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Linn LK275 goes to DC, BIGLY!

Craig B

Craig B

Re:trophile
An old friend just dropped off his LK1 and 2 x LK275 which have been in storage for many years now. These had been used to passively bi-amp Nexus LS-250 'speakers since new. He remembered there having been some distortion on one channel for some time before they went into storage.

I have had the LK1 in before, suffering from the none-responsive front panel keypad issue. Fortunately, the pre-amp is one of the earlier examples with the voltage adjustment pot on the control board. This has been working fine since having had a twiddle with it to find the magic spot where both the keypad and IR remote work.

As the LK275s hadn't been switched on for a very long time, I gave them a 'softish' start via a connected in series lightbulb and tested for DC offset. After 10 minutes, one amp was showing 38.2V on the right channel (note V not mV!). The left channel was at .053V. Within 30 minutes, the left channel heatsink was getting warm to the touch whereas the high DC right channel heatsink was still cold.

I haven't had the cover off for a visual inspection yet, however, we've already exceeded my very limited level of expertise wrt testing for amplifier faults, plus the individual amplifier boards are reportedly a bugger to work on, with through-board components being as tightly packed as sardines.

On a possibly related note, my research has turned up Linfomation concerning 'LK2 Reliability Modifications' that were to have been performed on all LK2(60)/LK275 amplifiers. There are references to bending a tant away from a hot resistor and replacing a couple of resistors that tended to overheat, one of which is buried beneath one of the large PS caps. I am certain that none of these mods have been carried out on these two amps.

I've included a link to the service manual which includes the reliability modifications for anyone who is interested in having a look.

Any and all suggestions gratefully received.

http://www.acousticpsychos.com/Files/Linn-LK2-pwr-sm.pdf
 
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I think these are pretty good amps, worth a bit of attention.

If you have DC and no warmth I think that might suggest that the output devices are failed, one short, one open. No current flowing so no heat.

Happy to be wrong, but this would be testable without serious dismantling, the channel modules come out and the connections to the transformer will still reach. Then you can get to the output device terminals and see what makes sense. As it's not caught fire yet this seems safe enough.

Of course that doesn't mean that replacing output devices fixes the amp...
 
Thank's Paul, I appreciate your having taken the time to contribute.
 
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Well this little project just keeps getting better. Apparently, my friend has long since lost the unique Linn XLR interconnects, possibly during his last house move. What is unique about them is that they are unbalanced with female plugs on both ends, so not a likely off-the-shelf option.

Although I am capable of doing nicely finished cables, a minimum of 4 x female XLR plugs are necessary just to get one source going. Specifically, one plug for the pre-amp end of a 2 x RCA to XLR source interconnect and 3 plugs for a single XLR to 2 x XLR Y-connector interconnect for between pre and power amps. IIRC, the originals were nickel plated, possibly Switchcraft or Neutrik; anyone remember?. I also recall that the wire appeared to be the same thin black ridged insulation stuff as Linn used on the tonearm interconnects. I do have a couple of 1.2m pairs of Linn Analog RCA cables that could be donated as parts.
 
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Not one of Linn's best decisions. IIRC the LK1-LK2xx should be two independent female-female wires. The serious user direction checks them by ear in all combinations to ensure that each channel has the right cable the right way around. Then I think you need a Y type 2-phono to 3 pin XLR for sources. Somewhere I have a DIY tape in-out 5 pin XLR to 4 phono job.

On this basis I strongly recommend avoiding the Isobarik Aktiv.

I have original LK1-LK2 cabling upstairs in a box, I'll look it out tomorrow. I don't think it's tonearm type cable, more screened twisted pair misapplied.

Paul
 
Thanks again Paul.

If you are willing to part with the LK1 to LK2 cables then please do let me know.

Craig
 
Perhaps the dealer had made them up from spare Linn tonearm leads then. Now that I think of them more, they were actually a 'V' pattern rather than a 'Y' which would support the idea that the centre ground lead had been ripped out, rendering two separate runs of cable per tonearm lead.

It seems odd to me that Linn would have gone with two single XLR cables, as each of the two output sockets on the LK1 are stereo and going for a second amp in passive bi-amping mode would then have required starting over with all new interconnects; perhaps a dealer lash up like these were. Also, Linn were clearly pushing bi-amplificaton at the time, as the contemporary Nexus manual lists this as an upgrade path option after bi-wiring. They obviously hadn't really thought things through here.

Regardless, as the one LK2 is toast, the plan now is to source a pair of XLR singles in order to get the LK1 and working LK2 back into service.

