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Post by Deleted on Mar 7, 2015 14:58:19 GMT
I'm a novice when it comes to technical knowledge so I'm hoping someone here can help with a query.
I bought yet another Exposure pre/power combo this week, a 3 and 4 from the really early days. its a gorgeous aubergine colour and sounds truly epic. It came with a known problem that I thought a re-cap might fix. Sadly it hasn't so I am looking for ideas. I can always get it serviced but would really like the satisfaction of sorting it myself and actually learning something.
Ok, the whine is loud enough to be clearly audible but its not volume dependant and the music drowns it out. It's a bit like a cross between a mosquito and a housefly near your ear, if that makes any sense. When I switch the amp off, the whine rises in frequency and makes a rather silly "whoop" sound as it finally shuts down. only takes about 3-4 seconds to go completely.
I've only ran the amp for short periods but the whine doesnt seem to change either in volume or pitch. It's also equal on both channels. I should add that it's a single transformer IV but its actually a frame transformer rather than a toroid. It really sounds gorgeous so I'm not wanting to change anything I don't have to.
Any ideas/thoughts/advice is welcome.
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Post by John on Mar 7, 2015 15:12:40 GMT
Try James He knows his stuff
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Post by Deleted on Mar 7, 2015 15:15:20 GMT
Hopefully he will pop in and have a gander at this thread.
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Post by John on Mar 7, 2015 15:17:17 GMT
Send him a PM He is very helpful
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Post by Mr Whippy on Mar 7, 2015 18:10:19 GMT
Is it there with the volume right down? Try removing the pre and short the two inputs and if still there, at least you'll know it's the power amp.
If you have more than one, can you not try a different combination?
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Post by Deleted on Mar 7, 2015 18:23:18 GMT
Whilst I do have other preamps, even exposure preamps, I can't connect them to this combo because it uses a single Din connection to send power to the preamp and signal to the power amp,must like Naim only with a domino 5 pin Din.
It's there irrespective of input or volume (the exposure has left, right and master volume pots).
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Post by MartinT on Mar 7, 2015 22:15:07 GMT
Output stage oscillation? Try changing speaker cables temporarily.
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Post by Deleted on Mar 7, 2015 22:19:29 GMT
I read a thread about amp noise on the PS audio website that was recommended to me. I tried the power amp on its own with no preamp connected and there's no noise at all. From what I can make out, PS Audio say that means it's not the power amp. The Exposure preamp draws its power from the power amp though, so I guess the problem could still lie in the power amp's supply to the pre, or the preamp itself, or indeed the cable.
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Post by Deleted on Mar 7, 2015 22:23:57 GMT
Output stage oscillation? Try changing speaker cables temporarily. Thanks, Martin. I can try other cables but I'm using NVA LS2 which should be about as innocuous as they come. The same problem was also there when the seller used the amp with his own cables (not sure what he used) so I suspect it might not make a difference. Worth a go though, Thanks. |
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Post by MartinT on Mar 7, 2015 22:52:42 GMT
Ok, from the new information it does sound like the power amp's power supply under load. I wonder if it's regulated?
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Post by Deleted on Mar 7, 2015 23:15:22 GMT
It's the un-regulated Exposure 4 (single version). I've had quite a few 4 power amps over the years but none as early as this one. The odd thing is that all the same casing holes are there to run phonos for signal, but it's wired like a Naim with everything going through the single 5 pin din.,
Memory is a fickle thing but it sounds better than any Exposures I've had since my last 3/Dual 4 and I honestly think it bests that combo. It certainly outperforms a 6/7 (Dual supply)/4 (Dual unregulated) that I currently have.
Other 4s I've had were fitted with a separate PSU board and caps for the preamp supply. This one isn't. It's totally original and has only had one owner from new, so I know it's the way it came from JF.
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Post by Sovereign on Mar 7, 2015 23:34:39 GMT
You may want to call Eposure direct and ask to speak to Tony, if he still works there, and try and glean some info. They of course will service it but if you can get some advice and fix yourself then that would be even better. Where i the worl are you?
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Post by Deleted on Mar 7, 2015 23:41:41 GMT
I'm way up North beside Newcastle Airport. We have a very good company up here who have serviced a fair few amps for me and I'm sure they could fettle this one. I'd hoped it was something basic that I could tackle, but it's looking unlikely. I really expected tibo be fixed bt a re-cap. I guess I could ring Tony and ask him if he has an idea where the fault may lie. If only it was wired like other Exposures, I could find out a fair bit more by substituting preamps and PSUs. Having heard how good it is, I'm reluctant to change anything other than correcting the fault.
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Post by Sovereign on Mar 8, 2015 0:25:52 GMT
Have you tried giving it a whack !
ONLY KIDDING !!!
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Post by Deleted on Mar 8, 2015 0:32:46 GMT
 I'd come off worst. It weighs a bloody ton! It will probably end up at Maughan's for a service if I can't work out what's needed. I just hope it comes back sounding as good as it does now but without the angry mosquito trapped inside!
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Post by gazjam on Mar 8, 2015 9:24:41 GMT
Coil whine from transformer windings?
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Post by Deleted on Mar 8, 2015 9:48:08 GMT
Coil whine from transformer windings? Thanks for that. I didn't want to suggest it because I'm lacking any technical knowledge , but that is what I came up with when I googled the subject. The only thing is, the PS Audio webpage seems to suggest it would still be there if I disconnected the preamp. It's dead silent without the preamp, so does anyone know if that rules out the transformer? The transformer is mechanically silent in operation when you are close to it. if it is coil whine, I have read a little on fixing the problem using various substances to dampen it. Does anyone have experience of doing such things with large frame transformers? I did read about steeping it in liquid paraffin wax until the bubbles subside. Also about damping with epoxy or Polyurethane but I will be relying totally on reading and advice as I have no practical experience myself. Sure, I could replace it with a toroid, but this one sounds so good I don't want to change it if I can hep it. I can solder so removing the transformer and sorting it wouldn't be a big issue, if this is the cause? |
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Post by Mr Whippy on Mar 8, 2015 10:35:35 GMT
If it was the transformer the problem would exist with or without the preamp connected, I would say. Can you not take a photo of the power amp's insides to show what the supply for the preamp consists of?
Is it not possible to make a new lead and separate the preamp supply line?
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Post by Deleted on Mar 8, 2015 11:11:45 GMT
I sure can, but I am perplexed as to where and what the PSU is in this older model. In later IVs there is a separate board and a couple of caps. In this older model, it just looks like the IV without preamp PSU does (they came in several different variations).
Effectively photographing the preamp PSU will mean simply photographing a load of wires rather than a specific board. The pic will be further impaired by the fact that the replacement caps I've used are much bigger and are just plonked in for now, rather than neatly fixed.
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Post by gazjam on Mar 8, 2015 11:33:26 GMT
Having been in a similar position of looking to breath new life into an old classic amp, in my case a Densen DM-20 pre, best course of action is to contact Exposure directly and talk to their Tech guys.
I've heard Exposure's customer service is very good, and If they are anything like Densen they will bend over backwards to give you what you need.
Exposure Electronics
Unit 18, Winston Business Centre
43 Chartwell Road
Lancing Business Park
Lancing
BN15 8TU
Tel: 01273 423 877
Fax: +44 1273 806648
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I'd come off worst. It weighs a bloody ton! It will probably end up at Maughan's for a service if I can't work out what's needed. I just hope it comes back sounding as good as it does now but without the angry mosquito trapped inside!
