MP66

The MP66 is a single ended class A tube preamplifier with transformers on input and output . It is inspired by designs from the 60's.

The MP66 is not neutral. The transformers and triode valves print their characteristics on the signal. The sound ranges from stunning transparency, with an overwhelming sense of dynamic, when softly driven, to soft valve limiting when pushing the gain further, to a “guitar amp” type of saturation when you push it into the limits. The transition between these modes is very smooth.

Highlights

• Pure tube audio path
• Class A, single ended
• Variable output level potentiometer allows driving the tube preamp from soft to hard and vary the harmonic content
• Air equalizer can make a "dull" or a "harsh" source sound right
• Two frequencies high pass filter
• high voltage 300V power supply
• No global feedback design
• Lundahl input transformers
• Cinemag output transformer
• 62 dB of gain
• Switchable first stage
• Soft start filament heating guarantees a long life to the valves
• Signal/Clip LED monitors clipping in 2 stages with 2 full wave rectifiers
• All low level signals switched by relays
• Golden contacts on relays and switches
• Neutrik XLR connectors
• Nicely damped quality conductive plastic potentiometers
• 1% metal film resistors
• High grade 105°C low ESR electrolytic capacitors
• WIMA film capacitors
• High grade double sided PCB with plated holes

More details...

The MP66 uses two slots in the SKMP case. It can be combined freely with 2 more preamps or one other MP66.

The MP66 relies on local feedback in all stages. The distortion ratio ranges from 0.1% at low level to 5 or 10% near clipping. This distortion is mostly second order with a level that decreases quickly with the harmonic rank. It is a very euphonic distortion that can enhance many sound sources.

The Air Equalizer can add or cut 3dB of level at 12 kHz. This is often all what is needed to turn a dull microphone into a detailed one or enough to change a harsh microphone into a smooth one.

The Lundahl LL1538 is one of the best existing input transformers. Built in Europe by Lundahl, it offers a huge bandwidth (10Hz-100kHz) and a very low distortion. In association with tube circuits, it brings a very warm vintage sound but still extremely open and detailed.

The Cinemag output transformer is more currently seen in solid state circuits. It has been possible to use it here in a 2:1 configuration because of the very low impedance ECC82 output stage. It brings to the circuit the warms of iron, without the dullness of typical tube output transformers.

The phantom power is applied to the XLR pins through 1‰ matched resistors to keep the CMRR high. The 48V voltage is filtered by a double RC network to eliminate any residual noise.

The DI, Gain, Pad and Phase switching is done by relays which are fed by a constant current source without any return through the ground. This is to eliminate all switching pops in the audio.

The clip LED if fed by two full wave rectifiers. It will flash green with audio levels of 40dB below clipping giving a visual feedback of the preamp activity. It will flash red if anyone of the two stages reaches the clip level, which we use to set to 3dB below the actual clipping.