Andy 40's JBA-4

[Hobastard]

I paid 15 postage for the bridge which still brought it in under retail.

[Andy40]

nice job!....and damn you!

[wokkaboy]

hey Hoby are you talking aussie dollars ? good deal if it is !

[Hobastard]

http://www.stewmac.com/Closeouts/Mig...ss_Bridge.html
All in Dollars Aust.

[wokkaboy]

good deal Hoby, sexy looking bridge

[WeirdBits]

Always good to keep an eye on the Closeouts.

[Simon Barden]

This has been niggling me, so I've been thinking, and Waz, you were right. What is probably happening with the treble bleed circuit is that when one volume is turned off, the combined output is connected to ground via the treble bleed capacitor. You now have to make assumptions for the pickup impedance but at 7k ohms, a 0.001uF/1nF capacitor has a high-pass cut-off frequency of around 22Hz. At 3k ohms, its around 55 Hz. So it's likely that almost all of the audible output signal is passing to ground via the treble bleed capacitor.

A solution to this is to use the 'Kinman' version of this, which is to have a 130k resistor and 0.001uF/1nF capacitor in series. The resistor stops most of the signal being passed directly to ground in this two pickup configuration, whilst still allowing some high frequencies to bypass the volume pot and keep the tone brighter as the volume is turned down. Google for 'Kinman treble bleed mod'.

Since doing some searching myself yesterday, I've now seen a lot of frequency charts showing the responses at different levels of volume turn down, and the 'Kinman' version does look less coloured than the parallel configuration. However, all of the responses were for a single pickup configuration, without any connection to another pickup circuit. But even the Kinman mod does mean that means that with one pickup turned right down, the other pickup's output is connected to a resistor and capacitor in series - which has a low cut-off frequency. Which is identical to the tone circuit! Except that the resistance is around half that off the tone pot when fully up, so that it is going to knock some treble off that pickup's output.

So you get a swings and roundabouts situation here. You win by having a brighter overall sound when the volume controls are partially reduced, but lose brightness when one pickup is turned off or nearly off. Not ideal if you want the full bright bridge sound from a Jazz Bass or want to hear the high-end from the neck pickup.

So, I would suggest that for a two volume, one tone arrangement, you don't fit the treble bleed circuits. They really do work best with on a single common volume arrangement.

On the modern Les Paul type arrangement where the both pups on position the output goes dead if you turn one volume pot down, then it's not a problem to have them on both volume pots, but it's not a good idea to have them if the wiring arrangement is the vintage style (which doesn't suffer from treble loss on volume reduction in the same way anyway).

[WeirdBits]

Exactly Simon, not good for jazz style twin volumes.

[Simon Barden]

I got something right! Whoot!

[wazkelly]

And I just stumbled upon it and thank Scott for his advice to remove and all was good again.

For what it is worth when playing around with the 2 x volumes if one is nearer to 10 than the other it dominates the signal coming out, so switching from neck to bridge and vice versa is a simple as slightly backing off the unwanted one, and both wound back to zero to mute (one might do it but just a habit to turn all vol's off).