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Topic starter
13/05/2006 8:07 am
School is out, and I had been sitting around doing nothing so I decided to try and make a simple booster for solos to pass time. The schematic I'm using is a simple npn transistor gain based off of the Brian May Booster pictured here 
.
I've added a switch, and instead of a battery I'm using a power supply that I have rigged up with RCA cables (I use this same setup on my other pedals, I modded them).
Problem:
I think there is a problem with how I have set up my VCC/+9 volt supply. I connected the positive end to where the positive end of the battery terminal is on the schematic. Now if I leave the ground of my supply unconnected I get a perfect clean when in non-distortion mode, but when I switch over I get no output (this makes me believe I'm not supplying my transistor correctly, probably caused by not having my ground connected). If I connect the ground of my supply to the ground bus I use for my guitar signal, I get nothing if I run in clean mode. But I get the signal boost when i turn it on distortion mode with a bad hum (What you get when your ground is messed up).
What the heck is going on????
Note this is the first time I've connected stuff on my own to guitar jacks, so I might have somethign messed up there although I did a test run using just a clean signal across them before anything else and got it working.
How I implemented a switch in in case that could be the problem:
I bought an On/Off Push/Pull switch for stepping on. Since it isn't a double throw, I came up with the idea to hook up both my transistor circuit input and my guitar's signal to one terminal of the switch. I connected the output of my circuit to the other terminal. That way when it is an open circuit, my guitar signal is forced to go through the the transistor circuit before it hits the output. When it is a closed circuit it will use theory of path of least resistance and skip the transistor circuit and go straight to the ouput. (at least this is my thinking)
Thanks,
Jameson
plz im a noob
13/05/2006 8:41 am
My advice is to remove all mods until you have the basic design working properly. Once you have that, you know that any problems are with your mods and not your implementation of the original.
I've been trying to get a treble booster working, on and off for ages, and it was only last week that I noticed that the diagram was wrong - they'd got the transistor connections the wrong way round on the perfboard layout.
I started with nothing - and I've still got most of it left.
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13/05/2006 3:22 pm
Sounds like you have a short or a voltage leak somewhere.
Take your multi-meter and start at your input and check your values at each point in the circuit.
It sucks, but it's guaranteed to find the problem.
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Topic starter
16/05/2006 3:29 am
I couldn't figure it out. I got real mad so i ripped up the circuit and made a simple four resistor bias i designed so that i knew what the voltages were supposed to be everywhere...same problem. I get the voltages I'm supposed to get and the transistor is in the active region. I haven't a clue.
plz im a noob
16/05/2006 4:59 pm
Umm, the schematic shows the bottom of the 9V is tied to the input jack. I don't think that is correct. The bottom of the 9V (or power supply) should go to ground/common.
Laz
Topic starter
16/05/2006 10:29 pm
ya, I was using a power supply with it (tied to ground) instead of the battery. There is something wrong with how I have my supply set up bc when I use the lab's power supply I don't get a hum. Going to try and figure it out with my professor next week.
Thanks for all the input fellas. When I get a fix I will post it incase anyone has the same problem for future reference.
plz im a noob
17/05/2006 1:08 am
Umm, the schematic shows the bottom of the 9V is tied to the input jack. I don't think that is correct. The bottom of the 9V (or power supply) should go to ground/common.
Actually, that's a pretty standard method of powering effects circuits. The input jack is a stereo (3-conductor) jack. When you insert the guitar cable, it makes the connection from the ring (where the - of the 9V battery is connected) to the sleeve that's the ground that's connected to the rest of the circuit. When the cable is not in the jack, the connection isn't made, so no current flows. So when you wire it as shown in that schematic, the act of plugging into the effect basically turns it on. If you don't wire it this way, the effect will drain the battery while you are not plugged into it. I've built a couple of pedals over the past few weeks using this sort of power circuit. It works nicely.
@Jameson: I'm having a hard time picturing what you're doing for the switching, and it's not shown in that schematic... What kind of switch are you using? I can't think of any working switching method involving an SPST... You might want to remove whatever switching you have, and try running straight through the effect just to isolate if the effect itself is broken, or if it's the the switching that's broken.
TZ
17/05/2006 2:42 am
ya, I was using a power supply with it (tied to ground) instead of the battery. There is something wrong with how I have my supply set up bc when I use the lab's power supply I don't get a hum. Going to try and figure it out with my professor next week.
You have some kind of grounding issue with the way the battery is wired.
The bench supply has it's own ground, or may be isolated (one of those two).
You might want to review your design. It looks almost like a Dallas Rangemaster (Beano).
Check out the great article on RG Keen's site http://www.geofex.com/
Click on "FX Projects" then "Dallas Rangemaster" then "How to build one"
I'm pretty certain they redesigned the circuit to avoid the problems you are experiencing.
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