Westlicht PER|FORMER Noise Fix

The PER|FORMER is a seriously powerful and flexible sequencer, although if you’re reading this then you already know that!

The only real issue I’ve experienced with the module is the presence of a very noticeable audible noise emitted directly from the module and present to some extent on the cv and gate outputs. The noise is louder when the screen is more illuminated and when a usb device such as the launchpad is connected. The display, usb power, microcontroller, dacs and analogue 3V3 voltages are all supplied by or derived from a 5V switching regulator – Recom R-78E5-0.1.0 – with max noise and ripple of 120mV according to the datasheet. This, and some posts on the ever helpful Mod Wiggler forum, suggested the regulator was the the likely culprit.

Example FFT of CV output with R-78E5 regulator fitted and launchpad connected to PER|FORMER showing a strong spur centred at 12.35 kHz with sidebands ~+/-4 KHz

I removed the regulator and connected the modules 5V track to a lab power supply via the vacant regulator output pad. With the module powered up and a reasonable ‘worst case’ 5V load of a fully illuminated launchpad and the ‘overview’ screen active the PSUs indicated:

+12V 10mA

-12V 13mA

+5V 278mA

And the noise was no more! Since I have a substantial 5V PSU in my case with plenty of headroom I decided to just utilise this, rather than an alternative regulator – so a molex KK connector was fitted where the regulator once was and a cable was bodged together to attach to the 5V rail of one of my bus bars et voila.

Where to connect a 5V supply, if not using a regulator (n/c is no connect)

If you haven’t got a 5V supply in your case, or want to avoid loading it significantly (worst case ~300mA) then there are two options:

1: Use a lower noise (and more expensive) switching regulator such as the Recom R-785-1.0 with max 30mV noise and ripple according to the datasheet.

2: Use a good old 7805 (or equivalent) linear regulator. Given the power involved with a 300mA load and the raised ambient temperature in your case, a heat sink is likely to be required for this and some thought will need to be given to the physical dimensions of the heat sink due to the proximity of the regulator pads to the power connector. The r78 is pin compatible with 7805 so it should fit nicely, so long as a suitable heat sink can be found.

My conservative heat sink calcs for L7805 linear regulator – pick a TO220 with 12degC/W or lower thermal resistance (not tested!)