Easy-vibe Debugging...(fixed :D - now with recordings)

[edash]

Hey everyone,

I decided to have a go at the John Hollis, Easy Vibe circuit recently, and used the pcb from Geofex (http://www.geofex.com/PCB_layouts/Layouts/easyvibe.pdf).

I've soldered the whole thing together, and there seem to be problems. There are two bias LEDs which should glow when the circuit is turned on, but these do not. There are also 4 LEDs coupled with LDRs down the centre of the board, all 4 of these LEDs are lighting, when the depth pot it turned up.

I get a very faint distorted popping signal through the circuit when the chorus/vib switch is in one of the positions.

Does anyone have any suggestions, or past knowledge about this circuit?

Many Thanks

PS. Just thought I'd add, I've not made any part substitutions to the circuit - and used the exact PCB given at geofex.

- Ed

[The Tone God]

Read the "What to do when it doesn't work" sticky and report back.

Andrew

[RDV]

Check bias LED polarity.

RDV

[edash]

I'll go and check the voltages at the pins of the chips and post them if that will help

I've triple checked the polarity against that of the schematic and the pcb, and it seems to be correct. I'll go check again just to make sure

Thanks

[spudulike]

Cant help much, but ... all 3 vibe pcbs I made (until I changed the trace) has a short under the red circle. This can give the symptoms you describe - check it carefully. The pad is too close to the trace and the trace should be routed further above it.



From my working vibe the voltages are below for comparison.

All measurements quiescent (ie no input signal)
Rate & Depth set mid-sweep

Battery (Off-load) - 9.22V
Battery (On-load) -  8.71V

D6 anode/LED6 - 0.57V
Bias Rail (LDR Common ie J1) - 3.77V

IC1

1  3.8 
2  3.8
3  0.35
4  0.00
5  3.78
6  3.79
7  3.80
8  8.65

IC2
1  2.65 - 4.41
2  2.98
3  3.78
4  0.00
5  3.76
6  3.78
7  3.78
8  8.65

IC3
1  2.64 - 4.38
2  3.30 - 4.11
3  3.26 - 4.04
4  0.00
5  3.75
6  3.78
7  3.79
8  8.61

IC4
1  1.06 - 7.35
2  3.71
3  2.44 - 4.98
4  0.00
5  3.76
6  3.76
7  3.76
8  8.57

Hope this helps ...

[edash]

Ok... I took these readings... Rather worrying 

Battery 8.55

D6 Anode / LED 6: 0.00
Rail (I think): 5.84

IC1

1 1.32
2 0.87
3 0.81
4 0.00
5 0.79
6 0.77
7 1.30
8 8.55

IC2
1 7.87
2 0.54
3 0.00
4 0.00
5 0.00
6 4.51
7 7.76
8 8.60



IC3
1 7.16
2 7.16
3 0.53
4 0.00
5 0.77
6 2.45 - 4.49
7 1.36
8 8.58

IC 4
1 7.91
2 0.00
3 7.60
4 0.00
5 0.00
6 4.50
7 7.70
8 8.55

I'd noticed that trace too spudulike, it did look a little dodgy - and I believe I'd already cut it. I've made sure it's cut now, but still no change

[jrc4558]

Check the bias votlage. Namely, what is the voltage at thefist anode of the first bias LED?

[edash]

Measuring from ground to the anode of that first LED, I'm getting 0v across it, and neither of the bias LEDs are lighting.

The coupler LEDs are all lighting up constantly, and I've checked - both the polarities of the coupler LEDs and the bias LEDs appear to be correct.

Could anyone who's made this circuit and got it working post the polarities of their coupler LEDs so I can check that I've got them right.

Many Thanks

[spudulike]

If youre looking at RGs pdf layout, the leds are above the ldrs and have the anode on the right. If you had them reversed then they wouldnt light at all.

Your problem is you have 0v on the vref (bias) rail - should be 3.8 volts (ish).
Check the value of R23 (should be 10k), and check for a short to ground on the pcb.

--------------------------

Ok, I've never seen a schematic like this on the web sooooo....

I redrew JH's hand-drawn schematic, added RG's component numbers then stuck my working voltage readings on it.

http://i30.photobucket.com/albums/c345/stompbox_layouts/Easyvibe/Easyvibe_debug.gif

[edash]

Ok, checked the vbias rail again - and there is absolutely no voltage running along it. I checked the area around R23, there is voltage in pin 8 of IC2 and subsequently the top pin of R23, but 0v on the bottom pin of the resistor connected to the rail. I changed the resistor for another 10K, and there is still no change.

I've also checked for any shorts to ground on the pcb, and haven't found any so far.

Thanks for your help.

EDIT: There is a voltage across this resistor if you measure the voltage between the two pins of the resistor, but none from the ground to the bottom pin.

[edash]

Found it! There was a minute short after all!

It was between the vbais and the copyright RG text

Thanks to everybody!

I'm delighted with this little thing, a brilliant addition to my collection!

Once again, thanks for the schematic spudulike, very useful - although the polarity of one of the 470uf caps (C9 and 10) seems to be opposite to the original schematic! Thanks!

[spudulike]

oops - fixed

[edash]

Ok, did two little recordings of the thing in action. All have reverb too.

Easyvibe: http://www.edash.net/misc/phaser.mp3

Vibrato, Slow - Fast
Chorus, Fast - Slow

Easyvibe + Ultra Flanger: http://www.edash.net/misc/phaser2.mp3

Note the slight click caused by the Ultra Flanger, yet to fix that :/

Hope you enjoy those

[petemoore]

  Very nice Edash !!
  EZ Vibe is a favo' mine also.
  Thanks Spudlike for the clean schematic with all the nice notes !!!

[guitar_199]

A question I have.......
The sample sounds more like a tremolo to me.... perhaps with light phasing...
Can the Easy-vibe get the nice, thick, rich, vibe tone   a-la Trower?  Is that just a matter of adjustment or does this one not quite go that far?

Bob

[spudulike]

Doesnt this depend on the LDRs you use ?

[edash]

I've been playing with the drive trimmer since the recordings and I have a slightly deeper more phasey tone than before.

I think it does depend on the type of LDR used, the ones I used were higher resistor 70ohm ones because that's all I could get at the time

[no one ever]

did you measure the swing of your photocells?

[edash]

I didnt

I just bought the ones I could at the time and decided to see how they were. They work, but the phase sound is a little weak - I might experiment.

Which LDR range has been seen to produce the best kind of result?