Modding EQ for Variable Q shape

[Barrylime]

Hi DIY people,

For a new project I'm building a small Orion console from some spare channels that came with a bigger unit. I have all of the required parts (extra master etc.), as well as new PCBS so I can build some extra channels (to get up to 16, or 24, (I have 15 spare channels, and 6 stereo returns).

I would really like to add one particular modification to this small console (seeing I will be making new faceplates, and can accomodate controls on a new (wider) faceplate).

The modification would be adding two pots (or a push pull...?) for variable Q shaping of the two mid bands..

Stock, every channel has a high and low shelf, as well as two mid bands, but none are variable in shape...

The EQ is good, but it's often too narrow, or wide, depending on the situation. (I'm only looking to change the mid bands, the high and low shelves are fine.)

Obviously I'm under no illusion that I can figure out exactly how/what to do myself. I have only (relatively) recently started my DIY adventure, and although I have purchased a book on circuits and design, and am trying to learn, I am not yet capable of this.

Therefore, my idea was to ask a professional to perform this mod to one of my channel (or show/mark exactly in the schematic/on the PCB what to do where) and create a small BOM with required parts, I could then easily perform the mod to all of the other channels I'd like to modify. (Provided the BOM is there, and I know what traces to intercept where, or what jumper go where...., etc. etc.)

I'm quite sure it's not as easy as replacing a resistor with a pot... for variable resistance....
I would love to know how realistic/feasible this mod is, so I can ask someone, perhaps someone knows a good person to ask..? I know it might be hard, but I just need to know how 'possible' it is given the layout and circuit.
Maybe (if it requires an additional op-amp, or whatever), I could get a small PCB made that attaches to the main board via jumpers.

When it comes to where to fit it physically, I have a few ideas, but for the purpose of this post, don't worry about whether there is enough room.

Below I have attached the main schematic, as well as linked some more relevant info.

I really appreciate your answers and time!!!


More files, schematics, and visual representation of the idea:

https://www.dropbox.com/sh/b699n2omdcwc6ze/AAAOH6n3-680r6gihH_gcU7Za?dl=0

 

[john12ax7]

You would need at least a dual opamp for each band plus some extra components. Have a look at the mid bands of the SSL EQ to see one way of doing it.

 

[abbey road d enfer]

It's a very extensive mod. You would have to use a different topology. You would need to depopulate the existing EQ, install an add-on PCB, and establish all the necessary connections.
It's so complicated it's not worth doing it, particularly considering there are inserts on this mixer, that you can use for additional EQ if needed.

 

[Barrylime]

Thanks for your replies @john12ax7 and @abbey road d enfer ! I understand it's not as easy as swapping out one component as I mentioned in the original post. However, I don't agree with you regarding that it's not 'worth it'. I guess 'worth it' is dependent on the person, although for most it might indeed not be. If I wanted one outboard EQ per channel, or 16 or 24 channels, it would cost a lot more (and take a lot more space) than paying the price of one/two/three 500 series EQ modules in research & development costs (outsourced to a pro). As I mentioned I could install a small adapter PCB board myself for the additional channels, and solder all components etc.
I also just enjoy the idea and general project, regardless of time/cost etc, and not because it's necessarily 'rational', or 'logical' haha.
I know I can hook up anything to the channel insert, I wouldn't be asking if wanted to do that haha.
I could share this mod and or adapter PCB with others in the future, there are many Orion owners.
All I want to know is how possible it is (I mean anything is possible I guess, if you redesign the entire channel PCB anything could be added). By which I mean, if I was to pay/hire/contact a professional to design a small adaptor PCB and figure out where to re-route the signal from etc., would it be something they're capable of if they put in a day's, or few days' work (provided they have an actual channel to experiment with and the schematics)?

Even if this is not the case, I have the editable files of the main PCB (as I'm making a few channels and had it reverse engineered) I could even ask someone to edit that directly, which might be the easiest... solution...?

Regarding the metal work, I have a family contact who I very recently discovered is willing to make me faceplates for free, so that won't add to the costs.

Thanks again for the reply/replies!!!!

Sorry for being 'that stubborn idiot', at least I'm not thinking I'm capable of designing/doing it myself haha (other than the actual adaptor board assembly, soldering, jumper installation, etc.), and want to outsource and ask an actual knowledgable pro..

Best,

BL

 

[abbey road d enfer]

All I want to know is how possible it is (I mean anything is possible I guess, if you redesign the entire channel PCB anything could be added). By which I mean, if I was to pay/hire/contact a professional to design a small adaptor PCB and figure out where to re-route the signal from etc., would it be something they're capable of if they put in a day's, or few days' work (provided they have an actual channel to experiment with and the schematics)?

