Problems with Easyvibe (high freq squeal)

[dthurstan]

Hi I built an easyvibe on pref board (http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/easyvibeboard_final.jpg.html) but I've got a few problems.
1. The most noticeable is a high freq squeal, which dissappears when the depth is reduced.
2. The sound is thin, as in it sounds more like a tremolo fx. It distorts at higher guitar vol (above 7 on my squire strat)

I'm running it off a battery at the moment. I tried replacing the 10uF with a 22uF, but the squeal is still there. I checked over the circuit for dodgy soldering or shorts, it looks fine to me. I've measured the volts on the IC's as follows;
   IC1
1   3.8 - 5.1
2   4.6 - 6.2
3   3.7 - 5.3
4   8.83
5   3.75
6   3.88
7   5.4 - 7.1
8   2.4  -3.8
9   3.84
10   1.3 - 3.8
11   0
12   1.7 - 3.7
13   3.88
14   1.8 - 2.6

   IC2
1   3.75
2   3.75
3   0.3
4   8.83
5   3.76
6   2.6
7   1.8 - 5.0
8   2.9 - 4.5
9   2.8 - 4.5
10   2.8 - 4.5
11   0
12   1.8 - 5.5
13   3.75
14   0.6 - 8.1

volts to circuit : 8.7, depth on full, medium speed. Any suggests?

Thanks

[dthurstan]

Hi

Well it's been a while. I'd like to say it's working but it's not 
I've been over the circuit again and again & nothing jumps out at me.
I've transposed spudulike voltages from 4 opamp design:

supply = 9.22
v = 8.71
vb = 3.77
rate = 1/2
depth = 1/2    
diode = 0.57

IC1
1   3.78
2   3.78
3   3.76
4   8.65
5   3.78
6   3.79
7   3.8
8   3.76
9   3.76
10   3.76
11   0
12   3.75
13   3.78
14   3.79

IC2
1   3.8
2   3.8
3   0.35
4   8.65
5   3.78
6   2.98
7   2.65 - 4.41
8   1.06 - 7.35
9   3.71
10   2.44 - 4.98
11   0
12   3.26 - 4.04
13   3.30 - 4.11
14   2.64 - 4.38

______________________________________

My Easyvibe -

supply = 8.79
v = 8.72
vb = 3.76
rate = 1/2
depth = 1/2
diode = 1.59

IC1
1   3.9 - 4.3
2   5.3 - 5.4
3   4.3 - 4.6
4   8.7
5   3.7
6   3.85
7   5.9 - 6.2
8   2.2
9   3.85
10   3.6
11   0
12   3.69
13   3.8
14   3.4 - 3.7

IC2
1   3.76
2   3.78
3   0.34
4   8.7
5   3.78
6   2.99
7   2.4 - 4.6
8   1 - 7.4
9   3.76
10   2.4 - 4.7
11   0
12   3.6 - 3.8
13   3.7 - 3.8
14   3.7 - 3.8

From what I can see IC2 is working ok, IC1 seems to be oscillating and my diode voltage is high. For the diode voltage I measured across the diode?

Any help would be much appreciated.

Cheers

[dthurstan]

Here are the details of the LDRs I used

Dark Resistance:20Mohm
Resistance @ Lux:20kohm to 100kohm

I've wrapped elec tape around the LDRs & LEDs, I copied slackers layout and he reported his working. But ppl have mentioned light interfering with the circuit.

[GibsonGM]

Those things really draw current; usually ppl. use a wall wart with them.  But that's probably not the issue.  Can you elaborate more?

Does it squeal if you turn the depth down a little? Does it sound OK in bypass? Do you have the switch for chorus/vibe, and does it do it on both settings?  Do you see the LEDs pulsing from dim to rather bright when it's on?
Light will certainly screw up a home-brew optoisolator...does it sound any better if you play it in the dark?   It should not distort your signal...

Next step is to audio probe the thing....listen to the output of each opamp stage and see which one is causing your problems. The malfunction will be somewhere in that stage!
Do you have an audio probe?  It's just a wire probe with a capacitor to block DC voltage, connected up to an amp.  I think this is a good candidate for its use.

A common problem with the EV is to connect points that should go to the bias voltage to ground.  Mine took me a while when I built it, but it is an awesome pedal!  Keep trying, and you'll get yours working.   

Posting a link to the specific schematic you used could help, too...there are a few out there.
~MP

[dthurstan]

Hey cheers for the tips.

At the moment it's not wired with a bypass switch, until I get it working.
The squeal does reduce when you reduce the depth.
It does have chorus/vibe switch and it happens on both settings.
All LEDs pulate, except the two bias LEDs.
I haven't tried it in the dark recently, but I do remeber it didn't make a diff. It might not of been dark enough.

Your completely right I do need to audio probe the circut that the first thing Im gonna do when I get a chance.
I think everthing is connected right. I'll check again.
I'm using the pref layout here http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/easyvibeboard_final.jpg.html
All my stuff is at work, coz I don't have much space were Im living now. So I'll post a pic of the Hollis schematic with the values from slackers pref board layout that I've made up.
I'll also take a pic of my board.

Thanks again, I'm def staying with this build the clips I've heard sound gret!

[GibsonGM]

Cool...I think you'll find a trouble area once you probe it.  I had a couple issues when I whipped mine up (small shorts across a couple of places, needed a magnifying glass to find them!).   It's complex for perfboard, so mistakes are very possible. 

