Help/advice needed with breadboarding several chorus circuits

[KarenColumbo]

Hi, guys,

In the last couple of days I tried to get some skill with breadboarding not-so-easy circuits. Some worked pretty well (distortion/overdrive), some did not.

Edit: I use a 9V wallbug (2A). Next I will try with a 9V battery. WHich I have to purchase first. Been a while since a needed such.

Those that did not work out were:

- Dimension P
- Little Angel
- Zombie Chorus (with updates by R.G. and John Hollis)

1. Each of them was meticulously checked, re- and re-re-checked with the respective schematic. I took no liberties other than substituting hard to get opamps with others I had - after checking compatibility.

Last try: Zombie chorus with schematic from the excellent geofex website (thanks again for doing this. It's a cornucopia for me).

2. I measured voltages where I could to ensure that the obvious supplies were given to those who need it. Checked out fine at GND, +9V and Vb in every case-
3. I got sound at the output (in all three build cases, not only Zombie) - but it doesn't "modulate". It's just a nice sounding version of the signal at the input.
4. I checked the LFOs with my Picoscope - they triangled alright (Zombie Chorus' depth-pot had no influence at all, but that's okay with me for the moment - maybe some connection problem - I will test with a fixed resistor next)
5. I rechecked every connection again. And again.
6. In all cases there was modulation (typical chorus warble) starting when I touched/wiggled the connections. But it didn't continue.
7. So I measured conductivity of those wires which seemed to have the most "impact" when being fatfingered. Everything quite alright (for a brand new breadboard)
8. I replaced each and every chip (4046s, 3007s, 2399s, opamps) several times - no change.
9. I made an audio probe to check the output of the opamp buffers - no change, just the input signal, buffered
10. I did an A/B comparison with the oscilloscope: A = input, B = delayed output of 3007 after the LP. No delay visible, the waves perfectly match. Same with B = FX out.
11. "Clone Mod" switch has no obvious effect.
12. I read an re-read build stories - to no avail

Edit: Since I'm a keyboarder, I'm obviously stuck in the 80ies. So chorus circuits are my love. So I ordered a bunch of every chip involved in these circuits - maybe those I used are ALL f$%&/&ed.

Question A: Is there anything obvious I'm overlooking?
Question B: How would you attempt breadboarding a Zombie? Consecutively from Out- to input? Chip by chip?

[njkmonty]

where did you  order your ics?    eBay /SmallBear/ Alibaba??

[GibsonGM]

Quick reply: I find that a lot of complicated and 'sensitive' circuits such as chorus etc. don't work well on a breadboard.  There are just too many places for wires to work loose, for parts to short together.     This tends to increase with a circuit's complexity.   Then again, there could be NOTHING wrong with your BB, and the chips MAY be bad, hard to say.....

Maybe there's a plan you could form, for building circuit blocks on the BB, testing them, then soldering them up in turn?  Personally when I hit some level (hard to say when that is), I just go for it, I build the thing permanently and don't try it first on BB, for the reason you're reporting! 

[KarenColumbo]

where did you  order your ics?    eBay /SmallBear/ Alibaba??

They are from mouser.com, RS components and Conrad. I re-ordered some of them (3007s) from CoolAudio yesterday.

Quick reply: I find that a lot of complicated and 'sensitive' circuits such as chorus etc. don't work well on a breadboard.  There are just too many places for wires to work loose, for parts to short together.     This tends to increase with a circuit's complexity.   Then again, there could be NOTHING wrong with your BB, and the chips MAY be bad, hard to say.....

Maybe there's a plan you could form, for building circuit blocks on the BB, testing them, then soldering them up in turn?  Personally when I hit some level (hard to say when that is), I just go for it, I build the thing permanently and don't try it first on BB, for the reason you're reporting! 

Yeah - I tend to do just that, too. But I wanted to "play" with the Zombie a bit - so I'd have the chance to i.e. cascade the delay, splice in a different LFO waveform and things of that nature ...

[duck_arse]

what is common to the builds, pots? the breadboard? some wires? can we see some photos of your BB setup, please?

