Schatten Design thumbwheel controls question

[Jazz_175]

I have a technical question to submit to the experts.
I'm going to buy Schatten Design dual thumbwheel controls to install in a new pickguard of my archtop.
At the moment I have a Gibson BJB floating pickup.
My question is:
- Should I buy the 250K version, "normally used in conjunction with single coil magnetic pickups", or
- the 500k one, "normally used with Artist II and Player Endpin jack preamps and 2 coil humbucker magnetic pickups"
?

I am addressing the same question but in the case I also decide to replace the pickup with a Kent Armstrong Handmade Adjustable Floating PAF - The Gold Standard
or with a Benedetto S6 Ebonova.Finally I would like to know if any capacitors should also be included.

Hope someone (PTC) can help.

[PTChristopher]

Didn't this come up a while ago?

My opinions:

>>> - Should I buy the 250K version, "normally used in conjunction with single coil magnetic pickups", or
- the 500k one, "normally used with Artist II and Player Endpin jack preamps and 2 coil humbucker magnetic pickups"

I prefer 250K with all three PU's you mention.

But yes, if you use a low capacitance cable, you will lose a slight but noticeable amount of extreme ice-pick treble using 250K vs. 500K.

So maybe go 500K if you really like the absolute max amplitude for the extreme high end of harmonics and attack.

The Schatten pots and board will typically come with a very small (and perfectly usable) .022 uf cap.

You could alter the tone pot wiring for a more sophisticated (but still simple) "greasebucket" tone circuit. But this makes only a small difference in your application (all three PU's are similar in this regard), and requires a mod to the board that might seem tricky.

So I suggest:

250K, plenty of high end.

The stock ceramic .022uf cap.

AND - a small bleed resistor from the input to the output of the volume cap.

For the bleed resistor value, I suggest 1/8 watt 56K ohm with the 250K pot, and maybe 82k to even as high as 100K with a 500K pot.

The bleed resistor extends the useful taper of the pot. Without it, you may find that the action from "10" down to "8" is too sensitive on the volume pot.

All my opinion.

Chris

[Jazz_175]

Didn't this come up a while ago?

My opinions:

>>> - Should I buy the 250K version, "normally used in conjunction with single coil magnetic pickups", or
- the 500k one, "normally used with Artist II and Player Endpin jack preamps and 2 coil humbucker magnetic pickups"

I prefer 250K with all three PU's you mention.

But yes, if you use a low capacitance cable, you will lose a slight but noticeable amount of extreme ice-pick treble using 250K vs. 500K.

So maybe go 500K if you really like the absolute max amplitude for the extreme high end of harmonics and attack.

The Schatten pots and board will typically come with a very small (and perfectly usable) .022 uf cap.

You could alter the tone pot wiring for a more sophisticated (but still simple) "greasebucket" tone circuit. But this makes only a small difference in your application (all three PU's are similar in this regard), and requires a mod to the board that might seem tricky.

So I suggest:

250K, plenty of high end.

The stock ceramic .022uf cap.

AND - a small bleed resistor from the input to the output of the volume cap.

For the bleed resistor value, I suggest 1/8 watt 56K ohm with the 250K pot, and maybe 82k to even as high as 100K with a 500K pot.

The bleed resistor extends the useful taper of the pot. Without it, you may find that the action from "10" down to "8" is too sensitive on the volume pot.

All my opinion.

Chris

Hello Chris,
thanks a lot for your answer.
You are right, some of these questions came up in different threads started by someone else, where I asked a couple of questions,
but I could not find the whole story,
(something here about pickups comparison
https://www.jazzguitar.be/forum/guita...ar-pickup.html)
so I decided to repost and I want to thank you again.

What I don't quite understand is how to place the capacitor of 0.022uf,
do you mean like this?
Wiring Schematic for Benedetto S-6 and S-7 Pickups
It is just because you talk above of a "volume cap", but in the picture of the benedetto the capacitors seems to be placed at the tone pot.

as for the resistor, are you saying that the presence of the resistor makes the volume pot having a more gradual effect?

Of course I am not going to do the job myself, but I want to go to the technician well prepared and informed in order to understand what he is going to do.