I built mine right from Hollis' pencil schematic...IF I'm reading yours right, pin 3 on IC2 might be low (mine is 3.6V or so, which is the same as the bias voltage at the top of the power supply diodes).  If that's your input, it means the bias voltage isn't right, and that's where I'd look, = distorted signal!

[dthurstan]

Yeah it has a distorted signal. Cool cheers.

[dthurstan]

Here is the Hollis schematic with the vero layout part values:



Heres a pic of my board:



I'm hoping to get some time tonite to build an audio probe & test the board.

Cheers

[solderman]

Yeah it has a distorted signal. Cool cheers.

Is there both LFO and audio in the same IC?
In that case you can get the noise from The LFO leaking in to the audio trough the IC plower rail.

[slacker]

Something's definitely wrong around IC1 pins 1,2 and 3, they should all be about 3.77 volts. As the squeal goes away when the depth is reduced that makes me think the LDRs are connected incorrectly, double check that they are all connected where they should be. Also, have you got R6 installed? You probably have but I can't see it on the photo.

[GibsonGM]

You'll have a better handle on it once you audio probe; at least you can get to a specific place to start checking!!  Odds are pretty good there's a short between 2 components (very hard to see, and this is a challenging perfboard project), something not connected to VRef, etc.   Post after you've done that.  Maybe with a shot of the solder side of the board, too ;o)

[dthurstan]

Hey

Finally got some time to work on the EZ again. Thanks for all the responses. I tidied up the LDR/LED section shown below.



Everything seems to be correct, all LDRs connected to Vref and the + inputs of IC1. Heres the back of the board



It probably doesn't look that neat but I can't see any solder joins to other rails. I ran a screwdriver across the length of them to make sure. Could it be a short on the components side (i.e. 2 components touching?).

I used an audio probe to see were the problem is. I start to hear the squealing at R6, on the - input pin 6. Then it's really loud on pin 5 + input. I only have to go near the LDRs and I can hear it!

I'm not sure if the signal is too distorted, it's sorta buried under the squeal from the LDRs.

Going of spudulike's voltages I think IC2 is fine, it's just IC1 thats the problem.

Posted by: solderman
Is there both LFO and audio in the same IC?
In that case you can get the noise from The LFO leaking in to the audio trough the IC plower rail.

yep IC2 has the input stage and then the LFO.

I'm not sure if it is leaking as when I probe the input stage it sounds fine. I think GibsonGM & slacker are right something is shorting, but what.

[slacker]

Looks like you haven't cut right through this track.



That's the track to pin 6 of IC1 so I bet that is the problem. It looks fine apart from that.

Where do you get blue vero from, I want some

[dthurstan]

Then it's really loud on pin 5 + input. Thats wrong!

It's louder on pin 7 the output. doh! pin 5 is nice and clean. so like slacker pointed out pin 6 soldering, cheers. That seems to be where the problem starts.

The blue board I got off my Dad. RS components do it:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0435175

I think they r worldwide.

Thanks again 

[GibsonGM]

Good eye, Ian...just got here; I'm sure I'd have spotted it too :LOL:  !!
Hope that does it for you, D.  Is it working ok now?

These EV's are tricky...I did 2 distortions, then jumped into this one, and it damn near killed me trying to get things right!  I finally rebuilt it, and moved the LFO off to a daughter board that is 3-4" away from the phasing circuitry...it is silent (had clicking from the LFO on version 1).

[dthurstan]

Success!!

I cut the track and it's working now. Good work eagle eyed slacker! Cheers

I can't believe I missed that, it was schoolboy!

Thanks to everyone for helping me out. I think what I've learned is work ur way thru the circuit from input to output, also an audio probe is a must.  It helps you understand the circuit.
I can now go back to the safety of 2 or 3 transistor fuzz circuits. 

Thanks again

Dave

[dthurstan]

For Completeness I'll post my final voltages:

supply   9.5
v           9.3
vb           3.8
diode   0.55

trim = max
rate = 1/2
depth = 1/2


IC1
1   3.8
2   3.8
3   3.6
4   9.3
5   3.7
6   3.8
7   3.8
8   3.8
9   3.8
10   3.7
11   0
12   3.6
13   3.8
14   3.8

IC2
1   3.8
2   3.8
3   0.3
4   9.3
5   3.8
6   3
7   2.1 - 4.7
8   0.7 - 8
9   3.8
10   2.3 - 5.1
11   0
12   3.8
13   3.8
14   3.8

Here is how the volages from the veroboard version relate to PCB version:
                        |  vero  |
         IC1   IC2
IC1   o   1      1
IC1   -   2      2
IC1   +   3      3
IC1   g   4      
IC1   +   5   5   
IC1   -   6   6   
IC1   o   7   7   
IC1   v   8      
            
IC2   o   1      7
IC2   -   2      6
IC2   +   3      5
IC2   g   4      
IC2   +   5   3   
IC2   -   6   2   
IC2   o   7   1   
IC2   v   8      
            
IC3   o   1      14
IC3   -   2      13
IC3   +   3      12
IC3   g   4      
IC3   +   5   12   
IC3   -   6   13   
IC3   o   7   14   
IC3   v   8      
            
IC4   o   1      8
IC4   -   2      9
IC4   +   3      10
IC4   g   4      
IC4   +   5   10   
IC4   -   6   9   
IC4   o   7   8   
IC4   v   8      

[slacker]

Cool glad it's working