Squealing with CD4053 based switching

[sfr]

I just threw together a PCB for bypass switching using a CD4053 with a CD4049 for latching with a momentary switch and to drive an LED.  Used the two schematics at Geofex (http://geofex.com/Article_Folders/cd4053/cd4053.htm)

Works fine, LED lights, voltages look good.  Used two 10K resistors for bias.  Running it off of my 9V power supply.  Was testing it with a DIY Dist+, since that was the only thing I had with a battery in it and I couldn't find more than on power cable to go to my power supply.  (My gig bag is at the studio)

When I turn the distortion and level knobs all the way up, I get a squeal out the amp.  Sometimes the squeal doesn't happen until I hit some strings on the guitar and then stop.  Using just the Dist+ on it's own, I've never been able to reproduce this. 

The thing isn't boxed up, many offboard connections are made at the breadboard.  I haven't had a chance to try it with other pedals. 

I've got to head out now, I can post voltages later, but in the meantime, anyone have any experience with these circuits that might shed some light on things I should look at that may be a cause of this?   

[sfr]

Realized the Dist+ didn't have a DC blocking cap at the input, just the output.  Added a 1uF cap, positive facing the switching board, negative facing the distortion; don't seem to get the squeal as readily on it's own, but it is still present when I start playing. 

Voltages:

Power in : 8.89V  (surprised me that my power supply was bit *low* - I don't seem to remember this being the case in other instances.
VBias: 4.45V

CD4049:
     (Voltages separated by a slash indicate voltage differences depending on toggle state.  I think I mixed up here and they aren't all listed the same way (whether "on" voltage precedes "off" voltage) but since this portion of the circuit seems to work properly, I don't think it's a big deal?)
1: 8.89
2: 0/8.88
3: 8.88/0
4: 8.88/0
5: 0/8.88
6: 0/8.88
7: 8.7/0
8: 0
9: 0
10: 0
11: 0
12: 8.8
13: 0
14: 0/8.88
15: 0/8.6
16: 0

CD4053:

1: 4.04
2: 4.35
3: .08
4: .09
5: .09
6: 0
7: 0
8: 0
9: 0
10: 0
11: 0
12: 4.3
13: 4.05
14: 4.35
15: 4.34
16: 8.89

[grapefruit]

Those voltages seem ok. I had problems with oscillation in a 4066 quad switch once because I forgot to GND the unused switches. I assume you have pin 9 grounded as in the diagram... I don't think it matters if the switch ins and outs are grounded.

Are your input and output wiring seperate?

Do you have a power supply bypass cap on the 4053?

Stew.

[sfr]

Those voltages seem ok. I had problems with oscillation in a 4066 quad switch once because I forgot to GND the unused switches. I assume you have pin 9 grounded as in the diagram... I don't think it matters if the switch ins and outs are grounded.

Yup, pin 9 is grounded.  Pins 5, 4, and 3 (the unused in/outs of the CD4053) have no connection as per the schematic at Geofex.  I'll dig out the meter and make sure those connections are good, however.

Are your input and output wiring seperate?

Not sure what you mean here?  Right now I have the board hooked up to 4 jacks, and the grounds from all four jacks tied together at the breadboard.

Do you have a power supply bypass cap on the 4053?

I have a 47uF cap going from the junction of the two bias resistors to ground, but no cap across 9V and ground if that's what we mean here.

[grapefruit]

Keep the input signal wire away from the output signal wire. Don't run them alongside each other. If they are right next to each other the high gain of the effect unit can cause oscillation. If it doesn't happen when the distortion control is turned down this seems like a likely cause. You could use shielded cable.

It may not help, but try putting a 100nF or similar cap physically near 4053 between +9V and GND.

Both these things may not fix the problem but it's worth trying. If they don't work then it's time to try and think of something else...

If you turn down

Stew.

[sfr]

Okay, standard keeping the signals apart stuff.  Yeah, I hadn't even thought about that, mostly because I've never gotten the distortion plus to squeal on it's own, and the wiring is a mess inside there.  So I kind of jumped to conclusions and assumed it was something going on with the switching circuit. 

Turning down the "level" seems to have more of an effect on cutting squeal than turning down the "drive". 

