Hi there
I just completed the Emma project and I am very happy with how it sounds. I was wondering if anyone could explain to me how I should wire the output transformer to match a 16ohm speaker, I tried looking at the documentation but didn't quite get it

Hi Jakobz,
In the original schematics the Pins 2 - 4 are used...  According to the data sheet of the Hammond 125C that results in a primary impedance of about 22,5 kOhms.
Based on this information I would use the Pins 1 - 4 for a 16 Ohm speaker (Impedance see table, about 22kOhm) ...
Best regards
Stoffel

According to the schematic that's correct.
But why are all the other LoW projects that are using the ECC99 poweramp wired for an primary impedance of 12.8 k ohms?

Greetings,
Jan

Hi Jan,
in short Terms: The first two LoW-Amps, LummerlandExpress and Emma used 22.5k to allow using a 12AU7 instead of the ECC99 (the LumEx-kit is even shipped with a 12AU7) by slightly mismatching primary Impedance when used with ECC99. The later developed LoW-Amps focused on ECC99 and abandoned the 12AU7-Option, therefore optimizing primary Impedance using 12.8k.
Greez
Sev

That's right.
The Lumex and the Emma do still sound pretty good with a 12AU7 but the other LoW that came after had a little problem with a 12AU7 and also the feedback that we got from the customers "forced" us to use the ECC99. It just sounds better.
But of course if someone wants to try a 12AU7 (and a ECC99) than one must just rewire the OT. The Hammond OT shipped with the LoW kits is very versatile .

Gruß, Dirk