Barry Porter "Net EQ"

[frazzman]

I know man.... But my backwards logic is that I don't want to bust my chops on these monster 6 pole switches if the main board is cooked

I've checked all the -/+ 18v on the opamp sockets... Can you recall if there any other docs that reference other voltages on the board ? Otherwise I might have to unrack my dual mono unit and start comparing.

With no switches and pots, you have open input pins on quite a few opamps. I would have made sure to analyse the circuit or at put in dummy loads if it was beyond my capability. If nothing else, just to make sure I wouldn't be driving an opamp death somewhere

Looking at the schematic on the bands, I am having a hard time figuring out how  you are passing audio at all with no switches or pots installed, but I am not a wizard

Your safe bet is to apply the dummy resistors as Ruairi suggested, if you want to see how it behaves before wasting time doing switches and pots.


Gustav

Hi Gustav,

Yes, you a right. I think it's my methodology which is a bit nonsensical. I did build one unit successfully with a few hiccups along the way.

I guess my aim was to tackle it in blocks but realistically that's not a very logical approach. I could easily sub in resistors as dummy pots, I probably should have considered that earlier.
Anyhow thanks for the feedback. It's onto the switches now.  This is an epic build, it's easy to want to try to dissect it into logical stages.

 

[druu]

I had some boards made up and if anyone is interested, I have three sets left over. Asking AUD$70/set (2) plus shipping/paypal. They are blue in colour.

Image here. Please email (click my username > Email) as my PM box is almost full, cheers.

 

[Unit-8]

After working in stealth mode all the time on it, I show you what I got.
But first of all I want to say thanks to Gustav to have provided the main PCBs, PSU PCB and for his valuable tips, Harpo for his own fantastic excel sheets and lots of useful informations, as well as to say thanks all those who have built this EQ before me and that have given many good ideas and solutions for its build. And last but not least, thanks to Barry Porter father of this terrific design which is passed to a better life some years ago. R.I.P.
And now some pics... Ok just one

 

[Unit-8]

Another one?

 

[Unit-8]

...and last one.

 

[Gustav]

...and last one.

What a great looking cable layout!

Gustav

 

[petermontg]

Not running short on the old Marlboro.... ;D

Tidy build.

 

[Unit-8]

Yeah it's true! But all Marlboro cans you see are already empty... unfortunately  :-\

 

[Vac11]

Hello,

can sombody explain me - how can I proper recalculate the Q value to 0,7 - 1 - 1,5 - 2 - 3 - 4 and gain value to +- 0,25 - 0,5 - 0,75 - 1 - 1,5 - 2 - 2,5 - 3 - 4 - 6 - 9?

Eventually how can I do a switch between the maximum amplitude (on +- gain switch with 20x 499R ) from 5 to 10 dB (0.5 vs. 1 db steps steps)? Would it be enough to make a separate switchable PCB with alternative values of R77,82,86,90 changed to 2K37 resistor?

Harpo´s excel sheet are very useful and clear (thank to Harpo!!!), but this not explain complexly...

Thx

M.

 

[Gustav]

like to share my version of the porter eq with you... unit has 6 bands now, first and last switchable to shelf by last q-position. all stepped with chiefdom switches. i did my own pcb with single band operation amplifier and also space for 2520 footprint.

Beautiful work.

Gustav

 

[G-Sun]

like to share my version of the porter eq with you... unit has 6 bands now, first and last switchable to shelf by last q-position. all stepped with chiefdom switches. i did my own pcb with single band operation amplifier and also space for 2520 footprint.

Yes, very nice looking indeed.
This is for mastering-use?
How does it sound/ work for you?
Pics of inside?

 

[AD797]

Hello!

I am very close to finish my build and need to say: this thread is soo usefull! Thanx to all.
And now my question: i plan to do my last band up to 25k. Is there a limit/filter at the board? Or just calculate the switch and all is fine?

Thank you!

 

[Harpo]

Welcome.
Replace the 20000 Hz value with 25000 in both peaking and shelfing calculation sections. Resulting recalculated resistive load of the driving circuit when keeping corresponding caps values seem still within NE5532s parts limits.

