Pan pot, separate volume pots, ratios, and output

[grok]

I've read a bunch of threads here on this issue, but I'm still not sure I've seen the definitive answer.  From a thread back in 2004, it was posited that the pan should accomplish virtually the same thing as two separate volume pots, because at the same output level, the pan pot adjusts the ratio of the two pickups.  Thus, for every setting of two separate volume controls, you can choose the appropriate identical ratio on the pan, and then adjust for the same output using the single volume control.  My question is, for two otherwise identical basses, one having volume-pan and the other having volume-volume, is the pan wired such that with volume at max and pan in the center, you have the same setting as volume-volume both set at max?  That way, you'd have the same max output.  At that point, variations in the pan knob would yield different ratios of the pickups, with total output regulated by the volume knob.
 
I suppose there's a corollary: is there a different tone achievable by, say, setting the volume-volume at 50-50, versus setting the pan at center and adjusting the single volume to 50% volume?  Likewise, would a 75-25 volume volume setting be the same as setting the pan to 3:1 ratio and adjusting the volume to achieve the same output?  Theoretically, it seems that the combination of volume-pan should be able to achieve every possible setting of volume-volume.  If true, then the advantage of the volume-pan setup is that you can adjust the ratio of pickups without changing the overall output, and having to adjust only a single knob (this assumes, of course, that the gain trim pots and pickup heights are set so that the two pickups have equal total output).  The advantage of the separate volumes would be the ability to mix in each pickup individually.  But each should be able to reach the same ratio and same volume, right?
 
On the other hand, the volume-pan would be able to achieve max output for ALL ratios of pickups, while the volume-volume setup would only achieve max output at full 100-100 setting.  I'll call this scheme 1.
 
I'm wondering if the volume-volume setup actually produces double the volume at full 100-100 as compared to the pan at center and full volume.  In which case the volume-pan setup at max output and centered pan might be more reasonably set to achieve, say, the same as 50-50 on a volume-volume (or 75-75, or whatever makes the most sense), in order for both basses to achieve all ratios at all volumes, but then the volume-volume would be able to produce higher output at its full 100-100 setting.  If this is the case, the volume-volume setup actually has more variability because it can achieve all ratios of pickups and at a wider range of output levels.  I'll call this scheme 2.
 
(I'm actually guessing the way it really works is a collapse of scheme 2 into a modified scheme 1 due to nonlinearity, as I'll try to explain below.)
 
I hope I've not managed to confuse everything here!
 
Anyway, for example, consider the following settings for volume-volume and volume-pan, for which I've tried to make them equivalent, with volumes stated as percentage and pan stated as a ratio of neck to bridge, and assuming scheme 1, that the 100-100 setting on a volume-volume equals the 100-1:1 (centered pan) on a volume-pan:
 
Vn-Vb...........V-P
 
100-100.......100-1:1 (centered)
75-75............75-1:1 (centered)
50-50............50-1:1 (centered)
100-50..........75-2:1 (pan turned to favor neck)
75-25............50-3:1 (pan turned to favor neck even more)
90-30............60-3:1 (same)
 
question: note that the volume-pan setup can now add volume and maintain the 3:1 ratio all the way to full output, but the volume-volume can only increase output at this ratio until it reaches 100-33, at which point adding output can only be done by adding to the bridge pickup, thus changing the ratio.
 
Under a scheme 2 regime where the max output of a volume-pan is at 75% that of a volume-volume, the above chart would look like this:
 
Vn-Vb..........V-P
 
100-100.........x (not possible)
75-75...........100-1:1 (centered)
50-50............67-1:1 (centered)
100-50.........100-2:1 (pan turned to favor neck)
75-25............67-3:1 (pan turned to favor neck even more)
90-30............80-3:1 (same)
 
You can see here that the volume volume has a setting that the volume-pan can not achieve.  Perhaps the internal trims can be upped to achieve the same total max output?  Thus, if both basses have the same total max output, as set by the maximum settings of the trim pots, we're back to scheme 1, where the max output of the volume-pan can be reached for ALL ratios of pickups, but the volume-volume setup can't duplicate this.
 
Finally, I wonder if these things are simply not linear, so that a volume-pan does not in fact achieve max volume for all ratios but instead achieves exactly the same as the volume volume, by keeping the ratio up as far as it can with increaseson the volume knob, until increasing the volume knob more necessarily changes the ratio because one pickup has already maxed out.  Thus, on the volume-volume set at 100-33, if you add output by increasing the bridge pickup. you'd actually be doing the same thing on the volume-pan by increasing the volume from 67% upwards.
 
