For those wanting to improve their turntable systems this is a brief overview of my Thorens TD160S, Hadcock GH228S and Lentek Head Amp upgrade and rebuild.
I have owned my Thorens TD160 Super, Hadcock GH228 Super, Lentek Entre 1 cartridge and Lentek head amp since they were each first released on the market. Their performance has always been excellent for the price. It still appears, after all these years, that for what I paid for this combination still takes some beating. However, after all this time I felt a rebuild and upgrade would be in order.
In the UK during the 70’s and 80’s I worked with George Hadcock on the testing of the GH228 Super arm and, I believe, that I own the only one in existence that has the seven ball bearing unipivot.
(Apologies for the out of focus picture, but by the time I realized it I had re-built the arm. However you can still clearly see the seven ball bearings)
There were, as I remember, two iterations of this bearing: a three-ball that was quickly replaced by the current four-ball assembly. The prototype seven-ball pivot provided significantly more stability for the unipivot and completely removed the minor play that could be detected in many of the four ball bearing assemblies that I tested. I cannot remember now why it never replaced the four-ball….maybe cost. My arm also has the prototype pulley bias anti-skating upgrade.
So let’s review the upgrades I did!
The Turntable Modifications:
- Added bitumen damping to the base
- Replaced the four felt pad feet with adjustable rubber point contact feet
- Added both the digital power supply and speed control tachometer from Phoenix Engineering – no longer in business – remaining products at HiFiHeaven
- Added an external thrust bearing to the motor
- Resiliently mounted the motor in order to isolate it from the main chassis
- Replaced the plastic motor pulley with the precision aluminum-machined version
- Revised the power and signal grounding and added a full set of sockets across the rear of the plinth to support power, safety ground, signal/technical ground, tachometer and balanced XLR connectors for the cartridge
- Added a modified carbon fiber brush assembly with anti- skating addition, as I occasionally had static problems
- Added the Osage GEM Dandy R.C.C record matt – see opening turntable image
The Arm Modifications:
- Upgraded the cartridge cabling to KAB SuperFlex Litz copper tonearm wire. This is made up of 40 strands of 50 gauge pure copper wire enclosed in a super flexible silicon; amazing cabling and easy to work with
- Replaced the cabling to the rear XLR connectors from the base of the Hadcock arm with a homemade-shielded balanced cable assembly using the above Litz cables. This pseudo-balanced connection was continued into the rebuilt Lentek head amp. (I understand that some designers/engineers do not take well to the term “pseudo balanced” as it is either balanced or not. However, I often use the term to describe an unbalanced connection that uses the high and low of a balanced cable to carry the signal, and the screen is ONLY used to electrostatically screen the inner two signal cables, being connected to ground at only one end.)
- Increased the pivot damping fluid to 600,000 cST from Turntable Basics.
The Headamp Rebuild:
The head amplifier was completely rebuilt using Vishay Metal Oxide resistors, Nikon Muse KZ electrolytics and Wima film capacitors. All connectivity was upgraded to gold plug and socket with KAB cabling. The transistor connections were replaced with gold sockets to allow me to experiment with different transistors – more on this later. Below is the circuit that was originally designed for Lentek by the late, distinguished British Electrical/Audio design engineer Peter Baxandall, who is well known for his active tone control design among many other contributions to the analog audio world.
During the rebuild the two 10uF electrolytics were replaced with 47uF. The parallel 100 ohm resistor and 10nF capacitor at the bottom of the schematic that connect the second channels 0 volt ground are to reduce/prevent potential ground loops.
The connectivity to the head amplifier from my Denon AVP pre-amp was also improved using very low capacitance screened cabling, about 150 pF per side for a three foot run. A pseudo-balanced connection from the head amplifier to the cartridge was created from homemade balanced screened cables using the KAB cables described above.
The Upgrade Work In Progress
I always think that a few pictures can replace a thousand words, so here are a few.
Thorens TD160 Super Turntable Upgrades
1. Added bitumen damping to the turntable base
An additional hole was drilled through the base, top LH corner, in order to allow for the later adjustment of the new motor thrust bearing screw due to possible wear, without having to remove the base. The other four holes are for adjusting the sub chassis mounts.
2. Replaced the four felt pad feet with adjustable rubber point contact feet.
3. Mounting the speed control sensor.
The above image shows the original fixed motor mount with original plastic motor pulley and sub platter.
