Converting Speaker Amplifier 110V -> 220V? - Page 1
Forum section: electronics / projects

author: ET Electronics
author_rank: Newbie
timestamp: July 15, 2018, 10:31:59 am
content: Hi Everyone,I was hoping I could get some input on the feasibility of converting my Klipsch Sub 8 amplifier board from 110V to 220V. I'll preface with saying that I have very limited knowledge of circuits but from what I've read and tested this should be possible by altering the connections on the multiple winding primaries of my device's transformer. The one thing that is confusing me is why there are five wires coming off the transformer's primary side. I've tested for continuity and it seems like orange/red are separated from black/brown/white and I get the same number of ohms between orange/red and black/brown + white so it seems like the number of windings are the same. The only oddball out is the white wire which seems to be directly connected to brown.My question is when I switch this transformer from its previous parallel setup to one in series should I just leave the brown lead unconnected? Are there any other things I should be worried about?Any and all help is much appreciated.Thanks

author: sokoloff
author_rank: Super Contributor
timestamp: July 15, 2018, 12:21:34 pm
content: In such a conversion from 120V to 240V operation, and assuming the diagram is correct, you can leave the brown wire capped off (not connected to anything, but insulated from everything).I can't see a functional purpose for having both the white and brown wire both "escaped" from the transformer housing if they're bonded together internally. If they weren't, I'd think one might be a case ground and the other a power line, but that's clearly not the case from the wiring diagram.

author: Ian.M
author_rank: Super Contributor
timestamp: July 15, 2018, 12:31:47 pm
content: I would suspect there's a thermal fuse between White and Brown, hence the need for an extra wire to support paralleling the primaries *after* the fuse for 115V operation.

author: sokoloff
author_rank: Super Contributor
timestamp: July 15, 2018, 02:18:24 pm
content: That would make sense!

author: ET Electronics
author_rank: Newbie
timestamp: July 15, 2018, 07:05:49 pm
content: So far I rewired like planned, hooked up to the sub to the wall and everything lights up like it's supposed to. I have to get the right fuse before I can continue to load testing. Genius me initially thought it was a good idea to just plug in the subwoofer without any modifications. Fingers crossed I didn't fuck up anything but I'm hopeful as there was no smoke just a fuse that blew.If this works I really don't understand why they didn't install a simple DPDT selector switch for voltage. They clearly designed it to be easily modified for the different regions but the manufacturer does not post the details anywhere. After testing, I plan on installing exactly that along with a proper AC inlet.Thanks for your input on what the 5th wire might be. It really put my mind to rest that I was heading down the right path.

author: IanB
author_rank: Super Contributor
timestamp: July 15, 2018, 07:18:32 pm
content: Quote from: ET Electronics on July 15, 2018, 07:05:49 pmBecause if they include the switch many people will plug it in with the switch in the wrong position and damage it. By not including the switch they are sending a signal to people "don't mess with this". It's safer that way.

author: ET Electronics
author_rank: Newbie
timestamp: July 15, 2018, 07:38:58 pm
content: Quote from: IanB on July 15, 2018, 07:18:32 pmI suppose but computer power supplies have had 110/220 selector switches forever. Plus it's not like it's unheard of. The following is a subwoofer in the same price class / size and is how I feel it should be.While I fully support voting with your wallet, I got my sub before I even thought about moving overseas. I've lost count of how many expat friends I have with similar stories of things blowing up. It's almost like you need a crash course in electronics before you move.

author: Relayer
author_rank: Contributor
timestamp: July 16, 2018, 01:18:56 am
content: Hello ET Electronics,Its not that simple converting a power supply from 110V AC to 240V AC by just changing the windingson the primary of the transformer and the mains fuse.For one, you need to make sure there are at least 2 main filter caps, or a single one with a minimumof 450VW rating on the primary side of the power supply.If there is only one cap, and its rated less than 200VW, then it will explode the moment you power it up.If there are 2 caps there, then you need to trace it out by looking at the tracks and make sure that theyare connected in series with each other.The correct rated fuse must be installed, though you are looking into it. Since the current capability of the110V configuration can supply higher currents, then the 240V option must have a much lower rated currentfor the fuse. Also, it MUST be a time-delay (slow blow) type.As for the primary windings, was the brown wire connected to the white one in its original state?If so, you may need to do the same when you make the conversion. It may be that the phasing between theprimary and secondary is important, but without seeing a schematic on it, it would be difficult to ascertain.But if you had access to a 2 channel oscilloscope, it could be determined that way.I hope the above helps.Regards,RelayerEDIT: Modified for Piondexter VVVVVVV