For practical purposes, of course, I have no doubt that each has its advantages and it comes down to how I make adjustments on the fly anyway.  But I'm just curious about whether they really are capable of the same thing.
 
Does this analysis make sense?  Why am I going here?  Because I'd like to upgrade the electronics in my custom, which currently has Elan electronics, and I'm trying to decide between signature and anniversary!
 
Mark
 
(Message edited by grok on April 14, 2008)

[tbrannon]

Timely post Mark- I just ordered a custom with Signature electronics and have had a couple people tell me to consider anniversary (because of the stereo output option).
 
I have a signature equipped Rogue at the moment and find the pan control to be intuitive to me- I've had several vol/vol basses in the past and have just never felt like I utilized the double volume controls very well in terms of shaping my tone.
 
So- I have nothing in terms of useful info for you, but I'll be watching to see what others have to say.
 
Toby

[grok]

I'm leaning toward the signature as well, just because I'm used to the pan control for adjusting tone on the fly without changing my volume.  And I'm not sure there'd be room in my bass for the anniversary package.  I also understand the anniversary is more expensive, though I can't find a price anywhere.  Do you know the price difference?
 
Mark

[terryc]

I think Ron's designs are to mimic the buffered setups in mixing desks, that is to provide equal gain with clarity and tone as opposed to unbuffered with passive pu's.
The Series II basses provide the ultimate mixing options with twin volumes and master plus a pu selector.
I guess for speed the pan control has the advantage, I have never found it an issue on my MK Signature.

[dfung60]

grok -  
 
This is always an interesting question (I almost certainly participated in some of the earlier threads you saw).  
 
People are always interested in the pan knob and are especially interested in why this isn't part of the standard passive Jazz-bass type setup.  A pan knob is limiting and impractical in passive instruments because the electrical relationship of unbuffered/passive pickups to the volume knob and cable causes the volume knob to be part of a low-pass filter on your signal.  You know this effect a little if you have a J- or P-bass and Tele guitar players really know this well - as you turn down the volume on the guitar, you'll find that you lose highs, similarly to turning down the tone control.
 
When you add an onboard preamp (straight gain or active tone control), the capacitance of the cable is isolated from the pickups, which has the effect of removing the filter effect.  You can turn the volume up and down without changing the tone.  This is great, but on most guitars there's only one active preamp that is part of the tone controls, which is fed by the combined signal of your pickups which were still blended passively and still suffer some tonal change.  EMG pickups have preamps inside each pickup, so they are totally active and can have a workable pan control; many Alembics also have independent preamps for each pickup.
 
The problem with the pan pot is that real-world considerations make getting the most useful part difficult.  A pan pot is usually two variable resistance devices that are attached to the same shaft and rotate in unison.  What you want each part of the panpot to do is smoothly increase the volume of it's pickup as you turn it from one end of the rotation to the other.  But it's quite hard to actually make this happen, because your ear perceives volume changes logarithmically instead of linearly.  If you increase the resistance of the pot from 10Kohms to 20Kohms it only sounds slightly different (-3dB) instead of sounding half as loud as you might expect.  The pot is built to compensate for this when it's constructed - this is what's called audio taper - the device is constructed so a 30 degree rotation has the same perceived difference in volume anywhere across the entire rotation of the knob.  These are the normal kinds of pots that you would have on your instrument and are a garden variety part.
 
The problem with a pan pot is that you need one side to be audio taper, but the other side needs to be reverse audio taper to smoothly change the volume on the other pickup.  Most panpots sold aren't like this, I think.  They use two regular audio taper pots in the stack, with one wired in reverse of the other.  When you do this, one pickup will have a smooth graduation in volume and the other will change very abruptly from loud to soft.  Because both pots are controlled from the same shaft, if your panpot is like this, there are many volume ratios which you can't achieve at any position of the knob.
 
Things get even worse in the middle, 50-50% position.  At this point, both pickups are not at full output.  If this where a passive Jazz bass, you're in a world of hurt now, because you're getting a treble loss on each pickup because they're both turned down.  You can get the full treble tone of either pickup at the extremes of rotation (e.g., no blend) but you can't get that tone in any blend combination.  Bartolini pickups are normally built as regular passives, followed by an active master EQ circuit.  Many basses that use Bartolinis have the blend knob before the EQ and suffer this treble loss when both pickups are on.  If you have an Alembic with independent EQ on each pickup, then this problem shouldn't be an issue.
 
