REQ. clean treble boost/buffer, small & simple

[robdean]

I have a guitar with a piezo and a neck humbucker.

The piezo has an active buffer I made (Tillman) and the neck position humbucker is quite dark.

I want to replace the three way switch between the piezo and the humbucker with a balance/blend pot, so guess I need to buffer/preamp the humbucker to function well paired in a balance/blend pot with the active piezo?

Whilst at it I'd like the humbucker active circuit to offer clean treble boost to add options to the humbucker sound.

Can anyone please suggest a simple small circuit I can build (to go inside the guitar) which will buffer the humbucker and offer treble boost, ideally via a pot. I have looked though lots of circuits but lack the experience to really know which might be the best bet.

Sincere thanks,
Rob

[motterpaul]

A couple questions just to double-check the situation:

The piezo is currently powered by a 9v battery? Or is it some other source (what is the voltage?)

The humbucker is currently mounted as non-active?

The humbucker sounds muffled and not as loud as the piezo?

Are you looking for more boost in gain, with tone controls, for the humbucker? Of just a "buffer" which may make it sound brighter, but may not raise the volume or give tone control.

If you have 9v available that you can use to power a boost for the humbucker, there are many simple circuits that will give you plenty of gain (clean boost) and that will offer some tone control to make the humbucker sound brighter. I would look at this one:

http://tagboardeffects.blogspot.com/2013/08/bmp-tonestack-w-lpb1.html

It is very simple, small and efficient and has a tone control. There are also many other simple boosts; the Brian May is a good one.

As for "blend" - there are ways to do that people here can recommend. Or you can go with a 3-way switch and independent volume output knobs for each pickup.

[Beaker]

Ouch, that's quite a lot to consider.

So you do not have a "convential" bridge pickup, just a bridge mounted piezo? What sort of guitar is it?

Well, you could use a twin gang balance blend pot with centre detente, and wire it like this - it's a common mod for a Fender Jazz Bass.

https://www.google.co.uk/search?q=jazz+bass+blend&biw=1366&bih=610&tbm=isch&tbo=u&source=univ&sa=X&ei=xnghVcX2BJbdarGagLgJ&ved=0CCAQsAQ#imgdii=_&imgrc=9B60JyW4v5fbFM%253A%3B3kgC_tpaJEAjrM%3Bhttp%253A%252F%252Ftclutherie.hypermart.net%252Fwiring%252F2JBWITHBLEND.jpg%3Bhttp%253A%252F%252Ftclutherie.hypermart.net%252Fwiring%252F%3B471%3B228

That will address the first part of your query.

Second part though, gets complicated. Why do you want two separate preamps - it does not make sense to me. Just use one preamp, with both pickups running into it. Tillman buffers distort easilty with humbuckers, so I would not recommend using one.

However, It strikes me that you might be just chasing your tail here, and do not appreciate the problems you might encounter. With respect, it is an easy trap to fall into, complicating things more and more, when there might be much simpler and way more effective solutions.Why not just buy a brighter humbucker?. Or if it is four conductor wring, put in a series/parallel switch - that will instantly brighten it up at the flick of a switch.

There are a lot of things here that could cause problems, so more info on exactly what you have, what you want to achieve, and why would be helpful.

[robdean]

Thank you for the help!

Yes, 9v piezo, yes humbucker is non-active.

Actually I'm not certain how the volumes of the two pickups will compare, since things are so half-complete, but sure the piezo buffer does not have much gain. I'd likely live with passive volume cut of the louder one if need be.

The humbucker position is neck and the guitar is semi-hollow so the sound is naturally quite fat and not all that bright. This need not be a big issue when blended with the piezo, but I'd like the option for a bright electric lead sound, which is why I like the option of treble boost.

Actually the guitar is a Crafter SAT, a nice guitar but it has a volume for each pickup and a three way selector. My main goal is to replace this with a master volume and a blend control, my secondary goal to add treble boost to the humbucker (which I have actually changed to a stacked P90 with series/split switching - the original was a P90 size humbucker). All the Crafter circuitry is on a complex PCB, including pots, so I just want to lift that out and replace it.

I imagine
piezo -> buffer -> passive tone -> blend control
magnetic pickup -> buffer/pre with active treble boost -> blend control

Thus controls are passive piezo tone, active mag treble, blend and master volume.

When playing live (currently a Tom Waits tribute band) I like to be able to change the blend and the volume fairly independently, which is why this mod is important to me - I find twin volumes too awkward when I want to adjust the blend but keep the volume constant (or vice versa).

I'm completely open to suggestions: I've done lots of passive wiring but am completely new to this kind of thing... the buffer I built for the piezo was my first vero build!

