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Heads with built in high pass filters


BillyBass

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There are a few heads that have high pass filter knobs on them, Mesa and Bergantino come to mind.  I have read, however, that high pass filters or 'rumble filters' are often built into heads but not advertised.  Do any of you know and brands or any particular heads that include a built in high pass filter?

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It's odd isn't it? Few amps guitar, bass or hi-fi will go down to DC (0Hz) and our hearing becomes less and less efficient as the frequency drops so we barely hear 50Hz. The best hi-fi amps usually go down to maybe 20Hz and the design of most amps inherently limits the frequency response at both ends. Basically just about all the amps we use have a frequency response that limits the upper and lower frequencies but I don't remember ever seeing  anything in an ad or a manual or a bass amp saying what that is.

 

That wouldn't matter if it wasn't so important. The speakers we use can't really handle those low frequencies. The excessive excursion pushes them into distortion, heats up the voice coils of speakers and can reduce the power reserves of the amp itself, but without information there is little we can do to protect our sound or our speakers short of an expensive fx box HPF which might be unnecessary if the amp has sufficient built in.

 

I can't imagine the manufacturers don't know the -3db point for their amps or how quickly the low end rolls off but nobody seems to say. 

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41 minutes ago, BillyBass said:

There are a few heads that have high pass filter knobs on them, Mesa and Bergantino come to mind.  I have read, however, that high pass filters or 'rumble filters' are often built into heads but not advertised.  Do any of you know and brands or any particular heads that include a built in high pass filter?

Afaik only a fraction of vintage stuff is without a rumble filter. Iow, all modern offerings have them.

 

A highpass filer with a control knob is a whole different thing.

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7 minutes ago, Downunderwonder said:

Afaik only a fraction of vintage stuff is without a rumble filter. Iow, all modern offerings have them.

All modern amps have them?  Really?  So the class D heads from Gallien-Krueger, MarkBass, Ashdown, Orange, Darkglass, Trace Elliot, TC Electronic etc all have built in high pass filters?  So no need to add a SFX micro-thumpinator to any amp unless its one of a small minority of vintage amps?

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25 minutes ago, Phil Starr said:

It's odd isn't it? Few amps guitar, bass or hi-fi will go down to DC (0Hz) and our hearing becomes less and less efficient as the frequency drops so we barely hear 50Hz. The best hi-fi amps usually go down to maybe 20Hz and the design of most amps inherently limits the frequency response at both ends. Basically just about all the amps we use have a frequency response that limits the upper and lower frequencies but I don't remember ever seeing  anything in an ad or a manual or a bass amp saying what that is.

 

That wouldn't matter if it wasn't so important. The speakers we use can't really handle those low frequencies. The excessive excursion pushes them into distortion, heats up the voice coils of speakers and can reduce the power reserves of the amp itself, but without information there is little we can do to protect our sound or our speakers short of an expensive fx box HPF which might be unnecessary if the amp has sufficient built in.

 

I can't imagine the manufacturers don't know the -3db point for their amps or how quickly the low end rolls off but nobody seems to say. 

I had a long conversation with Dave Green from Ashdown last year about the benefits of high pass filters and I'm sold.  

 

I think if there was an obvious improvement in sound they would receive more attention.  There isn't though.

 

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1 hour ago, BillyBass said:

I had a long conversation with Dave Green from Ashdown last year about the benefits of high pass filters and I'm sold.  

 

I think if there was an obvious improvement in sound they would receive more attention.  There isn't though.

 

The problem with capable adjustable HPF onboard amps is in the selling. The average bassist isn't well informed so when asking what the HPF knob does the sales guy says 'it cuts off low end' and the next words out of the shopper are 'show me something else'.

 

Iirc the Thumpinator is -3dB at 30hz and a 12dB / octave slope, higher than fixed filters on amps but too low for what most HPF users are after. Ymmv.

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2 hours ago, BillyBass said:

All modern amps have them?  Really?  So the class D heads from Gallien-Krueger, MarkBass, Ashdown, Orange, Darkglass, Trace Elliot, TC Electronic etc all have built in high pass filters?  

