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Post by roadtonever on Mar 10, 2011 13:14:13 GMT -5
I'm in need of help realizing a simple passive EQ circuit that replaces a typical tone control. I'm envisioning a way of controlling the frequency and height of the resonant peak with two control pots. I'm already half way there thanks to a neat inductor package by Bill Lawrence(Q-filter) which performs the function of shifting the resonant peak(beside the low-cut). So what I'm missing is the Q/peak height control. I understand a volume control does this as a by-product of it's operation, and since I rarely use it as such I'm wondering if it could be re-purposed by changing the contact points or something like a reverse treble-bleed. This is the base diagram I'm using:
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Post by roadtonever on Mar 11, 2011 8:55:09 GMT -5
Anybody wanna jump on this? Last night I pulled out the alligtor clips and I tried adding a regular tone pot w/o a cap to the diagram above and it didn't seem to work as I intended. I didn't give up and tried adding the control to different points in the circuit but only ended up mystified as it either interacted with the inductor control in an unwanted way or just worked as a volume control.
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Post by ChristoMephisto on Mar 11, 2011 9:10:11 GMT -5
Isn't there suppose to be a resistor parallel to the cap on the Q tone? BL suggests 5k for the neck, 25 for the bridge, throw in a 50k pot to vary it and that may help ya.
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Post by roadtonever on Mar 11, 2011 10:35:07 GMT -5
I'll want to try that out! I havent used a resistor in conjunction with the Q-filter as the 3.0H bass version specifies a .1uf cap and no resistor. I've read accounts of how adding the resistor sweetens the tone. If I'm not misstaken the resistor determins the peak (and notch w/ cap) heights. I currently have the inductor wired to a push-pull pot switching the cap in and out: Luckily theres a diagram that does the same thing but adds the resistor so I can keep my switching functionality: Anyway, I want give this a try with a 250k audio pot. Could you explain which lugs on the pot I am to use?
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Post by roadtonever on Mar 11, 2011 12:40:28 GMT -5
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Post by roadtonever on Mar 11, 2011 15:01:58 GMT -5
It works! The new control seems to open up the mids and generally sweetens the effect of the inductor and cap combo until the end of the rotation where it seems to defeat the cap(possibly due to the high 250k value matching the inductor control). It isn't too awkward to control despite being five times larger than the 50k suggested, but only once the right pair of pot lugs are connected. Connect them in reverse and the action is concentrated to a very small portion of the turn(audio taper pot used). The new control is a rather subtle in what it does tonally but I could see myself making use of it for fine tuning so I'm wiring it in proper and let it sink in. As for the issues: #1 can't use the new control with the cap disengaged, but that's more an issue with the original diagram. If anybody would help me with this one I'd be grateful. #2 Doesn't give me the range I had hoped for. Ideally I'd want to go from Yes/Rush to Steely Dan/Eagles with the turn of a dial. Forget a regular tone control I cant hear myself with one of those turned down. So far I've used a 500k master vol as a "tone control" and stayed within in the perimeter of the pre-amp gain control, sounds better to me but obvously operationally a PITA and output gets hissy when I go for the really warm and lush tones.
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Post by ChristoMephisto on Mar 11, 2011 20:26:09 GMT -5
Glad you found all the paperwork for me Over on DGB Studios they have a LC caculator www.geocities.jp/dgb_studio/lc_calc_e.htmAlways been interested in a Q filter, which is basically a single tone Varitone. BL's Tele inductor is about 900mH(iirc), and with his schem it's a boost around 1k1Hz. Using your bass 3H inductor it's about 290Hz. You would need a smaller cap to get a higher frequency boost. See if you can use a (smaller?) linear pot to control the Q's trim pot, you should be able to nail the peakiness better and use the p/p pot to switch cap/resistor values. If possible, see if you can make the Q tone pot a 'no-load' so at one end of the rotation it's taken out of the circuit. here's more calculations of Gibsons and Blue Hawks Varitone circuit to help ya... www.rootwerx.com/music/electronics/varitone/default.htmgood luck
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Post by roadtonever on Mar 12, 2011 19:10:08 GMT -5
I'm glad you want to offer help, ChristoMephisto! After all I'm electronically challenged. The inductor control is awesome to me because it seems to alter the tone at a basic level where some active EQ circuits I've demo'ed seemed kind of arbitrary and unintuitive. With the cap in it's reminiscent of a standard tone pot except it doesn't get muddy when you turn it down. Regardless of any peakyness and the like the new control has me very excited since its seems to function like a gradual control for the cap, in other words I can control how much of the lows get passed on. I didnt expect this at all. With the swtiched config I've used so far it's been either full on or full off. It has me seing the switch as redundant now and I'm considering a dual concentric pot. I remember seeing a A250k/A25k Fender one... I think I'll leave the cap values unchanged as I'm sure old Billy used som clever calculations to find the optimal value. Coming back to the peaky-ness it's probably not as much a product of the inductor but rather my desire of having extreme adjustment avalible on-board so I'm still hoping someone comes along with an idea for the reverse treble-bleed I dreamed up. I wonder if there is somehing one can do that involves all three lugs of the pot... Heres a short demo I whipped up of the inductor control: www.box.net/shared/s8yctmefma First half I manupulate the original control only, second half I manipulate both.
