Vintage Jazz Bass: Stack Knob Vs. VVT

Precisionb87 · #1 02-13-2011, 05:22 PM

As some of you may know, The fender custom shop is reissuing the 1960 Jazz Bass which features the concentric "stacked knob" configuration. This particular setup has also been offered on the American '62 J-bass for a number of years as well.
Jaco Pastorius said a couple times in interviews that the concentric knobs where the first thing to go for his fretted and fretless Js because he thought they had a negative effect on tone.
Having a little electronics background, and by looking at the wiring layout, I can see that the the effected tone and volume of each pickup in the concentric layout must then run through a 220k resistor, then to the output.
SO, I guess my question is; What is your opinion on the matter? and Has anyone done any scientific testing and measurements on this subject? How much voltage is being dropped across those resistors?

TheMinutemen · #2 02-13-2011, 05:38 PM

I played a 62 reissue for about 8 years at one point. If I ever went back to playing a jazz bass I would go with the stacked pots. I cant provide a technical reason for you, but I prefer them. Thought it gave the p/u's a little more range....if that makes any sense. I felt like I could almost get a p-bass sound out of the bridge p/u that I could not get with my American jazz. But then again, im an idiot.

Billy Low · #3 02-13-2011, 05:44 PM

I prefer the stack knob config. It seems to be a bit more flexible for me.

**line6man** · #4 02-13-2011, 05:53 PM

Quote:

Originally Posted by Precisionb87

Has anyone done any scientific testing and measurements on this subject? How much voltage is being dropped across those resistors?

If you really want to know, I'll hook my bass up to an oscilloscope tonight with a probe before and after a 220K resistor, and get you some pics of both waveforms.

Rano Bass · #5 02-13-2011, 05:56 PM

Boby Vega also modded his old jazz from a stack to a v-v-t setup.
He said it sounds better.

Low Class · #6 02-13-2011, 05:59 PM

3 knob sounds better.

Scobac · #7 02-13-2011, 06:01 PM

I thought the values on the concentric pot were different from the V.V.T. setup. I like the V.V.T. setup because I cant roll one pickup out of phase from the other and not worry about the tone being changed as well! Some times the inner shaft of the pot won't move independently of the outer shaft!

Precisionb87 · #8 02-13-2011, 06:24 PM

Wow, line6man. Yea, If you don't mind... For the sake of science of course.

@ everybody else, please don't just say that one is better then the other. Offer a slightly more detailed explanation. Volume? Tone? Both? Thanks!

Precisionb87 · #9 02-13-2011, 06:26 PM

oh, and if you do, be sure that the guitar is under some sort of input load.

vin*tone · #10 02-13-2011, 06:36 PM

Quote:

Originally Posted by Precisionb87

As some of you may know, The fender custom shop is reissuing the 1960 Jazz Bass which features the concentric "stacked knob" configuration. This particular setup has also been offered on the American '62 J-bass for a number of years as well.
Jaco Pastorius said a couple times in interviews that the concentric knobs where the first thing to go for his fretted and fretless Js because he thought they had a negative effect on tone.
Having a little electronics background, and by looking at the wiring layout, I can see that the the effected tone and volume of each pickup in the concentric layout must then run through a 220k resistor, then to the output.
SO, I guess my question is; What is your opinion on the matter? and Has anyone done any scientific testing and measurements on this subject? How much voltage is being dropped across those resistors?

The Original had the 220k Resistor but the RI does/didn't. I installed one in my 62AVRI to get more independence in the 2 tone knobs.

You can get a wider tonal range from the stack knob - One of my favorite settings has the bridge tone open and the neck bassy... but I'm very tempted to try a VVT in my 62RI to compare.

**line6man** · #11 02-13-2011, 10:05 PM

Ok, here are two pictures which each display three waveforms on the screen. I simply played a random note on my bass and hit save as quickly as I could to capture a random waveform from the bass.
Obviously this leaves a lot of room for the accuracy of the readings to be questioned, but hell, you've got 6 waveforms to look at, you can sort of average out the voltage differences from this data and still be reasonably accurate.

