parametric eq front panel

[ppa]

If you are using SVF with grounded inverters, I like to use the frequency pot approach where pot wiper goes full off (to ground) and you shunt the whole thing with a fixed resistor to set LF end, that way you have good fixed resistor tolerance frequency precision at both frequency extremes, and pot is used purely ratio-metrically.

JR

Could  you post a schematic of this circuit, John?
thanks

 

[JohnRoberts]

I don't have a schematic handy but this should be pretty simple to describe.

For a typical SVF where the integrator sections are ground referenced (+ pin to ground). The effective R for setting frequency can be the product of the attenuation of a pot divider to ground, times the nominal resistor value in series with the wiper. Generally such approaches use an end limit resistor in series with the pot ground terminal to establish a LF limit based on a fixed maximum attenuation. However this generally causes a tolerance issue as the bulk resistance of such pots are typically 20% tolerance so this LF will vary a like amount. Instead if we let the pot wiper go all the way to ground, the wiper resistor is multiplied by infinity so pot tolerance is completely removed from the frequency calculation at the LF end. Adding another fixed resistor from the top of the pot to the integrator input now establishes an accurate LF end limit, now limited by that discrete resistor's tolerance so 5% or better. This makes the frequency calculation slightly more complex as this LF resistor is always in circuit parallel with the pot/wiper R but now the frequency pot is as good as the resistor and cap tolerance for both end points, not just the HF end.

I hope this makes sense.

JR

 

[ppa]

I have understood it or I think to have understood it, thanks

At this point I would like to do a question:
I think is a good thing having a good precision on settings, but I have seen many mixing eqs with very poor knobs' ladders and pots. BTW I have seen the mastering eqs have very good precision on settings.

Is so important to have a very good precison on settings in an eq for mixing?

Everything has a cost, a pots selection has a cost, a 3RU chassis costs more than a 2RU chassis, the S&H of a 3RU chassis cost more than for an 2RU one, a 22mm knobs costs more than a 12mm one...ect.....

If no, Why paying for a thing not so important? (if it is not important)

 

[Gold]

I don't think there is an answer to your question. You'd have to have a sense of who the customer is. The only thing I would say is that I think gain matching is more important than frequency matching. I think the reason the Millenia Media EQ gets used in mastering is because you can select a big or small gain range. The GML 8200 with pots has the poor matching you would expect. Since the gain range is +/- 15dB (or 18, I forget) you can't match the sides easily for low gain stuff like in mastering. They sell more of those than the 9500's with switches at about twice the price.

 

[ppa]

I don't think there is an answer to your question. You'd have to have a sense of who the customer is. The only thing I would say is that I think gain matching is more important than frequency matching. I think the reason the Millenia Media EQ gets used in mastering is because you can select a big or small gain range. The GML 8200 with pots has the poor matching you would expect. Since the gain range is +/- 15dB (or 18, I forget) you can't match the sides easily for low gain stuff like in mastering. They sell more of those than the 9500's with switches at about twice the price.

thanks,

but the Millenia Media EQ sold for mastering eq is the standard version with pots?

In my eq is easy to insert a gain switch , I think two ranges: I have 14 dB for full gain mode.
Is 6 dB good for reduced gain mode?


 

 

[Gold]

but the Millenia Media EQ sold for mastering eq is the standard version with pots?

In my eq is easy to insert a gain switch , I think two ranges: I have 14 dB for full gain mode.
Is 6 dB good for reduced gain mode?

The mastering version of the MM uses stepped pots, not switches. The advantage is debatable.

I think +/- 6dB is a nice range for mastering. The EQ's I'm building are +/- 3dB but if I was making a commercial product I wouldn't do that.

 

[ruairioflaherty]

but the Millenia Media EQ sold for mastering eq is the standard version with pots?

In my eq is easy to insert a gain switch , I think two ranges: I have 14 dB for full gain mode.
Is 6 dB good for reduced gain mode?

The mastering version of the MM uses stepped pots, not switches. The advantage is debatable.

I think +/- 6dB is a nice range for mastering. The EQ's I'm building are +/- 3dB but if I was making a commercial product I wouldn't do that.

+/- 6dB is perfect for mastering.  I've used +8 once ever on my Maselec and when you're going that far a plug in will do just fine!

I strongly dislike stepped pots, there are usually too many steps making recall a painful process of counting 30 odd clicks.  I'd rather normal pots than stepped pots.

 

[ppa]

ok for 6dB for the reduced gain mode,

but for the mastering version should I use  rotary switches?

 

[ppa]

moreover,

could the PSU be external?

 

[Gold]

In my book a mastering EQ is switched. Plenty of people disagree. Lots of mastering engineers use the Massive Passive with pots. I think a pot with a 6dB range would be good enough for channel matching and recall. For better accuracy with a pot you could do a boost/cut switch so the pot only covers 3dB. I personally don't like having to use a boost cut switch but it's an option.

I think mastering engineers would like an external power supply because it's cool and theoretically quieter. Everyone else will hate it. Sure does make international sales easier.

 

[mata_haze]

+1 for External PSU and stepped controls.

Best,
Mattia.

 

[ppa]

I have seen that Massemburg mastering eq has +-6dB of max gain, so my mastering version will have 23 positions rotary switches for gain and center frequency settings, for Q setting (my eq goes from  .4 to 4 ) I will use a 12 positions switch.
There is a switch on front panel for the shelving option, my eq use the same cell for the shelving mode too. In the shelving mode the cell has linear phase to be more trasparent possible.
 

 

[ruairioflaherty]

It sounds like an interesting product! Can you tell us any more about the circuit.  You mentioned that it's state variable.  Did you include a hi pass filter?  Transformer or solid state i/o?

 

[ppa]

my eq's main features are the following:

- parallel cells eq

- cells based on SVF

- passive summing of the cells instead of the active summing used in sontec type eqs (sontec, massemburg, maselec...etc..)
 
- shelving mode done by the same cells, linear phase in shelving mode.

- DOA's in the mainboard and IC opamps in the cells.

- no electrolytic caps in the signal path

- trasformerlerss inputs and outputs.

 

[ruairioflaherty]

It sounds like a really interesting design!  Will this be a commercial product or a DIY kit?

 

[ppa]

It sounds like a really interesting design!  Will this be a commercial product or a DIY kit?

I have not thought it as diy product but first all I should make two for me and test them (mixing version the first and for mastering the second).
I have two italian studios interested to build it, so if there other studios interested (group diy member only) I could do a group buy.     

 

[mata_haze]

you can count me in for the mastering one!!


Mattia.