Passive bass cut control with no-load pot

[fig]

I was sketching a circuit for future reference and put a passive bass cut control at the end of 2 pickups in series (bass cut will be disabled in parallel). Same bass cut control that G&L uses (top drawing).

Online, I've seen schematics and diagrams showing the pot using 2 or 3 terminals (no issue, they work the same). But haven't seen, or read, of any using a no-load pot (bottom drawing).

I like the idea of electrically leaving only the cap in the circuit when the pot's in the no-load position. But with the pot's suggested 1 Meg resistance being so high, the no-load might not even be worth the effort to use.

Has anyone tried, or is using, a no-load pot in their bass cut control?

 

[Killed_by_Death]

see if you can even find such a pot first, because it's a Reverse Logarithmic taper on G&L instruments, not so sure there even IS a no-load version
you could create one, by cutting the trace on the wafer, but I'm not sure you can buy one

 

[fig]

see if you can even find such a pot first, because it's a Reverse Logarithmic taper on G&L instruments, not so sure there even IS a no-load version
you could create one, by cutting the trace on the wafer, but I'm not sure you can buy one

Yeah, all that is what I was thinking when I said "might not even be worth the effort" LOL.

 

[iiipopes]

In this application, a no-load, if it exists in linear or reverse audio taper, is elective, because when you dial in full bass, the capacitor is effectively bypassed, whether or not the pot is conventional or no-load. You will get a similar result using a standard linear 500 kohm pot with your choice of .0047, .0068 or .01 capacitors, depending on how much bass cut you want. I have experimented with this variant on Rickenbacker basses, which have the inline .0047 capacitor to the bridge pickup, and .01, which I have on some of my basses on J-bridge pickups to clean up the volume drop from the impedance drop with both pickups are dimed. Fender Jaguar guitars have the .0068. It's all a matter of desired "hinge" frequency for the cutoff.

 

[micguy]

Having no DC path around the capacitor when the tone control is in the no load position brings up the possibility of pops when you turn the control back down.

You have to know what the whole circuit is to understand if this will be a problem or not.

 

[fig]

...because when you dial in full bass, the capacitor is effectively bypassed, whether or not the pot is conventional or no-load.

True, is doesn't matter when the cap is totally bypassed:

I'm interested in the other end of the pot rotation:

I only started looking hard at the passive bass cut circuit two days ago. What struck me is why, with all my reading, the no-load wasn't mentioned for this circuit, yet the no-load is used extensively for standard treble bleed circuits, like this:

I have experimented with...

Yeah, gonna take a bit of experimenting to find the values that'll make my ears (the final judge LOL) happy.

Having no DC path around the capacitor when the tone control is in the no load position brings up the possibility of pops when you turn the control back down.

You have to know what the whole circuit is to understand if this will be a problem or not.

The popping crossed my mind, too, but the circuit is entirely passive, so i wouldn't think so. Can't be 100% sure until it's built. You know how things can look good on paper until the reality of a prototype throws it out the window LOL.

Anyway, here's the entire circuit. Passive Parallel-Series VVTT. Derived from shunt-style volume control circuits that @walterw has promoted and some players here are using. Series is shunt-style and should also provide tone control isolation (like a Danelectro series circuit) for each pickup. Parallel mode is standard parallel circuit.:
Parallel...

Series...

This is just an idea for future experimentation. I don't even have the parts to try yet LOL.

Back on point, I don't think the no-load bass cut will pop. Just not certain until this is built.

 

[micguy]

The popping crossed my mind, too, but the circuit is entirely passive, so i wouldn't think so. Can't be 100% sure until it's built. You know how things can look good on paper until the reality of a prototype throws it out the window LOL.

You can definitely get pops in a passive circuit - your pickups produce AC signals, and depending on when you throw a switch, you can end up with a capacitor with a decent amount of charge on it. When you throw the switch back, it can and will pop. In your circuit, with that switch next to the blocking capacitor, you'll get some pops - the end of the capacitor next to the switch has no DC path to ground. If you put a 10 Megohm resistor around the capacitor, you'll be happier with that aspect of your circuit. Your schematic is also missing a ground for the neck pickup circuit - assuming that's there, everything but the loose end on the capacitor has a DC path to ground.

 

[Killed_by_Death]

Ironically, the solution to popping switches is wiring a 1 MegOhm Resistor across the contacts, which you already have in the form of a pot.
TBH I don't think the no-load is going to make a difference vs. having a 1 MegOhm Resistance in the path:

[Invalid or Expired Link Removed]

You can't plug in Infinity (open) in the calculator, but basically everything 1 MegOhm & up gives the same results.

 

[fig]

TBH I don't think the no-load is going to make a difference vs. having a 1 MegOhm Resistance in the path:

[Invalid or Expired Link Removed]

You can't plug in Infinity (open) in the calculator, but basically everything 1 MegOhm & up gives the same results.

Perfect! I'd suspected as much with my "1 Meg resistance being so high" comment. You just proved it quite handily, sir, to my satisfaction. Probably answers why I couldn't find much about it in relation to passive bass cut circuits or G&L's PTB circuit LOL. Appreciate it, KBD.

Still gonna try it (minus the no-load) at the end of the circuit. The passive bass cut has been suggested in the forum a few times to tame the extra volume and bass that a series circuit can add.

@micguy I understand what you're saying. Fortunately, this bass cut is a two day old option and disposable. When the circuit gets prototyped, it'll take all of 60 seconds to test. It'll work, or it won't, ain't no thang LOL.

