4 position Q-Switch

[jazzyvee]

My redwood series I is such a beautiful sounding bass, it really needs to be a series II, but shipping it back to the mothership for a conversion would be outside my comfort zone. As an alternative I wouldn’t mind a larger q-boost option. If the existing switches could be changed to a 4 position switch like the pickup selector. The first three positions would be the same as standard and the 4th would be the same value as the series II CVQ fully open.


 I do have a number of those switches in my spares box, so would this be a simple DIY task or would it need Ron’s bench time to develop this.

[edwardofhuncote]

I'm not smart enough to know what about the switches determines the Q value of each switch position... some kind of resistors or other little squiggly-looking things? Some kinda' Wizardry. But I do like the idea. I remember a thread long ago where someone had the idea of a Q dial with something like 10 detents in its sweep rather than a continuously variable rheostat type. It's been long enough that I don't remember who. [flpete1uw] maybe? Haven't seen Pete here in ages.


I think your "One Click More" Q is a good idea, Jazzy. If those pickup selector switch spares you have could be repurposed for that, three cheers. If not, maybe there is another type of 4-position ball-bat switch that could perform this somehow.

[JimmyJ]

Hey Jazzyvee,

So really what you're asking for is MORE Q-boost, right?  Because the Series I switch gives you +6 / +9 but the Series II "goes to 11" (actually +15) when wide open.  I don't know enough about the circuit to understand how much differs between I and II but clearly the II pot indicates it is simply a change of resistance that alters the boost level - in that configuration.  So one would think a "stepped" version would also work.  I just don't know what other components need to be changed to achieve that additional 6db of boost.

Regarding your collection of spares, aren't the pickup selector switches already prewired for their original assignment?  Not sure they could easily be reassigned.  And frankly, if they're prewired you should hang on to them because they're a valuable replacement for somebody who needs it!

Keep in mind we are talking about jumping through some hoops here for a fairly subtle change of tone.  Maybe something only YOU will notice.  Jazzy, find out from Mica what all needs to change from I to II.  Does it involve the preamp board or is it all in the wiring harness?  If the latter, maybe upgrading a few components in the harness would get you there!  (I'm just making this up so keep thinking about it).

Or maybe you just need a SuperFilter pedal.   

Jimmy J

[edwardofhuncote]

Hmmm. 🤔

It hadn't really sunk in until I read Jimmy's post but it should have been automatic. I know on my two 5-string Alembics, (because my preferences have always been for less attenuation) I opted for Q-switch values of 0-3-6 dB. So maybe there is a possibility for a switch with values at the upper end beyond the standard values? If so, changing out just the switch(es) might be possible without the expense of a trans-Atlantic journey or the extended hospital stay.

Not for this cowboy. 🤠 It would never work again.

[flavofive]

Here's the thing about all this - you're right, it seems like "common knowledge" here on the forum that the Series 1's Q switch allows for +0 dB, +6 dB, and +9 dB of boost, and the Series 2's Q pot (knob) allows for +0 dB to +15 dB continuously.
But I don't know if that's actually true.  Here's why:

Circuit-wise, the components that control the Q are just resistors; about the simplest components of electrical circuits.
The thing is:  The Series 1 and Series 2 "Q" resistors do the same thing, and have the same minimum and maximum values.

The only difference is that the Series 2 is a 1000-ohm potentiometer (simply an adjustable resistor), which allows for a continuous selection anywhere from 0 ohms to 1000 ohms resistance from either end.
Whereas the Series 1 is just a 3-way switch plus two 510 ohm resistors.  This allows for a selection of 0 ohms, 510 ohms, or 1020 ohms from either end.
The important thing is the values.  Put simply:  The result is identical.  The only difference is that the Series 1 has 3 "presets", basically on / halfway / full, whereas the Series 2 is continuous.
(Technically yes, there is a VERY slight difference between 500 & 510 ohms, and 1000 & 1020 ohms, but the only reason for the difference is that 510 ohm resistors are far more standard than 500 ohm resistors, hence why they are used on the Series 1.  The actual difference it makes to the boost is very small; it definitely wouldn't account for the purported difference in the maximum boost from +9 dB up to +15 dB.)

I don't see anything in the Series 2 circuit that could account for any difference to the maximum Q boost.  The circuits are identical except for this (above) and the master volume, which wouldn't affect the Q boost.

I just double-checked this in a circuit simulation software.  Actually, at the highest Q switch setting, the Series 1 does achieve roughly +15 dB boost.
All this to say:  Jazzyvee, I think you are already getting to the same maximum boost with the Series 1, as-is.  That is, unless yours was custom-designed with a maximum boost that is lower than the "standard".


