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Buffering, or getting the "best" blended sound/level from passive pups

bongomania

bongomania

Commercial User
Oct 17, 2005
35,688
3,917
PDX, OR
www.ovnilab.com
Disclosures
owner, OVNIFX and OVNILabs
#1
I searched but wasn't able to find anything on this...

One of the known benefits of (some) active electronics is the ability to buffer the blend between pickups, to avoid drops in volume or other interference between the pups. OTOH, active electronics can add noise, especially compared to a well-shielded passive humbucker. Now I have an active P/JJ, and I love the evenness of the pup blending, but the noise level from the preamp is a little higher than I'd ideally like. Part of me wants to remove the preamp and put in a simple blend knob or switch, but I don't want the tone/level interference of a passive blend.

So: what is the lowest noise, lowest interference, most even-sounding way to blend two pups? Hint: please don't just say your favorite brand of preamp is noise-free, because I'm not buying it. :) Is there a way to do a passive blend that is at a more advanced level than just using a pot; or is there an active buffer device which adds no noise or artifacts?

Or am I asking too much- are we stuck with the two "normal" methods?
 
#2
From my own experience (having spoken with some very knowledgable people helps too) vol/vol is the way to go. A passive blend would have to have some carefully chosen technical profile in order to avoid loading one pickup to the other. No easy way out from this really.

Not much of a help, unless you are willing to spend some time educating yourself and trying to understand the physics involved in a circuit like that.
 
#3
fullrangebass said:
From my own experience (having spoken with some very knowledgable people helps too) vol/vol is the way to go. A passive blend would have to have some carefully chosen technical profile in order to avoid loading one pickup to the other. No easy way out from this really.
Click to expand...

I'd also say two volume controls is the only way to go. If you're really picky you might even go for volume controls wired as a L-pad: a stereo pot used as a singe volume control, where the total resistance is constant both at the pickup and the amp side.

Having said this: you might also try a basic buffering pre amp without any tone controls. They are often way less noisey.
 
#4
Sounds like what you want is a Bartolini AGDB (Adjustable Gain Dual Buffer). With this the pickups will be electronically isolated so that their impedances don't interact, and you can adjust the level of each pickup so that when your blend knob is centered it sounds "right".

Even with a volume-volume, the pickups impedances will still interact, it just does it a little differently because there is one less pot in the circuit (a blend is technically just two volume pots stacked, with one of the pots having a reverse taper, so a typical volume-blend-tone circuit has 3 volume pots versus a volume-volume-tone circuit which has 2).

That said........a buffered blend is not necessarily "better"..... it just depends on if it gets you the sound you're looking for. It'll definitely have a lot more adjustability in the "in between" areas, like 30% neck/70% bridge, etc., but the impedance interaction inherent in a typical two pickup circuit does do its own thing to the overall sound that a buffered circuit doesn't have. So a buffered blend is definitely something worth trying, but it's not necessarily "better"....... I've got two Modulus basses with passive blends, and I wouldn't touch 'em, they sound great just as they are. But I do have other basses that sound a lot better with active blend circuits ("active blend" is another term for "buffered blend", they're the same thing).
 
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#5
Thanks for the replies, guys. I was surprised to see recommendations for vol/vol, because I thought it was electrically almost identical to a pan pot. Thanks Bruce for the exact clarification on that one. Has anyone ever used the AGDB? I posted a thread about it a few months ago and nobody responded with actual experience with it. Any other ideas out there?
 
#6
I just installed an Audere wired Vol/Vol Z-mode and Active/Passive in a PJ. SHielding counts as far as noise goes. I'm not well shielded and there is a bit of noise, but considereably less than with the stock Fender.

It's too new for me to be out of the honeymon phase yet - but so far I like it ! I was after blend when I started. Talked myself into vol/vol. Operationally there really isn't much difference to me. Sonically it's supposed to be a better bet.
 
#7
I had an Audere (with no EQ) installed in a custom bass for exactly this purpose, and the bass was extremely well shielded, and I didn't like the s/n ratio. It's not that it was any hissier than any other preamp, but rather that the active mode (at least on hi and mid z modes) had slightly lower output than the passive mode, and yet it had the hiss of an average active circuit. Since the passive mode was louder yet had absolutely zero hiss, I pulled the preamp out. But of course the Audere does provide buffered blending, so it's a trade-off. :hmm:
 
#8
Hey Foks. I hope I'm not too far from the subject, but I was just about to do a separate post about my Schecter that I just converted to passive Vol Vol Tone as with all my other passsive basses. After being used to the active blend and such, it was quite noticable that now being passive, the actual sound,tone,feeling, etc. would change thru the travel of the passive pots. Meaning the sound seemed to be more pleasant and rounded with the pots rolled off a bit, where at full volume, there was more of an edge to the sound which I didn't care for as much. It semed with the preamp, the sound stayed the same throughout the entire travel of the pot. Any thoughts?
thanks
AP
 
#9
While I agree that an active buffered blend circuit will provide the smoothest blend between the two pickups, I have some misgivings about the compromised sound of onboard active circuits. After comparing several opamps in my EMG BTS circuit, I have found that the opamps with sufficiently low current draw for onboard use tend to affect the signal unfavorably.

