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Power amp cutting out at higher volume
2018-07-12, 16:46
Post: #11
RE: Power amp cutting out at higher volume
(2018-07-12 16:20)Cyclocyte Wrote:  Yes thanks Glyn - I've just just found reference to this - Apparently the cut-out kicks in at 70 deg C. Is there anything in what I have described which might cause overheating?
Hi, feeding a signal into a blown voice coil in the speaker could account for this.

Fluted Lp12, Valhalla, Cirkus, Michell Techno A, Goldring 2100. Elliot Sounds Phono pre. Marantz cd6006. Lehmann pre/headphone amp. 3 x LK100. Active Kabers, (Scanspeak D2008 tweeters). DIY Ikea coffee table rack.
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2018-07-12, 16:59
Post: #12
RE: Power amp cutting out at higher volume
Hello all,

Having sorted out the treble/bass wiring error on one of the speakers, I can confirm that the problem remains and that even on classical guitar music the LK100 used for base trips out at volumes above around 45 or above. I know I reported this to Linn years ago. Just looked up the email from 2002! - this was never resolved and the dealer I purchased it from closed:-



Dear Peter,



Thank you for responding to my complaint re the above.

My system includes a Wakonda pre-amp, 2 x LK100's active amplifiers, one of

them is used to drive the treble and the other the mid-range and bass (it is

the latter amplifier that cuts out when we have the volume set to above 45

or 48). I have 2 Keildhs. For input, I have a Linn Mimik and some Sneaky

Kudos. I also for input have a Nakamichi tape deck. The problem arises

regardless of from where the input comes, although it does tend to happen

more quickly if the music is very "bassy".



This problem has been on my system since I purchased it. I have complained

about it to Listen-Inn (the hi-fi dealers in Northampton) and they informed

me that this was normal and that it was occurring in order to protect the

speakers from overload. I didn't accept it then, as now, on the basis of the

fact that if the volume control is there it should be usable, except in

extreme circumstances. At the time (1995) pressure of work precluded me from

taking this up as an issue with them, but as the years have gone by, I have

got increasingly annoyed about this - especially in view of the fact that

this is an expensive system, and I do not expect this type of fault in a

high class system like yours.



Are you sure there is not a potentiometer somewhere inside the system that I

can't adjust in order to save the hassle of having to return the amp. ?



Look forward to hearing from you,



Yours sincerely,
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2018-07-12, 17:38
Post: #13
RE: Power amp cutting out at higher volume
Cyclocyte,

I’m not really sure what you hope to gain from posting the content of an email from 2002?

As far as I can see, you had already had the system for 7 (?) years at that point and were in discussion with Linn about it. As the system was out of warranty, I would have expected Linn to offer the opportunity to send the offending LK100 back for service. I presume that you never progressed this?

You’ve now lived with this issue for 25 years? As Linn no longer support the LK100 ( I believe) the opportunity to send it back to them is no longer there.

From what I’ve read, and apologies if I’ve missed anything, you clearly have a fault on that power amp and, as everything appears to be connected correctly, then your options appear to be:

Get the amp fixed - this forum usually recommends that you contact Darren at Class A Repairs in Sheffield to see what he can offer.

Replace the amp - probably as cheap as getting it repaired, but you would have to be confident in transplanting the Aktiv cards.

Live with it - as you have done for 25 years.

It doesn’t sound, to me anyway, that the problem lies with the preamp as I would expect issues on both power amps. Equally, I think the talk of a damaged drive unit is a red herring, but can you confirm that it does sound OK and that the damage you refer to is purely cosmetic?

One thing you can try, and it’s what I would do if the system were mine, is to swap the Aktiv cards between the two power amps, ie make the Treble amp into the bass amp. You may find that the existing bass amp is far happier with treble duties. However, to accomplish this, you would have to be happy to open the amps up (always unplugged from the mains, please) and swap the cards. Or... take them to a dealer and pay them to do it.

