Capacitor on a Blend Pot......What does it do?

[BelmontBiker]

Hello Everyone,
Waiting on my blend pot to arrive and can't stop wondering what the cap will do when wired this way? I have both Wilde pickups so I am wanting to wire this up they way Bill intended, but curious if/how the cap on the blend knob will affect things?

 

[crguti]

It is called the treble bleed mod. Backing off the volume knob attenuates the pickups’ high-frequency. The remedy is to install a capacitor, so when you roll down the volume you keep the tone but you just decrease the volume.

 

[BelmontBiker]

Thanks @crguti! so, I want to play with the different capacitors he lists to find what I like best.....I appreciate the explanation!

 

[BelmontBiker]

@crguti one more question? Can I do this if I use an MN blend pot? If so, I assume that I will just run the cap from on the same row of lugs as the J pickup. Should that work?

 

[crguti]

^yes, you can. You can also apply the treble bleed mod to the other pickup too. Be aware that this is only valid for passive pickups.

 

[BelmontBiker]

Great!!! Thanks so much!

 

[Crater]

Can I do this if I use an MN blend pot?

What they call a "blend" really isn't. It's a volume control for the J-pickup; this diagram has the pickups wired permanently in series. It uses a standard single-gang pot. I find it odd that they didn't bother to put the pot values in the diagram. Also, the master tone control is wired in a unconventional way, which shows the right hand terminal of the tone pot connected to ground. That means the resistance of the tone control is in parallel with the output, reducing the output level and some treble. A normal tone control has the pot's "can" connected to ground, but one outer terminal is left un-connected. Far be it from me to question the wisdom of Bill Lawrence.

MN type blend pots are for parallel blending of pickups, and that's not what you have in this wiring diagram.

 

[crguti]

I would go with this diagram instead:

 

[cheapbasslovin]

What they call a "blend" really isn't. It's a volume control for the J-pickup; this diagram has the pickups wired permanently in series. It uses a standard single-gang pot. I find it odd that they didn't bother to put the pot values in the diagram. Also, the master tone control is wired in a unconventional way, which shows the right hand terminal of the tone pot connected to ground. That means the resistance of the tone control is in parallel with the output, reducing the output level and some treble. A normal tone control has the pot's "can" connected to ground, but one outer terminal is left un-connected. Far be it from me to question the wisdom of Bill Lawrence.

MN type blend pots are for parallel blending of pickups, and that's not what you have in this wiring diagram.

This is what I'm seeing too.

Letting the highs through on the j pickup while killing the lows from it. It might sound good (I've never tried it), but isn't strictly speaking a 'blend.'

 

[BelmontBiker]

Thanks @Crater ! I will play around with some pots I have here 1st and see what I can learn. Have lots of wire and solder......Time to play and learn! I appreciate your feedback.

 

[ctmullins]

This is what I'm seeing too.

Letting the highs through on the j pickup while killing the lows from it. It might sound good (I've never tried it), but isn't strictly speaking a 'blend.'

I've tried it. With two P46s, so maybe a little different than a P46 and a J45. It's - interesting. There are good tones all the way through the sweep of the "blend", but I found it rather subtle.

High-passing the bridge pickup is also done by Rickenbacker. Originally the 4001 had a cap wired permanently in series with the bridge pickup; current 4003s include a push/pull to enable/disable this feature. The pickups are otherwise in parallel, not series like Bill's circuit. I've wired another of my basses this way, and removing the lows from the bridge pickup restores a lot of the mid-frequency cancellation that usually happens with a Jazz-type circuit. It's a completely different tone than neck-only and bridge-only, and sits in a neat spot sonically.

Both of these are different than what is usually called a "treble bleed" - that's a bypass cap wired across a volume control, and affects the overall signal going to the jack.

 

[Johnny StingRay]

I love reading these electronic posts. I have no idea what all of it means, but I am in awe of those who understand the diagrams and can put together bass electronics.
Maybe when my grandkids get older and I don’t have to babysit all the time, I can take a class and/or.....dare I write it!?!?......buy a cheap bass and learn how to upgrade it!!!

 

[fig]

Just passing through.

