Focusrite ISA430 problem - schematic needed

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electrocutioner

Member
Joined
Jul 1, 2009
Messages
10
Hi,
I'm new here! Hello to everybody!
I found the forum by google searching the Focusrite schematic.
Seems like a paradise of recording audio, here . Thinking for a long time to build a tube mic preamp or a tube DI.
I'm happy that I found the best forum for this kind of projects. Even Gyraf is here and I'm sure that other great guys will be.

At the moment I'm trying to find a Focusrite ISA 430 schem. I searched at the META META but didn't find anything. Does anyone have it?

The problem I have is that the Trim control that provides additional variable gain for MIC and LINE adds noise when you turn it up. Even if the MIC switched control is at low levels... Any help?
 
Hi,

I've only got a small part of the schematic reverse-engineered by someone  ???. But it's only the mic input and output amp. The trim control is probably on a different stage after the mic and line amp. It seems impossible to find the full schematic on the internet.

From your description I would try to replace the opamp that's providing the +-10dB. Probably an ne5532/34

I can mail the first part of the schematic, so you get an idea of which opamp you shouldn't replace :)
 
Hey, I opened the bottom of the chassis and look what I found!!!!
An extra ground wiring! Do you believe that Focusrite done this? Check the el.cap on the corner!

PCB001.jpg


....and I was wondering what is this thick wire that comes from the bottom of the chassis! What do you say? Take it off?
What about the cap?!
 
Never buy a used stuff before opening the chassis and check the inside!
I don't know what the previous owner was trying to do but I'm sure this extra ground wiring and the cap is not from Focusrite! Just look where they solder the ground of the cap!!!
That causes a ground loop and when I turn up the trim a 100Hz hum appeared to the signal. By disconnecting the cap there's no problem with the trim pot.
I'll take off all that weird ground wiring and hope everything will go ok.

audiox, thanks for the mail!
 
whoever did it went thru all the hassle of creating a star grounding config only to put a cap tied up to a different ground.

i bet if the cap is tied to that center point it will work as intended.  Whatever that intention was  ;D
 
Problem solved!
Don't know what the previous owner wanted to do but there were different kind of resistrors at each leg of 48V causing a hum when phantom power was on. Maybe that's why he was trying to solve the problem by adding an extra ground wiring and that cap that was grounded at the chassis!  ???

Thanks for your help and the schematics!

Does anyone have any other schematics for the Focusrite? I have only some parts... I'd like to find all of them to keep them with my Focusrite for future repairs...
 
Hi Everyone,

I'm sorry for dragging up a thread more than 4 months old,
but I badly need this ISA430 schematic as my own one's gone bananas!

I think it might be a grounding problem as hum/noise appears in a couple of places at once.
I'm finding it tricky to follow the layout blind.

Is it possible for someone to send this schematic to me?
Thanks!
 

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