[PTChristopher]

>>> you talk above of a "volume cap"

That's because I am an idiot. I meant to write "volume pot".

>>> What I don't quite understand is how to place the capacitor of 0.022uf,
do you mean like [the Benedetto wiring diagram]?

Yes, that will work just fine. But note that the Schatten board will have a little different setup because there is no grounded "can" on the micro pots.

But the Schatten board will also come with a usable diagram.

The one addition I suggest to either the Benedetto diagram or the Schatten diagram is a bleed resistor on the volume POT (not cap). This bleed resistor will go from the center contact on the volume pot to the contact on the volume pot that is connected to the "hot" wire from the PU.

But you may be perfectly happy with the Schatten setup without the bleed resistor.

>>> as for the resistor, are you saying that the presence of the resistor makes the volume pot having a more gradual effect?

Yes. I find the stock Schatten pot to be very abrupt from "10" to around "8". The bleed resistor makes the pot work more gradually.

Too small a bleed resistor will give the opposite problem. Nothing much will happen from "10" to "3", then the volume will suddenly drop abruptly.

Chris

[jorgemg1984]

Didn't this come up a while ago?

My opinions:

>>> - Should I buy the 250K version, "normally used in conjunction with single coil magnetic pickups", or
- the 500k one, "normally used with Artist II and Player Endpin jack preamps and 2 coil humbucker magnetic pickups"

I prefer 250K with all three PU's you mention.

But yes, if you use a low capacitance cable, you will lose a slight but noticeable amount of extreme ice-pick treble using 250K vs. 500K.

So maybe go 500K if you really like the absolute max amplitude for the extreme high end of harmonics and attack.

The Schatten pots and board will typically come with a very small (and perfectly usable) .022 uf cap.

You could alter the tone pot wiring for a more sophisticated (but still simple) "greasebucket" tone circuit. But this makes only a small difference in your application (all three PU's are similar in this regard), and requires a mod to the board that might seem tricky.

So I suggest:

250K, plenty of high end.

The stock ceramic .022uf cap.

AND - a small bleed resistor from the input to the output of the volume cap.

For the bleed resistor value, I suggest 1/8 watt 56K ohm with the 250K pot, and maybe 82k to even as high as 100K with a 500K pot.

The bleed resistor extends the useful taper of the pot. Without it, you may find that the action from "10" down to "8" is too sensitive on the volume pot.

All my opinion.

Chris

Hi Chris,

We've also talked in the past about this and I am going to add a resistor to my 500k to bring them closer to 250k / 300k.

The "bleed resistor" seems very interesting, my volume works too much on the 8 to 10 region. You suggest 1/8w resistors, I was only able to find 1/4w:

100k, MF 0,25W :: 100k - 910k :: Metal Film 0,25W :: Resistors :: Passive Components :: Electronic Parts :: Banzai Music

82k, MF 0,25W :: 10k - 91k :: Metal Film 0,25W :: Resistors :: Passive Components :: Electronic Parts :: Banzai Music

56k, MF 0,25W :: 10k - 91k :: Metal Film 0,25W :: Resistors :: Passive Components :: Electronic Parts :: Banzai Music

Are these ok?

Thanks!

[PTChristopher]

>>> You suggest 1/8w resistors, I was only able to find 1/4w

I only suggested 1/8 watt because they are very small and hide well under a pickguard for the Schatten type of pot setup.

0,25 watt is fine. Even larger wattage capacity is also fine, it just means physically larger resistors.

[jorgemg1984]

Thanks (once more) Chris. When I have tried all these things (it can take a while) I will report back to you.

[PTChristopher]

>>> will report back

That is really a very helpful thing to do.

I already know what I think works well, and only suggest things that I have actually done.

But having your opinion on this stuff, after trying it, makes it far more useful to the people who hang around here.

In my opinion.

Chris

[Jazz_175]

Going on with this project of installing the Schatten Design Thumbwheels volume controls with a new pickguard, ( I still have to order it, it's not easy to find it here), I was also considering the possibility to install a new Archtop bridge from Schatten Design,
Compensated Ebony Bridge With Suspended Sensor Element,
to go along with the magnetic pickup and mix both signals.
My question is then:
how do you control the volume and tone of both, magnetic and piezo.
Do you need one or two extra wheels.