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Post by sumgai on Mar 13, 2011 3:36:02 GMT -5
rtn, Be aware that a simple resistor cannot change the relation frequency to a cap's value. The same holds true for an inductor. Now, that being said, you've obviously hit upon something that you like. Certainly. The explanation is equally simple - the frequency response has been changed by broadending or narrowing the peak's point in the spectrum. You haven't moved the peak, but you have caused to have a greater, or lesser, affect upon those frequencies nearby. This is very noticible, as you've found. This all came about as a result of adding the inductor - you've created a "tank" circuit, one that is "tuned" by your controls. If you truly want to move the peak up or down the spectrum, you'll need to change the cap/inductor value directly, either by switching to another component (the Gibson Varatone comes to mind here), or using a variable component. ChrisK posted several images of these things, a long time ago, but they're now lost to antiquity, sorry to say. Suffice it to say that they aren't very cheap, they aren't very small, and being analog, they are very hard to 'dial in', to get the same sound you had yesterday. But your way is probably the best compromise I can imagine. Please, post a diagram of what you ended up with, I'm sure others here would like to ponder it, as well as me. sumgai
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Post by roadtonever on Mar 13, 2011 7:09:41 GMT -5
Sumgai, thanks for the explanation. I guess the illusion of the Q-Filter works for me. With what you wrote in mind the name chosen for the product strikes me as well descriptive. Here's the diagram you requested. I'm not sure if the leads going to the Vari-Q (How's that for a name?) are erroneously reversed or not as mine is still wired within the push-pull. The the main thing about that is taking advantage of the A in A250K I think. Of course a smaller control would be better. The pickups I'm using are stacked hot Strat-type singles at 3.2H and 5.0H combined in series. The high inductance gives a nice range for the controls.
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Post by ChristoMephisto on Mar 13, 2011 8:28:53 GMT -5
Nice demo rtn, almost sounds like a wah pulled back. If you can, take measurements of your Vari-Q pot maybe you can find a range that you like and can reduce the pot value. Have you tried different cap values yet?
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Post by roadtonever on Mar 14, 2011 16:43:47 GMT -5
So I tried measuring the useful range of the Vari-Q control in a pseudo-scientific way, with headphones outputting white noise over the pickups while viewing a spectrogram of the pickups output. I noted anything over 120-ish k would only change a few dB while everything under would change Bels. A 100k part would be OK but any lower would compromise the range of the control too much IMO.
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Post by ChristoMephisto on Mar 14, 2011 17:01:40 GMT -5
Put a 180k resistor across the outside lugs of the 250k Vari-Q pot, it makes it a 104k pot.
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Post by roadtonever on Mar 14, 2011 17:42:35 GMT -5
I've heard nasty stories:
Should I worry about it in this case?
One more question: Do you think a linear pot is better? If so, why?
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Post by ChristoMephisto on Mar 14, 2011 21:07:59 GMT -5
A little confusing, but it sounds like they are referring to what happens with the highs that are bled to ground. And with audio pots, half the rotation is only about 30% of the value compared to a linear pot that would be 50%
Play around with both for the Vari-Q
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Post by roadtonever on Mar 14, 2011 23:28:59 GMT -5
Thanks for keeping me company on my electronics explorations, Christo! Ordering some cheapo pots from a local electronics supplier would be in order, they're less than a Coke can a piece. I'll get 100k and 200k in log and lin and compare how they feel. Later on I'll look into dual concentric pots. Actually I've already read a bit, CTS and Alphas can take wafer transplants.
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Post by ChristoMephisto on Mar 15, 2011 10:39:03 GMT -5
What are you planning on using the dual pots for? Wanted to build one of these instead of in my guitar alexplorer.net/guitar/projects/jazz-box.htmlhe suggests a 50k pot to vary the effect, but he's not using a 3H in a bass. good luck
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Post by roadtonever on Mar 16, 2011 17:21:11 GMT -5
The dual concentric pot will be used for both the Q controls, in other words the lower part of the diagram I posted. Mainly to save space and make as much use of ever pot hole. The 3H probably does make a difference on on how much resistance you apply, one regular on the Lawrence forum strongly prefers a 120k resistor with his bass Q-filter, mentions it does away with peakyness. The guitar version is currently 1.8H though it seems clear to me 900mH values have been used before. I'll let you know about the current recomended cap and resistor values for the guitar filter once the Lawrences write back on my inquiry. Rothstein and Torres makes similar packages as pre-assembled modules, I vaguely remeber seing discussions about values used. I'm sure they come up when doing a discussion search on google. This might be another good reference: www.blueguitar.org/new/schem/_gtr/dual_mid.gif
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Post by ChristoMephisto on Mar 16, 2011 21:07:28 GMT -5
guess it's been a while if they've changed the value of the Q-filter from 900 to 1.8 Let me know the new values, got a pair of BL Tele Keystones that needs a new home and some new wiring.