Hope that helps,

‘troll
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2018-07-12, 18:22
Post: #14
RE: Power amp cutting out at higher volume
Hello trol
My main purpose in including this email was to emphasise the longevity of the problem. The only remedy offered to me by Linn at the time was to return the unit to the dealers ultimately for return to them. This was not possible because as I explained to them at the time, they were no longer in business. They did not give me the option of returning the unit directly to them. However as you say, this is history!
I have attached photos of the outputs from the LK100's in case there is something wrong here. No-one has commented so I assume not? The way I have got the pre-amp outputs is - from one pre-amp output to treble line input - and then from treble line output to the base line input. I assume thats OK?
I like the idea of swapping the active cards to convert the base amp into a treble amp because this may help both define and resolve the issue!
The base/mid driver central dome was severed nearly completely around the periphery and therefore effectively blown out so I removed the remnant, which was attached only by a slender piece of rubber. I just wondered whether this may have been caused by the treble being driven by the base amp? Whilst to my aging ears the driver still makes a decent sound my understanding is that it normally operates along with the other base/mid driver in an air sealed environment and that this contributes to the sound quality? I would obviously like to get this sorted out preferably without having to buy another complete pair of speakers.

Thanks for your help
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2018-07-12, 19:29 (This post was last modified: 2018-07-12 19:34 by moomintroll.)
Post: #15
RE: Power amp cutting out at higher volume
Looking at your LK100 photo, the speaker connections are correct.

Just to recap what you’ve said: your Wakonda is connected from phono out (L+R) to the treble amp inputs ((L+R), then the treble amp output is connected to the bass amp 8nputs (L+R). This is correct and referred to as “daisy-chaining”.

I’m going to assume that the damage to the bass/ mid voice coil cover is purely cosmetic. If you still have the cover, and that is intact, you could actually just stick it back into place with careful use of a rubber glue. If the drive unit were damaged, you could probably hear some distortion from it. Should you decide you wish to replace it, you may be able to source a replacement on eBay, but I would recommend you start a separate thread asking for advice on which drive unit it is and how to change it out.

What surprises me more, is that, if you have actually driven one speaker with the amps reversed, ie bass into treble and vice versa, that you haven’t actually blown the treble unit. Bass units driven by treble frequencies are no problem but not the other way round. You can confirm that the treble units are both still OK by playing music with only the treble LK100 switched on.

Back to your problem Lk100.

Check the phono cables from the Wakonda, especially the pair between treble and bass amps. Check them for any obvious damage or cuts. Open up the phono plugs (I assume they are Linn black cables?) by unscrewing the metal barrel and check the soldering for any breaks or loose wires.

Then check the speaker cables. Are they securely plugged into the speakers? Check the solder connections if you can.

If there’s nothing obvious, you can then try swapping the bass and treble speaker cables (AT BOTH ENDS!) ie, so you are now using the cables currently connecting treble amp L+R for bass L+R. Make sure you have CLEARLY marked BOTH ends of the speaker cables!! See if the fault remains or moves to the treble amp.

If it moves, then you have a cable problem.

If it stays, it looks much more likely that the bass amp (or Aktiv cards) is at fault. At this point, if you can swap over bass and treble cards, taking caution to make sure you reconnect the correct speaker cables to each amp/speaker. Whilst “ under the covers “ check to see if any components look to be leaking, bulging or blackened (although I doubt it due to the length of time involved) If the fault remains, then it’s the bass Aktiv cards at fault. If the amp now driving the treble (ie used to be the bass amp) fails, then it’s the amp at fault. I must stress that amps must be unplugged from the mains and left for half an hour for capacitors to discharge before delving inside. You should also observe static precautions to avoid further damage to delicate components. If in doubt, take to a dealer.

However... you may find that the fault disappears. This could be, either, down to the amp coping better with treble duties, or just remaking the card connections.

‘troll
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2018-07-12, 19:57
Post: #16
RE: Power amp cutting out at higher volume
Thanks for your response 'troll

I confirm that the connections from the pre-amp to the LK100's are as you have recapped.

Remarkably, the treble driver seems OK despite its unfortunate experience!

Ill follow your troubleshooting sequence. It will take me a while to go through this with repeat testing but I will feedback the results in due course.

Thanks again for your support
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2018-07-13, 09:08
Post: #17
RE: Power amp cutting out at higher volume
Do what 'troll suggests but I'm suspicious that the amp is sensitive to the real impedance it is seeing & always has been. As the bass amp works harder in any bi-amp configuration, swapping duties with advised caution will soon prove this or otherwise.

If the amp is happier with the lightened high frequency load you can make a decision as to whether you want to have it repaired to factory spec.
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