I absolutely welcome any corrections, if I'm missing anything!  Again, I understand this goes against the common knowledge, but literally I can't argue with the circuit - the numbers don't lie.

Jazzyvee, if you wanted an EVEN HIGHER boost, then that may be possible with modifications, but that would be beyond what the Series 2 does.
And if you simply want 4 positions within that same range, actually it gets very tricky.  Rather - it would be far easier to just rewire it to be a "Series 2" CVQ.  Ironically, the Series 2 component (just a single potentiometer) is significantly easier to wire up than the switch/resistor set in the Series 1.  The only tricky thing would be finding a compatible pot, which in this particular case is almost certainly available, but just a bit of effort to find the right one to fit the depth and physical space in the cavity.
I'm not saying you shouldn't send it back to Alembic; I'm not trying to deprive anyone of business or anything!  I'm just confirming that 1) I don't think you're actually missing any "extra" boost, unless you have a non-standard circuit, and 2) if you did want to change it to a CVQ, this would be readily do-able, unless I'm missing something.

[edwardofhuncote]

Series III... ?


(gimme' three steps...)

[flavofive]

Series III... ?


(gimme' three steps...)

 

[JimmyJ]

Hey Mike D,

Thanks for that great explanation!  I like it!  And it would mean Jazzy already has the max available HF boost.

I'm afraid the source of the confusion is these two FAQ posts here:
https://club.alembicguitars.com/index.php?topic=271.0
and here:
https://club.alembicguitars.com/index.php?topic=272.0

The +15 could easily be a typo, or the other way around with the Series I more like +6 /+12, I don't know.  But your description makes sense because I didn't think there was anything on the preamp board that changed between I and II. 

I expect Mica to jump in and settle this momentarily. 

Jimmy J

[FC Bass]

Fwiw: This is a Series II with Filter and Q (accidentally) full open. I was experimenting before recording and forgot to put the CVQs back to my preferred 1/4 setting (also forgot to clean the bass before recording) :-)

[jazzyvee]

Thanks for all the responses, i will have to re-read to understsand a bit better. Here is my situation, I have three,  series 5 string europas.
Series2 on left quilt maple and redwood series1 on right both have the thick ebony neck lams and the middle has burl maple top an purple heart neck lams.
Sonically the middle one has the more up front bottom end, i’m assuming due to neck pickup closer to the truss rod cover. The series 2 has the cleanest and more evenly balanced tone, the redwood sits somewhere in the middle and to me it has sweetest warm tone of the three and having always been a tone tweaker I can’t help feeling that this bass deserves to be a series 2 even if it does not have master volume. There have been requests on the forum for a long time about the possibility of an S1 to S2 upgrade kit but that has not appeared, i’m sure for valid reasons. So i’m just wondering if there is a simpler cost effective way to get the higher q.

[JimmyJ]

Jazzyvee,

That's a lovely collection you've got there!  And it looks like they all get along with no family squabbling.     

If what Mike (flavofive) posted is in fact true, your Series I with the Q-switch at full boost would be the same as Series II kit with the Q-pot all the way up.  We'll wait for confirmation on that from Mica.

It's also possible that what you are experiencing is simply the variation in outcome of handmade instruments. 

I've told this story before so bear with me...  I currently have 3 Series-II 5-string fretted basses made of the same wood and construction, same body style and dimensions, same electronics package, same strings.  TO ME, there are distinct differences.  #1 is my recording bass which feels like it has the sweetest top-end and most even and open tone across the fingerboard.  #2 is my live bass which has a stronger low-b string but is not as "open" in the higher frequencies.  And #3 is my practice-at-home or on-the-road-backup bass which I would describe as having a slightly mushy tone compared to the others.

I believe these distinctions are simply the luck of the draw as to how the wood grain runs and how all the pieces happen to work together.

But note that I said "TO ME".  Even if my mom were still alive I don't think she could tell which of the 3 basses I was playing.  She'd only know it was me.     

And the proof for me is that I've played live gigs on bass #3 when #2 had some issues and apart from the guitar tech nobody in the band or sound crew noticed.  I have also played on albums with bass #2 and it worked out fine.  Furthermore, on recordings I've made with #1 I have occasionally made repairs while on the road using bass #2 - so the resulting bass track on that song switches from #1 to #2 in several places.  And nobody said a word.

So Jazzy, always keep perusing your tone goals, I certainly appreciate the quest.  It's a personal thing which all of us do in our own way.  Maybe there is a way to modify your redwood to get a bit more top-end out of the circuit but I suspect it will never sound exactly like your Series II - TO YOU.  Everybody else will just hear Jazzyvee laying down the heavy bass lines. 

