Getting a passive HPF

[40 Hz]

I was simplifying for the sake of explanation. Once you're past the knee on the lower frequency on a shelving filter, the attenuation should be as consistent as makes no difference. It certainly won't have as much of an attenuation at excessively low frequencies.

Take a look at the schematic he posted, and the included frequency response chart. This HPF filter is a 12 dB per octave (second order) filter. It offers a sloped response below the filter cut-of point, cutting an additional 12 dB each octave lower the frequency goes. It does not offer a consistent level of attenuation below the cut-off frequency (the response is frequency dependent).

 

[40 Hz]

You mentioned fdecks HPF and not being able to afford it. The main reason it costs more is that it is twice the filter power as the one you had built. It uses two filters instead of one. The first is fixed at 35 Hz, the other is variable from 35 - 140 Hz. They both offer 12 dB per octave slopes. Any frequency below 35HZ therefore gets double attenuation, making it much more effective at protecting your speakers. Check it the details:

https://sites.google.com/site/hpftechllc/home/hpf-pre

 

[Bakkster_Man]

Take a look at the schematic he posted, and the included frequency response chart. This HPF filter is a 12 dB per octave (second order) filter. It offers a sloped response below the filter cut-of point, cutting an additional 12 dB the each octave lower the frequency goes. It does not offer a consistent level of attenuation below the cut-off frequency (the response is frequency dependent).

I agree.

The flat attenuation I was refering to was in respect to the SHELVING filter, which at its most simple is an HPF and LPF in parallel. The LPF is the cause of the shelf, resulting in the filter flattening out below some frequency

 

[bongomania]

I agree.

The flat attenuation I was refering to was in respect to the SHELVING filter, which at its most simple is an HPF and LPF in parallel. The LPF is the cause of the shelf, resulting in the filter flattening out below some frequency

This is an example of your error. A shelving filter is an LPF or an HPF, never both, neither parallel nor series. Either one creates a slope, and a shelf is just a slope. To create a steep slope usually requires multiples of one type of filter, either high or low, in series.

You must be thinking of a bandpass filter, not shelving. Like a single band of a graphic EQ. It still doesn't have that "constant level" attenuation you described, but it could be described as a combination of high and low pass, and it would not work as just an HPF.

 

[40 Hz]

I agree with Bongomania.

Mr. Bakkster Man, I don't want this to turn into an argument, but I think you either have a misunderstanding on what a HPF does and who it works, or you aren't explaining yourself properly. Audio filters never flatten out (go horizontal). Filters are created with capacitors and inductors that behave differently according to the frequency that is passing through them. Look again at the frequency response chart included with the schematic - the response never flattens out. It continues to drop as the frequency drops. The frequency response on this HPF is flat (horizontal) ABOVE the cut-off point, but those frequencies are unaffected by the filter. Are you seeing something different?

 

[boomertech]

Here is a typical response for a HP shelving filter. At the -3dB point there is a slope down to the maximum cut of the filter. Below the slope, where the shelf lives (highlighted in green), all of the frequencies are attenuated by the same amount.



-Frank

 

[Skrogh]

This is an example of your error. A shelving filter is an LPF or an HPF, never both, neither parallel nor series. Either one creates a slope, and a shelf is just a slope. To create a steep slope usually requires multiples of one type of filter, either high or low, in series.

You must be thinking of a bandpass filter, not shelving. Like a single band of a graphic EQ. It still doesn't have that "constant level" attenuation you described, but it could be described as a combination of high and low pass, and it would not work as just an HPF.

Actually, in this case, you are the one being wrong; or having a misunderstanding of the terminology.

