EL34 Single Ended Amplifier Open Baffle Loudspeaker DIY Turntable
  Garrard SP25 Mk II   Lenco L78  PWM Controller for my Ultrasonic Vinyl Cleaner 

September 2021:

Revision of a Lenco L78 Mk I (1972)

Lenco produced hundreds of thousands of record players of this type in the 1970s.
The Lenco L75 as an entry-level model.
The Lenco L76 with a different tonearm as an option and the Lenco L78 as a luxury version with possibly an automatic shut-off.

But they are all based on the effective Lenco idler-wheel drive and are extremely suitable as a restoration project.

Lenco is actually the only turntable manufacturer that has kept the intermediate wheel principle for the consumer market well into the 1970s.
It wasn't until the mid-seventies, with the advance of Japanese belt-driven turntables, that they succumbed to a belt-driven player.
That choice also meant the end of the so popular Lenco turntables.

Idler Drive

Listening to an idler drive turntable is a very different experience than listening to a belt drive model.
Idler drive turntables let the music come first.
You will find yourself tapping your foot instead of focussing on sound quality. Idlers simply have incredible musicality and energy.

For many years the belt drive system was regarded as the only serious way to drive a top quality turntable. For fifty years it was
almost impossible to buy anything else. There were a few direct drive models around but those were really only used by DJs.
In recent years however, there has been a renewed interest in the old idler drive models from the sixties and seventies.
Models likethe Thorens TD 124, the Garrard 301 or the Lenco L75.
Once restored these old beasts are thought by many to outperform even the best of today’s turntables.

This is achieved by the use of a strong motor with lots of torque and the absence of belt stretching losses. The result is a drive system that simply keeps going, undeterred by stylus drag and that does wonders for the rhythm and timing of the music.

Inside top view Inside bottom view

Cartridge of this turntable :

Stanton 500 Mk II

Stylus before cleaning

and after cleaning
  • Type: Moving Magnet
  • Output Voltage: 3.1 mV
  • Freq Response: 10Hz - 20kHz
  • Tracking Force: 0.5 - 3.0 g
  • Mass: 5 g
  • Channel Separation: 35 dB
  • Channel Balance: 2 dB
  • Load Impedance: 47 kΩ
  • Dynamic Compliance: 25 x 10-6cm/Dyne

Tonearm wiring uses a standard color code for channel and polarity ID:
  • White = Left Hot
  • Blue = Left Ground
  • Red = Right Hot
  • Green = Right Ground
If the cartridge pins aren't color-coded the same way, they will have letter identifications next to them.

The Lenco L78 Tonearm

Refurbished tonearm L78

If you look at the technical side of this Lenco tonearm, you see that the horizontal bearing is based on a so-called knife bearing. The knife is placed right through the arm, which rests on two V-blocks. These blocks were made in the 1970s from a plastic, which unfortunately degraded over time. Sometimes there is nothing left at all. So you have to see what you want.
If you want to use the original arm, you should definitely replace the V-blocks. I use brass blocks for this.

But then you're not there yet.
Also the wiring is always corroded and needs to be replaced. When you've done all that, you'll have a good Lenco arm again.

Old V-Blocks of the L78

New Brass V Blocks

Revision of the Lenco L78 bearing

This is an act that you really should not skip. A well-running bearing is crucial for the final sound quality. First of all, the bearing is completely disassembled. Use the correct tool (seegering pliers) to remove the circlip neatly. Then the cover plate, followed by the carbide plate, on which the ball rests, is released.

By unscrewing the screw on the side of the bearing, you can carefully slide the bearing pin out. All parts are now free.
Clean everything with a soft cloth and put the bearing housing in bearing oil. Heat the oil to about 80 degrees Celsius and leave the bearing housing in the oil for half an hour at this temperature. As a result, the sintered bronze is nicely filled with clean oil again. Then you let it cool down and you can put the bearing back together neatly.
A little bearing oil in the bushing and the bearing is ready for use again.

Aftermarket idler wheels

If you want to replace your idler wheel, you can choose a new aftermarket idler wheel. To be honest I don't think any of these idler wheels are a good alternative to the original Lenco wheel.
They are nicely made idler wheels, though. Usually fitted with an O-ring.
My experience is that an O-ring is a bad solution and here's why.

