Mix bus transformer and summing box with Siemens Sitral amp with demo

The listing is for two boxes together as they are mono.

Each box has 16 balanced inputs and one balanced output.

Each box is a mix bus transformer which is in essence the passive summing mixer built with fine 1% precision metal film 10 kOhm resistors and followed by classic transformer balanced amplifier in eurocard format.

Summing amplifier cards are Siemens Sitral with Haufe transformers and OPA171 op amps. The best bass I have ever heard so far. The amplifiers were recapped in 2024.

You can use them as:

- mix bus transformer to imprint transformer sound in your mix and reduce the amount of compression you want to put on the final mix. Perfect for digital recordings made ITB to process it through analog gear at the end after DA converter.

- summing box to sum up to 16 busses (drum bus, bass, vocals, synths, guitars, orchestra, what else... 16 balanced stereo busses is a lot). It is not 32 channel mixer, it is 16 stereo busses summing.

Modern ITB workflow is the perfect source of stems to sum them up and master then.

Chassis donor is Digidesign888. I was too lazy to brush it so I just used black marker to hide its redundant IN/OUT/WHATEVER marks, which you can always reuse if you would like to install some additional buttons/knobs/etc. Just wipe the marker away with some IPA or ethanol at your convenience.

Outputs are transformer balanced.

The gain of the channels can be set at the front panel up to the level you expect to gain stage the whole mix further (see photos).

Meters are built around LM3915 and considered more as "for fun" rather than real level metering, for the next reason: you can calibrate them internally (see photos), but their visibility is rather limited anyways. Meters are connected to the unbalanced output of the amplifier card. Added to make these processors less of black boring boxes!

You can find the demo comparison of similar boxes including listed on youtube @HappinessMastering.

The eurocard 31 pin connector description added, just in case you want to modify something (see photos).

Enjoy!

No returns.