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

[fullrangebass]

East preamps are a great way of matching pickups in both passive and active mode (Invalid Link Removed. I am most happy with my East preamp on my R-bass (I will post a review on that) but we are talking about fully PASSIVE circuits, if I am not mistaken.

 

[bongomania]

Couple of points:

The load difference between three pots and two is worth noting, but is not a night-and-day difference, and would not (as far as I can tell) bear significantly on the way two pickups will interact with each other, at least not enough to where a V/V setup could be said to have "much less noticeable interaction" compared to an otherwise identical V/B setup. I will be interested to see if anyone has empirical data (not anecdotal opinion) contradicting what I just said. I couldn't find the long previous thread on this subject, but I did read it back at the time it was active, and what I think I remember from it was a general consensus that there was NO audible difference. Do I recall incorrectly?

Does the East preamp buffer the pups even while in "passive" mode? Many (most?) preamps do not buffer the pups in passive mode. I'm happy to include all types of active system in the discussion, as long as they aren't just pat statements like "Brand X preamp is the best."

 

[A9X]

Interesting! Could you elaborate on that please?

I thought I replied to this a couple of days ago, and here's what I typed up then.

Most preamps still use the passive controls before the preamp's input to do the volume adjustment and balance between pickups, whether it's a V/V or V/B. Instead, I much prefer to run each pickup individally into an active device and then do the V/B before a final line driver and the output socket. For a two pickup pre this means at least 3 stages to draw current from the power supply, and if thats battery, then it's a major impact on possible playing time between changes over a simple passive V/B and a single stage that many pre's consist of. Some have an extra stage for a Baxandall type feedback tone controls, and if gyrators are used, add more current drawing stages.

All of these stages are usually poor sounding low current draw devices, whether opamp, BJT or FET. Muso's seem to demand huge signal life from batteries which means that the balance of engineering compromises tilts towards low current. I've been an engineer my entire working life, and though I've worked in other areas of electronics apart from audio, those who know me will tell you I've spent a huge amount of time over many years systematically reading, developing, testing and measuring audio circuitry to try to correlate the measurements with what's heard. My research comes down to a couple of simple 'rules'; keep it class A, keep each stage as linear and quiet as possible (before feedback, if used), use as little feedback as possible and keep overload conditions rare and brief and as non-obnoxious sounding as possible (ie lots of headroom). All this can be relatively easily acheived and good sounding, but it's damn hard to do off a 9V battery and < 1mA draw. Lot's may say " but my brand X sounds great", and it may to them, but I doubt they've heard the no compromise version on-board to have a reference.

 

[bongomania]

Ah, so you built your own preamp. Do you use phantom power for it?

 

[Philbiker]

I have a Bartolini TBIBT in a shoe box somewhere you can have if you're interested. It's just the chip. You need instructions, detent pots, capacitors, and a battery connector to use it. A buffered preamp circuit. Worked great last time it was in a bass. Make me an offer I can't refuse. It won't be difficult.

 

[higgi]

Couple of points:

The load difference between three pots and two is worth noting, but is not a night-and-day difference, and would not (as far as I can tell) bear significantly on the way two pickups will interact with each other, at least not enough to where a V/V setup could be said to have "much less noticeable interaction" compared to an otherwise identical V/B setup. I will be interested to see if anyone has empirical data (not anecdotal opinion) contradicting what I just said. I couldn't find the long previous thread on this subject, but I did read it back at the time it was active, and what I think I remember from it was a general consensus that there was NO audible difference. Do I recall incorrectly?

This may be anecdotal, but I noticed a huge difference volume wise. I have switched back and forth between vol, blend and vol, vol on the same bass at least three times in the last 2 weeks. I wanted the simplicity of a single volume knob. But what I kept noticing was that the center blend position was much quieter than either pickup soloed.

I could see the difference on my VU meter. When I switched to vol, vol the with both pickups on max, similar to center blend position, the fully blended sound was just as loud as the either pickup soloed.