I decided to mount the Hall Effect device under the inner platter for two reasons:
- I could run the platter without the second one to inspect the system.
- The cabling could be completely hidden from view.
Phoenix recommends the use of the larger platter as it marginally improves the speed accuracy and stability. I could not imagine it being any more stable than 33.333 +- 0.003 RPM.
I also added a counter balancing weight, diametrically opposite to the small magnet that is attached to the underside of the platter that activates the Hall Effect Device. The magnet is so light that I do not believe that this was necessary but it was easy to achieve with the turntable dismantled, just make sure the counter balance isn’t magnetic, I used a small brass nut that weighed exactly the same as the magnet.
The Phoenix hardware is amazingly small, very well built, very easy to fit and use and has a good range of useful features. Bill Carlin, the owner of Phoenix Engineering and designer of this product, responded to all my questions within just a few hours of me dropping him an email, excellent support. UPDATE. Phoenix Engineering has now closed its doors to business.
4. Adding the external thrust bearing to the motor.
Prior to assembly the T nut flange was meticulously cleaned together with the base of the bottom motor bearing and then wiped with de-natured alcohol to remove any residues. Super glue was then used to bond the T nut flange to the bearing, the raised part of the bearing centering the T nut to its correct location. A little molybdenum grease and the ball bearing were then inserted and the hex screw was adjusted just enough to remove any vertical shaft play without causing it to bind on the thrust bearing. The hex screw was bound with PTFE tape in order to make it very snug in the thread so that it would not work loose. I did purchase a spring(s) to pre-load the ball bearing but decided against it, as it seemed to cause the thrust bearing to become too tight. As can be seen in the second image I also ended up using a longer T nut in order to give the screw more thread.
Although I do have a new unused spare motor I did not want to use it as the existing match between the capacitor value and the original motor showed no signs of a poor phase match as no discernable vibration could be felt if I held the motor in my hand when it was running.
5. Resiliently mounting the motor in order to isolate it from the main chassis.
The lower washers, sitting on the spring, were selected so that their inner diameter would allow the three motor mounting shafts to slide through them and rest inside the rubber grommets. This maintained the isolation and kept the motor more stable allowing the screw adjustment to raise and lower each shaft within the grommet.
6. Replaced the plastic motor pulley with the precision aluminum-machined version.
Prior to mounting the motor isolation system, the original turntable chassis motor mounting holes were drilled out to the same size as the inner diameter of the mounting grommets. The platter protection support spindle shown in the second image, also had to be modified as it interfered with the motor suspension installation under the chassis. This new arrangement allowed me to raise and lower the entire motor assembly and tilt it in any direction in order to get a perfect belt fit in the middle of each pulley. This ensured that when I use the 33 and 45RPM manual speed change, without the Phoenix motor speed control, the belt would sit correctly on the pulleys.
Contrary to popular belief, exotic/synthetic oils are not necessary for sintered brass bearings, the one shown above is more than sufficient and is recommended just for this purpose. I found that 2 cc’s was just enough to fill the bearing when the spindle was inserted. It took quite some time to go down – about 3 minutes of spinning the platter.
7. Upgraded connectivity and grounding connections
In order to ensure there were no ground loops the safety and signal grounds were separated each one being connected through its own cable to the main racks ground buss bar. The connectors are: signal ground; tachometer; AC power; separate safety ground. The two missing male XLR’s for the cartridge signal were added to the LHS of the signal ground at a later date.
8. The modified Anti-Static Arm
The anti static brush system did not work well when first installed in that it would continually get thrown off the record by the centrifugal force of the record. Also because of its position the supplied arm rest could not be used. I therefore added a small stainless steel arm and pulley system that carried both the new arm support and the anti-skating pulley. After adjustment, this ensured that the anti-static arm now tracked with my cartridge arm and provided a convenient place to rest the arm when not in use.
After reading many very positive reviews about cleaning records in order to remove static, and of course dirt, I decided to purchase a vacuum record cleaner.
This manual vacuum cleaner, the least expensive in the Nitty Gritty line, is very easy to use, a little noisy, but does an outstanding job using the Nitty Gritty Pure 2 cleaning fluid. It removed all my static issues and the improvement in pops and clicks and overall reduction in vinyl surface noise are excellent. A full review of this cleaner is coming soon.
