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Wiring resistor to compressor input

opivy3056

opivy3056

stardust in a light beam
Oct 14, 2004
1,050
449
Spangereid, Norway
#1
Im going to try and fix my McSqueeze's input clipping problem by wiring a 4.7k resistor to the input jack. (the electrician at work is going to solder it for me)

Does anyone know where I could find a diagram showing where the resistor fits into the circuit?

-thanks
 
#2
I've temporarily forgotten, is the McSqueeze a Ross clone or an Orange Squeezer? The various DIY pedal sites have those schematics posted. But essentially, it's just the first resistor in the circuit right off the input jack. Easy to find.
 
#6
Yeah, he should definitely understand. If you look at the schema, you see where Sw1a connects to a line that goes to C1 at one branch, and R1 at the other? I believe you want the new resistor to go directly between Sw1a and those two other points (slightly different from what I said previously). If you connect it directly to the input jack, then it will have an effect on your signal even when you bypass the effect. If you just replace R1 with a larger value, I don't think it will reduce your input gain at all. So really you need to steal some voltage right after the footswitch.

Nifty, or anyone else, am I making sense?
 
#8
Nope, the other one. The one going to the board is "ground", the one going to the switch is "hot" AKA your bass signal. "Sw1a" is where the signal comes back out of the switch and goes into the effect (from switch to board).
 
#9
I don't know if this will help, but here's another way of looking at it.

You want to find the wire that goes from a terminal of the switch to the spot on the board right where C1 and R1 are connected together. If it's a short wire, you might be able to simply replace that wire with the new resistor. If that's not possible you'll have to unsolder the wire and insert the resistor. This might be easiest to do at the switch end of the wire - ie; solder the resistor to the switch terminal.




WARNING: TECH NOTES
You're creating an attenuator (or voltage divider network.) Ignoring C1 and everything after it for a moment, lets look at what's happening.

Code: 
from switch
     o
     |
    .-.new resistor
    | |
    | |
    '-'
     |   ||
     o---||-----
     |   ||
     |     C1
    .-.
    | |R1
    | |
    '-'
     |
     |
    ===
    GND

Your signal is a voltage, voltage across a resistor causes current to flow. Likewise, current through a resistor creates a voltage.

In the original schematic, all your signal (voltage) is applied across one resistor, R1. This means that all the voltage also appears at C1.

In the revised schematic, your signal is applied across two resistors, R1 and the new one. The current flowing through the new resistor causes a voltage to be created across that resistor. This voltage is effectively subtracted from the full signal voltage, leaving a fraction of the full voltage to appear at C1. That fraction happens to be the ratio of the two resistors.

So, without going into how it's created, here's the formula for those playing along at home.

Vx = (Vin x R1) ÷ (R1 + Rnew)

Without plugging in the voltages you can work out the ratio of the resistors which will give you the attenuation "factor" - if you will.

4.7M ÷ (4.7M + 4.7k) = 0.999

Pretty mild, you might want to up the ante, but try it first.
 
#10
After taking the pedal apart I made a more careful analysis of where the wires are going.

From the input jack there are 3 wires.

First goes to the power supply (which im guessing has something to do with having to plug a 1/4 cable to make it turn on)

Second goes to the pot for "level" control.

Third goes to the back of the switch (the switch has 9 wires total running to/from it)

So you're saying the resistor belongs between the input and the switch??

Also, if 4.7k is too mild, what might be more suitable?

-thx
 
#11
The R belongs after the footswitch. You have to find a wire that leaves the footswtich and goes to the board, and makes connection with a resistor and a capacitor. Your new R will essentially replace that wire from the switch to the board.
 
#12
opivy3056 said:
Third goes to the back of the switch (the switch has 9 wires total running to/from it)

So you're saying the resistor belongs between the input and the switch??

Also, if 4.7k is too mild, what might be more suitable?
Click to expand...
The switch has three groups of three connections. You're only interested in one group of three. It will have one wire connected to the input jack, one connected to a different switch terminal, and one going to the circuit board. The new resistor ideally would replace that last wire between the switch and the circuit board.

I only said you might want to increase the 4.7k! If you're going on good advice, stick with it, at least to begin with. Go up one step in the standard resistance values (to 5.6k then 6.8k etc) if you want to experiement. Plug values into that formula in place of the 4.7k to see the difference.
 
#14
You're going to have to do some work of your own, you know. :p Open the box; find the first resistor in the circuit (R1 on the schematic); write down the pattern of colored stripes on that resistor; then Google "resistor color codes". Seriously, it is worth it to you to take all of those steps and figure it out. After you've done all that, check back with us to confirm the answer. :)
 
#16
opivy3056 said:
i e-mailed pedalworx and they said to match the value of the input resistor.

Any idea what the value of that resistor is?
Click to expand...
Isn't it on the schematic that bongo posted?!

Be advised that two identical resistors in the configuration I posted will cut the input signal by 50%. Do you really want to attenuate that much?

Where did the value of 4.7k come from in the first place anyway?
 
#18
Well, I don't know whether they knew what they were talking about, but in light of my calculations, and the fact that 4.7k may NOT be an informed choice, I'd be tempted to look at something bigger.

How bad is the clipping? Is it just noticeable or totally intollerable or somewhere in between?
 
#19
Its only when I dig into the notes. And not REALLY noticeable unless I listen for it. But its definately there. The clipping isnt too harsh (almost sounds like an overdrive pedal).

I pluck pretty hard over the bridge pickup on my jazz, sort of a jaco-esque style.

Ill stop by radioshack on the way home from school tomarrow and grab a different pack of resistors, which value would you (niftydog) reccommend for the problem ive described?
 
#20
I would think you're looking more in the region of 100-500k. Maybe it was meant to be 470k? That'd get you closer to 10% attenuation.

One option would be to buy a 1M trimpot and wire that in, then twiddle and test until you're happy. Remove it then measure the resistance, replace it with the closest standard value resistor.
 

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