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High Pass Filters


funkydoug

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41 minutes ago, Bigwan said:

The main problem you would have is deciding what is the "relevant range". 30Hz HPF cutoff? 40Hz? 10kHz LPF? 6kHz? Would be easy to make them switchable, but it adds to expense, complexity and enclosure size. 

Good point. I guess options would be along the following lines (and btw these are just my best guesses at appropriate cut offs - more than happy to be over-ruled by folk who know a lot more about this stuff than me!)

a) fixed cut off HPF: 30Hz and LPF: 10kHz

b) switchable cut off: HPF 30Hz and 50Hz; LPF 6kHz and 10kHz

c) variable cut off: same ranges as the Broughton

but with 24dB (or more if possible) cut for each option.

Over to you in terms of what that would mean in terms of cost and enclosure size? 

 

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You don’t usually want a steep roll off on the LPF, since they are typically used as a vintage speaker sim, which has a smooth gradual roll off. The main purpose of the Broughton LPF is at the end of the chain to tame drive pedals before they go to the PA or hi-if bass rig.

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The 'series 3' of the FDeck HF Pre design has a 12dB/Octave fixed frequency (35Hz) HPF, followed by a variable frequency 12dB/Octave  (35-140Hz) HPF so you will have 24dB/octave anywhere below 35Hz.

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

Although a circuit diagram is not available for the series 3, adding a fixed frequency HPF to a variable frequency HPF would not be difficult for an average electronic DIY enthusiast.

David

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38 minutes ago, Mottlefeeder said:

The 'series 3' of the FDeck HF Pre design has a 12dB/Octave fixed frequency (35Hz) HPF, followed by a variable frequency 12dB/Octave  (35-140Hz) HPF so you will have 24dB/octave anywhere below 35Hz.

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

Although a circuit diagram is not available for the series 3, adding a fixed frequency HPF to a variable frequency HPF would not be difficult for an average electronic DIY enthusiast.

David

Cheers - looks like just the ticket! The only glitch here is that "Unfortunately, the HPF-Pre is not available outside the US."

But I think @Bigwan is gearing up to come up with something for us that is going to corner the European market and which will render the SFX Thumpinator history :) 

Interestingly the Thumpinator (which is hand made) cuts out everything below 28 Hz to leave the B string notes intact, so choosing to cut everything below 30 Hz seems not a bad shout - and maybe 28Hz is the better number?

Did someone previously say that the amount that the Thumpinator can cut by is not limited to 12dB (and can potentially be considerably in excess of 24dB)?

Edited by Al Krow
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9 minutes ago, Bigwan said:

Let's just say I'm sharpening my pencil... 

Excellent. Well if you can come up with something that covers what the Broughton does and also delivers a 24dB cut, then you're onto a winner.

If you can go one further and shrink it to the size of a COG T16 (with all the connections on the same side) you know you've already won and you'd better start gearing up for orders from the US, Europe and Japan :) 

Edited by Al Krow
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@Bigwan very much looking forward to what your sharpened pencil comes up with!

Finally found where this fabled 'Lo Fi' B3n patch is with the HPF filter effect built in; it's not in the original effects list but in their subsequent May & June 2017 updates if anyone else was an early buyer of the B3n but, like me, hasn't updated their machine...now to go hunt for an USB cable that's compatible with the B3n - why do each of my pedals with an USB interface each have a different one?!

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1 minute ago, Al Krow said:

@Bigwan very much looking forward to what your sharpened pencil comes up with!

Initial thoughts are, as per the FDeck, -12dB/oct fixed HPF (it is possible to make the cut-off switchable but that adds to the enclosure size), -12dB/oct variable HPF, plus a -12dB/oct LPF. 

It'd be unlikely to fit in a 1590A though. Need ganged pots for the variable HPF and LPF (for the uninitiated a ganged pot is 2 pots mounted on a single shaft).

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6 minutes ago, Bigwan said:

Initial thoughts are, as per the FDeck, -12dB/oct fixed HPF (it is possible to make the cut-off switchable but that adds to the enclosure size), -12dB/oct variable HPF, plus a -12dB/oct LPF. 

It'd be unlikely to fit in a 1590A though. Need ganged pots for the variable HPF and LPF (for the uninitiated a ganged pot is 2 pots mounted on a single shaft).

From what @Chienmortbb said earlier in his really helpful summary: "12 dB per octave is too shallow, 24dB is the minimum in my opinion. That rules out the Broughton. It would be better than nothing but imho not much."

The Broughton is already available with a 12dB cut in a nicely packaged unit and the Thumpinator as a compact HPF; both 'tried and tested' pedals. Getting it into a 1590A is a 'nice to have' but certainly not essential. The 24dB cut is the key driver / differentiator here.

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Just now, PaulWarning said:

just set up my Zoom B1on with 4 Ac Bs pre stacked, all set to 9 on Depth 50 on gain, level on 100 everything else on 0, took off the speaker grill, made no difference at all to speaker travel, more snake oil? or am I missing something?

Are the effects blendable like on the B3?
Each effect has a blend, but so does the whole patch.

Is one running at 50/50?

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50/50 (wet/dry). 

 

Looking through the B1on user manual it does't look like you and blend patches with a clean signal. So I'd except to see some difference in speaker travel for low notes.  

Here's a quick test I've done. With one AC BS Pre on the B3. The synth is running a sine wave 2 octaves below, so it's a bit extreme (near the end of the clip I turn the depth knob up and down to see the difference):

 

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11 minutes ago, Jus Lukin said:

Now that is interesting. They really ought to be additive, and I can hear adjustments on the lower of my usual two with another filter set higher. I wonder what's going on there? Thanks for all your testing- I may do a basic hook up of my gear just so I can knock about with it properly myself!

It was quite a quick look. I'll do another test and zoom into the low end to see what's happening...

 

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14 minutes ago, Jus Lukin said:

Now that is interesting. They really ought to be additive, and I can hear adjustments on the lower of my usual two with another filter set higher. I wonder what's going on there? Thanks for all your testing- I may do a basic hook up of my gear just so I can knock about with it properly myself!

Could be down to the limited processing power of the MS-60B (and also the B3 which Bartleby has and which I understand are both the old Zoom chipset family)

2 hours ago, PaulWarning said:

just set up my Zoom B1on with 4 Ac Bs pre stacked, all set to 9 on Depth 50 on gain, level on 100 everything else on 0, took off the speaker grill, made no difference at all to speaker travel, more snake oil? or am I missing something?

 I'm kinda with Paul on this one; I found the AcBs Pre far less effective than the simple GEQ with -12dB at the 50Hz setting. Ok we're starting to get into the audible range at 50Hz, I accept.

@bartelby I'd love to see the AcBs Pre graphs side by side with the GEQ at -12dB and everything else set the same?

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Brilliant, thanks!

No contest: the AcBs Pre is the winner; and you probably get the optimal position with either one or possibly two of these stacked depending on how much of the audible lows you want to take out. Any more i.e. 3+ is significantly eroding desirable bass frequencies.

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2 minutes ago, Al Krow said:

Brilliant, thanks!

No contest: the AcBs Pre is the winner; and you probably get the optimal position with either one or possibly two of these stacked depending on how much of the audible lows you want to take out. Any more i.e. 3+ is significantly eroding desirable bass frequencies.

Remember you can derrière about with the depth control in each instance.

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