SOLVED Unity volume question for Arkaim (Megalith) owners

[Dan M]

My pedal is very loud. Unity is with the IN and OUT barely cracked open. If I put them at 9 o’clock, the volume increase launches me into the next room.

Tone wise, it sounds correct. It is just ridiculously loud.

Does anyone have a same or different experience?

**Edit: The picture below is unity volume, where 7 o’clock would be OFF, you can see the in and out controls are barely bumped open.

Dan

 

[giovanni]

I see that the output pot has a linear taper (B100K). Maybe you can try using an audio taper instead (A100K) and see what happens?

 

[Feral Feline]

C100k would be better than A100k if the volume is crazy right off the bat.

I've just recently got the PCB so haven't built it up yet, but I've heard it's a loud circuit.

However, it sounds like perhaps you've got an incorrect resistor somewhere or something — loud is good, but not when it's bunched up in the first 1/10 of pot travel.

 

[giovanni]

Why C100K? Reverse log means more resistance at the beginning of the pot run no? Which for the volume pot means more volume. Am I reading it backwards?

 

[Dan M]

Excellent points, thank you both.

It’s a fairly small build, I’ll double check the resistor codes. (I’ll admit I’ve misplaced a 4.7 for a 47 or a 470 in the past )

 

[Dan M]

Looking at the circuit, I’m wondering if the input would also be better as a linear or log instead of a C1M, as it’s pretty sensitive also.

BUT, I agree the first step is double check the rest of the circuit values before I start changing things. (And I don’t have any of the pots in stock right now)

 

[Feral Feline]

Why C100K? Reverse log means more resistance at the beginning of the pot run no? Which for the volume pot means more volume. Am I reading it backwards?

My understanding, after reading RG Keen's "The Secret Life of Pots", is the A-taper spreads out the control at the top end of the dial — this would mean that the bottom end is more or less the same as a B-taper.

C-taper is the opposite of A-taper, and spreads the control at the bottom end, ie it will take more turning of the knob before you get any resultant action.

 

[giovanni]

From that graph I read the opposite: when the rotation is at 50%, the log taper gives you 10% of the resistance while reverse log gives you 90%. Since the volume pot is a voltage divider, the smaller the resistance, the lower the voltage and thus volume. So my hunch is that the log taper will give you lower volume for the first part of the run, which is what’s needed here. Maybe somebody else can confirm since I’ve never actually tried it!

 

[Feral Feline]

How I'm looking at it is that if you've got way too much volume between 7-o'clock (0) and 8-o'clock with the B-taper, the A-Taper offers even less change at that end of the dial, it's still going to be "touchy" until you get to the mid-way mark where it starts to spread out. Look at the chart again, C-Taper does very little in its last bit of rotation, all the control is in the first half of rotation.

More resistance on a volume pot = less loud, as more of the signal is being dumped to ground. Less resistance means more of the signal is allowed through to the output = louder.

Gain pot would be a different story, for example in something with a feedback loop such as in a Tube-Screamer, where increasing resistance gives you more gain.



That's my view, myopic or not, I don't know...

Try this: offboard wire the volume pot, put a 100k resistor between the board and the input (lug 3) of the volume pot, whatever taper, 100k-ohms — with the extra 100k in series you have a 200k-max pot with a minimum of 100k. Fire up your build, set the volume where you like. Now jumper the 100k resistor... does your volume increase or decrease?

 

[giovanni]

I think your logic is correct but I am not convinced your assumption is (no offense!): more resistance on the volume pot does not give you less volume but more, because the voltage is proportional to the voltage divider established by the pot. Say the resistance between lugs 1 and 2 is R2 and the resistance between lugs 2 and 3 is R1. When the output voltage is taken between lugs 1 and 2, the voltage is proportional to R2/(R1+R2) where R2 is zero with the pot all the way CCW (no signal), and R1 is zero with the pot all the way CW (all the signal passes through). So if you want less volume for more of the run of the pot, you want R2 to be smaller when, say at 12 o'clock (compared to a linear pot). The log pot gives you exactly that, while the reverse log gives you the opposite. I measured a 100K pot and found 0 ohm between lugs 1 and 2 when all the way CCW; about 20Kohm when at 12 o'clock and about 100Kohm when all the way CW, which I believe is consistent with the graph above and with my interpretation.
Does that make sense? LMK if I am totally messing this up

 

[Feral Feline]

No offense taken, quite the opposite.

BOTH your posts (#8 & #10 above) make sense. I stated in another thread just a while ago that I can never figure out which way a pot will do what it does until it's physically in circuit. — I'm hoping to learn something here and better understand how these things work! My breadboards are packed away, or I'd try this out.

I'm still thinking if you've got a finite amount of volume that is dumped into the circuit straight away at 7-Oclock, then the A-taper (looking at Keen's graph) offers very little control over that volume in the first half of its rotation (indeed even less control than the linear B-taper's first half). C-taper offers all of its control in the first half of rotation, as shown in the graph.

Whatever pot taper you use — A/B/C/W/other — the overall amount of volume doesn't change, just the way it's dealt with differs.

 

[Dan M]

Well, I waited until I had a larger tayda order ready and then added some pots.

I swapped the output from B100k to A100k and the input from C1M to B1M.

In both cases I now have more control in the first half of rotation, which makes sense.

I don’t think anything was wrong with the pedal. I’m guessing it was designed to kick hard and smash the front of your amp. Which it will still do with the knobs cranked. So I guess this is really a modification as opposed to a repair.

It’s a sweet pedal.

 

[Feral Feline]

Thanks for the follow up!

Looks like I had it ack-basswards; @giovanni, you were right on the money.


I need to breadboard this before I forget to do so.
Hurry up breadboards, arrive already!

 

[giovanni]

Awesome! Glad it worked.