Compensating output levels in PJ sets

[bea]

Hi there,

actually nearly a FAQ. Compensation of the large difference in output levels in a PJ pickup set. Usually the P cannot be lowered sufficiently to compensate or You might want to have the more aggressive tone of a split coil not too far away from the strings.

A transformer with a ratio of about 3dB (1:1.4) would probably be sufficient. I am aware on the effect of the transformer on the resonant frequency of the pickup - pickups like the Dimarzio Ultrajazz might actually profit from that effect.

I found a few transformers in the Xicon TM... series - but i am afraid the core would already suffer from saturation effects in the lower registers. Any hints for more capable but still small transformers? Maybe with a 25mm core?

[Helmholtz]

Not sure, if I understand. Why not simply wire a suitable resistor in series with the louder PU? Any loss of highs can be compensated by a capacitor in parallel with the series resistor.

[okabass]

" suitable resistor in series with..."
Or a 50...100 kΩ trim pot.

[bea]

This is just what i'm going to replace....

[Helmholtz]

This is just what i'm going to replace....

Why?
A good quality miniature high impedance/inductance step-up audio transformer will probably cost more than a new PU. Unsuitable transfomers will cut bass response.

[bea]

I did not get the sound right. A voltage divider with treble bleed resistor usually sounds "weak" in that range.

[nhbassguitar]

I'm assuming the P pickup is the louder of the two. Depending on how tall the pickup is, you might be able to lower it more than you're able to now by shaving the foam to half height with a utility razor blade. You can also try Stewart-Macdonald's foam with built-in springs, and put that foam only directly under the pickup ears (where the screws go through), which I believe would let you run the pickups really low. You could cut the foam to a very small size to limit its contact with the bottom of the pickup body.

The only downside I can think of is that if you move the pickup(s) so low that the strings are only barely in the magnetic field, then that reduced-volume pickup may also sound flat and non-dynamic, as if you were playing through a preamp with a weak vacuum tube.

[bea]

The only downside I can think of is that if you move the pickup(s) so low that the strings are only barely in the magnetic field, then that reduced-volume pickup may also sound flat and non-dynamic, as if you were playing through a preamp with a weak vacuum tube.

And that's why i'm considering using a transformer.

Actually one of my target basses has the J-pickup so close to the bridge that it would profit of a lowering of the trebele resonance frequency.

[David King]

Cinimag makes some of the nicest DI and other audio xformers around. They used to be in the $50 range.

I'd suggest dropping 1000 turns off the P pickups and/or demagnetizing them slightly. Likewise you could bring the turns count of the J pickup up to 10,000 turns.

[LtKojak]

The simplest solution in this specific case would be a "blend" pot.

[copperheadroads]

Beef up the Jazz pickups output by start winding with smaller wire or finishing with smaller wire like 43 gauge so you will have to change & join wires half way through the wind .

[bea]

I just tried the transformer idea, using a Monacor LTR-110. This is a fairly cheap yet still good line transformer with a secondary for 1:1 and one for 1:0.5. connecting them and using them as an autotransformer with a 50Ohms source and a load of 33k worked fine. But with the high impedance pickup the sound was thin, and the level was very low. Looks like a strong mismatch.

(I bought the transformer for DI-out in a forthcoming tube amp project, a task where it is doing very well.)

Well, the probably best thing might be a really hot J-pickup for the bridge matching the split coil as suggested above... and in one of the two basses in question that's the only option anyway, because space is lacking for the transformer.

The "blend pot" approach is what i'm more or less using now, realized by a four way switch.

[Helmholtz]

A transformer for a PU needs to have a considerably higher primary inductance than the PU's to not load down the PU especially at bass frequencies. Meaning 20H or more with a Hi-Z PU.

[bea]

That's what i actually expected when i thought about the idea the first time - but i wanted to try. (And it was fun to see an autotransformer actually transforming upward on the scope).

As i don't want to bother with ultra fine wire i think i'll send a request to Christoph Dolf.