Here is an example of a hi-pass and a shelving filter:

They are both single-pole and have a cut-off at 40Hz.
The shelving filter shelves at -12dB

And here is a frequency response ad approximating bode-plots:

(I accidentally calculated the cutoff of the shelving filter wrong... The cutoff is at 53.3Hz, and not at the supposed 40Hz - move the blue bode-plot a bit to the right in your mind)

But as you can see frequencies below ~10Hz are left at ~-12dB

 

[inmate13]

You mentioned fdecks HPF and not being able to afford it. The main reason it costs more is that it is twice the filter power as the one you had built. It uses two filters instead of one. The first is fixed at 35 Hz, the other is variable from 35 - 140 Hz. They both offer 12 dB per octave slopes. Any frequency below 35HZ therefore gets double attenuation, making it much more effective at protecting your speakers. Check it the details:

https://sites.google.com/site/hpftechllc/home/hpf-pre

Main reason that i didn't go for fdecks is due to '' problems '' for EU shipping. Fdeck doesn't have CE certificate so i can't get it directly from builder, 2nd thing is shippin costs and taxes in Slovenia, id have to pay extra 20% on the price.

So when talking to JamitFX we decided to build a pedal on it's own, not '' inventing boiling water '' , just to make a HPF pedal available for EU bass players ( southern and central ).

I can easly call this pedal MARK I or somekind of prototype because it will develope more in terms of usage or personal wishes ( custome ones ).

I will test it out today and if i will have more time, I will post some frenquency print screens on here.

 

[boomertech]

You had a custom pedal built that was CE certified?

-Frank

 

[inmate13]

I don't think so Frank i mentioned CE for fdeck only because customs check that when something is above 50€ or something like that and they would basicly just throw it away. I personally don't care about CE

 

[40 Hz]

Mr. Inmate13: I use HPF filters that are built into my PA system crossover, and they are very effective in protecting the subwoofers and allowing the PA to go louder. I have two kids that play bass and I think I am going to have them build the active version you showed the schematic. They have mastered soldering recently, now it may be time to learn about filters (and maybe it will keep them for damaging the speakers on their practice amps!). I am interested in hearing you review of the unit you had built.

To all my friends that are arguing about the filter types: I think there has been some confusion about filter terminology (including some mistakes on my part). If Inmate13 wanted a passive HPF, it would essentially be the same circuit used in a speaker crossover, with the capacitors and inductors chosen to create the proper slope and cut-off point. The circuit most likely used for this purpose would be a second order butterworth filter. I have built a lot of passive speaker crossovers, and if the frequency response ever did flatten out, it would be so low it would be inconsequential. I always like to learn things, and I am trying to teach my kids electronics, so I would appreciate anyone correcting me if my thought process is wrong here.

I came across this when browsing the internet a minute ago. If the following comments are right, then this HPF would be a "bandpass" filter.


Bandpass filters are designed to eliminate some portion of the spectrum either below or above a designed cutoff frequency. An example would be the subwoofer output of your home theater amplifier (lowpass filter). It keeps the high frequencies out of the subwoofer.

Shelving filters are designed to boost or cut specific frequencies, leaving the remaining frequencies unaffected. The tone controls on home stereos or instrument amplifiers are examples of shelving filters. You use them to boost or cut the bass, mid or treble frequency range.

 

[Matthijs]

The fdeck passes european customs just fine as a single item. I have one. Francis can't ship them himself, because he then has to comply with eu regulations. Someone else can send one to you without any problems. The schematics for Fdeck's hpf are also available, so you can build an identical unit yourself.

If your design is cheap and simple it might be an interesting addition for the European market. There are already several European high end HPF/pre's available. What is the input impedance for your design? Will it work with a DB?

 

[SirMjac28]

Get a Microthumpinator and be done sir.

 

[inmate13]

The fdeck passes european customs just fine as a single item. I have one. Francis can't ship them himself, because he then has to comply with eu regulations. Someone else can send one to you without any problems. The schematics for Fdeck's hpf are also available, so you can build an identical unit yourself.

If your design is cheap and simple it might be an interesting addition for the European market. There are already several European high end HPF/pre's available. What is the input impedance for your design? Will it work with a DB?

I am totaly sure it does pass, but I would have to pay 20% for taxes + shipping

Where did you find any other HPF in pedal enclosure except SFX Thumpinator?

@mjac28: I would get one, but let's say that this one was a lot cheaper.

@40 Hz: I would also use built-in HPF if i had one

 

[bongomania]

Hmmm, looks like I owe Bakkster an apology. I am sorry!

