tripitaka Posted June 11, 2023 Posted June 11, 2023 30 minutes ago, 21stcenturyquaker said: No, previous amp was a Naim 250. Either way you have had some extraordinary bad luck. So let's say a wire had come loose from a driver, shorting the amp outputs - that could certainly stuff the amp (if it didn't have an internal protection circuit) but then the drivers would then have to be 'unshorted' in order for the 39V to subsequently blow the voice coils. I would be looking inside the speaker to see if a wire is dangling.
21stcenturyquaker Posted June 11, 2023 Author Posted June 11, 2023 6 minutes ago, VanArn said: Fuses are necessary to prevent expensive mishaps such as burnt circuit boards and power transformers. There are fuses in the amplifier: I don't know what they do but all appeared intact when I looked inside.
21stcenturyquaker Posted June 11, 2023 Author Posted June 11, 2023 5 minutes ago, tripitaka said: I would be looking inside the speaker to see if a wire is dangling. The crossover appeared ok when I inspected it yesterday. Should I remove the drivers?
21stcenturyquaker Posted June 11, 2023 Author Posted June 11, 2023 Last week a family member had attempted to play some music - unsuccessfully - while I was out: everything was switched on except the preamp. Could this have caused a problem?
tripitaka Posted June 11, 2023 Posted June 11, 2023 47 minutes ago, 21stcenturyquaker said: The crossover appeared ok when I inspected it yesterday. Should I remove the drivers? Nah, sounds like thats not the problem then. You've just had bad luck with amps
tripitaka Posted June 11, 2023 Posted June 11, 2023 46 minutes ago, 21stcenturyquaker said: Last week a family member had attempted to play some music - unsuccessfully - while I was out: everything was switched on except the preamp. Could this have caused a problem? Wouldn't have thought so, unless they messed about with the output terminals as well
Addicted to music Posted June 11, 2023 Posted June 11, 2023 1 hour ago, 21stcenturyquaker said: There are fuses in the amplifier: I don't know what they do but all appeared intact when I looked inside. For most class A, A/B amps modules there are usually 2 main fuses, they protect the PSU positive/negative rails from shorting. You’ll also have a 3rd mains fuse. I have to asked a stupid question for clarity. Usually digital multimeters do not display a zero in front unless it’s less than a volt. Was it displaying 0.39V or 39V. Here a pic of voltage of a 9V battery 1
21stcenturyquaker Posted June 11, 2023 Author Posted June 11, 2023 38 minutes ago, Addicted to music said: I have to ask a stupid question for clarity. Usually digital multimeters do not display a zero in front unless it’s less than a volt. Was it displaying 0.39V or 39V. I have just tested it again - the multimeter set at DCV 1000 as before - and it now reads 000 Yesterday it read 039 Not 0.39 or 39
tripitaka Posted June 11, 2023 Posted June 11, 2023 16 minutes ago, 21stcenturyquaker said: I have just tested it again - the multimeter set at DCV 1000 as before - and it now reads 000 Yesterday it read 039 Not 0.39 or 39 Ok then I've concluded that your house is haunted, suggest contacting a team of ghostbusters 2
pete_mac Posted June 12, 2023 Posted June 12, 2023 19 hours ago, tripitaka said: BTW, what other kind of current would you expect an amplifier to be putting into a speaker, if not Direct Current? I couldn’t see this question answered anywhere… but amplifiers spit out AC. DC is the enemy of you speakers. 2
Dean Gale Posted June 12, 2023 Posted June 12, 2023 4 hours ago, pete_mac said: I couldn’t see this question answered anywhere… but amplifiers spit out AC. DC is the enemy of you speakers. At idle it should read as close to Zero DC as possible 19 hours ago, Addicted to music said: Most likely possibility is that something has failed and is outputting DC. Get a cheap multimeter set it to max DC volts range to see if output has DC. some do, if you check the Magnaplanar range out, they have a fuse in series with the input. This is the other cause, playing loud can over heat the voice coil to the point where it will just stop and you have an open circuit in the coil. Driving amplifiers clipping (Beyond the Rail voltage where the limit is will output DC that’s not good. Any DC energy will heat the coil fast. Old Kefs have fuses , some old Tannoys and seen them on Wharfedales too but don't tell the bloke who knows everything 1
pete_mac Posted June 12, 2023 Posted June 12, 2023 19 minutes ago, Dean Gale said: At idle it should read as close to Zero DC as possible Indeedery! 1
Richard Tremain Posted June 13, 2023 Posted June 13, 2023 On 11/06/2023 at 3:16 PM, tripitaka said: Do passive speakers have fuses? That's a new one on me. I've blown my fair share of speakers and it was usually me playing them too loud (coz when the sound is not distorted one doesn't always realize how loud it is) BTW, what other kind of current would you expect an amplifier to be putting into a speaker, if not Direct Current? Edit: PS. I've been asking idiotic questions for years on this forum, it's how I learn Common for passive spk to have 1amp fuse especially in earlier years perhaps cost or just neglect less common now. But 2 burnt out Bass drivers is result of this more modern approach. 1
Sub Sonic Posted June 13, 2023 Posted June 13, 2023 On 11/6/2023 at 8:55 PM, andyr said: Aah but fuses ... degrade the sound, Murray! @andyr clearly you’re not using expensive enough fuses! 1
andyr Posted June 13, 2023 Posted June 13, 2023 44 minutes ago, Sub Sonic said: @andyr clearly you’re not using expensive enough fuses! Very probably, SS!
