Small Clone with dual LFO - working...

[Pushtone]

When I wanted to build a dual chorus I hit the
and found this informative thread.
http://www.diystompboxes.com/smfforum/index.php?topic=42004.0

I decided to try Marks approach and add a second LFO and a SPDT footswitch to the Tonepad Small Clone Chorus.
I extracted the LFO traces and made a kinda daughter board.


I works! I've wanted to stack two boards for a while now.
On the testing bench the dual controls are exactly alike with the same range of speed and depth.
Just like having two choruses with one MN3007 chip!

But I have one big problem...
switching the LFOs causes a HUGE pop!. 
Louder than any LED pop. Sounds like a sonic BOOM with the 100 watt amp.

Would anyone care to comment about reducing the LFO switch noise?
I would love some feedback before I go moding and mucking up the "working" PCB.

I'm using the Tonepad PBC for the Small Clone Chorus.
http://www.tonepad.com/project.asp?id=8

I inserted a SPDT switch right after D3 and before the 39k resistor.
My second LFO starts at the 39k resistor. I took this for the input to the LFO.

I'm wondering if the 10uF cap after the 39k restistor is doing it?

Thanks

[the dude]

Nice work, The pop I would assume is some sort of dc offset, check the output with a voltmeter see how much voltage is being injected into your amp. Maybe try having seprate power supply's or maybe try to add a mix pot instead of a switch, I dont know if either of these will work but worth a try.

[rockgardenlove]

You could try doing the switching with silicon instead of hardware(as I think you're doing now).

[puretube]

try a pulldown-R (100k...1M) parallel to the 10µ.
(don`t ya just hate schemos without designators???)

[skiraly017]

I'm curious as to why you just didn't add additional pots for Speed and Depth instead of creating a daughter board? I've built a dual chorus off a single board/single MN3007 with no issues.

[Pushtone]

I'm curious as to why you just didn't add additional pots for Speed and Depth instead of creating a daughter board? I've built a dual chorus off a single board/single MN3007 with no issues.

I looked at that. I concluded that switching pots would use all the poles on a 3PDT switch with none left over for an LED.
Switching LFOs would only require a DPDT and there would be a spare pole for LED indicator.

I would love to learn how you switched pots.
Does it make noise when switching?
Do you have two LEDs to indicate which set of controls are active?

I can ditch the second LFO and switch between pots but I really want an LED for each set of pots.

[skiraly017]

It's been a long time since I did it, but there's no noise with switching between the two settings and I do have an On/Off LED as well as a Ch.1/Ch.2 LED. I would have to go back and look at it again. I do remember it taking me forever to figure out how to do it. If you're interested I'll make an effort to diagram it.

[Pushtone]

If you're interested I'll make an effort to diagram it.

I'll be experimenting with it tonight.
I'll try a few different way to switch the pots as well as Puretube's suggestions.
I think I'll try moving the switch on the other side of the 39k/10uF too.

Thanks skiraly,
I might ask you to take a look at your build if I come up scratching my head.

I consulted the service tech here at work and he thinks the loud boom is coming from the
CD4047 reseting its clock. He also thinks that switching pots will cause the same noise.

Thanks for reporting your success at this. Now I know it can be done.
I'm all fired up to experiment.

[markphaser]

Are u putting the LFO's in series or in parallel with the BBD chip? need a LFO mixer to summ the 2 LFO's together

If your just A/B the 2 LFO's it could be a switch popping sound adding a capacitor across the switch popping sound with a dummy load resistor so your grounding the LFO#1 from LFO#2 when u switch

u really didn't need to build that daughter board u just needed to add a extra speed and depth pot and A/B them u just use one LFO not 2 LFO's the only things thats different is the extra speed and depth pot have 2 LFO's is overkill for just A/B

Bi-Mode mean 2 BBD chips and 2 sets of LFO's one out of phase

[potul]

Maybe it's a stupid thing but, could you wire the depth pot like this?...



And use 20k pots instead of 10K. The pot response probably will change and no longer be linear, but I think it would work, and with only one spdt. So then, one remaining for the LED.

Potul

[PenPen]

Very interesting. I had a request for a Trem/Chorus that I decided to design with a dual LFO, so seeing this thread is very useful. I didn't even think I'd need to worry about pops. I'll keep this in mind now. Thanks!

I'll keep watching to see how this turns out. I'm wondering, I'm not sure of the design of that chorus but I wouldn't think there would be any way for the LFO voltage to get directly into the signal path, causing the pops. Does that chorus have the LFO bleed into the signal path?

[Pushtone]

Maybe it's a stupid thing but, could you wire the depth pot like this?...



And use 20k pots instead of 10K. The pot response probably will change and no longer be linear, but I think it would work, and with only one spdt. So then, one remaining for the LED.

Potul

Hi Potul,

For some reason your drawing didn't display for me. But I was able to view it by pasting into address bar.
http://photos1.blogger.com/blogger/5491/2130/1600/bi-pot.jpg


Anyway...
I don't think I tried that so thanks I'll give it a go.

I tried, WITHOUT the second LFO, switching the wipers of both RATE and DEPTH pots.
Then I tried switching lug-3 on the RATE and DEPTH pots.

pots in standby effect the active sound at little.
I'll give 20k pots a try too. Thanks.


