All about Tubes, Tube Circuits, Tube Gear

Sunday, March 9, 2014

Overdoing and Removing Cavity Shielding

Without making too much out of the loss of treble / sparkle due to ground/shield capacitance, it is true that this effect is quite measurable and audible, and can also lead to undesirable side-effects.

The Zexcoil fellow recently studied shielding on cabling from pickup to controls as a result of some anomalies noticed in cable brands, and as a side-issue he measured also the capacitance effects of cavity shielding. I believe he measured conductive paint (graphite) used to shield pickup cavities, but one should expect that even more dramatic effects will be found when using copper shielding.

Copper Shielding

Some recommend copper as preferable because it is a much better conductor, and a better Radio Frequency (RFI) shield for noise reduction. And this has become more important in a heavily polluted radio environment we now live in, with multiple sources of interference, from cell-phones to satellites.

To get equivalent shielding with conductive (graphite) paint, one must usually use two or three coatings and build a thick layer.

However, a disadvantage of copper is that it is also a natural capacitor.

This capacitance effectively bleeds treble to ground, and can also cause or alter natural resonances and frequency response.

So people have discovered on their own that removing either paint or copper shielding restores the sparkle or clarity and dynamics of single coil pickups, and even modern noiseless ones.

The drawback is that of course the noise and hum returns to the signal path.

I recently acquired a MIJ body already fully shielded with copper, and routed only for single coil size pickups. Obviously the concern was that I would lose the expected sparkle and dynamic response from either single-coils or stacked noiseless pickups.

Looking at the problem closer, it was obvious that far too much shielding was used to shield the cavity, and that much of it was superfluous and could be removed while retaining most of the effective shielding of the cavity.

For instance, as I will show in the photo, a large amount of the shielding inside each pickup cavity can be removed without degrading shielding.

The inside facing, and sandwiched walls do not need to be shielded in these cavities, because they are already shielded by the outside walls and edges.

Removing the copper from these sides dramatically reduces the stray capacitance of the cavity, while preserving the shielding against outside RF sources.

 Photo 1:

Here you can see where I have cut out the top half of the shielding in the middle pickup cavity.   The middle pickup is certainly heavily shielded already from being sandwiched between the other two cavities.    Stray RF coming at the guitar endwise is caught by the outer shielding and the other pickups.

 Photo 2: 

Here is shown that much copper laying in the bottom of the cavity has been cut out, drastically reducing the stray capacitance expected along the cables/wire leads running from pickups into the controls area.  This copper does little to shield the pickup network from RF, but adds a significant amount of capacitance to ground for the signal path.  Also, the copper is an added hazard that can short out or ground bare wire, eyelets or solder-points on the back of a pickup, if it is lowered too far into the cavity.

If the pickups are not suffiently brought back to life by this removal,
one can go even further, either leaving narrower strips, or simply disconnecting most of the copper from ground. There is no need to remove all the copper unless the results are not satisfactory. Its a law of diminishing returns here, and some shielding is desirable, even with "noiseless" pickups.

Saturday, March 1, 2014

Lace Holy Grails - Swelling of Pickup

I bought some used Lace Holy Grails on Ebay.

When they got here, I started to install them in an Anodized PG,
and noticed they had swollen somehow, so that the plastic covers
(which are glued on with these ones) were binding in the hole,
and preventing the pickups from rising up higher without forcing.

I don't want to file the anodized (new) pickguard,
although I probably would have, if it were simply a plastic one.

I am suspicious that either the glue melted in the sun or was a poor choice
in the first place.

I haven't established whether the pickup covers were originally glued on,
i.e., by Lace, or if this was done by previous owner(s) to prevent them rattling or being removed.

If anyone has Lace Holy Grails, I'd like to know if the covers are glued on.

Secondly, I am wondering what the cause for the swelling is:

(1) glue swelling or bubbling over time,

(2) glue reacting with potting / coatings in coils.

