How can I add a tone control to an AMZ Mini Booster?

[steveyraff]

Hey guys,

I was going to just follow the vero for the AMZ booster as shown here: http://tagboardeffects.blogspot.co.uk/2013/01/amz-mini-booster.html

But then I read about a few mods here : http://www.muzique.com/tech/miniboo1.htm

Now I am wondering how I might be able to combine the two? I'd love to add the tone control but I am a noob and a bit lost as to how I'd incorporate it into that tag board?

I'd also like to add the double LED fat switch mod.

Any help tips highly welcomed,

Regards,
Steve.

[Mark Hammer]

The AMZ Mini-booster page shows how to add a simple treble cut control that is essentially identical to the sort of tone control you'd find in a guitar  It doesn't require any change to the tagboard layout.  Just run a wire from the input lug of the volume pot to the tone control pot, then to the tone cap, then to ground.  The drawing shows it going to the cap first, but the order makes no difference.  If you solder the cap from one of the tone pot lugs to the back of the pot, you can just connect a wire from the back of that pot to ground.  That way, there are only two wire connections required.

Another possible mod to consider, which is alluded to on Jack's page, is changing the frequency balance of the boost.  C3 "bypasses" R3, for whatever portion of the audio/AC spectrum passes through C3.  Since that provides a lower-impedance path to ground for that AC, it gets boosted more.  As shown, the value of C3 provides boost to pretty much the entire guitar signal.  If C3's value is made smaller/lower, then the boost is applied less to the low frequencies, and more to the mids and highs.  As Jack notes, you could make it more of a treble booster by using a smaller value for C3, as well as for C4.

Here's a different mod that could provide variable low-end boost.  It's stolen from the Fuzz Face.

If you look at the Fuzz Face schematic, you see a 1K pot in the same location as R3 is for the Mini-Booster.  The same drawing shows a 20uf cap approximately where C3 is in the circuit, except that it is not connected directly to the transistor, but to the wiper of the pot.  The end-to-end resistance of the pot, connecting the transistor to ground, is 1k, but the resistance between the cap and the transistor changes as you rotate the pot.

So, let's replace R3 with a 1K linear pot, replace C3 on the board with the suggested 0.1uf cap, and connect a 10uf cap between the wiper of the pot, and ground, in exactly the same orientation as the Fuzz Face diagram shows.  What will that give you?  Our new added pot will provide a constant treble boost (which you can roll off with the "Tone" control), but an additional adjustable mid and bass boost.  When the pot is rotated such that the 10uf cap is directly connected to the FET, you get full-range boost.  Rotate it the other way and you get less and less full-range boost, but the treble boost stays in place.  So, you can get full range boost, and roll off your treble to taste, or you can keep the treble and provide less boost to the bass and mids, if you feel like it, and variations between.

How do you implement it, physically?  Once you pull R3 from the tagboard, you simply run a pair of wires out to the outside lugs of the 1K pot.    Since one of those wires will be connected to ground, you simply solder the 10uf cap between the wiper (where the + end of the cap goes) and the ground side of the pot.

Pretty flexible circuit, huh?

[steveyraff]

The AMZ Mini-booster page shows how to add a simple treble cut control that is essentially identical to the sort of tone control you'd find in a guitar  It doesn't require any change to the tagboard layout.  Just run a wire from the input lug of the volume pot to the tone control pot, then to the tone cap, then to ground.  The drawing shows it going to the cap first, but the order makes no difference.  If you solder the cap from one of the tone pot lugs to the back of the pot, you can just connect a wire from the back of that pot to ground.  That way, there are only two wire connections required.

Another possible mod to consider, which is alluded to on Jack's page, is changing the frequency balance of the boost.  C3 "bypasses" R3, for whatever portion of the audio/AC spectrum passes through C3.  Since that provides a lower-impedance path to ground for that AC, it gets boosted more.  As shown, the value of C3 provides boost to pretty much the entire guitar signal.  If C3's value is made smaller/lower, then the boost is applied less to the low frequencies, and more to the mids and highs.  As Jack notes, you could make it more of a treble booster by using a smaller value for C3, as well as for C4.

Here's a different mod that could provide variable low-end boost.  It's stolen from the Fuzz Face.

If you look at the Fuzz Face schematic, you see a 1K pot in the same location as R3 is for the Mini-Booster.  The same drawing shows a 20uf cap approximately where C3 is in the circuit, except that it is not connected directly to the transistor, but to the wiper of the pot.  The end-to-end resistance of the pot, connecting the transistor to ground, is 1k, but the resistance between the cap and the transistor changes as you rotate the pot.