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2018, 01:39:22 am
content: Quote from: Relayer on July 16, 2018, 01:18:56 amWell, that's the most useless post I've read today. Linear power supplies typically don't have much on the primary side in the way of filter caps and unless its a big toroidal transformer(and the O.P's isn't), typically don't have a NTC thermistor.Also the correct fuse rating for 230V operation would be half that for 115V operation if the fuse was chosen to protect the load. However its very difficult to adequately protect a transformer with just a primary side fuse,(if you need to protect a transformer, you need correctly sized secondary side fuses + a resettable thermal trip)so the main job of the primary side fuse is to protect the line cord against overheating with the possible risk of fire by blowing if the primary side wiring shorts or if the transformer fails with a shorted turn or its secondary is short-circuited. As the wiring remains the same CSA, the service manual may not require the fuse to be changed when changing the primary configuration for a different voltage(which is more common for smaller transformers). To prevent a fire risk if the transformer overheats due to a sustained overload, there is commonly a non-resettable thermal fuse buried in the windings in series with the primary.OTOH if it was a SMPSU, you'd be *mostly* correct apart from that idiocy with square roots.Edit - this just got added:Quote from: Relayer on July 16, 2018, 01:18:56 amThat advice (to use an oscilloscope) is*DANGEROUS*and unless you have a CAT II or better rated isolated differential probe + the knowledge how to use it correctly is likely to result in you blowing up your scope or possibly even your electrocution.Also it would be exceptional for the primary to secondary phasing to matter at all in a linear PSU.

author: Relayer
author_rank: Contributor
timestamp: July 16, 2018, 02:59:52 am
content: QuoteThanx dick...QuoteI did say it was from memory, idiot, or can't you read?And yes, I was thinking in regards to a SMPS, my bad there...QuoteWhat scopes or people these days are still using CAT II probes?Another thing Poindexter, I was just giving an example of using a scope to determine phasing.If I were to tell the OP to rent a scope or sponge one from a friend, then yes, I should also tell him of the risks.I would have waited for his reply in regards to him having a scope.If he does have a scope, then he should have the knowledge on how to use it, as well as being aware of the safetyaspects when measuring live circuits.Its yobbos like you who just jump in and criticise, flouting safety issues, yet youshould be going around the electronics part of this Forum and condemn everyonewho suggest a noob to go and check voltages in the primary of a SMPS because theycould risk electrocution.The OP should be made aware of this, but this particular OP seems to have hadsome experience fooling with power supplies.Relayer

author: ET Electronics
author_rank: Newbie
timestamp: July 16, 2018, 06:35:57 am
content: Quote from: Ian.M on July 16, 2018, 01:39:22 amIan thanks for clarifying Relayer's post as I did not get what he was referring to. There are no capacitors on the primary side and wires from the wall go directly into the transformer, my crude drawing below is the original configuration of the incoming wires. If this mod required doing anything on the secondary side I probably wouldn't even bother.Am I correct in understanding that I need to switch to a 1 amp fuse from the 2 amp that was there? This makes complete sense and I'm glad you both brought it up as I didn't think about it. One last thing, there's this XL CTX film cap that I'm not entirely sure what it does. Could someone explain this and if I need to change it to something else?Again thanks for all your help.

