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Lenco L75 Restomod

How to take this excellent turntable into the 21st century

Product: Upgrades to base Lenco L75
Manufacturer: not for sale, TNT-Audio DIY design
Author: Piero Canova - TNT Italy
Published: November, 2021

Introduction

For some years, in the car world, the so called "Restomod" has become more and more popular. In simple words it is the restoration of historic cars respecting the look, but updating the mechanical parts, taking performance and safety to today's level. It began as a way to eliminate some evident flaws of the original design (brakes not braking, poor suspension, unreliable carburetors, etc) but then step by step it involved the entire car maintaining the beauty of the original design, but upgrading all components achieving a performance even superior to modern vehicles. I wanted to try something similar in the turntable world and so some time ago I looked for a turntable that could be found at a reasonable price and with the potential for some substantial upgrades. The Lenco L75 was the perfect choice since it is still easily available, it is simple and solid, and the parts are reasonably cheap, which is good, since big modifications often mean big mistakes. Furthermore, it has some parts, like the motor and platter, that are first class, so with the right modifications, it is possible to reach reference performance. As usual my modifications must be inexpensive and respect the original look: it is always possible to do something better, but the cost might equal that of a new turntable and the look will be totally different. I have included several pictures to help explain the modifications.

Let's start working

Usually you find, on sale, complete Lenco L75 turntables. Some people restore them to the level they were when they left the factory, but our purpose isn't this, rather a Restomod, so the outer appearance must remain almost unchanged. I first disposed of the weaker performing parts so the factory plinth and the tonearm were replaced with something more up to date. I have kept the main board with the same colors and switches, the spindle and bearing, the motor and platter. Let's see in detail the modifications.

• Spindle and bearing housing: as in most of the turntables of the time, the main spindle rotates inside a supporting tube and rests on a ball bearing at the bottom. The thrust bearing is a small plastic disk with a small indentation on the bottom where the ball sits. The shaft is chromed, but the finish is rough compared to the shafts you see today. The image here below shows in detail the construction and the parts in the spindle and bearing housing (images courtesy of Lenco Heaven website).

I recommend two improvements: the replacement of the metal ball bearing (number 5 in the right image), which is likely to be worn and flat-spotted, with a ceramic ball and the use of a PTFE based lubricant. I have tested several oil grades including some very thin, but they work well with modern shafts and bearing housings where tolerances are very small. I did try also a cup on the bottom replacing the plastic cup (number 9 in the right image) to provide an oil reservoir to keep the shaft well lubricated, but this seems not to be the right solution. To remove the shaft it is enough to remove the circlip on the bottom (number 8 in the right image) with circlip pliers. Next the thrust pad comes out from the bottom together with the ball. Finally you loosen the screw in the middle of the bearing housing (number 5 in the left image) and the shaft will exit from the bottom. Clean everything with a microfiber cloth or similar that doesn't leave dust or debris, lubricate it well, and insert it inside the bearing housing. For a ball bearing replacement you can use a ceramic ball intended for mountain bike bottom brackets: they have excellent load carrying capability and also very low friction. The size ranges from 3/16" to 5mm. Put some lubricant on the cup at the bottom of the shaft, insert the ball and reassemble the thrust bearing and the circlip. Overall cost is 2€ for the ball, 10€ for a can of oil and 15€ for the circlip-pliers if you don't have a pair.

• Idler wheel: most Lenco turntables have plastic idler wheels. They aren't the best, both in precision and mechanical tolerance and it is very likely that the one you will find on your turntable will be very worn. There are several suppliers of high quality metal wheels: I have chosen one from Audiosilente with the outer edge in silicon rubber. To replace it you must remove the tiny circlip on the tip of the shaft: be careful doing it because it is a spring under tension and if you lose it you will be very likely spend quite some time on your knees looking for it. Lubricate the shaft with the same oil as with the main shaft and you can mount the new idler wheel. The total cost is 53€

• Idler wheel spring: there are several articles on the internet concerning the problems generated by the spring holding the idler wheel to the platter and the motor shaft. In short, being a spring an elastic component, the pressure can vary due to elastic oscillations, which also means that the speed can vary. The most reliable solution is to get rid of the spring and to replace it with a weight using gravity as a constant force. I measured how much the spring was elongating in use and I applied some weight to the spring until it reached the same extended length. The result I measured was 90g. A fishing line and a lead weight will be perfect: you can easily adjust the weight to 90g since lead is very soft and as lead is dead, any vibrations should be damped. The next step is to drill a 4mm diameter hole in the main plate at 120mm from the upper side (the one opposite to the switches) and 25mm from the left side (always with switches next to you). In order to avoid the wire touching the metal plate I have used a thin spacer of nylon which is self lubricating and I have glued it so to be offset as in the picture. You will knot the fishing line on the bearing shaft of the idler wheel where the spring was connected and to the 90g weight on the other end. Warning: this solution limits the range of speeds available; if you need 16 rpm you will have interference between wheel and line. You can change position of the hole to get 16 rpm, but you will lose 78 rpm. The position I suggest is optimized for 33 1/3 speed. The whole mods will cost you a maximum of 5€.

