A touchy subject - more tales from the bench

[Mark Hammer]

Digging through the big bin of boards-that-were-never-debugged-or-boxed this past week, I pulled out a Tonepad Phase 90, and a Geofex Big Cheddar V6.  The Phase 90 had never worked and the Big Cheddar had previously worked, but not any more.

First thing I thought I'd do is confirm that the 2N5952s were oriented properly, and it turns out mine were opposite to what the Tonepad layout showed.  I think mine are Fairchild.  I just threw in 4 unselected trannies, flipped around so that the pins were where they ought to be, and found I could get decent phasing if I tweaked the trimpot back and forth, but there was no modulating sweep.  I used my meter to look for an LFO signal, and I wasn't getting any.  Hmm, I wonder if it has anythng to do with the dual caps I was using on the LFO output?  Since I had no 15uf caps handy, I had paralleled a very small 4u7 and 10u to get in the ballpark and soldered that in place, with the leads from one of the caps wrapped around the base of the leads from the other.  There was enough room for it, and the caps were not going to prevent situating the board under a pot.  But, I figured I'd check it out anyways, so I unsoldered the cap-pair from the board.  Yikes!  The + and - leads from the caps had a web of solder between them, effectively shorting the LFO output to ground.  So THAT was why there was a trimpot sweep but no LFO sweep!  I deftly removed the solder web/bridge, stuck the cap-pair back on the board, and bingo I had sweet phasing.  BTW, I added a 470k pot in series with the 1M resistor from the trimpot, and found it very useful for adjusting the sweep range.

In the case of the Cheddar, I found the board was going to be a tight fit for the chassis I had selected (a homemade sloped front).  I resoldered and bent one or two of the caps over so that the board could fit under the pots.  Installed the board and got a VERY very low signal no matter what I did.  So, I took the board out again to figure out what the heck was up.  Turns out that when I bent one of the caps over, the additional lead I had allowed on the component side for the bend was touching a pin from the adjacent op-amp, and the pot was applying pressure that made the contact non-intermittent.  Moved the cap over (though I think I'm going to unsolder it and slip some wire insulation or heat shrink over that lead), and bingo, sweet fuzz.

Note to all you beginners:  I've been at this for over 30 years, and it STILL happens.  Make a point of checking not only the copper side of the board, but the component side....and sometimes between the components and the board.  The answer to getting your pedal up and running might lie there.

[DougH]

Here's a problem I had with my "ac15" amp this week:

When the amp was sitting on the spkr cabinet, every time I played a 6th string 3rd fret "G" it got a horrible buzzing. It was the resonant frequency of something that was breaking contact. I checked the tube sockets first. One of the 6bm8's crackled when I gently pushed on it, so I swapped them and the problem stayed at the same socket. So I retensioned the socket but that didn't help.

Turns out my problem was the friggin' screen resistor lead broke off at the tube socket and was making intermittent contact. 250vdc clicking on and off, nice... No wonder this amp sounded great one day, bad the next. I thought my hearing was just getting really fickle or something. (I always suspect it's me, first. Like I was just kidding myself that the amp sounded good when I first built it, etc. Don't know why I do that...) Replaced the resistor and it sounds real good again.

Note to self- don't re-use old resistors with bent up leads that may have weak spots...

[nelson]

I'll join in.


I made a Wolf Bagger Aliaser the other week. I reused a footswitch, input and output jacks from an old effects pedal that I never really liked(Fuzz factory clone).

I have it pretty much optimised to limit offboard wiring errors: I use board mounted 3PDT, pots and connect the boards with a 2.54mm pitch jumper cable. I find most debugging occurs because of offboard wiring connections and shorts etc.

So, I put the aliaser in an enclosure and wire it up, tighten the input/output jacks etc.

Then, I plug it into my amp to give it the vigorous testing procedure I usually go through: Twiddle the knobs, play a few licks.

I discover it has no output in either bypass or engaged mode.

So, obviously something is shorting the guitar signal at some point in the bypass circuitry.
I check about 50 times that everything is connected as it should be, check the continuity of the footswitch about 20 times.
I scratch my head, perplexed, as the signal routing is as it should be and I can't identify any problem.

I sit it down for 20 minutes and go have a glass of wine.

I come back after (several) a glass of wine.

The issue is staring me in the face. I had tightened the mono output jack so that the ground lug was shorting against the signal lug.
I seperated them and voila! Lovely(ugly) aliasing.
Now, I would expect this if I had used cheap jacks. However, I never buy cheap jacks as, really, they are false economy: like buying an american car.