FWIW, as a simple reference, the voltage drop from a 1KHz 1V Sine wave from a function generator with a 50 Ohm output impedance was somewhere between 80mV and 100mV.

Quote:

Originally Posted by Precisionb87

oh, and if you do, be sure that the guitar is under some sort of input load.

1M Ohm input impedance on the scope. That's about the same as most amps/preamps/etc.

I don't know the output impedance of my bass, but it should be noted that I used a PJ bass with both pickups parallel, as I don't own a standard Jazz bass with two single coils. The output impedance should be a little bit higher than a standard J.

SJan3 · #12 02-13-2011, 10:22 PM

Far too technical for me but I owned both '62 Jazz reissue and Lakland JO USA, both concentric knobs. I felt that it was too difficult to dial in different tones on the fly during a gig.
I find VVT much more inviting and, as someone else said, no fear of tone affecting volume or visa versa. Also, the stack knobs had a brittle feel that I didn't like at all.
I sold both the '62 reissue Fender and Lakland and now play an American Jazz with VVT. Much happier!

walterw · #13 02-13-2011, 10:40 PM

OK, help me out here (i'm not an ET).

on that scope, up/down is the voltage positive or negative from the zero line, right?

what is left/right telling us?

**line6man** · #14 02-13-2011, 10:44 PM

Quote:

Originally Posted by walterw

OK, help me out here (i'm not an ET).

on that scope, up/down is the voltage positive or negative from the zero line, right?

what is left/right telling us?

The X axis is time.

Concerning the voltage differences, each vertical square represents 20mV.

walterw · #15 02-13-2011, 10:48 PM

OK, that's what i thought.

so the two graphs show (on average) a bigger swing from negative to positive with each hit and a slightly closer to true sinewave shape without the resistor. that to me would imply a louder, clearer tone without it.

**line6man** · #16 02-13-2011, 10:57 PM

Quote:

Originally Posted by walterw

OK, that's what i thought.

so the two graphs show (on average) a bigger swing from negative to positive with each hit and a slightly closer to true sinewave shape without the resistor. that to me would imply a louder, clearer tone without it.

The waves look about the same to me, just at different amplitudes.

walterw · #17 02-13-2011, 11:45 PM

did you what, set the scope for a certain frequency, then play a note at that frequency to get the wave?

it looks like the first batch are all more similar, and all more closely approximate one big cycle, while the second batch are all over the place.

the first batch also look like they spend more time away from zero, which to my untrained eye implies a larger signal (though the second batch does have a couple of bigger peaks).

**line6man** · #18 02-14-2011, 12:26 AM

Quote:

Originally Posted by walterw

did you what, set the scope for a certain frequency, then play a note at that frequency to get the wave?

it looks like the first batch are all more similar, and all more closely approximate one big cycle, while the second batch are all over the place.

the first batch also look like they spend more time away from zero, which to my untrained eye implies a larger signal (though the second batch does have a couple of bigger peaks).

The scope is set so that the amount of time each square (Or division, as it's properly termed.) represents is in the range that you can see the waveform clearly. If it's too slow, the waveform is stretched out so much that you just get a line scrolling across the screen, and if it's too fast, the waveform is scrunched together so tightly that you just see a giant rectangle across the screen. 1ms/div was the appropriate time setting to get a good look at the peaks of the waveforms from a bass.

The actual waveforms mean nothing, in this case. What is important is the change in amplitude that you see between them.
When you play a bass through a scope, you basically see squiggles dancing on the screen. These 6 happened to be what was on the screen the instant that I hit save to capture them.

**woolysock** · #19 02-14-2011, 12:47 AM

Hmmmm... I have 62ri from 1997 w stacked knob configuration. Sounds great. The bridge pup tone knob only affects the bridge pup, and the neck tone knob only affects the bridge pup. It's a moot point though because I run both pups full volume and tone knobs wide open. Sounds great.

Mr_Dave · #20 02-14-2011, 04:58 PM

I do like the sound of stack knob basses but I prefer the VVT setup in general, I find it way easier to adjust on the fly too