Amplifier test panel with speaker protection

I put together a fixture for testing amplifiers that allows switching between a dummy load and speakers. The speakers have a speaker protect circuit to protect from a blow out from an output signal offset voltage. Not brain surgery but a handy tool for the audio shop.
Link to schematic: 1drv.ms/b/s!AgRy1tCE6lTdrzv12...
Link to the speaker protect: tinyurl.com/yx5zkbcb

[@FluxCondenser]

Nicely done.

[@RobsFixitShop]

Thanks. I was just using it last night. The stereo I was working on had spade terminals for the speakers so just I just made myself a new set of jumpers and I was up and running!

[@fabriziocordasco5381]

Hi Rob, good tutorial, i have a question, would a simple resistor dummy load work for silent recording of a solid state of a guitar amp? I have a 50w solid state guitar amp 4ohm output, i want to connect the amp speaker output into a speakers simulator box that has a speaker level input and a speaker thru input, now if i connect a 4ohm 50w resistor dummy load into the speaker thru input of the box and no real speakers will it work? Thanks

[@RandallDibble]

Canned Heat - Need more Heat Sinking if you're going to run the amp for any length of time !

[@alfredneumann4692]

Why not using some BNC-Connectors for the scope?

[@RobsFixitShop]

I see XRayTony just did a similar panel that uses BNC connectors with a voltage divider. I kind of like moving my probes around but the BNC connectors really look sharp. The video is here: kzbin.info/www/bejne/h4SbeJqLjNOVp5I

[@vicvergauwe5736]

Hi Rob , I like your amp test panel :-) Can you publish the wiring diagram and specify the speaker protect circuit please ?

[@RobsFixitShop]

Thanks Vic. I put a link to the schematic and the speaker protect in the video description. So far I have really been liking it!

[@vicvergauwe5736]

Thanks Rob for the link to the schematic and the speaker protection kit ! Have a nice day :-)

[@waynethompson8416]

Interesting little panel. I think that if I ever make one, I will make it useful for 4Ω, 8Ω and 16Ω plus speakers. I would use two 4Ω resistors in series followed by an 8Ω resistor and connect the "hot" lead to just the first 4Ω resistor for 4Ω speakers, to the end of the second of the in series of 4Ω resistors for 8Ω, and to the 8Ω resistor for the 16Ω load. Do you see any issues of using the speaker protection in your panel if you are working on a receiver that also has one built in?

[@RobsFixitShop]

I was to do it over I would have done 4 and 8 ohms. I never use the 16. I have not had any problems with the speaker protection and I love having it. I wish I would have put a switch to turn it on and off instead of unplugging the power supply

[@richardweisman6556]

Are all the devices attached directly on the sheet of aluminum or are some isolated from ground? The speaker jacks seem to have plastic on both sides.

[@RobsFixitShop]

I tried to keep both channels isolated so the aluminum is not connected to ground. The speaker protect circuit actually connects the right and left ground so when going through the speakers the 2 channel grounds are connected otherwise completely they are isolated

[@richardweisman6556]

@@RobsFixitShop thanks for the information; I am a newbie and the reply really helps. The speaker protect is mounted thru brass stand offs to the aluminum which probably puts it on a common ground, right?.

[@RobsFixitShop]

I checked and the speaker grounds are isolated from the panel. You're right though that I should've used nylon standoffs.

[@bixy9347]

Why 16 ohm wouldn’t 4 ohm be more common.

[@RobsFixitShop]

I was thinking the same thing after I got it all set up.

[@cougar1861]

It would be instructive to have had a better explanation of how, exactly, the destruction of the that "inspired" this interesting project.

[@cougar1861]

Of course, I meant, "the destruction of the AMP occurred that inspired ... " But now that I know you are monitoring your video comments, and "hearted" mine, would you give the explanation? I'm in the process of teaching myself electronics and will have an oscilloscope before long. I've heard the horror stories of destroying a scope with "incorrect" hookup to the device under test but I have not heard of destruction of the DUT itself!