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2018, 06:56:28 am
content: @Relayer,So, how would *YOU* safely check primary to secondary phasing of a mains transformer using an ordinary oscilloscope and probes?Also, in what circumstances do you believe that the phasing matters, i.e. swapping L and N right at the transformer primary would make a difference?N.B. I am *not* talking about checking phasing between two primaries, or between two secondarys - that's *IMPORTANT*, but there are better/easier/safer ways to do that than using an oscilloscope.@ET Electronics,The 0.1uF class X1 filmcap is there to improve the whole device's immunity to mains borne EMI and RFI. As its got a 250V AC rating, you don't need to change it , just keep it connected across L and N of the incoming supply.On the fuse issue - if it is in series with the primary, then yes you should fit a 1A fuse of the same type (timelag or anti-surge) in place of the 2A fuse currently fitted as converting from 115V to 230V will halve the primary current. However it wont be a large risk to leave it - its already too large to protect the transformer itself even at 115V, and probably cant be reduced below 1A without compromising reliability.

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2018, 07:52:46 am
content: Quote from: Ian.M on July 16, 2018, 01:39:22 amNo doubt it was with the best of intentions. Give him a break!Quote from: ET Electronics on July 15, 2018, 07:38:58 pmThose voltage selector switches are becoming less common. Most modern computer PSUs can work off 100VAC to 250VAC, without flipping a switch.I agree, this could be much easier. Another common solution is a voltage selector switch or jumpers, on the inside of the case or behind a panel, which needs a tool to remove.Quote from: Ian.M on July 16, 2018, 06:56:28 amYou're right. Phasing doesn't matter.For educational purposes, it can be safely checked, using an oscilloscope. Connect the transformer's primary to an AC source, isolated from earth, the safest being the secondary of another mains transformer, preferably a non-hazardous voltage such as 24VAC and compare the phase of the primary and secondary voltages using an oscilloscope.

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2018, 08:49:44 am
content: Actually, pri-sec phasing can matter in high sensitivity valve audio applications due to capacitive coupling between primary and secondary and (if present) may require readjustment of the 'hum bucker' pot across the heater winding that grounds it to best null out the mains hum. Its rarer than hens teeth for it to matter in a single transformer linear PSU modern device.

author: ET Electronics
author_rank: Newbie
timestamp: July 16, 2018, 11:35:17 am
content: Another newbie question but how important is polarization for this circuit? I wanted to install an inlet with a switch on the back but I'm unsure if I should go with an IEC 60320 C6 (cloverleaf) and just leave the ground unconnected (something about these kinds of circuits being ungrounded to avoid noise) or a C8. The other option is, of course, a C14/C18 but that has a corresponding unnecessarily thick wire. I've been very careful to maintain proper polarization as the original US plug easily does so but I hate dangling wires and would prefer to install an inlet. From what I can tell, euro plugs without a ground don't maintain polarization (well not the easy to find standardized ones at least, I'm sure there's something out there).

author: Simon
author_rank: Unknown
timestamp: July 17, 2018, 01:38:57 pm
content: Quote from: Relayer on July 16, 2018, 02:59:52 am21 posts and your already insulting people? Did you plan on staying here long?

author: Zero999
author_rank: Super Contributor
timestamp: July 17, 2018, 07:30:00 pm
content: Quote from: Simon on July 17, 2018, 01:38:57 pmTo be fair, I thought Ian's post was also uncalled for. Fair enough, he might have thought the reply wasn't helpful, but it was well-intended and he'd clearly taken some time in writing, so it's understandable he got cross when he read Ian's rude response.

author: Simon
author_rank: Unknown
timestamp: July 17, 2018, 07:57:58 pm
content: Yes i have had a chance to read a bit more. Ian could just have added the information he felt necessary. However name calling is the main trigger for moderation as it is generally a point of no return. i have chosen not to uphold the golden rule in this case and let Relayer settle in.

author: Ian.M
author_rank: Super Contributor
timestamp: July 17, 2018, 08:00:41 pm
content: I wasn't having a very good day so was perhaps more forthright than I should have been. I generally attack the (lack of) technical merit of the post, not the characteristics or personality of the poster. If I find myself sliding over the line, I try to take it as a warning I should take a step back from the topic.However, I didn't specify how many posts I'd read for that to be the most useless, so IMHO 'Relayer' had little excuse for jumping to personal insults, after posting a reply that was the technical equivalent of an overripe cow patty, and being called on it.I hope Relayer does 'settle in', and isn't too 'thin-skinned' to survive the rigors of debate on a technical forum.