I will also add that +15db (if that is indeed the number) is a LOT of gain at any frequency and you may risk amplifying hiss.

Carry on now.  Keep going!  "Tone Tweaker" (or maybe just "Toney") might be a good nickname for you.   

Jimmy J

[jazzyvee]

Here's the thing about all this - you're right, it seems like "common knowledge" here on the forum that the Series 1's Q switch allows for +0 dB, +6 dB, and +9 dB of boost, and the Series 2's Q pot (knob) allows for +0 dB to +15 dB continuously.
But I don't know if that's actually true.  Here's why:

Circuit-wise, the components that control the Q are just resistors; about the simplest components of electrical circuits.
The thing is:  The Series 1 and Series 2 "Q" resistors do the same thing, and have the same minimum and maximum values.

The only difference is that the Series 2 is a 1000-ohm potentiometer (simply an adjustable resistor), which allows for a continuous selection anywhere from 0 ohms to 1000 ohms resistance from either end.
Whereas the Series 1 is just a 3-way switch plus two 510 ohm resistors.  This allows for a selection of 0 ohms, 510 ohms, or 1020 ohms from either end.
The important thing is the values.  Put simply:  The result is identical.  The only difference is that the Series 1 has 3 "presets", basically on / halfway / full, whereas the Series 2 is continuous.
(Technically yes, there is a VERY slight difference between 500 & 510 ohms, and 1000 & 1020 ohms, but the only reason for the difference is that 510 ohm resistors are far more standard than 500 ohm resistors, hence why they are used on the Series 1.  The actual difference it makes to the boost is very small; it definitely wouldn't account for the purported difference in the maximum boost from +9 dB up to +15 dB.)

I don't see anything in the Series 2 circuit that could account for any difference to the maximum Q boost.  The circuits are identical except for this (above) and the master volume, which wouldn't affect the Q boost.

I just double-checked this in a circuit simulation software.  Actually, at the highest Q switch setting, the Series 1 does achieve roughly +15 dB boost.
All this to say:  Jazzyvee, I think you are already getting to the same maximum boost with the Series 1, as-is.  That is, unless yours was custom-designed with a maximum boost that is lower than the "standard".


I absolutely welcome any corrections, if I'm missing anything!  Again, I understand this goes against the common knowledge, but literally I can't argue with the circuit - the numbers don't lie.

Jazzyvee, if you wanted an EVEN HIGHER boost, then that may be possible with modifications, but that would be beyond what the Series 2 does.
And if you simply want 4 positions within that same range, actually it gets very tricky.  Rather - it would be far easier to just rewire it to be a "Series 2" CVQ.  Ironically, the Series 2 component (just a single potentiometer) is significantly easier to wire up than the switch/resistor set in the Series 1.  The only tricky thing would be finding a compatible pot, which in this particular case is almost certainly available, but just a bit of effort to find the right one to fit the depth and physical space in the cavity.
I'm not saying you shouldn't send it back to Alembic; I'm not trying to deprive anyone of business or anything!  I'm just confirming that 1) I don't think you're actually missing any "extra" boost, unless you have a non-standard circuit, and 2) if you did want to change it to a CVQ, this would be readily do-able, unless I'm missing something.

Interesting but it if i put the q to max for series I & II, play a left hand hammer off and on, whilst sweeping the filter knob the wah effect i can hear is definitely more pronounced on the series II.
As a contrast, on my series I and II shorties, the effect is the opposite, though the overall sound of the koa topped series II is overall a significantly less bright sounding bass than the maple topped seriesI.

Maybe i need my ears checked. 🤪😂

[jazzyvee]

Thanks Jimmy, you have shared that story and it was in my head as i started the thread. And in a blind test I could not guarantee 100% i could tell which bass was being played as the settings of tone ( which you don’t really mess with), would make that harder. When i play any one of my basses to me they have what i refer to personally as an alembic accent with each one having a slightly different character. I’m not looking to reproduce the same sound on another bass but give the redwood the opportunity to have a wider tonal spectrum. But with all these things cost is always a consideration and if this is not a goer, i’m still loving this bass and this is the Dreaming for now section. 🤣🫣

[jazzyvee]

