AMZ Mosfet Boost weirdness...

[Xavier]

I'm really happy about the sound of this circuits. Gives nice spank to the sound when at minimum settings and BIG boost when maxxed, very clean sounding.

- I added the 100k pull down resistor to ground, at the end of the circuit. Still popping (loud pop !!)
- How can it be than the boost only happens at the last 75-80% of the pot, BOTH WITH 5KA and 5KB pots? I thought I was using a linear pot, but then I used an audio taper pot and the effect was the same. Pretty weird.....

EDIT: Search function is my friend . I have just found out that a reverse taper pot (5kC) would help, and that has led me to the "Secret life of pots". Looks like using a 30K resistor would do the trick, but I'm unsure how to do it.

www.pisotones.com method for doing this. Example.

I need a 5KC pot. To achieve this you need a linear pot 5x the value you want to achieve. This means 25KB in this case. The tapering resistor needs to be the value of the pot you need ,plus 20% of its value (5K + 20% of 5, that is 1= 6K). So with a 25Kb pot and a 6k resistor you get a 5kC.

In the AMZ Boost, volume lugs 2 and 3 are bridged, so can anyone tell me how should I solder the taper resistor in the pot?

[bioroids]

Hi!

You should put the resistor between both extremes of the pot. The middle lug will be connected to one of the extremes too.

I dont know how much "reverse log behaviour" you are gonna get with the tapering resistor. The good old way is to use a log taper pot, but wired backwards (the boost will be at full in the "minimun" position).

Or get a reverse log at Small Bear

Luck

Miguel

[Xavier]

Fixed !!!!

Found a 10KC pot, just wired a 10K resistor across the lugs and it works !!. Now I know what anti-log pots are for 

Anyway, I have a hole in the enclosure (used it for another project before the booster) and there's a DPDT on it. I've been messing with some capacitor values just to see if I could use it as a pseudo treble booster, but lowering the cap value only seems to have an effect upon the overall volume and nothing else. Any suggestion?

[petemoore]

  ....you're messing with the input cap?..try the output cap.
 

[bioroids]

Maybe you are not lowering the input cap enough, you can go down, maybe to 4n7 or 2n2 for really low cut. You will loose some level and a good deal of fuzz when yuo cut the lows, but it has good sounds available.

Or better, take the DPDT out and put a pot Joe Gagan style for controlling the exact amount of bass you want to cut. I'm not sure where to find a schem, but a search for Easy Face, Brontoboost or Gagan should make it appear.

Messing with the out cap is good too, but cutting lows before the circuit yields more interesting sounds to me.

Luck!

Miguel

[Xavier]

  ....you're messing with the input cap?..
 

well, not really, I have the DPDT before the input cap. Actually the cap I'm messing around with is an added cap, so it's input-toggle (with additional cap)- input cap.

Maybe the value is actually too low (120pF). I have seen some treble boosters using a 500pF input cap and that's been the first value, but there was little difference, so I tried one even smaller. Doesn't seem to cut bass but the whole output...... I can imagine 4n7 or 2n2 will have very little (if noticeable) effect

[bioroids]

Are you adding the cap in parallel or in series with the original?

[Xavier]

Are you adding the cap in parallel or in series with the original?

In series (me thinks). pins 1-2 bridged, pin 3 input, pin 4 output (to input cap), pin 5-6 have the added capacitor across. That is right, isn't it?

[bioroids]

It seems you are adding it in series (i'm not sure how the numbers correspond to the pins though). In that case, 500pf or 100pf is way too low, you will loose almost all signal except really high treble. I suggest tryin a 4n7 and see what happens.

It is better if you replace the input cap (big) for the small one (say 4n7 if you like the sound) and then use a SPST to switch in parallel the original cap to recover the lows. The caps in parallel will add, so it would behave as the original circuit.

Luck

Miguel

[Xavier]

I'll try thanks !!!!