Graphic Eq (Stereo) For Fun

Hi all,

checked here around with search option , unfortunately seem that nobody had interest (till now)
to build a stereo graphic eq ,

too "simple" project or not useful on a pro rig ?  :

I would like to  own 1 a bit different from the "normal" type … ,
with stereo faders for the frequencies control  (single stereo fader for control each related frequency )
any help about is welcome
cheers

GEQ (graphic EQs) "were" pretty popular for live sound reinforcement to notch out feedback frequencies in stage monitor speakers and for crude sound shaping between different performance spaces.

I saw one home brew console decades ago that use small GEQ in every input strip. The studio owner did a lot of advertising work and the GEQ allowed him to dial in mixes quickly.

JR

Interesting timing on your post here as I have just recapped an old ADC Sound Shaper 2 Mk 3 graphic eq that I picked up at a yard sale for a few dollars some time back.
12 bands per ch, all inductor. Sounds very nice. I think it will sound fantastic on Worly, or B3.  It uses JRC 4558/4559/4560 opamps that I'm considering replacing but I'll use it a bit before I go down that road.

It might be worth looking around for something similar and do a refurb.

Jeff

One of my more successful patents while working at Peavey [US05737428  Roberts] (and subsequently copied by Behringer with their own patent), was FLS "feedback locating system" the illuminated LEDs above one GEQ slider with the loudest bandpass.

This was a quick and easy aid for reducing feedback, or finding proper frequency band to EQ.

JR

It is possible to pick up some very good graphic eq's for not much money nowadays.  I have a pair of Klark Teknik DN27(a).  In my view they are one of the nicest sounding GEQ's you can get.  They have a very simple circuit with only 3 op amps, and an inductor for every band, & sound peachy.    For the money I paid for them I wouldn't bother DIYing them,  you couldn't get 27 inductors made for the £75 I paid for each one. 

The killer problem with DIY graphic EQ is cutting all those slots nice.

If a system needs EQ, it probably needs different EQ left and right. I would not want to pay more for dual sliders and lose the ability to EQ L and R differently.

PRR said:

The killer problem with DIY graphic EQ is cutting all those slots nice.

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Nah, now you can just send a cad file somewhere and they send you back a panel. Like many things today, you just have to be good at using the computer.

And I too like the inductor GEQs. They are measurably quieter for one because there is no active gain in the passband and only 2-3 op amps are required to do many bands (2 in the DN27A which is a very good GEQ BTW - I have one).

A GEQ makes a great "cabinet simulator". Add a steep high cut like from a Pultec HLF3-C and it would be very convincing I think.

Oh thats interesting John , I didnt know that was one of yours ,

I used a few Peavey and Behringer mixers with it built in ,but never found the need to engage  it  . For a small band that dont have a sound engineer or in  a room with bad acoustics FLS works  well I think . I found with practice in a live situation I would instinctively know which band on the graphic to reach for when I heard the feedback note ,its almost always the lead singers fault in any case  ;D so you nip in and notch his stage monitor .

I'd keep a 58 up at the desk with me for monitor talkback , handy at sound check , and ocassionally during a performance if things were getting out of hand onstage ,if the band were really good Id gently tap on mic at the encore in time with the applause and send it out front of house just to get the air moving in the room a bit more , neither the crowd or the band are even aware of the sonic shockwaves ,if you have lots of low end headroom you can punch em right in the junk ,there carried away with anticipation, their bits are wobbling all over the place and the band explodes onto stage , there wouldnt be a dry eye or panties  left in the house .


I think we had a discussion on graphics before and the general concensus was a proper inductor based unit wins most of the time . Sometimes Ive found  31 band graphics usefull on bass , for cutting low end honk and making each note  appear at the same volume , .I get by on basic console 4 band eq for almost everything ,
I think an inductor based graphic for messing sounds up is a good plan , with misuse you can probably coax some interesting harmonics out of the inductors.

Im liking the look of the DN27, similar but with Transformer coupled ins and outs . bound to be loads of them knocking around from old Pa systems.