Ironically the similar Crafter SA model does have a blend control, but for other reasons I preferred the SAT: I was a bit dismayed to find how much of a single module the electronics are, making replacement rather than modding my only practical option.

Again, sincere thanks, and I'll take a run at that circuit you suggest unless this info prompts a different suggestion!

[robdean]

Beaker - thank you! I think my post to motterpaul answers your questions and I'd be really grateful for your advice based on that...
BTW you are very right: I had indeed considered a second Tillman for the humbucker, but I tested it and discovered that the mag pickup distorts it. Intermittently but nastily. I'm very glad of the confirmation as I was going to re-test it to confirm!

[Beaker]

Thanks for the reply Rob, answers a lot of questions.

Tom Waits tribute band - I doff my cap to you sir!

So your intention is to gut the guitar, and replace the existing preamp circuitry with a simple Tillman buffer?

[robdean]

Beaker - not really, though the buffer is a part of it!
Tillman buffer needed 'cos of a piezo won't give good results without, then I guess active mag pickup circuit needed so that the mag pickup can be blended with the piezo buffer output (since any given blend pot will otherwise be the wrong value for one or the other output). Treble boost would be a great addition to the mag pickup since I'm building a circuit. The piezo already seems usable through the Tillman buffer, though passive tone would be helpful to take brittleness off the top.

The Tom Waits tribute is new - just played first gig. I joined impulsively but am loving it:
http://youtu.be/6tXgEyQbNVU

Rob

[Beaker]

I'm still not understanding where the Tillman buffer comes in on this. The guitar has a LR Baggs active preamp circuit for both pickups, which is already buffered. I really don't understand why you have added another one.

Have you ever heard a "raw" signal from a piezo? It's like dragging a terrified cat down a blackboard. This is the reason why active preamp circuitry is so complex for piezo pickups - to turn the signal into something resembling an acoustic guitar.

If you are suggesting replacing the Baggs circuit with a buffer, it will sound horrific! It needs a good preamp.

One thing springs to mind though - what exactly does the toggle switch do? (I think I know, but don't want to assume.)

[robdean]

Beaker,

For reasons explained above I'm attempting to replace the entire circuitry of the guitar.

I realise you may think I'm crazy, or that the results might be lousy, but it's what I want to attempt!

I can add an off-the-shelf pre to the piezo if need be... I have one or two around. My current goal is to add clean treble boost to the magnetic pickup and blend this with the active piezo output: I anticipate using a blend pot in the low tens of k (?)

Thank you again...

Rob

[Beaker]

I asked if you wanted to gut the guitar, and you replied "Not really". I gave you an answer based on that.

If the toggle switch is just a pickup selector, you should be able to simply replace it with a blend pot as I detailed in my first post.

And swap your humbucker series/split for a series/split/parallel switch.

As for the rest of it, good luck!

[robdean]

Beaker:

My answer was 'not really' because replacing the entire circuitry calls for much more than the buffer: hence my original question. I may be wrong in adopting this buffer for the piezo but it's not what I was asking about: I have a host of external preamps and graphic/ parametric eqs if need be, and my aim is to succeed in attempting this circuit, even if some might think it misconceived. Before posting anything here I played the piezo through the buffer into an amp and found it in and of itself to sound fine.

I explain above that I can't mod the circuit (such as swapping out the switch for a blend pot) because it is all on a single unit circuitboard. If I could mod it I'd not need to replace it!

[motterpaul]

I was one who suggested a toggle switch, although I didn't mean to exclude the idea of a blend pot, either.

I assumed the circuitry for the piezo was already in place, with power and an output volume control, and because any added clean boost/tone for the humbucker would also be active with an output volume of its own, I didn't really see the need for a blend pot,  I just actually thought some kind of on/on/on three-way toggle between the two pickups would take up less room and be more efficient than a blend pot.

But - of course, one could rewire things and use the blend pot in place of the output pots of each circuit, but it gets a little complicated finding a pot that works equally well for both preamps. A switch with separate volume pots seems to offer more control in my mind (most guitars have switches, not blend pots).

But I will add that I was only thinking about the humbucker, because I don't know all that much about piezo preamps.

[Beaker]

It was Rob's suggestion in his first post, that he wanted to replace the 3 way toggle switch with a blend pot, so that was why I suggested how to do it.

The issue seems to be that the pots and switches are soldered to the preamp cicuit board. I still think that de-soldering the switch from the board, and replacing it with a blend pot on flying leads, is the best way to go here; though it might need another hole drilling in the guitar, so it can be positioned clear from the PCB.

