Yet another Easyvibe problem - cap keeps blowing

[Bucksears]

I finished wiring up my Easyvibe in the case (no bypass switch) and tried it out. I could hear it 'vibing' and was pleased that things worked out on the first try.
But......
Within seconds, I hear a small pop and air releasing inside the pedal. I pulled the power and figure that something somewhere isn't right. As I was feeling around the components to see if something was hot, I noticed that the C9 (470uF) was too hot to touch. The cap was bulged out at the top. I checked the wiring and everything seems correct. So I tried another cap. The second that I connect the guitar cable into the input jack, I feel the cap heating up immediately. The positive (+) lead of the cap is directed toward the 9V.
Has anyone else had this problem? Could I have a batch of bad caps? It seems to be working correctly other than that. I didn't have time to play around with the controls to give an opinion about the build, though.

I'm excited about this one as it seems to do the rotary thing more like I want it to than the Phase 100 does.

Thanks,
- Buck

[Bucksears]

*just wanted to note also that these are 10v caps. On the schem redraw that I saw, the author indicates that the electro caps should all be 16v.
Could that be it?

[alderbody]

*just wanted to note also that these are 10v caps. On the schem redraw that I saw, the author indicates that the electro caps should all be 16v.
Could that be it?

although i haven't seen the schem, i believe 10V electros are a little "low-rated" for this application.

And since the author recommends 16V caps, you should at least use 16V ones.

What's your supply voltage?  9, 18, 24Volts?...

[Torchy]

Dont forget that tolerance ratings also affect the working voltage of the caps. IMO 10V is way too close to the supply rail.

I was always told to use caps with at least twice the voltage rating of the supply, but 470uF/35V are h u g e. 16V would be the way to go. I've built a few vibes now, always used 16V caps and never had a problem either battery or psu fed.

[mikey]

I'm using 10v 470uF caps and havent had any issues with 9v wall or 9v battery. 

Hmm... C9 is right in that area where the traces get REALLY close on R.G.'s layout.  Take a look at the area where R18 jumps the trace leading to the negative leg of C9.  Make sure there's a gap there between the lower R18 pad and the trace that leads to C9.  Actually I have no idea if a bridge there would cause a cap to blow but something to check.

[d95err]

Check (and re-check) the polarity of the cap - are you sure it's not backwards?

[Bucksears]

Check (and re-check) the polarity of the cap - are you sure it's not backwards?

Per the schematic, the pos(+) side of C9 is oriented TOWARD the 9V supply, which is how I have it.
I'll see if I can track down a 16V 470uF cap a plug it in there, but I'll also troubleshoot any solder bridges and do a once-over on the parts values to make sure they're correct. It's just odd that it audibly works, but this cap is having a problem.

- Buck

[GibsonGM]

Hi Buck...I just ran thru a bunch of debugging of my Easyvibe...have you tried hooking up the power without the cap in there, and using a DMM to see what voltages are present before AND after the cap?  Could be a short somewhere nearby (happened to mine), and something weird could be happening.   I used perfboard, so I can't help with that 'area' that's been mentioned on the layout.  Used 35V (yeah, they're big)...16v was the minimum...I've read in many places to always use caps around 2x supply voltage.  Good luck, it's a fun circuit, I use mine out a lot...now if I could only cure the LFO tick!!! 

[Torchy]

...now if I could only cure the LFO tick!!! 

Try using a higher or lower value cap for C8.

[Mark Hammer]

I'm using 10v 470uF caps and havent had any issues with 9v wall or 9v battery. 

....yet.

470uf is a spec, that has some variation within limits.  9v is a battery spec...within limits.  10v is a cap spec....also within limits.  Make the battery a little higher, the true voltage rating of the cap a little lower and........

This is why the recommendation is to use a voltage rating that is at least 1-1/2 times the anticipated supply voltage or signal amplitude: to anticipate natural variation.

Note that although a 470uf cap smoothing out a supply needs to be rated at least 150% the supply voltage, caps in the signal path do not require such a stringent rating.  The input cap on just about any pedal you own is unlikely to ever see a voltage applied to it that is anything more than a couple of volts.  That being said, if you blindly stuck with a 25v rating for every cap you buy, it probably wouldn't cost you that much more (if at all) and you wouldn't have to think/worry/calculate about it.

