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Leak Sandwich

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Graham Slee View Drop Down
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    Posted: 16 Jun 2011 at 3:34pm
Thanks to member ABPest (Adrian) I am now the proud owner of four Leak Sandwiches...

Now, before you think I've gone off my trolley, these are not leek sandwiches that you can eat but Leak Sandwich loudspeakers.

How do they sound? Well, on 1 metre tall stands they sound quite good. I am sure they were made as floor standers - you'd think so in 1962 (approximate year of manufacture) when speaker stands weren't the must-have hi-fi accessory of the day - but they do sound quite good on stands. And I don't have the floorspace to stand them on the floor.

Coming up: My crossover upgrade on these speakers. Having scoured the web I could not find sufficient info, so I decided I'd take one apart and start taking pictures, etc. I'll document the proceedings here shortly.

Graham
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fattybatty Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jun 2011 at 6:56pm
'Sounds' interesting Wink
 
They're heavy too LOL

Edited by ABPest - 16 Jun 2011 at 6:58pm


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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jun 2011 at 9:38am
It's picture time!

      

Above: What's in a "sandwich"? Answer: a grille board carrying the tweeter (lent up against the side of the speaker); a not so appealing baffle board; a large 12" (300mm) bass driver, and a crossover. The threaded rod stuck out of the back of the bass driver passes through the wooden block that carries the crossover and is secured to the back panel, thus bracing the cabinet.



Above: The old crossover network. Non-polar 20V electrolytic capacitors (manufactured by Plessey) were the order of the day (1968 stamped on the inside of the cabinets - they started making the "Sandwiches" around 1962). The trouble with them being that without a polarising voltage (yes, they may well not be polarity conscious but today we know they still require a polarising/or DC voltage) they will heavily distort at their turnover frequencies, which in this case are arranged to be around 1kHz (where our hearing is most sensitive).



Above: the new crossover capacitors fitted (they were eventually siliconed in situ). These are polyester film types of the stacked film variety which are non-inductive, unlike the round "audio grade" capacitors high-end loons all go ape about - which are highly inductive...

With only two values available (1uF and 4.7uF) it took a little ingenuity to get the right overall values. The original values were 16uF, 8uF and 1uF. I matched that within 2% with these series/parallel capacitor networks. I measured the original caps to see how much more accurate the replacements were... the 8uF measured 9uF and the 16uF measured 20uF. For their age you'd have expected the original capacitors to be much lower in value due to aging but that wasn't the case here - Plessey knew how to make long lasting capacitors!



Above: The Leak Sandwiches take their place in our office/workshop/demo room (yes guys: this is a full half of Graham Slee HQ).

So how was the improvement? Gob smacking! (for the want of a more arty farty description).

If I hadn't been so mentally drained and emotionally destroyed by the total ass of a job which doing this upgrade was in reality, and the time it took - working flat-out for 8 hours, I'm sure I would have enjoyed the listening experience a lot more. Suffice it to say that given the technology in those days... Eh! they had the technology! So why didn't they use it?  ...these would have been serious trouble to many a competing loudspeaker manufacturer. As seems usual for Britain, Leak spoiled the broth for a "ha-pence" of capacitors - not any more! Even considering the toil that went into this upgrade I doubt if I could do better if I had £2K to spend. Worth the effort!


Edited by Graham Slee - 17 Jun 2011 at 9:40am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jun 2011 at 9:11pm
Wow! Thanks for the pictures and expert observations, especially about the company cutting corners on the parts.
 
I must admit my utility room (and the kitchen table) does look a little like this creative zone - anyone else up for a confession?
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo UL, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links. and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jun 2011 at 8:14pm
Due to lack of space (these speakers need a bigger room than my 200 sq ft/20 sq m office) this project is for sale at what it cost me.

£50! buyer collects.

(there are a total of 4 speakers, two of which had their crossovers modded by yours truly)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigjim72 Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2012 at 9:02am
Hi Graham- I have been reading your posts about the Leak speakers with great interest. I have a pair & would be very interested in replacing the caps but have little to no experience of doing a job like that.Would it be possible to list the components used with a wiring diagram an idiot could follow?
Thanks in advance.
Jim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 Aug 2017 at 8:25am
Circuit Diagram

Leak Sandwich Crossover

Note the additional two 1 micro farad capacitors in the dotted line box. This was an afterthought to make the capacitance a closer match (16.1uF).

If viewed alongside the earlier photograph and orientated the same way up, it will be easy to replicate the circuit.

I have been asked a number of times for a kit of parts, so here goes:

Pack comprises 8 x 1uF and 12 x 4.7uF (suitably rated for amplifier power up to 100 watts) TDK capacitors (EPCOS) stacked film type (non-wound).

NB. Lead length is short so they will need extending to suit (careful not to melt the case!).

Price UK: £50 (inc VAT) plus shipping. Please use contact form stating your location to order and for an accurate price including shipping to your destination.




Edited by Graham Slee - 04 Aug 2017 at 8:44am
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