I believe you don't realize what it takes to do what you want.
Where are you gonna put the additional potentiometer for the BW control?
Where are you gonna put the new PCB?
can you source the correct potentiometers?
Producing the schematic is easy, making it work in the existing channel may not be so.
Someone undertaking this task will want to cover their a.s and provide for possible multiple revisions (I would...).

Even if this is not the case, I have the editable files of the main PCB (as I'm making a few channels and had it reverse engineered) I could even ask someone to edit that directly, which might be the easiest... solution...?

Editable, how? If it's gerber files, forget about it. If it's files from a software package, you must find someone who has the same software and knows how to use it.

Regarding the metal work, I have a family contact who I very recently discovered is willing to make me faceplates for free, so that won't add to the costs.

I don't know how this console is made, if it's fully, semi-modular or single-plate, but I can assure you that the person undertaking the elecronics will want to have a right of scrutiny on the metalwork. If he/she does not, he/she is a daredevil.

 

[Barrylime]

I believe you don't realize what it takes to do what you want.
Where are you gonna put the additional potentiometer for the BW control?
Where are you gonna put the new PCB?
can you source the correct potentiometers?
Producing the schematic is easy, making it work in the existing channel may not be so.
Someone undertaking this task will want to cover their a.s and provide for possible multiple revisions (I would...).


Editable, how? If it's gerber files, forget about it. If it's files from a software package, you must find someone who has the same software and knows how to use it.

I don't know how this console is made, if it's fully, semi-modular or single-plate, but I can assure you that the person undertaking the elecronics will want to have a right of scrutiny on the metalwork. If he/she does not, he/she is a daredevil.

Thanks again for your insights, in case I'm coming across like a stubborn ignorant newbie, I undoubtedly am, and again appreciate your insights as someone who actually knows what they're talking about. I really don't mean to be disrespectful, and understand it gets tiring replying to these types of post all the time! I have read many archived threads where people propose cool ideas, but are obviously not skilled enough to actually complete/realise them, and am aware it is not an easy undertaking. Hopefully this won't become one of those threads, and there will be progress posted in the months to come on this EQ mod. As I mentioned before, I'm not designing it myself, I want to employ someone to do this, and then follow the BOM/example/manual provided by them (assuming I find someone who can figure out how to make it work).

This (the tiny orion project) is a long term project, that will hopefully be finished in 1-2 years, not something that will be fully finished before the end of summer. As I mentioned it's definitely a I want to do this and it will be fun and a great learning experience type project, not a, great value for money invested project... haha

The original console is modular, so the 'left over' channels I have, can (and are normally) connected by Ribbon cables, nothing else, it's a very simple design compared to other console I have seen. I know this because I have the actual complete larger Orion, in which modules can be clicked into the ribbon cable, and pulled out and moved around, wherever you want (as long as the jumper settings for the floating subgroup are correct).
So there are separate LED meters, channels, stereo returns, and a master etc., all connected to a ribbon cable.

Because the 'tiny Orion' will consist of some newly built and already existing channels (I have spare 15 existing channels, 6 stereo returns, and a master, and a PSU, mostly NOS), I was going to need to make new faceplates anyway for the extra channels. This sparked the idea of modifying the faceplates to be wider (see below as to why), and then I realised this would also free up space for the potential bandwidth controls. I am currently in the process of assembling the reverse engineered rev. 1 channel PCB (visible in the photos above), in order to ensure it works properly before I progress to the next stage. I am also making a frame for this 16 or 24 channel desk (I'm still deciding how big I will make it), but I will only start drawing this when I know the dimensions of the final modules of course. This also means that I can accomodate the size/shape of channels and controls. Ideally as I mentioned, I really don't want to change the main PCB, as that would allow me to use the existing spare channels with a different faceplate, and I wouldn't have to build 16 channels from scratch. As I already mentioned, I either want to build 1 or 9 channels, so I can get to a total of 16 or 24. I'm not modding the master, stereo returns, or led bars etc.

I have had the existing faceplates 3D laser scanned by a local business and have editable DFX and Autocad 3D files which I can use. My family member is also able to edit and use the software (solid works, autocad, etc.) I'm making the faceplates wider than they are now anyway, so I can put my 500 series racks (I own already) directly under the channels in the frame I'm building, and have them in line with the channels. These will just be connected to the inserts, not integrated into the circuit in anyway, just so they are easy to reach and physically positioned directly under the channels.
Before I have the new faceplates made, I would obviously make sure the modification and extra adapter PCB that will be installed work, and that there is space, also within the frame, so it can be integrated into the faceplate design.