[mikey]

I'm using 10v 470uF caps and havent had any issues with 9v wall or 9v battery. 

....yet.

470uf is a spec, that has some variation within limits.  9v is a battery spec...within limits.  10v is a cap spec....also within limits.  Make the battery a little higher, the true voltage rating of the cap a little lower and........

This is why the recommendation is to use a voltage rating that is at least 1-1/2 times the anticipated supply voltage or signal amplitude: to anticipate natural variation.

Note that although a 470uf cap smoothing out a supply needs to be rated at least 150% the supply voltage, caps in the signal path do not require such a stringent rating.  The input cap on just about any pedal you own is unlikely to ever see a voltage applied to it that is anything more than a couple of volts.  That being said, if you blindly stuck with a 25v rating for every cap you buy, it probably wouldn't cost you that much more (if at all) and you wouldn't have to think/worry/calculate about it.

Easyvibes are the only build I've gone under 16v caps.  After seeing this thread though I'll replace the 10vs and consider myself lucky.

[Bucksears]

Replaced C9 & 10 with 35v 470uF electrolytic caps and C9 STILL heated up too hot to touch and started expanding. I unplugged everything immediately.
Something somewhere is messed up; I've gone over the layout with a fine tooth comb and don't see any solder bridges. I'll have to recheck the wiring and the parts.

Do electrolytic caps usually go (-) ground? I guess it depends on the circuit.

Thanks,
- Buck

[Eric H]

Just because I'm a contrarian: the voltage on electrolytics is --working-- voltage, not max voltage, and a 10v cap is fine for a 9v supply...that's what the manufacturers say, anyway.


-Eric

[GibsonGM]

Hi Buck,

Electrolytics, if they're polarized (i.e., they have a "-"  on them)...the minus always goes to the part of the circuit at lower potential.  Some fuzzes etc. have a positive ground...so the "-" would not go to ground, but the other way around, since the power "feed" is from the negative battery terminal.  Ground is just a common reference.  Easy Vibe is negative ground, so yes, the "-" goes to ground.   

A symptom of misconnected or shorting caps is that they get hot, can swell/pop/smoke/smell...are you sure the power supply is hooked up correctly? What voltages do you get on either side of the cap, referenced to ground??   I've seen this happen due to a short far from where the part is affected....my easy vibe had a short from one of the diodes in the last stage to ground, and screwed my LFO all up.

Easiest fix is to attach negative DMM probe to battery "-", and trace thru the power supply and up to your cap, noting voltages along the way...especially at the cap in the bias (potential trouble area, be sure it's 1/2 V+)....ground is the "-" line in the Easyvibe, btw, threw me a little when I made one.  All grounds in the circuit should read 0 volts referenced to battery "-".  Hope this helps and that I"m not repeating stuff you already know...you'll get it figured out!

[spudulike]

[Bucksears]

Thanks Gibson and Spudulike.
I'm sure there's a short somewhere; unfortunately, it's going to be tricky testing voltages with that cap in there. I'll do some connection (beep) testing with my MM and see if anything is connecting to the ground and voltage rails that shouldn't be. It's killing me as I REALLY want to get this circuit working.
Thanks again,
- Buck

[Paul Perry (Frostwave)]

The only way a 35V 470uF cap could overheat, that I can think of, is if there was AC across them, instead of DC. Makes me worry about your power diodes..

[Bucksears]

As far as power goes, I'm using one of the connections on my Godlyke Powerall. I'm guessing that it's putting out the same voltage as it does as I've measured with my JFET distortions, about 9.06v.
I have the (-) of the power jack going to the shaft connection on the input jack, not necessarily to ground. That should be fine, though, correct?

- Buck

[GibsonGM]

My C8 doesn't seem to be the 'ticker'...I para'd a bunch of values in there, no diff, even just jumpering it. Maybe I'll desolder and try a very large cap in there.  BUT, jumping a .1 uF to ground from the hot input mostly silenced it, along with all of my highs  I don't know what that indicates.

I perf'd the circuit using the original Hollis schem; it's probably because i have the LFO and 1 filter section on the same chip (TL064's).  And all the LED wires run over the OA"s...bad layout!   Adding a .1 uf bypass on power supply pins did nothing, either.  Sorry, this is OT, but Buck might run into this, too...otherwise the vibe is great, esp. when run with distortion (the tick is not that obvious unless not playing).