• Deadening/dampening of the main board: among the most common flaws of turntables of this vintage is the poor deadening of the structures. Platters are made in metal alloys that ring if tapped and the main top plates are normally in thin pressed steel, which means they do resonate and transmit any vibration generated by the electric motor and those coming from any external sounds directly to the tonearm and cartridge. There are several recipes to deaden the main plate and the components inside the turntable. I have chosen a foil made of a PE foam on the outside and a sheet of lead inside, It is used in the building industry where you need very efficient sound-proofing of a room; the foam works very well on medium and high frequencies while lead, with its high mass, is perfect for absorbing low frequencies. You can cut it easily with a pair of household scissors and you can glue it with any normal glue. It is expensive, but we need limited quantities so the whole should not cost you more than 30€.

• Platter: take the Lenco platter and hang it with some wire and then knock on it with your knuckles. It will start ringing for a while with a quite annoying pitch. I did try several solutions like rubber band on the outer ring and blu-tack on the centre part, but none really made me happy. The best solution I found is to use a heavy mat and glue it onto the platter, physically coupling them. The two best solutions for me are either a heavy rubber mat with on top of it a CFRP mat like in the picture or a graphite HD 6mm thick mat. The key is that they must be solidly coupled with the metal platter so I glued them together using a removable spray glue because it is easy to remove the material if you want to go back and doesn't leave any unpleasant residues to clean. With glue, the combination platter + mat becomes dead and it also adds some mass to the platter. This modification is a bit more expensive since HD graphite mat costs 290€ and Millennium Audio CFRP mat trades at 300€.

In both cases you will need an extension of the spindle in order to hold the record and on top that a record clamp. You need an engineering company with a turning machine to make you a small rod, 7mm diameter and 20mm long, slightly concave on one end and convex to the other, matching the profile of the top of the spindle (number 4 in the right image on top). Fortunately, the Lenco spindle isn't very convex on top so they can do it with ease. You can use brass, aluminum, stainless steel, plastics; to fix it on the spindle you can glue it. You need a jig for the gluing the spindle extension so it will be perfectly vertical and centered. Take a small block of PE or PP and drill a vertical hole 7mm diameter. Check that your extension slides freely inside it. Put a drop of cyanoacrylate on top of the spindle, place the jig ove the Lenco spindle and then push the new extension into the hole to glue it. Cyanoacrylates do not glue polyolefins so when you remove the jig the extension will remain in place. Any clamp will be ok; I have chosen the HD graphite one since it is quite heavy, but a metal one will be also OK. It is only important that the clamp doesn't apply too much stress on the extension when you remove it.

• Power cable: as far as possible, I prefer flexible cables for the turntables in order to reduce the vibrations transmitted by the cable to the turntable. The Lenco L75 hasn't a ground connection so you can either stay with the standard cable but I prefer to use a high quality two conductor mains cable with standard blue and brown insulation. I use two ferrite rings to redice EMI and a wall-plug of your choice. I did test some expensive plugs, but honestly I haven't found any noticeable improvements. This section will cost you around 10€ for all the changes.

How does it sound?

Immediately you will notice that the turntable is much more quiet. Idler wheel turntables have several positives, but complete silence isn't normally their strong point. The turntable speed is now much more precise and wow and flutter are in the league of a good modern turntable. This quietness and precision, together with the dampening lets the qualities of an idler wheel turntable shine: bass solidity and extension, PRaT and musicality. In comparison to the unmodified turntable the sound is much more detailed and precise having lost the typical character of many turntables of the '70 that make everything nice an pleasant. Now, it is as if a veil of dust has been removed and, if the record is of low quality, this becomes immediately evident also when the recording quality is high, the track immediately hits you. It is now a first class turntable with a clearly defined character that deserves a tonearm and a cartridge of very good quality to express all the Lenco L75 potential. Reliability is as good as the best; just set the speed properly and it will give you many hours of excellent music. There aren't any complicated electronics, electronics or belts getting sloppy or dry; just once a year, change the tyre on the idler wheel and it will go on almost forever. It performs well with all music genres, but in my opinion, I have found it works really well with big orchestras. Does it sound better than my beloved direct drive turntables or a high level belt driven turntable? I can't say that, but rather that the more you increase the level the more all the above technologies converge to a sound that is similar; possibly it loses something in noise floor level, but we are talking about tiny details. More radical improvements like changing the main plate with a thicker one will further improve the performance, but it is really building a brand new turntable.

Conclusions

With an investment in improvements worth some 100€ excluding mat and clamp and some handwork you can have a turntable that will look vintage at first sight, but that after few minutes of playing won't leave any doubt about being in a different league. With a tonearm looking a bit vintage, but of good quality ( a SME M2 or a Jelco SA-250 will be perfect), let your friends listen to it. Some will remember when Lencos were the standard turntable in DJ consoles, but the quality of sound will be a surprise.

© Copyright 2021 Piero Canova - piero@tnt-audio.com - www.tnt-audio.com

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