Need help with Zombie Chorus

[Otsismi]

I've built this chorus on a home etched board but it does not work correctly. The guitar signal comes through the amp but it gets distorted when I pluck the string. Harder the pluck, more distorted. I posted this problem with IC voltages, high res pics, and reports on the original thread on another forum, but I got no help as the people reading the thread had no debugging skills. It appears from my voltages and my blatty distortion that I'm having a power or bias issue. Can an experienced debugginator please lend some sage counsel? The audio probe gets to the TL074, then I have problems. All photos are in the google gallery link.

https://plus.google.com/photos/111154127389059828188/albums/5937022895265187233

Tl074
1. 1.51
2. 1.46
3. 1.44
4. 9.23
5. 5.96
6. 6.92
7. 6.92
8. 1.55
9. 1.52
10. 1.52
11. 0
12. 1.45
13. 1.56
14. 1.37

MN3007
1. 9.22
2. 4.56
3. 1.47
4. 0
5. 0
6. 4.63
7. 6.36
8. 6.39

CD4046
1. 0
2. 4.56
3. 4.63
4. 4.63
5. 0
6. .96
7. .96
8. 0
9. 1.41
10. .78
11. .62
12. 7.32
13. 0
14. 9.22

[Scruffie]

Yeah very misbiased.

Off the top of my head, I seem to recall that the zombie HAD to use a TL062 to bias correctly because of its weird bias set up, as you have a quad, I guess a TL064 might solve this issue.

Using a quad seems like a bad idea to me in general though...

[Otsismi]

The schematic and pcb are verified. Google 1590a chorus and you'll find the original thread on the other forum.

[Otsismi]

Checked for solder bridges and cold solder joints with the beepy function on the multimeter. Switched the tl074 again. No change

[armdnrdy]

As Scruffie suggested, try a TL064.

The circuit wasn't designed for a TL074. The original IC is a TL062.

I took a look at the thread on the other site...and I don't see many builds and zero sound samples.

I've tried TLO74s in builds that called for other op amps and they did not work. (it depends on the circuit)

I have also had LFOs not oscillate with certain op amps. (even op amps designated on the original factory schematics)

This is definitely something you want to try! If the effect is working but the signal is distorted....this might be your fix!

[Otsismi]

The effect is not working. I get no chorus. But I will try the tl064. The main reason why I'm building this circuit is because I have a manager at work who will pay me boutique pedal money to build him a chorus in a 1590a. Are there any other MORE verified builds that I can check out? I'm wary about the little angel due to bad experiences with noise levels on pt2399s

[deadastronaut]

not sure about 1590a size..

but the tonepad small clone is very nice imo.....

maybe the 1590a micro surgeons have shrunk it..

[Otsismi]

Well I ordered a tl064. We'll see what happens

[Mark Hammer]

The difficulty with the Zombie (though not a deal-breaker) is that it uses the same bias voltage for both the BBD and the audio path.  A bit of a compromise, I'm afraid.  And because of that you will rarely see BBD-based circuits, be they chorus, flanger, delay, or whatever, that use the exact same bias voltage for both Vref and the BBD input bias.  Apparently, the use of the TL062 allows for that bias to be "recycled", where other op-amps do not.

I will also express some hesitation here about the use of a quad op-amp, be it a TL074, 64, or whatever.  The problem is that the LFO circuit (which uses only two of those 4 op-amp sections) frequently produces an annoying "ticking" sound.  Use of a low-power op-amp (Like the 64) reduces, but does not eliminate that.  Moreover, the TL06x series, despite their advantages as far as current consumption go, produce more hiss.  Essentially the TL07x and 6x series trade current draw for noise; the 7x being quieter but needing more current. 

The ideal is to use a low-current dual op-amp for the LFO and a low-noise op-amp for the audio path.  BUt of course, using a TL072 for the audio path still doesn't eliminate the biasing challenge, so the real ideal is:
- a low-noise dual op-amp for the audio path
- a low-current dual op-amp for the LFO
- separate biasing for the op-amps and the BBD.

The Zombie is a very clever bit of design, and actually sounds nice once working properly, but it relies on a fairly specific set of circumstances and compromises to do that.  I made one for myself, but I wouldn't make any for other folks.

[duck_arse]

I'm using that lfo circuit configuration for a p45 at the moment. the LMC6482 is a cmos, low current dual, and working very nicely, when built on a seperate board to the audio section.

the tl06x is the low power versions of the tl08x, and the 07x the low noise version. the TLE207x datasheet says it is a direct replacement for the 07x and 08x, but is still miles behind the tl06x current consumption. was the low current consumption the only reason for using the 062 in the zombie? perhaps the cmos would replace that too.

[Otsismi]

So what's the answer? Little angel? One chip chorus?

[deadastronaut]

tonepad small clone imo...

[Mark Hammer]

I have to agree with Rob.  By the time one addresses all the various corners that were cut in the Zombie, so as to assure optimal performance, what you end up with as a Small Clone.  Just seems easier to me to head straight for the goal, instead of driving yourself nuts with patches for this and that.

[Otsismi]

Small clone pcb on tonepad is too big. The small clone is a great pedal. Maybe it just can't be done that small. I've seen videos of people claiming to have a small clone in a 1590a but I can't find any project files.

Btw thank you all for the help you've given me. I've come so far, and I couldn't have done it without this community.

[mth5044]

Sounds like now is the time for you to learn how to make a layout!

[Mark Hammer]

Small clone pcb on tonepad is too big. The small clone is a great pedal. Maybe it just can't be done that small. I've seen videos of people claiming to have a small clone in a 1590a but I can't find any project files.

Btw thank you all for the help you've given me. I've come so far, and I couldn't have done it without this community.

I think "solderman" has a layout for a 1590A.

If you feel compelled to use boxes that small, I recommend looking into SIP chips as a way of conserving space.  Not only do they have a smaller footprint, but they also provide a lot more flexibility in terms of layout.  remember, when there is only one row of pins, you have the freedom to put components on this side OR that side.

[deadastronaut]

^ yep, google nevermind chorus..

[Tony Forestiere]

http://solderman.fatabur.se/Future%20project/Nevermind.pdf