I think I killed my working Brownface Trem pedal

[waldner]

I have posted about this on the BYOC forum but nobody has had an answer yet so I though I'd try the knowledge of this powerful group:) 


I built the BYOC Brownface Harmonic Tremolo pedal and when complete she worked great.  It did have a little more noise than I was hoping for and in trying to troubleshoot that noise I believe I shorted the (+) and + connections that go from the board to the DC Jack (RED and YELLOW connections near top).  Ever since that moment the pedal doesn't work and the LED doesn't go on.  I'm wondering what I could have blown?


I tried looking at the schematic but it's a bit fuzzy and hard to read.  I've built lots of tube amps but not many pedals that use all of these little transistors.  I guess I didn't realize that 9V of battery power (I was using an external Volto battery pack supply plugged into the DC Jack) could blow anything. 

Any ideas on how to troubleshoot and figure out what part or parts I blew up? 


Here's a link to the PDF build instructions.  Toward the end is the schematic.  http://byocelectronics.com/brownfacetremoloinstructions.pdf

[sluckey]

I believe I shorted the (+) and + connections that go from the board to the DC Jack (RED and YELLOW connections near top).  Ever since that moment the pedal doesn't work and the LED doesn't go on.  I'm wondering what I could have blown?

I doubt that caused any harm. All that's going on there is the battery gets disconnected whenever you insert the power plug from the external power supply.

You must have a plug inserted into the input jack in order to operate.

Has this pedal ever worked with that external Volto battery pack? Did you check the voltage of the external Volto battery pack? And is the polarity correct? This circuit doesn't have a reverse polarity protection diode so wrong polarity could possibly kill a lot of transistors and electrolytic caps.

[acheld]

Similar thing happened to me some years ago.   

I could not trace out what happened --  so, I desoldered all the transistors and the electrolytic caps, purchased new and then reassembled the board (very and painfully) carefully.   It worked.  Not expensive.

Check and recheck the wiring of the power jack.   It is very possible that has been mis-wired as the diagram showing this is not as clear as it might be.

I would assume that this is a 9VDC +ive center (virtually all pedals are).   And that your Volto battery pack is also center +ive.    I do have some devices that are center -ive . . .

[Keppy]

I would assume that this is a 9VDC +ive center (virtually all pedals are).

The standard for most OTHER electronics is center (+), but the standard for pedals is center (-), with the negative supply grounded. This is why you don't see metal power jacks on pedals, because it would short the plug sleeve carrying +9v to the grounded enclosure.

[acheld]

You're so right, my bad.   

I've ruined at least one pedal by mixing up the power supplies. . . .

[Keppy]

You're so right, my bad.   

I've ruined at least one pedal by mixing up the power supplies. . . .

I used to sell a pedal that required a 48v supply, and the only one I could find was center positive and used the same size plug as a regular Boss supply. It was legitimately terrifying sending those to people, no matter how many warnings I put on it. Although, come to think of it, they were a lot more likely to destroy their OTHER pedals than the one I sent them.

[Keppy]

To the OP, I don't see a ton of things on that schematic that are sensitive to reverse voltage. The electrolytics for sure, and possibly the transistors. The transistors might survive though, given that the reverse voltage will only harm them if the internal diode junctions are pushed to the point of conducting in reverse. That doesn't always happen in a 9v circuit.


If you haven't already, try the steps here: https://aronnelson.com/diywiki/index.php?title=Debugging
In particular, measuring DC voltage on the pins of each transistor will tell us what we need to know.

[waldner]

OK, I solved the problem.  It turns out that the LED was the only thing blown and in this design it's part of the circuit.  I replaced the LED and it works again    


Miracle!  I'm really glad I didn't have to start replacing all kinds of transistors. 
Thanks for the support.


By the way, this is a really good sounding harmonic trem effect in case anyone is interested.  The trem sounds a hell a lot like my 63 Vibroverb amp, so much so that I made a laser print sticker for it and named it after the amp.

[sluckey]

I just listened to some YouTube demos of this pedal. Sounds very nice! Speed and Depth controls are much more versatile than the original tube circuit.

[waldner]

The only problem with it is that it's more susceptible to noise than most other pedals.  Depending upon the power source and position, it can let some thump and whining sound through the amp.  It may just need to be powered by a 9V battery

[Keppy]

The only problem with it is that it's more susceptible to noise than most other pedals.  Depending upon the power source and position, it can let some thump and whining sound through the amp.  It may just need to be powered by a 9V battery

I don't see any power supply filtering on that schematic, though I do see a 100uF cap in the BOM that is unaccounted for. There's no reason for a circuit like this to have unsolvable issues with PS filtering. If the 100uF cap is already serving that purpose, try putting a 100R dropping resistor between the cap and the power jack. Some folks also have success putting a smaller cap like .1uF in parallel with the bigger cap to reduce ESR at higher frequencies.

[waldner]

I don't see any power supply filtering on that schematic, though I do see a 100uF cap in the BOM that is unaccounted for. There's no reason for a circuit like this to have unsolvable issues with PS filtering. If the 100uF cap is already serving that purpose, try putting a 100R dropping resistor between the cap and the power jack. Some folks also have success putting a smaller cap like .1uF in parallel with the bigger cap to reduce ESR at higher frequencies.

I would like to try this but can you explain exactly where to connect the 100 ohm dropping resistor from and to?  Like from the positive of the 100uF cap to which of the 9V power jack connections?   I've attached a pic showing where the 100uF electrolytic is on the circuit board.


Thanks!

[Keppy]

can you explain exactly where to connect the 100 ohm dropping resistor from and to?  Like from the positive of the 100uF cap to which of the 9V power jack connections?

It's been awhile since I wired one of those jacks, so I'm honestly not sure which wire carries the +9v. It's easy enough to find with a meter, though.


The easiest way to connect the resistor is probably to disconnect the 9v power jack wire at one end (either is fine) and reconnect it through the resistor to the same spot. That won't be as durable of a connection, but you can worry about that after seeing whether it improves the noise.