Amek Mozart Neve EQ Topology

[richiyobs]

Attached B.Porter mic amp i was referring...
I'd like to know in wich console i could also Watch at his designs...Cadac? Soundcraft?

 

[abbey road d enfer]

I don't think BP claime the invention of this arrangement.
Graeme Cohen made the "double-balanced" circuit in 1984. I don't think he invented it either. I believe he took the oppotunity of the existence of the LM394 and the TDA1034 to put in practice an earlier idea.

 

[GreyboxAudio]

for some reason the high/low shelf part of the circuit does not seem to work on my pcb... I've tried to build a second circuit on another pcb and made sure to test every component for continuity while building. The Low shelf circuit will just pass audio without any actual equalization and the high shelf goes bonkers. I've set the repository to public and have uploaded the PDF in case someone wants to have a look: https://github.com/greyboxaudio/Purrtico-M/blob/main/Purrtico_M.pdf
Simulating the same circuits in LTspice works fine.

 

[richiyobs]

just simulated your schematic.... RV1 in middle position produces a sort of shelving boost, if i'm not wrong that should be zero gain when in the middle, when its max value is ccw it cuts in bell mode, at max value cw it produces bell boost....

varying RV3 the shelv slope is squared, with a deep resonance....with RV1 in middle position

i practice electronic just for hobby, so don't take it truth, it's what i found running your attached simulation in older post... i wanted to look at that filter response

do you have a schematic, from which you are taking inspiration?
I'm curious since i don't know that particular arrangement for filter section... i saw SVF but with a different arrangement...

https://audioxpress.com/article/audio-electronics-optimizing-variable-frequency-tone-controls

this Self Douglas article helped me to better understand how to mod a semiparametric into shelving, i'm building and studying Harrison eq at the moment.... and i wanted to switch HF section to shelv since that eq originally had only LF bell/shelv

 

[GreyboxAudio]

for some reason the high/low shelf part of the circuit does not seem to work on my pcb... I've tried to build a second circuit on another pcb and made sure to test every component for continuity while building. The Low shelf circuit will just pass audio without any actual equalization and the high shelf goes bonkers. I've set the repository to public and have uploaded the PDF in case someone wants to have a look: https://github.com/greyboxaudio/Purrtico-M/blob/main/Purrtico_M.pdf
Simulating the same circuits in LTspice works fine.

UPDATE: after some more careful debugging I found two small soldering mistakes and now my high-shelf version works! I'll take a closer look at the low-shelf version this week. But at least I can now rule out any manufacturing defects or layout issues.

 

[GreyboxAudio]

just simulated your schematic.... RV1 in middle position produces a sort of shelving boost, if i'm not wrong that should be zero gain when in the middle, when its max value is ccw it cuts in bell mode, at max value cw it produces bell boost....

varying RV3 the shelv slope is squared, with a deep resonance....with RV1 in middle position

i practice electronic just for hobby, so don't take it truth, it's what i found running your attached simulation in older post... i wanted to look at that filter response

do you have a schematic, from which you are taking inspiration?
I'm curious since i don't know that particular arrangement for filter section... i saw SVF but with a different arrangement...

https://audioxpress.com/article/audio-electronics-optimizing-variable-frequency-tone-controls

this Self Douglas article helped me to better understand how to mod a semiparametric into shelving, i'm building and studying Harrison eq at the moment.... and i wanted to switch HF section to shelv since that eq originally had only LF bell/shelv

I have to admit that the schematic is a bit confusing. I've designed the schematic/PCB to allow for both high- and low-shelf to be built from the same PCB which is why not all components are supposed to be populated. I'll make that clearer once the design is ready for prime time. All EQ bands are based on the AMEK MZ-15-RN EQ module (schematics are in the AMEK technical documents topic here in the forum) and I've attached my simulation file.

 

[richiyobs]

it's very difficult to read that Mozart schemo, since eq pots and switches are on different page! must print them on 2 separate pdf
running your simulation, this is also difficult cause your filters section are individual so it's not possible to check their total output, and so their interaction, responses and other stuff to check....
should be cool to have a completed sim to run, otherwise I can complete it on my own so as to understand how this eq works compared to others i'm breadboarding on the bench

best

 

[abbey road d enfer]

it's very difficult to read that Mozart schemo, since eq pots and switches are on different page!

What schemo are you referring to? AFAI can see, those in this thread are all self contained.

running your simulation, this is also difficult cause your filters section are individual so it's not possible to check their total output, and so their interaction, responses and other stuff to check....

Since it's a cascaded design, there is no "interaction" apart from that resulting in cumulating responses.
Any interaction here wouldbe the result of a fault or poor grounding or decoupling.
Parallel Eq's, such as Barry Porter's may interact.

 

[richiyobs]

What schemo are you referring to? AFAI can see, those in this thread are all self contained.

