MP12

The MP12 is based on one discrete Op-Amp, one input transformer and one output transformer.

When built with Cinemag CMMI-8-PCA and CMOQ-2S transformers, it delivers what is called the “LA” sound, popularised by the famous American consoles of the 70's : the punchy midrange and tight bass tone of the iron. This MP12 is great on drums, electric instruments and generally all close miked sources.

When built with the Lundhal LL1538 1:5 transformer on input and the high nickel Cinemag CMOB-2H or Lundhal LL1517 on output, the MP12 becomes an extremely transparent mic pre that will capture all sound sources with extreme finesse and will be great in all distant miking applications.

Highlights

• Compatible with the API* 2520 pinout, it can receive many discrete Op-Amps like Skulptor, API, John Hardy, Millennia, Forssell, SCA, JML.
• Compatible with many input transformers like Cinemag, Lundhal, OEP, Jensen, Sowter, Altran.
• Compatible with many output transformers like Cinemag, Lundhal, Edcor
• 70 dB of gain
• Dual gain potentiometer for precise gain setting, even in high gains
• Signal/Clip LED monitors signal with full wave rectifier
• Variable output pad for those who like to drive it hot
• Optional capacitor coupling
• Optional DC servo
• All low level signals switched by relays
• Golden contacts on relays and switches
• Jumper selectable input impedance (with dual primary input transformers)
• Local adjustable voltage regulator for compatibility with all DOA's and better channel separation
• 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

Input transformer options

Cinemag CMMI-8-PCA : Built by Cinemag, formerly Reichenbach, this transformer is the closest to the original. It is responsible for a large part in the final sound.

Lundhal LL1538 : This is one of the best existing microphone input transformer. Built in Europe by Lundhal, it offers a hudge bandwidth (10Hz-100kHz) and a very low distortion. It will be the transformer of choice when you want to capture the source and only the source.

OEP A262A3E : This transformer is a very interresting alternative to the classics. For a lower cost, it will give more "iron" characteristic to the sound of your mic pre. More color in a warm vintage way.

Other transformers : The three above transformers are available as options in our kits but the MP12 can work with many others. Look at the "MP12 Input transformer options" document here.

Output transformer options

The output transformer also plays an important role in the mic pre sound, but to a lesser degree when compared to the input transformer.

Cinemag CMOQ-2S : This quadfilar line output transformer is the closest to the original. Its large steel core is an important part in the final fat sound.

Cinemag CMOB-2H : This transformer has a high nickel core (80%) giving much lower distorsion at all frequencies. It should be prefered when looking for sound transparency.

Lundhal LL1517 : This is also a very good choice when looking for versatility with very large bandwidth and low distortion.

Edcor WSM600/600 : This low cost steel core transformer will give you a nice "iron" colour, fat, vintage type of sound.

Other transformers : The four above transformers are available as options in our kits but the MP12 can work with many others. Look at the "MP12 Output transformer options" document here.

Discrete Op-Amp options

The best results will be given by DOA's that are optimized for the input transformer ratio. Look at the "MP12 Input transformer options" document here.

SK25 : A discrete Op-Amp that we developed as a replacement for the API* 2520. Our measurement and listening tests show that it behaves extremely close to the original.

SK99A or B : Low noise, high performance discrete Op-Amp that will perform extremely well in the MP12.

SK47A or B : Discrete Current Feedback Op-Amp that is pin compatible with the 2520. Low noise and very musical distortion characteristics (mostly second harmonic and decreasing level with the harmonic rank) make it a very interesting alternative.

Other DOA's : The above DOA's are available as options in our kits but the MP12 can work with many others like API2520, Millennia MM-99, Forssell JFET-992, SCA SC25, JML99v, John Hardy 990C, ...

More details...

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 input transformer is loaded by the RL1 resistor, which defines the input impedance and much be chosen to match the transformer characteristics.

The gain level is set by a dual values potentiometer and a switch that splits the gain range into two parts : “Lo gain” and “Hi gain”. This allows a precise gain setting even in the high range. The lower position of the 3 ways switch inserts a pad before the transformer.

U1 is a DC Servo that monitors the DC output level of the DOA and injects a bias voltage into the minus input, canceling the DC. It guaranties an output DC lower than 0.2mV on the transformer primary at any temperature. It can be deactivated by not inserting the IC in the socket.

The output of the DOA can be DC or AC coupled to the output transformer, by inserting or removing jumper JMP4. With most DOA's, DC coupling will be preferred but capacitor coupling is needed with current feedback Op-Amps like SK47.

The potentiometer P2 forms a balanced output pad. This is useful in two cases. With some high ratio transformers, the minimum gain can be as high a 12dB, with the input pad inserted. This can be too much with some very hot microphones, close to loud sources. The second case is when you want to drive the DOA hard for special saturation effect. In both cases, the output pad allows reducing the output level to match the converters.

The DI and Input Pad 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 a full wave rectifier. It will flash green with audio levels of 40dB below clipping giving a visual feedback of the preamp activity. It will flash red if the DOA gets close to the clip level, which we use to set to 3dB below the actual clipping.

The audio supply voltage is regulated on board, in addition to being regulated in the external PSU. The voltage can be adjusted between +-12V and +-24V. This ensures a very stable supply and an excellent channel separation. The relays and LED supplies are taken pre-regulator. The ground return is split into two paths, Signal and Power, giving a very clean ground reference to all the critical stages.

* API is a registered Trademark of Automated Processes Inc.