GregWormald Posted June 13, 2023 Posted June 13, 2023 3 hours ago, Sub Sonic said: @andyr clearly you’re not using expensive enough fuses! 2 hours ago, andyr said: Very probably, SS! Imagine using $900 fuses and having them continue to blow as you search for the problem. 1
mbz Posted June 13, 2023 Posted June 13, 2023 Possible scenario as previously mentioned is you have a blown output or driver or transistor which is dumping near rails voltage on the speaker line. Sadly parts fail. Preferrably the amp should have some speaker protection circuit that (amongst other things) monitors for Vdc and opens/breaks the speaker connection when inexcess on 0.5-1Vdc is detected. Relay based circuits are quite common, after market kits can be purchased on the bay for about $10-, add a small transformer and fuse they can be retro fitted for about $25 parts. One issue is that you need to match the relay with the amp, ie, the relay must be able to release when the short occurs, for large amps you may get a shorting current of 70-100A! which can weld the relay closed making it impossible to release. The diyaudio guys have done some good work in this area using power fets rather than relays, either way we all need to be proactive in this area. If your power amp does not have a protection circuit then think about the consequences... 1
21stcenturyquaker Posted June 13, 2023 Author Posted June 13, 2023 9 minutes ago, mbz said: If your power amp does not have a protection circuit then think about the consequences... 2 pairs of speakers have been the consequences so far 1 1
21stcenturyquaker Posted June 13, 2023 Author Posted June 13, 2023 25 minutes ago, mbz said: Possible scenario as previously mentioned is you have a blown output or driver or transistor which is dumping near rails voltage on the speaker line. Sadly parts fail. Preferrably the amp should have some speaker protection circuit that (amongst other things) monitors for Vdc and opens/breaks the speaker connection when inexcess on 0.5-1Vdc is detected. Relay based circuits are quite common, after market kits can be purchased on the bay for about $10-, add a small transformer and fuse they can be retro fitted for about $25 parts. One issue is that you need to match the relay with the amp, ie, the relay must be able to release when the short occurs, for large amps you may get a shorting current of 70-100A! which can weld the relay closed making it impossible to release. The diyaudio guys have done some good work in this area using power fets rather than relays, either way we all need to be proactive in this area. If your power amp does not have a protection circuit then think about the consequences... Given my experience this certainly seems like a good idea. I have requested a schematic from Hugh for the amp. Obviously I'd like it repaired and fully serviced - recapped, and even a protective circuit if that's deemed to be a good idea - but I don't know a suitable tech for this work. Plus, last time I checked the output voltage it wasn't outputting anything significant, and no different to the left channel. Obviously I don't have confidence to use it as is.
21stcenturyquaker Posted June 13, 2023 Author Posted June 13, 2023 I shall pose the service question to the Aksa amplifier user forum which was recently brought to my attention. 1
andyr Posted June 13, 2023 Posted June 13, 2023 15 minutes ago, 21stcenturyquaker said: I shall pose the service question to the Aksa amplifier user forum which was recently brought to my attention. Whereabouts is that?
21stcenturyquaker Posted June 13, 2023 Author Posted June 13, 2023 Stereo amps and preamps - owners forum.
andyr Posted June 14, 2023 Posted June 14, 2023 (edited) 1 hour ago, 21stcenturyquaker said: Stereo amps and preamps - owners forum. Aah, thanks - yes, that would be a good place to find out what service people are around. btw - will send you a PM, shortly. Edited June 14, 2023 by andyr
21stcenturyquaker Posted June 14, 2023 Author Posted June 14, 2023 It seems that replacement drivers are readily available on eBay. How can I test if the speaker is ok? Obviously I don't want to repeat the whole disaster over again if the speaker is ultimately responsible. As I said previously, there didn't visually appear to be damage to the crossover.
surprisetech Posted June 14, 2023 Posted June 14, 2023 On 12/06/2023 at 4:34 AM, Addicted to music said: There is no protection that I know of if you overdrive a speaker, this is also a major cause of speaker failure. Carefully chosen Polyswitch (PPTC Thermistor) in series with each driver will do the job. They are fast-acting and self resetting. I've always installed them in my PA speakers and never had a driver failure. Especially great for protecting compression drivers against bursts of sustained HF feedback. I'm currently repairing a pair of HK Audio speakers for a local folk music club. Compression drivers got cooked because the incandescent lamps used for protection didn't act fast enough. I'll be replacing them with Polyswitches.
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