Kemo M040N Preamplifier Module
Kemo M040N Preamplifier Module is rated out of 5by 2.
Rated 1 out of 5
from Severe Ocsillations - No Noise Rejectiontl;dr The device is not useable. I'll retract my bad review if someone can give me technical info on how to fix the debilitating oscillation issues.I tried wiring up this preamp to the Kemo 40W power amp. I noticed really bad oscillations that when amplified pushed my speaker to the excursions. I grounded the inputs, used fat wire from the 12V SLA battery, used factory lead length for all connections :: the result was huge uncontrolled ~20Hz oscillations.The mfg recommends a 100micF cap "if you have noise or hum". So I added a 100micF bypass cap in close proximity to the preamp, and the oscillations changed frequency. I tried several caps of varying values up to 4700micF and I got the oscillations down to about 0.5HZ but it still pushed my speaker to max excursion.I thought the preamp might need a minimum load to function properly, so I wired the preamp's output to one side of a 10K pot and grounded the other side to the single point ground using shielded twisted pair from preamp to pot and from pot wiper to power amp. At zero output to the power amp it was as quiet as a mouse. If I cracked open the pot even a tiny bit, those 0.5Hz oscillations were present.Lastly, there is no noise cancellation or common mode rejection ratio at all such that lead length and/or shielding is CRITICAL. I have designed many amplifiers in the past and I use solid build practices for single point ground, decoupling the signal ground from chassis ground via an RC network, physical separation of power/speaker/input wires and acute attention to shielding. On this preamp - nothing realistic works.In short, this preamplifier is terrible.I will gladly retract my harsh criticism and admit a "doh" moment if someone has application notes on how to implement this device to eliminate the severe oscillations and prevent all the lead length induced hum using a realistic cable plant layout.With true customer focus, Parts Express has refunded my money. Thanks for that Parts Express!
Date published: 2013-11-26
Rated 5 out of 5
from TURNED MY 5 STRING BASS INTO THUNDER!ALL YOU DIY GUTAR BUILDERS SHOULD TRY THIS BABY OUT! I KNOW IT SOUNDS CRAZY BUT THAT I AM. CRAZY ABOUT THIS PRODUCT. THIS PACKAGE IS SMALL ENOUGH TO MOUNT TO YOUR VOLUME POT AND ADD YOUR 9 VOLT DC BATTERY AND TURN YOUR PASSIVE PICKUPS INTO A HIGH GAIN ACTIVE SYSTEM. THE WIRES MAKE IT A SNAP TO SOLDER TO THE POTS AND OUTPUT JACK. PLUGED INTO MY CLASS D POWER AMP, MAKE SURE YOU HAVE A GAIN CONTROL ON YOUR AMPS INPUT STAGE BECAUSE THIS BABY PUTS OUT SOME POWER!!! AND BIG TIME CLEAN. MY G STRING SQUEALS LIKE THE PROS! THE HARMONICS ARE EAR PIERCING! THAT'S RARE FOR A .055 G STRING. BELIEVE AND HAVE A BLAST OR BELIEVE ME NOT AND WISH YOU DID!!
Date published: 2013-09-02