Calrec PQ 1061

[TomWaterman]

Nice one Peter.

Care to share your workings? I got lost trying to figure it out.

-Tom

 

[peterc]

Hi Tom

At the resonant point, the impedance of the cap is equal to the impedance of the coil. In proper terms, the capacitive reactance is equal to the inductive reactance (it's been a while, my terms might be a bit rusty... :? )

So we have Xc = Xl

Xc = 1/(2.pi.f.C)
Xl = 2.pi.f.L

So 1/(2.pi.f.C) = 2.pi.f.L

Solve for L

Regards
Peter

 

[TomWaterman]

Thanks Peter.

The thing that confuses me is the 1061 circuit. If you look at it, the cap is in parallel with the inductor right? not only that but all of the filter caps C23-30 are in parallel with the selected cap via 10meg resistors.

So what effect do they have on the filter type. Is this a standard RCL filter or is it something more exotic. I was trying to find a filter that matched in the sound engineers handbook but got lost with all the parallel parts in the 1061.

Any thoughts?

-Tom

 

[gyraf]

The 10M resistors are there only to suppress clicks when switching (by providing the capacitors with a discharhe path)

Jakob E.

 

[TomWaterman]

Ah ha!

That makes perfect sense Jakob! Thanks.

-Tom

 

[peterc]

When the particular cap is selected, that 10M resistor is shorted out. A 10M resistor in series with a cap is virtually an open cct in this application.

Peter

 

[TomWaterman]

Thanks for the extra info Peter.

just thought I'd bump this again incase Kevin got his PCB sorted....

-Tom

 

[kevina]

Tom et al

sorry guys running late.had a couple consoles come in toasted that need to be back on the road tommorrow.

kevin

 

[cannikin]

I'm on the edge of my chair.. :grin:

Take your time Kev :wink: :guinness: :guinness:

 

[peterc]

For those who want to wind their own inductor for the project, I've done all the calculations & found a suitable part for this. I'm going to wind one this weekend & see how it turns out (no pun intended..... :? )

EDIT:
See post about 4 down from here.


Peter

 

[TomWaterman]

Peter, do you reckon there would be any way in which a suitable MF eq could be based around the sowter neve inductor....just thinking about off the shelf solutions for DIY builds.

9805 Neve T1230 2/1.2/0.7 H 75/58/44 ohms

Only three taps but could that be increased to make a 6 position MF eq by just changing cap values and still be useful?

-Tom

 

[peterc]

Hi Tom

There is a reason for the large inductances involved.

You could get the correct frequencies by changing the caps proportionately, but the Q (bandwidth) of the EQ would change. Hence, so would the sound....

I've included all winding the details for the avid DIY-er! I'm going to try one of these soon using an MMG RM12 core (F44 material).

Regards
Peter

 

[peterc]

OK, the bug bit, so I wound a coil using .25 mm dia wire on an RM 12 core. I could only get enough wire on for the first 4 taps, up to 2.4H. I'll try another with some .16 wire I have sometime.

At the 2.4H tap the DC resistance is 16ohms. So the Q at 1Khz is 942 (Xl/R). I think that is pretty good AFAIK??? Please correct me if I'm wrong.


Peter

 

[peterc]

New coil today. Used .16mm wire on the same core (RM12) & it worked fine, space to spare. Q for the 3.5H section was 540.

Peter

 

[kevina]

also if you look at the schematic there is a jumpered resistor in parrallel with the coil to adjust "Q" I cant imagine diyers are not gonna bring that out to the panel as a switch and putter with values

kevin

 

[TomWaterman]

Thats great work Peter! Sorry for ignoring your handy work - just been wrapping up my final week at uni - can't believe I'm finished.

Looking forward to seeing how that indictor will turn out in circuit.

Is it easy to purchase lams etc for DIY chokes in small quantities - would it be worthwhile having a load made at either Cinemag or Sowter or can everyone build inductors of suitable performance for less cost etc?

Do you think you have the right values for the 1061 circuit now?

-Tom

 

[peterc]

According to the simulator, the values are spot on. I managed to get the winding to within about 7% worst case.

Is it easy to purchase lams etc for DIY chokes in small quantities

The kinds of core assemblies used by Neve & others for these types of coils are available from Mouser/Farnell/RS et al.

would it be worthwhile having a load made at either Cinemag or Sowter

One of my reasons for winding my own cores is the cost of a Sowter for example. If the Neve coil is 34 UK pounds, this makes the project a non starter for me. The exchange rate is way too high.

Peter

 

[chrissugar]

Peter,

Can you give us more details about the RM12 core?
What AL it has? I suppose it is ungaped. In the Farnell, RS, Distrelec, Elfa catalogs you can find similar cores from different manufacturers, can you suggest a specific model?

chrissugar

 

[peterc]

Chris

I used a core from MMG-Neosid made from F44 material 29-940-47.
http://www.neosidcanada.com/fercor/cores/rmcor.htm

The equivalent part from Farnell looks like this one: 305-6855

RS have an MMG RM10 which is what I wanted to use originally but be careful of the wire thickness : 29-850-44

Al is in the 4000 region.

Peter

 

[TomWaterman]

Cheers Peter - its good to know.

How do you think your choke will sound?

I was looking around for Steffen's inductor winding page page but couldn't find a working link. Anyone know if its been removed from the web?

-Tom