It's not like I'm already sitting here with a hot soldering Iron haha, all of the channels are in a storage box, and I'm casually drawing out the main frame that will hold the modules in illustrator, as far as this is possible without knowing the new dimensions for the faceplates (which is dependant on this mod working out, or not, and where the pots could be fitted).


Cheers,

BL

EDIT: Regarding the backside and the channel output faceplates, I have a bunch of these spare, as well as the panel for the outputs of the master section. The bigger desk I have at my studio came with loads of spare parts basically, seeing the original owner fused two smaller orions together.

 

[abbey road d enfer]

OK, got you. It's not really modding an existing EQ. You want to by-pass the existing midbands and graft a parametric EQ.
You have some choices:
State-variable, like SSL, Urei
Twin-tee, like GML
CAPS, as in Steve Dove's Studio Sound articles
Wien-bridge like Audient
You must make a choice. If someone tells you they all sound the same, don't belive them, but if someone tells you X is the absolute best, he'd better have stronger arguments than "it sounds better".

 

[ruffrecords]

@Abbey, you know these type of circuits much better than I do - in the existing design what determines the Q of the mid bands?

Cheers

Ian

 

[Barrylime]

OK, got you. It's not really modding an existing EQ. You want to by-pass the existing midbands and graft a parametric EQ.
You have some choices:
State-variable, like SSL, Urei
Twin-tee, like GML
CAPS, as in Steve Dove's Studio Sound articles
Wien-bridge like Audient
You must make a choice. If someone tells you they all sound the same, don't belive them, but if someone tells you X is the absolute best, he'd better have stronger arguments than "it sounds better".

Well I don't mean to bypass the existing midbands necessarily, I just want to add a Q width/shape control to the existing 2 bands, using two pots for controls, or one dual concentric pot. I basically want to substitute the pre-set width/shape of the Q of the two midbands with a variable option I can change. Your idea of bypassing the design and inserting a small totally different EQ (if there is space etc., I'd have to figure that out with the new faceplate design), is also pretty cool, and perhaps easier.., although I don't dislike the EQ, I just find it a little bit too much, or little, when I really want to cut or boost something by more than a few DBs. Like when I want to add some oomph to a snare, or crackle to a snare, the boost is often a little bit to narrow, resulting in me not boosting the frequency as much as I'd like to, seeing it's sounds to extreme and focused in a small area. Same for cutting, often I cut too much, for instance annoying resonances or whatever, or mud, it just ends up removing some nice frequencies around the area too because it's not narrow enough. I guess if there was a nice little EQ that fits one a small PCB, and I could remove the current EQ components, that would allow me to insert it instead of the existing EQ, and I could move the existing holes up a little bit to the left, to where the new controls are.

I have put a few lines out at his point, waiting to hear back from some people. Like @ruffrecords, I'd also be interested to know what component(s) determines the shape of the existing set bandwidth. Would it be as simple as changing this component (or components) out for different values in order to get a more narrow or wide boost/cut?

 

[abbey road d enfer]

@Abbey, you know these type of circuits much better than I do - in the existing design what determines the Q of the mid bands?

Cheers

Ian

It's the ratio between the two caps in the modified Wien-bridge. A true Wien-bridge has equal caps and res. Increasing the cap value in the series leg increases "Q" (decreases BW) but also increases Boost/Cut.

 

[abbey road d enfer]

Well I don't mean to bypass the existing midbands necessarily, I just want to add a Q width/shape control to the existing 2 bands, using two pots for controls, or one dual concentric pot.

I'm not that thick. I understand what you want to do, which is akin to turning a Harley-Davidson gearbox into an automatic.

 

[Barrylime]

@abbey road d enfer Okay, understood, in which case bypassing the EQ and replacing it might be a more viable option. (I don't know a lot a bout bikes but I'm assuming your analogy is similar to turning an apple into an orange haha).

 

[ruffrecords]

It's the ratio between the two caps in the modified Wien-bridge. A true Wien-bridge has equal caps and res. Increasing the cap value in the series leg increases "Q" (decreases BW) but also increases Boost/Cut.

So with the caps equal the Q would be one? The cap ratio is now 3 so presumably the Q is 3?

