Attenuator transformers used in conjunction with a multi position switch provide a high performance volume control function. Sowter proprietary winding technique ensures 100 kHz bandwidth at all switch positions. The transformer action of these attenuators ensures the loading circuit sees a low driving impedance regardless of the switch position. This ensures the maximum bandwidth potential of the whole circuit can be realized at all gain settings. As the attenuation is related to the number of turns at the winding tap, the attenuation is exactly matched between stereo channels. The Mumetal core ensures very low Total Harmonic Distortion. High input impedance to minimize loading on the driving circuit. Mumetal can to ensure minimal hum pick-up. The transformers provide good dc isolation and can be used in balanced or unbalanced circuits.

These transformers should be driven from a source impedance as low as possible but will work well with a source up to 10k ohms. Where necessary a blocking capacitor should be used to ensure no dc is applied to either winding. The secondary load can be any value the higher the better. A Zoebel network is not required  to damp high frequency resonances which are non-existent. These transformers provide isolation and may be used for balanced to unbalanced conversion or vice versa. It is recommended to use a separate transformer in a high noise environment or if long cables are to be used. If a ratio change, high common mode rejection is required or dc in either winding is required we will be happy to recommend a suitable transformer to be used in concert with 9335. Depending on the circuit configuration this may be possible with minimal loss of performance

IAG stepped attenuator is designed using a Sowter 9335 -50db attenuator transformer and a Shallco "C" series 27 position switch in a mumetal shielded enclosure.  The transformer is prewired to the the switch inside the enclosure with only the input and the output connections exiting the case. 

The Sowter 9335 attenuator transformer is normally in a mumetal case but in this application it is used without the case for reduced size. The whole assembly will be shielded in a new mumetal case.  

The Shallco switch used is a very high quality switch with silver plated contacts which are gold plated only at the solder lugs and has a very smooth feel. The switch is modified for low rotational torque making it very easy to turn even with small diameter knobs.

Fully encased attenuator assembly ready for installation in chassis of your choice or in an existing power amp or preamp (assuming there is space).  The entire package is 2"x2"x3.25" in depth and has a.375" threaded mount with a .250" shaft.

APPLICATION EXAMPLES