0.047 cap question

[gareth]

And it's not about how to remove it for once.

Anyone know precisely what frequencies/amplitude that the cap worked at/on specifically ?

[Seans]

That's the tone cap, or did you mean the .0047 treble pup cap. A friend did draw the frequencies involved in this cap for me, maybe some time digging them out, although I'm sure you'll get answer before that.

[gareth]

That's the tone cap, or did you mean the .0047 treble pup cap. A friend did draw the frequencies involved in this cap for me, maybe some time digging them out, although I'm sure you'll get answer before that.

I did indeed mean that

[cassius987]

I have looked at what it does on an audio spectrum before (GarageBand's "EQ Analyzer" feature). I think I remember a steady continuous drop starting at 80-100 Hz but I'll check tonight. Remember that our ears really hear the low E more as 80 Hz than 40 Hz; etc.

I used to use the bridge pickup with the cap soloed on a jazz gig with my 4003FL and no one ever looked at me funny--it sounded quite good. But I had to increase the gain. It made getting each rapid-fire note of "Spain" to cut through a lot easier. I think my bandmates really liked the increased articulation. For recording I used the neck pickup soloed, but live it was too boom-y for most of the coffeehouses (etc.) that we played at.

If you used a 0.047 cap instead the cut would start at around 10x lower frequency... so low that it would not register in the signal but the pickups still would not interact. Good if you're a fan of that mid-rangey, non-comb filtered sound. But this is not compatible with an RWRP mod.

[cassius987]

Correction, the dip starts at about 200 Hz.

[songdog]

To a first approximation, the frequency should be determined by the capacitor value and the value of the volume pot. So it will vary in different configurations: 250K or 330K volume pots, and mono (where both volume pots are connected) or Ric-o-sound output (where the two pickups are isolated). f = 1 / (2 * pi * R * C).

In this simplistic model 200 Hz is about right, assuming mono outputs and 330K volume controls. It would be around 270 Hz with 250K volume controls. Cut those numbers by half for Ric-o-sound (only a single pot loading the circuit).

This totally neglects the effect of the neck pickup in the mono configuration, though, and also leaves out the complex impedance of the bridge pickup, treating it as a simple voltage source. Still, I think it's a useful approximation.

[cassius987]

Good point Bill, and I will add that my test bass was my 4003FL with a modern stock harness and modern Hi-Gains. To measure the cut I soloed the bridge pickup but it was mono output so still loaded down. Using your formula I calculate 205 Hz cutoff with a resistance of 165K (330K/2). 500K (loaded down to 250K) volume pots would result in 135 Hz cutoff using the same formula. 250K (loaded down to 125K) volume pots would result in 271 Hz with that formula. Etc. And like you said, in a Ric-O-Sound situation, the cutoff frequency would be cut in half. I don't remember if I used to use Ric-O-Sound or mono output when I soloed the treble pickup with cap for jazz groups but it would have been a good idea.

I wonder what you would get with that formula if there was no loading resistance on the signal? If ohms went to infinity? Hm.

[jps]

I take it the load (input impedance) of the device (amp, effects pedal, etc.) the bass is connected to also has an affect on the corner frequency?

[cassius987]

I definitely think so Jeff, as I have noticed input impedance plays a HUGE role in how "thin" sounding the tone becomes when using the cap. Higher input impedance = fuller sound.

[jps]

.....as I have noticed input impedance plays a HUGE role in how "thin" sounding the tone becomes when using the cap. Higher input impedance = fuller sound.

That is what I have noticed in a big way, too. It is easy to test with my UA LA-610 Mk II as I can switch the input impedance from 47KΩ to 2.2 MΩ.

[songdog]

Yes, there was just a discussion of this under "Volume & Tone Circuit necessary?". The load on the pickup affects the sound you get from it.

As a very rough analogy, it's a bit like a speaker and a cabinet. They can't be considered in isolation, they work together. Put a speaker in two different cabinets, or two different speakers in one cabinet, and you'll get very different sounds. Sometimes the differences are a matter of taste, and sometimes they just don't work.