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Variable HPF


DanOwens
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4 hours ago, DanOwens said:

Hi all,

 

I want to build this: https://guitar-electronics.eu/en_US/p/High-Pass-Filter-HPF-kit-ULTRA/330

 

BUT - I want the cut off to be higher than 200Hz - more like 8kHz. Which component would I change to raise this?

 

Thanks

Why? Bass guitar, heck almost any instrument isn’t going to sound good with everything below 8kHz cut out! 
 

I would look at the Vong and miniVong at musikding as alternatives …

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Why on earth would you want to cut everything bellow 8kHz?

 

On a bass there's hardly any signal left at that point, and for sure is way past all fundamentals.

 

You are aware that this is a High Pass Filter NOT a Low Pass Filter or High Cut Filter, right?

 

Even then 8kHz seems high for a bass, regular bass cabs, without high freqeuncy horns that is, usually have a pretty steep cutoff of frequencies beyond about 3.5kHz or so, and, as said, above 8kHz there won't even be much signal left coming from a bass in the first place anyway.

 

Though a High Shelve Filter set at 8kHz on the other hand would kind of make sense for a bass, because a sufficiently large enough cut would create a curve that would start the decline way bellow 8kHz, but then again a 10kHz or even 12kHz High Shelve Filter would probably make even more sense if the purpose is to kind of mimic the roll off of a regular bass cab, however yet again a second order, that is -12dB/Oct, Low Pass Filter set to around 3.5Khz or so actually would be a much more appropriate tool to achieve this and much more likely to give a satisfactory result.

 

Telling us what it is you want to achieve would help, cause honestly to me, and I assume most other people reading your OP, it does sound like you might not be aware of the right tool for the job you want to get done, whatever that might be, but then again I suppose it is possible that you actually do know exactly what you are doing, and that I just can't imagine what application a HPF set to 8 kHz could possibly be good for.

 

 

Edited by Baloney Balderdash
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Ah yes - it’s for a fingerboard ‘clicky’ pickup for my very poor attempts at upright slap. The Shadow Rockabilly preamp has a switchable hi pass at 4k and 8k and I was hoping to replicate this. 

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I don't think that switch is for the low cut.  "Switch to select either 4 kHz or 8kHz base frequencies for the TREBLE control"
https://cdn.shopify.com/s/files/1/1601/8433/files/SH_RB-Pro_owners_manual.pdf?6866837466035804435

 

You shouldn't need a HPF on the click pickup - is it creating a problem just blending it straight in?

 

Still get the HPF though - to control rumble feedback on your main pickup.

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Hmm, the manual also says that its low cut range is 400Hz-6khz, which is very high (both the low and high range).  I'm trying to recall my slap setup from many years ago - I had independent eq, but my click didn't really have that much low frequency output to start off with.

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It can be done but it depends what you're trying to achieve - raising the max frequency to something like 4khz but keeping the low end at 20hz is certainly possible, but the sweep range of the pot would become extremely wide and it would be very difficult to dial in specific frequencies in between. You could counteract this by using a larger pot value or raising the lower end of the range as well - a 2kHz to 4kHz for example - but as others have said that doesn't seem particularly useful.

 

There's 4 components you would have to change, 5 if you change the pot. The cutoff frequency is defined in this specific case by this hastily scrawled formula - 

 

1205388823_PXL_20220809_114335336_2(1).thumb.jpg.2604610468a616f34b2f987c37fac4ea.jpg

 

You'll have to do 2 calculations, one for the minimum pot sweep (where rv1 and rv2 are 0) and one for the max where they're 100k. This formula requires the resistance values to be in ohms and the capacitance values in farads - see if you can calculate the cutoff values of the circuit as it is (spoiler alert - the max isn't actually 200hz). If all this sounds like Greek and you don't understand the formula or how to calculate it I can point you in the direction of some good beginner resources. 

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On 09/08/2022 at 12:55, bobbass4k said:

It can be done but it depends what you're trying to achieve...

 

Thanks for such a thorough post, BobBass4k. Those resources would be greatly appreciated! Ta

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Could try a graphic equalizer in the effects loop. There's a Peavey Q1311 31 band that covers pretty much everything on Ebay for £40 at the moment. Guess it could go in the effects loop. Also good for tailoring sound for different situations.

Edited by Japhet
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