Behringer Autoquad - modding HP filter slope

[Gertius]

Okay, I feel I´m slowly becoming the Behringer guy here ha

Anyway I have an old Autoquad here of which I´m using the high and lowpass filters which I really like.

Both filters have a slope of 12dB/oct, which is already nice, but I would be interested in modding the HPF to become 18dB/oct.
As far as I understand the difference is that I would have to increase the order of the filter (second order to third order).
By somehow adding another opamp stage?

Should this be a relatively easy mod?
Would anyone know more about the device to plan it? Either schematics or have any info if it´s a direct copy of other manufacturers gear like some of the other Beh´s?

Thanks in advance,
Christian

 

[emrr]

Only chipping in to say used autoquad and intelligate are about the cheapest filter sets one can buy. Why build anything at all?

There are a lot of good filter calculators online, I'd dig around and find some relevant options.  It may be harder to insert in a HP/LP system like this than just one or the other. 

 

[analogguru]

Only chipping in to say used autoquad and intelligate are about the cheapest filter sets one can buy.

The (XR2000) Intelligate is a 1:1 clone of the Aphex 612 - the first series of the XR2000 even used the Aphex 1537A VCA.

The same circuit topology used in the Behringer XR2000 for LPF and HPF can be found in SSL consoles, Calrec PQ1549, in the Amek 2500:

in the Harrison console:

and dozens of other units and therefore can´t be "that" bad (only because it wears the name "Behringer")

The XR2000 Intelligate uses only different pot and component values than the Amek 2500, and the XR2400 Autoquad has exactly the same filter section as the XR2000.

Below is a picture of the filter section. 

... I would be interested in modding the HPF to become 18dB/oct..

With only one additional capacitor and a third slider you would be in the boat ..... but from where do you take a triple potentiometer - negative logarithmic ?

And that´s the main problem to mod it to 18db/oct .

 

[emrr]

Only chipping in to say used autoquad and intelligate are about the cheapest filter sets one can buy.

Another one without any real technical knowledge is spreading the typical bullsh*t rumours as facts.

I think you have a serious language problem, and maybe you got up on the wrong side of the bed, throwing insults right out of the gate. 
You seem to see a class issue that doesn't exist.
Cheap: They can be bought for $50 or less on ebay.  That's a great deal for functional filter sets.

 

[analogguru]

Only chipping in to say used autoquad and intelligate are about the cheapest filter sets one can buy.

Another one without any real technical knowledge is spreading the typical bullsh*t rumours as facts.

I think you have a serious language problem, and maybe you got up on the wrong side of the bed, throwing insults right out of the gate. 
You seem to see a class issue that doesn't exist.
Cheap: They can be bought for $50 or less on ebay.  That's a great deal for functional filter sets.

Maybe your reading skills are improvable ?:

Anyway I have an old (rem.: Behringer) Autoquad here of which I´m using the high and lowpass filters which I really like.

Both filters have a slope of 12dB/oct, which is already nice, but I would be interested in modding the HPF (rem: of the already existing Behringer Autoquad) to become 18dB/oct.

Why should he build or buy anything when he already has a Behringer Autoquad he only wants to modify ?

Do you have any matching contribution for the fellow´s desire ?

 

[emrr]

Maybe your reading skills are improvable ?:

Yours certainly are, along with your social skills. 

Why should he build or buy anything when he already has a Behringer Autoquad he only wants to modify ?

He shouldn't buy anything, nor did I suggest he do so.  I was celebrating the existence of such a cheap and effective 12dB/oct filter set.  Different from his question.

Do you have any matching contribution for the fellow´s desire ?

There are a lot of good filter calculators online, I'd dig around and find some relevant options.  It may be harder to insert in a HP/LP system like this than just one or the other.

 

[analogguru]

I was celebrating the existence of such a cheap and effective 12dB/oct filter set.  Different from his question.

And why didn´t you start an own thread for this celebration ?  Fun on thread-derailing ?

BTW, four weeks ago I bought 2 pcs XR2000 each for € 13,-- (= < $ 50,--), and there were even more, but too expensive with € 13,72 and € 16,50:

http://www.ebay.de/itm/Behringer-Intelligate-XR2000-XR-2000-/330905003664#ht_500wt_989
http://www.ebay.de/itm/Behringer-Intelligate-XR2000-XR-2000-/330905002315#ht_500wt_989

And yes, it is true, two months ago I bought 2 pcs PEQ305 (5-bd Parametric EQ) each for € 20,-- (including shipping).  Three weeks ago a bought a SNR208 (8-ch Denoiser) for € 12.50.  So there´s really a lot to celebrate - enough for an own thread.

Do you have any matching contribution for the fellow´s desire ?

There are a lot of good filter calculators online, I'd dig around and find some relevant options.  It may be harder to insert in a HP/LP system like this than just one or the other.

Unfortunately the filter calculators will not help him much in practice - he urgently needs triple pots.... neg log.  Any idea ?

