What I described was the way we did it at Neve back in the 70s. And the way we monitored then was at the output XLR via a (31267) 10K:600 trasnformer into the monitor section (which is basically what you have in your original block diagram).
Yes, I had assumed the headphone circuit would be fed with an unbalanced connection. I am planning to use your 'improved' headphone circuit design - I take it I can feed that with a balanced input. The fun bit will be finding space for those %&*^$ lovely Sowter output transformers! ;-)
These will be fine as line level input transformers but they are not suitable as output transformers. If you want a compact 2K4:600 output transformer at a reasonable price, OEP do the K30A11C. This is not available through distribution or shown on their web but it is a standard product. They do a special version for me with an iron core which will handle more level at 20Hz.
Thanks for spotting that - I will fix that.
My thinking is that I need to take the PFL feed from post insert (to ensure I can hear what the insert is doing ) - which is balanced at that pont, and then bring it back post main outputs (to ensure that the PFL only goes to monitoring and leaves the main outputs alone) - which is also balanced. To be honest I hadn't really thought through the PFL, but it is obvious that it is a bus, and therefore would need a bus amp amp and transformer. I suppose it would need to be a balanced bus, with dual bus amps and transformers? Is this a viable concept, or do I need to completely rethink how PFL is done?I had thought to standardize using the Electro-Mag E1257 as my output transformer. I have already ordered a tranche of them (let me know if you ever need a couple on short notice). These would be used for the channel outputs feeding the inserts, and the transformer that feeds the main outputs from the 2 bus - although I see from your previous post that that the bus output should be 10K:600.
I forgot you are using the ElectroMag output transformers. They are 2K4:600 which is exactly what you need to balance the output from the twin line amp. 10K:10K is just what you need for any line level input like insert returns.
You have built quite a few consoles with, I imagine, most of the possible options, so it's likely you know whereof you speak ;-) Is there no discernable difference between the OEP alternatives and the top shelf tranformers, or is it more a matter of accepting 95% (or whatever the relative values) of the performance for 50% of the cost? Perhaps another way of putting it is: If price were no object, would you still be happy with the OEP alternatives for your console?
Interesting question. I have only once measured a Sowter transformer, you usually just take it on faith that they will be good. The one I tested was their 1461 which is 2K4:600 output transformer. It was equal to or better than the OEP and Carnhill at mid frequencies but below 40Hz its distortion rose unacceptably quickly compared to the others. Overall I judged its performance to be worse than the other two. I had the OEP one modified so its performance equalled or bettered the Carnhill and it is still only £40. Of course, for a compact output transformer the ElectroMag is the best.
Hi Ian,
Note that the 9610 is a 1:10 mic input transformer and the K30A06C is a 10K:10K line level input transformer so not quite apples and apples. I think you may have meant to compare the 9610 with the A187A15C.
