DPDT bass-cut switch

[axedoctor]

Hi All - 

After reading numerous posts on this forum, I registered today in order to receive some advice about ideas I am kicking around for a strat operation.

Seems that incorporating some sort of bass cut circuit provides interesting value and perhaps especially so if combining single coils in series.

I am not quite ready to assign one of my pots to adjust the bass cut effect, but instead am considering a DPDT on-on-on toggle to select between two bass cut options with the center position a total bypass of the effect.

My first thoughts are to select an appropriate capacitor in series between the top of the treble tone control and the volume control input with the common lugs of the switch in parallel with this capacitor and wired to short it out in the "center" position. The "up" and "down" positions of the switch would then select either of two resistor values to complete the desired RC impedance component.

Functionally, quite simple - so then ... I am wondering what values of {C, R1, R2} you believe might provide useful bass cut adjustment given the various parallel/series combinations between the three pickups.



many thanks in advance for your consideration of requests from a newly minted resident

 

[newey]

axedoctor-

Hello and Welcome to G-Nutz2!

Sorry, but I had to move your post from the tone control sub-board. You're more likely to get an answer here anyway, more people will see it.

JohnH's "Guitarfreak" calculator does (IIRC) simulate the G & L bass-cut control, so you could use that software to play around with values to see how much cut you'll get.

BTW, if the center position is to be a bypass of the effect, you could probably use an "on-off-on" type switch which may be easier to source and/or cheaper. I don't think you need to short the cap in the center position, simply disconnecting it should also work.

[reTrEaD]

Dec 20, 2016 21:53:07 GMT -5 newey said:

BTW, if the center position is to be a bypass of the effect, you could probably use an "on-off-on" type switch which may be easier to source and/or cheaper. I don't think you need to short the cap in the center position, simply disconnecting it should also work.

I think the cap needs to be shorted, Newey. It's placed in series with the signal before the volume control and forms the top half of a simple high-pass filter. The bottom half is the resistance of the volume control.

Disconnecting would leave you with no signal path to the volume control.

BUT . . .

Your idea of using an on-off-on switch is still useful if the "bypass" is at one of the on positions.

Also, here's a link to a pertinent thread:
Bass-cut and the G&L PTB system

A switched (on-on-on) version with suggested values is near the bottom of the first page.

[axedoctor]

rTrEaD - 

I have read through "Bass-cut and the G&L PTB system" and had originally placed this question within a reply to that thread since my goal is closely related to the one described within. The architecture is a little different though because my goal is to provide two settings, neither of which produce such severe diminishing of bass tones as was required by the original questioner.

I have already downloaded the GuitarFreak tool, but am still getting my feet wet with it ... perhaps some additional time spent working with it will provide the insight I am looking for, although sage advice is always valuable.

thanks for trying to help point me in the right direction

[ChristoMephisto]

I came up with a bass cut switch with a dpdt center off switch.
guitarnuts2.proboards.com/thread/5053/bass-vi-series-parallel?page=2
Might have to scroll down a bit.
Down is bypass, middle is one cap and up is both caps added.

[axedoctor]

CM - 

This wiring is yet another way to obtain 3-state functionality with the DPDT.

I see that your application is for some significant tonal effect for a bass guitar and is accomplished with two capacitor-only impedance units.
My quest is to determine a pair of impedances (perhaps using RC combos) that will give me some more subtle tonal variation of the lower frequencies for a stratocaster with single coils in either parallel or series ... just wondering if anyone here has already explored this area and might have suggestions.


 

[reTrEaD]

Dec 21, 2016 9:07:13 GMT -5 axedoctor said:

(perhaps using RC combos) that will give me some more subtle tonal variation

Yes, a resistor in parallel with the capacitor will mimic having the bass control at a modest value. Lower resistance = less cut.

Perhaps a 2.2nF cap with a 330k resistor where C1 is in CM's drawing. That would establish something moderate as the larger cut in the center position of the switch. Maybe a 150k or so where C2 is in CM's drawing. That would make for a more subtle cut.

You can accomplish that with just a SPDT on-off-on if you prefer.

