Should I make an onboard "activator" (active buffer with benefits)?

[Drayve85]

Thanks for the link, I wasn't aware of this product.

There's no buffer that I'd call advanced. It's a basic circuit block. The devil is in the details. You simply cannot get the full benefits of an onboard buffer unless you eliminate the standard high value volume pot between the pickups and the buffer, which is a significant source of hiss when backed up. In this situation, it greatly adds to the pickup's output impedance, ruining your noise floor. The Redeemer does not replace the volume, it comes after it (I checked their wiring diagrams). There goes the biggest advantage to having it onboard. You might as well put it in a pedal or belt pack with a short cable from the guitar, and it would work in just the same non-ideal way.

Also, it draws 3mA (for reference, mine's at 0.22mA), which is quite thirsty IMO for an onboard buffer. Their math is questionable, too. At 3mA, a 9V battery (~450mAh) would last about 150 hours, not the 300 they say. Moreover, the noise floor they quote (-125dBu) cannot physically happen except when the volume pot is fully cut, at which point a passive guitar would be even quieter (dead short on output, zero noise!).

Allow me to do some calculations. The pickups themselves, with the volume up, have at least 5kOhm of resistance (it gets a lot higher with the volume backed off), which sets the lowest theoretical noise floor out of the guitar to about -116 dBu, even if your buffer were an ideal "wire with gain". A 500k volume pot at 50% adds 250k of series resistance to the pickups, which bumps the noise floor to no less than -99dBu (17 dBs more, or 7 times the full-volume noise!). Add 60dB of small signal gain from a compressor + distortion, and your noise floor is now up at -39dBu. That's some forking loud hiss.

My buffer removes the 250k or 500k volume pot and replaces it with a 5k, post-buffer volume. At 50%, that pot is a 2.5k resistance to the output. That's worth, by itself, about -119dBu of noise over a 20kHz bandwidth. Add to that half of the combined noise (remember, the pot is at 50%) of the 5k pickups (-116dBu) + my buffer's self noise (-118dBu, the equivalent of a single 3k resistor). Comes down to about -116dBu, real life noise floor, with volume at 50% (uncorrelated noise adds in funny ways). Now, add the same 60dB of gain from i.e. a compressor + distortion, and you're up to -56dBu. HUGE difference from the -39dBu above. Like turning on Dolby C on a cassete player, if you've experienced that. You can now easily skip the noise gate.

Same guitar, same 50% volume setting, different buffers.

Apart from that, I commend the Redeemer's makers for the generally correct, no-nonsense explanations of how it works and why you'd want one. Too many makers spread bullshit in any number of audio subfields.

/endrant

Having said all this, I don't think I'll make this into a product, as it makes very little business sense. For starters, just the pot I want to use costs me about C$15 in small quantities (Bourns 91 series), and the op amp about C$4... And I won't make anything any less than the best that I know how to make, so I won't use any lesser parts.

I love your idea, and I’m sure there are many people that COULD use it, and many that want to use it. But, it might be one of those things like Paul Reed Smith and John Mayer were talking about; a great idea that nobody would buy. For whatever reason. Unless you could find a way to market it that would catch peoples attention. Please don’t take this as a slight, I like your product idea, I’m just thinking about the general guitar playing public. Sometimes we can have the mind and attention span of a five year old!lol

 

[JTEX]

I love your idea, and I’m sure there are many people that COULD use it, and many that want to use it. But, it might be one of those things like Paul Reed Smith and John Mayer were talking about; a great idea that nobody would buy.

I actually agree with you. Most people won't care, or even understand what difference it makes. Just slap a noise gate at the end of the chain and it's good enuff Until you roll off the volume and it cuts you off.

I have lots of ideas, but no real motivation to market them. Day job too comfy, not hungry enough.

 

[jwin615]

Awesome spec out! I'll be first in line if you do decide to launch. Or even just do a short run(or if you have a prototype crowding your desk, wink wink).
Theoretically, since your R&D is already invested, if you were to do a one off/short run, how many units would it take to be worth your time?

Pitching a few boards to indie guitar companies may get you a few sales as well. I know that the guys over at HALO guitars are very approachable and this would fit well in their demographics.

 

[JTEX]

Awesome spec out! I'll be first in line if you do decide to launch. Or even just do a short run(or if you have a prototype crowding your desk, wink wink).

