reverb distortion

Hardware questions and issues with the FV-1

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bxc1986
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reverb distortion

Post by bxc1986 » Wed Sep 07, 2016 7:36 am

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/ProductDet ... -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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Post by frank » Wed Sep 07, 2016 10:43 am

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.
Frank Thomson
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bxc1986
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Post by bxc1986 » Wed Sep 07, 2016 8:59 pm

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?

ice-nine
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Post by ice-nine » Thu Sep 08, 2016 5:05 am

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.

bxc1986
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Post by bxc1986 » Thu Sep 08, 2016 6:09 am

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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Post by frank » Thu Sep 08, 2016 8:54 am

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.
Frank Thomson
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bxc1986
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Post by bxc1986 » Thu Sep 08, 2016 12:27 pm

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 :D
if you have any more, it is much appreciated

ice-nine
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Post by ice-nine » Thu Sep 08, 2016 2:59 pm

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-x32k768 ... al-90-3046

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

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Post by frank » Thu Sep 08, 2016 7:10 pm

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 :D
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.
Frank Thomson
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Post by ice-nine » Mon Sep 12, 2016 10:09 am

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.?

bxc1986
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Post by bxc1986 » Tue Sep 13, 2016 11:32 am

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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Post by bxc1986 » Wed Nov 30, 2016 3:34 pm

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/0B5Y2Kf ... sp=sharing

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Post by frank » Fri Dec 02, 2016 8:45 am

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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Post by amz-fx » Fri Dec 16, 2016 7:17 am

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

bxc1986
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Post by bxc1986 » Sat Jan 07, 2017 4:18 pm

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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