MOSFET REPLACEMENT (Sound Projects X-tender active speaker) - Page 1
Forum section: electronics / repair

author: tohtorizorro
author_rank: Contributor
timestamp: August 29, 2025, 02:28:22 pm
content: Hi all!I'm trying to repair a Sound Projects X-tender active speaker. They're supposed to be quite good, but apparently prone to overheating during hot summer days. This one had two fried MOSFETs with all the pins shorted together, which I believe also took out the fuse.I found the transistors on DigiKey, but since they're listed as obsolete, I started wondering whether more heat-tolerant or otherwise better-suited replacements might be available.I'm being a bit lazy here and haven’t traced their exact position in the circuit or anything. I really should learn to choose a proper transistor replacement with more confidence on my own, when I have the time. But in the meantime... 😅 These are TO-220 packages mounted on the main heatsink of the amplifier. Their specs (Vds 650V) and physical location (next to the bridge rectifier & relatively far from the speaker outputs) suggest they might be part of the PSU.The part code is:STP32N65M5 (TO-220)DATASHEETI’m still planning to order the original parts and only experiment with alternatives, so ideally any replacement candidates should also be available on DigiKey to avoid double shipping costs (this is kind of extra work anyways). BUT, if a clearly better option comes up, I could just skip the originals altogether. Any distributor would do in that case (preferably European, e.g. TME).I should probably just order the original parts and move on, but let’s give this a shot, or Is it even possible to provide solid replacement suggestions based on this info? 🙂Thanks!

author: olometaboy
author_rank: Newbie
timestamp: August 29, 2025, 09:24:09 pm
content: You can use the M9 version STW65N023M9-4https://www.farnell.com/datasheets/3968620.pdf

author: tohtorizorro
author_rank: Contributor
timestamp: August 30, 2025, 11:38:17 am
content: Quote from: olometaboy on August 29, 2025, 09:24:09 pmHey, thanks!!!The spec looks good but unfortunately the pinout doesn't match the common TO-220 G-D-S pinout as the originals. In fact it has an four pins: gate, drain, driver source and power source. I hadn't even heard of such MOSFETs beforeI'll try to come up with some candidates and post them here for approval.

author: Vicus
author_rank: Regular Contributor
timestamp: September 09, 2025, 09:00:16 pm
content: It seems a nice speaker. What brand of transducers does they use?For your question this should workhttps://www.tme.eu/it/details/ixtp32n65x/transistori-con-canale-n-tht/ixys/

author: wraper
author_rank: Unknown
timestamp: September 09, 2025, 10:19:21 pm
content: Quote from: olometaboy on August 29, 2025, 09:24:09 pmDid you post a link to a first random MOSFET you saw? Completely different part, with completely different specs except max voltage, in completely different package.

author: wraper
author_rank: Unknown
timestamp: September 09, 2025, 10:49:30 pm
content: Quote from: Vicus on September 09, 2025, 09:00:16 pmAlthough it will work, it has higher RDS(on)which means more heating. Here are a few suitable parts that will heat less due to lower RDS(on), have similar gate charge and 25V or better max gate-source voltage:FCP067N65S3NTP067N65S3HNTP082N65S3FSTP45N65M5

author: tohtorizorro
author_rank: Contributor
timestamp: September 12, 2025, 11:53:47 am
content: Thank you for everyone contributing!I had to set the speaker aside for a bit but will get on with it next week.Quote from: Vicus on September 09, 2025, 09:00:16 pmThe actual speaker element is kind of special since it has two elements in the same housing:https://www.bcspeakers.com/en/products/coaxial/15/8/15CXN76Quote from: wraper on September 09, 2025, 10:49:30 pmSo, would you say that in most instances lowerRDSONis OK? I've heard that you can replace an electrolytic capacitor with too low ESR on a SMPS and was thinking the safest bet would be to match everything else but the maximum values forVDSSandID. However, as you said, lowerRDSONwould of course reduce heating also.I really should just order a bunch, try them out and see what happens but haven't had the time and really appreciate all the help!

author: wraper
author_rank: Unknown
timestamp: September 12, 2025, 12:29:47 pm
content: RDS(on) only affects voltage drop on the MOSFET. Circuit like this does not "see" it as it's a negligible part of the voltage that is switched. Basically the only remotely common case when you should not use part with lower RDS(on) (not considering other parameters) is when voltage drop on the MOSFET is used for current monitoring.