EZ1290 Preamp PCB


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SKU: ACS738531 Category:

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This DIY EZ1290 PCB is the same circuit found in the Neve 1290 preamp which is popular because it serves as the preamp for the famed Neve 1073 module.  This build is very well documented and sounds amazing.  Please refer to the “Build Guide” and “BOM” tabs below.

“The EZ1290 is a carefully designed replica of the classic Neve 1073 preamp without EQ and Line-­‐Input. The 1290 number originates from Neve’s very own 1290 preamp which was essentially a 1073 sans EQ” – Martin Adriaanse, designer.

Some helpful tips from designer Martin Adriaanse:

How did you get the rear panel drilled?

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. 15/16 is perfect for Neutrik XLR’s. 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. Drill those with a 1/8″ drill.

Can I use some other transformers besides the Carnhills?

Yes, original St. Ives or Marinair 10468 and LO1166 would be a good start. Other than that it’s Carnhill or bust in my humble opinion.

BC184C is now obsolete. What should I do?

You should be able to find them on eBay if you’re really wanting to use BC184. Another option is to use MPSA18. 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. Other than that it is a great substitute: http://www.digikey.com/product-detail/en/MPSA18RLRMG/MPSA18RLRMGOSCT-ND

Can I use BC184L instead of BC184C?

Don’t use the L’s. The pinouts are different.

How much does it cost to build one channel, complete with case and power supply?

Count on about $200-$300 per channel, not exactly free, but a good deal nonetheless. ☺

At higher gain settings, all I get is a very high pitched noise, or screeching, audio drop out??

Ah, the sound of oscillation. This is usually caused by:
not using shielded wire throughout
running mic input wires too close to line output wires (especially unshielded)
having the 10468 (VTB9045) too close to LO1166 (VTB9049)
malfunctioning 2N3055

Also check the resistor values around the gain switch.

Is it ok if I use unshielded hook up wire for audio connections such as transformer to XLR, transformer to PCB etc?

In a word, NO! 🙂 Just use some mic cable (in the BOM) – it has a shield.

What cable should I use for the 4pin XLR cable (PSU case to Rack case)?

I recommend some 3 (or 4) conductor 18AWG, stranded, with shield (use the shield to connect both cases together). Most electronics stores will carry this type of cable as it’s commonly used for alarm installation. Home improvement stores might also carry it. I have not been able to find it in small quantities online (less than 1000′ spools).

What type of standoffs (mounting pillars) should be used to mount the EZ1290 boards?

Any nonconductive (nylon) standoffs will work. Don’t use metal (conductive)

I’m getting 50/ 60Hz hum?

Try moving the power transformer away from audio, preferably outside the rack case.

Can I fit it all in a 1U?

Yes, but you have to use the narrow board output transformer: VTB1148 available from: http://www.audiomaintenance.com/ you may also have to mount some of the larger capacitors flat, and bend the fins on the 2N3055 heatsink down a bit.

Do I “HAVE TO” bias this preamp? I don’t have a scope and/or signal generator.

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.

How do I add Polarity/PAD/DI to this preamp?

I think this is probably the easiest way: http://www.jlmaudio.com/JLMDI.htm

I’m having some problems.

Here’s a random list of things to check:
check transistor voltages
check resistor values and capacitor orientations.
Reheat all solder joints (including on the transformers, XLR’s).
Did you solder in the jumper (labeled jumper on PCB).
Is 2N3055 bolted to the PCB using conductive (metal) standoffs?
How’s the PSU voltage?
Meticulously check the wiring on the input/output transformers.
Are you using shielded cable for audio connections?

Any other hints?

Be 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 wall

Be sure to adjust the PSU for correct voltage **BEFORE** you connect to the EZ1290

Also, be sure to follow the assembly guide, BOM and this FAQ very precisely; read them a few times before you start. Those that have usually end up with a properly functioning, amazing sounding mic pre. ☺

Weight 1 oz
Dimensions 6 × 4 × 0.25 in

Build Guide

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