Barry Porter "Net EQ"

[jplebre]

Just wondering what would be the benefit of the lowpass filter (LC) on the input.

only thing I can think of is if it's set to something like 20Hz for mp3 encoding but...

 

[Harpo]

Just wondering what would be the benefit of the lowpass filter (LC) on the input.

Keeping RF out.

only thing I can think of is if it's set to something like 20Hz for mp3 encoding but...

Operating range of this EQ limited between >0Hz ... 20Hz would make this EQ useless.

This is a L/C filter, cutoff is @ 1/(2*PI() * SQRT(L*C)) with L in Henry and C in Farad.
With given values 30uH for the common mode choke and 100pF for the caps, this LFP is set @ 2.9MHz.

 

[jplebre]

Blue is a must! Just to honour the man.... Barry Porter.

Sorry I misread. I confused dagoose post with this picture where there's a low-cut not low pass
disregard

 

[dagoose]

Just wondering what would be the benefit of the lowpass filter (LC) on the input.

Keeping RF out.

only thing I can think of is if it's set to something like 20Hz for mp3 encoding but...

Operating range of this EQ limited between >0Hz ... 20Hz would make this EQ useless.

This is a L/C filter, cutoff is @ 1/(2*PI() * SQRT(L*C)) with L in Henry and C in Farad.
With given values 30uH for the common mode choke and 100pF for the caps, this LFP is set @ 2.9MHz.

Thanks! Didn't really check the frequency myself, i'm bad at math but my guess was something like 100khz. It's way higher then I expected it to be.  8)
Just wondering why the BPEQ has it, and let's say any other EQ doesn't?

 

[skal1]

ok  lads be looking at the porter eq for a whille , i was just wondering how many banks are need for each pot of the eq.

cheers

skal

 

[ruairioflaherty]

it's all in the schematic Skal.  Freq is two deck, level and Q are single deck.

You'll want to build it with switches, not pots.  No need for 24 freqs per band, 12 is plenty. 

 

[skal1]

R , i see it now, p9-a and p9-b is a dual pot yes.

skal

 

[Harpo]

R , i see it now, p9-a and p9-b is a dual pot yes.

..as well as P12a/P12b.
There is also P6a/P6b/P6c and P15a/P15b/P15c. Same pot values, but 3-deck for the peaking or shelfing HF- and LF band.
P3a/P3b wants a rev.log.taper with differing from other pots parts value for the highpass-filter.
When substituting these frequency setting pots with switches, the attached resistors will not be all the same. Just sayin...

 

[ruairioflaherty]

Skal,

If you're considering building this I'd look at simplifying things.  I'm not sure the shelves are necessary and a software HPF will work well for you. 

Cheers,
Ruairi

 

[skal1]

yeah i was thinking that myself ,of ditching  the lf/hf shelf band sections, but that leads me to not having a clue about which frequencies to choose for the peaking bands .

I have seen the prism eq , and that seems to have  lots of frequency chooses , but are they need?


so i thing ithe best thing for me to do is research about the most useable frequency for a mastering eq.



skal

 

[skal1]

harpo if i do not want to use the shelf , could i leave  P6a/P6b/P6c and P15a/P15b/P15c ?, this will make the frequency 2 deck yes.

cheers

skal

 

[Harpo]

harpo if i do not want to use the shelf , could i leave  P6a/P6b/P6c and P15a/P15b/P15c ?, this will make the frequency 2 deck yes.

Keep P6a/P6b and P15a/P15b or substitute with 2 deck switched resistors for the peaking LF and HF bands.
You leave out the parts for the "c" connecting section, IE:
Don't fit C77,C81,C52,C38,D4,K4,LED3,P15c,Q4,R91,R54,R35,R38,R116,S3,U8 and jumper (or switch for band bypass) K4-pins2/3 for leaving out the HF shelf.
Don't fit C79,C80,C45,C37,D3,K3,LED2,P6c,Q3,R78,R50,R34,R36,R103,S2 and jumper (or switch for band bypass) K3-pins2/3 for leaving out the LF shelf.

 

[skal1]

nice mate


skal

 

[ruairioflaherty]

so i thing ithe best thing for me to do is research about the most useable frequency for a mastering eq.

The best thing to do is lots of mastering before committing to something in hardware.  Then you'll know what you need. 

When picking frequencies think in terms of octaves.  I could easily live with 12 steps per band on a 4 band eq if they are spaced correctly.

 

[dirtyhanfri]

Is there any chance to get a layout for this board for home etchers?

BTW nice build protools, and thanks for the uraltone link I didn't know that shop, but looks nice

 

[ruairioflaherty]

The original Porter layout is double sided, not very home etch friendly.  There were gerbers only.

 

[dirtyhanfri]

The original Porter layout is double sided, not very home etch friendly.  There were gerbers only.

Ok, then I will make a order to pcbgrinder, thanks for the info

 

[ruairioflaherty]

No problem, I think Gustav's boards are great value and they have been built by several people without issue.  I spent the late evening studying a 2x4 foot printout of the Porter schemo while sipping 10 year old Laphroaig Cask Strength.  Very enjoyable!

 

[Nescafe]

but FI the law bending 1K5 resistors (R114,115,111,112,...) at the CCW end of the frequency pots will then be one side connected, doing nothing, when the pots get substituted with the switched string of series resistors. The calc sheet is based on listed values in the calc sheet, so if you FI keep the series resistors (R87,61,83,58,..., these are in parallel to prementioned law benders, connecting to virtual ground and 0V reference voltage, and already part of the series string at the switches), the filters center frequency will be different (FI the previous 2kHz-20kHz range would respond for a 1.528kHz-4.896kHz range instead when you keep the 3K6 resistors R61 and R87 instead of using 0Rs/shorts).

Harpo, can You explain more about this?
When keeping (R114,115,111,112) and also (R87,61,83,58) the full CW is right:
1/(2*PI()*SQRT((3600)*22E-08*(3600)*22E-08)) = 20095.32

But I don't understand how to calculate the R value in the middle and in the full CCW 

Thank You.

 

[Harpo]

When keeping (R114,115,111,112) and also (R87,61,83,58) the full CW is right:
1/(2*PI()*SQRT((3600)*22E-08*(3600)*22E-08)) = 20095.32

But I don't understand how to calculate the R value in the middle and in the full CCW 

You are mixing up Barry's schematic and parts values (using a 10k lin pot and 2 resistors in a Wye-config) with my adaption for a single stepped series resistor.
As Barry suggested in his readme file "If reverse log pots are used for the frequency controls, they should be wired in series with the resistors feeding the integrators, and the resistors to ground omitted. The integrator capacitors will need to be re-calculated,..", my Excel files are based on this variable series resitor and re-calculated cap value.
If you want to keep Barry's parts fitted in place and only substitute the 10K lin pot, read on wye-delta transformation to get the needed step values (your '3600' is the simplified minimum result value with the pot in CW position). The needed resistor value still is 1/(2*PI()*freq*C, and keeping Barry's 2n2 cap value, the effective resistor value will be varying between 3600 and 37600 ohm for Barry's range 1924Hz .. 20095Hz.