[axedoctor]

many thanks ... this gives me a starting point to explore the effect using the GuitarFreak tool

still think it will require the DPDT 3-way to accomplish the bypass option, but I'll muse on your SPDT assertion as that could be housed within one of the pots

[JohnH]

Just to note that with the basic Bass-cut controls, with the pot set to minimum resistance, it is fully bypassed, no need for a specific centre-off switch position unless you really want that on the switch.

Let me know any issues with GF. The first goal is to make sure it works for you with the buttons and sliders responding properly - which is all about making sure macros and active x controls etc are running.

If I was building a bass cut control with two settings, id have a 2.2nF and a 0.47nF cap, and run them via a switch through a 1M log pot (or better, anti-log, ie Type C, rare though).

[axedoctor]

Hi John - 

Thanks for responding. I am new to the world of guitar electronics and have been educated & inspired by your posts and the thoughtful effort you have put into your Excel tool. As mentioned in my original post, I am attempting to include some level of meaningful bass cut without utilizing one of the three control pots. My first thoughts have been to choose a single capacitor (to set a quasi corner frequency?) and then a pair of resistors to establish the intensity of the tonal shaping. Perhaps my understanding of the impedance effect is not quite correct, but if it is then suggestions for C, R1 & R2 would be appreciated. Seems that reTrEaD thinks that 2.2nF, 330k & 150k might be an interesting combination.

WRT GuitarFreak, I have started to play around with the controls with some level of success. If I make the selections on the buried pages, then it seems to percolate up to the main page properly, but if I attempt to make selections on the main page, I have encountered "not enough resources to complete operation" (or some similar statement). So I just try to be careful. Also, I am not clear on how to define what signals should be displayed in the chart section. Some of your posts indicate that there is considerable ability to do so, but I have not seen any instructions on how to accomplish this.

Also, your web site indicates that you certainly have idyllic surroundings to inspire your guitarnutz hobby. 

[newey]

I'll muse on your SPDT assertion as that could be housed within one of the pots

Not sure what you mean there, axedoctor. If you're referring to using a push/pull pot (as being "housed within" ), RT is still talking about a three-position switch.

[JohnH]

Dec 21, 2016 19:49:04 GMT -5 axedoctor said:

Hi John - 


WRT GuitarFreak, I have started to play around with the controls with some level of success. If I make the selections on the buried pages, then it seems to percolate up to the main page properly, but if I attempt to make selections on the main page, I have encountered "not enough resources to complete operation" (or some similar statement). So I just try to be careful. Also, I am not clear on how to define what signals should be displayed in the chart section. Some of your posts indicate that there is considerable ability to do so, but I have not seen any instructions on how to accomplish this.

Also, your web site indicates that you certainly have idyllic surroundings to inspire your guitarnutz hobby. 

There are various displays but the clearest for just comparing electrical effects is 'electrical only' which just covers the circuit as a simple electrical filter.

Other options add the effects of string vibration and pickup position etc,

You can select this from the menu at lower right of the main graph on any of the first three pages. The 'Graph' page is just a larger clearer copy of what is shown on the other pages but does not have activecontrols of its own (hmm, could add that though)

BTW, which GF version of GF are you using (eg Excel or Libre-office?) and what are you running it on?

[axedoctor]

Dec 21, 2016 23:14:25 GMT -5 JohnH said:

Dec 21, 2016 19:49:04 GMT -5 axedoctor said:

Hi John - 


WRT GuitarFreak, I have started to play around with the controls with some level of success. If I make the selections on the buried pages, then it seems to percolate up to the main page properly, but if I attempt to make selections on the main page, I have encountered "not enough resources to complete operation" (or some similar statement). So I just try to be careful. Also, I am not clear on how to define what signals should be displayed in the chart section. Some of your posts indicate that there is considerable ability to do so, but I have not seen any instructions on how to accomplish this.

Also, your web site indicates that you certainly have idyllic surroundings to inspire your guitarnutz hobby. 

There are various displays but the clearest for just comparing electrical effects is 'electrical only' which just covers the circuit as a simple electrical filter.