Still makes noise when switched. I hoping thats because its all splayed out on the test rig.
Maybe one of those problems that goes away when neatly boxed. I hope, that is!

Not writing the second LFO off yet. Still have a few thing there to try. Like moving the switch point.

Thanks for the replys 

[Mark Hammer]

Seems to me that an approach similar to what is used in the BF-2 could be used.  There, the Manual DC offset voltage is treated as one control source, and the LFO is treated as another.  The Depth control is essentially a pan control between the two control sources, such that more of one source implies less of the other.

Okay, now let's imagine that the two LFO outputs are passively mixed via equal-value resistors at a summing node.  If the resistance of one of those mixing resistors goes high, then that source is effectively rendered negligible.  Lets say that the mixing resistors were each 1M.  A SPDT or DPDT switch could be used to shunt the resistor on one side of the node with a smaller value (e.g., 47k), such that you either let LFO1 dominate or LFO2 dominate.  Nothing is ever really out of circuit, per se, just made to have a very very negligible influence on the sweep.

[markphaser]

Matched 1% percent resistors would be the job they use them for phantom power preamps or differential op-amp stages
or use trim variable rheostat pots

Rheostates can get confussing from linear Vs audio because one end goes to the wiper and which side of the pot terminal do u use
the left or right terminal. With Audio Rheostate pot if u use the left terminal and the wiper its ""Different"" than using the wiper and the right terminal

For Bi-Mode u want to REVERSE sweep so a "reverse taper LDR" would be the best its different that putting the LFO out of phase right
Mark Hammer?

U can hook up the LDR like a audio or linaer Rheostate or a voltage Divider


 

[Processaurus]

Okay, now let's imagine that the two LFO outputs are passively mixed via equal-value resistors at a summing node.  If the resistance of one of those mixing resistors goes high, then that source is effectively rendered negligible.  Lets say that the mixing resistors were each 1M.  A SPDT or DPDT switch could be used to shunt the resistor on one side of the node with a smaller value (e.g., 47k), such that you either let LFO1 dominate or LFO2 dominate.  Nothing is ever really out of circuit, per se, just made to have a very very negligible influence on the sweep.

'fraid I have nothing to contribute to the switch popping, but I think the idea of mixing the LFOs is fantastic.  If you added an extra pot to pan between the LFOs, you could have your footswitch select between the mix, and the first LFO.  The mix could get you something like that nonlinear pefftronics Rand-o-matic sound, or if you panned it all the way to the second LFO, the footswitch would do what you're doing now.

[markphaser]

They can have seperate DC offsets one LFO having a negative DC offset and the LFO#2 having a positive DC offset so when u add them to more of a complex waveform

Or LFO#1 is sweeping normal forward and LFO#2 is sweeping reverse

[potul]

Hi Potul,

For some reason your drawing didn't display for me. But I was able to view it by pasting into address bar.
http://photos1.blogger.com/blogger/5491/2130/1600/bi-pot.jpg

I don't know what happened, yesterday it worked. Ok, here you have the dwg again in a different location:



Potul

[Pushtone]

This was supossed to be a long weekend of stompbox building but it was
a long weekend of roof repairs. It's been raining like crazy in the North West.

I did find some time between the flashing and taring to poke at the dual Small Clone.
I got it switching between the LFOs without the poping noise. Yeah!

Big thanks to Mark Hammer,
your suggestion to add a second LFO (from the old thread above) works great,
and I learned a little something about LFOs too.

I figured out that I tapped the output of the LFO in the wrong spot.
I originally put the SPDT switch between the CD4047 and the 39k/10uF. This caused huge pops.

Locating the SPDT switch just before the wiper of the DEPTH pots instead of
before the 39k/10uF made the LFOs switch noiselessly.
And there are no extra holes to drill in the mainboard to do this.

Works great now. 

Here's the wiring diagram I used with the dual LFO.
It uses:
1. The Tonepad Small Clone Chorus PCB (Thanks Fp)
2. A second LFO lifted from the Tonepad PCB.
3. A DPDT footswitch to select between LFOs and two LEDs.
4. Two sets of control pots.

http://www3.telus.net/david65/pedal-pics/Bi-Chorus-Works.gif





Before I got it working with the second LFO,
I tried the suggestions in this thread.
No go, still POPs, but thanks for the suggestions.

Then I tried to get it to work with just one LFO.
I tried several wiring configs for two sets of pots, one LFO and a 3PDT switch without luck.

The problem being the controls for the standby channel interact with the active pots.
I did not try this with 20K DEPTH pots as suggested but it dosen't matter,
the pots will interact because of the split impedance imbalance.

I have to conclude there is no way for one LFO to switch between pots
using a DPDT or 3PDT without some interaction between control sets.
I know others have done it but I'm from Missouri (the Show Me State)
and I would like to be proven wrong.

I'll have this splayed out on the breadboard for a few more day if anyone
would like to suggest a wiring config for pot switching with one LFO.
I'll try it out and report.

Here is one example of pot switching with one LFO.
It has interaction between control sets and makes a ticking sound.
http://www3.telus.net/david65/pedal-pics/Bi-Chorus-NoWorks.gif


Ready to test more wiring ideas.