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Post by cynical1 on May 6, 2011 12:32:14 GMT -5
Way back in 2008 we meandered into the subject of treble bleed capacitor and resistor values for bass guitar in the severely wandering thread Why no 3 volume pots in a design?We never really nailed anything specific for the bass, and the project referenced within that thread is coming close to being started. So...as JohnH has spent a good deal of time researching the issue for guitars, and has posted a brilliant analysis here aleady....I'm tossing this one out to see what the prevailing wisdom holds for basses. The bass will have 250K pots, and a variation on the "Free Woman Tone" mod on a master tone control, but with values of .056 uF and .033 uF, which offers the bonus value of .020 uF. So...any suggestions, rumors or conjecture? Happy Trails Cynical One |
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Post by JohnH on May 6, 2011 15:35:03 GMT -5
cyn1 - I'd be happy to run some numbers, since my spreadsheets could easily be adapted to bass guitar. The key info needed is some data on inductance, resistance and if possible, capacitance of typical bass pickups.
Treble response seems to be surprisingly important in bass rigs. Bass cabs often have a piezo tweeter in them, and Boss EQ pedals designed for bass have sliders up to 10kHz, instead of 6.4kHz on a guitar EQ
John
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Post by JohnH on May 6, 2011 17:10:15 GMT -5
Further on this: this table, has values for P bass and J bass pickups. buildyourguitar.com/resources/lemme/table.htmShall we assume yours are like the P bass for inductance and capacitance (6H and 15pF), and also use your 10k resistance measurement? John |
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Post by cynical1 on May 6, 2011 19:00:26 GMT -5
The P-Bass pickup is probably close. The Peavey Super Ferrites are a different matter. I've been all over the net for years looking for something hard and fast, but I've come up dry everytime. They are much like Jazz bass pickups, but hotter. Not blistering enough to throw your amp into fits, but you put some gain behind them and crank towards 11 and you can get some very aggressive tones out of them. But if you ramp the gain down and blend the volume controls towards a bridge inclination they get clean and almost pretty...and returns harmonics that just sing. A very under rated pickup, IMHO. This is what it looks like in comparison to a standard Jazz bass pickup:  Over the years I've grown to love these things, and properly shielded they're relatively quiet for their output. I can't think of anything better to put in their place, so I never thought about yanking them. The P-Bass pickup will just move in between them. Here's the Peavey wiring diagram for the Foundation.  Currently there's a .020 mfd capacitor on the tone control, which is as bright as I'd like it. Any more brightness and the bridge pickup would be unusable...which why I'm dropping in the .056 mfd and .033 mfd caps (which will still give the the .020 mfd in the middle of the Woman Tone switch position) to give the super ferrite neck and the p-bass pickup a bit more bottom end. The diagram does show a .001 mfd cap on both volume controls. I pulled the control plate to confirm, and that's what's in there, sans resistor. The chart you linked to only show values for a cap with no resistor. The current cap value in my bass doesn't even track on that chart. So...how does the that chart correlate to the current GN2 of a recommendation of a 150k resistor/1 nf cap for a guitar treble bleed? Thanks for staying with me on this one, John. We sort of beat this to death in the last thread. I was afraid no one would come back for this one... Happy Trails - Cynical One |
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Post by JohnH on May 6, 2011 19:23:57 GMT -5
OK, so lets think of a 10k P-bass pickup, and Jazz pickups also. What do you think the resistance of the J pickups is? (an estimate based on measuring the whole guitar would be fine). Also, will there be any switching, or will all 3 volume controls be across the output at all times?
The table I linked to was not really about TB circuits, more focused on adding caps to change response, but it is a good source of pickup data.
John
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Post by cynical1 on May 6, 2011 23:12:43 GMT -5
If I hear back from Becky that this is a pre-split Lawrence pickup I might get some specs with the reply. In the meantime, using a generic 10K p-bass pickup would work. The Peavey Super Ferrites are another matter. I don't have a meter here anymore...took it to work and it grew legs. I can borrow the crappy meter we have at work, but that won't be until Monday. I did fire off an e-mail to Peavey asking them for any\all available design specs, so if they come through that should nail it down pretty close. If not, then I'll muddle through it on Monday. Here's the original design drawing for the bass as edited by ChrisK back in 2009:  The Les Paul switch will probably get replaced for a SP3T on-on-on switch, as room is tight, and the Free Woman Tone values have changed to .056 mfd - .033 mfd, but the other controls and pots are the same. The only thing up in the air are the values for the treble bleed. Happy Trails Cynical One |
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Post by JohnH on May 7, 2011 16:07:54 GMT -5
I see danger here....
This is a video that ozboomer found, and it starts with:
"..last night I had an unpleasant surprise about treble bleed....."
Nasty...I hate it when that happens.