Since it's a cascaded design, there is no "interaction" apart from that resulting in cumulating responses.
Any interaction here wouldbe the result of a fault or poor grounding or decoupling.
Parallel Eq's, such as Barry Porter's may interact.

i was following these 2 part schematic.... just to learn something new about this different SVF arrangement and its bandwidth control

 

[GreyboxAudio]

The sim is technically complete and if you want the signal to pass through each stage sequentially you can connect the output of each stage to the input of the next stage instead. But IIRC my simulation uses a single pair of variables for all 4 simulated gain pots which you would also need to modify accordingly. The filters are SVF biquads (see Figure 4 https://pdfserv.maximintegrated.com/en/an/AN1762.pdf) and I have rearranged the layout in the simulation in accordance. I've also attached my original sim file that I built from the MZ-15-RN schematics. The layout follows the AMEK schematic and I have also added notes which parts correspond to what potentiometer/switch connection in the schematic.

 

[abbey road d enfer]

The sim is technically complete and if you want the signal to pass through each stage sequentially you can connect the output of each stage to the input of the next stage instead. But IIRC my simulation uses a single pair of variables for all 4 simulated gain pots which you would also need to modify accordingly.

This would be easier if you used the potentiometer that's easily usable from LTspice.
For example, you could go there https://groups.io/g/LTspice/filessearch?p=name,,,20,1,0,0&q=potentiometer
and find Baxendall with potentiometers.zip

 

[GreyboxAudio]

This would be easier if you used the potentiometer that's easily usable from LTspice.
For example, you could go there https://groups.io/g/LTspice/filessearch?p=name,,,20,1,0,0&q=potentiometer
and find Baxendall with potentiometers.zip

yes and no. For my own analysis workflow it was easier to just define the resistance values of the two resistors as two global variables that are referenced by all four resistor pairs. If I had used potentiometer models I would still have used a single global variable that is shared by all 4 potentiometers. In that case richiyobs would have had to reset all 4 potentiometers to independent values as well.

 

[abbey road d enfer]

yes and no. For my own analysis workflow it was easier to just define the resistance values of the two resistors as two global variables that are referenced by all four resistor pairs. If I had used potentiometer models I would still have used a single global variable that is shared by all 4 potentiometers. In that case richiyobs would have had to reset all 4 potentiometers to independent values as well.

Each one his own, but I find the potentiometer much easier to step and also closer to a traditional schemo layout.
When I se your .param statements, they are more complicated tah a potentiomter where you just adjust one parameter, without teh risk of enering values that don't match the nominal resistance.
For example, your statement ".param G1=4k7 G2=1" requires changing two values, that's two risks of mistake nad nothing will tell you that ".param G1=4k7 G2=1k" is wrong. Using the potentiometer model prevents errors due to typos or miscalculations.
I've modified your schemo with potentiometer models and .step staements, which, IMO are easire than editing resistor values.
I can step all potentiometers simulaneously if I wish.

 

[GreyboxAudio]

Each one his own, but I find the potentiometer much easier to step and also closer to a traditional schemo layout.
When I se your .param statements, they are more complicated tah a potentiomter where you just adjust one parameter, without teh risk of enering values that don't match the nominal resistance.
For example, your statement ".param G1=4k7 G2=1" requires changing two values, that's two risks of mistake nad nothing will tell you that ".param G1=4k7 G2=1k" is wrong. Using the potentiometer model prevents errors due to typos or miscalculations.
I've modified your schemo with potentiometer models and .step staements, which, IMO are easire than editing resistor values.
I can step all potentiometers simulaneously if I wish.

discrete resistors sound warmer

 

[abbey road d enfer]

discrete resistors sound warmer

Depends what brand/type. I prefer SFER conductive plastic in my simulations.
I tried carbon comp for fixed resistors, but they drift too much.

 

[GreyboxAudio]

Depends what brand/type. I prefer SFER conductive plastic in my simulations.
I tried carbon comp for fixed resistors, but they drift too much.

touché

 

[GreyboxAudio]

PCBs have arrived and I've at least got the parametric mid band correct The shelving filter still needs some de-bugging because I've accidentally wired a potentiometer incorrectly. To keep the BoM a bit more flexible I've assigned simple pin headers as footprints for the potentiometers. However this "Hack" does not work for dual potentiometers because KiCad uses a different numbering scheme for double row pin headers and I forgot to manually edit the footprint of RV4 .

I've now been able to fix the low shelf as well I'll hopefully have the full EQ built by the end of the week and then I'll put it in a 1U case to test the ergonomics.

 

[GreyboxAudio]

Three's a crowd: 1x Purrtico TLA and 2x Purrtico M combined as a complete four band EQ.

 

[GreyboxAudio]

I've tuned the low shelf to basically match the 5033. Now it's only the high shelf that I need to decide how to tune. I feel like the Mozart RN/9098/5033 have comparably steep high shelves and something more gradual, like a 1073 or Siemens W295b where you can boost the high shelf *a lot* and it still sounds natural, would be more useful...

 

[richiyobs]

https://bertomaudio.com/eq-curve-analyzer.html
do you know this other plugin analyzer?