Those that have usually end up with a properly functioning, amazing sounding mic pre. Meticulously check the wiring on the input/output transformers.Īre you using shielded cable for audio connections?īe careful with mains voltages! (120V-220V) It can really hurt (or kill) you! Don’t touch anything on the PSU while it is plugged into the wallīe sure to adjust the PSU for correct voltage **BEFORE** you connect to the EZ1290Īlso, be sure to follow the assembly guide, BOM and this FAQ very precisely read them a few times before you start. Is 2N3055 bolted to the PCB using conductive (metal) standoffs? Reheat all solder joints (including on the transformers, XLR’s).ĭid you solder in the jumper (labeled jumper on PCB). I think this is probably the easiest way: Ĭheck resistor values and capacitor orientations. How do I add Polarity/PAD/DI to this preamp? I would highly recommend getting a scope and generator, but in a pinch you can adjust the 5k trimpot on the EZ1290 board until TR3 collector (the casing of 2N3055) measures 22.66 volts to ground. Yes, but you have to use the narrow board output transformer: VTB1148 available from: you may also have to mount some of the larger capacitors flat, and bend the fins on the 2N3055 heatsink down a bit.ĭo I “HAVE TO” bias this preamp? I don’t have a scope and/or signal generator. Try moving the power transformer away from audio, preferably outside the rack case. What type of standoffs (mounting pillars) should be used to mount the EZ1290 boards?Īny nonconductive (nylon) standoffs will work. I have not been able to find it in small quantities online (less than 1000′ spools). Home improvement stores might also carry it. Most electronics stores will carry this type of cable as it’s commonly used for alarm installation. I recommend some 3 (or 4) conductor 18AWG, stranded, with shield (use the shield to connect both cases together). What cable should I use for the 4pin XLR cable (PSU case to Rack case)? In a word, NO! 🙂 Just use some mic cable (in the BOM) – it has a shield. Is it ok if I use unshielded hook up wire for audio connections such as transformer to XLR, transformer to PCB etc? Having the 10468 (VTB9045) too close to LO1166 (VTB9049)Īlso check the resistor values around the gain switch. Running mic input wires too close to line output wires (especially unshielded)
☺Īt higher gain settings, all I get is a very high pitched noise, or screeching, audio drop out?Īh, the sound of oscillation. How much does it cost to build one channel, complete with case and power supply?Ĭount on about $200-$300 per channel, not exactly free, but a good deal nonetheless. Other than that it is a great substitute: ĭon’t use the L’s.
One important detail about using MPSA18 in place of BC184C is that MPSA18 will need to be mounted backwards (rotated 180 degrees on its vertical axis) on the PCB. You should be able to find them on eBay if you’re really wanting to use BC184. Other than that it’s Carnhill or bust in my humble opinion.īC184C is now obsolete. Ives or Marinair 10468 and LO1166 would be a good start. Drill those with a 1/8″ drill.Ĭan I use some other transformers besides the Carnhills? Then put the connector in the hole (use a carpenter’s square to align the connectors straight on the case) and mark the small 4-40 flat screw holes. I laid it out with a ruler and center punch, pre-drilled with 3/8″ drill and then punched with a 15/16″ Greenlee punch. Some helpful tips from designer Martin Adriaanse:
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