I have just completed my first electronic project since high scholl 25 years ago. It's a AMZ MOSFET booster. It works but has a few issues.
1- There is a buzz when you hit a note, even with the gain all the way off. It is a very unmusical buzz that really ruins the tone.
2-Gain control is full on when turned counterclockwise - I may have wired it backwards
3-The DPDT true bipass switch pops when engaged. What capacitor and where do I put it to alleviate this issue.
4-How much gain am I supposed to get? While it does boost the volume considerably in a very clean fashion (buzz aside), I read that it shoud be up to a 35 db gain. Mine seems to more than double the amps volume but I thought 35db would be even triple.
I used an NTE 490 in place of a BS 170 and a 68K resistor at R1 instead of a 62K resistor (couldn't find one).
I'm no expert so if someone else chimes in by all means listen to them. Ok let's see here ...
1) You may not have biased the fet correctly. There are instructions on the AMZ page on how to do this. I hooked up a 100K pot in place of the 62K resistor and adjusted until my voltage read the correct value. I then measured the pot and replaced it with the nearest value resistor. It's easier if you use sockets to do this.
2) I think you answered your own question - sounds like the pot is wired backwards
3) Switch popping is very common and nothing to worry about. Place 2.2M resistor to ground on the input. For an example check out the Fuzz Central page - most (or all?) of Phillips pedals use this technique.
4) The Mosfet Boost is a CLEAN boost. It's made to boost volume. It sounds like you may be looking for a little "dirt" on the boost. Try the LPB-2 Electro Harmonix Boost if that is what you are looking for or send in for the AMZ CD.
I hope this helps. Good luck :D
AL
I have some trim pots. Could I use one of these? How do you wire one in?
something around between say 10k and 100k.
to use a pot as a V/R [raviable resistor] use the wiper [center lug] and an outside lug.
Look at Aron Nelsong Rocket schematic for an example of how this resistor goes. the Rocket is a Bipolar affair, just imagine when looking, for the purposes of wiring a trimpot, that the Drain gate and Source...are like the Colletor, base and Emitter....
Or use a socket for that resistor, use a pot as a Variable Resistor [connect the V/R where the leads of that resistor would go] to find the resistance that sets up bias on a given transistor...connect the battery, attach the black DMM lead to ground and the red one to the drain...changing the value of the drain resistro makes the Drain sit at different voltages...adjust the resistor till there's a reading of between 4.5v and 5V [approximately]...
for the sake of my fingers I'll be blunt...if that Doesn't work there's a wiring or R value error in the circuit, or something... try that for now...if you have questions, post.
Well, I tried my booster with my tube amp and absolutely no buzz. I then tried it again with my Cube 30 and there was a little more noise but not the annoying buzz I first heard. Could it be from an outside source. Very weird. I have noticed that the pot I used is noisy and cheap. The booster does a great job of pushing my tube amp into a sweet overdrive.
Is the noise a problem? I'm not familiar with the cube 30 - is that a solid state or tube or (gasp) digital? If you are worried about noise - what is the circuit housed in? If you're using a plastic box you're open to noise introduction.
AL
Quote from: ALIs the noise a problem? I'm not familiar with the cube 30 - is that a solid state or tube or (gasp) digital? If you are worried about noise - what is the circuit housed in? If you're using a plastic box you're open to noise introduction.
AL
The Cube 30 is a SS amp with - yes - digital amp models. heh, it's a great practise amp. I used a Hammond 1590 BB aluminum box.
I'm not sure how the SS amp will react to getting hit with so much signal (35dB boost is alot!) - that could be the source of the buzz, as well as the reason the amp is not getting as loud as you think it should, its hitting a hard limit, and the distortion created is unpleasant.
Actually, I've come to the conclusion that the sound is dirty AC power boosted by the box. It comes and goes and last night I couldn't hear it. The bottom line is that aside from a cheap pot wired backwards, the box sounds great with my tube amp and I am given confidence to try my next project which will be a Blue Magic distortion or a compressor.