I like simple circuits that aren't the norm, so I diagrammed out this one. Turns out it's the P and J in series, each with it's own standard tone control (the P tone will act as master as indicated). Master volume at the end and we're golden. I love simplicity. 'cause I'm a simple minded guy LOL.

Busy now, but I'll make a cleaned up schematic (to put in my notes) and post it here in a few hours. I did a similar series VVTT awhile back, will post it also. Some differences with the Wilde version, but still each series PU with it's own tone control.

 

[JeezyMcNuggles]

It is called the treble bleed mod. Backing off the volume knob attenuates the pickups’ high-frequency. The remedy is to install a capacitor, so when you roll down the volume you keep the tone but you just decrease the volume.

Is that true? Running a capacitor on every pot will keep the frequency spike the same when lowering volume?

 

[dkelley]

Is that true? Running a capacitor on every pot will keep the frequency spike the same when lowering volume?

No.
But it IS true of volume controls. I had not thought of blend controls using them - and I haven't seen that on blend controls before, and the example in this thread is not actually a blend control. But in the later schematic you see a proper dual gang blend pot wired correctly, and no caps on it, but you can def put one on the master volume pot. Maybe blend too, maybe not - I'm not sure and would have to analyze the circuit (Which I'm not doing tonight).

Without the cap the tone gets muddier much faster as soon as you start turning down the volume control from 10.

It's been done on les pauls and other guitars for ages, and is popular with USA fender strats... and some basses.

The math behind choosing the value is actually incredibly complex, but there are enough examples out there that you can see good suggestions, and nothing wrong with experimenting with your ears. It does work as a high pass filter that engages once the volume pot is anywhere less than wide open, number 10 on the dial.

Honestly though - it's kinda subtle.

 

[fig]

Here's a schematic of the Bill Wilde diagram that @BelmontBiker posted. It's in my notes now. Because the two tone controls have a common ground, the end control (after P pickups) will become an overall master control as indicated in original diagram. I rather like this idea.:

Here's my schematic I'll be trying when I receive the parts (this one's never been built, as far as I know). Volume and tone control for each pickup, no Master tone or Master volume. I'll be testing this setup with a master vol, though.

In this series VVTT, each volume and tone control is constrained to return it's power/freq to it's own source of power (the pickup). Neck power/frequencies returned only to Neck PU, Bridge power/frequencies returned only to Bridge PU. It's a property inherent in electrical power source circuits and used in many different industries. This circuit sounds good on paper, anyway LOL:

I'm guessing, but there will probably be tonal differences between the two. Only the player can decide what suits him/her. I know I'm trying both when my orders get here. I might like Wilde's circuit hella lot better than mine LOL.

 

[BelmontBiker]

Wow.....Amazed by the deep level of understanding! Thank you all for your input. Sounds like it is worth trying "Bill's way" and if all else fails I can change it up to the Seymour Duncan diagram......I won't pretend to know what exactly I am doing, but I can follow a diagram and use a soldering iron, the rest will be what it sounds like. Thanks Again!!!

 

[byacey]

In Bill's circuit, the J is always in series with the P set, and the control isn't volume, only a tone control allowing more highs through for the J, or not. The J pickup is never really shut off completely and will always buck or boost according to the LF phase between the pickups. Fig's revision appears to offer more tonal possibilities.

 

[JTE]

Because a real blend pot is two volume pots ganged on one shift (at center both PUPs are wide open, as you sweep from center one pickup doesn't change as the other is turned down), one could put a treble-bleed cap on each side.

 

[fig]

I had not thought of blend controls using them - and I haven't seen that on blend controls before...

Because a real blend pot is two volume pots ganged on one shift (at center both PUPs are wide open, as you sweep from center one pickup doesn't change as the other is turned down), one could put a treble-bleed cap on each side.

I'd never seen or heard of treble bleed caps on a blend either. So the caps would be positioned between each blend deck input (wiper arm) and each blend deck output? (yes, I installed Orange Drop caps in the schematic lol).:

If the drawing is correct, one thing I see is the two treble bleed caps being permanently connected together. Not sure what happens with that.

Plus, adding a Master volume with a bleed cap might create a flux capacitor. Possible time travel implications...