Passive mid cut

[Guest]

Hi guys,

Whilst scouring the internet for control cavity mods I recently came across a really novel idea: the [url="http://alexplorer.net/guitar/mods/tbx.html"]TBX tone control[/url].
In most instances, this wouldn't be particularly useful on a bass, but it got me thinking - seeing as one can cut treble or bass, wouldn't it be possible to create a passive mid cut control, either by modifying the cap / resistor values on the TBX or by using a Push / Pull tone pot (with various gubbins attached to it) to switch between standard treble cut and mid cut?

There's [url="http://www.talkbass.com/forum/showthread.php?t=168064"]a similar topic on Talkbass[/url] which mentions the BluEQube used by Dingwall, but I'd really like to have a go at doing this myself.

Any ideas?

[silverfoxnik]

[quote name='Baldwin' post='155474' date='Mar 11 2008, 06:43 PM']Hi guys,

Whilst scouring the internet for control cavity mods I recently came across a really novel idea: the [url="http://alexplorer.net/guitar/mods/tbx.html"]TBX tone control[/url].
In most instances, this wouldn't be particularly useful on a bass, but it got me thinking - seeing as one can cut treble or bass, wouldn't it be possible to create a passive mid cut control, either by modifying the cap / resistor values on the TBX or by using a Push / Pull tone pot (with various gubbins attached to it) to switch between standard treble cut and mid cut?

There's [url="http://www.talkbass.com/forum/showthread.php?t=168064"]a similar topic on Talkbass[/url] which mentions the BluEQube used by Dingwall, but I'd really like to have a go at doing this myself.

Any ideas?[/quote]
No idea on this at all, as I'm not in any way up on electrics/electronics.. But I think it'd be an excellent thing to have to give greater tonal variety & flexibility to passive basses.. Good luck with it!

[Buzz]

Unless I'm very very much mistaken (95% chance), Passive EQ's only offer cut and no boost on amps. I'm sure if you can have it on an amp, you could wire up a pot to do it on a bass with a bit more gubbins.

[clauster]

Circuit diagrams here whih may give you a good starting point

[url="http://www.duncanamps.com/technical/tonestack.html"]http://www.duncanamps.com/technical/tonestack.html[/url]

[alexclaber]

It can be done as the bluEQube shows. But you could just as easily run a neck and bridge pickup in parallel to get the same effect, as the phase cancellation causes a similar midrange cut - the wider the spacing, the more obvious the cut. I think that's why the J-bass pickup arrangement works SO well. With neck pickup you get a low midrange accentuated sound, with bridge pickup you get a high midrange sound and with both you get the scooped sound. Simple yet magical.

Alex

[bremen]

[quote name='Baldwin' post='155474' date='Mar 11 2008, 06:43 PM']Hi guys,

Whilst scouring the internet for control cavity mods I recently came across a really novel idea: the [url="http://alexplorer.net/guitar/mods/tbx.html"]TBX tone control[/url].[/quote]

odd - calls for a 82.5K resistor and a 22.5uF capacitor, neither of which are standard values. A 22uF cap would completely kill the signal from a pickup anyway (0.047uF is the usual high-cut).

[quote]In most instances, this wouldn't be particularly useful on a bass, but it got me thinking - seeing as one can cut treble or bass, wouldn't it be possible to create a passive mid cut control, either by modifying the cap / resistor values on the TBX or by using a Push / Pull tone pot (with various gubbins attached to it) to switch between standard treble cut and mid cut?

There's [url="http://www.talkbass.com/forum/showthread.php?t=168064"]a similar topic on Talkbass[/url] which mentions the BluEQube used by Dingwall, but I'd really like to have a go at doing this myself.

Any ideas?[/quote]

If you put an inductor in series with a capacitor in series with the 'tone' pot that'll cut mids. The frequency at which this happens depends on the values of the inductor and the cap. If you're interested I can do some calculations.


It will also depend very much on the inductance and DC resistance of the pickup(s). Not sure how to calculate that.


Yes, it would be a simple matter to use a switch to select topcut/midcut.

[Lfalex v1.1]

Good thread!

I like passive tone controls in all their forms, as I find them more subtle than active ones.
With regard to pick-ups' DC Resistance and Inductance, contact the manufacturers.
Lots of them seem to quote DC Resistance on their pick-up specs...

[Guest]

Thanks for all the replies so far!

[quote name='bremen' post='155846' date='Mar 12 2008, 11:03 AM']...odd - calls for a 82.5K resistor and a 22.5uF capacitor, neither of which are standard values. A 22uF cap would completely kill the signal from a pickup anyway (0.047uF is the usual high-cut).[/quote]

Yeah, according to [url="http://reviews.harmony-central.com/reviews/Effects/product/Fender/TBX+Tone+Control/10/1"]this TBX review[/url] it sounds like arse with the default wiring. Apparently the thing to do is use the same cap value with either a 120k or 220k resistor in parallel instead. This [url="http://blueguitar.org/tbx_doc.gif"]diagram[/url] suggests 220k, but most of the reviews I've found mention a 120k. I know very little about electronics, so I'm not sure which will give you the "better" sound.

Why would the 0.022uF cap kill the signal? I thought the lower the value a cap, the less highs it would cut.

[quote name='bremen' post='155846' date='Mar 12 2008, 11:03 AM']If you put an inductor in series with a capacitor in series with the 'tone' pot that'll cut mids. The frequency at which this happens depends on the values of the inductor and the cap. If you're interested I can do some calculations.[/quote]

It would be great if you could, as I have no idea how this would work! Does the value of the inductor control the mid rolloff frequency, or would that be determined by the cap value?

[quote name='Lfalex v1.1' post='156480' date='Mar 13 2008, 09:01 AM']Good thread!

I like passive tone controls in all their forms, as I find them more subtle than active ones.
With regard to pick-ups' DC Resistance and Inductance, contact the manufacturers.
Lots of them seem to quote DC Resistance on their pick-up specs...[/quote]

I'm going to have a go at shielding my Jazz later today, so I'll try and measure the pickups then. Let's hope my cheapo multimeter has survived the winter.

[bremen]

[quote name='Baldwin' post='156550' date='Mar 13 2008, 10:24 AM']Thanks for all the replies so far!



Yeah, according to [url="http://reviews.harmony-central.com/reviews/Effects/product/Fender/TBX+Tone+Control/10/1"]this TBX review[/url] it sounds like arse with the default wiring. Apparently the thing to do is use the same cap value with either a 120k or 220k resistor in parallel instead. This [url="http://blueguitar.org/tbx_doc.gif"]diagram[/url] suggests 220k, but most of the reviews I've found mention a 120k. I know very little about electronics, so I'm not sure which will give you the "better" sound.

Why would the 0.022uF cap kill the signal? I thought the lower the value a cap, the less highs it would cut.[/quote]

you're right, but I read the schematic as 22.5uF. 0.022 would make much more sense.

[quote]It would be great if you could, as I have no idea how this would work! Does the value of the inductor control the mid rolloff frequency, or would that be determined by the cap value?[/quote]

A combination of the two. I'll get round to it, nudge me if you don't hear from me!

[Guest]

Just a quick update - I found a video of somebody who made one of these controls himself and dropped it into his Tele. Fired off a message asking him for some pointers and not really expecting a response.

What did I get? A schematic complete with part numbers and a concise walkthrough, all within a couple of hours - really helpful guy!

I can post the details if anyone's interested.