1073 HPF question..

[Redtns]

Hi all, 

I'm wanting to add HPF's to some of my old mic amps, and figured I'd try the switchable 1073 (B182) inductor circuit. I was just looking at the schematic, obviously dead simple, but I was naturally puzzled nonetheless! I've hopefully attached the drawing I'm talking about. If not, the 9th page here: https://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

The dotted line on the original Neve schematic surrounding the caps and inductor (but not the switch) - what does this represent/mean? Not a big deal, but I've not seen it anywhere else and was curious as to what the thinking was here?

The ten caps shown - what units are they showing? What does "0.47" mean? It's the only part on the whole schematic without this information..

I'm sure these are stupid questions,  but if you don't ask you can't learn!

Thanks!

R

 

[warpie]

The cards maybe?

 

[L´Andratté]

Yes, dotted lines indicate what is on which card and what is wired offboard.
Capacitors without units are usually (but not always) in uF, which would make sense in this case, like

0.47 = 0.47uF = 470nF.

 

[dmp]

I added the Neve HPF to a pair of preamps I built. It's a sharper rolloff than a R-C HPF. You can see them here mounted with the board up, inductor down.
I don't remember where I got the little PCBs for them but you wouldn't really need them.

https://groupdiy.com/index.php?topic=22828.msg661370#msg661370

The capacitor values, C, are indeed in microFarads. The inductor values, L, are in Henries.
The corner Frequency of the 12dB/octave rolloff = 1/(4*pi*sqrt(L*C) 
Where L is in Henries and C is in Farads.
The bottom connection on the inductor should be audio ground (labeled E,R and B-)

 

[PRR]

> caps shown - what units are they showing? What does "0.47" mean?

Can't be Farad-- in 1971 a half-Farad cap would be the size of a trashcan.

Can't be picoFarad-- an inch of wire is more than a half pF.

Nano is very dubious because not in wide use in 1971.

There is another clue. The top of the coil is marked "10H" and is fed by a "1.0" cap. Assume "1uFd", with 10 Henry that makes 50.2 Hz, which is a very likely lowest-step on an audio bass-cut.

 

[ruffrecords]

Just a note to say the response should be 18dB/octave. There are three zeros in the circuit, two due to the caps and one due to the inductor.

Cheers

Ian

 

[abbey road d enfer]

Note that proper response is achieved with proper source and load impedance. The input is driven by 1.2k and the output should be loaded with approximately same.