DIY equalizer based on Studer 169 (standard and mastering)

[3nity]

Whats wrong with the front panel???
It looks wasted

 

[bobine]

Could you plot one of the low boost frequencies on full boost and see if it changes at all when you change which high frequency band you have selected.

Here are LO boost plots with changes in the Hi freq bands. The group on the left is the lowest LO band (small effect) and the group on the right is at the highest LO band (significant interaction).

 

[bobine]

Whats wrong with the front panel???
It looks wasted

I think it was silk screened on the wrong side. This is the only way it works.

 

[MikeClev]

Thanks for the plots Bobine! Looks like the interaction shifts the highest low band by 600hz.... more than an octave, quite a serious amount! I guess as long as people know it happens and that it affects the highest of the low bands people can compensate...

Personally I'm going to rejig the circuit to isolate the high and low EQs with an opamp...

Thanks to Audiox by the way for his work, I do appreciate it! Just trying to understand the design a little more.

 

[dandeurloo]

are the mastering versions of these still for sale?

 

[benlindell]

are the mastering versions of these still for sale?

The mastering version is the same board as the regular, just different resistors for the switches. Gustav in the WM used to sell the boards for this, message him to see if he's gonna do another run.

 

[[email protected]]

hi audiox,

great project btw!

any chance of an editable version of the copper mirror?

i've just etched one, and I'm having problems drilling the holes, i could do with revising it slightly to make bigger pads?

 

[andre tchmil]

I have a few Neutrik NTL audio transformers available in the black market. Offered in pairs

 

[cstella]

Hi all. So after a few years I am finally building these boards!

I have decided to make even smaller gain steps for a mastering version. (+/- .5 , .5 , .5 , 1 and 2dB)

I will also be adding HP and LP Filters (2 pole Butterworth) ala the BAX Mastering EQ.

Thanks to benlindell for posting the trace cuts needed. Also your tutorial on using Fuzzmeasure to do the sweeps is awesome!

http://blog.benlindell.com/?p=112

I have successfully gotten the Low Freq steps bang on by using

R3-8 = 465R +/- .5dB

R2 and R9 = 910R +/- 1dB

R1 and 10 = 1.8k +/- 2dB

and 7.5k adding to the ends using benlindell's cutting guide

I am having some problems with the High Freq though. When I try to apply the same logic I would think

135R +/- .5dB

270R +/- 1dB

540R +/- 2dB

Plus 1090 adding to the ends of the strings.

Well when I do this I don't get anywhere close to this. I have tried many combinations but I think I am missing something.

Any help would be greatly appreciated!

Thanks, Charles

 

[benlindell]

yea man, this one was kinda tuff to get perfect for me too. send me your email and I'll send you a tutorial I wrote up on it that I don't think I posted anywhere, yet.

Hi all. So after a few years I am finally building these boards!

I have decided to make even smaller gain steps for a mastering version. (+/- .5 , .5 , .5 , 1 and 2dB)

I will also be adding HP and LP Filters (2 pole Butterworth) ala the BAX Mastering EQ.

Thanks to benlindell for posting the trace cuts needed. Also your tutorial on using Fuzzmeasure to do the sweeps is awesome!

http://blog.benlindell.com/?p=112

I have successfully gotten the Low Freq steps bang on by using

R3-8 = 465R +/- .5dB

R2 and R9 = 910R +/- 1dB

R1 and 10 = 1.8k +/- 2dB

and 7.5k adding to the ends using benlindell's cutting guide

I am having some problems with the High Freq though. When I try to apply the same logic I would think

135R +/- .5dB

270R +/- 1dB

540R +/- 2dB

Plus 1090 adding to the ends of the strings.

Well when I do this I don't get anywhere close to this. I have tried many combinations but I think I am missing something.

Any help would be greatly appreciated!

Thanks, Charles

 

[rmaier]

Ben, I'd be interested in the tutorial as well. I'm trying to figure out a similar problem with my build using the 500 version of this eq.

 

[Dr nEon]

Hey Guys!

I'm planning on building the mastering version of this 169 project to use over my mix buss.

I would like to add in the presence/absence filter, though, as I often add a touch in the mids, as well as hi and lo,  So my question is: what would be the preferred way to do this..

Could I refer to the schematic for the 500 series version, and build a small card for just the midrange section, and insert it after the HI/Lo section ,at the node just before the output op amp?

Or could the mid-range filter be simply placed across pads C and D with  100uF coupling caps before and after?

Any thoughts would be appreciated.

Cheers
nEon.

 

[audiox]

Or could the mid-range filter be simply placed across pads C and D with 100uF coupling caps before and after?

That was the original purpose of the C-D insert.

But it would probably be easiest to use the 500 series PCB and replace the potentiometers with rotary switches.

