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reverb distortion
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Wed Sep 07, 2016 6:36 am    Post subject: reverb distortion Reply with quote

so I've made 3 reverb pedals that did not have this issue, but the last 2 I've built have, if you plug in a power supply while powered it causes distortion in the reverb, if you plug in the power cable then add power it's completely fine(plugging dc plug into pedal before plugging into the wall), something about plugging in a hot power cable makes it distort, I've done some research and thought it may be the crystal
here is the crystal I'm using from mouser

http://www.mouser.com/Search/ProductDetail.aspx?R=AB38T-32.768KHZvirtualkey52750000virtualkey815-AB38T-32.768KHZ

here is the datasheet

http://www.mouser.com/ds/2/3/ab38t-ab26t-180532.pdf

I'm using a 15pf capacitor to ground with the crystal as the fv-1 datasheet states to
do I need to change the cap? use a different crystal? or is it a different issue?
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frank



Joined: 19 Oct 2005
Posts: 972

PostPosted: Wed Sep 07, 2016 9:43 am    Post subject: Reply with quote

Crystals are one of those things that can be very picky, you would need to contact the crystal manufacturer and ask them the recommended caps to use. The 15pf works in many cases but you may need to increase it, have 2 caps, add a series resistor, etc. things only the crystal manufacturer can tell you.
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Frank Thomson
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Wed Sep 07, 2016 7:59 pm    Post subject: Reply with quote

I contacted the manufacturer and he just spouted a bunch of theory about pierce or colpitts oscillators without ever really telling me what I needed for the fv-1 application, is there a crystal that you recommend and know to be reliable with the 15pf cap as called for in the datasheet that I can just replace the crystal with?
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ice-nine



Joined: 24 May 2012
Posts: 125

PostPosted: Thu Sep 08, 2016 4:05 am    Post subject: Reply with quote

Try a 33p cap with the oscillator it may or may not cure the issue, are you sure it is the crystal causing the problem in the first place as it could be something else.
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Thu Sep 08, 2016 5:09 am    Post subject: Reply with quote

ice-nine wrote:
Try a 33p cap with the oscillator it may or may not cure the issue, are you sure it is the crystal causing the problem in the first place as it could be something else.


I'm pretty sure it's the crystal I'm not 100% but all the research of done into the matter points to the crystal, I'll try adding different values of caps and see what happens, I tried with no cap at all and it definitely made it worse. I checked the power and buffer.... all check out, it seems to be something in the chip and respective parts, I'm kind of lost because the first 3 I built I used these same crystals with a 15pf cap and have had no issues, but with these new builds I've been having problems. I don't know a lot about theory behind the crystal so I'm out of my depth
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frank



Joined: 19 Oct 2005
Posts: 972

PostPosted: Thu Sep 08, 2016 7:54 am    Post subject: Reply with quote

Every crystal is a little different so if the manufacturer doesn't have a suggested circuit then try the following:

1. Try 15pf on both legs
2. Try 33pf on one leg
3. Try 33pf on both legs
4. Try a series resistor (1K ohm) between crystal and X2
5. Try a parallel resistor (100K) across the crystal

I've been using Citizen crystals with good results.
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Thu Sep 08, 2016 11:27 am    Post subject: Reply with quote

frank wrote:
Every crystal is a little different so if the manufacturer doesn't have a suggested circuit then try the following:

1. Try 15pf on both legs
2. Try 33pf on one leg
3. Try 33pf on both legs
4. Try a series resistor (1K ohm) between crystal and X2
5. Try a parallel resistor (100K) across the crystal

I've been using Citizen crystals with good results.



