Passive treble boost

pertyman · #1 03-21-2013, 05:57 AM

Hi,

I saw that the new Streamer CV has a passive bass and treble electronics.

Does anyone know how to make a passive treble boost control ?

Where can I find schematics for that (I searched all over the internet and didn't find) ?

Thanks,

Guy

Crater · #2 03-21-2013, 07:15 AM

You can't boost anything with a passive circuit, you can only cut frequencies. G&L guitars have had passive bass & treble controls for years. The treble control is the standard tone control, a capacitor in series with a pot connected to ground. The treble control is a pot in line with the signal, with a capacitor between a center leg and outer leg on the pot. When the bass pot is completely "on" it acts as a straight wire. As you turn the pot down, the series resistance increases, reducing all of the signals, but the treble frequencies are bypassed around the pot by the capacitor.

InternetAlias · #3 03-21-2013, 07:21 AM

Mind you, this only works on mid to high output pickups. When you cut a lot of meat on a low output pickup, you'll lose a lot of signal, which is why this idea isn't as promoted as it seemingly should be, if some guitars have it stock, it is because their electronics are built around this concept. That being said, I've played a custom jazz with a pair of duncan quarter pounders and passive EQ controls (bass/mid/high) and it worked INCREDIBLY. So uh, go for it, try it, you can always rewire back if you don't like it or it kills too much signal.

Steve Dallman · #4 03-21-2013, 07:26 AM

If you are looking to just increase the treble, you can increase the value of the volume pots and replace the tone controls with "no-load" pots. If the volume's are 250k, replacing with 500k or even 1meg audio pots will load the pickups less and will yield more treble.

pertyman · #5 03-21-2013, 07:31 AM

Thanks !

Quote:

Originally Posted by Crater

The treble control is a pot in line with the signal, with a capacitor between a center leg and outer leg on the pot. When the bass pot is completely "on" it acts as a straight wire. As you turn the pot down, the series resistance increases, reducing all of the signals, but the treble frequencies are bypassed around the pot by the capacitor.

So it's a high pass filter ?
Is it any good ?
I think it will only make the sound "thinner" with no bass at all...

pertyman · #6 03-21-2013, 07:35 AM

Quote:

Originally Posted by InternetAlias

I've played a custom jazz with a pair of duncan quarter pounders and passive EQ controls (bass/mid/high) and it worked INCREDIBLY.

Is it a costume electronics or I can purchase it somewhere ?

InternetAlias · #7 03-21-2013, 07:47 AM

Quote:

Originally Posted by pertyman

Thanks !
So it's a high pass filter ?
Is it any good ?
I think it will only make the sound "thinner" with no bass at all...

Depending on the situation, you might want that, for example, if you have a p bass or some other one pickup bass. However, that is still regulated by a pot, so you could turn the knob to taste. Also, do realize that 1meg pots act mostly as an on/off switch, since the volume changes too rapidly.

Quote:

Originally Posted by pertyman

Is it a costume electronics or I can purchase it somewhere ?

The guy who made it makes his own bass guitars, so he made the EQ himself, I don't know if there are some that are commercially sold. If you can solder and implement new pots into your control cavity, you can get a really nice passive EQ for around 10$ of raw materials, I am planning on doing this sometime (don't need it with my jazz, though).

bassmeknik · #8 03-21-2013, 07:59 AM

Quote:

Originally Posted by pertyman

Hi,

I saw that the new Streamer CV has a passive bass and treble electronics.

Does anyone know how to make a passive treble boost control ?

Where can I find schematics for that (I searched all over the internet and didn't find) ?

Thanks,

Guy

It sounds like you want to change the slope of the existing tone controls (change values of pot and cap) to alter the tonal flavor of your bass. As mentioned you can not boost with a passive circuit so I recommend starting with the cap and going with a higher value for the volume pot. Try looking at a few diagrams of similarly equipt basses that you like the sound of and copy their tone circuit. This is inexpensive to try out if you can solder, just buy a selection of cap and pot values (near the stock value or to copy another bass diagram) and try a few schematics to see what sounds good.

ctmullins · #9 03-21-2013, 08:41 AM

Quote:

Originally Posted by InternetAlias

Also, do realize that 1meg pots act mostly as an on/off switch, since the volume changes too rapidly.

Um, no. What you're describing has to do with the taper of the pot, and has nothing to do with the resistance of the pot.

Search "log taper versus linear taper" for details.