My static problem stopped after using the Nitty Gritty Model 1 record vacuum washer and MoFi anti-static record sleeves. This is probably the second best addition I have ever made to my vinyl listening experience….excepting this entire upgrade. The reduction in surface noise and pops and clicks was astonishing; at times, and with certain pressings, it is almost like listening to CD’s in terms of background noise between tracks and during quite passages.
Hadcock GH228 Super Arm Upgrade
Not too much to show here. I replaced the original stiff cabling with the new KAB Litz wire (it’s wonderful to work with and makes setting up this arm much easier) and used re-claimed gold plated DB25 female/male pins for the cartridge connections and arm grounding connection. It turned out that the arm tube is electrically isolated from the grounded pivot and I should have run a 5th separate ground cable for it. Using the grounded side of the left or right hand channels to ground the arm tube introduces an almost imperceptible hum into that channel as the cartridge is wired pseudo–balanced….too late to run the extra ground now!!
As I couldn’t get the large silicon syringe tip into the arm well I dispensed some into a smaller 3cc syringe. I think I now have enough for several lifetimes. I have always filled the pivot damping well in order to get maximum damping, as I understood that was how George designed his arm to work. However, I have come across users who get excellent results when using little or no damping depending upon the cartridge in use.
Lentek Head Amplifier Rebuild
As the head amplifier components were very old, and I had a problem with one of the transistors going noisy, I decide to completely rebuild it. I removed all the original components and replaced them with the following:
- Electrolytics – Nichicon Muse KZ 20%
- Decoupling capacitors – Wima Film 5%
- Resistors – Vishay metal film 1%
- Transistors – See comments below.
Note: Extra holes were found, associated with all transistors, showing that this board revision was set up to handle different transistor types.
I added all gold plug & socket connections in order to allow me to easily remove the board for any component changes and change the transistors in order to determine what devices provided the lowest noise. The transistors tested were:
- BC461/BFX85 – The devices specified by Baxandall
- BD376/BD375 – Original devices in the head amp when I received it
- 2N4403/2N4401 – Recommended low noise devices for head amps
- 2N5194/2N5191 – Equivalent to the original devices that went noisy
Believe it or not, the original devices specified by Baxandall provided the lowest levels of high and low frequency noise. Absolutely no discernable differences could be heard in sound quality between any of the devices.
So was all this work worth it?
A resounding yes! I will sum up the changes to the system following everything I did:
- Lower turntable rumble at 33 or 45RPM. My system has a high pass filter set to 3Hz and my subs’ cones stopped flapping around at a typical listening level of 80dB (my room is fairly flat to 5Hz at 100dB SPL). See the following link for a full technical overview of my purpose – built listening room.
- No discernable thrust bearing noise from the motor, which had started to occasionally tick.
- I finally got the platter to spin with no discernable vertical motion by carefully cleaning the mating surfaces and painstakingly adjusting the relative positions of the inside and outside platters.
- The Phoenix power supply and speed control provided a significant improvement to:
- Long decaying notes
- A rock solid RPM reading – even if I removed the speed feedback the turntable was still very stable. Reverting to no AC frequency control produced an RPM value that was at the mercy of the AC mains frequency and other frictional forces, and was measurably and audibly, less stable.
- Imaging was now more precise
- Sound stage was significantly improved
- Image depth was more precise
- Bottom end was tightened up…not that the system really needed it
- Mid-range was smoother
- Top end was slightly more detailed
Just one observation about the Phoenix speed control that is simplicity to install and works wonderfully. When I first used it to change the speed to 45RPM there was a noticeable increase in motor vibration, which I put down to the phase shift that was created by the motors capacitor now being incorrect for the increased AC motor frequency. So for a while I used to manually move the belt using the Thorens speed control when I played 45RPM LP’s. Recently I have returned to using the Phoenix electronic speed control as for whatever reason it no longer seems to create the earlier noted vibration.
Unfortunately, my Entre cartridge is now ‘long in the tooth’ and I feel that re-tipping it is both too costly and might change its sound (for the worse). Plus the cantilever/coil elastic mount may be coming to the end of its useful life. So I am now in the market for a new cartridge, moving coil or?? Any suggestions in the below $500 range? (Note that my arm is low mass but can be heavily damped and the Entre is high(ish) compliance.
Vinyls back and Sony is leading the big boy charge.