Because both pots are driven on the same shaft, you can't really dial up any ratio you want - you only get the combinations that were pre-built into the pot when they made it.  At the midway point, you get something like 50-50.  But you can only get 60-40 if there's a position of the shaft that happens to put the two pots into a 60-40 ratio. If both sides have the proper taper, then you probably can find that ratio somewhere (probably not where you expect though)in the rotation, but, for instance, if one of the pots is not reverse audio taper, that position may just not exist.  You can dial in any arbitrary ratio with independent volumes, since each pickup can properly be set to any output level 0-100% independently.
 
Because the proper pan pot would be so rare and people with passive blending want it, there's an alternative pot you can buy out there intended for this purpose.  It has two pots with a custom taper - one pot has audio taper for 50% of it's rotation and stays at 100% for the other half of the rotation.  The other pot on the shaft is at 100% for the first half of rotation and reverse audio taper on the other half.  With a pot like this, both pickups are at full output in the middle position which solves the passive blend control problem.  But when you rotate this device away from center, one pickup is not changing in volume while the other is decreasing.  You should be able to find any ratio in this device, but again, it might not be where you expect it to be.
 
If you've made it this far, you can see that the problem is caused by the need for audio and reverse audio taper and then connecting both the pots to a single shaft.  The individual volumes don't have any of these problems.  What the indivdual knob set up loses on is that you can dial up any blend but you can't easily raise or lower that level while holding the blend.  But if you're considering all this complicated stuff, you can more easily fix this with a master volume knob which is again a garden-variety pot serially taking the output from the two pickup volumes.  
 
Is it a coincidence that this happens to be the basic configuration of the Series II bass?  I don't think so!  (Because the Series bass is stereo, the master volume pot on a Series II is a dual pot too, but it has two regular audio taper pots that run in the same direction, so it's not too exotic).  
 
By the numbers, I think it's pretty hard to argue that a blend knob can do more for you than individual volumes. But if it's easier for you to use and, er grok the pan pot, then go for it!
 
You also asked a bit about maximum output levels and whether indiv volumes will be louder.  The answer to the latter is probably yes, but you probably wouldn't really notice the difference.  The reason the difference exists is because, in the middle or 50-50% position, both pickups in the panpot model are turned down at least 25% and possibly more.  But I think it's unlikely that you would notice the output difference in any meaningful way.
 
Sorry in advance for any brain-burn,
 
David Fung

[terryc]

David..I soldered a treble bleed capacitor onto my Strat to stop the loss of highs..a mod worth mentioning???

[grok]

Thank you, David, for a cogent explanation.  These are exactly the kinds of things I was thinking about.  And your last answer provided useful info, in that at the 50-50 position of the pan pot, each pickup is putting out less than its full volume.  So to achieve the equivalent of the 50-50 position of a pan pot with a volume-volume setup, you'd set both volumes to something like 75% or so.  And then adjust to taste from there, adding a bit of one, subtracting a bit of the other, or even boosting or diminishing both.  This would seem to offer a bit more flexibility than the pan, though in practical application it may be very little.  I usually play with the pan at or near the mid position, and tweak a bit depending on how I fit in with the rest of the band.  With a volume-volume, I'd tweak two knobs to taste.  Easy enough.  So if I'm trying to decide between signature and anniversary electronics, the other advantage of the latter is its pickup selector, and its ability to do a stereo split of the pickups, though my current rig wouldn't support that.  Maybe I need an SF-2....
 
Mark

[LMiwa]

There are pan pots made where the center is 100% of each pickup. They are made so that for each of the stacked pots, half of the rotation is 100% and the other half is audio taper. As you move away from center, it cuts one pickup but does not increase the other. The down side is that the center pan position is 3db louder than either end.
 
Also, there are a number of ways to wire a passive pan pot, some of which have far less of a filtering effect. I believe Rick Turner did an excellent series of columns in Bass Player a few years ago on this exact topic.

[bob]

Another thank you, David. I knew that pans were generally a bad idea for passive instruments, but now I sort of understand why.
 
But I'm still trying to figure out what conclusion I would personally come up with after reading all this. Actually, I know that I prefer a pan, and it doesn't bother me in the slightest that some others prefer multiple volumes - but this is a recurring topic, and it still seems a bit fuzzy to me.
 
Given that the original question here was in regard to Signature versus Anniversary electronics, we know that we have active electronics, with a separate preamp per pickup, so we can disregard the tone control issue.
 
So then there is the matter of what sort of tapers we actually get with an Alembic pan - and I don't see anything about that. It seems there have been some issues over the years, such as noticeable volume changes either at the extremes, or just slightly either side of center (I could only find a post on the former, but I'm nearly certain I've read about the latter as well). I believe both of these have been addressed, and that the current pans work very nicely.
 
