Designing an audio test load switch panel - Page 1
Forum section: electronics / projects

author: Voxman
author_rank: Contributor
timestamp: December 18, 2024, 06:18:55 pm
content: Okay I know I'm asking for a kick in the butt, but!Please understand my poor brain doesn't work like it used to and for the most part I can work around to get solutions to problems.However I just can't seem to visualize conceptualize if what I want to design is doable with the components I have at my disposal.First let me say about 8 years ago (before brain got too muddy) I designed and built a patch switching control board for load resistors.It allows me to test amps under with several different resistive loads ( 4 and 8 ohms). It even has LEDS that illuminate to indicate what load is being used and if a speaker is connected. Pretty simple just a lot of wires .... It handles 2 separate circuits for stereo testing. so I used two 3PDT switches for left and right channels that control whether the amp is under a load or the speaker...switch is wired to the LEDs that indicate Load or Speaker. Also there are two DPDT toggle switches for selecting the impedance loads either 4 or 8 ohms also with LEDs to indicate which load is connected. So a total of 4 switches to accomplish this stereo flexibility.Well now I want to add a 3rd resistive loads to the switching panel for 16 ohm loads.I have 4 -100 watt non-inductive loads resistors to accomplish this but because my brain is so fuzzy these days I cannot come up with a working solution using the switches I have now. And I still want to keep the LEDs to indicate what switching configuration the panel is in.I designed 3 separate circuits that accomplish the proper switching but I'm unable to combine the switches in a manner that provides the results I need.I have one circuit that is 4 ohms using 2 resistors ( 200 watt capable)Another that does 8 ohms with 1 load resistor (only 100 watt capable)And last one that does 16 ohm using 2 resistors ( 100 watt capable).I've included the circuit diagrams so you can see what feeble ideas I've come up with. The limitations I keep running into is the fact the switches only have 2 positions. I thought about using a rotary switch but my brain started seeing stars.Ideally I'd like to have 200 watts on all the loads but I think that's impossible with what I currently have to use. I can buy more resistors if someone has a way to incorporate them into the circuits to produce the 200 watt loads.So that's what I'm attempting to accomplish. I don't know if it's possible using the components I currently have. I would gladly procure anything different to get this designed and operating.I don't want to have jumper cables involved to make this work. It's needs to be completely operated by just a few switches (again if possible).If anyone is up to the task to help design this patch panel I would be very appreciative and probably would send a gift card/coupon or two to the fireman's ball.If anyone knows of a particular website or link that has circuit diagrams related to my request, please pass them along.I could probably spend the next month or two racking what's left of my mental powers to design something but I know there's quite a few folks out here that could whip one up in 1/2 hour os less.I'm not lazy ... just old.Thanks very muchGaryPlease excuse the crappy labels... Apple just did an update that totally screwed up the photo editor tools.... but they're working on a fix...oh boy can't wait.

author: themadhippy
author_rank: Super Contributor
timestamp: December 18, 2024, 11:04:52 pm
content: with the resistors you've got 100w at 8 ohms is about it,but getting the 3 different load resistances only requires buying a 4 pole 3 way rotary switch and knitting it together something likehttps://tinyurl.com/26my895p

author: donlisms
author_rank: Frequent Contributor
timestamp: December 21, 2024, 04:29:34 pm
content: In this, I have ignored the LED's and the speaker/load switching as separate issues. The interesting part, I think, is how to switch the load impedance between 4 / 8 / 16. This can be done with two SPDT switches, but I think there is a better alternative -- a DP3T switch, like the CK 7211 or 7411. This is effectively a pair of SPDT switches that can be switched "left left / left right / right right". In other words, the middle position is half of each, and you get three out of the four possible combinations.The forth combination that you'd get with two separate switches is a redundant 8 ohm setting.The 7211 (2 pole) and 7411 (4 pole) are my favorites because I normally work with low currents. You'd probably want a different switch with the same configuration, for higher currents.I think it's a pretty clean solution to the problem, though... I would rather just use connections for the various combinations, rather than switches. I just don't like the idea of putting too much high-quality current through a switch, even when they're rated for it.I drew it and verified it with Falstad.You can see that the LED's could be added by using four poles, and the speaker/load switching is external to all of it.