Passive Bass Cut Advice

[MES_C]

hello all, I finished my last build a few months ago. I wasn’t completely happy with my passive bass cut knob because it cut too much volume. But I was tired of fiddling with the thing, so I just called it good.

But now I was wondering if anyone could suggest a way to reduce the volume loss.

Heres a rough diagram of what it looks like:

(If its unclear let me know)

thanks for your help

The thing does sound cool for songs with lots of fast strumming, so its not a complete waste.

[borge]

What guitar and type of pups are you using it with?

I think your cap value is too small ie the cutoff freq. is too high and is perceived as a volume drop.

as cap value and/or pot value decreases cutoff freq. increases. ie halving the cap value doubles the freq. value.

G&L use a .022uF cap and 1meg pot, so their cutoff frequency would be 22x lower that yours ie more bass passes through.

If you want to find out (roughly) what the values are:

Cutoff freq.(Hz, cps)= 1/(2piRC)

where R= resistance, C=capacitance, pi=3.14159265.

[Donovan]

What guitar and type of pups are you using it with?

I think your cap value is too small ie the cutoff freq. is too high and is perceived as a volume drop.

as cap value and/or pot value decreases cutoff freq. increases. ie halving the cap value doubles the freq. value.

G&L use a .022uF cap and 1meg pot, so their cutoff frequency would be 22x lower that yours ie more bass passes through.

If you want to find out (roughly) what the values are:

Cutoff freq.(Hz, cps)= 1/(2piRC)

where R= resistance, C=capacitance, pi=3.14159265.

So his cutoff frequency is about 168... very close to the standard 4th string, 2nd fret E. I'd be curious to know what the frequency turns out to be once you find something you like. I am also wondering if a guitar does produce any frequency below the 80'ish of standard low E. Intuitively, I'd guess it doesn't, except for induced noise from the outside world, which is useless anyway. If you get the chance, that might be an interesting and subtle point to starting testing for cutoff frequency. All you'd have to do is add another of the same cap in parallel with your current configuration.

[Keegan]

I'd try around 70-80Hz, you could get that just by adding another .001uF in parallel. You may even need to go lower and use a third .001uF cap for about 50Hz, but I doubt it.

edit: btw, .001uF and 1Mohm is 159Hz. And how is 4th string 2nd fret an E? Isn't that an F? Or do you mean on guitar? In that case it'd be 330Hz at that fret, 165Hz at the 6th string open E. Lowest note on a bass is 82.5Hz, but the Q of a filter like this is probably pretty big so I think 80Hz or possibly even lower would work.

edit 2: Wait, by the diagram it looks like you have it wired as a volume knob with a treble pass, not a tone knob.

Volume:

It should be wired like this, in parallel with the output, not in series:

Edited May 27, 2009 by Keegan

[AndrewCE]

I'd try around 70-80Hz, you could get that just by adding another .001uF in parallel. You may even need to go lower and use a third .001uF cap for about 50Hz, but I doubt it.

edit: btw, .001uF and 1Mohm is 159Hz. And how is 4th string 2nd fret an E? Isn't that an F? Or do you mean on guitar? In that case it'd be 330Hz at that fret, 165Hz at the 6th string open E. Lowest note on a bass is 82.5Hz, but the Q of a filter like this is probably pretty big so I think 80Hz or possibly even lower would work.

edit 2: Wait, by the diagram it looks like you have it wired as a volume knob with a treble pass, not a tone knob.

Volume:

It should be wired like this, in parallel with the output, not in series:

he's trying to cut bass, not treble

[Donovan]

I'd try around 70-80Hz, you could get that just by adding another .001uF in parallel. You may even need to go lower and use a third .001uF cap for about 50Hz, but I doubt it.

edit: btw, .001uF and 1Mohm is 159Hz. And how is 4th string 2nd fret an E? Isn't that an F? Or do you mean on guitar? In that case it'd be 330Hz at that fret, 165Hz at the 6th string open E. Lowest note on a bass is 82.5Hz, but the Q of a filter like this is probably pretty big so I think 80Hz or possibly even lower would work.

edit 2: Wait, by the diagram it looks like you have it wired as a volume knob with a treble pass, not a tone knob.

