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Sunday 11 February 2024

A "New" Retro Streamer - Pushing the LK Envelope

For information only: this post is not a set of instructions nor is it intended to encourage any kind of modification of electrical products. As they say: "Do not try this at home".

Some of you may have read through the first "episode" of what has now started to be a theme - modernise a Linn LK enclosure with a streamer, or, from the other perspective, taking a modern streamer down the retro route.

That little excursion is available here. It covers off the history of the LK boxes and describes the Sneaky Music DS also used in this project.

A quick recap - that story covers converting an example of the iconic Linn "LK" enclosure into a streamer as purely a source component, using a Linn Sneaky Music DS in "source only" mode.  That's possible in a non-ventilated case, but to use the full features of a Sneaky, including the power amplifiers, that needs a ventilated case, so something from the all-in-one or the power amp sections of the LK range of products.

The other difference is that in the previous project I wanted to present only the source component connections to the outside World, but with this project the intent is to provide all of the Sneaky's connectivity so all of its functions can be enjoyed. Let's see how it panned out..


Ingredients this time:

- Linn Sneaky Music DS

- Linn LK85 Power Amplifier (with dead mainboard)

- Lots of M3 fasteners


- Strip the interior out of the LK85

- Trial fit the Sneaky MDS board and PSU

- Work out all the fittings etc., similar to the previous project

Did That Happen?

No. And, yes.

Starting with the LK85, which had a dead mainboard, all the innards were removed - as it happens the LK85 toroidal transformer was repurposed into an LK140 power amp that had a healthy mainboard but a dead transformer.  So the LK140 won't produce the power it used to, but its back up and running and can be used again.

The LK85 chassis stripped bare looks like this:

The back connector panel is at the top of the image, the toroidal transformer mounting hole is midway down on the right then the ventilation and substantial heatsinks.

The ventilation and heatsinking on the LK85 and give confidence that the comparatively low power amps in the Sneaky Music DS will be adequately cooled.  Next it was time to remove the heatsink from the base of the LK chassis - this involves drilling out the securing rivets.

Drilling out the heatsink rivets

This left lots of space to work in side the chassis but also a base plate that wasn't particularly secure.  So once the heatsink was out its mounting holes, that also mate to a centre strengthening plate, were replaced with M3 nuts and countersunk bolts.

Countersunk bolts replacing the heatsink rivets

So that's the basic starting point.  Time to have a look at how to layout the Sneaky boards inside the LK chassis, which is likely to be different to the previous project because there's now the need to look after the power amp and it's heat production.

And then something struck me - once the Sneaky MDS is relieved of its clamshell outer panels, the remaining chassis looked very similar in width to the LK.  If all went well, perhaps the whole Sneaky chassis would slide down into the LK with no modification? A quick check and I found that it is EXACTLY the same width as the LK - so no, it won't slide in easily.  Because the LK box has a chassis with sides and then the top / side panels are a slide over clamshell, the internal side walls are not visible on a fully assembled product. A few measurements told me that it would be possible to cut away sections of the chassis side panels and integrate the entire Sneaky MDS into the LK rear panel - so no need to strip the Sneaky boards / PSU and no need to use jumper cables from those boards to a custom back panel.

Cutting away the side and rear panels ready to accept the Sneaky MDS chassis in its entirety. Around 3/4 of the length of the side panel has been removed.

Trial fitting of the whole Sneaky MDS chassis into the newly cutaway LK inner panels.

In the above picture you can see that the external width of the Sneak MDS is exactly the same width as the LK chassis and in this trial fit, this was confirmed.  The 4x threaded bosses in the top of Sneaky chassis are the mountings for the external clamshell panel.  They are replicated on the underside and their positioning means that only 4x standoffs can be mated to them to supply support and fixing in to the LK. Plus the height up from the LK base means no need to powerfile away the LK's old threaded bosses, so one less job to do.
I didn't have standoffs of quite the right length to screw directly into the Sneaky chassis, but adding an nut to the threaded section before mating them up gave exactly the right clearance.

Making the standoffs in stock a couple of millimetres taller

Threaded standoffs fitted into the Sneaky threaded bosses that normally provide a fixing point for the outer clamshell panels

Underside of the Sneaky chassis with standoffs in place

4x holes were drilled to align in the LK chassis and another trial fitting undertaken. Note that the front to back location of the Sneaky chassis aligned the original back panels of both products.

Alignment of the remains of the LK rear panel (along the bottom of the picture) with the entirety of the unmodified Sneaky rear panel. Together they don't vertically add up to the same total of the old LK back panel, leaving a gap across the whole width

The only modifications needed to the Sneaky are two fold.  First, and easiest to describe, is swapping the original front blue panel LED to the green "power" LED next to the on-off switch of the LK.  This just involved a swap of the connector (as per the previous project) and re-routing of the cable.  The second part was to accommodate using the front power switch.  This required a slight tweak - the brown positive cable from the IEC rear panel socket that goes directly to the PSU was unsoldered and effectively routed round to the power switch on the front before going back to the PSU. Handily, by fitting a rubber grommet around the Sneaky's front LED mounting hole, it was possible to route this cable without and modifications to the Sneaky chassis.

The LK power switch assembly as removed from the amp.  The IEC socket is cut off leaving the 2x brown cables going to the switch

This is the Sneaky front LED mounting point.  A rubber grommet protects cables passing through - this was used for the mains switch cable and the LK green front panel LED

Front panel switch fitted with a 2 pin connector

The redirected brown cable is sleeved and makes its way neatly under the PSU output cable off to the front panel power switch

Passing out of the Sneaky chassis to the front panel

Adding a 2 pin connector to mate up with the connector added to the front panel switch leads

And that's about it. Except for that gap across the top of the rear panel.  The material for this was taken from the top of the original LK back panel, but mounting needed to be resolved.  Handily some offcuts of aluminium panel from the last project were just the right width to create a pair of mounting brackets.  These were cut to length, bent to shape and bonded to the back panel gap filler. They then sit neatly onto the Sneaky's upper clamshell mounting points.

Offcuts cut to size for their new role

Offcuts bent into brackets

Bonding the newly fabricated brackets to the newly created back panel filler panel. Note use of universal clamping equipment

And that was largely that.  Some primer and matt black spray paints finished off the exposed LK chassis edges and spruced up the rear panel.  I used satin black on the first of these projects and gave matt black a try here.  I will keep to the satin for future project.

So here it is, the second of the LK streamer projects.  This was a simpler build than the previous one and is probably the route I'd use again in the future.  It has the benefit of exposing all the functions of the Sneaky but it has the downsides of needing a vented enclosure (harder to get hold of because the amps are probably mostly still in use) and it doesn't have that more bespoke feel to it. There is one further advantage - the Sneaky needs the absolute minimum of changes, so could be converted back to standard in about 15 minutes.

Rear filler panel mounts

LED and mains switch cables pass through the grommeted LED hole of the Sneaky. Connector of the power switch cable

A neat final result

Base panel labelled up with the new information.  LK mains transformer mounting hole plugged with a rubber bung

As per the plan - absolutely no clue that this is anything other than an LK power amplifier

Until you turn it around and find a whole bunch of unexpected connectors.  As you can see in this picture the top filler panel, the unmodified Sneaky back panel and the remaining lower edge of the LK back panel marry up well to make an (almost) seamless result.

And finally...

Here is the Sneaky going through its boot up sequence, using the original green LK LED rather than its own blue LED.

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