AMPEX MX-10/MX10/2 LINE 4 MIC TUBE PREAMP STEREO MIXER WAS TESTED BY PROFESSIONAL SOUND ENGINEER /30 YEARS EXP Start Price USD 1,000.00 Current Price USD 1,000.00 Time Left - Bid Count 1 Buy It Now Price USD 1,000.00 Reserve Price - Start Time Monday, October 13, 2008 End Time Friday, October 17, 2008 Location irvington, NJ See more about 'AMPEX MX-10/MX10/2 LINE 4 MIC TUBE PREAMP STEREO MIXER ' Description  MX-10 4 in LINE MIC /2 out /STEREO? tube mixer with 4 Beyer input transformers. WITH CASE.BEYER input transformer:"German made Beyerdynamic  input transformers. These transformer have a single (not split) primary, a single secondary and a shield. The step up ratio is about 1:15 which translates to 200 ohms to 45,000 ohms, perfect for a tube microphone input, or moving coil step up to normal 47K phono stage impedance. The secondaries can also be terminated with high resistance up to about 100K without significant degradation of audio quality. Ampex used these transformers in several of their products (including the MX-10 tube mixer and nuvistor based MR-70 mic preamps) and simply attached the secondary directly to the grid with no other terminating resistor.I find that with typical microphone levels and source impedances (100-200 ohms) the low end is flat to 20 Hz with low distortion into secondary loads as low as about 40K. The transformer physical size precludes them being used with line levels, but as mic or MC phono transformers they are very tame and well refined. The top end is excellent. Most high ratio input transformers (even expensive ones like UTC, Triad, Peerless) tend to have a sharp rise above their high frequency spec (20,000 Hz or whatever) which results in ultrasonic ringing that you usually want to damp with a capacitor (or network) across the secondary. These actually have a gradual rolloff around 20,000 Hz, which results in a sweet treble sound even without special termination with a very good 1K square wave response, with very little overshoot or ringing. " VERY GOOD WORKING CONDITION ! Place a Bid!