Thursday 19 November 2020

Tektronix TDS-340a CRO

A mansplainer on DIYAudio just told me my TDS-340a has an LCD, not a CRT.

This photo is to put him in his place.

Saturday 14 November 2020

Building the Per-Anders Sjöström QSXM2

I don't always just build my own toys. When other designers make really beautiful kit, I buy their PCBs and go to town.

Such is the case with a few of Per-Anders' designs. He and I share a common design rationalle, which can best be summed up as "components are cheap, if more of them makes it perform better, go for it!".

A perfect example is the QSXM2 phono preamp. Something like 200 resistors, 110 transistors, around 100 caps. It's really not mucking around. It's a preamp that leaves no stone unturned in the search for performance. I'm keen to see if I can improve on the basic phono pre in my NAD3240PE, and this one looks like a very good candidate. I've built some othe Per-Anders designs (mainly head-amps), and have been very impressed.

So I ordered a PCB from his website, downloaded the design doco, and started work:

I've set my work area up with a nice new A2 cutting mat, which protects it from the soldering iron and scratches. There's no need for the microscope for this guy, as it's all through-hole.

So far I've done all the resistors (I had comprehensive stocks, which will now need to be replenished), and I'm on to the caps, many of which I'll have to order in.

I'm looking forward to trying it out!

Sunday 8 November 2020

Annual HP 3585B stinky capacitor hunt

One of the hazards of using elderly test equipment, such as my HP 3585B, is old capacitors. HP loved using tantalums, which while having great low ESR, are also teensy little time bombs. Occasionally (typically at turn-on) there's a stink, and that's the sign that another one has let go.

So this happened the other day, and I spent a couple of hours sniffing the little blighter out, quite literally, as they're quite pongy and your nose is a great diagnostic tool.

This is quite a beast of a spec-an, weighing in at around 35kg. It's really beautifully made, with gold plated circuit boards. I started by pulling boards one at a time and giving them a quick once-over.

Eventually I found it, at the back of the input module on the underside of the unit.

This one is a little 2μ2 20V Kemet axial tantalum. Luckily I have a few in a drawer. So I whipped it out and popped a new one in, and now it's good as new (until next time).