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My FONS CQ30 Modification Story.

Michael Kazarinov

After using the DD turntable Technics SL-1200MK2 for about a year (and being perfectly happy with it!), I’ve decided to try some belt drive turntables and test for myself the commonly proclaimed superiority of BD over DD.

Typical candidates for my future belt drive turntable would be classics like Thorens, Ariston, AR, Systemdek or Linn. Close study and following modifications that I performed on the typical Thorens TD-160 left me with the mixed feelings, mostly b/c of the poor original build quality of the turntable.  And recently I came across the FONS CQ30 TT made by Fergus Fons company  (late 70’s) from Scotland. All above mentioned models were developed in early 70’s by small group of people, who knew each other very well, worked in the same time, and tried to solve the same problems. As a result, the turntables that they developed shared some common design features, like suspended sprung chassis, and some common problems, like the fact that Linn filed for patent protection against Ariston and Fons. (Some people said that Fons is a further advancement of the original Ariston). I am not the expert in the TT history, more can be found on the Internet, like the post here:

http://www.audiokarma.org/forums/showthread.php?t=100781&highlight=FONS+CQ30

So for me it wasn’t important who did what, but rather the particular features of each TT, and the influence of these features on sound reproduction.

The features that set FONS turntable aside from the others:

1. The motor is mounted on the sprung chassis along with platter and tonearm. The benefit of this is that the belt alignment is always good, and there is no wow-flutter due to belt motion between the fixed motor and the bouncing platter (A problem for AR/Linn/Thorens types, where the motor is attached to the fixed chassis, and any suspension’s motion would cause a change to the belt tension, and results in an increased wow and flutter).

2. Heavy platter is one piece cast, 1/4" thick plate, 1/2" rim and 3/8" walls on the barrel, about 2.5 kg, has higher moment of inertia (better stability), and no possible distortions originated in the contact surface between the platter and sub platter design typical for Thorens.

3. FONS developed a unique hyper concentric main bearing with concentricity of the order of 0.75 micrometer, which is claimed to be the best in the industry. As a result, the rumble level is -80 db, tens times better than any other turntable in that line.   

4. It uses a DC motor, so there is no 60, 30 or 5 Hz rumble associated with an AC motor.

5. FONS was developed to use the SME tonearm from the beginning. That not only made installation of my SME tonearms easy, but also insured proper suspension tuning for the platter-tonearm combo. 

6. Not so obvious, but still very important for the proper cancelation of parasitic modulations, is the design of the sprung turntable in which the center of the suspension and the platter bearing were positioned above the sub-platter, and not under it (like in Linn or Thorens). 


Original FONS before modification:

Inspection of the construction of the box and inner parts shows that there are a lot of places for upgrades and modifications. Obviously, FONS was investing a lot into the platter-bearing design, and had saved on the other part’s production to be able to keep up with its rivals. The box (plinth) is light, without any sound damping treatment, and screamed for upgrades.

My FONS modification

The upgrade combined some typical advice for the vintage gear restoration, setting up classic tables with suspended sub-chassis like Linn, numerous modifications of the Thorens tables, and FONS specific mods.


Areas of specific attention

During the record play, there are three groups of the mechanical motion and resulting distortions of sound reproduction. Imperfection of the motor-platter group results in the rumble, wow and flutter; interaction of the stylus and the platter produces various vibrations and unwanted resonances; turntable itself is physically connected to the room via feet and stand, and acts as the sensitive receiver to all audible actions, like steps or sound from the speakers.  Each group has to be controlled separately and specifically to the physical nature of the distortion.

Part 1. Motor-platter group. Improvement of the mechanical noise and distortion.

Lowering the rumble: All typical steps. Service motor, polish pulley and platter, belt adjustment, service the platter bearing.

Old sealing removed

New motor oil and new sealing

Pulley polished

Platter polished

Test for the motor–platter group: belt has to run in the middle of the pulley.

Part 2. High frequency reproduction: sub-chassis treatment

The common advice and typical mods done for the numerous Thorens is to damp the sub-chassis (and/or bearing hub). The whole idea of a suspended sub-chassis turntable is to separate and insulate  mechanical vibration (including but not restricted to resonances) in the platter area and the rest of turntable mass using isolating springs. The physics of this is questionable since there are six (6!) independent degrees of freedom for the platter motion, and the standard approach considers only one (up and down). Sprung sub-chassis turntables are promoted by manufacturers because they are much cheaper to produce. There is obvious advantage of dumping metal sub-chasses using cork liners,  and not obvious ideas how to tune sprung sub-chassis unit.

The FONS sub-chassis suspension is more complicated than on Thorens likes. It has two springs for each suspension point, and the springs’ force constants were designed for a system with the stock platter and SME 3009 tonearm. You cannot change the weight load not only b/c of the shift in the resonant frequencies, but simply because there is no room for the vertical play. Usage of the damping material inside of the spring is even more questionable. The spring acts as an over-damped oscillator and could be replaced with a piece of rubber for the same results.

Step 1. Dampening the top and the underside of the motor plate with damping material

Metal Sub-Chasses

Sub-Chasses damped with cork sheet from both sides

To damp the sprung sub-chassis, cork self-adhesive sheets were used. Upper side of sub-chassis and the bottom side of sub-chassis are treated with the same cork material.

To get the best possible sound reproduction it wasn’t enough to damp the sup-platter and rebalance it. Even when the compliance of the sub-chassis was in the optimum range (check by pressing down on the platter in different places and see that the platter would bounce at 2-3 Hertz ), there are possibly some higher frequency resonances when playing parts with extremes of groove velocity. So I had to place some additional damping.

