Dummy load
Printed From: Speakerplans.com
Category: Plans
Forum Name: New Projects Forum
Forum Description: Forum for new speakerplans projects, in memory of Tony Wilkes, 1953 - 2014
URL: https://forum.speakerplans.com/forum_posts.asp?TID=108833
Printed Date: 27 March 2026 at 7:52am
Software Version: Web Wiz Forums 12.08 - https://www.webwizforums.com
Topic: Dummy load
Posted By: Teunos
Subject: Dummy load
Date Posted: 07 December 2024 at 9:38am
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Previously we've always had a single channel 8R/4R switchable load made from a boiler heater coil (huge open wire wound resistor) where the 4R is tapped from the middle, encased in silversand. It still works fine, but it only had a single speakon and a single mains socket outlet for plugging in 4mm banana jacks (this fits perfectly!). So last summer i decided to make a new version. It should be capable of testing 4 channel amplifiers in 8R, or dual channel amplifiers in 4R. It's based around 4*2kW (@120V) heater elements, each element measures around 7.5R. The cavity around the elements is fully stuffed with fine grain silver sand to absorb the heat from the elements. The volume of the box was designed such that the silver sand inside wouldn't get above 60C after 2 minutes of sustained 4x1kW loads. Looking back this is probably a bit overkill as the box got quite heavy. Box is made from scrap wood, 15mm HPL laminated birch from an old kitchen and some fenol coated birch.  Drying the silver sand out in the sun, to then be poured into the case before the side was glued in place.  The connector panel is made with 1x Speakon per heating element and 2 switches that set channel 1 and 3 to a 4R load by wiring channels 2 and 4 in parallel to them. I've also 2 sets of 4mm safety jacks to easily connect a high voltage probe for the scope or a multimeter. The switches took a while to get in as apparently DPDT switches aren't very common in the netherlands for general purpose electrics usage. Nominally rated for 16A, i guess they will be fine for the relatively short usage they will see higher sustained currents than that.  The PCBs are some custom ones i've drawn in Kicad, basically just a simple breakout so you can solder a wire into a hole instead of to the terminal. And the final product.  ------------- Best regards, Teun. |
Replies:
Posted By: Earplug
Date Posted: 07 December 2024 at 10:17am
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Nice job -- but I would have used water cooling - with the option of making a cuppa while testing!!  ------------- Earplugs Are For Wimps! |
Posted By: njw
Date Posted: 08 December 2024 at 12:25am
Very neat, my only attempts at a dummy load have been an old voice coil immersed in oil or wiring an old kettle and heater together with some very dodgy wiring.
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Posted By: Pinyorouk
Date Posted: 08 December 2024 at 7:54pm
| Very nice. Well done! |
Posted By: FartyMcfly
Date Posted: 24 January 2025 at 7:57pm
Hi! Do you mind letting me know where you bought the heating elements for this project? I am also in NL, in Amsterdam. And the silver sand - is that just the stuff that you get in 25KG bags from Gamma etc? Or something more specialised? I wanna build a dummy load to test my Admark AD442 (claims to be 4kW per channel) and I have quickly realised that using wirewound resistors is gonna be stupidly expensive, so this solution looks perfect. Alvast bedankt! Rob
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Teunos wrote:Posted By: Teunos
Date Posted: 27 January 2025 at 7:59pm
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Sure thing Rob; They are the 2kW version of this ad; https://nl.aliexpress.com/item/1005005115301592.html" rel="nofollow - https://nl.aliexpress.com/item/1005005115301592.html however i see this specific link sold out, probably plenty similar ones out there. The sand is indeed just from Hornbach. Make sure to dry it properly though or it won't compact well. FYI; I've tested a DAP TA-4.3400 on full load, which i'm pretty sure of is an Admark/Sinbosen job too, without any problems, except for the breaker tripping after a while. Based on that, i can guesstimate what the outcome of the Admark test will be. Alternatively, feel free to drop by around Oss and we can use this load. ------------- Best regards, Teun. |