Hmm. I have a whopping 5 PCBs at this prototype stage, which is the smallest quantity I could order. I'll install one of them in a guitar right away, which leaves 4 with no determined fate. How's about US $50 for a perfectly working, but not fully production-polished unit? It would include the stuffed PCB, with wire leads, and my favorite volume pot money can buy (if you can even find it) : a TT Electronics P260P series, 10k log, 1 Million cycles rating! Schematic included. It's just a buffer. Details make or break it.

 

[jwin615]

Hmm. I have a whopping 5 PCBs at this prototype stage, which is the smallest quantity I could order. I'll install one of them in a guitar right away, which leaves 4 with no determined fate. How's about US $50 for a perfectly working, but not fully production-polished unit? It would include the stuffed PCB, with wire leads, and my favorite volume pot money can buy (if you can even find it) : a TT Electronics P260P series, 10k log, 1 Million cycles rating! Schematic included. It's just a buffer. Details make or break it.

PMed!

 

[Fama]

Hmm. I have a whopping 5 PCBs at this prototype stage, which is the smallest quantity I could order. I'll install one of them in a guitar right away, which leaves 4 with no determined fate. How's about US $50 for a perfectly working, but not fully production-polished unit? It would include the stuffed PCB, with wire leads, and my favorite volume pot money can buy (if you can even find it) : a TT Electronics P260P series, 10k log, 1 Million cycles rating! Schematic included. It's just a buffer. Details make or break it.

Is this the same as the prototype in your store? Because I might just grab one from there if so.

 

[JTEX]

Is this the same as the prototype in your store? Because I might just grab one from there if so.

Yes, I put it there by request. One gone, 3 more left.

 

[jwin615]

@JTEX, I didn't see you mention the 3 settings before(unity, boost, treble boost), which is a welcomed addition. So, if I wanted to have the boost switchable on a push pull, short 2-3 on board and switch the 1-2 connection.
But if I wanted to say switch between mild boost to high boost(say 3db to 12db), could I short 2-3, then switch the 1-2 junction between a short(12db) and a parallel resistors.
So 3dbish would be short 1-2 and gain adjustment at ~9kohm.
And 12db boost would be ~3k resistor across 1-2(with gain adjustment remaining ~9k) giving about 2.2k parallel resistance to the feedback loop. I'm I missing anything here? Still on the first cup of coffee.
I like the idea of a small boost for noisefloor/cable loss/etc but with a switchable "lead" boost.

 

[JTEX]

@JTEX, I didn't see you mention the 3 settings before(unity, boost, treble boost), which is a welcomed addition. So, if I wanted to have the boost switchable on a push pull, short 2-3 on board and switch the 1-2 connection.
But if I wanted to say switch between mild boost to high boost(say 3db to 12db), could I short 2-3, then switch the 1-2 junction between a short(12db) and a parallel resistors.
So 3dbish would be short 1-2 and gain adjustment at ~9kohm.
And 12db boost would be ~3k resistor across 1-2(with gain adjustment remaining ~9k) giving about 2.2k parallel resistance to the feedback loop. I'm I missing anything here? Still on the first cup of coffee.
I like the idea of a small boost for noisefloor/cable loss/etc but with a switchable "lead" boost

I'm on the 3rd coffee here I haven't fully made up my mind abut the 3 modes, but I'd be tempted to use an On-On-On toggle to switch between them and see what i find most useful. I put the schematic out there so people can tweak it whichever way works best for them, and decide whether to use the 3 "modes" -- or just one, or two. It's still a prototype, definitely not a "frozen" thing -- but the fundamentals are there. Experimenting is highly encouraged. I will eventually clean up the schematic a bit, maybe put a proper 3-pin header symbol in there, but it's usable as is. The "flat (ish)"/ "trebly" caps will eventually be on sockets, since i want them to be easily swapped out. It makes a huge difference how you hit a distortion pedal or compressor -- with a more or less bassy source, and with a lower or higher overall signal level.

Basically, you can use this circuit to make low output (but hopefully great sounding) pickups as hot as you want without adding significant noise, and you can take out any unwanted muddiness they might have by high-passing them with a cap. That would lose you some level, but you can dial it back in with the gain trim.

 

[JTEX]

is that just a nut from a cliff style jack with interior threads tapped into the sleeve?

Precisely!