Author Topic: Help Please  (Read 9711 times)

hiimbryan

Help Please
« on: August 13, 2009, 09:22:45 PM »
Hi, I'm new to making guitar effects pedals and this beginner project is my first attempt.

I don't have a 3PDT so I used a DPDT without an LED. I put it all together, and the bypass works, but when the effect is engaged I get nothing.

I used an audio probe and sound comes out of the board whether it's bypassed or not!

Any ideas?

Thanks.

caspercody

Re: Help Please
« Reply #1 on: August 13, 2009, 09:32:13 PM »
how did you wire the DPDT?

When looking at the switch, from the back, the bottom two terminals should be wired together. One side of the middle terminal goes to the tip of the input jack. The other middle terminal goes to the tip of the output jack. On the top terminals, the side you have going to the input jack, goes to the input on the board. And the top terminal side you have going to the out put jack, goes to the output on the board.

hiimbryan

Re: Help Please
« Reply #2 on: August 13, 2009, 11:05:23 PM »
Yup, i wired it like that. And the bypass works fine.

I disconnected the I/O wires to the circuit board and the switch seems to be working fine.

Does this mean there's a short on my board?

Edit: Okay, I checked the voltage difference between various points and ground and there seems to be a voltage everywhere until I get to the output capacitor. Does this mean the capacitor's blown?
« Last Edit: August 13, 2009, 11:53:06 PM by hiimbryan »

caspercody

Re: Help Please
« Reply #3 on: August 14, 2009, 09:31:00 AM »
What project are you building?

hiimbryan

Re: Help Please
« Reply #4 on: August 14, 2009, 11:30:55 AM »
Just the NPN boost. The beginner project.

hiimbryan

Re: Help Please
« Reply #5 on: August 14, 2009, 02:03:09 PM »
Okay, so after messing with it for a while, I hooked it up again.

The signal now gets through to my amplifier, but it is very low. I have to turn my amp and guitar all the way up to hear anything. This works no matter which way the transistor's oriented.

Help  ???

aron

Re: Help Please
« Reply #6 on: August 14, 2009, 03:51:10 PM »
You need to put the black probe on ground and the red on the transistor pins and report the voltages.

hiimbryan

Re: Help Please
« Reply #7 on: August 14, 2009, 04:05:43 PM »
Emitter: -2.70 V
Base: -2.75 V
Collector: -8.70 V

The Emitter's voltage difference slowly drops about 0.01 V per second. I don't know if that's something I'm doing wrong or what.

aron

Re: Help Please
« Reply #8 on: August 14, 2009, 04:14:36 PM »
I'm assuming you had the red on ground and not the black, otherwise your batter is reversed. Can you double check?

hiimbryan

Re: Help Please
« Reply #9 on: August 14, 2009, 05:34:35 PM »
Yes sorry, they were plugged into my DMM incorrectly, those voltages are positive now  :icon_razz:

aron

Re: Help Please
« Reply #10 on: August 14, 2009, 06:23:55 PM »
>Emitter: -2.70 V
Base: -2.75 V

Check your transistor orientation and your wiring around the base and emitter. What transistor are you using?

hiimbryan

Re: Help Please
« Reply #11 on: August 14, 2009, 06:27:48 PM »
I'm using an NTE 123AP Transistor. The diagram was vague as to which lead was the emitter and which was the collector, so I'm only about 80% sure it's oriented correctly. Is there an easy way  to find  out which lead is which?

aron


aron

Re: Help Please
« Reply #13 on: August 14, 2009, 07:56:04 PM »

hiimbryan

Re: Help Please
« Reply #14 on: August 14, 2009, 08:18:49 PM »
Thanks for the info  :)

I checked out all of those and  still no sound  :(

Now I'm checking out the pot. I'll post the resistance between the lugs of the pot, does this sound right?

Red on ground; Black on Input: -5.09 k
Black on ground; Red on input: no reading

Red on input; Black on wiper: no reading
Black on input; Red on wiper: between -5.09 k and -4.77 k (varies with knob)

Red on ground; Black on wiper: between 0 k and 5.4 k (varies with knob)
Black on ground; Red on wiper: same as above.

I don't think I really understand which part of the circuit the signal is going through. Does it go in the base of the transistor, out the emitter, across the 22uF cap, then across the 100k resistor, or what?
« Last Edit: August 14, 2009, 08:59:09 PM by hiimbryan »

aron

Re: Help Please
« Reply #15 on: August 15, 2009, 01:01:58 PM »
I thnk you have some type of wiring mistake on the board. Can you post a picture of your board?

hiimbryan

Re: Help Please
« Reply #16 on: August 15, 2009, 04:01:49 PM »
Okay I'll post a picture in a little bit. Thanks so much for all the help by the way.

I think the problem is my IC socket I'm using for the transistor. It seems to work when I mess with the transistor a little. Should I just try soldering the transistor straight in there?

aron

Re: Help Please
« Reply #17 on: August 15, 2009, 09:17:44 PM »
You could do that.

hiimbryan

Re: Help Please
« Reply #18 on: August 18, 2009, 08:25:34 PM »
So I put the circuit together on a prototyping board and same problem.. All the wiring, capacitors and resistors check out with my DMM. Unfortunately when I audioprobe I get no signal out of the collector, which is where the signal is supposed to come out amplified correct?

My transistor is oriented correctly. I've tried 2 transistors, NTE 123AP and 2N3904.

Also, will the circuit work if I were to take the pot out, just at max volume? For troubleshooting purposes.
« Last Edit: August 18, 2009, 09:23:01 PM by hiimbryan »

hiimbryan

Re: Help Please
« Reply #19 on: August 19, 2009, 02:31:32 AM »
Okay, so in order to test my pot, I rigged up a voltage divider circuit with a 3k and 2k resistor, and a 47uF electrolytic cap, and it works! Wooh!

Its annoying how long it took for a simple fix, but I learned alot through debugging this thing. Thanks for the help Aron.