Its all about what occurs when you have treble bleed circuits with reverse wiring, as in the diagram above. When you turn one pickup all the way down (which is the reason to have reverse wiring if at all), the TB cap on the turned-down volume pot ends up across the whole output, resulting in death by tone loss.
John
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Post by cynical1 on May 7, 2011 17:27:47 GMT -5
Well...that's a suck...
So, if this will happen with the 1000 pF capacitor and 150k resistor, why have I never noticed any issues with the two existing .001 mF caps?
First impression is that if I only do the treble bleed on the bridge volume I'll only lose the high ends when turning down the bridge and ramping up the neck...which is usually what you do on a 2 volume Jazz type bass to deepen it up...
I admit, I followed most of his explanation, but am at a loss on how to fix it, short of just leaving the two .001 mfd caps alone and just doing the treble bleed cap & resistor on the P-Bass pickup volume only.
I am slowly creeping out of my depth here...
Happy Trails
Cynical One
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Post by JohnH on May 7, 2011 18:38:50 GMT -5
Im thinking that if the standard version with 1000pF only works ok in practice, then, it is likely to be the way to go. The reversed wiring needs the upper leg of the volume pot to rise to a high level in order to seperate the pickup from the others when turned off. The TB resistor messes that up, so maybe its better without in this case. Out of neck and bridge, if one pickup is generally up higher and the other is lower or at zero, then the lower one would maybe be better with no TB circuit. Both up high is never a problem.
But is there any way to get switching into it for all the pups, so you can properly switch off N or B and also cut out the loading due to its volume pot? If so, you can do guitar-normal forwards wiring and use the parallel TB circuits, with values to be determined. You'd think that if that was possible, it would give the clearest outputs from each pickup or combo.
John
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Post by cynical1 on May 7, 2011 21:03:55 GMT -5
Im thinking that if the standard version with 1000pF only works ok in practice, then, it is likely to be the way to go. I've never noticed the bass to lose any high end from the bridge with the neck pickup turned down. In fact, I still need to roll the tone down to around 7-8 to keep the bridge pickup from becoming too bright. So, just to make sure I'm following you here, put the 1000pF cap on the Jazz type single coils and just leave out the resistor, exactly like it is set up now...right? So, what about the P-Bass pickup? It's out there all by itself on its own volume control. Would the same value of 1000 pF apply here, or as we beat to a bloody pulp in the last thread, should it change in size based on the lower octave? It varies depending on the tone I'm after, but neither pickup volume is ever completely set to zero. This is more to eliminate any single coil hum then anything. I use basically the following "quick sets": Neck Vol=7 - Bridge Vol=3 - Tone=3 Neck Vol=7 - Bridge Vol=7 - Tone=7 Neck Vol=3 - Bridge Vol=8 - Tone=8 It may fluctuate one way or the other depending on the pedal or effect used...or how I hear it that day...but I can count on one hand the times I've had all the controls pegged to 10's. I spend probably 70% of the time somewhere between the second and third quick set. I would prefer not to do that, as the single coils on their own, especially with a bit of gain on them, then to get noisy through effects pedals. As long as the volume on one or the other is on at least 3 the whole bass quiets down nicely. I am more then happy with the current .001 mfd caps in there now. I was thinking the full treble bleed would be an improvement, but as seen in the video, with the design the way it is, it's going to hurt more then help...but I'm cool with only using it on the p-bass pickup. Which begs the original question...does the 1000 pF and 150k resistor value still hold for a p-bass pickup, or do the values need to be modified for the lower registers? ...and since we're about 9-10 posts into this thread it's about time for someone to yank it mercilessly off topic... Thanks again for staying with me on this one, John. I really want this one to be right. Happy Trails Cynical One EDIT: Perhaps I'm merely going to display my utter lack of knowledge here, but isn't a diode the equivalent of a check valve? Would a diode work in a passive circuit, or do they require some active power source to function? |
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Post by sumgai on May 8, 2011 0:55:55 GMT -5
...and since we're about 9-10 posts into this thread it's about time for someone to yank it mercilessly off topic...  The Strat is in full tear-down mode, as we type. Expect fresh, focused! pictures RSN. (But probably not here.) The pertinent part here is, I'm contemplating pulling out the Volume pot entirely - everything runs balls-out, any controlling going on takes place on the floor, or at the amp. Lemme sleep on it........ sumgai |
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Post by JohnH on May 8, 2011 1:09:52 GMT -5
sumgai ...2011 was a difficult year in the quilting business. With essential supplies running short, sumgai had to revert to extreme measures.... |
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Post by sumgai on May 8, 2011 12:04:32 GMT -5
John, The wife laughed so hard at that one that I thought I was gonna have to take her to the Emergency Room, she about busted a gut! ;D c1, was the yank good for you?  |
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Post by cynical1 on May 8, 2011 12:11:12 GMT -5
c1, was the yank good for you? I knew I could count on you guys... |
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