[Jakobz]

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

[RoehrenJeans]

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

[Triple_Ristretto]

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

[sev]

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

[Dirk]

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