Inductor pathology

[spuffock]

I am prompted to say a little on the subject of inductors, due to a problem recently seen with a new model of guitar amplifier. The kit in question had obviously been designed by a graduate with a computer, because, while theoretically very good, it suffered from a total ignorance of the fact that inductors are affected by external magnetic fields. When switched on, the amplifier output a 50 Hz squarewave, due to pickup of the mains transformer field by a matching transformer in the input stage.
How the thing got to production without anyone trying it I shall never know.
:lol: I bet there are other stories like this.........................

 

[stevez]

Product design can be quite the challenge. One would expect products to be tested in ways that represent the intended use and within the intended environment. Sounds like someone went right from design to production and skipped the testing.

 

[Nigel Goodwin]

There are various other possibilities as well, for example it's quite common for the production department to make changes to reduce costs.

The poor designer might have designed it well, and the prototypes performed as expected - then production mess it up!.

I had a LONG!! running argument with Sony over repeated failures of the mains transformer in a 100+100W RMS Sony amplifier (it's internal thermal fuse failed after about 9 months). My argument was that the mains transformer was far too small for the job (the amplifier was rated at 100W per channel continuous sinewave, both channels driven), which was why it kept failing. Comparing the size of the transformer to other toroids I estimated it to only be rated about 80W - in my opinion, FAR too small.

The amplifier itself had plenty of room for a larger transformer, and I've always assumed it was designed with a larger one?, and production fitted a smaller one to save costs!.

BTW, the cost of the proper Sony (too small) transformer was something like 150 GBP - a much larger, properly specified, transformer would only be about 25 GBP.

Sony's only comment was to offer 10% off the price of the transformer, and that they have had very few failures of the transformer.

 

[stevez]

The transformer is a good example of where manufacturers make a choice in terms of robustness/reliability - possibly based on their assumptions on how a product will be used and the criteria used by consumers to select their product over others. Sounds like in this case the amplifier would perform for a short term as specified - and someone assumed that most users would run at much lower levels.