Re: Attenuator for amp testing.
« Reply #20 on: November 27, 2017, 01:36:51 AM »
Something else to watch, with respect to the 'speaker dummy load box', is that is obviously heats up when used.

That changes the resistance somewhat of the aluminium power resistors that I use, which are *not* the 'non inductive' types and nor are they 'precision', being 10% tolerance 'cheapies'.

In practice, I measure the spec'd 8ohms to be around 8.5ohms when cold ....  and that drops somewhat when they get warm ... down to 8.3ohms or so.


Of course, my bench digital multimeter (my most accurate) and handheld digital meter, both are not so accurate measuring low resistances ...  being both quite old and 'budget' to begin with!

If I had the funds, I'd like to get some precision non-inductive resistors, parallel a bunch of them to reduce the tolerance errors, heatsink them some more *and* get some 'low resistance' accurate meters - perhaps of the '3 wire' variety   ..   THEN one might have some reasonable 'certainty'  that an '8ohm load'  box is *actually* that   8)

IF one was to invest in a decent bench audio interface, say an RME of the 1Kusd persuasion, AND a few hundreds of usd for proper metering, and then a hundred usd or so for a better dummy load box, one could well reduce the measurement errors by some tens of percent   ;D


If I was 20 years younger, given the highly developed state of the DIY audio world, in general, AND the awesome capabilities of  current audio interfaces and 'Room EQ Wizard' measurement software ...   I would surely do so!

Now, it's a race between age, funding, listening environment and ear capability - 'near enough' is mostly 'good enough'  :)

AND it goes without saying, that even with a high precision resistive load box and audio interface setup, real world applicability of said performance measures are pretty rubbery at best.

Real speakers are very far from ideal, nor are 'single frequency sinusoidal excitation' measures very representative of  'good sound' .

Still, we are 'engineers' - constrained by time, cost and end result in the 'real world'.

We do what we can, in the time allotted, for the beans available to the best of our educated estimation!

And when all is 'said and done', often at the 'end of the day', *still* we enjoy the performance achieved ....   perhaps abetted  by 'a few beers'   ;D
« Last Edit: November 27, 2017, 02:32:13 AM by alexc »
I ping therefore I am


Re: Attenuator for amp testing.
« Reply #21 on: November 27, 2017, 01:53:53 AM »
I recommend listening to some the classic greats ...  like the remastered Stax series CDs ..  Booker T and the MGs and the other 'house talent'

Some good, sensitive speakers, not too loud, with minimal class A tube amps and decent converters   8)
I ping therefore I am

abbey road d enfer

Re: Attenuator for amp testing.
« Reply #22 on: November 27, 2017, 03:11:59 AM »
I have a feeling we have lost the OP...  ???
Who's right or wrong is irrelevant. What matters is what's right or wrong.
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Re: Attenuator for amp testing.
« Reply #23 on: December 12, 2017, 05:22:38 PM »
Back on topic, in another thread I suggested using cooker elements as high power loads. A 2KW 115V heating element has a resistance about about 7 ohms.



'The only people not making mistakes are the people doing nothing'