gtkc.net

Electronics

Here are some electronics projects I have built in recent years.

This is a simple, but high quality (discrete) preamp. I found the concept for this circuit on this Zetex data sheet, and then using pspice, optimised the component values and arrived at the circuit given here. This uses three cheap and widely available transistors as the basis for the design.

Discrete preamplifier

Non oversampling DAC

Gigawork 24/192 "Big DAC"

I bought this module off Ebay, and built it into an old JVC Tuner chassis. This has the CS4398 DAC chip, CS8416 receiver, and no USB or upsampler chips. This is commonly known as the Gigawork 24/192 "Big DAC" in DIY circles. Pictures can be found in my gallery here.

Home Brew Power Amp MK1

This power amp was based around two 'LJM MX50X2' modules purchased off Ebay from a Chinese vendor.
The original MK 1 version was built into a disused Cambridge A5 enclosure, but the Cambridge heatsinks were simply not up to the job.
The MK II version was built into a new enclosure - a Rotel RB-956AX power amp chassis, and used the Rotel mains transformer.
For the MK III version I swapped out the Rotel transformer for two Cambridge A5 transformers.
Click above links for pictures.

Mains filter

I had a scrap APC3000 UPS, and looking inside it, I noticed that it had a mains filter section.
After dismantling it, and an hour or so later, I had managed to carefully remove the mains filter section by cutting it away from the main PCB.
I built this into an aluminium box from Maplin.
There are some pictures here.

Marantz CD-17 modifications

Having owned the CD17 for quite a few years, I decided to try out some modifications. I upgraded the main PSU smoothing caps (3300uF -> 10000uF) and several other replacement caps were fitted upgraded, and Oscons were used in the digital sections. I also replaced the OPAMP output stage (NJM2114) with LM4562 chips on 'Brown Dog' converters.
Did it improve the sound? Well I guess that's purely subjective.
It always was a detailed player with superb bass, and it still is. There are pictures here.

Headphone Amp

I bought this module off Ebay - it was sold as a 'JHL' (rather than JLH!) but it is a variation on the original John Linsley Hood headphone amp design.
Performance did not live up to expectations, and this has since been dismantled, and the PCB now resides in my 'junk box'.
The differences between this and the original JLH design have been documented on the DIYAudio website, and maybe one day when I'm feeling bored, I will change the parts out.
There are some pictures here.