But yeah, right now my in and out are right next to each other on one side of the board, and my fx in and fx out are right next to each other on the ther other side of the board.  I'll go about cleaning things up and see what happens.

[sfr]

Still waiting on some more shielded cable to come in the mail, so I'll see what that does.   Moving the cables apart as much as can doesn't seem to impact noise.   I did notice that once I start getting that squeal my bias voltage drops about .04 -.05 ; could this be a sign I'm not doing a good job keeping the output near the bias voltage.

Tried to reproduce things with store-bought pedals to make sure the mess of cable inside the pedal wasn't contributing.  Couldn't get it with the DS-1, the Metal Zone got the same squeal.  Again, can't get that squeal w/o the bypass board. 

Cap across power is the next thing.

[sfr]

100nf cap across pin 16 (9v) and pin 9 (ground) at the CD4053 doesn't seem to help.

[sfr]

Okay - I rebuilt the whole thing on breadboard, tried to get the ins and outs as far apart as physically possible.  Same results.  Tried various bias resistors, and tried the 100nF cap across power and ground.    Tried shielded cable.  Nothing seems to be working.  With many (not all) distortions I have, both home-brew and store bought, largish gains create a crazy squealing noise with the bypass system that I don't get without the bypass system.  In fact, despite my best attempts, I'm unable to reproduce this awful oscillation w/o the bypass system.   

Again the squeal may not be present until I hit a note, but it sort of rides on top of the notes, and when I stop hitting a note, it starts to squeal a whole lot.

Could this be because the chips I used are "HCF4053BE" and not "CD4053"?  I forgot about this until now - they turned up when I was ordering from Mouser, and my perusal of the data sheets made it appear the chips where identical.

[sfr]

Sorry to bump this *again* . . . but I'm still beating my head against the wall on this one.

Well, I pulled the latching circuitry (using the CD4049) and replaced it w/ a latching switch, one the off chance that was somehow contributing to things.  No luck there, not that I thought that it would.

I did another layout on the breadboard with shielded cables again, just to make sure I hadn't screwed anything up, and still the squeal with some distortions. 

I did find that it only squeals if I run through through the switching chip twice - if I take my output right from the distortion box w/o running it back into the switch, or I input directly into the distortion box and take the output from the switching chip I get no squeal.  (Did that make sense?)  Does this tell me anything? 

I thought maybe I could use the other switch on the chip - it would move the input and output farther apart.  Would that help?

Does anyone have a copy of the schematic for switching on one of the Danelectro pedals?  Don't those use the 4053s? 

Anyone have any other recommendations for alternate electronic switching I could use, if I can't get this stuff working?

[sfr]

I found a schematic for the Danelectro Pepperoni Phaser over at Experimentalists Anonymous ( http://experimentalistsanonymous.com/diy/index.php?subdir=Schematics%2FPhasers&sortby=name ); the big differences between R.G.'s layout ( http://geofex.com/Article_Folders/cd4053/cd4053.htm ) for CD4053 switching and the implementation here are that the Danelectro only switches the output between that of an op-amp buffer and that of the effect, rather than a "true bypass" style switching the input and output around the entire effect.  Given what I found and posted about in my last post about the squeal not being present when the signal only went through the switch once it seems that this would solve my problem, but I'd prefer not to have a buffer before every effect in the multi-fx unit I'm looking to build - at least I think I don't.)

The other differences however, are a smaller input capacitors (1uF instead of 2.2) and smaller value resistors both tying the inputs and outputs of the CD4053 to VBias (220k instead of 1M) and across the output and ground (10K instead of 1M - is this because of the opamp buffer?)  The bias voltage is also derived differently, but I don't imagine this would make a difference in the function of the switch. 

The inhibit pin and unused switches are not shown - I assume they are tied to ground.

Tomorrow I'll change things up on the breadboard one at a time taking these into consideration, but in the meantime, does anyone know how these changes would effect the circuit?   

I get the feeling I'm grasping at straws here.

[R.G.]

I'm not sure what to tell you.

I've used that CD4053 switching myself - many times, and in a variety of connections. I've never run into this and it's not obvious to me why you're getting it. The Dano pedals all use it, I think.