 

[AD797]

Thank you Harpo! Youre calculation is great by the way. But i have a question regarding it... would it possible to do the chart with wish frequency´s and q´s? Or is there a way to do it anyway?

 

[AD797]

ok, now i am at a point where i need some help.  :

i don´t own a oscilloscope but need to do the in/out balance.
would it be possible to replace the input section by a that 1206 and the output section by a that 1646? At which point of the circuit should i connect the out of the 1206 and at with point should i connect the in of the 1646? has someone experience here?

thank you!

 

[Gustav]

ok, now i am at a point where i need some help.  :

i don´t own a oscilloscope but need to do the in/out balance.
would it be possible to replace the input section by a that 1206 and the output section by a that 1646? At which point of the circuit should i connect the out of the 1206 and at with point should i connect the in of the 1646? has someone experience here?

thank you!

Do you still need help with this?

Gustav

 

[Gustav]

I am redrawing the schematic in Eagle (I'll share the Eagle file when I am done with a first draft).

1.The values of the bipolar caps seem excessive throughout  (and needlessly bipolar?). Also, I can't see why C7 is even there. Am I missing something obvious?

2.I dont understand the transistor in the relay switching supply. As far as I can tell, it works as a current amplifier, but if thats it, I am guessing its there to limit current in the supply rail until the short distance from the transistor to the relay in the board design.

I found the current draw for the relays I use to be  very modest, so I have a really hard time figuring out how and why this is beneficial. I'm tempted to scrap the transistors and supply the 12V direct.

3. In and output seems like a design aimed at better-than-usual /best-possible CMR. Like the second last poster, Im leaning towards replacing this with a 120x/164x combo with no needed trimming.

Any input?

Gustav

 

[Majestic12]

I am redrawing the schematic in Eagle (I'll share the Eagle file when I am done with a first draft).

1.The values of the bipolar caps seem excessive throughout  (and needlessly bipolar?). Also, I can't see why C7 is even there. Am I missing something obvious?

2.I dont understand the transistor in the relay switching supply. As far as I can tell, it works as a current amplifier, but if thats it, I am guessing its there to limit current in the supply rail until the short distance from the transistor to the relay in the board design.

I found the current draw for the relays I use to be  very modest, so I have a really hard time figuring out how and why this is beneficial. I'm tempted to scrap the transistors and supply the 12V direct.

3. In and output seems like a design aimed at better-than-usual /best-possible CMR. Like the second last poster, Im leaning towards replacing this with a 120x/164x combo with no needed trimming.

Any input?

Gustav

1. The value of the caps is indeed a bit high... lower values would work as well. Mr. B.P. was probably a bit paranoid about DC offset and phase shifting.

2. The transistor switching of the relais comes from good mixing desk design. It's better to have only a small switching voltage running through some distance of a mixing desk instead of a much higher current when switching the relais directly.
In mixing desks there is also the possibility of having some sort of logic  chips behind the switch functions which need to have a transistor as a relais driver.

3. THAT 1XXX series chips as in and output work just fine. I already did this in a prototype channel of the BP and it can easily replace the complete circuit blocks without any noticable change in sound.

You have to keep in mind that this EQ was designed to be used in a mixing desk, so some of design decicions where surely due to that.

 

[Gustav]

Thanks for covering it all, M.

On this point...

1. The value of the caps is indeed a bit high...

Unless theres something I am not incorporating for total R in RC calculations, I am seeing slots where even a 6,8uF poly would be plenty high, but of course, I am not considering  the DC offset and phase shifting mentioned.

I'll finish up drawing it and keep the bipolar caps for now.

When the porting of the existing circuit is done, I want to experiment with digital potentiometers and a little programming.

Gustav

 

[Gustav]

Last question before finishing up the first draft.

I attached a portion of the schematic


Is this correct?

RC filter (R73, C71), then a voltage divider (R71, R72), followed by a non inverting opamp (U12), functioning as a unit gain buffer?

In case it is correct - is the opamps input impedance affected by R73? I realise it wouldn't make much difference, being parallel to R71, but I am curious.

Gustav