Pure Mu utilizes the simplest tube compressor topology. There is only one active stage of 4 parallel coupled tubes per channel, input transformer and output transformer. Therefore Pure Mu.
The side chain features are mostly like the ones in Vari Mu. The attack range goes down to extremely fast and release has a separate switch to add a second time constant in parallel, often called an “auto release”. In Pure Mu and Vari Mu this is done right. The primary release can still be chosen from the 11 positions, and “Dual” switch is used to add 1 or 2 seconds of secondary release.
L and R side chains are kept internally and electronically separate and share one set of controls with an adjustable link switch. What is this for? Imagine that you have very loud transient on extreme right or left. With the link control in “Off” -position, only one channel will be compressed. With the link “On” the both channels are compressed the same amount. Now, usually these options are fine enough but these are the inherent limitations: Link Off – stereo field will collapse for a moment. Link On – ALL material will follow the transient and “duck”. Many times the ideal is somewhere in between. There’s also another trick in the adjustable link: The channels will track each other very little during fast attack and more on release. In this way you can get the best of both worlds if it suits the material. Intermediate positions offer different degrees of linking.
As always in Knif products, there are no potentiometers. All controls use Elma rotary switches. Signal and power wiring is teflon insulated silver plated copper and is soldered directly to turrets on circuit boards. This combines reliable and neutral signal routing to the possibility of unlimited soldering and desoldering without damages to wires or PCB. Case is built from machined aluminum plates and blocks as usual.
As in Vari Mu there are trimmers on the front panel for tube balance and meter zero. Power supply has a soft and delayed start.
All tubes in the unit are NOS without modern equivalents, but still very common and easy to get.
The question I often get is “What is the difference between Vari Mu and Pure Mu, how to choose?”
Although the topology is different, Pure mu being much simpler, the sound is not that different, because both follow same design rules and components are of the same high quality. Also the side chain is very similar. So, mostly it is about the features. Pure mu is simpler to use, more affordable, Vari Mu more versatile.
Price (VAT 0) 3900 €
Amorphous core output transformers +350€