Other options add the effects of string vibration and pickup position etc,

You can select this from the menu at lower right of the main graph on any of the first three pages. The 'Graph' page is just a larger clearer copy of what is shown on the other pages but does not have activecontrols of its own (hmm, could add that though)

BTW, which GF version of GF are you using (eg Excel or Libre-office?) and what are you running it on?

John - 

I am running GF6.4 in Excel 2010 under Windows 10

I see and can select the charting choices that you mention, but it seems that it always displays 4 data sets (SSL-1 full response, Fender 57/69, SSL-1 envelope, SSL-1) with X-axis in log frequency and Y-axis in dB level. Wondering how you might have used the tool to extract data to produce charts with frequency response plots at multiple settings of the various control pots or multiple values of certain capacitors or resistors that have appeared in some of your posts.

also, what is the significance of the "envelope" and "smooth envelope" options for the "full response" charts?

btw, my training and work experience is developing test & measurement HW & SW for production testing of mixed signal semiconductors, so I ought to be able to grasp most of this guitar circuitry, although dealing with multi-stage passive networks does present some challenges that can be circumvented with the use of op-amps that allow isolation of various stages and the maintaining of a constant impedance throughout the entire signal path



 

[JohnH]

In GF6.4, you can have up to 10 saved traces. These are controlled by the 'save' and 'clear' buttons at lower left. There is one red live trace. If you want to record this, type a legend for it if you want to, and hit 'save'. Then make another setting and hit 'save' again, etc. That is how the multi-trace graphs are made. Then hit 'clear' to erase them all. There is also the 'Reference' button, which is similar to 'Save' but does not get cleared by the 'clear' button.

'Full response' includes everything that the system models, and it is rather spiky since every string harmonic is plotted separately with gaps between. 'Envelope' smooths this out by replacing each separate harmonic with a smooth function that covers them all while still picking up the comb-filter effect caused by pickup location and combinations. 'Smooth envelope' is similar, but plotting the maximums within a +2/-3 semitone range to make it smoother.

[axedoctor]

aha ... found the chart control (lower right, btw) so I will start to play around with this

perhaps my page set-up or laptop screen aspect ratio is not quite correct, but there seem to be a number of places where controls and displays overlap

ex : Bridge and PhaseB select boxes with right side of PU-Select menu
      Bass Cut pot selector and full scale pot size input box
      R3% slider and result display box

also, I have not found a control for the Bass Cut capacitor C6

wondering why you did not place the Volume Control and Bass Cut pot size selections (250K, 500k, etc)  and Bass Cut capacitor selection (C6) on the Tone Sheet

[JohnH]

Thanks for the feedback and questions.

The bass cut cap has a slider just beneath the bass cut pot. In the current download, it comes set at a starting value of 2.2nF

The controls were set up so that everything that is normally required is all on the main page. The Tone page was intended for use when exploring non-standard tone circuits. It has all the pot knobs but not the volume and bass pot values. But there is no reason why it couldn't have them too, and like other knobs, they would be ganged so that moving the value can be done on any page. I might add that.

Graphics are a always a trick, and there is definitely a possibility that things look differently on different machines. It can be related to screen res and font size, and I'm learning all the time how to try to control these aspects. As soon as I unlock it for editing, things start moving around if I am not careful! The current version (date 21/8/16)is looking fine on my two machines today though.

Id be interested to see a screen shot of how it looks for you. One of the issues I have with GF is that I usually get very little feedback on it, beyond 'cool!' or 'WTF?!'
cheers

[axedoctor]

ahhh ... found the control for C6

attempted to attach a screenshot illustrating my previous comments

Attachments:

[JohnH]

That's pretty much how I'm seeing it, apart from the pickup selection boxes which seem to be wider at your end.

So from that point, to test out your bass-cut ideas:

Pick a pickup that is near to what you have
Press 'reference' to clear the current reference trace and replace it with the live trace
Start playing with the bass cut slider and cap values. The bass pot is set as 1M, but if you want to try no bass cut resistor, you can type a very large value into its yellow box. The bass pot does not have a slider, just a box to input into.
Press save to record various traces