The ring never gets positioned exactly around the wheel. The O-ring is also not the same thickness everywhere, which does not benefit the concentricity. Also, when the engine is switched on and the start on the plateau, there is quite a lot of force on the ring, causing it to shift, which is pushed up or even twisted, resulting in poor rotation and a lot of noise. You could solve this by gluing the O-ring (if not made of silicone) to the idler wheel and then grinding it around on a lathe. A big job. But that doesn't mean you have a good wheel.
It remains a compromise!

Original Idler Wheel

Aftermarket Idler Wheel

What have I done:

1) Everything well cleaned, started with the wooden housing.
2) Then all bearings cleaned, oiled and greased where necessary.
3) Tonearm V-Blocks replaced.
4) Cleaned stylus with my Ultrasonic Cleaner, using just warm water and a few drops of detergent.
4) The cartridge adjusted with Stevenson Alignment Protractor. Download Stevenson Alignment Protractor
5) Adjusted the 4 chassis springs to level the chassis.
6) Replaced audio cable for a beter one.

What more needs to be done?

1) Search for a dust-cover and hinges.
2) Looking for a second Headshell ( for a quick cartridge change ).   done
3) Replace the fixed audio cable with RCA terminals.   done

Added RCA terminal

Second Headshell with Nagaoka JT511
  • Type: Moving Magnet
  • Output Voltage: 5 mV
  • Freq Response: 10Hz - 28kHz
  • Tracking Force: 1.2 - 2.0 g
  • Mass: 6.0 g
  • Channel Separation: 25 dB
  • Channel Balance: 1 dB
  • Load Impedance: 47 kΩ
  • Dynamic Compliance: 10 x 10-6cm/Dyne

Lenco L78 Manual (Multi-Lingual)

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September 2021:

Restoration of my Garrard SP25 (1967)

The Garrard SP 25 is a popular model that has been produced in many different versions. The SP25 came on the market in 1964 in two versions. The SP25 with a punched iron plateau and the more expensive SP25H with a cast heavy non-ferrous plateau.

Garrard SP 25s are cheap and have real period charm. If you can find a well preserved one, especially with the rubber tipped idler wheel in good original condition, then you’ll be able to enjoy the gutsy, upfront sound that they offer. So much about the SP25 is down to the cartridge fitted; the arm isn’t good enough for a finely balanced, high compliance elliptical design, so you’re best using the pickup that was so often supplied when new – a Goldring G800 or G850. With tracking weights of 3 grammes they’re not going to be put off by the highish friction (in modern terms) of those massy pickup arms. Other good matches include the Shure M75/6, and the Arcam C77 if you’re really feeling adventurous.

I'm using a Shure M44 - 7 at the moment together with the EAR834 Phono Pre Amplifier.

  • Moving Magnet, Output Voltage 9,5mV
  • 20Hz - 20kHz with a Channel Separation of 25dB and 2dB Channel Balance
  • Stylus Tip is 0,7 mil ( 0,0177 millimeters ) Spherical

Download Shure M44-7 datasheet

Some people modify the SP25, usually removing the automation; indeed Garrard itself did this with the Disco Driver 80, a rather oddball offshoot of the SP25/VI. It will sound better, but make sure you don’t allow the deck to lie dormant with the idler gear engaged (i.e. ensure you don’t turn it off from the mains whilst still in play mode) because you could flat-spot the idler wheel. Carefully set-up in a decent plinth and correctly lubed and fitted with a decent – but mechanically compatible – cartridge, the deck will sound powerful, musical and full of energy and drive. Poorly preserved and/or stored, it will have chronic wow and flutter problems, and lots of rumble too – so choose carefully!

What have I done with this record player:

Everything well cleaned, started with the wooden housing.
Then all bearings (of which 3 were stuck) cleaned, oiled and greased where necessary.
Now the Garrard SP25 works again...

What more needs to be done?

1) Repair Anti Skating
2) Someone disabled the "auto" mode and removed an important part. I hope to find this part and can fix it.
3) Change original audio cable for a better cable.
4) I can hear the platter ringing at 78 rpm. I have to check why and try to fix this.
5) There are scratches on the plexiglass lid (I want to remove them with polishing paste)

The main reason for me to use the SP25 is that I have over 150 shellac records and they spin at 78 rpm, need a different sytlus because the groove spacing and grooves are wider and they are mono recordings.
The advantage of this SP25 is that an interchangeable headshell is used on the tonearm. I can also play 'normal' records with different cartridge and stylus.
Among other positive aspects, the SP25 has 4 speeds: 16, 33, 45 and 78 rpm and ik love this turntable...