[KarenColumbo]

The common elements would be

- breadboard brand
- wires (flexible and stiff ones for most V+/- connections)
- Wallbug
- most resistor and cap brands

Here's a pic of Zombie build no. 3 (the one right before my post)



It's more or less a 1-to-1-copy of the previous build on a bigger BB - I tried to cut down on some wire length.

[blackieNYC]

Try the bigger breadboard again, but pull this one apart, check your values, and try a completely different layout approach. Start from the other end, or somewhere in the middle.
Once you've got a bag of parts that are the right value, don't hesitate to tear the thing down completely and start again.
The (well, my) Golden Rules:
1. It's never a bad part.
2. Sometimes it's a bad part. 

[Mark Hammer]

Just so you know, Coolaudio does not make an MN3007 replacement.  They make a 3207 that is widely used, but not its predecessor.  The 3207 can be used in the circuit, but several connections will need to be changed.

FWIW, the Zombie tended to rely on use of the TL062, in order for the bias voltage in the stock circuit to work properly.

[KarenColumbo]

Just so you know, Coolaudio does not make an MN3007 replacement.  They make a 3207 that is widely used, but not its predecessor.  The 3207 can be used in the circuit, but several connections will need to be changed.

FWIW, the Zombie tended to rely on use of the TL062, in order for the bias voltage in the stock circuit to work properly.

Ah, I see. Well - I still have 7, 8 of those MN3007, unused and in static bags, so maybe I#ll be so lucky.

Okay - seems I need some TL062ies - or have a look at a more available approach. Thanks for all your comments. I won't give this up!

[Cozybuilder]

The Zombie is a nice sounding chorus, I included a flashing LED triggered by the LFO, below was my final schematic. If I were to do it again, I'd change the power section to series Schottky (1N5817) --> 47R then (100uF and 100nF ceramic) in parallel to ground, giving a noiseless V+.

[Mark Hammer]

John Hollis adopted a minimalist approach where he tried to get the most utility for the fewest parts.  I admire that a lot.  Unfortunately, that approach involved a little bit of crossing one's fingers and hoping for a good outcome.

Normally, BBDs will require a bias voltage applied to the signal input.  John futzed around with the Vref on the audio path and "reused" the Vref applied to the first op-amp stage as the bias voltage for the BBD.  (You will notice there is a DC path from op-amp stage 1 to the BBD).  I gather doing that successfully is what requires use of a TL062. 

Sadly, the TL062 is not the quietest op-amp in the world.  Low current, yes, but quiet no.  The alternative, which is less risky, but uses more parts, is to simply use a "normal" V+/2 as Vref, stick a DC-blocking cap between op-amp 1 and the BBD, and have a separate bias trimpot as found on most other chorus units.

Admittedly, John's Vref / bias is a shot in the dark anyway, so a more dependable audio quality is likely to be obtained by using a separate bias trimpot for the BBD.

Again, not at ALL a slight against John's very elegant design.  But if you want it to work quietly and cleanly for yourself, use a TL072 or even NE5532 for the input and filter sections before and after the BBD, some form of low-power dual op-amp for the LFO (e.g., TL062, TL022, LM358), and a separate bias trimmer.

[KarenColumbo]

Just to clarify things: I'm not in it for the thrill of building something just to build it. There's two sides to this, maybe three:

- I want to thoroughly understand the technology behind the chorus, so I can "re-invent" my own take of it any time. Even if this fascinating piece of FX history has been around for ages and possibly every angle has been discovered umpty times before and thus the explorer mojo has been depleted a loooong time ago.
- I want to have modulation delay as an integral part of all those FX I'm hearing in my brain Alas, they involve up-octaving, fading in of sounds ("sweller" I believe this is called), "shimmering" of reverberation, velocity sensitivity and what-not and who's-your-father and all. Which is why I tend to take sudden detours and diversions - but the main goal remains in focus all the time.
- I do have a FV-1 dev board, too - a thing, beautiful in itself, that's exactly the opposite of what I try to achieve here. But that's a different side of the coin. I got some skills as a programmer, but none as an electronic expert - so that's what I have to change first.

And I want to achieve all that without actually knowing what I'm doing - YET. I'm a stubborn old bastard, so it will take time, money and a lot of nerve to see this through - or until I really get to the point where I say "it's been nice, time to move on" ... NOT.

This was my pledge - as a sort of Thank You to all here This is very important at this moment of my life