If anyone has a pair of old LK1/LK2 interconnects and/or source cables going spare, I'd be interested in hearing from you.
 
A bigger upgrade for Nexus owners than bi-amping them would have been to sell them and buy some better speakers (also a cheaper option)!
 
Agreed, however, as my friend is passing it all on to his 20-something y/o daughter for use in her first home, I suspect the Nexus to be somewhat of an upgrade from her Beats headphones, just. :)
 
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I have copies of the lk 275/280 service manual, fault finding manual and diagrams if needed.
Rgds
Stuart
 
Thanks for offering Stuart.

I did manage to find those docs, however, I lack both the knowledge and experience to effectively trace errors in amplifier circuits. I would like to learn to do so but it probably isn't a good idea to make a start with someone else's amp.:eek: I do have a number of '70s Japanese amps and receivers, some of which I intend to re-cap as a learning experience; that is, once I've fully lost the will to work for a living anymore (aka the self-employed's version of retirement). Depending upon the outcome of those learning experiences, I'll likely as not dive into my coveted collection of NAITs, that is, assuming I haven't electrocuted myself, or succumbed to solder smoke inhalation, first.

In the meantime, I have a nice Fluke DVM and have managed to re-bias and/or adjust offset to good effect on those that allow such. Apparently the Linn LK2xx isn't among those, relying instead upon properly functioning matched components in the transistor long-tailed pair, IIUIC.

Cheers,
Craig
 
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Craig, I found my cables. I don't really want to dispose of them since I still have the amps. But the original LK1-LK2x interconnects are female-female XLR (obviously) and the cable is a hefty screened twisted pair with the screen connected to pin 1, which I believe is standard balanced audio, other than usually it would be female-male output-input. You could get things going with a pair of standard microphone cables and female-female adaptors. Or just make some, the beauty of XLR is that even the fancy ones are good value. By a couple of standard mic cables and change the male end, about £12 all in by the look of it.

The Kairn came with a pair of phono-XLR using standard Linn 'analogue interconnect' which is a simple coax. The Kairn's PSU blew up, I think the LK1 still works.

The Kairn had 3 pairs of phono outputs, and every Linn power amp subsequent to the LK2xx had an in and an out for daisy-chaining. The 'Aktiv' setup involved crossover cards internal to the power amps so this was for bi-amping and active setups.
 
Cheers Paul. Mic cable makes perfect sense. As it happens, there is a musicians' shop not far down the high street from me.
 
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If I remember correctly the XLR plugs on the cables had a wire connected between the left input pin and the NC pin. Same between right input pin and NC pin. That way it didn't matter which way you plugged them in.
 
I see what you mean Bob. With XLR plug sockets 2 and 3 bridged at the power-amp end, the cables wouldn't be handed L vs. R.

They would still be directional though. If the bridged sockets end were connected into the LK1, rather than into the LK2, they would provide a summed L+R mono, as pins 2 and 3 are L and R respectively on both output sockets 1 and 2 on the LK1 (pin 1 is 0v on both pre and power).

No wonder all those Linn disciples were convinced that cable directionality was a 'thing'.:D
 
Bob B. said:
If I remember correctly the XLR plugs on the cables had a wire connected between the left input pin and the NC pin. Same between right input pin and NC pin. That way it didn't matter which way you plugged them in.
Click to expand...

Actually, I think Bob is right, sort of...... :)

Just pulled apart one of my Aktiv-LK280 ICs. Each XLR connector has red, blue & screen. No pins in either XLR are wired together in the connector. The screen goes to the same pin (1) at each end which matches the 0v on the back of the power amp, but red & blue are crossed over, which I think means they'll go any which way you want.

Never given any thought to connectivity, the previous owner had comprehensively labeled all six cables "low/mid/high", "left/right" & "source/amp" :D

Unfortunately the Aktiv box is under a heap of stuff in the storage room, and the amps are on top of a wardrobe......perhaps this could be an opportunity to set up the Briks over Easter :)
 
Thank you for having a look and reporting back Chris.

It seems that these are wired as per standard XLR cables but for having female plugs either end.

Happy Isobarik Easter!

Craig
 
You are right re. directionality connectivity with the LK1 Craig. I was remembering when Linn changed the screened interconnects to the arm cable and at that time I was using a Kairn, so the cables had phono plugs on the scource end and you couldn't get it wrong. I do remember the wire link on the XLRs though. BTW I did think the arm cable was an improvement over the screened cable.
Cheers.
 
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