 

Certainly do the issue is not that they have them but what they are. 

 

2 hours ago, BillyBass said:

So no need to add a SFX micro-thumpinator to any amp unless its one of a small minority of vintage amps?

 

If it does something you need then yes. You have no control over the build in high pass filtering of an amp, it is wherever it is, normally fairly low on a bass amp. So if you want it higher, you need something to do the filtering for you.

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The trick is to remove all the troublesome stuff that causes problems without taking away anything that makes the bass sound good. Easier said than done of course but there's a balance to be struck and it's usually something around 30-40Hz as the -3db point and 24db/octave filtering which is sharper than the natural roll off of most amps.

 

There are multiple reasons for doing this and the optimum will vary. Mixing live I've filtered out everything below 50Hz and no-one has noticed once the bass is in te mix.

 

Anyway here is the problem. This is the excursion of a typical speaker at 200W in a ported cab. As you can see the cone moves further as the frequency falls. The port takes over at 40Hz and below that the cone is flapping about madly. For this speaker the most it can move is about 4mm and then it leaves the safety of the magnetic gap. Below 100Hz it's pretty much into distortion at 200W and that is going to distort everything, not just the bass. Below the port tuning it's crazy, the cone can't physically move 25mm in both directions and you'll end up with a damaged speaker. All this to make frequencies you can't hear. Below is the excursion with a Thumpinator 

 

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image.png.c375da9b986a26815b45c2377febb289.png

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3 hours ago, BillyBass said:

All modern amps have them?  Really?  So the class D heads from Gallien-Krueger, MarkBass, Ashdown, Orange, Darkglass, Trace Elliot, TC Electronic etc all have built in high pass filters?  So no need to add a SFX micro-thumpinator to any amp unless its one of a small minority of vintage amps?

They're there for sure. Try using a tone generator to go lower and lower, but be careful you dint find yourself listening to harmonics or other distortion. 

 

The questions are though: where are they? How steep? Is that where your cab wants it? What about your tonal preference? Can you adjust? 

 

If I'm doing reggae, straight into a huge wall of million watt subs, I'll be setting it super low or turning it off. Rock with a pick, using just a small 1x12" cab? 80 Hz or so please! 

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5 hours ago, Downunderwonder said:

The problem with capable adjustable HPF onboard amps is in the selling. The average bassist isn't well informed so when asking what the HPF knob does the sales guy says 'it cuts off low end' and the next words out of the shopper are 'show me something else'.

 

Iirc the Thumpinator is -3dB at 30hz and a 12dB / octave slope, higher than fixed filters on amps but too low for what most HPF users are after. Ymmv.

 

I put the question to sfx who make the Thumpinators back in 2019 and received this response which was instructive:  "I do not publish the slope of the micro-Thumpinator filter. The only thing I can tell you is that the micro-Thumpinator cuts at more than 12 dB/oct." All the best, Max [sfx]

Phil's charts in the post above really do demonstrate how effective it is in reducing unnecessary speaker excursion in the sub-audio range. Be interesting to know if any amp's HPF are comparably good? My guess is that a few may be, particularly where they are an advertised feature, but many are not given the additional component cost etc.

Perhaps worth pointing out that it's not either / or - a Thumpinator in series with the amp's HPF should work in tandem to eliminate unwanted low end.

I do like where the Thumpinator cut-off is set i.e. just below the low B fundamental on a 5 string. Perfect for us 5 string players - although I appreciate we're going to be much more focussed on the 1st and 2nd harmonics, it's nice to know that the fundamental is still in there!

 

Edited by Al Krow
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32 minutes ago, Al Krow said:

I do like where the Thumpinator cut-off is set i.e. just below the low B on a 5 string. Perfect for us 5 string players - although I appreciate we're going to be much more focussed on the 1st and 2nd harmonics, it's nice to know that the fundamental is still in there!

 

I have one of the mini-HP-Kongs so I can adjust where the cut off is set.

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1 hour ago, Al Krow said:

Perhaps worth pointing out that it's not either / or - a Thumpinator in series with the amp's HPF should work in tandem to eliminate unwanted low end.

