Circuit mods: Do these cancel each other out?

[jakeac5253]

I have a volume mod to each of my volumes which consists of a 330k resistor and 1000pF cap between the first and second lug. I want to put a capacitor across the pickup to roll off some highs. The capacitor will go from the input lug where the hot lead is to the exact point where the pickup cold lead/ground is. Since the cap across the pickup is there to cut the highs and the cap across the pot is there to preserve the highs I think trouble could arise. What do you think?

[dougw]

Every one's ears are different, but if the pickups are too bright, that is probably not how I would approach this. The volume mod you have is to preserve some top end when you roll back the volume. Does the guitar have a tone control? Have you tried rolling it back a bit to knock off some of the top end? I think you will find if you want to go the fixed cap approach you will likely need a resistor in series with the cap. One other thing that comes to mind is you might try reducing that 1000pf cap you already have in there to something like 470pf or even 330pf. I find that 1000pf is too large a value to my ears and makes the guitar too bright when I roll back the volume. If you can say what sort of guitar, pickups, and how the controls are set up, it might be easier to get some more concrete answers. Hope this helps.

Regards,
Doug

[jakeac5253]

Every one's ears are different, but if the pickups are too bright, that is probably not how I would approach this. The volume mod you have is to preserve some top end when you roll back the volume. Does the guitar have a tone control? Have you tried rolling it back a bit to knock off some of the top end? I think you will find if you want to go the fixed cap approach you will likely need a resistor in series with the cap. One other thing that comes to mind is you might try reducing that 1000pf cap you already have in there to something like 470pf or even 330pf. I find that 1000pf is too large a value to my ears and makes the guitar too bright when I roll back the volume. If you can say what sort of guitar, pickups, and how the controls are set up, it might be easier to get some more concrete answers. Hope this helps.

Regards,
Doug

Thanks for the quick response. I thought that higher value caps let in more bass in this mod because more bass would be passing the cap? I was even considering raising the value to 1500 or 2000pF to lose less mids on rolldown. Is this backwards?

It's a Jackson RR3. Pickup in question is SD JB to 500k pot and 500k tone in 2 volume master tone setup. I bought some 100k resistors and I was thinking about soldering one across the outside lugs of the volume pot to do the same thing. Was just curious about this specific mod.

[dougw]

Well, I wouldn't put 100K resistors across the pots. That is too low a value for humbuckers. The JB's are bright pickups. The SD site says some folks use 250K pots to smooth them out a bit.

Progressive - JB Model™ SH-4 and TB-4 - Seymour Duncan/Basslines

You can accomplish this without changing your pots out by putting 500K resistors across the outer two terminals. If that is too dark, or the output is reduced too much, you can try different values between 500K and 1M. You can use different resistor values on each pickup if you like.

Your a bit confused on capacitors. Capacitors attenuate low frequencies and pass high frequencies. Whether they are create a low pass or high filter is determined by the topology of the circuit.

So, if it was me, the first thing I would do is remove the bypass cap/resistor off the volume (just unsolder one end) and try different resistor values across the pot until I found the sound I wanted. I would then reconnect the bypass resistor/cap. It that made the sound too bright, I would reduce the cap value and perhaps increase the resistor slightly, say to something like 420K and 470pf.

[jakeac5253]

Well, I wouldn't put 100K resistors across the pots. That is too low a value for humbuckers. The JB's are bright pickups. The SD site says some folks use 250K pots to smooth them out a bit.

Progressive - JB Model™ SH-4 and TB-4 - Seymour Duncan/Basslines

You can accomplish this without changing your pots out by putting 500K resistors across the outer two terminals. If that is too dark, or the output is reduced too much, you can try different values between 500K and 1M. You can use different resistor values on each pickup if you like.

Your a bit confused on capacitors. Capacitors attenuate low frequencies and pass high frequencies. Whether they are create a low pass or high filter is determined by the topology of the circuit.

So, if it was me, the first thing I would do is remove the bypass cap/resistor off the volume (just unsolder one end) and try different resistor values across the pot until I found the sound I wanted. I would then reconnect the bypass resistor/cap. It that made the sound too bright, I would reduce the cap value and perhaps increase the resistor slightly, say to something like 420K and 470pf.

