Passive electronics: Mid cut

[mongo2]

Villex offers up to 12dB passive boost through his PRTB line of products (Passive Rotary Tone Booster)

Passive boost?

 

[fullrangebass]

Yes indeed!!! 12dB boost

 

[DerHoggz]

This is really interesting.

Would ths be possible to apply to low frequencies? That would be sick.

 

[SGD Lutherie]

Passive boost?

Yeah, I believe he's using a step-up transformer for the boost.

 

[mongo2]

Yeah, I believe he's using a step-up transformer for the boost.

Hmmmm, interesting.

 

[SGD Lutherie]

Hmmmm, interesting.

I'm just speculating.... Villex is the guy who invented the Lace Transsensor and Alumitone pickups, so it only makes sense that he's doing something similar.

 

[fullrangebass]

This is really interesting.

Would ths be possible to apply to low frequencies? That would be sick.

He is applying it to the low frequencies and the result is really impressive esp with the PRTB II

 

[southernrocker]

http://www.guitar-mod.com/rg_passive.html

I have the push-pull mid cut in my jazz. It's not incrediblely noticeable, but it takes the harshness out of slap.

 

[fullrangebass]

The villex system has this, I didn't really like the way it sounded. The mid control took some highs along with it so it wasn't useful for getting any kind of sharp mid scooped sound.

By using the PRTB and the Mid-control results in sharp mid scooped sound

 

[toniwonkanobi]

Old thread, but do you guys know if it is possible to have a pot that provides passive treble cut like a normal tone pot, and then when turned the opposite direction, a passive mid cut?

Dingwall offers this functionality on their Super P basses (passive models), and they call it "Tone-Fusion." They have a center detent, and counter-clockwise is for passive tone cut (as to be expected), while clockwise rotation of the knob leads to the passive mid cut.

Rothstein essentially offers the same functionality as Dingwall, except that they are using a push-pull pot as a selection for treble vs mid cut, and the knob only rotates counter-clockwise. Not a big deal, but in my experience, push-pull pots have a different feel compared to conventional pots, and generally suck at life as well. I'd like to avoid said sucking at life if I can.

Any ideas?

 

[eukatheude]

Couldn't you just use a specific cap value? If i understood this thing right, with a 800nf cap on a 250k pot you should cut roughly at 800hz. Or i got this completely wrong?

 

[Crater]

Couldn't you just use a specific cap value? If i understood this thing right, with a 800nf cap on a 250k pot you should cut roughly at 800hz. Or i got this completely wrong?

But a standard passive tone control doesn't just cut those frequencies, it's cuts everything higher too. The higher the frequency, the more dB is removed, the 800 Hz (or whatever) is just the "knee" frequency, I believe that's where the filter is -6dB crossover point. Frequencies higher than 800Hz are cut even more.

 

[abemo]

You might be able to use that cap if you also bypassed the mid cut pot with a smaller cap to let the highs through unimpeded, but I believe SGD had a fairly detailed description of the proper way to do this with a cap and an inductor.

 

[SGD Lutherie]

Couldn't you just use a specific cap value? If i understood this thing right, with a 800nf cap on a 250k pot you should cut roughly at 800hz. Or i got this completely wrong?

The frequency that the tone control cuts at is also determined by the impedance of the pickup. Passive tone controls are not really RC networks like those in the link. It's more of a resonant low pass filter and uses the pickup as part of the circuit.

So the higher the impedance of the pickup, the more affect the cap has on the tone. This is the original series active EMGs use .1µF tone caps, and still the control does very little.

 

[eukatheude]

So i should take into account the pickup impedance by just adding it to the pup impedance?

 

[azwipe]

Anyone know how to wire the Radio Shack audio transformer for this? It has 5 wires - white, red, blue black and green. Trying to diy a mid-cut switch.

Unfortunately I sent Stan Hinesley money for a mid-cut switch almost 2 weeks ago via Paypal, and he hasn't responded to any emails since.

You need a capacitor and an inductor. This is commonly known as a Varitone control. They usualy have 5 different value caps and a bypass position on a rotary switch, but Gibson included a single knob midrange cut control on the Ripper bass.

If you want to try it, the easiest thing is to go to Radio Shack and pick up the audio output transformer they sell (Model: EI-19, Catalog #: 273-1380). You want to use the 1K Primary as an inductor. Then try using that with a .1 cap. The inductor would go between the cap and ground, wired like a standard tone control.

Smaller cap values will raise the notch frequency, and larger values will lower it.

You can also use a transformer model TL021-R that you can find at Mouser Electronics. Torres sells a Varitone kit that uses that same part.

Here's the Ripper schematic.

 

[khutch]

Old thread, but do you guys know if it is possible to have a pot that provides passive treble cut like a normal tone pot, and then when turned the opposite direction, a passive mid cut?

Dingwall offers this functionality on their Super P basses ...

Rothstein essentially offers the same functionality ...

Well, you are probably long gone by now but while I could find little about this on the Dingwall site other than the improbable assertion that the circuit is too labor intensive to put in all their basses, Rothstein tells you quite a bit. Start with a center detent 500k pot, a 1Meg might work even better but they use a 500k. Wire the pickup signal to the center lead on the pot. Wire a traditional tone cap to one of the outer leads of the pot. Wire a series LC "notch filter" to the other outer lead of the pot. Rothstein appears to even give you design equations for the LC circuit although I only glanced at them. When you are in the center detent position both tone circuits have 250k in series with them and are effectively disabled. Turn the pot one way and the traditional tone cap is progressively engaged, turn the pot the other way and the passive mid cut is progressively engaged. If you have trouble getting the components I suppose you could buy the Rothstein and then graft their components on a center detent 500k or 1Meg pot. Rothstein claims to use a special taper on the pot. Don't know what that might be but I would guess that if you can find a center detent pot with a non-linear taper that is symmetrical when turned either way it is likely that they are using that pot.

Anyone know how to wire the Radio Shack audio transformer for this? It has 5 wires - white, red, blue black and green. Trying to diy a mid-cut switch.

David said to use the 1k winding. Radio Shack says the transformer has:

1,000-ohm center-tapped primary
8-ohm secondary

so two of the wires are the secondary winding and three are the primary which is center tapped. If you use a VOM to measure the winding resistances (which will NOT be 8 Ohm and 1k btw) the secondary is the two wires which connect to each other but not to any other wires. The primary is the three wires that are all connected together. The center tap wire will show equal resistance to the other two. Leave the center tap wire unconnected, leave the secondary wires unconnected, use the two outer wires in the primary winding.