[PTChristopher]

>>> how do you control the volume and tone of both, magnetic and piezo [pickups]? Do you need one or two extra wheels.

To just answer your question:

You would need two separate volume controls, but arguably you could get away with just a single master tone control.

BUT,...

In my opinion, it can be rather unsatisfying to try to blend the piezo and magnetic PU's at their passive high impedance.

I have tried it a few times, and while you can sort of do it with separate volume controls, it can be very touchy to find a sweet spot when blending the signals.

I have been far more satisfied with the results by buffering each PU to get the impedance down, then having the 2 volume controls and either one or two tone controls after the buffers.

EDIT: If anyone out there wants to get very technical, the actual impedance drop through the buffer is really not that much on the magnetic PU. But after the buffer, we have isolated the inductance and capacitance within the magnetic PU from the volume and tone controls (and the cable). This helps quite a bit.

I have buffered all three ways that I thought practical for on-board use:

- Dual low noise op-amp IC (or even just a not-so-low noise chip)

- Dual super-simple single NPN transistor pre-amps (super low current draw and very reliable.)

- Dual single-FET pre-amps along the lines of the Alembic Stratoblaster, now called the Alembic Blaster. (The Stratoblasters were susceptible to blowing FETs - although I did not seem to have this problem with a few home-brew versions. I have no idea why.)

My spell-checker thinks Stratoblaster is not a word.

Anyway:

Yes, you can use them both (mag and piezo).

It can be a pain to blend them at the high impedance of the magnetic PU and the even-higher impedance of the piezo. But, strictly speaking, it does work-ish.

Better to use a two-channel on board pre-amp and controls. I know of no specific source for this. I have always just made them myself.

The Schatten 250K and 500K pots are not the best choice for a pre-amped signal. But you can get thumbwheel pots down in the range you will likely need. 25K is arguably a better size for the pre-amped signal. For a tone control I'd test with both 50K and 10K as well - depending on the pre-amp design.

While I genuinely believe that this is a useful summary of the situation based on actual experience, I suppose it is also a long and dis-satisfying answer. It happens.

Chris

[PTChristopher]

Deleted a short view on "impedance" and instead added a quick edit note on impedance to the above post.

[Jazz_175]

Hey Chris,
thanks for the answer, which had the effect of discouriging me from the idea of mixing the two signals.
I think I'll go only for the magnetic pickup.
The explanation on the impedence was interesting, even if you deleted it.

[PTChristopher]

>>> explanation on the impedence was interesting, even if you deleted it.

It had two problems in my opinion.

- Beyond the reasonable scope of a forum
- Technically the example missed too many fundamental things, and could be very misleading.

So better without it.

>>> doscouriging me from the idea of mixing the two signals.

Well, the piezo does capture the longitudinal string vibrations that are virtually non-existent in the magnetic PU signal. So I can see why some really like the idea of including the piezo. It is a bit of work to make the mix sound good.

All in my opinion.

Chris

[Spook410]

I'm installing an Armstrong handwound PAF in the new Yunzhi guitar as soon as the taps get here (you would think they could pre-drill and tap them.. sigh). I got some Bourne (they were out of CTS) mini-pots with an audio taper but even as small as they are, looks like any place I put them on the pickguard they will either be in the way or not fit. This brings me to using Schatten thumbwheel controls. I'm guessing from this thread that they are not an audio taper hence the recommended resistor mod (much appreciated). I plan to use a .047uf cap and 500K pots. I will also strive to provide feedback after things are installed.

[PTChristopher]

S'410,

The Schatten pots are audio taper (or at least they act like that - I never measured them).

Excessive volume drop early in the volume control (ex. from "10" to "8") in a passive guitar circuit comes from the mix of too big a pot (understandable that some prefer hi-value pots) and the audio taper.

The resistor I suggest will effectively move the taper away from the steep audio taper and toward a more linear taper.

(It does not actually change the taper of the pot - it just creates the effect of a taper change.)

A DIY mini-Guide to Bleed Resistors:

1. If your taper is excessive from the proverbial "10 to 8", try a bleed resistor from the input end contact on the pot to the center ("wiper") contact.

