I blew a transistor, is this what I did wrong?

[Noplasticrobots]

I have a circuit I'm working on for this month's FX-Ex. Without divulging too much information I'm wondering if you can tell me what I did wrong.

I have a brand new 9v battery measuring 8.96v and the circuit on my breadboard. The circuit uses trannies in series. One tranny has a diode connected to it's connector from +9v with the negative side to the tranny. I've been using this circuit for quite some time with no problem, but the old battery was measuring 6.58v.

Yesterday I plugged a cord into my amp's input and the other end accidentally into the circuit's output. I heard a pop and some smoke come from the first transistor or input cap (it happened so quick I couldn't tell). I plugged it back in to see what went wrong and found the diode connected to the tranny from +9v was getting warm. Did plugging the cord into the circuit's output cause the blow, or is the brand new battery causing the blow? The diode is a 1N4001 and is rated for more voltage than 9v! Any ideas?

[Noplasticrobots]

Edit to the above post, the diode is connected to a Collector, not connector.

Ok, so I was able to sit down with the circuit yesterday and I installed new parts and plugged everything in right. I still got the diode overheating. The problem is, without this diode, the circuit is completely different.

I'm looking at the datasheet and I can't find the voltage rating for it but I know it can handle more than 9v!

So my question is if I put a resistor in series witht he diode to keep the voltage regulated, will this prevent my problem (I'm away fromt he breadboard right now)?

[Paul Perry (Frostwave)]

I can't say much without seeing a schematic.
BUT, here's an idea..... if you look at how a transistor is drawn, it looks like two diodes.. well, it behaves like two diodes as well. And if you happen to arrange things so that it is possible for unlimited current to run thru one of these diodes (possibly by an external diode) then, it will fry.
Or, possibly, your output jack is wired so that you momentarily short something out when you use it, I don't know.

[Ge_Whiz]

The voltage spec for the 1N4001 is a reverse-bias voltage - hardly any current will be flowing. Unfortunately, from your description, it would appear that you have the diode forward-biased, when it can pass up to one amp - more than enough to blow your transistor.

[GibsonGM]

I'm with Ge Whiz....I doubt the diode gives enough current protection...try putting a 10k pot in series with it, set to max resistance first, then hook everything up & dial in what sounds good.   Maybe also add a 100 ohm resistor before or after the pot to make sure you can at least limit current to 90mA (see tranny sheet for max current rating, you may need to go higher on the resistance).   The transistor may be drawing way more current than it can handle, and is running away & destroying itself.   Just a quick guess.

Of course, all this assumes there's no short at the output or other problems!

[Noplasticrobots]

Thanks for the suggestions! There's no short at the output, (or anywhere else for that matter) so I'll give that pot trick a try. Thanks again!

[GibsonGM]

Anytime, Noplastic...asking questions helps us all!    Just remember that the current source feeding a BJT is generally on the collector...something has to be there to provide the proper collector current for the BJT to function properly, so the diode alone isn't enough - it has to be 'set' with a resistor.   Took me a lot of net searching to understand biasing and so on, but it was worth the effort.  I'm still no pro, but the knowledge does help in setting up boosters or debugging.   Is this for a clipping project? You can still parallel a diode from base to collector in many cases, as long as it's not carrying current (i.e., the current in it must be regulated before entering the diode).  See the Big Muff for an example. 

Another thing I always check for before plugging a new effect into an amp is the presence of DC at the output...can cause weird problems down the line (porking your amp being one of them...). 

[Noplasticrobots]

Nice tips thanks Gibson! How would I check for DC at the output with my multimeter? Set it to measure DC voltage and see if I'm reading any?