too much bass in AMZ Mini Booster Build

[Hav]

Hey all

Built this tiny booster after reading a lot of reviews about its nice clean boost.

http://tagboardeffects.blogspot.co.uk/2013/01/amz-mini-booster.html

Didnt have all the values, so subbed a couple.

End result is a muddy / or bass heavy booster... Could you tell me which part it would more likely to be?

I replaced the NP 3.3uf with a NP 1uf & and 10pf with a 6.8pf ceramic.

Everything else is the same!

Thanks in advance :-)

[thelonious]

If it is working properly and you just don't like the amount of bass it is letting through, you can adjust capacitor values until you like the sound. Specifically you can change the 47n to a 22n or 10n, and/or change the 220n to a 100n.

However, I don't usually hear these called muddy - so there might be the possibility that something else is wrong.

Oh, and the two capacitor values you replaced would not have caused it to be muddy.

[Hav]

oh!

Yes well, its definitely reducing the treble and what sounds like increasing the bass. Definition is disappearing compared to the bypass signal..

Il have to check it ive got all other components right, tried on 2 guitars and getting same problem.

[thelonious]

The first things to check are: 1) That all of your 1M resistors test as 1M, and 2) that your 6.8pF cap tests in the pF range. It won't test as 6.8pF because your meter's test leads are probably higher capacitance than that, but it ought to test as <50pF.

[Hav]

hmm

i checked again with DMM and the two 1Ms to the left are only showing around 400-500k... the 1M on the right is showing pretty much 1M. They are definitly the right value and I definitly checked before I put them in that they were showing correct readings/.. could they be showing this because its all soldered in?

I checked this with the power DISCONNECTED.

Thanks for advice!

[Hav]

just checked with 9v powered in,

the readings of 2 1Ms on the left come up to around 900K... \

[ubersam]

Built this tiny booster after reading a lot of reviews about its nice clean boost.

It is nice, but it isn't exactly clean. There's some clipping going on.

I replaced the NP 3.3uf with a NP 1uf & and 10pf with a 6.8pf ceramic.

Those are fine. The 10pF is just for RF filtering. I would insert a 10K resistor inline with the input cap to improve the RF filtering, maybe raise the 10pF up to 100pF.

i checked again with DMM and the two 1Ms to the left are only showing around 400-500k... could they be showing this because its all soldered in?

Yes.

The 47nF cap and the 1M to ground form a HP filter with the cutoff at around 3Hz (i.e. it's reaaaaly low), everything from that point on up gets boosted. Try dropping the input cap to 10nF or 4.7nF to raise the cutoff to around 15Hz or 33Hz.

[thelonious]

Your resistors are not the problem, then.

+1 to what ubersam said.

Just for kicks, you should try removing that 6.8p cap from the circuit. If it is actually a much higher value (for instance, if it got switched with a 680pF or 6.8nF cap), it could be causing your symptoms. Plus, what ubersam said is right---if you need RF filtering (which you might not), you might as well use a 10K/100p or 4k7/220p combination.

[Hav]

im so sorry but what is RF filtering exactly?

[thelonious]

RF = Radio Frequency.

A resistor and capacitor in this configuration make a lowpass filter (ignore the units kΩ and nF):

which does exactly what it sounds like - allows frequencies lower than a certain cutoff frequency to pass. The values of the resistor and cap determine the cutoff frequency. You can read lots about it and/or try a filter calculator if you want.

RF filters help keep circuits stable and efficient by removing frequencies you don't want to be amplified. The mini booster's lowpass filter has a cap to ground, but no series resistor. It still works because there is always series resistance---cables, your guitar's volume pot when not at max, the output impedance of pickups or previous pedals, etc. Ubersam's suggestion to add a series resistor gives you more control over the cutoff frequency and makes the filter more effective in a number of circumstances. Usually, it's not a big deal not to have one because we mostly care about filtering out radio frequencies, which are so high that nearly any series resistance and cap value will kill them.