SwedishLuthier Posted March 18, 2007 Report Share Posted March 18, 2007 (edited) I recently got myself a Torres “Midrange and Tone Switch” http://www.torresengineering.com/midandtonswi.html As I understood the function it would act as a normal tone (treble attenuator) in the “push” position and a s a mid cut filter (band pass) in the “pull” position. When trying it out the tone control position is maybe the best tone control I have ever heard. Cuts very good but only the parts I would like and leaves much mid in the sound. Now the problem: When pulled it DO cuts a little mid, but it still cut as much treble as in the push position. If I draw the two circuits they look like this (one schematic and one as it looks): Now to my question: What can I do to get this circuit to act more like a “true” mid cut (not cutting the treble) in the pulled position? I am no electronics wizard and I cannot understand what the resistor is doing in the mid cut circuit. As I under stand it (and the way it is described in books by Hiscock and Brosnac) the inductor acts as a low pass filter that lets everything beneath a certain frequency through and the capacitor acts like a high pass filter that lets everything over a certain frequency through. When connected in series and inserted between the “hot” and the ground the capacitor and inductor bleeds the mid to ground and let the treble and bass be unaffected. I would be very happy if anyone had any suggestions for modifications to this circuit. I don’t really have access to a lot of different inductors. The best mods would be if I only have to play around with capacitors or resistors. Edited March 18, 2007 by SwedishLuthier Quote Link to comment Share on other sites More sharing options...
SwedishLuthier Posted March 21, 2007 Author Report Share Posted March 21, 2007 Anyone? Quote Link to comment Share on other sites More sharing options...
GregP Posted March 21, 2007 Report Share Posted March 21, 2007 I don't think you can just "mid scoop" with a passive circuit, can you? Quote Link to comment Share on other sites More sharing options...
fookgub Posted March 21, 2007 Report Share Posted March 21, 2007 I don't think you can just "mid scoop" with a passive circuit, can you? Sure you can. This little circuit is a notch filter. Ok, try this. The impedance of the network is Z = 1/[1/R + jwC] + Rv + jwL, where w is radial frequency, R is the resistance of the fixed resistor and Rv is the resistance of the variable resistor. You need the inductance in Henries. The resistance of the inductor doesn't tell you a whole lot. How was that 4k impedance measured? At what frequency? You could maybe back the inductance out of that. Anyway, If you have Matlab or anything like that (Excel would work), you can plot the impedance (plot the magnitude) and get an idea of what the frequency response might be. The center frequency is w0 = 1/(LC)^.5 (radians/second). So you could move the notch down (thereby keeping more highs) by increasing C. Quote Link to comment Share on other sites More sharing options...
curtisa Posted March 22, 2007 Report Share Posted March 22, 2007 Lose the resistor in parallel with the capacitor - I think this is where your highs are being shunted when you alter the tone control. You'll probably find that you'll have to fiddle a bit with different value capacitors to get the right sound you're after. Don't forget that your pickups are indirectly also part of the circuit, predominantly inductive and resistive, which will have an effect on the frequency response of the mid cut circuit. Just grab a fist full of different value capacitors and a pair of aligator clips and start swapping them in and out. Smaller values of capacitance will increase the frequency of the mid cut, larger values will reduce the mid cut frequency. This page may also help a bit too: http://home.online.no/~jaeioluf/sound/eqpassiv.htm Quote Link to comment Share on other sites More sharing options...
SwedishLuthier Posted March 22, 2007 Author Report Share Posted March 22, 2007 Thanks for the info guys. The Impedance is from the data sheet of the transformer. According to one source the inductance is 1.5H. Did that help? And BTW I think I have written the wrong resistance, but I cannot find the data sheet right now (at work). I’ll have to check that. Thanks for the link Curtisa, I’ll have to check it later on. Looks like a good place to start. According to the calculator at DGB Studio (excellent place for non electric-heads like me http://www.geocities.jp/dgb_studio/index_e.htm) the centre frequency 675 Hz. And that would be perfect. Now I only have to figure out why it cuts the treble too. I have palyed around with the circuit, cutting out the resistor, adding caps in parallel, thus increasing the value, but to my ears it only cuts the treble even more. Hmmm… Quote Link to comment Share on other sites More sharing options...
SwedishLuthier Posted March 22, 2007 Author Report Share Posted March 22, 2007 Thanks for the encouragement guys. Short report from the test. I went through the workshop, collected most of the caps I had lying around and soldered them in parallel with the existing capacitor, via switches so that I could switch them in and out. It turned out to be a very effective method. When I doubled the capacitance I got a pretty decent result when turning the knob down to “1” instead of “0”. When turning that last bit most of the treble still disappeared. But the result at “1” is really good. I have a Tel with home made T90s pickups (Tele-shaped P90s). These pickups rock, but they lack some twang. With the modified mid cut at “1” I got a sound similar to the sound from a “vintage pickup” equipped tele. There are plenty of treble left, the bass is left unaltered and the mid is scooped out a little. No dramatic things but generally what I needed. It also adds to the vintage-sound-vide that the guitar also drops slightly in the volume, but I can live with that- I also tested it on a HB equipped guitar that also switch the coils from series to parallel. The modified mid cut worked well with the coils in parallel but slightly less good when the HB at full blow. But switching to parallel is maybe the first thing to do if you need less mid range… Next step is to measure the resistance of the pot in the “sweet spot” and solder an extra resistor in series to emulate that position at “0” so that it is much faster and exact to operate. Hope that that doesn’t change the way the filter works. Quote Link to comment Share on other sites More sharing options...