InternetAlias · #10 03-21-2013, 09:09 AM

Quote:

Originally Posted by ctmullins

Um, no. What you're describing has to do with the taper of the pot, and has nothing to do with the resistance of the pot.

Search "log taper versus linear taper" for details.

Ah good, seems I accidentally wired a lin pot a few months ago

Meddle · #11 03-21-2013, 09:12 AM

"Passive" and "boost" are mutually exclusive terms. That extra energy has to come from somewhere!

ctmullins · #12 03-21-2013, 09:14 AM

Quote:

Originally Posted by Meddle

"Passive" and "boost" are mutually exclusive terms. That extra energy has to come from somewhere!

And yet, the Villex PRTB exists and works. !!

It's a puzzle to me; it really is.

InternetAlias · #13 03-21-2013, 09:39 AM

Quote:

Originally Posted by ctmullins

And yet, the Villex PRTB exists and works. !!

It's a puzzle to me; it really is.

It sacrifices energy from one range and uses that current to amplify frequencies at a more desirable range. Incredible concept, not so much so for bass guitars though. Now that I think of it, wouldn't it be an incredible idea to make an ultra high output pickup (like, 25k ohm) and use it to power a preamp? The pickup would obviously sound terrible, but if it had great output it could actually give a nice boost on the preamp!

Cadfael · #14 03-21-2013, 11:23 AM

I have the "bass cut filter" in my 424 pages compilation, too.
The description is in German ...

For the wiring diagram I used my $150 Johnson MM 5-string copy, which has an MM PU with normal treble and the passive bass cut. For basses with "more than just good" punch, a passive bass cut makes sense (like in my Johnson). The in line 1nF bass cut capacitor (plus pot) lets it sound a bit more than a "weak Fender" bass.

SGD Lutherie · #15 03-21-2013, 02:09 PM

Quote:

Originally Posted by ctmullins

And yet, the Villex PRTB exists and works. !!

It's a puzzle to me; it really is.

They use step up transformers. The Villex pickups are probably similar to Lace Alumatone or the older TransSensor pickups, since Villex invented those. I'm guessing they are more like the TransSensors. So they use a low resistance single loop coil, and a current transformer to boost the signal up. Then they are able to work some tone controls into the scheme of things. It's very clever.

Also passive treble cut tone controls give a small, but real boost when they are all the way down. This is because they form a resonant low pass filter along with the pickup coil, and it moves the resonant peak of the pickup very low.

The Fender "grease bucket" tone control was made to eliminate that boost, which never made any sense to me. That's the best part of a passive tone control!

SGD Lutherie · #16 03-21-2013, 02:11 PM

Quote:

Originally Posted by InternetAlias

It sacrifices energy from one range and uses that current to amplify frequencies at a more desirable range. Incredible concept, not so much so for bass guitars though. Now that I think of it, wouldn't it be an incredible idea to make an ultra high output pickup (like, 25k ohm) and use it to power a preamp? The pickup would obviously sound terrible, but if it had great output it could actually give a nice boost on the preamp!

I used to run low impedance pickups into a power amp with a singe JFET preamp in the bass.

khutch · #17 03-21-2013, 02:42 PM

Quote:

Originally Posted by Meddle

"Passive" and "boost" are mutually exclusive terms. That extra energy has to come from somewhere!

Depends on how you define boost. A passive circuit can boost the voltage or current of a signal. As pointed out above transformers do this all the time and they are passive. What you cannot boost is the both the current and the voltage at the same time because that would be a power boost and if you want to boost the power the energy to do that has to come from somewhere, as you say.

In many cases when you connect a tone capacitor directly to the pickup (ie, set the tone pot to zero Ohms) you get an underdamped second order low pass filter that does boost the voltage for frequencies a little below the cutoff frequency. The switched tone cap or "tonestyler" tone controls let you do this at a variety of frequencies. That kind of response is probably not what the OP is looking for. I don't know off hand of any way to build a variable boost/cut passive treble circuit but evidently Villex does and they use a transformer so I would try to find out more information on their design and copy, or buy, it.

Guitar pickups have a much lower characteristic impedance than guitar amplifiers have. So there is a power mismatch between the guitar and the amp. If you devise an impedance matching circuit to put between them you will transfer more power to the amplifier input without violating the second law of thermodynamics and that results in a higher voltage at the amp input than the direct connection between amp and pickup allows. That opens the door to the possibility of a cut/boost passive tone control as well as a broadband level boost.

Ken