Full disclosure:  I have a micro-thumpinator but have had trouble with it.  It may just be faulty but whenever I stick it on my pedal board it affects the sound quite badly; I get a hollow farting sort of sound.  It worked ok at first but gradually got worse so I removed it.  I then put it back on after 6 months and everything was fine for a couple of weeks and then the same happened.

 

I still want to filter out the below 30Hz stuff but not with a micro-thumpinator.

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2 minutes ago, BillyBass said:

Full disclosure:  I have a micro-thumpinator but have had trouble with it.  It may just be faulty but whenever I stick it on my pedal board it affects the sound quite badly; I get a hollow farting sort of sound.  It worked ok at first but gradually got worse so I removed it.  I then put it back on after 6 months and everything was fine for a couple of weeks and then the same happened.

 

I still want to filter out the below 30Hz stuff but not with a micro-thumpinator.

Yup that does sound faulty. Max at sfx is a good chap - why not get in touch with him and ask him to check whether there's an issue with it. You never know, he may even offer to replace it.

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4 minutes ago, BillyBass said:

Full disclosure:  I have a micro-thumpinator but have had trouble with it.  It may just be faulty but whenever I stick it on my pedal board it affects the sound quite badly; I get a hollow farting sort of sound.  It worked ok at first but gradually got worse so I removed it.  I then put it back on after 6 months and everything was fine for a couple of weeks and then the same happened.

 

I still want to filter out the below 30Hz stuff but not with a micro-thumpinator.

That makes sense o your comments then as Al said why not get in touch and see what they have to say

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6 hours ago, Phil Starr said:

I can't imagine the manufacturers don't know the -3db point for their amps or how quickly the low end rolls off but nobody seems to say. 

Ashdown publish their figures for the RM800 EVO ii, (which I have), and their other solid state amps, as -3dB @ 17Hz and 30KHz.  The CTM-300's frequency response is from 35Hz -18 KHz.  So does this mean the solid state stuff has a rumble filter that kicks in at 17Hz?

 

@Phil Starr and @Al Krow I will speak to Max again.  

Edited by BillyBass
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43 minutes ago, BillyBass said:

Full disclosure:  I have a micro-thumpinator but have had trouble with it.  It may just be faulty but whenever I stick it on my pedal board it affects the sound quite badly; I get a hollow farting sort of sound.

 

Yes, sounds faulty where a componant such as a capacitor is degrading and really affecting the frequency response.

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18 minutes ago, BillyBass said:

@Phil Starr and @Al Krow I will speak to Max again.  

 

Let us know how you get on and whether he manages to sort it for you.

 

 This thread has got me thinking about moving my Thumpintor off my home "creative" board, given that I'm not playing at much volume there, and putting it as an always-on pedal underneath my little gigging HB board which I've recently put together...turns out there's enough clearance for it 👍😄

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1 hour ago, BillyBass said:

Ashdown publish their figures for the RM800 EVO ii, (which I have), and their other solid state amps, as -3dB @ 17Hz and 30KHz.  The CTM-300's frequency response is from 35Hz -18 KHz.  So does this mean the solid state stuff has a rumble filter that kicks in at 17Hz?

 

@Phil Starr and @Al Krow I will speak to Max again.  

I don't think it's likely to be a filter as such (without any knowledge at all about the ABM's design) Any series capacitor in an amplifiers circuit will act as an HPF. They are frequently used for decoupling DC voltages where you want the signal to pass but need to block the voltage in one part of the circuit from affecting another. One of the things the designer will have to calculate is what effect each has on the overall frequency response of the amp. Someone with very good hearing can detect sounds between 20-20,000Hz so many amps were designed with a target of below 20Hz as the -3db point. If Dave Green is sold on HPF then it may be deliberately designed into the CTM, if so then another good reason to go Ashdown.

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Many amps have HPF's, mostly added in the past 15 years, once designers recognized how valuable they are to the performance.

 

All amps I have designed over the past ~20 years have had them, between 12 and 24dB/octave, and in the Subway amps, all but the D-800 have variable HPF's. Differences in slope and alignment are representative of the specific task and character desired for the amp's overall goals.

 

Edited by agedhorse
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