(3) glue partially melting or swelling in the sun (the pickups have a noticable brownness to the tops (only).

(4) I am also wondering if someone had previously tried to darken or age them using coffee staining or heat. This might have damaged the original glue and/or expanded the plastic covers.

(5) Someone perhaps using improper glue to fix the covers and this just not working out one way or another.

(6) Maybe someone tried to heat and soften or loosen the glue, to remove the plastic covers and see inside, but this tactic failed? Now the pickups are out of shape.

I am obviously concerned because any tampering may have also affected the sound or reliability of the pickups, even if they appear to function.

Does anyone have experience owning, examining, and/or installing these pickups?

Notably, do they come glued together?

Has anyone ever had problems with them swelling or binding in slots?

Noiseless Stacked Single Coil Pickups: Entwhistle and Dragonfire

I just purchased a set of Dragonfire Noiseless stacked single coils,
and two Entwhistle 57 Noiseless stacked single coils, on Ebay.

The Dragonfires were about $60 USD a set plus $12 shipping and $15 import duties/handling = $88 ($30 USD per pickup = $35 Can.).

Dragonfire Strat Pure Noiseless Pickup Set


 The Entwhistle 57s were $30 USD + $10 shipping
(no import/handling duties to Canada) (=$40 USD each or $45 Can.)

Entwistle ASN 57 Alnico noiseless

 First off, they look near-identical, except the Entwhistles (unlike the Ebay pic),
had four metal eyelets and a 4-wire cable, whereas the Dragonfires were
simplified, with three eyelets and a 2-wire cable, prewired.

Presumably, the Dragonfires have simplified the wiring because there is only
really one feasable wiring option (e.g., series) and less chance for wiring errors
by buyers.

The Entwhistles are advertised as Alnico magnets (and there are no under-magnets, just the pole-pieces) and they look identical to the Dragonfires.

The Dragonfires are advertised as copies of Fender Noiseless 'vintage',
and so presumably the Entwhistles are also copies of that basic design.

Both look near-identical and appear to have been made from the same factory.
Something of importance to those looking for the best price.

 Differences in wiring harnesses shown below:
The Entwhistles allow for bypassing the noise-cancelling coil,
and other wiring options for experimenting, whereas the
Dragonfires are pre-selected but simple to wire up.

There is probably no RWRM configuration for the 'middle pickup' option,
since the noise-cancelling coils remove the need for fancy phase reversals,
or magnet inversions.  The quack' factor however will be different with the
extra coiling, but probably no different at all from standard Fender noiseless.

Both sets seem to have identical magnet staggering, probably as a result of
the use of the same Alnico magnet sets.

A quick measurement of the Dragonfire coils showed no difference in DC
resistance between the Neck and Middle pickups, (e.g. 10.18k for both),
while the Bridge pickup is slightly overwound (e.g., 10.21k for bridge).

Presumably had I ordered a full set of the Entwhistles, there would also be
a similar difference:  They make you specify which position you want for
each pickup bought on the Ebay page.

Although there is no electrical difference between the Neck and Middle,
there may be another difference, for instance a different grade of Alnico
magnet or different degaussing, for each position.   They are clearly marked
on the back to prevent mixups.

I am not set up to measure magnetic differences or resultant impedances.

I fully expect both sets to perform about as well and sound very similar to
the standard ('vintage') Fender noiseless, or slightly better.

I am not imagining to be able to tell much difference.

those buying these pickups should be aware that REMOVING any extra shielding, i.e., copper or even paint in the pickup-cavities, or reverting to an unshielded plastic pickguard might give the best results, as the metal shielding is
known to roll of the treble response and dull the pickup sound.

So far it looks as though the Dragonfires are a licensed copy of the Entwhistle, which is roughly a knock-off of the Fender Noiseless, but with probable improvements by Entwhistle, who appears to be the designer behind these
nice, cost-effective Noiseless pickups.