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  • Writer's pictureJim Cathey

Making MC275 work with ATC SCM 150 Classic Passive Speakers

I often get asked if the vintage MC275 can drive the 15” driver on the ATC SCM 150 Classic Passive?

Generally, two smaller low-frequency speakers are selected in a speaker design instead of a larger 15”, primarily because a larger size is harder to control, especially with a tube amp. It is true, and I was faced with this question while deciding what speakers to select, the cabling, the power, tube, and AC power.

First, ATCs have been used in Studio for a long time; hence their drive is solid and fast with a history of outstanding performance. Along with this, features like the three sets of speaker posts and world-class mid-range made the speaker an easy decision. Next, I needed some strong power tubes like the Genalex Gold Lion KT88 power vacuum tubes manufactured in Russia. I have tested many KT88 branded tubes, and the Genalex consistently demonstrated a strong/fast reaction with no early roll-off. These have to be the new Genalex, not the vintage that was originally made in the U.K.  Although those vintage Genalex tubes are popular, if you can find them, they are not nearly as strong or fast and roll-off in the higher frequencies. Finally, when driving the speakers, there is a negative electrical signal push back that can overwhelm a tube amp and shorten the life of the tubes, primarily the power tubes. Transparent Audio was able to custom make my speaker cables tuning their built-in cable network to compensate for the amplifier, the speaker, length, and cable type, including the ability to dampen the negative signal feedback. The last piece was power; 2x power is available for each amp via the PS Audio P20 power regenerators; 1 P20 per 2 MC275’s. In addition, each 15” driver had one dedicated MC275 operating as a monoblock.

The selector on the right is switched to that position and there are bridges in the middle
Amp in monoblock mode
Amp in monoblock mode with bridges

The combination of the strong ATC 150 drivers from commercial studio products, the latest KT88 Genalex power tubes, the Transparent Audio network-enabled speaker cables, the S Audio power regenerators and vintage MC275’s in monoblock mode made it possible to drive the 15” speakers. A perfect recipe, I would say to create an excellent audiophile quality sound system.

To sum up, if you prefer tube amps and a large low-frequency speaker, it’s possible to control it even with a vintage tube amplifier, provided done with a combination of proper components.

You can find out more about the above components through these links


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