When phonograph records are made, the sound being recorded is deliberately distorted by reducing the volume of the low frequencies and increasing the volume of the high frequencies. This process, known as 'pre-emphasis', allows the low frequencies to be accommodated in the limitations of the record groove and reduces the effect of high frequency surface noise. If pre-emphasis was not carried out, the bass notes in the music would create a groove in the record that oscillated so wildly that the stylus could jump out of it on playback, and the treble notes would be drowned out by the surface noise of the stylus in the groove.

On playback, the pre-emphasis must be reversed in order to restore the original sound. This is known as 'de-emphasis' or equalization (EQ).

Modern vinyl records use a method of pre-emphasis and de-emphasis adopted by the Recording Industry Association of America (RIAA) in the 1950's, and the EQ curve used is known as the RIAA curve.
However, before the RIAA curve was adopted, each record label used its own EQ curve for recording and, for these records (78rpm and early vinyl), the correct EQ curve must be used for playback.

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February 2021:

PWM Controller for my Ultrasonic Vinyl Cleaner

How does the "Scrubbing Bubbles" Cleaner work?

An ultrasonic generator agitates the cleaning medium (water, plain or with surfactant) with high-frequency pressure waves that produce microscopic (approximately 2.5µm) bubbles.
Those bubbles grow and collapse, releasing heat and tiny, powerful jets of water that can loosen and remove dirt from the record grooves, tarnish from jewelry, and so on.

(So, that "Scrubbing Bubbles" headline is not accurate:
The bubbles themselves don't scrub; rather, it's water jets far smaller than either the smallest record groove or the smallest carbon-fiber bristle, which by the way is about 60µm.)

The PWM Controler

PWM is a digital type of modulation in which a technical variable (e.g. electrical voltage) changes between two values. A square pulse is modulated at a constant frequency, the width, width or length of which varies. The ratio between pulse and pause is called the duty cycle.

Pulse width modulation (PWM) is mainly used in control and regulation technology.

Although the pulse width modulation signal is an alternating voltage or rather mixed voltage, it can be used to regulate the output of direct current consumers such as light emitting diodes, motors, heating resistors and the like. Instead of controlling these parts and components via the level of the operating voltage, the voltage or current is simply interrupted for a short time using pulse width modulation. This creates a certain relationship between voltage pulses and pauses. The ratio determines the effective voltage.

Example: If the ratio between pulse and pause corresponds to 50% each, the result is an effective voltage of 12 V with a pulse voltage of 24 V.

I want to be able to set the motor of the ultrasonic record cleaner continuously in speed.
The reason for this is that heavily contaminated records rotate more slowly in order to be able to clean them even more efficiently.

This motor spins at 4 rpm at 12VDC, that's too fast. 2 rpm is fine for most records. For really dirty records I want 1 rpm.

That's why I want to build this PWM controller ...

NE555 Astable Circuit Calculator

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January 2013:

Turntable Project

The base is made from walnut, 40mm (1,6 inch) thick.
I will use an AC Motor of the Thorens TD160 mkII, also the platter and platter bearing.
The table is completely solid, with holes cut, of course, for the motor, bearing, On/Off switch and arm mounting.

Building the base from walnut.

A long way to go...

I'm using the Rega RB300

First hole, the main bearing.
I used 40 mm ( 1,57 inch ) Walnut for the Turntable. It's build out of 4 piece walnut to avoid distortion. All holes are machined with high precision.
The distance of mid platter to the tone arm pivot must be exactly 222 mm ( 8,74 inch )for the used Rega RB 300 tonearm.

The used Synchronous motor is from an old Thorens TD 160 Mk II. Also the Platter is from the TD160 Mk II

After weeks of calculating and building...

The Spikes are from eBay...

Motor: Thorens TD 160 Mk II Synchronous 220 VAC/50 Hz
Platter: Thorens TD 160 Mk II Aluminium 300 mm / 1,5 kg, Belt driven
Cartridge: Denon DL110

This turntable/tonearm combination was evaluated by 3 of my friends over the last weeks.
The TT1 is very quiet even with old and frequently played records. It further surprises by producing a stable, solid soundstage with a respectable representation of front-to-back depth on suitably recorded albums.

The 180g pressing of Cat Stevens 'Tea For The Tillerman', further shows how the bass is tight, tuneful, fast and weighty.

Next step: Extended Synchronous Motor

TYP LSR 11/16

October 2014:

the Audio Technica AT20 SLa is added.


This is a legendary cartridge, considered one of the best MM designs ever made.
During its lifetime it appeared in somewhat different versions, the differences between them are primarily in the styli - with the SL or SLa having the tapered aluminium cantilever and the SS (top version made) having a beryllium cantilever.