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Post by roadtonever on Mar 22, 2011 8:14:00 GMT -5
Sure enough linear taper made for a nicer control, removed a major hot spot. Thanks for the idea! I haven't received a reply from the Lawrences about the Q-filter values, I imagine they're swamped with work at the moment since they're launching the a new pickup series. I'll make sure to let you know once they write back. In the mean time these stock diagrams could be worth checking out: s1203.photobucket.com/albums/bb390/wildepickups/Wiring%20Diagrams/ Some have values for the Q-filter although it's not specified if it's for the 900mH or 1.8H. There's also some interesting wiring diagrams that might get you inspired.
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Post by sbgodofmetal on Mar 22, 2011 14:28:43 GMT -5
here's one i've been working on its meant to be a separate unit from the guitar though it uses a tele 3 way and 2 on/on switches to select and or combine tones. the highs are 1 meg pots using .001uf and .020uf caps. the mids are 500k pots with .039uf and .047uf caps and the lows are 250k pots with .050uf and .100uf caps, and a passive overdrive unit(guitars pickups require 10k ohms or more to drive the unit properly). black ice overdrive capacitor with a on/on bypass switch and 250k volume. all pots are wired as tone level pots except for the 500k master volume and the 250k overdrive volume pot, with 1/4'' mono input and output jacks. this unit is to be placed right after the guitar in your effects chain
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Post by roadtonever on Mar 24, 2011 7:56:23 GMT -5
Like the addition of on-board OD, interacts nicely with the EQ controls? Would be a thrill to hear a demo of it. I think most of us have trouble reading that diagram tho', trying to keep it a secret or something?
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Post by sbgodofmetal on Mar 24, 2011 12:42:09 GMT -5
naw just a crappy camera phone i'm still working on getting the money saved up for parts i was also informed on another thread that instead of paying $30 for the black ice you could just use 2 diodes and come out cheaper with the same effects as the black ice and the lovely part is unless you want LEDS its completely passive no batteries or power plugs required
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Post by sbgodofmetal on Mar 24, 2011 13:27:13 GMT -5
if anyone reading this can see the diagram well enough help me add a stompbox switch to either activate or bypass it like an fx pedal
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Post by ChristoMephisto on Mar 24, 2011 13:37:04 GMT -5
if anyone reading this can see the diagram well enough help me add a stompbox switch to either activate or bypass it like an fx pedal doesn't the diode thing act like a tone pot meaning it parallel to the tone's path instead of in series like a pedal should 'turn off' of you disconnect the signal with your switch shown
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Post by JohnH on Mar 24, 2011 14:31:40 GMT -5
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Post by sbgodofmetal on Mar 24, 2011 15:22:06 GMT -5
JohnH i've aready been pointed to it on another thread and its been mentioned above as a cheaper alterantive @mephisto its an on/on bypass from just the EQ to the EQ plus diode clipping (passive overdrive) what i'm wanting to add is another bypass on/on that will add or bypass the passive EQ alltogether so you can use just the guitars tone or stomp the switch and add the EQ
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Post by sbgodofmetal on Mar 24, 2011 15:30:26 GMT -5
as far as the diode acting as a tone i'm not experienced enough to know anything about it my diagram was based using the black ice because i simply didn't know about the whole diode thing so i'll do some more digging and redraw it later thank you ashcatit and johnh for pointing out that diode alternative to the black ice
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Post by ashcatlt on Mar 24, 2011 18:10:04 GMT -5
this uses a 3pdt to allow an LED. If you don't need the LED, you can use a dpdt stomp switch and ignore the center column of lugs and everything attached to it.
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Post by JohnH on Mar 24, 2011 20:25:34 GMT -5
just a small aside on stomp-switches:
Down here, I can buy those blue 3x3 switches like ash shows, and they are solid and reliable long term. Ive also seen black 'Fulltone' switches offered, more expensive and supposedly better, but the generic blue ones work well.
But we can also buy an even more solid looking black dpdt stomp switch, which I bought several of before the 3x3 ones were available at our local supplier (Jaycar). They all went flaky with unreliable contacts within a few months. Contact cleaner gets them going again - but only for a week or so.
I suspect that there are few actual makers oft these switches, so similar results may apply with those from other retail suppliers.
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