I really appreciate you both for chiming in. I've posted this circuit twice (without bass cut) in the past, asking for eyeballs to dissect it. 0 responses both times. Thanks for taking the time.

So the actual subject of this thread's been answered. The no-load isn't needed because a 1 Meg pot value is so high, it'll makes no discernible difference in or out of the bass cut circuit. Good enough for me...otherwise locating or making a no-load was gonna be a hassle LOL.

 

[Killing Floor]

Couldn't you use a switch in the place of a pot? Or save space with a push pull? Reason I ask is that pots don't always have true 100% and some don't have true 0%. But I'm interested to hear.

 

[fig]

Couldn't you use a switch in the place of a pot?

I wanted it adjustable, but a cap and switch is a thought, for sure. Might be all I need. Might even use only the cap, no switch. Gonna determine all that during testing.

Or save space with a push pull?

I'd consider push/pull if needed. But I currently only have a volume control wired so I have 5 spare holes. I'm ok with space.

Reason I ask is that pots don't always have true 100%...

That's true, but this application as a 'bass tamer' isn't critical, so tight tolerances aren't needed. I just needed a range of adjustability. Even 90% and 'not quite 0' would probably be fine for this application. My ears would tell me if it's acceptable or not.

 

[ripbobbysheehan]

Anyway, here's the entire circuit. Passive Parallel-Series VVTT. Derived from shunt-style volume control circuits that @walterw has promoted and some players here are using. Series is shunt-style and should also provide tone control isolation (like a Danelectro series circuit) for each pickup. Parallel mode is standard parallel circuit.:
Parallel...
View attachment 4055477

Series...
View attachment 4055479

This is just an idea for future experimentation. I don't even have the parts to try yet LOL.

Did you ever end up trying this circuit? If so, how'd it work? I've been thinking of doing something very similar so anything lessons you've learned from your experience with it would be extremely helpful. Thanks!

 

[fig]

Did you ever end up trying this circuit? If so, how'd it work? I've been thinking of doing something very similar so anything lessons you've learned from your experience with it would be extremely helpful. Thanks!

I eventually made most of the circuit on a breadboard to test it. I say 'most' because I didn't add the passive bass cut or the isolation resistors while testing. Those two items have proven themselves for years, so they'll work. They would just take some jinking with values to make the player happy.

So I only tested the series/parallel switching and it worked fine. Played with it while breadboarded for awhile, then disassembled it. Wasn't interested in putting in my bass, just wanted to make sure the switching worked, which it did.

For what it's worth, if you're not interested in the tone isolation or bass control circuits, a TB member showed an easier series/parallel switching than mine by using a 2p2t switch instead of a 3p2t switch like I used. If I ever go back to series/parallel switching with independent volumes for each pickup, I'll be using his version.

Parallel:

Series:

You can remove the Master Tone and use separate tone controls for each pickup (for vtvt).

 

[SharpCat]

Series mode, seems like the neck volume is ...odd--you're losing the ground reference.

 

[fig]

Series mode, seems like the neck volume is ...odd--you're losing the ground reference.

It's kinda cool how it works. This is the 'shunt' method of series pickup control. This method adjusts the pickup power itself. To turn each pickup on, put some resistance between its + and -. To turn it off, short out the connection between the + and -. The pot (configured as a rheostat) is the adjustable resistance between + and - of each pickup. I learned this method from TB's own walterw.

Anyway, maybe this drawing (with pretty, pretty colors) helps understand why a system ground reference isn't needed for the Neck volume to work properly. The - of the Neck pickup is it's own ground reference. FWIW, I call the hard ground on the left the System Ground, which makes the whole circuit work with the rest of the system (pedals, amp, etc). The - of each individual pickup I call the Return Ground (or Signal Ground).

I'm gonna stop here. Does this drawing make sense, if I understood your concern correctly?

 

[SharpCat]

That is very nifty. Thanks much for explaining it to me.

 

[DDawg]

i think I'm the member who supplied the info on this series/parallel switching scheme. I've wired up a lot of basses like this and it works great.
Adding a passive bass cut control along with a treble bleed tone control in the circuit works fine as well.
I prefer to add a switchable cap in series with the bridge pickup before the bridge volume control like a RIC, which is basically a passive bass cut for the bridge pickup. I've also tried using a pot instead of switch to control the cap, which works fine if you want more control. I don't think using a no-load pot would make any difference tonally. I've tried different values of caps from .0047 to .01, and I find that the .0068 works best for my tastes. The inline cap is useful in both parallel and series modes. After series-parallel switching, I think the bridge pickup cap is the best addition for a passive bass. It's also makes out of phase actually usable if you also have phase switching on your bass.

 

[fig]

That is very nifty.

I thought Danelectro and shunt were the only two methods for series pickups volume/blending control. Later found a Bill Lawrence (of pickup and cool circuit design fame) circuit that only uses one regular pot to control both pickups. Found his diagram in the forum and online, then made a schematic. One standard pot as a series blend control, and with a flick of a switch, turns it from a series blend into a neat tone control. The guy thought out of the box, in my opinion.

For those passing thru, here's the Danelectro and Shunt method compared for series pickup control.:

Then along came Bill Lawrence. His original wiring diagram is at the top.:

 

[SharpCat]

Do we have suggested pot values/types for the Bill Lawrence circuit? You're sure right--he is unrivaled.

 

[fig]

Do we have suggested pot values/types for the Bill Lawrence circuit?

Yeppers. Here's the full original I got online. I omitted the text part to make the drawing in previous post shorter LOL.