Frequency Range 5-50k Hz (AT20)
5-45k Hz (AT15)
Frequency response 20-20kHz +/-1db (SS only)
FIM distortion at recommended tracking force, DIN 45.452
Channel Seperation @1kHz (db) >30db AT15/20SLa
>33db AT15ss
>35db AT20ss
Channel Seperation @10kHz (db) >23db AT15
>25db AT20SLa
>30db AT20ss
Channel Balance @ 1kHz (db) <0.75db
Output Voltage (mV @ 5cm/s)) 2.7 mV
Tracking ability at 400Hz at recommended tracking force
Compliance, dynamic, lateral (10Hz)
Compliance dynamic, lateral (100Hz)
Compliance static
Stylus type Nude Square shank Shibata
Stylus tip radius (minor / major)
Equivalent stylus tip mass
Cantilever Tapered Aluminium (SLa)
Beryllium (SS)
Tracking force range (g) 0.75 to 1.75
(1.25g nominal)
Tracking angle 20
Coil Impedance @ 1kHz (ohm)
Coil DC resistance (ohm) 500 ohm
Coil inductance (mH @ 1kHz) 350mH or 450mH (SLa)
450 mH (SS)
Weight (g) 8g
Suggested resistive Load (ohm) 47k ohm
Suggested capacitive load 100 - 200pf
Replacement Stylus ATN20SLa, ATN20ss
ATN15SLa, ATN15ss
Alternative Styli Designations (Pfanstiehl code)

*AT publishes their dynamic compliance specifications relative to 100Hz . The actual compliance at 10Hz will be higher.

The Audio Technica AT20 SLa cartridge features a wide frequency response, with a smooth curve resulting in a natural and uncoloured sound, without the high frequency harshness which results from peaky response.

A major side benefit of smooth high frequency performance is decreased groove wear.

The shape of the needle point is an important criterion. An elliptical stylus is higher quality than a conical one. The so-called Shibata needle is by far the best needle shape. The breakthrough in needle grinding was forced by the Quadro technique - the breakthrough in CD 4 compatibility was the SHIBATA needle.

The Line Contact shapes (Super Fine Line, Van den Hul, Fritz Gyger, Hyperelliptical, MicroRidge, ...) are all considered to be mere modifications of the SHIBATA needle. Once SHIBATA, always SHIBATA "

Calculate Turntable Motor / Pully

Calculate Tonearm / Cartridge Capability The Home Of Turntables

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July 2012:

Single Ended EL34 Amplifier

Driver Tubes: 6J8P
Rectifier Tube: 5Z3P
Power Tubes: EL34
Frequency Response: 16Hz - 22kHz -3/+0dB
THD: 0.1% @ 1kHz
Weight: 18kg


My plan is to replace most of the resistors with Carbon resistors and the coupling capacitors with better ( MKP and oil/paper? ) caps.

Some resonances at 25kHz and above of the OT's.
I should buy beter OT's.

Distortion @ 1Watt

Amplifier Circuit (modified)

Calculate Amplifier Damping Factor

Power Supply Circuit (modified)

Calculate RC and LC Filters for Tube Power Supply


I changed all electrolytic capacitor of the power supply (47uF and 68uF) with 3 x 22uF Mundorf MKP capacitors (66uF) and 33uF.
The PreAmp Stage capacitor (47uF) will be replaced with 4 x 10uF MKP.
All other capacitors in the signal path are now (russian mil) Paper In Oil capacitors.

One capacitor to go...

Tube Upgrade

I changed the "normal" 6CA7 China tube with the execllent Shuguang Treasure 6CA7-Z

The 6CA7-Z tube's construction features gold grid wires and a new internally coated black glass bottle. This unique HPCC coating is known as High Polymer Carbon Compound glass coating and is unique for its ability to reduce stray electron emission that can otherwise reflect off the glass. Shuguang also uses their new "Super Alloy" technology. Originally applied to aviation, aerospace, and military applications, this technology has been successfully used by Shuguang to accomplish directional solidification and single crystallization. This greatly improves the ability of electron emission and electron current stability. This new Shuguang Treasure series required additional parts selection quality control processes, improved vacuum techniques and additional burn-in time and testing.

This Shuguang Treasure 6CA7-Z tube is their premium export grade and purchased direct from Shuguang in China.

Read the TNT review: Shuguang Treasure 6CA7-Z and KT66-Z - vacuum tubes

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