The jacks I bought were the PPP ((for lack of  better words) own brand jacks.

They are good quality. However, even with the best quality components "shit happens".
So, yeah, check your jacks haven't shorted amongst themselves.
I know I'll look out for it when faced with a similar dilemna.
I've since changed to different jack sockets, where this problem cannot occur.
Mainly neutrik stereo switched jacks.




l

[iaresee]

On Tuesday night I built a little switch box with LEDs to use with my amp and my new looper. The amp uses a TRS to switch channels and turn the volume cut feature on-off. I want the volume cut to be handled by a footswitch like it is now. But I want the looper to handle the channel changes. Oh, and instead of a volume cut, I wanted to treat it like a volume boost. So the indicator LED is off when the feature is on (cutting the volume) but on when the feature is off (full master volume).

And I wanted to try to cram it all in to a 1509A.

After a few burnt fingers I got it all sorted out. I have a TRS input. The tip goes to a red LED, a resistor and then to the tip on a TS output. The TS sleeve goes to the sleeve on the TRS input plug. The ring on the TRS input goes to one side of a 2PDT switch and returns to the sleeve on the input plug. On the other side of the switch, wired opposite to the plug, is +9V from a power input jack, a resistor and a green LED.

I do not work well in small spaces. But I got it together and decided to test it before knocking off.

First I plugged in a 9V adapter to check the green LED that indicates "boost" mode is happening. Plugged it in, stomped the switch and the LED quickly went green -> yellow -> orange -> black. With that lovely odour of fried semi-conductor material floating up to my nostrils. I mis-spec'ed the resistor. I thought all the greens I had were high intensity LEDs and I used a 2k2 resistor. Opps.

No problem. I'll fix it this weekend. I figured I'd try the red LED with the amp to see if works right.

Plug it all together with a little spare momentary I have to do the actual channel change. Fire up the amp. Stomp the momentary and...fffffft...there's that smell again. Damn it. While I did check the TRS connections with Koch, I forgot to ask the voltage the amp puts across T-S and R-S. It's 12V, not 9V, so I again mis-spec'ed the resistor and put too much current through it.

I rushed it. I was too worried about the wiring puzzle and forgot to ask all right the electrical questions. I'll try again this weekend. But this is definitely my first and last 1509A build. I just can't handle the stress that it creates in my head cramming everything in their!

[kurtlives]

Been working on building this big 9 tube Fender amp for a while now. Finally finishing it, but I was having some buzzing issues.

After going through everything on the amp, tapping it, tightening it, I found the issue. Turns out the 4 unused pins on my octal socket for the GZ34 rectifier were loose enough to vibrate. Cut the extra pins off, bolted the chassis back in nice and tight and it was good to go. No more buzzing.

Not really interesting, more one of those "I didnt think that would happen" moments.

[tranceracer]

I'll chime in on a recent latching relay issue this past weekend.  Just built a PC board latching relay ckt and it wouldn't work...  hmmmm....
Troubleshot for hours, by sanding between the pads verifying solder joints, replaced the 4049 IC, verified voltages... still no click-click when I pressed the momentary tactile switch... hmmmmm...

Discouraged and peeved, I gave up and went to bed.  The next morning w/ a fresh cup of coffee began to troubleshoot it again...

Re-reviewed the schematic and a dim flash in my head said "Hey you dolt, didn't you breadboard this thing a while back and run into the same problem and had to change out a resistor or something"... DOH!  I had the wrong value resistor.  Swapped the 10K w/ a 1M and BAM! *CLICK* *CLICK* 

The power of a good nights rest and a cup of java! 

[MikeH]

I spent 3 days debugging a superfuzz with RGs help because I read the datasheet wrong.  I was looking at it as though the pinout was shown looking down through the casing, when in fact it was the opposite.  So it didn't matter how many times I verified the pinout, because I *just knew* that the trannys were in the right way. 

[Barcode80]

I had an easyvibe i built a couple weeks ago. got everything soldered in, wiring, etc. all was well. plugged in the pedal to the supply, clicked the switch a few times, and the LED wouldn't come on. The LED is generally the first thing I wire when populating a box, so I knew that wasn't it. So I blew about 8 hours overs the course of a few days debugging, all to no avail.

Then it hit me.

I turned over the pedal once more, unscrewed the bottom once more, and glanced at the switch. lo and behold, i in fact did not wire the ground leg of the LED to the switch. grrr.