Most of the opamps I've tried have introduced colorations and a loss of transparency. The LM4562 sounds head and shoulders above the others that I've tried (LF442, OP275, OPA2134, OPA2604, TLE2072A, TLO72, AD822, AD823), but requires over 10 ma, which makes it impractical for battery operation. If pure organic tone is what you are after, I would have to recommend remaining passive unless you can provide the current necessary for high quality electronics. Perhaps a balance between sound quality and current demands can be more easily accomplished using discrete components.
 
#10
12bass said:
While I agree that an active buffered blend circuit will provide the smoothest blend between the two pickups, I have some misgivings about the compromised sound of onboard active circuits. After comparing several opamps in my EMG BTS circuit, I have found that the opamps with sufficiently low current draw for onboard use tend to affect the signal unfavorably.

Most of the opamps I've tried have introduced colorations and a loss of transparency. The LM4562 sounds head and shoulders above the others that I've tried (LF442, OP275, OPA2134, OPA2604, TLE2072A, TLO72, AD822, AD823), but requires over 10 ma, which makes it impractical for battery operation. If pure organic tone is what you are after, I would have to recommend remaining passive unless you can provide the current necessary for high quality electronics. Perhaps a balance between sound quality and current demands can be more easily accomplished using discrete components.
Click to expand...
I couldn't agree more esp wrt audio signal electronics and current draw.
Best bet is phontom power a la Alembic. No compromises there.

To the OP: I prefer a vol/blend circuit with individual buffers per pickup.
 
#12
fullrangebass said:
From my own experience (having spoken with some very knowledgable people helps too) vol/vol is the way to go. A passive blend would have to have some carefully chosen technical profile in order to avoid loading one pickup to the other. No easy way out from this really.

Not much of a help, unless you are willing to spend some time educating yourself and trying to understand the physics involved in a circuit like that.
Click to expand...
THis doesn't make sense.
A vol-vol will create load just the same as a blend. There is no electronical difference between the 2 systems.
If you use a passive instrument with offphase coils (ie single coil jazz bass) you will suffer load. Of course, none of this with a pair of humbuckers.
 
#13
A9X said:
I couldn't agree more esp wrt audio signal electronics and current draw.
Best bet is phantom power a la Alembic. No compromises there.
Click to expand...

That's what I was afraid of! I do some dabbling in electronics, and I spend a lot of time reviewing the headroom and s/n performance of compressors, and it was becoming clearer to me that higher available current draw is "the key".

A9X said:
To the OP: I prefer a vol/blend circuit with individual buffers per pickup.
Click to expand...

Interesting! Could you elaborate on that please?
 
#14
Found this report in the DIY section of the Head-Fi forum. Interesting comparison between discrete and opamp bass preamp circuits.

Invalid Link Removed

They don't mention the monitoring system. Perhaps it wasn't able to adequately resolve the sonic differences?
 
#16
I converted my ESP C304 from active to passive. I like the tone much more. I tried used the vol, blend, tone arrangement. It had a little volume drop in the mid position of the blend pot,. If you rolled off the highs with the tone control then the volume dip was very, very noticeable. So I went to the vol, vol, tone. Much better results to my ears. I also installed a push pull pot that switched the two humbucker into single coils then added those single coils in series again for a humbucker. With the switch engaged it sounds like a music man. With both humbuckers on full, it sounds a little more muddy than the single coils in series.
 
#17
Jazz Ad said:
THis doesn't make sense.
A vol-vol will create load just the same as a blend. There is no electronical difference between the 2 systems.
If you use a passive instrument with offphase coils (ie single coil jazz bass) you will suffer load. Of course, none of this with a pair of humbuckers.
Click to expand...

Any time you introduce resistance into a circuit you alter the load - with a blend pot you have added one more pot per pickup and one more load variable (unless you remove the master volume pot).
 
#18
bongomania said:
Thanks for the replies, guys. I was surprised to see recommendations for vol/vol, because I thought it was electrically almost identical to a pan pot.
Click to expand...
A panpot is basically two potentiometers stacked on top of each other. So in a VOL/BLEND situation you have three panpots, in VOL/VOL there's only two. That's a big difference from an electrical standpoint. There's a long thread here somewhere about VOL/VOL versus VOL/BLEND.

Personally I like VOL/VOL.
 
#20
I was looking for that long thread on Vol, vol vs. vol blend. It did not show up in search. Could I get a link?

A custom taper pot is only going to effect were your knob is turned to for a particular pickup to pickup ratio. The center connection is a wiper on a strip of resistance material. The resistance on both sides of the wiper will always add to the full value of the pot. So for center position of a 500k then there will be 250k on either side, no matter what the taper.
 

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