Volume:

It should be wired like this, in parallel with the output, not in series:

Woh, I am dyslexic!

I have no idea how I was of by that amount, and yes, I meant on guitar. Sorry, I thought that's what his project was... and I also thought 80 was the low E, so 160 would be 4th fret, 2nd string. 80 is a bass' low E???? I have been misinformed and am going to have to kick someone's a$$!

[Donovan]

Actually, Keegan, I think you are wrong about the frequencies... so I'm not AS dyslexic, but my math still sucks.

Bass low E = 41 Hz

http://en.wikipedia.org/wiki/Bass_guitar_tuning

Guitar Low E = 82 Hz

http://en.wikipedia.org/wiki/Guitar_tunings

[Keegan]

Oh. The guitar tab program I use is set to E3 by default, which is 165. Odd. I assumed it was to the correct pitch. I guess they just moved it up so it'd fit on the staff more nicely.

Found another source that says it's E2(82) for guitar and E1(41) for bass.

Whoops.

Sorry, didn't realize cutting bass was different. That makes sense now though. You're allowing the higher frequencies to pass while reducing the volume of anything that can't go through the cap.

So yeah, you might want to put 2 or 3 .001uF caps in.

Are we talking about a bass or a guitar? I'm so confused. 100Hz is recommended bass cut for guitars and 50Hz for bass http://www.recordingwebsite.com/articles/eqfreq.php

Edited May 28, 2009 by Keegan

[MES_C]

Thanks for the help everyone, it never occurred to me that the formula borge gave would apply to my filter.

I'll pick up a handful of caps next time I'm at radioshack and try to find a good break frequency in the range suggested.

looking forward to talking with you all again

[borge]

remember the R value is the max value the pot will give, the '10' pos.........so cutoff freq changes with the spin of the knob.......

I think Q value is probably just as, if not more important than freq.

Reverend guitars also have a bass cut on guitars, maybe find out what value cap they use compare to the .022uF G&L use and go from there.

And we still don't know what guitar or bass and pups you're using?

A vintage bridge pup in an all maple strat is going to be a different story to a deathbucker 5000 in the neck pos. of an LP......

Also, Keegans link is in regard to recording studio EQ which is almost always applied to the recorded audio ie after effects, amps and speakers and the rest of it have done their (huge) part, I'm not sure how much those values apply to the raw guitar signal, also refer to my first sentence again

[dz_alias]

I tried wiring a passive bass-cut in my guitar and I can't discern a difference between the pot at 1 and 10. I used a 500kohm pot and a .001uF cap. What value cap should I use instead to get a noticeable effect? I'm using single-coil size rail humbuckers in a Stratocaster.

EDIT: Nevermind. I added another .001uF cap in parallel and it worked perfectly. Tehe :3.

EDIT2: If I wired the tone circuit (bass and treble cut) to a push/pull pot and ran it out of phase in parallel with the original signal, would that make it a mid cut?

Edited June 4, 2009 by dz_alias

[MES_C]

I think I can take it from here, but I appreciate your interest so here is a link to the thread on this guitar. The body is low quality pine, neck is maple, and pickups are some unknown brand off of eBay.(bridge= ~16K, neck= 5-6K)

I looked up "Q-value" you mentioned, and I found some information under resonant filters. How does it apply this filter?

Also, here are some plot spectrums from audacity, they may or may not be helpful...

initial

full bass cut

full treble cut

thanks

[Donovan]

Also, here are some plot spectrums from audacity, they may or may not be helpful...

initial

full bass cut

full treble cut

thanks

I didn't know audacity could do that... where is that?

[Akula]

Select the audio you want to analyse, click on Analyse in the toolbar, then click Plot Spectrum.