[BDuguay]

I built a BYOC Wah for someone and it didn't work. I had successfully built a number of them previously but this one was giving me fits.
Long story less longanized, I finally found a shorted cap. I removed the cap and discovered that one of the leads had scraped against the sharp edge of the solder pad when I inserted it and the resulting 'leg material' had formed a tidy little bridge shorting out the cap. The cap was a radial type so I would have never seen the problem from a quick visual inspection because the problem was hidden between the cap and the PCB.
That little nugget is now permanently locked away in the troubleshooting section of my ever depleting memory bank.
B.

[MikeH]

I turned over the pedal once more, unscrewed the bottom once more, and glanced at the switch. lo and behold, i in fact did not wire the ground leg of the LED to the switch. grrr.

Ha ha ha!  I've totally done this one before.  it ranks right up there with "forgot to plug in the chips" for me.

[tranceracer]

I turned over the pedal once more, unscrewed the bottom once more, and glanced at the switch. lo and behold, i in fact did not wire the ground leg of the LED to the switch. grrr.

Ha ha ha!  I've totally done this one before.  it ranks right up there with "forgot to plug in the chips" for me.

++1 !   

[DougH]

I turned over the pedal once more, unscrewed the bottom once more, and glanced at the switch. lo and behold, i in fact did not wire the ground leg of the LED to the switch. grrr.

Ha ha ha!  I've totally done this one before.  it ranks right up there with "forgot to plug in the chips" for me.

++1 !   

I've done that too. One of those things that happens when you use IC sockets. Another fun one is when you forget to plug the speaker in to your amp... 

[jefe]

+3

Add me to the list of dummys who forgot to plug in their ICs. 

[kurtlives]

I turned over the pedal once more, unscrewed the bottom once more, and glanced at the switch. lo and behold, i in fact did not wire the ground leg of the LED to the switch. grrr.

Ha ha ha!  I've totally done this one before.  it ranks right up there with "forgot to plug in the chips" for me.

++1 !   

I've done that too. One of those things that happens when you use IC sockets. Another fun one is when you forget to plug the speaker in to your amp... 

Thats not a funny one  I can afford frying chips not OTs 

[nelson]

+3

Add me to the list of dummys who forgot to plug in their ICs. 

Done that. Here's another dumb one: ever forgotten to solder a joint on a PCB?

Ever since I've soldered methodically and then triple check every joint is soldered.

Last time that happened it'd been late at night and I thought I'd soldered every connection. It turned out Id forgotten to solder about 10 points. It was a big heavily populated circuit. But, still, now, every circuit gets divided into lines I now solder in a row.  

Nothing more forehead slapping than when realised you've forgot to solder half the board!

[skiraly017]

The short and skinny...

Many Small Clone builds under the belt but the most recent one didn't work. Signal while engaged and disengaged but no chorus. Checked everything twice and even swapped out the IC's. An hour later I realized there was a trim pot staring me in the face that hadn't seen the business end of a screwdriver.

[BDuguay]

+3

Add me to the list of dummys who forgot to plug in their ICs. 

Been there, done that, bought and wore out the T-shirt.
B.

[ayayay!]

My acoustic amp suddenly got "farty" the night before a gig.  I had to shelve it.  After 2 months, I came back to it Sunday, isolated which speaker it was, and started fruitlessly Googling for a replacement speaker. 

In my frustration I ran my finger over the edge of the speaker foam to clean off some dust.  "What's this hard spot in the foam???"

That would be a Radio Shack 1/4" stereo adapter that my 3 year old somehow dropped into the ported opening in the back of the amp, that somehow got perfectly wedged between the foam and the speaker assembly.

Moral of the story:  Inspect EVERYTHING.

...and don't let your 3 year old near your stuff.  She's like Stewie Griffin, I swear...

[Mark Hammer]

+3

Add me to the list of dummys who forgot to plug in their ICs. 

Been there, done that, bought and wore out the T-shirt.
B.

Not only have I worn out the t-shirt; I've used it to wash the car!

[starekase502]

Here's a problem I had with my "ac15" amp this week:

When the amp was sitting on the spkr cabinet, every time I played a 6th string 3rd fret "G" it got a horrible buzzing. It was the resonant frequency of something that was breaking contact. I checked the tube sockets first. One of the 6bm8's crackled when I gently pushed on it, so I swapped them and the problem stayed at the same socket. So I retensioned the socket but that didn't help.

i have a peavey classic 30 had the same problem everytime i hit low g cracking soung.  I though omg im going to have to start pulling things apart and get all into it, going to be pricey and a pain.  turns out the nut on the mid control was loose and when i hit low g the pot would vibrate causeing a bad conection easy fix