August 24, 2015

Rigol DS1054Z digital storage scope - decoding I2S signals

I recently got one of these great little digital scopes. It has a few serial bus decoding packages (on a try-before-buy basis). You get 36 hours to play with them. Unfortunately they don’t include I2S bus decoding. I2S is a bus standard commonly used for transferring digital audio around, for example between ADCs and DACs.

No matter! You can capture and export full-resolution traces of signals via a USB memory stick. This seems to work best if the stick is FAT formatted rather than FAT32. The file format is .CSV which is great for importing into Excel and viewing. You can then use Excel’s charting function to provide a decode of your signals with much greater time-resolution than you can see on the scope’s display itself (which is still pretty good). For example

July 9, 2015

Low-noise +/-12v linear power supply for Phono Preamp

Ages ago, I built a John Linsley-Hood design of phono preamp, first published in ETI magazine in 1992. This was considerably better than the phono stage in the integrated amp I was using at the time (a Creek CAS4040).

For a couple of decades I ran this from my bench power supply, so it was definitely time for its own PSU. Rather than etching my own circuit board, nowadays kits are available via eBay that save a lot of that messy work. I wanted something based on the LM317 / LM337 regulators, as they are known to have superior noise performance and regulation compared to the standard 7812 / 7912 family.

July 3, 2015

Simple electronic water leak detector

The following circuit is a very simple water leak detector, which I made 25+ years ago (!!) following my fiancée having a washing machine go wrong and leak all over her apartment.

The circuit is not ideal - there are better designs out there. It was built with ‘what I had in my scrapbox at the time’. It’s purely analog, relying on the gain of the Darlington pair to provide reasonable on/off behaviour. This can actually be an advantage, as the sound will get louder as the leak becomes more serious and conducts more water.

October 10, 2013

Simple Optical Compressor for bass guitar - construction

An extremely simple yet capable compressor circuit is published by Elliott Sound Products,here (link updated 31 Dec 2023).

Compressor Mk I

I built the circuit exactly as-is (in an Altoids tin).

Care was taken to optically couple the bulb to the photocell (LDR), using a perspex rod, wrapped in smooth tin-foil. The perspex came from eBay: http://stores.ebay.co.uk/thewholesaleposco2009

as did the miniature “Grain of Wheat” bulbs: http://stores.ebay.co.uk/GnA-MODELPARTS?_trksid=p2047675.l2563

This was put together, and sealed in heatshrink tubing, to make it fairly lightproof from external light sources. The rest of the components came from http://cpc.farnell.com (free postage) or from my junk box.

July 11, 2013

Sony Vaio VPCEB4L1EWI - Heatsink clean and refit

This time, it’s a Sony Vaio VPCEB4L1EWI, with i3-380M CPU. About two years old. Running Prime95 stress test, the cores were reaching 85 deg C and the fan was rather noisy.

1. Strip off the back plate, undoing all the visible screws, taking careful note of where they all go back - there are several different sizes and types. The back plate then snaps off - be careful with the small white lugs on the upper side here. One came off despite me taking care.

February 4, 2013

Improving an Ashdown Little Giant bass amplifier

I have an Ashdown Little Giant amp. Several reviewers have mentioned that this amp is not at loud as it should be (e.g. here).

It all depends on whether the output levels coming from your bass are enough to drive the output stage fully. I have an active bass, but even with the input set on max, to get a decent output level I need the output volume control set to around 3 o’clock.

October 30, 2012

Sony Vaio VPCF13M0E - CPU heatsink clean and re-fit

My work laptop (a Sony Vaio VPCF13M0E) had become very noisy, with the fan running full speed as soon as it did any actual work. A bit of googling found that this was a common problem. The original heatsink paste becomes dried up, and doesn’t conduct heat well.

Here’s some pictures of the steps I took to fix it. Obviously ONLY ATTEMPT THIS if you know what you’re doing, and the machine is out of warranty.

December 14, 2008

SATA drives and Acer T135

Acer T135 with and new SATA drives - a snag

Just came across a nasty little snag with SATA disk drives. I thought I’d write it up, in case you run into something similar.

One of our family computers is an Acer Aspire T135, around 3 years old now. The 80GB hard drive is getting rather full and slow. Time for an upgrade.

Step 1 - check what the existing PC can do. It has a spare SATA connection on the motherboard, so that seems like the best way to go. There is plenty of space in the case for a new drive. There is a spare SATA-compatible power connector (different to the old-style 4-pin Molex’s) dangling in the case. I’ll need to get a new SATA data cable for the drive.