you actually NEED to snag all of this in one switch?  I doubt it, and I suppose many would be content to simply cancel the dry signal and twiddle the rate and depth controls to adjust to taste.  For those who would like a properly tailored switchover from chorus to vibrato (somewhat, though not exactly, in the direction of what the old CE-1 does/did), what I described should be able to do it.

[col]

If you've heard the beginning of "Curfew" by The Stranglers on the album Black and White then it's similar to that but at high settings far more extreme. I don't have the facility to record it and put it on here unfortunately.
Basically, 33pF gives a useable chorus all across the speed range apart from the last few degrees. Minimum seeting on this gives a phasey sound which is why I'd like to reduce it and see if I can get a flange type effect.+10pF (43pF) gives a useable chorus for half way and then severe de-tune. + 47pF (80pF) gives a useable chorus only at minimum, beyond that it just gets silly! Even with the reference signal it still sounds like a variable speed turntable. I can get a very useable vibrato from it with the main signal cut out but not at the extreme settings.
I still need to get an 8 or 9v zener and try it. I might get a 9v regulator if that doesn't work and try that. I should be able to call in and pick one up tomorrow but it might get to the end of the week before I can put it in.
I don't use vibrato in any of my bands current set of our own material but I do use chorus quite a lot and the chorus pedal was the only one left that wasn't DIY. I might have to write some new stuff to irritate the drummer.
I repaired two chorus pedals recently, just jack and power supply problems, an Arion and a Frontline. The Arion had a vibrato switch but it wasn't anything like as deep or noticable as this one, in fact it was crap on both settings. Suprisingly the Frontline was quite good!

[col]

SUCCESS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

After messing around with zener diodes etc. I tried a 1k trim pot between the +ve tag on the socket and the board. This now works perfectly but has to be adjusted for different wall warts. The resistance needs to vary between 87 and 123 Ohms meaning that I can't just replace with a 100 Ohm fixed resistor and it is really sensetive. At next practice I'll set it to my multi point regulated power supply and leave it at that. I'm really pleased as it sounds fantastic and I can get such strange noises out of it as well.
It now seems so obvious that I don't know why I didn't try it before. 
I will replace the 1k trim pot with a 220 or 250R as soon as I can get one so that I can set it a bit more accurately.
So it seems that the chips can be subbed with some difficulty and re-arrangement of the layout. I might try the delay circuit that the spec sheets show, or I might try the one in Chatwin's book "Advanced projects for the electric guitar" which uses them. It will have to wait though as I want to build John Holiss's Ultimate Flanger next.  I have the parts and have done a stripboard layout but there are a few problems with it that I need to sort out before I actually do it.
Thanks for the help and suggestions with this.