Dummy Loudspeaker pt1 (not yet perfect)

[@MakeOrRepair]

It is completely usable for testing most amplifiers, just doing another version with a little more attention to detail! Not bothering to show the build because it is all chassis mounted and will depend on what parts are salvaged - stick it in a box and wire it up!

[@t1d100]

A very clever solution for the attenuation issue! My speaker dummy load needs are not nearly so elaborate as yours. In considering my needs, desires and functions, I was ending up requiring a lot of expensive switches and components. It occurred to me that all I needed was the resistors and some means to connect them, conveniently. I ended up just mounting the various resistors on a heat sink and terminating each, individually, to banana socket eyelets. These eyelets are mounted on the front panel. I can achieve any combination of resistors, with jumper wires. I can also access the signal at any point with my test gear. For my needs, this arrangement will work quite adequately. I also mounted it in my DIY e-load case, which had lots of spare room. This makes use of its fan and power supply for both types of loads. So, there is economy, there, as well. I ended up with a universal load center, of sorts.

[@MakeOrRepair]

First attempt was mainly things on hand. Switch cost is certainly an issue. I thought about 2 and 1 ohm as well, but it gets costly. I might think about it with relays in future. But what normally happens is I keep thinking how I could make it better, then it gets too expensive.

[@bansci]

Nice project! The quant asylum load seems to be shooting for 12db attenuation, how come you're aiming for higher? Is it you want to test at higher power? Have you thought about having a multi-tap? Say 10/20/40 dB attenuation steps? Then you can maximise your analysers dynamic range. Keep up the good work!

[@MakeOrRepair]

The main reason is that when testing amps with faults, I want attenuation before the analyser to help keep it safe. On thevanalyser 0 to 12db all uses same attenuation but changes the full-scale, so these impact dynamic range. The next step adds in an Attenuator at the front end but with 100k input impedance that has a big impact on the noise floor. Putting a specific attenuation in the low impedance load gives attenuation with much lower noise impact than the internal attenuation. I lose almost 40dBv of range, but no impact on noise. Using internal attenuation I would lose 24dBv range but the analyser noise floor goes up a lot. Perhaps I'll try and explain it in pt2.

[@MakeOrRepair]

Forgot about the multi-tap. Yes that would be a good idea thanks. I might add it later. I also intend to add a protective limiter on the output just in case.

[@bansci]

Thanks for the reply! Regarding the 12db, I meant the external load available from quant asylum, rather than the analysers internal attenuator. Interesting that exists though!