So, let's replace R3 with a 1K linear pot, replace C3 on the board with the suggested 0.1uf cap, and connect a 10uf cap between the wiper of the pot, and ground, in exactly the same orientation as the Fuzz Face diagram shows.  What will that give you?  Our new added pot will provide a constant treble boost (which you can roll off with the "Tone" control), but an additional adjustable mid and bass boost.  When the pot is rotated such that the 10uf cap is directly connected to the FET, you get full-range boost.  Rotate it the other way and you get less and less full-range boost, but the treble boost stays in place.  So, you can get full range boost, and roll off your treble to taste, or you can keep the treble and provide less boost to the bass and mids, if you feel like it, and variations between.

How do you implement it, physically?  Once you pull R3 from the tagboard, you simply run a pair of wires out to the outside lugs of the 1K pot.    Since one of those wires will be connected to ground, you simply solder the 10uf cap between the wiper (where the + end of the cap goes) and the ground side of the pot.

Pretty flexible circuit, huh?

Wow!

Thank you so much! What a detailed response. I think you've gave me just about all the info I could possibly need to start a new project with this! Cool!

One thing that is slightly confusing me - the double LED 'Fat Switch' mod. I understand this works by placing the LED between the incoming 9V supply and the tagboard itself? So the incoming voltage is dropped depending on how many LED's it is being passed through on its way to the board, thus reducing headroom. One thing that confuses me about this, is shouldnt there also be some additional resisters in place when the incoming supply is being routed through the extra one or two LEDs? I thought without resisters it would burn out the LED's?

I may just be very confused in my noob mind lol Sorry.

[Mark Hammer]

Wow!  Thank you so much! What a detailed response. I think you've gave me just about all the info I could possibly need to start a new project with this! Cool!

One thing that is slightly confusing me - the double LED 'Fat Switch' mod. I understand this works by placing the LED between the incoming 9V supply and the tagboard itself? So the incoming voltage is dropped depending on how many LED's it is being passed through on its way to the board, thus reducing headroom. One thing that confuses me about this, is shouldnt there also be some additional resisters in place when the incoming supply is being routed through the extra one or two LEDs? I thought without resisters it would burn out the LED's?

I may just be very confused in my noob mind lol Sorry.

1) You're most welcome.  Part of what gives this place the ambiance and "culture" it has is responses to queries that help to empower newbies.  They nearly always turn into someone who helps others down the road.

2) If the power supply only has LEDs in its path, or is supplying current in excess of what the LED/s can safely pass without burning up, then yes, you are entirely correct; there will be a need for some sort of series resistance to limit the current passing through the LEDs.  But in this case, the current is being drawn by the booster circuit, and that circuit does not require enough current to exceed what the LEDs can withstand.  In a sense, the circuit is filling the role of the series resistor your gut says ought to be there.  So, your instincts are correct (good on ya!), but you were misdirected by the presence of a circuit, when you were looking for a resistor.

3) Jack's use of blue LEDs is simply a convenience because of how much a single LED drops the voltage supplied.  Pretty much any string of diodes can be used to obtain a desired voltage drop.  So, one could, for instance, replace either or each LED with three 1N400x series diodes, in series.  Or, for example, if you wanted to get fancy, a person could use a rotary switch to introduce progressive half-volt drops in supply voltage, using 1N4148s, or whatever.  The use of a pair of LEDs introduces big-enough stepwise differences in supply voltage in a simple and convenient way.  A person could choose to get even simpler, or more complicated, without compromising the overall circuit.

4) When LEDs are used simply as diodes, there may or may not be enough current passing through them to make them light up in a visible way.  They don't need to light up to serve as diodes, though.  Nevertheless, if you can find some superbright LEDs (>3000mcd rating, requiring less current for the same degree of ilumination), it is quite possible the small amount of current drawn by the booster circuit will be enough to make the LEDs light up a bit, in which case mounting them on the chassis can lend a decorative element if you want.

[steveyraff]

4) Nevertheless, if you can find some superbright LEDs (>3000mcd rating, requiring less current for the same degree of ilumination), it is quite possible the small amount of current drawn by the booster circuit will be enough to make the LEDs light up a bit, in which case mounting them on the chassis can lend a decorative element if you want.

Ooooh, I am SO doing this! That sounds cool! Thank you so much man. I can't wait to get started with this one. I'm sure I will have a question or two when I take into building it, but this is all great info to get me started.

Cheers!