You were right on the resistor bit, I tried a 1m resistor that I had lying around and that sounded much better. The 100k sounded too dark, but surprisingly not as bad as you would think for showing the pickup a parallel resistance of 83.3k I believe haha. Now I am at 330k and I think it is better, but I may pop for 400k or 450k. Just something that's closer to 'standard' but allows me to be a tad bit individual.

About the caps, I will assume that you are correct in calling my bluff on that bit too, because I was wrong on the resistors. The way I see it is the same way you are describing it though. Caps kill bass, and the higher the value, the less bass it kills. Right? So if I think the treble bleed cap is making the guitar too bright as I roll down the volume, I should get a larger cap. This makes sense because in this instance the signal is passing the cap, whatever makes it through the cap passes on to the later signal path. Who knows, I've been wrong before, show me the way.

[David Schwab]

Pickup in question is SD JB to 500k pot and 500k tone in 2 volume master tone setup. I bought some 100k resistors and I was thinking about soldering one across the outside lugs of the volume pot to do the same thing. Was just curious about this specific mod.

You want to knock high end off a JB? It hardly has any high end! Use 250K pots. Or turn your tone control down. That's what it's there for.

[David Schwab]

The JB's are bright pickups.

You are joking right? 16.4 k and an alnico magnet? They do have a big upper mid peak, but they aren't bright pickups. The 250K pots lowers and flattens the resonant peak.

I find unless you are using distortion they are pretty muddy sounding pickups.

[dougw]

No, if the guitar is too bright as you roll the volume off, you need a smaller cap. The higher the value cap, the more high frequencies will pass. Like I said, I would try a 470pf in there.

[dougw]

Depending on the guitar, the can sound very bright. Most folks ears don't make a distiction between upper mid peaks, as you mention, and over brightness. Even the SD site mentions that have a lot of top end.

"Compared to the SH-14 Custom 5, the JB has a stronger treble detail. Some players use it with 250K pots to smooth out the highs."

So, why quival over what I call bright. The solution is the same, change the loading on the pickup.

[jakeac5253]

You are joking right? 16.4 k and an alnico magnet? They do have a big upper mid peak, but they aren't bright pickups. The 250K pots lowers and flattens the resonant peak.

I find unless you are using distortion they are pretty muddy sounding pickups.

Thanks David, FWIW, I am using the JB for high gain. I love the honky mids, it helps my chords to stay defined under high gain. But like you said once you add heavy gain to it it gets grainy in the highs.

[jakeac5253]

No, if the guitar is too bright as you roll the volume off, you need a smaller cap. The higher the value cap, the more high frequencies will pass. Like I said, I would try a 470pf in there.

That is very interesting. I will have to try a 470pF cap! Thank you.

[David Schwab]

Depending on the guitar, the can sound very bright. Most folks ears don't make a distiction between upper mid peaks, as you mention, and over brightness. Even the SD site mentions that have a lot of top end.

"Compared to the SH-14 Custom 5, the JB has a stronger treble detail. Some players use it with 250K pots to smooth out the highs."

So, why quival over what I call bright. The solution is the same, change the loading on the pickup.

Play the pickup clean, and it's a pretty dark sounding pickup. A Lawrence L-500 is a bright sounding pickup.

[Mark Hammer]

We shouldn't really debate upper frequencies as if they were a monolithic entity. JBs may not have a glassy sheen to them that would make Johnny Guitar Watson flash a gold tooth, but that doesn't mean that ALL of the lower treble and upper mids is desirable or a good complement for whatever the pedals, amp and speakers do.

If loading provides a useful dulling of the pickup, then I'd suggest use of a 500k-1M trimpot that might let you dial in the degree of loading by ear, rather than futz around with different fixed resistors.

Note that it IS possible to have a useful compensation to the volume pot in order to retain the usable portion of the upper spectrum when you turn down, while taming the undesirable portion of the upper spectrum via a small-value cap strapped across the input and ground lugs of the volume pot. The constraining factor is that the part you don't want has to be higher up the spectrum than the part you do want. And it probably needs to be much higher up, too, since these various compensation methods have VERY shallow slopes and are pretty nonselective. If you need the toneshaping to be more selective than that, then I suspect you want to consider use of an EQ pedal.