When you use vol, blend at full blend position there is either 125k or 250k ohms of Resistance in line with both pickups. In full blend position with vol, vol(max, max) there is 0-3 ohms in series with either pickup. So to me it would be obvious why there is a volume drop in center position of a vol, blend system. The drop in volume became more obvious as I rolled off highes with the tone knob, so I can also see why a buffer would minimize the effect of blending.

 

[Philbiker]

This may be anecdotal, but I noticed a huge difference volume wise. I have switched back and forth between vol, blend and vol, vol on the same bass at least three times in the last 2 weeks. I wanted the simplicity of a single volume knob. But what I kept noticing was that the center blend position was much quieter than either pickup soloed.

I could see the difference on my VU meter. When I switched to vol, vol the with both pickups on max, similar to center blend position, the fully blended sound was just as loud as the either pickup soloed.

When you use vol, blend at full blend position there is either 125k or 250k ohms of Resistance in line with both pickups. In full blend position with vol, vol(max, max) there is 0-3 ohms in series with either pickup. So to me it would be obvious why there is a volume drop in center position of a vol, blend system. The drop in volume became more obvious as I rolled off highes with the tone knob, so I can also see why a buffer would minimize the effect of blending.

You're talking about an improperly designed blend pot. Unfortunately, these are very common, complicating the situation. Detailed in the existing thread.

 

[A9X]

Ah, so you built your own preamp. Do you use phantom power for it?

Yes. As I already have an Alembic Series, I intitally used that supply, cable and 5 pin XLR. My new 'rack' preamp has the power supply and conector built in.
The Alembic S1 has my pre, and my two Hohners will be getting it soon, and when I get around to putting some DarkStars in my beater T40, probably there too.

 

[higgi]

You're talking about an improperly designed blend pot. Unfortunately, these are very common, complicating the situation. Detailed in the existing thread.

This was the stock blend on my ESP. You would have to have ganged pots that tapered to the center position from one side and held constant at 0 ohm from center to the other side. And they would need to be reversed from each other. I haven't seen one like this.

Thank you for the link, that's the thread I was looking for. I don't know why I couldn't find it.

 

[bongomania]

Bump! I know I'm not done with this subject yet... anybody else?

What about combining a few ideas from this thread and the "Redeemer" thread... using a pair of unity-gain buffers, one per pickup, each with their own battery, mixed down to a single output. The mixer stage could even have its own battery. The output impedance could be converted back to the original z of the passive pups if desired. Aside from the obnoxiousness of three batteries, what are your thoughts?

 

[PilbaraBass]

Bumpola

Bartolini TC-2...but I can't find anyone who carries them...

 

[bongomania]

Right, that is a buffer... but is it any good? Is it any different in tonality or s/n ratio compared to Bart's regular preamps, or anybody else's preamps?

 

[Matthijs]

I would not know the actual figures, but its my impression the s/n ratio is way better compared to most other pre-amps. But the 'measurement' is done with my ears and only compared to pre-amps with full tone control.
I've been using a bart TC-1 (the 1 channel version) for over 10 years just as a buffer and a signal boost. I prefer it's sound to the passive sound. I wouldn't know how it would stand up to other op-amp circuits.

By the way, do they still carry the TC-1 and TC-2? that would be a long time for a electronic gizmo to stay in business.

 

[PilbaraBass]

I would not know the actual figures, but its my impression the s/n ratio is way better compared to most other pre-amps. But the 'measurement' is done with my ears and only compared to pre-amps with full tone control.
I've been using a bart TC-1 (the 1 channel version) for over 10 years just as a buffer and a signal boost. I prefer it's sound to the passive sound. I wouldn't know how it would stand up to other op-amp circuits.

By the way, do they still carry the TC-1 and TC-2? that would be a long time for a electronic gizmo to stay in business.

they're still listed on the bartolini site...doesn't mean that they still have them, though

However, when you're talking single and dual boost-only...such a simple circuit...what is there to change or update?....so, even if they're not available anymore, they SHOULD be

 

[bongomania]

Bump!

