Off-Grid,  I find that many computer speakers need 9 VAC Power,  (I need) - Page 1
Forum section: electronics / general

author: RJSV
author_rank: Super Contributor
timestamp: September 23, 2025, 06:54:33 am
content: Hey there !Recently bought a pair of typical table top PC speakers, (garage sale) but after got home I realized that my battery stock doesn't include AC capability, at 9 VAC, or 12 VAC.I know I could make a couple transistor multi vibrator, but wondering if there is a simple purchase I could do ?Google search keeps misunderstanding, thinking that I wanted 9 VDC to 120 VAC...I'm thinking the easiest way is to BUY a regular, 120 VAC output inverter, and...employ a small step-down transformer !Seems ironic, somehow. Perhaps buy TWO little inverters, and salvage the transformer out of one unit (a 9V to 120 V reversed).Off-Grid here ! Thanks, Rick B.

author: jonovid
author_rank: Super Contributor
timestamp: September 23, 2025, 07:20:48 am
content: table top PC speakers - is there a way to tap into the DC inside the speakers

author: Andy Chee
author_rank: Super Contributor
timestamp: September 23, 2025, 07:26:06 am
content: Open the speakers and ascertain whether the AC input actually splits into bipolar voltage rails.There's a good chance that the AC input may simply be rectified into a single DC rail, and if so, the solution is trivial.... plug the DC power supply into the speakers.

author: RJSV
author_rank: Super Contributor
timestamp: September 23, 2025, 07:00:57 pm
content: Thanks.It's printed on back, rated 9 VAC at 240 mA. So that's roughly a couple watts (2 1/4 watts using the RMS value).We do have good 120 volts via household inverters, so it's still going to be useful, to find and buy a regular wall-wart, (usual cannon connector). That way I can measure things inside the PC Speaker.Paranoid about connecting things to my Android phone headphone output,...2 blown up phones so far (this year). But prices weren't too killer, at least I'll find out. Plus, having a 'real' wall wart providing the AC will give realistic measuring, of the internal DC requirements.Yet another task, but MUSIC RULES my day!Rick B.

author: TimFox
author_rank: Super Contributor
timestamp: September 23, 2025, 08:04:35 pm
content: Quote from: Andy Chee on September 23, 2025, 07:26:06 amAssuming that the AC input feeds a simple rectifier to a single rail (as suggested above), a DC power supply will go directly to the DC rail, in the same way as in old-style "AC-DC" radios.The wart itself is usually just a step-down transformer from 120 V to the advertised 9 V (both voltages RMS), and the rectified DC will be roughly 11 or 12 V including diode drops in the rectifier diode(s).Almost all warts have only two poles on the connector, for a simple AC voltage (or DC voltage for those warts with internal rectifiers).The other possibility in the speaker's construction uses a more complex switch-mode design to derive a two-rail supply from 9 VAC, but that's unlikely.

author: Ian.M
author_rank: Super Contributor
timestamp: September 23, 2025, 08:45:31 pm
content: .... or as Andy hints, it may connect one side of the AC to system ground and use two half wave rectifiers on the other side to develop balanced positive and negative rails. That would be a PITA to rework to run from DC without an AC source and without introducing noise from an inverting buck converter.

author: RJSV
author_rank: Super Contributor
timestamp: September 23, 2025, 11:57:39 pm
content: Ah shoot; you beat me to it;...Common Sense !I already just tried that, (and the cannon style connector fits)! Reasoning that it's, roughly X 1.4 to get peak from RMS (Root-means-Square) that would be 9 X 1.4 = 12.6 Volts peak...although I did forget to include maybe .8 volts for the drop at the rectifier. But that still gives11.6 V peak in the math.Don't need to sweat if it gets 12.9 v anyway, at these, 2 Watt power ranges.But, mainly I've partially wasted some reader's time. Outcome is nice, though, already I've obtained the good BASS in enough volume. A continuous 11.9 VDC rather than an AC that reverses at about 12 V peak is starting to look very similar, in outcome.I try to be too smart, and neglect the basics, first year High School shop class level Stuuuupid!Great outcome though ! Come on ZZTOP hits, in my 'shop'. (Outdoor umbrella).

author: RJSV
author_rank: Super Contributor
timestamp: September 24, 2025, 12:00:58 am
content: Besides, those PC Speakers were $ 2 at the garage sale, and smartphone loss would be less than $ 40 if something blows.