As a Guitar Tech, I am familiar with this kind of arrangement (though not familiar with this particular guitar). There are several Telecaster type guitars available, (as well as other types,) that feature an under-saddle piezo pickup (for "acoustic-type" tones), alongside the usual (passive) neck and bridge pickup. Every one that I have seen, has a blend pot, to allow the amount of piezo signal to be blended in with (usually) the bridge pickup. Invariably the pickups are wired through a single preamp in these guitars. I've yet to see a guitar that features seperate preamp boards for each pickup.

And yes I know that true active pickups have a tiny onboard circuit board built into them!

[robdean]

Thank you both for your help with this. I'm going to build a circuit or two and report back! It'll likely be at least a week, as I have to wait on components and then ideally find a window where I don't need to actually be playing the darn thing for a few days...

[motterpaul]

I am not a guitar tech, although I have definitely done my fair share of work & research, I wouldn't begin to call myself an expert, especially on piezos.

Blend pots, or a switch to turn on both pickups with separate volume controls, - in the end both seem to accomplish the same thing.

But as you said, the passive piezo sounds bad. That seems to indicates the piezo preamp must be pretty pretty specialized for that pickup. Along those lines, I kind of liked the idea of a specialized preamp to fix just the humbucker. Different gain & EQ.

So I won't say I know the perfect or best solution, but I also agree on the coolness of a Tom Waits tribute.

[Beaker]

I rescued (broken truss rod) an old '70's mahogany Takamine "Martin" copy that had a raw piezo undersaddle pickup - no preamp, just wired to a volume and tone pot. Acoustic, it sounded magnificent, but through an amp or into a PA, it sounded utterly horrific! I ripped out the piezo and fitted a Fishman soundhole pickup instead.

Take a look at almost any electro-acoustic guitar these days, and you get 5 band EQ, notch filters, phase switch etc. - and all to try and make the piezo sound like an acoustic guitar!

To me, that's a classic case of trying to roll a stone uphill. As you may have guessed, I'm not a fan - I much prefer magnetic soundhole pickups. Way simpler, and to my ears at least they sound better - I just loath that piezo "quack".

I'm a big fan of the KISS concept (Keep It Simple Stupid). It always seems to me that the simpler the solution, the better the result, which is why I would recommend replacing a too dark neck pickup, with a brighter one, or getting it rewound by a pickup maker to do the same.
It's also why I would be reluctant to ditch a perfectly good preamp, designed to match the pickups in this guitar, for any "Home brew" solution.

Far too often, I have had to pick up the pieces, after someone "Had a great idea", and ended up turning a silk purse of a guitar, into a sow's ear.

That's not to say I'm a purist dinosaur though - I just love all those mad 60's British and European guitars, with their bonkers wiring, multiple switches, and onboard effects. All my guitars are modded in some way too, some of them radically.

So please don't think I'm ragging on you here Rob, I'm not. If you have a clear vision of what you want to achieve, and how to go about it, by all means go for it. I really hope your modification project turns out great.

[robdean]

Well I've taken a run at it and even the first try has turned out pretty well: I just buffered the new humbucker using the second most basic JFET buffer on this site, sent that and the Tillman-buffered piezo via a 20K balance pot to a passive volume.

The high impedance of the Tillman pre seems to bring out the best in the piezo, which remains a little bass-light but very natural sounding. The best sounds are blends between 1/4-3/4, but all are usable. For the piezo I have a small off-the-shelf preamp/4-band EQ I could fit inside the guitar but may well stick with what I have as whilst less flexible it sounds clear and clean - it blends with the mag very nicely.

It took a trim pot to match the pickup volumes and what with that and other factors the output could be louder. I'm going to try the tonestack/boost next - possibly on just the mag pickup, maybe across both. Also I might try treble bleed across pots affecting the mag pup, as I'd like it a bit brighter (it's the third and best pup I've tried in that neck position).

Already this is better for my needs than the stock circuit, which uses a hell of a lot of components to achieve I-know-not-what. I have no doubt at all that if I can find time to refine this, it'll really work out great. Thank you for the help and encouragement... I'm new to active circuitry!

[motterpaul]

Thanks for following up with us. It seemed like it would work, and I recommended that BMP with LPB way up above because I find it to be a very utile way to add gain and tone control.

Tone pots sound like a good idea, too.

[robdean]

Yeah, motterpaul, it's your suggestion that got me going with this!


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At 21 Apr 2015 21:29:01, motterpaul [via Guitar FX Layouts]<'[hidden email]'> wrote: Thanks for following up with us. It seemed like it would work, and I recommended that BMP with LPB way up above because I find it to be a very utile way to add gain and tone control.

Tone pots sound like a good idea, too.

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