Fostex 812 mixer mods

A

Aharon

New member
Hi everyone,this is my first post.
After quite a few years idle I'd like to set up a studio again.
I have all the "old" gear,for mixers I have an 01V and a Fostex 812.
I was wondering if the Fostex could be improved by changing opamps,caps etc.Also ,as it is now when you switch the phantom it switches ALL the channels to 24V,maybe I could snip the power wire going to let's say 6 of the channels so I can use condensers and dynamics at the same time.
Does anybody have any experience modding this mixer,is it socket mounted,soldered directly to the PCB etc?
Thanks for any info and help/tips.
Aharon
 
Aharon said:
Hi everyone,this is my first post.
After quite a few years idle I'd like to set up a studio again.
I have all the "old" gear,for mixers I have an 01V and a Fostex 812.
I was wondering if the Fostex could be improved by changing opamps,caps etc.Also ,as it is now when you switch the phantom it switches ALL the channels to 24V,maybe I could snip the power wire going to let's say 6 of the channels so I can use condensers and dynamics at the same time.
Does anybody have any experience modding this mixer,is it socket mounted,soldered directly to the PCB etc?
Thanks for any info and help/tips.
Aharon
Click to expand...

Dynamic mics will not be harmed by the presence of properly implemented phantom power. Are you certain the 812 puts out 24v and not 48?
I don't believe that Fostex used sockets. At least they didn't on my 450-16, the performance of which was greatly improved via a complete IC upgrade.
 
Thanks for posting RRuskin.
The manual states 24V phantom to all channels when turned on,never actually meassured.
Guess I''m in for a treat if I have to desolder the op amps from the board but you say it greatly improved so it will be worth the effort.
It probably has 4580s all over.
Aharon
 
Aharon said:
Thanks for posting RRuskin.
The manual states 24V phantom to all channels when turned on,never actually meassured.
Guess I''m in for a treat if I have to desolder the op amps from the board but you say it greatly improved so it will be worth the effort.
It probably has 4580s all over.
Aharon
Click to expand...

I had all of my original IC's replaced with 5530's. Those units aren't available anymore but they sure made a big difference.
 
812 mods

Wonder if anyone will see this:
I've been messing with channels from my 812 on and off for about 6 mos. mostly off. Replaced the amps with 2134's. Nice. It requires some funky wiring. Bypassed the blocking caps, including the gain setting circuit, so it goes out for a sec when moving the knob but comes back. Scope shows no offset. Actually, be careful. I checked each cap for DC before bridging it, and some showed DC, so I didn't. will probably replace those, along with the phantom power caps. I'm not interested in the whole mixer as it's flimsy and noisy (flourescent display makes a lot of that). I just want to rebox 4 or 6 channels as a small portable mixer.
Today I changed the caps in the high EQ so it would peak at 22k instead of 10k. What's up with that, anyway.... A 10k PEAKING EQ as top end? Blechk.
Now its all "air". I'll have to check the manual sometime to see if it's specked as a shelving or peaking eq. But the scope doesn't lie.
 
more 812

I might add that the Phantom caps ARE 24v.
response is very flat from single digits out past 20k. 3db down at 50k. Of course that's feeding a high-impedance scope. your mileage may vary. Bypassing the old caps cleaned up the square wave response nicely.
 
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