2. Start with a resistor roughly 20% of the pots value in most cases. This can be off by quite a bit depending on the impedance of the PU and the overall load on the circuit, but ya gotta start somewhere - and often it is just great at 20%.

3. Now see how it works. If you still have too much volume drop from 10 to 8, try a SMALLER resistor.

4. If the volume pot is now doing too little from 10 to 8, and/or you have still too much volume at 2 or 3 but the volume then falls suddenly as you turn down past that - try a larger resistor.

If you want to go advanced, you can mix a second resistor and a cap in the bleed circuit as well. This will control the tone shape as you drop volume. But that is a longer topic and maybe beyond the scope of a forum.

Chris

[Spook410]

I usually prefer an audio taper but since this will be my first thumbwheel, will just have to see. Good to have a ready method to mitigate the first half of that log scale if I need to. When the Schatten's get here I'll check their taper just because and report back. As for adding another cap (guessing you're referring to the treble bleed mod) I probably will keep it simple since this guitar won't get out much. For that matter I could just drop in a volume pot and be done but what fun is that?

[PTChristopher]

Yep, you may very well love the Schatten pots as delivered. I am sure that many do.

It is somewhat ironic to read opinions about the wonders of high value audio pots amongst Les Paul players consider ing the actual pots currently used in the guitars.

Go figure.

Anyway, best of luck with the thumbwheels.

Chris

[Spook410]

True.. it seems odd that everywhere online 500K/.47uf is represented as 'normal' for humbuckers when you have 300K/.22uf standard in Les Pauls/335's/175's and many others. Since this particular guitar will almost always be plugged into a computer I'm looking to retain more of the high end. I still may say to heck with it and not even put in a tone control since the signal is headed to a parametric EQ anyway. If this were a typical application involving an amp, I think the 250K/.22uf choice you mentioned would be a better starting point.

[nosoyninja]

Hello guys,

Just wanted to jump in here and say I've been enjoying this thread with lots of interest. I am having a custom archtop made -which I would like to share with everyone later, when my build date gets a little closer (8 months waiting list!)- and I've been struggling with the idea of mixing a magnetic PU with a Piezo archtop bridge like Jazz_175. My current thinking leans toward using a stereo jack on the axe that'll go out to an acoustic guitar amp with two channels where the mixing and matching is easier to do. This would be a very practical solution along with 3 thumbweels on the pickguard for magnetic tone, magnetic volume, and piezo volume. But I wonder if some sort of onboard preamp would be required for a volume pot on the piezo-bridge?

The point would be to have a versatile choice of tones for live applications where an acoustic tone would be amplified. The piezo bridge is complemented with the magnetic pup to round out the sound. For studio recording, a mic would take the place of the piezo bridge and provide a more suitable source. But for chaotic, noisy live situations, this system seems to be a good compromise, doesn't it?

Cheers!

[Spook410]

Caveat: I'm pretty sure is correct but can't say I have a lot of depth on this. Piezo's are very high impedance. You would need a pretty large value pot (like over a meg) and even then you would have problems losing frequencies to the capacitance of the piezo itself because when you drop the pot in, you basically are building a high pass filter. Piezo's capacitance is in the 500pF range so you would be rolling off just below 400 hz (or so.. and not a frequency range you want to be losing). The alternative is an active circuit but that takes a battery which is a pain.

If it were me, I would just run a separate out to a Hi Z input designed to handle a source like a piezo (acoustic amp, mixing board) and deal with it there.

[PTChristopher]

************************************************** ********
EDIT: I have made a mistake in this post. I got really sloppy about the practical problems of a piezo and frequency response in a passive circuit. My basic point is that a passive mixer (two volume pots) for a piezo and a magnetic PU can work, but it is very tricky to useand really not all that practical. My drift into the piezo problems and signal load are sort of off-point, and also incorrect. Spook410 eventually steers the thread back on track.
************************************************** ********

>>> My current thinking leans toward using a stereo jack on the axe that'll go out to an acoustic guitar amp with two channels where the mixing and matching is easier to do.

