The Trimodal Stereo Power Amplifier is based on the design by Douglas Self & approved kits supplied by the Signal Transfer Company including the protection circuit to give full speaker protection in the unlikely event of a fault.
This version features many component changes and my own power supply design using dual transformers & bridge rectification to give dual mono performance.
This outstanding design is the result of many years analysis of the various distortion modes that can occur in the various stages of power amplifiers. The design adopted uses 3 stages, each stage has been optimised for low distortion and works with local feedback. Some global feedback is also used to lower output impedance amongst other benefits.
A key aspect of the design was to ensure the amplifier remains stable into a wide range of speakers and using a wide range of speaker cables. Instability in power amplifiers is not uncommon because they have to drive speakers which can present a very reactive load. Symptoms of instability can be high levels of distortion, overheating of components or just momentary distortions resulting in poor sound reproduction.
At the press of a button the amplifier can be changed from Class B to Class A operation. In Class B power consumption is only 7W (no music playing) and yet distortion is only just measurable. In Class A the very low level of cross over distortion inherent with Class B is eliminated but power consumption is much higher. Sound reproduction is very similar in either mode and may not even be detectable in some systems.
Output power is 30W per channel, which is adequate for most domestic situations and often preferable to high power amplifiers. Speaker loads down to 4 ohms nominal impedance are OK.
Input impedance is selectable at either 2KR or 8KR. 2KR gives lowest noise level and should be OK with most active pre-amplifiers. 8KR has slightly higher noise level but probably not audible.
Price is £990.
The amplifier is similar to the one reviewed here but gives better sound reproduction (in my opinion) REVIEW