author: Relayer
author_rank: Contributor
timestamp: July 18, 2018, 01:56:59 am
content: Hello Ian.M,QuoteI don't mind the debate or being corrected, it was more to do with:QuoteA more subtle and less scathing approach and I would have been OK with it and I would havestood corrected.This also:QuoteI did say it was from memory. The last time I tackled the same problem was around 2003 when the fristX-Box's were released.Yes, I admit I made quite a few errors in my assumptions, but on your part, it seemed like you needed toattack someone for their stupidity on the day.All said and told, I don't need the confrontation, a simple, "I have to disagree with what you've written" attitudewould have avoided my negative response.I hope no hard feelings.Regards,RelayerEDIT: My sincerest apologies to you ET Electronics for this kuffuffle in your thread by not staying on topic.

author: Ian.M
author_rank: Super Contributor
timestamp: July 18, 2018, 03:26:42 am
content: Sorry, as I just explained ' subtle' temporarily escaped me. I just didn't see *HOW* you could confuse it with a SMPSU when the O.P.s original post has a photo of a line frequency transformer. Normally you'd have got a reply like this from me:@Relayer,Errrr........ does this look like a SMPSU to you?

author: Circlotron
author_rank: Super Contributor
timestamp: July 18, 2018, 04:13:35 am
content: Quote from: Relayer on July 18, 2018, 01:56:59 amI remember doing a 120-240v conversion on one of those. Cut a single track to disable the voltage doubler. Of course, it would have helped a lot if I had also thought to change the 120vac MOV...

author: Simon
author_rank: Unknown
timestamp: July 18, 2018, 07:07:17 am
content: Just use a stepdown transformer.

author: Zero999
author_rank: Super Contributor
timestamp: July 18, 2018, 07:44:56 am
content: Quote from: ET Electronics on July 16, 2018, 11:35:17 amDo not use a two pin connector, with no ground pin. Going from the picture, the amplifier is not double insulated, which means its chassis must be connected to earth. The polarity of the phase and neutral is generally unimportant, but it's always better to get the side with the fuse in series with the phase conductor.

author: ET Electronics
author_rank: Newbie
timestamp: July 18, 2018, 01:22:45 pm
content: Quote from: Hero999 on July 18, 2018, 07:44:56 amNo grounding going on anywhere, even the original plug was only a polarized two prong plug. Doesn't matter as it doesn't seem the amp is outputting anything, I might have blown something else down the line when I originally thought it would be a good idea to just plug it in. Now it lights up like it's receiving power and doesn't blow the fuse but isn't thumping at all. Still not sure if it's the receiver acting up or the sub but I tried just plugging in an audio source directly from my phone and it didn't seem to do anything.While this thing is probably fucked it's still an interesting learning experience trying to make it work. Now to try to figure out how a TDA7294 works. Planning on taking the board to a Hackerspace and check it a little better than with my shitty multimeter and possibly problematic transformer. Just out of curiosity, are these linear transformers supposed to get insanely warm? Even though I got no output the thing got really warm, even in the "off" mode. I remember when it worked on 120v we use to unplug it when it wasn't in use as the back felt warmer then somehting in standby should.Quote from: Simon on July 18, 2018, 07:07:17 amWhere's the adventurous learning experience in that? Plus I'd have another thing wasting electricity and possibly humming.

author: Relayer
author_rank: Contributor
timestamp: July 19, 2018, 12:59:08 am
content: Hello Ian.M,QuoteI have to admit I was pretty brain-dead that day. I was thinking of an the first X-Box's PSU's when I was writing itand it never occurred to me that it was a transformer supply and not a SMPS, even though the X-Box was aswitch-mode jobby as well.I have to admit, that not working in the industry since 1998, I've lost quite a few brain cells since then.Regards,Relayer