The capacitance of a stereo cable and the high impedance of the piezo are a possibly tricky combination. But if you keep the cable fairly short and can stand a bit of extreme high end loss, this could work for you. In my opinion, it's a matter of your opinion of the slight high end loss.

>>> This would be a very practical solution along with 3 thumbweels on the pickguard for magnetic tone, magnetic volume, and piezo volume. My current thinking leans toward using a stereo jack on the axe that'll go out to an acoustic guitar amp with two channels where the mixing and matching is easier to do. This would be a very practical solution along with 3 thumbweels on the pickguard for magnetic tone, magnetic volume, and piezo volume.

Well, a passive volume on the piezo would best be a very high value to limit the total load (passive volume plus cable plus input impedance of the eventual amp).

The piezo manufacturer may have a recommendation for a passive volume pot value. If not, I would start at 1 meg ohm as an absolute minimum, and seriously consider 5 to 10 meg. Again, your opinion of the sound is a huge part of the equation. Some consider a rolled off high end a very good thing with some piezo pickups.

>>> But I wonder if some sort of onboard preamp would be required for a volume pot on the piezo-bridge?

That is the standard method for good reason, and an on-board battery is not so awful as it may seem.

[S'410]>>> when you drop the pot in, you basically are building a high pass filter.

Yes, you are passing the highs to ground. But this is commonly called a "low-pass filter". The idea is that yes, you are passing highs to ground, but the net effect is that you are passing lows onward in the signal chain. It's awkward terminology.

Anyway, I think that with a skilled pilot, a completely passive setup combining a piezo and magnetic PU can work. And a stereo system will help in some ways (but add the challenge of the stereo cable capacitance issues).

But an active on-board system will ultimately be easier to use.

In my opinion.

Chris

[Jazz_175]

I just wanted to draw your attention to the fact that you can find some technical details in the Schatten Design Web Site.
If you go here:
Downloads - Technical Support

You can find for example the following file:
Combining piezo pickups with a mag or a mic
It doesn't say much, but it can be a good starting point.

Also here you can find some more info
Combining magnetic pickups with piezo pickups

[PTChristopher]

Nice links for tech details.

If I may give some unsolicited comments:

- From the pickups (or any type) we are not providing power. We are providing analog information to later serious gain stages in the amp. So "impedance matching" as discussed in terms of speaker output is not the issue we have here.

- The reasons that you want a volume pot with a significantly higher value than the calculated impedance of the pickup are:

1. You do not want to load down the signal, which causes loss of information. An "impedance matched" volume pot, would definitely load down the signal and cause the loss of some information.

2. This information loss is not equal in degree throughout the frequency range of the PU output. For that matter, the actual impedance is also not the same throughout the frequency range.

So we use larger pots to limit the actual information loss in the analog signal.

Does that make any sense?

I can just imagine that the impedance values in the links above could seem confusing compared to the volume pot values often recommended.

Chris

[Spook410]

It is tricky terminology, but I think a piezo is a high pass. Looks like:

V---||---o------o -> Signal
. ........ |
.......... z
. .........z
. ........ |
......... //

This will block everything below a certain frequency based the value of the cap and resistor. (V=source, ||=cap, z's=resistor, //=ground, .=nothing, formatting)
For 500pF, 1Megohms, you block everything below 318hz. Not good. This is why a piezo sounds thin and nasally when you plug directly into a guitar amp.
If you up the resistor to 10Megohms, you block below 31.8Hz. No so bad.

And yes.. I cheated and looked some stuff up (hey, college was a very long time ago). Dailey's 'Electronics for Guitarists' has a very good discussion in Chapter 2.

[nosoyninja]

Wow.

Lot's of useful info, thanks guys! If I want to keep the balanced cable out idea to have seperate signals at the amp, it looks like the best option would be to use an onboard preamp for the piezo whether I'm adding a volume pot or not.

PTChristopher , what do you mean by extreme high frequency loss? above 10khz? I'm sure there's lots of useful info above that frequency range if we get nitpicky, but probably nothing you couldn't live with (again, I'm looking for a practical solution for the stage, not for recording).

I will be discussing all of these issues with the luthier and see what he thinks is the best solution.

Thanks!