Rob Flinn said:
Anybody built one of these ? Looks like quite a good tool, just wondering if it's as good as it looks ....
there is an issue with
ALL LCR bridges when it comes to measuring inductances. Those that are used in audio have a magnetic core, and as a result, their value changes with frequency and level. If measuring the nominal value is the issue, it must be done at the specified frequency and level*. LCR meters operate at very low level and don't offer much choice in terms of frequency (generally 100/120 and 1k).
When I made inductor-based graphic EQ's, I bought an expensive Racal-Dana bridge, and found out the measured value was an approximation of the in-circuit value; typically the 100Hz, 1kHz and 10kHz values were different, which is normal, but not very accurate if the inductor is to be used in a 315 or 3.15k band.
The Racal-Dana ended up in the assembly line, used to check consistency of the inductors before inserting them.
Capacitors also vary with frequency and level (and DC), but much less so.
In conclusion, these LCR meters are good for rough evaluation, but not for accurate prediction of in-circuit frequency response.
*The most spectacular changes are with tube amp transformers, where the inductance can vary as much as 1:10.