Ibanez - PQL Parametric EQ

Dirk_Hendrik · Post by **Dirk_Hendrik** » 06 Mar 2008, 08:42

And, while drawing the thing I wondered about the fact that this was the last Parametric EQ pedal that Ibanez issued. No more in the 10, 5 and 7 series

nevertheless,
The Ibanez PQL Parametric EQ's schematic now ready for download:
http://www.dirk-hendrik.com/ibanez_pql.pdf

analogguru · Post by **analogguru** » 06 Mar 2008, 09:11

Thanks for the schematic.... but.... hmmmm... how should I say that ?

- Are you sure about the values of R2, R3 and C2 ? 10n with 470 Ohm ?
- Cx1 and Cx2 have 22n ? normally between 220p and max 1n ?
- the configuration of R46, R48 and C19 looks a little bit uncommon, "doubtful"

analogguru

Dirk_Hendrik · Post by **Dirk_Hendrik** » 06 Mar 2008, 10:08

In the CX's you may very well be right. I'll recheck the other 2 for certainty since you mention em..... but spent quite some on those spots already..

estragon · Post by **estragon** » 06 Mar 2008, 11:36

Cool! Interesting circuit. Reminds me that Boss PQ-4 surfaced a few weeks ago also.

Another oddity in the schem is that the first stage (U1.B) has a high frequency pre-emphasis that adds more than 20 dB between 3 kHz and 30 kHz. If you follow the bypass route via C8, Q2, C9, R18, U1.A, there is no de-emphasis counterpart!

The Bass control section looks odd, but the network is rather complicated to evaluate without a simulation. Maybe it does work, but in a way seems to be entangled with the High network.

Supafuzz · Post by **Supafuzz** » 06 Mar 2008, 12:18

estragon wrote:Cool! Interesting circuit. Reminds me that Boss PQ-4 surfaced a few weeks ago also.

Another oddity in the schem is that the first stage (U1.B) has a high frequency pre-emphasis that adds more than 20 dB between 3 kHz and 30 kHz. If you follow the bypass route via C8, Q2, C9, R18, U1.A, there is no de-emphasis counterpart!

C2 should be 10uF

The Bass control section looks odd, but the network is rather complicated to evaluate without a simulation. Maybe it does work, but in a way seems to be entangled with the High network.

Looks like an attempt to make bass eq peaking instead of shelving, as you said, a quick sim should show wtfigo there. Mid EQ pretty run off the mill standard with its inherent shortcomings. To be fair, it's not supposed to be studio EQ.

Dirk_Hendrik · Post by **Dirk_Hendrik** » 06 Mar 2008, 15:23

Supafuzz wrote: C2 should be 10uF

And is 10n

Seems like I'll have to shoot a couple of photo's to keep te "doubters" satisfied.

Supafuzz · Post by **Supafuzz** » 06 Mar 2008, 15:54

Dirk_Hendrik wrote:
Supafuzz wrote: C2 should be 10uF
And is 10n

Weird, weirder, what's weirdest?

Dirk_Hendrik · Post by **Dirk_Hendrik** » 07 Mar 2008, 09:46

OK, Please click that link again. I've made a few updates of "misreadings" (some stupid), and simulated the whole thing to determine if the performance and functionality was as one would expect.

As for the input stage, I have to stick with that 10n cap and 470 ohm config.

As for the question what is the weirdest... well in my simulations that is that when I push the mid level contol to max boost it will start to act as a 14db cut again. Only when I go to a 7k/43k setting and lower to 25k/25k it will act as a booster.

analogguru · Post by **analogguru** » 08 Mar 2008, 17:38

R19/C10 is suspicious too since it will not have any influence - except for tone-"experts" - as shown...

analogguru

Supafuzz · Post by **Supafuzz** » 08 Mar 2008, 21:27

analogguru wrote:R19/C10 is suspicious too since it will not have any influence - except for tone-"experts" - as shown...

analogguru

R19 has been changed on the schematic to 470R so C10, R18 & R19 provide de-emphasis for the >1kHz emphasis in the input opamp but leaves a nice peak at ca 40kHz . Ok, so it's meant to act like a brute force hf noise suppression (it works better with dynamic processors than EQa). Preemphasis + EQ treble boost with these low grade opamps....drive the treble EQ into clipping and with the 40kHz peak you'll be adding britghtening intermodulation products - you just got yourself "I wanna be an aural exciter but I'll be damn if I know wtf an exciter is except for the blue pills beginning with a V".

analogguru · Post by **analogguru** » 08 Mar 2008, 21:54

R19 has been changed on the schematic to 470R

Thanks for the info... the last i downloaded was with 510k for R19.
The complete circuit appears to me a little bit "brutal".

analogguru

DimebuGG · Post by **DimebuGG** » 03 Sep 2008, 04:46

Hi

I draw my own layout and tested it and it works(minus the FET switching).

Although i'm quite unsure if this schematic is correct upon reading the previous posts. I don't know either know how the original sound.

So, how are VR4 and VR5 wired?

-I wired VR4 and VR5(these are dual gang, right?) this way:

VR4 VR5
a: 3,2 1 a: 3 2,1(connected)
b: 3,2 1 b: 3 2,1(connected)

Is this correct?

Ibanez - PQL Parametric EQ [schematic]