I tried all of those combinations, and still distorted reverb, and 5 didn't even allow a signal to come through, I guess I'll order some citizen crystals and see if I have better luck
I just can't seem to pin point whats causing the distortion, but only in certain powering on/off intervals
thank you for the suggestions Very Happy
if you have any more, it is much appreciated
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ice-nine



Joined: 24 May 2012
Posts: 125

PostPosted: Thu Sep 08, 2016 1:59 pm    Post subject: Reply with quote

Try a different crystal, I build quite a few FV-1 pedals and have never had this problem while plugging in a PSU jack while powered from a battery. I have since stopped building battery powered pedals but these are the crystals I generally use.
https://www.rapidonline.com/ael-x32k768l101-32-768khz-12-5pf-3x8mm-radial-cylindrical-watch-crystal-90-3046

I'm sure you should be able to find the same in your country.
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frank



Joined: 19 Oct 2005
Posts: 972

PostPosted: Thu Sep 08, 2016 6:10 pm    Post subject: Reply with quote

bxc1986 wrote:

I tried all of those combinations, and still distorted reverb, and 5 didn't even allow a signal to come through, I guess I'll order some citizen crystals and see if I have better luck
I just can't seem to pin point whats causing the distortion, but only in certain powering on/off intervals
thank you for the suggestions Very Happy
if you have any more, it is much appreciated


Hmmm, odd. I would have thought you would see something with one of them. I would try other crystals, could be something with these ones I've not run across before.
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ice-nine



Joined: 24 May 2012
Posts: 125

PostPosted: Mon Sep 12, 2016 9:09 am    Post subject: Reply with quote

Out of interest, after you plug in the external power and experience this distortion. What happens if you then change effect to another one through the S0-S2 pins. Does the next effect also have the same distortion or does sound correct.?
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Tue Sep 13, 2016 10:32 am    Post subject: Reply with quote

I found the issue! it was a crappy 3.3v regulator from China, I ordered some better quality regulators and the problem is gone! thanks for all your suggestions!
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Wed Nov 30, 2016 3:34 pm    Post subject: Reply with quote

ice-nine wrote:
Out of interest, after you plug in the external power and experience this distortion. What happens if you then change effect to another one through the S0-S2 pins. Does the next effect also have the same distortion or does sound correct.?


it still distorts even when i change the program, i thought i had it pin pointed to the regulstor but it seems to be doing it again, if i pull the power out and in real quick it seams to fix it, but if the pedal is engaged while powering it distorts, i cant find any reason why it does this

here is my schematic, hopefully you can view it

https://drive.google.com/file/d/0B5Y2KfKaPJ8xVmNsZ0NZTlhMOGs/view?usp=sharing
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frank



Joined: 19 Oct 2005
Posts: 972

PostPosted: Fri Dec 02, 2016 8:45 am    Post subject: Reply with quote

It is hard to read the schematic but is that a 5V regulator you are using?
It looks like you are running 2 diodes in series from the power jack?
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amz-fx



Joined: 06 Sep 2006
Posts: 32
Location: Louisiana, USA

PostPosted: Fri Dec 16, 2016 7:17 am    Post subject: Reply with quote

The schematic must be wrong as there is no way it could work with the input tied to ground.

Make sure pin 4 of the opamp is going to ground, and the 1M tied to 1/2 Va is connected to the + input.

regards, Jack
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bxc1986



Joined: 06 Sep 2016
Posts: 10
Location: welcome, nc

PostPosted: Sat Jan 07, 2017 4:18 pm    Post subject: Reply with quote

frank wrote:
It is hard to read the schematic but is that a 5V regulator you are using?
It looks like you are running 2 diodes in series from the power jack?


it says 5v because its to same to-92 package in my eagle cad library but in the build its a 3v regulator, and yes those are diodes in series from the power input, I took those out when I troubleshooted and the distortion was still there, I may have found the issue

this is from the datatsheet,

Digital power should be bypassed with a ceramic capacitor to ground with very short leads to the part. Ideally, the design
will be onto a double sided PCB with the lower layer as a solid pour, connected to ground. This provides a convenient low
inductance connection for bypass capacitors through vias. A single sided PCB can be used provided that a large ground
area is included beneath the chip and surface mount bypass capacitors are connected from supply pins to this ground as
close to the chip as possible

if the pour on my pcb design is not suitable could that cause the weird distortion?
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