It is not unusual in older EQ designs for the boost/cut to vary with the Q setting (e.g Pultec EQP1A) so maybe a similar compromise might be acceptable to the OP?

Cheers

Ian

 

[Barrylime]

@ruffrecords That sounds like it might be a worthwhile compromise if it it's the easiest way to make it work, obviously I could try this on one module first. The manual states that: ''The HMF (High / Mid Freq.) section has level and frequency controls with varible frequency ranges from 600 Hz to 15,000 Hz and has a maximum boost or cut of 16 dB. The bandwidth has a Q factor of 1.5. The LMF (Low / Mid Freq.) section has level and frequency controls with varible frequency ranges from 40 Hz to 900 Hz and has a maximum boost or cut of 16 dB. The bandwidth has a Q factor of 1.5''.

 

[abbey road d enfer]

So with the caps equal the Q would be one?

Yes.

The cap ratio is now 3 so presumably the Q is 3?

1.732 (sqrt 3)

It is not unusual in older EQ designs for the boost/cut to vary with the Q setting (e.g Pultec EQP1A) so maybe a similar compromise might be acceptable to the OP?

With most EQ topologies (except SVF), the interaction between BW and max cut/boost is absolutely impractical.
For the Wien bridge, all other things being equal, a caps ratio of 1 results in max B/C of 9.5dB, 14dB for a ratio of 2, 17dB for a ratio of 3, and 36dB for a ratio of 30.
The ways to achieve complete independance of Q with B/C are rather complex.

 

[calaverasgrande]

Not familiar with this console at all.
That said, wouldn't it be more conceivable to have a Q width switch than a knob?
If Q is determined by capacitance, perhaps that's an easier approach.
This might leave you with only 2 or 3 choices, but that is still more than you have now.
Also, a toggle type switch is much easier to squeeze into a faceplate that wasn't designed to accommodate an extra knob.

 

[abbey road d enfer]

If Q is determined by capacitance, perhaps that's an easier approach.

Changing the capacitance ratio also changes the boost/cut, so it's not independant. making it independant requires adding a mechanism that varies B/C whilst Q is changed. Easier said than done..

 

[Barrylime]

Changing the capacitance ratio also changes the boost/cut, so it's not independant. making it independant requires adding a mechanism that varies B/C whilst Q is changed. Easier said than done..

I think this all is pointing to (as you already suggested), bypassing the midbands (or not even bypassing them and keeping them the way they are) and having a small new small form factor EQ designed which can fit next to the existing one, for fine/wide adjustments. (Of course with the new wider faceplates, otherwise it wouldn't fit). This is not the EQ I want/need, but something with this small form factor would fit next to the main pcb provided the new wider faceplate can accomodate is.

Of course a custom EQ could be made so the PCB sits parallel and the pots are mounted to the sides, so it doesn't require as much space (unlike the one in the link which is made to fit inside a standard 1u rack unit strip).

https://groupdiy.com/threads/studer-169-961-eq-again-stepped-midrange-4x-in-1ru.63563/

 

[Barrylime]

In fact, given the small size of an EQ like the one above (although again it's not the EQ I'm looking for, but a good example of a tiny form factor design), I could even put it at the bottom of the modules. It would end up being like, you EQ using the stock EQ, then sit back down in your chair, and reconsider your life & EQ choices. Then, you use the in-reach finer EQ for adjustments haha (although that could probably lead to unnecessary boosting/cutting to make up for bad decisions lol).

 

[porkyc]

Mr. Grumpy here.
A. I can't help but feeling the rest of the world would make an outboard EQ if you are going to make anything. How many times at once do you need this capability?

B. You said, " I would love to know how realistic/feasible this mod is."

I would suggest that everyone here has answered your question as to the feasability of this.
ie not much/none!
You cannot easily modify a wien based bandpass filter to switchable/variable Q, the Q is a function of the ratio of the capacitors, as obviously is the frequency range. You also have to pad the input to the wien (with the higher Q) to maintain the +/- range, so the amount of switching that has to take place.................... No thanks!!

C. Having said "none" however, you could do daughter board(s) that replaces the wien with a SVF with switchable Q. The switching is simple (changeover/shorting out of a resistor). This would be a pull-pot on the level pot, (cheaper than on the dual RA frequency pot). 2 dual chips.
The point of the SVF is that the 3 parameters are independent (in theory).
This is how a Nashville based manufacturer did this. You either ordered stock EQ with wien circuits or enhanced EQ with SVF sitting in the same place in the circuit. The inverting pass amps were on the main board, the tuned circuits were on daughter boards.
My2p's worth.