 

[Dr nEon]

Hey audiox!

Thanks for the reply. So I have the option to do it either way..

I was hoping to do the mastering version, simply because you made such a beautiful neat pcb layout for the switches.

Can I ask... as regards purity of signal path, do you think there is any disadvantage in the mid band coming before the Hi/Lo section (as it would be using pads C-D) , as opposed to after the HI/Lo section, the way it is on the 500 version?

Appreciate your help.

Cheers

nEon.

 

[JoleFIN]

Finally after 2,5 years of break with this I got myself together to finish this build (at least in a sense I can use it .. might later add bypass switches and a power switch but for now it runs smooth on the rack with some other stuff I built earlier)!

 

[Eje2005]

I´m having some problems with this. Did the Mastering version with Ben´s help, got the steps to work perfectly, but here´s my problem:
Input straight to D, if i take the output from E (+) it´s reversed polarity but with no DC-offset, If i take the output from F (-) It´s correct polarity but with a DC-Offset.

On the I/O´s im running Cold to ground, in fact my whole system is like that.

Should it help to just enter @ A/B and use that buffer?

Thanks

 

[audiox]

Input straight to D, if i take the output from E (+) it´s reversed polarity

The EQ section (D to E) is inverting.

Should it help to just enter @ A/B and use that buffer?

Path A to E is non-inverting. U2A also provides a low source impedance for the EQ section.

On the I/O´s im running Cold to ground, in fact my whole system is like that.

Why not using balanced connection?

 

[Dr nEon]

Hey Eje2005,

The hub of my studio is a soundcraft desk with an unbalanced patchbay, so like you, I have to run unbalanced -  I  build the DIY gear with balanced i/os, and then wire the looms to the desk p/bay in the manner appropriate (see rane diagrams).

I'd recommend you use the buffer and wire up your input to point A.  For your peace of mind, I can tell you that the eq sounds brilliant this way, in my unbalanced situation. The only issue is a 6dB level drop, typical of this situation. On other projects (e.g. Calrec eq) it was ok to change the value of input resistors, to compensate for this drop. I'd like to know if that idea could be used here, too? Or anywhere else in the circuit that could make the gain back up?

I have a further question or two for audiox, or anyone else who may have the answers:

My mastering version (hi &lo) is done, sounding fab.. so now I'm hacking around with inserting the midrange filter at the C-D point via coupling caps.  I've quickly etched the midrange portion of the 500ser card, just to experiment on..

About the coupling caps, currently I have:  C > 100uF cap > mid range filter > 100uF cap > D

So,  1 -  Is the first 100uF cap unnecessary? Could C connect directly to mid section?

      2 -  I see that C16 on the mastering version is 220uF(upped from 100uF on 500 series ver.), and I love the sound of it.  So would it also make sense to make my coupling caps 220uF instead of 100uF?

      3 - I've added a switch to bypass the midrange when I don't need it. Since the midrange section inverts the polarity, I've used a 4PDT switch, so that I can simultaneously flip the input (points A & B) whenever the mids section is engaged - thus preserving the output polarity at E & F.  It seems to be working fine, but I'd be keen to hear if anyone spots a potential problem with this arrangement.

hoping someone can help me put the icing on the cake on this fabulous project!

Cheers

nEon

 

[audiox]

The only issue is a 6dB level drop, typical of this situation. On other projects (e.g. Calrec eq) it was ok to change the value of input resistors, to compensate for this drop. I'd like to know if that idea could be used here, too? Or anywhere else in the circuit that could make the gain back up?

Unity gain, unbalanced: R27=10k

Is the first 100uF cap unnecessary?

I would use it.

So would it also make sense to make my coupling caps 220uF instead of 100uF

Changes the "linear" frequency response -3dB point from approximately 1 Hz to approximately 0.5 Hz.

I've added a switch to bypass the midrange when I don't need it. ...  It seems to be working fine, but I'd be keen to hear if anyone spots a potential problem with this arrangement.

The only "problem" I can see is the switching noise caused by the small DC voltage at the op-amp outputs.

 

[Dr nEon]

Hey audiox!  Just the man...and just the info I was looking for! Thanks for the quick response.

Unity gain, unbalanced: R27=10k

Cool! ..and, just for the record, in my case R28 should also be 10K then, since I have the polarity switch thing goin' on...

Changes the "linear" frequency response -3dB point from approximately 1 Hz to approximately 0.5 Hz.

;D ;D ;D  Ok, so I'll leave the 100uFs well alone! 

Actually, although I understand concept of the -3dB point (or think I do...), I don't know how to calculate it, just looking at a schematic.... I'm googling to find a decent tutorial on the subject..

Thanks again for this great project!