Step 2. Tonearm plate acoustic dampening

2 mm around the base removed

Acoustic damping with cork sheet 

Additionally, I had to check that the arm leads are free and are not rubbing the sub-platter.

Part 3. Mid frequency reproduction: Box acoustic dampening.

The typical recommendations are:
- isolation of the 3 suspension springs from the sub-platter using additional gaskets and/or silicon. Cannot be done on FONS b/c there is no extra space for even 1 mm additional gasket.
- dampening the area around the motor and the underside of the top plate with heavy damping material

- readjustment of the sprung suspension
- lining the underside of the whole upper board with dynamat for further isolation

Before

After

 

'Dynamat' was used for damping the turntable box (base cabinet).

Part 4.  Low frequency reproduction: A heavy base, improved floor-standing support stand for better low-level dynamics.

This is the area with the most controversial recommendations. Some say that for the best bass reproduction any turntable has to have a heavy massive plinth. On the other hand, some people remove bottom plate to prevent unwanted resonances in the closed box coursed by the tiny movements of the stylus following the groove.

Based on my understanding of turntable physics, I believe that the massive base is required to compensate for the rotation of the sub-platter, originated by the friction in the groove. Common material used for a new bottom plate (due to the big mass and size acting actually as a plinth) could be MDF or birch plywood from 1/2" to 1"+.

I made a new plinth from 1” MDF using old bottom plate as a template.

Plinth was treated with RDC as well.

Next, I compared the sound of the turntable with a solid bottom to one without the plinth (open box), and after evaluation, I decided to drill a few holes to “open” the box. (Difference in sound wasn’t so obvious, and later on I couldn’t decide if it originated from the box construction, a beer I had before, or if it came from the dynamic stabilizer brush on V15-V that I forgot to flip up.)  

Before

After

New four feet underneath new plinth provided better foot fall vibes isolation. It improved isolation significantly, but still, has not eliminated such influence 100%,  so one needs to find a suitable location for TT to isolate the turntable from it's environment.  I tried three different types of feet, including solid rubber, metal cones, and finally choose a composite, with rubber bottom and spring inside.

And the final steps are to install and set up the specific tonearm to get the correct overhang, azimuth, and vertical tracking angle (VTA), and antiscating force, and to recheck the set up a three-spring suspended TT as a whole.

Part 5.  Fitting tonearms.

I had two SME tonearms in my possession, and I decided to test which one is a better fit for the FONS.  

Version # 1 : SME 3009 S2 improved tonearm

 

 

Version # 2 : SME III tonearm

 

Part 6. Comparison and Evaluation:

Both tonearms performed exceptionally well, producing clean, original sound of the record. Turntable has great transient response (it sounds fast and clean). Bass is deep and tight. Clear, open midrange. With such high level of the turntable itself, the only audible difference I’ve detected was originated from the difference in cartridges and their setups (see the list of cartridges I used).
At the same time, I found that SME III performed better in the area of steps shock defeat. I can explain it only by the lower position of the center of mass of SME III compared to SME 3009.

You can see test results on Youtube: FONS CQ30 turntable trackability test.
Or here:

Part 7. Modes that I did not apply to the FONS:

1. Damping the platter and bearing hub. To properly dampen the platter requires the same level of precision as you need to build a new platter. Dampening the bearing hub is not obvious and depends on the materials used for the bearing hub and their coefficients of thermal expansion.

2. Usage of the damping material inside of the spring is even more questionable. For springs filled with foam see no-no example and discussion here: http://www.theanalogdept.com/susp_tim_bailey.htm

I removed factory installed small foam pieces.  They did not offer any dampening to solve the foot fall problem.  Even worse, they transmitted vibrations from the base into the sub-chassis.  The spring filled with foam acts as an over-dampened oscillator and could be replaced with a piece of rubber for the same results. By removing the foam, isolation was improved.  No foam inside of the spring to dampen spring oscillations.

 

Part 8. Some reference information.

1. Technical details:

Metal-To-Metal Turntable Bearings. FONS suggested using graphite lubrication. I did not have original oil, so I used low speed auto gear grease. Some bicycle grease or molybdenum grease could be used as well. Next generation turntables (typically direct drive) commonly use synthetic motor oil. As an extreme recommendation, some say that for such low speed motion there is no need for lubrication at all.

This matter should be investigated further on.

RDC (Resonance Dampening Compound): 'Dynamat' was used to damp the box. To damp the sprung sub-chassis the cork self-adhesive sheet material was chosen for it's high damping coefficient and the light weight. 

Physics. Mass of the sub-chassis, platter and armboard together with springs perform as a typical mechanical damped oscillator, that forms a low-pass filter – i.e. only frequencies below the resonant frequency of that oscillator will propagate into the groove-needle system and further into amplifier. To make it even more complicated, different components like stylus, tonearm, platter have their own resonances, which working together could amplify or kill each other.

The further investigation of such relationships would be the topic of my next “research project”.

2. Equipment used:

Solid State sound evaluation:

Phono stage: PS Audio GCPH connected directly via balanced outputs to
Power amp: Bryston 4B-ST
Main speakers: Polk Audio RTi150

Tube sound evaluation:

Phono stage and Preamp: Adcom GFP-555
Power amp: Audio Research D-76
Main speakers: Thiel CS-2

Cartridges used for evaluation:

MM Phono cartridges: Shure V15-III, Shure V15-VxMR, Shure M97xE, Stanton 681
MC Phono cartridges: Pioneer PC-401, AT-30E

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