- Well done to the Tories
- Covid Policy in 500 Words
- The EU headscarf ruling, or how to undercut your own argument.
- How Great Would This Be?
- A Jet-Lagged R4
- Idée Fixe
- My Rejected Submission for "Thought for the Day"
- A Sense of Proportion
- My missed career as a theologian.
- Big increase in the price of paper ahead.
- Never as planned
- Wat de mens gescheiden heeft
- Found on an old hard drive
- Any sufficiently advanced technology
- "For A Successful Life"
- Awash with rage
- Watch, anyone?
- Stand Up for What You Believe in, or Maybe Not
- Convert Now, Before You Change Your Mind
- That Time of Year
- Group Smarts
- The Final Copernican Revolution
- The Long March
- Dalton's Beetle
- No problem
Never as planned
Anyone seriously looking at distortion in resistors should take care to test at high frequencies. At 5 euros a pop (Farnell price), the Vishay MPM divider series are reassuringly expensive but I've just had to eliminate it from a preamplifier circuit as at 20dBu and 20kHz it produced 0.001% THD. That's a stupendous amount coming from a precision resistor.
Also out are reed relays. Those wonderful red Coto's are the choice for reliable switching at low currents and voltages, but at 30mA (and again at 20kHz) I found about 7uV of 3rd harmonic across the contact, which as expected came down a bit as the coil voltage was increased.
The irony (pardon the pun) is that I'm discovering all this whilst building a relay-switched gain control to replace an esoteric audiophile Japanese potentiometer that was plainly distorting. Mentioning this to the manufacturer (TKD) elicited exactly no response at all. Mind, you can get virtually zero distortion from even a cheap linear pot if you use it as the feedback divider in an inverting amplifier. Clearly doing the same with a logarithmic pot is a waste of time. Doing so with an expensive logarithmic pot is a great way of discovering just how many relays the same amount of moolah can buy.
Sunday 23 September 2012