Tubetec said:

Oh thats interesting John , I didnt know that was one of yours ,

I used a few Peavey and Behringer mixers with it built in ,but never found the need to engage  it  . For a small band that dont have a sound engineer or in  a room with bad acoustics FLS works  well I think . I found with practice in a live situation I would instinctively know which band on the graphic to reach for when I heard the feedback note ,its almost always the lead singers fault in any case  ;D so you nip in and notch his stage monitor .

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I spent a few years at trade shows marketing FLS... That was an all too common response at trade shows  "real men don't need FLS". I would ask the crusty old (luddite) sound men how do they read the tiny numbers over the sliders in a dark bar?  :

I'd keep a 58 up at the desk with me for monitor talkback , handy at sound check , and ocassionally during a performance if things were getting out of hand onstage ,if the band were really good Id gently tap on mic at the encore in time with the applause and send it out front of house just to get the air moving in the room a bit more , neither the crowd or the band are even aware of the sonic shockwaves ,if you have lots of low end headroom you can punch em right in the junk ,there carried away with anticipation, their bits are wobbling all over the place and the band explodes onto stage , there wouldnt be a dry eye or panties  left in the house .


I think we had a discussion on graphics before and the general concensus was a proper inductor based unit wins most of the time . Sometimes Ive found  31 band graphics usefull on bass , for cutting low end honk and making each note  appear at the same volume , .I get by on basic console 4 band eq for almost everything ,
I think an inductor based graphic for messing sounds up is a good plan , with misuse you can probably coax some interesting harmonics out of the inductors.

Click to expand...

I consider GEQ another obsolete or borderline technology. If you want to discuss differences the more significant difference is not components used but topology. Not to shock anybody but the transfer function for all 1/3 octave GEQ are not the same... There are constant Q (promoted by Rane), and variable Q for two at least, perhaps more.  For TMI see https://www.rane.com/note101.html

I wasted a few years unsuccessfully  lobbying AES standards committee to come up with a concise definition for Q in boost/cut EQ sections...  (I gave up mainly because I didn't have a pony in the race anymore).  Long story short different designs exhibit clearly different boost/cut bandwidths and sound different due to different circuit topology, not components used.

Im liking the look of the DN27, similar but with Transformer coupled ins and outs . bound to be loads of them knocking around from old Pa systems.

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As I mentioned GEQ were widely used for live PA, since feedback killers and parametric EQ are now widely available there should be lots of GEQ available cheap...  Perhaps they would make good doorstops or landfill***...?

JR

*** mea culpa I am probably personally responsible for many of those now surplus GEQ...

Agree totally ...  there is a local maker, here in Oz, doing stereo EQ  ..  for the eby market. Quite premium price too  ..  it's a well made opamp based graphic, about 5 bands with good quality parts and selection for good stereo tracking.

I'd like to see a 1RU stereo eq with one set of controls for both channels, based on the neumann w492 eq - it's a great performer and I think it would be quite doable with regards to matching.

Some alps-japan stereo pots would do the 'level control' matching pretty well, I think  ... or the conductive plastic types too.

Add a switched (pair of) traffo balancing line amp section, api-style, and it could be a great proposition without getting too crazy.

My build of the w492 (audiox ), a typical dual channel 2RU eq, tracks pretty darn good for stereo as it is, but for a 2-chn bus why not a 1RU stereo version. I could imagine pairing up, say with a stereo gSSL type compressor, would make life pretty easy.

Sometimes having to match control knob settings can be a little bit of a drag, beating down 'off-the-cuff' changes to sound pallet cause there's too many knobs  ..  x2  !

So yep - good idea I think.

Jeff Goodman2 said:

Interesting timing on your post here as I have just recapped an old ADC Sound Shaper 2 Mk 3 graphic eq that I picked up at a yard sale for a few dollars some time back.
12 bands per ch, all inductor. Sounds very nice. I think it will sound fantastic on Worly, or B3.  It uses JRC 4558/4559/4560 opamps that I'm considering replacing but I'll use it a bit before I go down that road.

It might be worth looking around for something similar and do a refurb.

Jeff

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Thanks to everybody for post !!! 

12 bands are sufficient for "fun" on stereo track
with stereo faders
single hand for eq control

another option the  separate L-R gain control for balance when required as well

Tubetec said:

Im liking the look of the DN27, similar but with Transformer coupled ins and outs . bound to be loads of them knocking around from old Pa systems.