bscur Posted March 22, 2007 Report Share Posted March 22, 2007 I bought one of those a while back, but lost the instructions. Can you tell me what the two wires do again? I remember there were only two wires to solder. Thanks, Brad Quote Link to comment Share on other sites More sharing options...
SwedishLuthier Posted March 23, 2007 Author Report Share Posted March 23, 2007 The white wire to "hot" and the black to ground, easy as that. And I really recomend the mod described above. Just substitut the 220K Ohm resistor with another capacitor somewhere around 0.039 microF. Big difference in sound Quote Link to comment Share on other sites More sharing options...
SwitchfootOnPRS Posted March 24, 2007 Report Share Posted March 24, 2007 Hey...I'm a new person here. I've read the sustainer thread. Great stuff! Ok... about the Mid cut stuff... I've got an amp (Laney LA30) that has a boost/cut pot and a frequency pot... you can choose which frequency, Mid, Treble, Bass (continually variable) and the amount of boost/cut Why use a Mid/Treble pot when you can have a continually various one So... do you know of anyone who makes this in one pot (push is one pot, pull is another) if you do that would be really healpfull! Switchfoot Rules! Quote Link to comment Share on other sites More sharing options...
SwitchfootOnPRS Posted March 24, 2007 Report Share Posted March 24, 2007 Hey...I'm a new person here. I've read the sustainer thread. Great stuff! Ok... about the Mid cut stuff... I've got an amp (Laney LA30) that has a boost/cut pot and a frequency pot... you can choose which frequency, Mid, Treble, Bass (continually variable) and the amount of boost/cut Why use a Mid/Treble pot when you can have a continually various one So... do you know of anyone who makes this in one pot (push is one pot, pull is another) if you do that would be really healpfull! Switchfoot Rules! Quote Link to comment Share on other sites More sharing options...
SwitchfootOnPRS Posted March 24, 2007 Report Share Posted March 24, 2007 sorry for posting the same thing twice stil figuring this out! Quote Link to comment Share on other sites More sharing options...
SwedishLuthier Posted March 24, 2007 Author Report Share Posted March 24, 2007 We are talking about a passive "on board" circuitry here like the traditional tone pot, not like a parametric EQ like on your Laney that would require a battery and some very complicated electronics (compared to the capacitor/inductor thing) Quote Link to comment Share on other sites More sharing options...
SwitchfootOnPRS Posted March 25, 2007 Report Share Posted March 25, 2007 Understood... But I want A wah on my guitar! Thanks! Quote Link to comment Share on other sites More sharing options...
SwitchfootOnPRS Posted March 25, 2007 Report Share Posted March 25, 2007 Yah, with the boost/cut I meant 9volt So... What about a pushpull for the volumes of two pickups; put a LP's controls into two knobs Quote Link to comment Share on other sites More sharing options...
curtisa Posted March 25, 2007 Report Share Posted March 25, 2007 I don't think push/pull pots work like that. A PP pot is exactly like a normal p[ot except with a switch that is actuauted by the action of pulling or pushing the shaft. You could wire it up so that the switch selects which pickup is passed to the volume control, but you can't set the volumes independantly - it's still just one pot. Quote Link to comment Share on other sites More sharing options...
Reaper Posted March 26, 2007 Report Share Posted March 26, 2007 (edited) Yah, with the boost/cut I meant 9volt So... What about a pushpull for the volumes of two pickups; put a LP's controls into two knobs I've never seen what you're describing (a push pull so that each switch position selects a different pot internally), and frankly, I'm not sure it's mechnically feasible.... But you could look into these: concentric pots (Concentric pots at warmoth) Two shafts, two stacked knobs, directly on top of one another. Wire your volume to one, tone to the other. Edited March 26, 2007 by Reaper Quote Link to comment Share on other sites More sharing options...
SwitchfootOnPRS Posted March 26, 2007 Report Share Posted March 26, 2007 Thanks! That's sorta what I meant. Of course it wouldn't be a standard PushPull Pot... Just make it (I suppose) so that the shaft will interlock with either pot mechanism depending on how you pull it.... Or just have the whole thing in increments of 1/10 the circle and have a star shaped shaft end which goes up and down and shape the inner pot that way. Then, the two SEPERATE pots will always be in sync But the dual pot is simpler than making one myself (I only wish that I could) Thanks guys that was the answere I was looking for! Quote Link to comment Share on other sites More sharing options...
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