For the moment, let's assume that what we get is a proper taper and reverse  taper. If I understand correctly, then this should allow for any possible ratio of the two pickups. There is still the point that it may not be exactly where you expect, but my reaction to that is so what? It's not like I have a little scale printed beneath the knob, or even that I know in my head exactly what ratio I'm looking for - I'll turn it until I hear what I'm looking for.
 
So the first remaining point of significance, I believe, is that a pan (of the type I'm assuming) will not give me 100% output of both pickups simultaneously, something which I could do with separate volumes. And again, so what? As you note yourself, it's unlikely to be a meaningful difference.
 
I'm still a little curious about that myself, and it seems there are at least two potential considerations. One is about the maximum possible output level of the instrument, which (for identical settings of the internal trim pots) would be slightly greater for the multiple volume setup. Does that matter? Frankly, I've generally been happier with the sound I get from a lower volume setting on the instrument, and more of the gain in the rig. This seems to be mostly a matter of reducing some (very low level) noise in the electronics, or perhaps the cable - I don't believe I hear a difference in tonal quality. But in any case, I can't see that slightly limiting the maximum possible output of the instrument could be a concern.
 
The other possibility is that perhaps (maybe) you can get slightly different tone out of the pickup at maximum volume, versus the highest volume you could get when panned to center. Other than personal preference on the issues of convenience with different controls, one of the key questions (at least in previous threads) remains unanswered: can you really get different sound, or not? To put that another way, if you turn down the trimpot from max to maybe 75% or even 50%, and then adjust volume elsewhere to match, does it really sound any different? I haven't tried this in a while, but my recollection is no.
 
Maybe I'm missing something or am making invalid assumptions, but if (a) we have a proper set of tapers on the pan, and (b) there is no audible tonal difference between the output of a pickup at max versus some point moderately less than that, then I would have to conclude that it all comes down to ergonomics or convenience of the controls - not flexibility in what can be achieved.
 
And unless you add a master volume, I simply cannot comprehend how two separate volumes could possibly be more convenient than a pan. But that's just my preference speaking.

[tbrannon]

Bob,
 
You hit the nail on the head for me with this statement And unless you add a master volume, I simply cannot comprehend how two separate volumes could possibly be more convenient than a pan. But that's just my preference speaking.
 
I've only owned two basses in my life that were setup vol,vol.  I ended up having both of them rewired because I just never did get the hang of the two volume thing.  
 
I'm a simpleton though.

[dfung60]

Bob -  
 
I left out a couple of things when I wrote my original long response.  One of those was a more emphatic statement that ultimately it's a matter of what's convenient to you rather than what theoretically should be better on paper, and I'm actually in total agreement with you on that.  With basses that blend at the passive level, there are real problems that are tricky to overcome with pan pots, but with dual preamp active systems, it's much more a matter of what you like.  Ultimately, you need to like the sound you're getting regardless of how the signal path looked to get there.
 
lmiwa pointed out that there are special taper pan pots out there that try to address this problem (Stew-Mac lists them although they are often out of stock).  I was well aware of those, but figured everybody's head would be spinning so hard already that nobody wanted to have yet another variation thrown in.  This part addresses the problem of the center position being turned down and therefore having an effect on the tone of a passive bass.  This is definitely a useful part if you want to have pan on a passive bass and would be useful on an active bass as well (the Stew-Mac custom part isn't in the right value for most active EQ systems but you could work around that).  You should be able to blend to any ratio of the pickups, but the places in the rotation where you find certain ratios may not be where might guess they would be.  Again, that's OK because you will care more about the resultant sound rather than achieving a pickup blend ratio accurate to 2 decimal points...
 
The difference in max volume is unlikely to be more than 3dB which would be a noticeable but not huge volume difference (+3dB is double the voltage, but you need a +10dB increase to perceive the difference to be twice as loud).  As I mentioned before, you can let your sound engineer worry about differences at this level, but I don't think you'd notice much difference.  
 
Theoretically, there shouldn't be any difference in the end tone regardless of whether you favor low or high levels on the instrument as long as the amp gain is adjusted to yield the same output level.  In practice, you will hear a difference that has to do with amp headroom.  If you run high output levels from the instrument, then you are more likely to create more overdrive/distortion in the front end of the amp.  Adding distortion will have an audible effect and will tend to sound more compressed as well.  When you notice the difference between these two setups, I think that's probably what you're hearing.  This is not only steady state distortion, but a lot of this is the initial attack of the string which may briefly distort, then clean up for the sustain portion of the note's envelope.  I'm a grindy guy myself and would always prefer a little more output from the instrument.  
 
Ultimately, your ears are always the best guide!
 
David Fung