 

[analogguru]

Hallo Gertius,

schätz mal auf Deutsch werden sich da weniger Leute mit sachfremden "Feiern" einmischen, die noch nicht geschnallt haben, dass es in Österreich keine Känguruh´s gibt und daher meine Muttersprache deutsch ist. 

Gruß aus Wien,

analogguru

 

[emrr]

Wow, just wow. 

 

[Gertius]

Hi guys,
please, I ask you to try and get along. No need to get into each others´ hair for what is most likely just a misunderstanding.

Thank you both for your contributions!

Let´s just say that we´re all happy that the cheapo, underrated Beh boxes exist.
And maybe they will be even better if it would be possible to mod them

Also, Kooma was so nice to post schematics of the XR2400 in the files section. Thanks heaps for that as well, Kooma!

So, analogguru, can you make anything of those schematics?
Also you wrote that it is mandatory to get triple negative logarithmic pots for the mod.
Let´s say I could somehow manage to source those parts, could you assist me in planning out the mod in detail?
Is there a maybe way around that part? In some other places I read that if you wire positive log pots the other way around it would work as a neg one...

I do have a background in electronics (I´m a "Radio- und Fernsehtechniker"), but my apprenticeship was 11 years ago, and since then I have studied and done mostly software.

Cheers!
Christian

 

[Gertius]

Here I have attached a pic from an SSL filter section.
analogguru, it seems to relate to what you wrote about the triple pot, but then I also see a second opamp stage.
Also when I last searched on the web I found this:
http://www.hardwarebook.info/Bessel_18dB_Highpass
which also depicts two opamp stages for the 18dB filter.

What topology is the one you are referring to? Bessel/Butterworth? Something else?

Could you please go more into detail of the mod you were describing?

 

[emrr]

The following site has the most comprehensive selection of calculators I've found together in one place. If you spend some time with them you will gain greater understanding of what's possible, and what's problematic.  Maybe start here:

http://sim.okawa-denshi.jp/en/Sallenkey3Hikeisan.htm

 

[analogguru]

What topology is the one you are referring to? Bessel/Butterworth? Something else?

Could you please go more into detail of the mod you were describing?

Below you have the schematic of the modification of the HPF for an 18 dB slope without a second opamp.  The cap values you can calculate to your taste on the link posted by emrr.

Good luck finding triple pots now.  Keep me informed about the source when you have found some.

analogguru

 

[analogguru]

Of course you can build your on multiple with trimmers (see picture attached).

analogguru

 

[PRR]

> Another one without any real technical knowledge

Please read Forum Rules:

Personal attacks ... will not be tolerated.

 

[Gertius]

Guys - wow!
What great information here.

Thanks to all of you again!
The mod is basically laid out there in front of me.
Now all that´s left to do is find/build the pots, calculate the filter on emrr´s link, and build the circuit proposed by analogguru.
Can´t wait to start tampering!

I love it!

Thanks again.

 

[Gertius]

Hi guys,
would this seem like the right pot?
http://www.audiomaintenance.com/acatalog/om-01-080_extended_info.html

Here is one with a pic, but with different features:
http://www.audiomaintenance.com/acatalog/om-01-018_extended_info.html

Do you think 3x47k will get me somewhere?
I would already be happy if I could realize the range between 30 and 350 Hz.
But when I use the filter calculator it always gives me at least one resistor < 10k. Maybe realize that with a parallel resistor?

Maybe I´ll order just one or two first, to try out the mod.

I f the mod would work out I´d be interested in doing a collective order. Any of you also interested?
I would take 25, it would be great if we could get the price of 50.

P.S.: another different question. I´m having difficulties reading the schematics of the Autoquad filters´ resistors. It seems to be saying 909E, do you know what that means? I´m sure they don´t mean Exoohms, right?
I´d like to keep using as many parts of the original design as possible.

 

[henk]

You can mod the XR2000 and XR2400 in the same way as the MDX2000...............
only i would not change the sidechain , only the audio chain i would change........... and for that you can read it in the MDX2000 post.

 

[radardoug]

You don't have to use a pot, you can use a 3 gang rotary switch, and make it up to suit. Lots of good switches around, the Goldpoints especially would work but expensive. The Goldpoints have provision for putting the resistors on the switch, in two versions, surface mount and through hole, 24 positions.

 

[Gertius]

The following site has the most comprehensive selection of calculators I've found together in one place. If you spend some time with them you will gain greater understanding of what's possible, and what's problematic.  Maybe start here:

http://sim.okawa-denshi.jp/en/Sallenkey3Hikeisan.htm

So, I tried to recalculate the existing filter in the Autoquad to get a grip on the filter design tool on this page:
http://sim.okawa-denshi.jp/en/OPseikiLowkeisan.htm

But as far as I can see it doesn´t match up with the schematics.
I enter the C´s with 150n and 68n and the R´s in one case with 100909 Ohm (result fc = 15.6 Hz) and in the other case with 909 Ohm (result fc = 1733.6 Hz). In my mind the result should say 30Hz and 3000Hz. Can anyone please tell me what I´m doing wrong?