Click to expand...

Some of the DN27's I've had are transformer coupled.  All of them have holes on the back panel to mount Sowter transformers.  Although I think this was an optional extra.      Some also have a relay circuit so that if the power supply blows they revrt to bypass to keep the show going.  Not quite sure how pleasant this would be if the GEQ was set to notch out some serious feedback.....

Rob Flinn said:

It is possible to pick up some very good graphic eq's for not much money nowadays.  I have a pair of Klark Teknik DN27(a).  In my view they are one of the nicest sounding GEQ's you can get.  They have a very simple circuit with only 3 op amps, and an inductor for every band, & sound peachy.    For the money I paid for them I wouldn't bother DIYing them,  you couldn't get 27 inductors made for the £75 I paid for each one.

Click to expand...

Still use them as FoH EQs. They are a bit modified, though.

Recently I picked up a Klark DN22 for very cheap, restored und modified it quite a bit. Now it actually sounds very nice and is a great new addition to my colour palette.

jensenmann said:

Still use them as FoH EQs. They are a bit modified, though.

Recently I picked up a Klark DN22 for very cheap, restored und modified it quite a bit. Now it actually sounds very nice and is a great new addition to my colour palette.

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The general advice was to recommend 2/3rd octave GEQ for gentler FOH sound shaping, 1/3 octave for monitor world to suppress narrow feedback modes.

===

Since most sound reinforcement PA is mono, Stereo GEQ are not that common, more common was dual mono...  For recording studio stereo mixes, a potential GEQ application is to EQ the Left and Right differently to create some perceived localization for instruments with significant content boosted or cut differently in the two sides. 

JR

The old trick was to take a mono recorded guitar and send it to two GEQ's and set them so that on one graphic every other frequency is cut or boosted all the way up or down and the same on the other but the opposite direction. Then pan them hard left and right. Sometimes works great to add some dimension and spread.

Jeff

On the last in house sound gig I did I had it down to where the FOh graphics were bypassed , between system processor ,speakers and  channel eq ,I was getting exactly the sound I wanted , it was only guest engineers who felt the need for them , ,most were quite alarmed when I told them they were bypassed  and presented them with faders flat or no house geq 'smiley'  face Some would get into a awfull flap even very experienced guys , and end up making a total hames of it , Id be supping long necks at the bar at that stage, with only a quick power down and tidy up left to do later in the night  8)
Often the support act ended up with better sound ,cause the main acts engineer used his eyes instead of his ears to set up the graphics .I had a more or less standard setting on the desk eq with a 58 ,so you only required a minor tweak  to compensate for the performer and it sounded great .

I never tried comb filtering on purpose Jeff , that definately looks like a good way of doing it though  ;D

Tubetec said:

On the last in house sound gig I did I had it down to where the FOh graphics were bypassed , between system processor ,speakers and  channel eq ,I was getting exactly the sound I wanted , it was only guest engineers who felt the need for them , ,most were quite alarmed when I told them they were bypassed  and presented them with faders flat or no house geq 'smiley'  face Some

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The first thing I did when at an unknown venue  was look at the GEQ. If  it looked like a pretty picture I bypassed it.  It usually sounded better that way.

JohnRoberts said:

Since most sound reinforcement PA is mono, Stereo GEQ are not that common, more common was dual mono...  For recording studio stereo mixes, a potential GEQ application is to EQ the Left and Right differently to create some perceived localization for instruments with significant content boosted or cut differently in the two sides. 

JR

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Of course …

but this is for fun 

As far as cutting slits for sliders, just use pots.  Rotary knob graphics are not unheard of.  Even Neve built one into the "Green Phone" mixers for SABC.

Rotary pot graphics kind of defeat the design premise of graphical representation of EQ from slider positions...  OTOH one can argue the EQ is only showing the delta or change to signal, not signal itself.

JR

PS: At one time  years ago I hypothesized about a para-graphic EQ, essentially a parametric EQ with a graphic display.  A matrix of slide pots used up/down for boost/cut. The up/down pot assembly could slide left/right to vary center frequency lower/higher. The icing on the cake was a Q pot with a trick knob using a rack and pinion mechanism to represent bandwidth wide/narrow... Too clever to actually do for real life.  8)