Using a trimpot for lowering pickup output

[kyolic]

Ok here is my setup:

Neck: JB JR
Middle: JB
Bridge: Pearly Gates

The output of these pickups differ from each other hugely (in this order: Pearly Gates > JB > JB JR) and causing me problems. I am happy with the output of JB JR so I need the two other pickups to give the same output as it. There is a volume and a tone pot on the guitar. Volume pot controls all three pickups at the same time and this is what I want. I don't want to touch it anyway.

So, my idea is wiring a trimpot to JB and Pearly Gates in order to adjust their output to my liking and leave it that way in the cavity.

This is the best solution I can find for balancing the volume between three pickups (I tried adjusting height of the pickups and it doesn't work). I know that I can wire some resistors instead of trimpots but this will never satisfy me as I will not be able to adjust the output accurately.

Now I have two questions:

1- What value must the trimpots be?

2- I am aware that lowering the the output of a pickup with a trimpot will suck out some treble from it. So, can I wire a treble bleed circuit to the trimpot as we wire it on pots, in order to eliminate said treble loss?

BTW, these two pickups are on Seymour Duncan Triple Shots however Triple Shot's are not the reason for this output imbalance. This has been the case for 25 years.

I appreciate if somone can draw the place of such a trimpot, on this diagram (even in a sketchy way):

Thanks in advance.

[JohnH]

We can help with that. The starting point would be to wire a 500k trimpot exactly like the normal pot in the diagram, and add a TB circuit with 150k and 1nF cap in parallel.

But, there's a question and and issue or two!

When you feed a pickup through a pot, at less than max, the impedance rises. So once you have set the volume to match as wanted, as a separate pickup, if you then combine it with another pickup which has no pot, the other pickup will dominate the mix.

And a question: If you have the Triple Shot system on your pickups, then they should each have a parallel setting, which will be clear and powerful but about 6db less volume than the series wiring. If so, how does a parallel wiring of the PG or JB compare to series wiring of the JB Jr? That would have been my first target for matching volumes. But even if it's not quite right, it would be good info and maybe a good basis.

[kyolic]

JohnH here is the graph for output values of the pickups. It is the exact same riff played through 3 pickups.

There is a difference of about 3 decibels between JB Jr and JB when they are in serie. And there is a difference of about 2 decibels between JB and PG when they are also in serie. Adjusting heights doesn't work at all as JB is all burried down in the cavity. Actually I can balance JB and PG as PG still has some space for getting lowered. But balancing both with JB Jr is impossible with height adjustment. So assuming that JB and PG are balanced with height adjustment of PG, I need to find a way to balance them with JB Jr which is other than height adjustment.

[JohnH]

Thanks, that's great information! We can apply some science to try to find the best outcome.

A couple more questions:

What sort of switching and pots are on the guitar, after the pickups?
Also, do you tend to play just single pickups or are combinations important too?

[kyolic]

Ok first of all, I was able to balance JB and PG by adjusting height of PG. Now they are almost equal. So the only problem here is balancing both with JB Jr.

What sort of switching and pots are on the guitar, after the pickups?

There is a tone and volume pot which are both push-pulls for controlling JB Jr. Also there is a 5-way switch.

Also, do you tend to play just single pickups or are combinations important too?

Combinations are extremely important too!

[kyolic]

Here is the new graph after PG height adjustment:

Now if we can balance JB and PG with JB Jr, all will be perfect.

[JohnH]

It looks like you probably want to get around 3db reduction, and the tripot design should be set up to work well at say 0 to 6 db?

So I'd suggest a 500k pot, treble bleed with 150k in parallel with a cap, but try a selection of caps 1nF, 1 5nF, 2 2nF 3 3nF. These are cheap, so might as well experiment using aligator clips to see what you prefer. As you adjust the pot to choose a level, the optimum cap may change, to suit your preference.

Also, given a bit of extra loading due to these pots, you might consider changing your tone pot to no-load, to compensate.

[kyolic]

Yep 3 dB reduction makes perfect sense. Yet I have no idea about where to wire the trimpot. Can you please show it on this diagram JohnH?

[newey]

Back in reply #1, JohnH said:

The starting point would be to wire a 500k trimpot exactly like the normal pot in the diagram,

Just as it is shown. Then, the wires that are shown in the diagram as going to the output jack are wired "downstream", to whatever other switches/pickups are involved. What you see on the diagram becomes a single-pickup module for your scheme. You'll have 2 of these modules, one for the JB and one for the Pearly Gates.

[kyolic]

Newey as far as I understand, you are talking about replacing the pot with a trimpot (please correct me if I am wrong) but this is not what is desired.

I need to wire a tripmot in that circuit shown in the diagram so that the pickup volume is reduced about 3dB.  So the circuit itself remains intact, except that a trimpot is added. However I need to learn where exactly it should be placed. That is what I am asking.

This is the last step for solving the issue so I appreciate if someone can draw the placement of trimpot on the diagram.

[JohnH]

like this....

[kyolic]

JohnH:

[newey]

There is a volume and a tone pot on the guitar. Volume pot controls all three pickups at the same time and this is what I want. I don't want to touch it anyway.

What I meant is that your set-up has a master volume, not an individual volume for just one pickup, as is shown in the diagram. So, that volume pot won't be there in your scenario, you'll just have the trimpot wired (as JohnH shows) after the triple shot pickup ring and before the switching, V and T pots, etc.

[kyolic]

Ah, I see now. As JohnH has drawn it on the diagram, I am good to go. I will use the exact wiring he drew. Thanks for the clarification.

[JohnH]

I drew it that way since you asked me to, and it shows how to add the trimpot after the triple-shot pickup.

But Im sure that on your actual guitar, the red wire will go to a switch rather than to a pot.

This setup with the trim pots, is electrically very similar to an LP, where instead of a trimpot on each pickup, there is a volume pot on each one. I have that on my LP, using the same values of 500k pot, 150k resistor, and a cap as shown. I just did some testing with it, turning down one pickup just a tad, which is what you are seeking. In my case, the cap is 1nF. It works fine, and the mix of say, a slightly turned-down bridge with full neck is still good, but there is less bridge in it. That is, the amount of reduction of the bridge within the combo mix is more than the reduction as a single pickup. You'll be able o experiment carefully to find the right balance for yourself. But I do expect that you might prefer one of the larger cap sizes for your use. Ill be interested in how it works out!

[kyolic]

For the treble bleed circuit, first I'll go with 150k and 1nF and see how it works. It  is the current setup on my volume pot and I am totally happy with it.

Speaking of 'amount of reduction of the pickup within the combo mix is more than the reduction as a single pickup' issue, I am sure that I will be able to find a sweet spot with two trimpots (one on JB and one on PG). I will definetely post the results here.

Also you are right that the red wire will be going to the switch as I have a 5-way blade on my guitar. Yet, I am sure that tech will figure it out as I have a diagram showing the main idea.

Thank you again and again JohnH.