Thanks Jimmy, you have shared that story and it was in my head as i started the thread. And in a blind test I could not guarantee 100% i could tell which bass was being played as the settings of tone ( which you don’t really mess with), would make that harder. When i play any one of my basses to me they have what i refer to personally as an alembic accent with each one having a slightly different character. I’m not looking to reproduce the same sound on another bass but give the redwood the opportunity to have a wider tonal spectrum. But with all these things cost is always a consideration and if this is not a goer, i’m still loving this bass and this is the Dreaming for now section. 🤣🫣
As for the high q settiing, my intended use is at the lower frequency end of the filter range not the top. Generally i’ve found adding q to the top end works best for me when i have done gigs with acoustic guitar bands or slapping. Other than that it’s used subtly. I think.
I might add i’m really enjoying you bass playing and tone on that Phil Buckle album i’ve been listening a lot to recently. 👍🏾

[mica]

I asked my dad to chime in on this discussion. Here's what he sent me:

regarding the club thread:

in this active filter, lots of parameters interact making explanations
complex.

but, here goes:

one set of the 510 Ohm resistors controls the feedback of the opamp and thus the gain and the Q of the filter.  minimum Q is the feedback is taken from the top of the resistor divider network, so it's unity gain.  as the switch is changed the feedback is reduced, so the gain increases which also increases the Q.

The toggle switch is three positions with center OFF.  so in low Q position, the yellow and orange leads of the ribbon cable are shorted together for maximum feedback.  in the center or medium Q position, the signal on the yellow lead comes from the center of the two 510 Ohm resistors, and the ratio of the 510 Ohm resistor on the terminal with the orange lead to the sum of the other 510 Ohm resistor and the 620 Ohm resistor connected to common (green lead).   In the high Q position, the switch shorts out the lower 510 Ohm resistor so the feedback is the ratio of the upper 510 Ohm resistor to the 620 Ohm resistor.  So the toggle switch shorting one or the other or none of the 510 resistors makes thinking about the action tricky.

the other half of toggle switch has a similar set of two 510 Ohm resistor and the 630 Ohm resistor to common.  this network is connected to the first 5.1 kOhm resistor for half of the frequency control. In the low Q position, the 5.1 kOhm resistor is connected directly to to the output of the preamp section, Red lead, so the full signal of the preamp for the bass pickup is presented to the filter frequency control.  in the center position, the frequency control is fed by the voltage divider formed with the top 510 Ohm resistor in series and the lower 510 Ohm resistor in series with the 620 Ohm resistor.  And in the high Q position the the switch shorts out the lower 510 Ohm resistor so the voltage divider is still the top 510 Ohm resistor in series and the 620 Ohm resistor in parallel.   Thus the increase in gain caused by the feedback resistor, is compensated exactly by the incoming resistor divider so the overall gain remains constant.

Because there is variation (tolerance differences) in components especially the capacitors, and the ratio of the two section of the frequency control, the Q isn't always close enough to the design Q, so we trim the circuit Q after assembly of the parts by adding a small capacitor across the 3.3 nF capacitor to lower the Q or across the 6.8 nF capacitor to raise the Q to the desired level, so you may see one or the other of these added capacitors in a given instrument.  We select the capacitor using a capacitor Decade Box which has steps of 100 pF along
with a modification of a variable capacitor if 24-124 pF so we get the necessary effective capacitor to get the Q we want. Then we measure the capacitance and select one or sometimes two in parallel capacitors to trim the filter Q to the desired level.

Adding rotary switch can work to select a setting from a resistor network, and the pickup selector type of switch would be ideal (so-called "shorting" switch action -- make before break action) so the as you rotate the switch when both contacts are connected to the resistor network, the Q goes down briefly as you rotate the switch.  This is much better than a non-shorting switch (almost all rotary switches are non-shorting) where the momentary disconnection of the lead as the knob is rotated can cause the gain of the opamp to increase alot and make
a momentary oscillation or chirp noise everything you change the Q.

One possible network would be to use the existing 620 Ohm resistors that connect to the volume control low end (green wire of the ribbon cable for the bass pickup) and three 200 Ohm resistors in series connected to the 4 contact positions on the switch.  The high Q switch position connects to the 630 Ohm resistor, and the low Q position with the final 200 Ohm resistor connects to the orange ribbon cable lead.  the yellow ribbon cable lead connects to the center contact of the switch.  Finally you can add a 10 kOhm variable resistor across the 620 ohm resistor and use that to adjust for the maximum Q you desire.  One side of the 10 kOhm trimpot connects to the ground side of the 620 Ohm resistor and the center (wiper) contact of the trimpot connects to the junction of the 620 Ohm resistor and the rotary switch contact for high Q.

Do the conversion for one pickup first, and then if satisfactory, do the other pickup Q switch using the corresponding points of connection (the rbibon cable colors are different (black for the common, grey for the top end of the resistor network (low Q position of the rotary switch) and white for the center contact of the Q switch ).