Control questions

[David Houck]

Bob; it seems to me that I recall Mica posting on this subject quite some time ago, though I could be mistaken.  But it does seem that she, or someone, posted a reasoned explanation of the difference between separate volumes and a pan.  But I don't remember the explanation.

[rnolan]

Hey All, well this is a very old (2004) topic, I was sent the link in another thread/post as we were talking about 2 vols (as I have on my Brown) and other setups.  I don't know much about the Series II and other Alembic electronics (yet) but I'm an audio engineer so I know a bit about other parts of the discussion, so in case anyone's interested:
First Pan and Blend are 2 different things. Typically Pan takes a signal and routes it to 2 separate buses (eg Left & Right), Pan pot directs more or less of the signal to either bus, think mixer, signal in vertical channel, bus horizontal (FX bus, monitor bus, main L/R buses). Often there's a 3db cut/drop built in to the centre position (as signal is going equally to each buss (so 3db increase in overall output), Same idea for speaker crossovers BTW.  Then there is Blend, 2 signals in (from each PU) combined to 1 out (to master vol) so where you dial the pot controls how much of one PU vs the other gets through.  Also most vol pots (and faders on a mixer) just let the signal through, full open = all signal passes, turn down (increase resistance to signal flow) so less gets through full off no signal. Concepts the same for both active and passive just done a bit differently in the circuit.  Otherwise, if it boosts it's now a gain control not a vol pot.
The dual ganged opposing pot has been around a long while, eg the ADA MP1's FX loop send/return pot.  Designed to maintain unity gain (what goes in (volts wise) is what comes out (volts wise)) so you can adjust for instrument level FX vs Line level.

The PU vol pots may well be different at different settings?, partly depends on how linear the pot is, but also, less output = less gain into the filter (so also depends on the filter design how it reacts to that).

The advantage of the master vol from my take on it is, it's like a mini mixer. You can set the vol pots and or blend? how you like them and then turn that up and down to suit without loosing the PU balance.  Now normally this wouldn't be such a big deal. But these Alembics have such a wide tonal pallet I can understand why you'd want to preserve the exact balance between the PUs.

Now how this works into the Alembic "quasi stereo" circuit I'd have to either play around with one (which I don't have) or see a circuit schematic.  eg how does the master work in with the separate PU outs ?  Anyway the above concepts stay the same regardless. Seems it would good to find Mica's post that David alludes to as she (obviously) knows the circuit and what she's talking about. 

[gearhed289]

I've been interested in this topic for a while too. My (completely unfounded) theory is this - a blend (or pan as Alembic calls it) control in the center position has both pickups at full volume. As you rotate toward the bridge, you're turning down the neck pickup volume. As you rotate toward the neck, you're turning down the bridge pickup volume. Then they go through the master volume. So (again) theoretically, a blend performs the exact same function as 2 volumes, just in a different manner. Or not... 

[bigredbass]

Bear in mind this is coming from someone who thinks owning a S2 and running it thru a SuperFilter and God Knows what else is waaayyyyy beyond what my grey matter could handle.  Not enough grey matter for that many knobs !

My Elan Five has Sig electrics.  The Pan ostensibly is a 50/50 blend at the center notch (yes, you can feel it).  Having said that:

a) In my case, I'm running P/J Activators with the J backed up right to the bridge.  Believe everything you've heard in terms of the P being much higher output than the J.  If you are looking at an Alembic with a J bridge, I've seen more than a few where the installation is about a pickup width away from the bridge, I would definitely recommend that.

b) Of course, this is exaggerated by the pickup placement.  The string just ain't moving much next to the bridge.

c) Gain-wise, these are low-imp pickups, so raising/lowering affects tone mostly, not much change raising them for output.

d) And ultimately, the preamps in the back determine the overall blend the most.  In my case, to approach getting them 'even' at the midpoint requires a lot on the aft preamp and a much less on the neck preamp.  Of course, that's the beauty of the preamps, you're just not tied to the values in the pots or the native output of the pickups alone.

Remember this is with PJ's and Sigs, can't comment much on the same application with AXY's or FatBoys.

I'm essentially looking for that PJ tone, so mine's set to where I'm hearing all that P beef with some J articulation at the mid point.  If I need more Jazz tone, I'll pan back a bit, and if I want a P bass sound, l'll lean it forward.  Like most pans though, I don't think (I could be wrong . . . . ) that full throw either way 'solos' that pickup, it sounds like you never completely lose the other.  I set the preamp gains with the pot on the middle detent so my adjustments are centered.

Joey

[dfung60]

Individual volumes will have a bit more flexibility than a pan pot, but whether you care is a matter of convenience and preference. 

With individual volumes, you can think of setting the level from either pickup continuously from 0-100%.  The resultant outputs are summed together. 

When a pan pot is implemented with a ganged potentiometer (two separate potentiometers on the same shaft), the position of one pot is locked to a setting on the other pot.  This will give you a blended balance between pickups, but you can't set arbitrary relative levels anymore. 

There's something else happening here too, which bsee touched on.  Making a ganged panpot isn't easy.  If you think about how it works, one of the two pots is "normal" - when you turn it clockwise, the output level increases from that pickup.  The other half of the ganged panpot is wired in the other direction - it's full on when fully counterclockwise, then decreases as you turn it clockwise.  That rate of increase/decrease is called the "taper" of the pot. 

If the components of the panpot are regular taper with the full output range distributed across the rotation, then you have a problem in the 50-50% position - both pots are mid-taper, so the output level is not at maximum.  On a passive pickup guitar (Fender or Gibson), this is bad, because turning down the volume pot affects the tone as well as the volume (you lose highs).  With active pickups on an Alembic, there's no effect on tone, but the output level would be lower. 

As bsee ponders, you could make a panpot with a special taper such that the increase/decrease of the output level happens on half of the pot's rotation, then stays at full volume for the other half of rotation.  Now the middle position has both pickups at full output and all the other positions are 100% one pickup and some amount of the other - that should give you the effect of individual volume controls because all ratios are available, although the output level may be higher or lower than the same mix on individual volumes.  Special panpots like this are available as a custom manufactured part.  I don't know whether this is what is in an Alembic. 

Personally, I find individual pots more intuitive - I tend to think "a little less neck pickup" or "a little more bridge pickup" and that doesn't translate mentally into turning the blend knob for me.

David Fung

[edwin]

David just nailed it. And while I like the two volumes with master volume pretty well, I actually prefer the blend pot if it is done the way David suggests. I believe Alembic does do this, or at least that's how it seemed to me with my old shorty SI. Getting the pan done right along with keeping the signal path stereo is pretty cool.