adr compex transformers

hey there,
i have an old compex compressor from a helios desk here. id like to balance it. im pretty sure its just a 10k:10k on input and 600:600 on output. now my actual question is this: will i have to re-calibrate the unit when adding balanced lines? i remember calibration being terrible on these.... cheers

The i/o levels are the same since the transformers are 1:1 ratio.

thanks mate. should have known this myself....

In the AD&R docs for the F600/F700/F760 it shows 10k:10k input and a 600:600 wired in step up (1:4) on output - but in mine i have 1:1 - 600:600's  (BBC LL88's) on input and output and it works great. I think the thing to watch out if going the 600:600 route is for some ringing or resonance  from the 600Ω driving the 10kΩ input of the Compex.

One thing i can say tho, specifically in regards to the 760-RS is that the circuit/power supply common is not connected to the chassis - so in and out pin 1's are tied to chassis, which is referenced to the 3rd wire ground - but in a transformer coupled device this sometimes causes noise issues - in my studio I had to run a wire out to a biding post on the back of the chassis from the 0V point in the power supply to reference the ground plane of my console - after that, the device is really pretty decent in regards to signal to noise...

as for the calibration changing - it shouldn't - there will be some insertion loss maybe - but that shouldn't be an issue...

post some pictures when you get it done - i love those console Compex's!

hey,
i need to bump this. its all pretty much done. but im unsure about a zobel network on the output transformers. im not too good with stuff like that. im using the ll/88asc on outputs (600:600). also wondering if i should terminate the outputs with a 600 ohm resistor. thanks a lot!

And here is a pic for mutterd. I dont have a proper camer plus i can not flip it around right now. Ill post a Front pic once its done. Anyone able to help with the zobel network?

Some more

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in his build collin used a 1.5k and 10nf for zobel. but he uses carnhill transformers. would these values work for me as well?

You need to suss out the right values for you're particular transformers.  Colins values might work, but, they might not....  If you do a search on zobel networks you will find info on how to determine the network. 

Rob Flinn said:

You need to suss out the right values for you're particular transformers.  Colins values might work, but, they might not....  If you do a search on zobel networks you will find info on how to determine the network.

Click to expand...

thanks Rob,
i think im maybe too dumb then. im really bad with the oszi... i just found this document though. it shows how adr wired the transformers back then. and they do not use any zobel. only suggest a 600ohms resistor for termination. so i think ill just keep it oldschool so to say  (and cheap out a little