Am I reading this schematic correctly?

[pucho812]

This is part of a mic pre, it’s the input section.
Looking at how it is drawn am I correct in thinking that pins 1 and 3 are the primaries of the mic input transformer? And that pins 2 and 4 are the secondaries? They also appear to have a 1k resistor between primary and secondary connection…

 

[Gus]

Think common mode

 

[JohnRoberts]

rf choke for reducing RFI....

JR

 

[Brian Roth]

That is a (common mode?) filter for some sort of noise reduction. Note it is marked as "L1" hence an inductor.

OOPS...I'm late to the party....thought I had posted reply half hour ago!

Bri "remember to click Post Reply"

 

[Brian Roth]

@pucho812 ....You must be looking at an Amek diagram. In my files I have the schemos for a 9098i desk and it also has an L1 marked as VT30972.

Bri

 

[Tubetec]

These type CM inductors are in the Amek BC3 also , might have been Ruperts idea .

 

[Brian Roth]

Mic preamp schemo from the older "original" Anek 9098 desk (split vs inline).

Bri

 

[electrog]

https://groupdiy.com/threads/amek-neve-9098-9098i-query.4317/

 

[zamproject]

These type CM inductors are in the Amek BC3 also , might have been Ruperts idea .

Not sure it's a -Rupert- idea, hopefully he didn't invent everything
I see this RF filter in most Studer mic in, broadcast specification request this I suppose, like the BC3.
I suppose back then, when operating radio program from field, control room in the truck with the transmiter antena on the roof of it, you better have a good HF filter ?

 

[JohnRoberts]

Not sure it's a -Rupert- idea, hopefully he didn't invent everything
I see this RF filter in most Studer mic in, broadcast specification request this I suppose, like the BC3.
I suppose back then, when operating radio program from field, control room in the truck with the transmiter antena on the roof of it, you better have a good HF filter ?

the ancients are always stealing our new ideas...

JR

 

[pucho812]

Thanks guys, that explains it all.
Love this place, such knowledgeable folk

 

[FIX]

The choke helps with RF and CE regulations, as well as simulates a little transformer like "boing" as if it were a transformer.

 

[amplexus]

i've got a big 32ch frame BC3 and I immediately recognized this from the thumbnail... I think i've been in that desk too much.

 

[HP200CD]

I've not seen anything like this before. To cancel common mode noise, then the two windings must be out of phase, and the 1K resistors must be matched, right?

 

[ccaudle]

I see this RF filter in most Studer mic in

My understanding is that EBU equipmement requirements mandated immunity to high RF levels, so you will see similar in anything sold for broadcast use in Europe.

 

[Tubetec]

It was explained , the choke is bi-fi wound with the windings connected in reverse so HF mush is neutralised ,
I dont see why a lower current off the shelf common mode inductor ,wired correctly wont do,

Were in an increasingly hostile environment as far as HF is concerned ,these measures make a lot of sense in new designs,

Having to tweak the neutralising networks with a scope across the stages of each channel in a big console PITA ,

I have the 24 bay BC3 , fully loaded you could cook eggs on it after prolonged power up ,
I might swap out alternate channels for blanking panels to see if it runs without fever .

 

[amplexus]

It was explained , the choke is bi-fi wound with the windings connected in reverse so HF mush is neutralised ,
I dont see why a lower current off the shelf common mode inductor ,wired correctly wont do,

Were in an increasingly hostile environment as far as HF is concerned ,these measures make a lot of sense in new designs,

Having to tweak the neutralising networks with a scope across the stages of each channel in a big console PITA ,

I have the 24 bay BC3 , fully loaded you could cook eggs on it after prolonged power up ,
I might swap out alternate channels for blanking panels to see if it runs without fever .

I put fans in the armrests of mine connected to a temp dependant speed controller. Made a world of difference and almost silent!