jhaible

Neve 1073 inductor questions
« on: September 20, 2004, 05:24:56 AM »
Hi,

I've been analysing some parts of the Neve 1073 circuit over the weekend.

Now I have two questions about the Presence circuit, and the inductors that are used there.

(1) Why are there 2 seperate inductors? The T1530 is tapped already to
     make different L values available. Why not just add another tap
     instead of using the separate 200mH choke?

(2) For the lower frequency bands, L's _and_ C's are switched.
     This results in a fairly constant Q for the different (lower)
     frequency bands. On the upper bands, however, only the C's
     are switched, and the inductance is left constant. This results
     in an increasing Q with increasing center frequency.
     Why have they chosen this behaviour? (Without full parametric
     control, you always have to choose - so I'm basically asking
     about the musical background for such a decision.)

JH.


Tekay

Neve 1073 inductor questions
« Reply #1 on: September 20, 2004, 10:07:54 AM »
Hi JH!
Carnhill makes a custom version with a 200mH tap instead of the 220mH!
Part no VTB1952.
For the higher freq's you can calculate the caps for the two extra taps to get higher Q! Or through in the Hi Q switch which is standard on the 1084 and 33102 moduls Think it's a 7k5 switched in over the 2k7 resistor on the BA211 board!
Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se

jhaible

Neve 1073 inductor questions
« Reply #2 on: September 21, 2004, 09:24:39 AM »
Quote from: "Tekay"
Hi JH!
Carnhill makes a custom version with a 200mH tap instead of the 220mH!
Part no VTB1952.
For the higher freq's you can calculate the caps for the two extra taps to get higher Q! Or through in the Hi Q switch which is standard on the 1084 and 33102 moduls Think it's a 7k5 switched in over the 2k7 resistor on the BA211 board!


Hi Thomas!

Actually my question was mainly about the philosophy behind the choice of Q as it is, not about how to change it. But the additional info is welcome, too!

Thanks,

JH.

Tekay

Neve 1073 inductor questions
« Reply #3 on: September 21, 2004, 01:44:18 PM »
Ok!
Understand what you mean! To make the Q constant you have to change both the C and L.  "C" sets the highpass and "L" the lowpass.

Another thing is what Neve call Hi Q! If you push the Hi Q switch and lower the boost a little you'll land on almost the same curve as if you turn the control all the way up with out pushing the Hi Q!
Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se

gyraf

Neve 1073 inductor questions
« Reply #4 on: September 21, 2004, 01:59:15 PM »
Actually, the way "Q" changes with frequency when switching C's alone (within reason) sounds quite nice subjectively..

Splitting the inductor in two may have to do with lessening stray capacitance from the auto-transformer effect in the inductor. I've had similar problems in my G14 eq..

Jakob E.
..note to self: don't let Harman run your company..

jhaible

Neve 1073 inductor questions
« Reply #5 on: September 21, 2004, 06:31:57 PM »
Here's something which might be a very stupid idea to avoid these big inductance values, and use components from OEP and TOKO instead, which I can get within 24 hours. Look at this and tell me how crazy it is!
(;->)

http://www.oldcrows.net/~jhaible/neve/jh_neve_presence_inductor_idea.pdf

If it doesn't work, I can still use the transformer for other projects, so I guess I'll give it a try. I have carefully made transformations of the parasitic resistance of all components, and thus decreased the original 2k7 value that goes to the amp input summing node to 910 Ohms.
The signal level should just be ok for these components, too.
I have no idea of stray inductance and parasitic capacitance effects in this, though.

What do the experts think?

JH.


 

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