 

[Cristo]

for those interested,

Here's some interesting info, from Rane Profressional Audio reference:

balance control A control found most commonly on professional and consumer stereo preamplifiers, used to change the relative loudness (power) between the left and right channels. Attenuating the opposite channel makes one channel (apparently) louder. This is most often done (in analog designs) with a dual potentiometer with an "M-N taper." An M-N taper consists of a "shorted" output for the first 50% of travel and then a linear taper for the last 50% of travel, operating oppositely for each channel. Therefore, with the control in its center detent position, there is no attenuation of either channel. Rotating it away from the center position causes one channel to be attenuated, while having no effect on the other channel, and vice-versa. Contrast with pan and crossfade controls.

pan (panoramic) control A control found on mixers, used to "move," or pan the apparent position of a single sound channel between two outputs, usually "left," and "right," for stereo outputs. At one extreme of travel the sound source is heard from only one output; at the other extreme it is heard from the other output. In the middle, the sound is heard equally from each output, but is reduced in level by 3 dB relative to its original value. This guarantees that as the sound is panned from one side to the other, it maintains equal loudness (power) for all positions. Contrast with balance and crossfade controls.

I believe this describes the "quiet in the middle" phenomenon some people experience.

Others have experienced little blending until the control is turned almost fully in one direction or the other. I believe this stems from using a log taper instead of linear. If the control is set to halfway between the center detent and the bridge, the blend should be 75% neck and 25% bridge. But, if the control is log taper, this point would not occur until near the end of the control travel.

So I think the issues people have described are occurring because they have log taper pan pots, whereas they results they desire would come from a m-n taper balance pot.

 

[bullT]

I hope not being wrong... but artec works with piezos, and they have at least four cheap "buffers?" http://artecsound.com/vtc.html

http://artecsound.com/mt3.html

also they say: High Impedance Input design can match with any Active and Passive Pickup and also Low Impedance : Link Removed

regards

 

[bongomania]

In the middle, the sound is heard equally from each output, but is reduced in level by 3 dB relative to its original value. This guarantees that as the sound is panned from one side to the other, it maintains equal loudness (power) for all positions.
...I believe this describes the "quiet in the middle" phenomenon some people experience.

No, the 3dB drop is to accommodate the sound being presented at equal volume from two speakers. It would not be heard as a 3dB drop if the two signals were mixed to a single output. It is well-established that pickup coils "load" each other's signals, and at equal levels that causes both signal levels to drop. A buffer blocks the loading effect.

Others have experienced little blending until the control is turned almost fully in one direction or the other. I believe this stems from using a log taper instead of linear. If the control is set to halfway between the center detent and the bridge, the blend should be 75% neck and 25% bridge. But, if the control is log taper, this point would not occur until near the end of the control travel.

This sounds correct to me.

 

[A9X]

No, the 3dB drop is to accommodate the sound being presented at equal volume from two speakers. It would not be heard as a 3dB drop if the two signals were mixed to a single output. It is well-established that pickup coils "load" each other's signals, and at equal levels that causes both signal levels to drop. A buffer blocks the loading effect.

The buffer will only block the loading effect if there is one per pickup, and the blend control is after the buffers.

Two pickups, individually buffered would get around 6dB of gain when both were added together at full volume as 20log(2) is 6dB. There'll be some differences +/- depending on frequency, frequency response of each pickup (which varies depending on position on the scale), phase differences because of positioning along the scale and different output levels because of different construction of the pickups and levels, again because of scale positioning.

 

[bongomania]

The buffer will only block the loading effect if there is one per pickup, and the blend control is after the buffers.

I see what you're describing, but I was under the impression that an active mixer circuit (which is what I would expect in an onboard preamp) uses active blending, not a passive blend fed into a single buffer component. Is that right or wrong?