Here's an ugly thought - can it be because it's on breadboard? Breadboard has some ugly if subtle side effects.

Check to see that on the switch chip you have a 0.1uF ceramic cap between + and - very near the chip. Tie Inhibit and Vee to ground, as well as all unused control inputs (a, b and c, pins 9, 10, and 11.) The unused switch sections can all be shorted together and tied to ground or to Vbias.

Do you have every single unused input on the 4049 tied to ground or +? No floating inputs!

[sfr]

I'd like to think it's not because of breadboard, as I've had the same problems with the circuit on PCB.  (I accidently etched the wrong iteration of my PCB, so there where a couple of iffy things - but both around the CD4049 used for latching, a jumper for 9V on the underside of the PCB, and a bent up leg running to the LED current limiting resistor. )

I hadn't grounded the unused input/outputs, just the controls.  I just added that cap and grounded the unused input/outputs.  Still the same problems.  I'll try hooking things up to the PCB and making those changes and see if things are different.

I guess I'll put in an order from chips actually labelled CD4053 and not the HCF4053BE I've got, as I've mentioned below.  The datasheets seem to make them seem identical, but maybe I'm wrong. 

[sfr]

Okay - I tried one last time - I took the Dist + board out of it's box, wired in the in/outs directly to the pcb for the 4053 switching circuit, tied all grounds together and wired 9V to the same place for the both the effect and switching board.  I used a TI CD4053BE this time, not the HCF4053BE (although I can't imagine that making a difference) still got squealing/oscillation w/volume and gain at max, although this time it seemed that both needed be at max to get the noise, not just the volume. Didn't the change in tone of the squeal when tweaking the Distortion Plus's pots, as I had previously.  Squeal still waited until after I stopped playing a note to start. 

Added 2.2uF caps on the in and the out of the FX (after realizing once again there was no input cap on the board - there was an output cap after the opamp, but I went ahead and added another one after the clipping diodes and volume pot; probably unneeded.)  Also added the 100nf cap, soldered directly to pins 9 and 16 on the CD4053.  All unused controls were already grounded, also grounded all unused ins and outs.

This is all on my PCB - which as I mention above, was etched from the wrong iteration and has a few minor edits to make it work.

Finally got rid of the squealing - seems good, although this seems to indicate that this circuit can't be used as a bypass in a separate box. 

Only issue now is what I'm perceiving as a change in the distortion characteristics when running through the bypass - it still sounds like it's on the *verge* of oscillation/squealing.  It's gets gritty in a funky, not-so-musical way, almost like the bad distortion you get overdriving something digital - sustain dies out in an almost fuzz-face-esque manner at times.  Hard to describe whats going on, but regardless, it doesn't sound "right" to me.

I'll have to go through and measure voltages, and probably disconnect the distortion plus board to try it on it's own and make sure I'm not just making myself hear things that aren't there.  But right now, I'm frustrated again with this thing.

Does anyone have a confirmed working layout for the CD4053 boards, preferably with the CD4049 for latching?  (I was stupid and ordered about 30 of each of these chips before I figured out if this was going to work for me - I also have the parts for and am about halfway through constructing a large batch of "pancake" switches like on the Geofex website - which is why I'm still struggling to make this work rather than saying "screw it" and going with mechanical switches.)  I figure I should give another board a shot, maybe I'm just repeatedly missing something. 

What values have people used for the Vbias resistors on this circuit?  I'm not sure how to calculate what value to put there with all these those 1M resistors between the input/outputs and VBias. 

[RaceDriver205]

Have you changed the CD4053 chip for a fresh one at any stage? Sometimes (tho rarely) individual parts can go bad.

[sfr]

Racedriver -

Yes, I have.  Tried a couple makes as well.   Haven't tried swapping anything in the Distortion Plus - I wonder if I could have damaged anything on that . . .

[R.G.]

I'm a little perplexed at your problems. I've used the CD4053 for bypass switching in many forms and it's just not that touchy.

If you want me to have a look at your schemos and layouts to see if I can spot a problem, I'd be happy to do that, all under a nondisclosure agreement if you like.