My argument was based on measurements I had done of a wide variety of EQs and filters. Not one of them behaved like the images shown here, with flat response at -12dB. Also I have always seen the word shelving used in the way I was using it. But I can see that my understanding was faulty, and I need to look into it further.

 

[Bakkster_Man]

Hmmm, looks like I owe Bakkster an apology. I am sorry!

My argument was based on measurements I had done of a wide variety of EQs and filters. Not one of them behaved like the images shown here, with flat response at -12dB. Also I have always seen the word shelving used in the way I was using it. But I can see that my understanding was faulty, and I need to look into it further.

No worries! I figured there was just a terminology mixup somewhere. It wouldn't surprise me that 'shelving' has multiple uses. It seems shelving EQs are more common in digital mixing plugins than analog boxes.

Take a look at the ISA,Q431 for a well known filter with shelving functions in addition to bandpass/stop and HPF/LPFs. This one also has the option to use the shelves just in the compressor sidechain, making them useful to trigger more quickly within certain frequency bands.

 

[inmate13]

OK I've spent an hour today with this lil pedal and my final toughts are exactly what i wanted and what this pedal is supposed to do.... in short... WOW

My rig contains HiWatt Maxwatt 4x10, Custom 4x10 and Carvin DCM1000 power amp. Rig runs on 4ohms ( cabs are 8ohms )

On the floor i have Hartke VXL preamp, GLX ( copy of boss pedals ) limiter and compressor, tuner.

Bass was my main working horse Ibanez BTB 775 wired to passive with Galli 0.145 set of strings. It is tuned A# all the way down.

1st test was with HPF first in chain and without limiter and compressor with switch on PASSIVE. I turned the FREQ knob while playing the B string with my finger slowly all the way up to find '' the spot ''. I clearly heard how the boomines goes away the further i turned the knob... ok it works... those were my first toughts . Then i went directly to VXL and turned the volume up to the level that causes CLIP light on amp to lit and drivers on cabs begin to rumble. I pluged back into HPF and into VXL and plucked the string.... the clip light didn't lit... OK that's nice so i '' slapped '' the B string lil more and more to see where it would go clipping. Clip lighted up with lil more powerful playing but the clear bass sound was still there.

So in terms of frequencies the amp wasn't fed with sub content and it didn't have to amplify them. Thats why i was able to play '' heavier '' or louder.

Then I flipped the active switch on HPF and a signal goes thru buffer. I instantly noticed that the sound was more clearer and punchier and again it took me a while to clip the amp.

In 2nd test i've put HPF after the VXL and then into amp. The results were even better. On noon setting on VXL volume I couldn't clip the amp and sound was even better and punchier. Heck... I turned the volume knob on 2'clock on VXL and just play it was damn loud and the clip went on a lil.

Far best results were when i plugged the bass in compressor and then into VXL and HPF. I could basicly do anything on the bass from hard pluck, ripping it with pick, slap the s*** out of it and the rig was singing. So i think this is the chain I will use on my board.

And one notice about the Carving amp... in aprox 1 hour of playing the heat fan NEVER went on!!! And the drivers on cabs didn't jump out. So this tells me that HPF works.

HPF is going to stay ON always because i love my amp and cabs and now i can play heavier or louder if needed. BTW.. on band practice I'm usually on 11' on VXL, today I went to 2' and amp handled it. Limiter is going for sale because i don't need it anymore.

Here is a pic on the board:

PS: On the left you can also see another JamIT product. It's a power supply running on 12V.

 

[Matthijs]

I am totaly sure it does pass, but I would have to pay 20% for taxes + shipping

Where did you find any other HPF in pedal enclosure except SFX Thumpinator?

@mjac28: I would get one, but let's say that this one was a lot cheaper.

@40 Hz: I would also use built-in HPF if i had one

There's the Lehle bassswitch and there's an other one that's been posted about in the DB side. Both are pretty high end and expensive. There also is the fishman platinum that's readilly vailable in Europe, not really a pedal and not that high end.

 

[inmate13]

Ohh i'd love to have basswitch for preamp