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Bass-cut


G_urr_A

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Wow Saber, now someone who knows all the answers.  :D

Well I definitely don't know ALL the answers but hopefully I'll be able to answer most of them.

As I'm on topic, what about a band pass filter? Wouldn't it be nice to get some wah-like sounds? Or a twin-T filter... though that should be active circuit yet.

Looks like you know what your talking about so I won't be able to shoot much bull here. Well... the most effective circuit would have to be active, like inserting an actual wah-type circuit in your guitar, or maybe some kind of parametric EQ. But if you want to keep the simplicity of passive circuitry, I don't think there's much you can do without significant loss of overall signal level. After all, you would be cutting highs AND cutting lows at the same time with no amplification to maintain a decent overall level. You could always try using the circuit above before or after a typical low-pass tone control circuit and have both pots ganged on 1 shaft so that as you turn it clockwise, you cut less treble while you cut more bass. That might give you a pseudo-wah effect but I doubt it will be very effective.

And for the circuit that I posted, I would use the highest possible value (like 1M if it's used in a typical guitar circuit with typical volume and tone controls). And linear taper would be better than log, but inverse log would be even better in this case if you can find one (and they do exist). I would just put a switch instead of a pot though because that would cut the bass most effectively at a perfect 6dB/octave roll-off while only the capacitor is in the circuit. If your a little adventurous and want the best of both worlds, you could open up the pot and cut the carbon film at the CCW end so that it's completely open when turned totally CCW.

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G_urr_A, maybe my previous post has already given you the info you need. If not, do you intend to have the bass-cut permanently "ON" or will you use a switch to turn it "ON" and "OFF" or do you want to add a variable control knob like in my diagram? It would help if you could tell me the resistance value of you volume pot (250K? 500K? other?) The lower the resistance value of your volume pot is, the better attenuation you will get from the bass-cutting pot at full cut but the quicker your battery will drain, and I don't know how low you can make your volume control's resistance value without adversely affecting the active pickup's signal. 100k volume control might be a good compromise.

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You posted while I was editing my post. :D

The maximum amount of bass-cut will be equal to the volume pot's resistance divided by the sum of the volume and the bass-cut pot resistances. So the bigger your bass-cut pot resistance is compared to your volume pot, the more you can cut the bass. Let's say you kept your 500k volume and added a 500k bass-cut pot. Then the most you could cut your bass would be 1/2 or 6dB. I doubt it would be enough.

If you used a 100k volume pot and a 1M bass-cut pot, then your bass would be decreased to 1/11 of its original amplitude which is a 20.8dB cut. That sounds more reasonable. And a .0015uF capacitor would give you a cutoff frequency of around 1kHz (if you use a 100k volume). Using a smaller capacitor would raise the cutoff frequency, giving you less bass as a result. I think you now have enough info but I'll happily answer any other questions that might arise.

P.S. Using a 50k volume, 500k bass-cut and .003uF should give identical results to the above values. That way you would have one less pot to buy since you already have a 500k pot. Nevertheless, experiment and play it by ear.

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I just went to the EMG website and found out that the EMG 85 output impedance is higher than I expected at 10k. So using lower volume pot values will decrease the signal level slightly. You may have to juggle the values and find the best compromise and let your ears be the judge.

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actually a 6 db cut is huge.my eq only has a 12 db cut.

But when you're shaping a raw guitar signal before sending it through distortion, 6dB might not be quite enough, added to the fact that a simple passive filter like this only has a gentle rolloff of 6dB per octave. With pre-distortion EQ, I usually like to have at least 10dB to play with. But if you find a 6dB bass cut enough to give you the sound your looking for, then great; you can keep the 500k volume pot, add a 500k bass-cut pot and use a 300pF capacitor to get the 1kHz cutoff frequency. Like I said before, play with the values and let your ears be the judge. I'm just trying to supply as much info as possible to guide whoever may want to try this mod. Cheers.

P.S. Just to put things in perspective, note that every 6dB cut represents halving the signal voltage (it's 3dB for halving power). So a 12dB cut is 1/2 of 1/2, or 1/4 the original signal voltage.

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Thanks a lot for all this info! Just one theing, won't the much smaller volume pot affect the volume? (I guess it shouldn't, but I'll just ask a pro to be sure.

Like I said in a previous post, I went to the EMG website to find that the output impedance of the EMG was higher than expected at 10k, so the value of the volume pot may be more significant than I first expected.

So what that means is that with a 100k volume pot instead of a 500k, I calculated a drop of around 0.65dB in overall signal level. A 50k volume would cause a 1.4dB drop. A 250k volume would drop it by 0.17dB. Since these are active pickups, the drop would be even across the frequency spectrum so you wouldn't lose more highs than lows, for example. You would have to rely on your ears to decide what drop is noticeable or acceptable.

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it would be nice to have a tutorial available about the difference in pot values and a basic overview of guitar electronics in language that might be understandable.(unlike most of what you find on the net)maybe you could supply such an overview?

there are tutorials about everything else but i think not too many people(including me)have a good understanding of the details.

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Like I said in a previous post...

Oh, noticed that now. Seems you guys managed to reply 4 times or so while I was writing that question, cause I don't remember seing any of those posts.

I don't know when I'll have the time to try this mod (in the middle of a major computer mess right now, and school and upcoming saxophone concerts don't really help...), but I'll try to remember to report what happens.

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it would be nice to have a tutorial available about the difference in pot values and a basic overview of guitar electronics in language that might be understandable.(unlike most of what you find on the net)maybe you could supply such an overview?

Well... it would take a lot of time and work. The hardest part is probably to make it simple enough so that the non-technical reader wouldn't lose interest. Sort of like a "Guitar Electronics for Dummies". :D But I'll try to put some stuff together, a bit at a time.

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