By ARS, Dec 19 2017 05:49PM
ARS has finally joined Twitter
ARS has finally joined Twitter
An A1 recently arrived at the workshop in typical condition, noisy volume, intermittent input selector and no doubt a few other issues once the top cover/heatsink was removed. What was a suprise was a somewhat different PCB inside which on first inspection appeared to be that of a Musical Fidelity B200 instead (this uses a MOSFET output stage and doesn't run in class A)
Once the PCB was removed it was quite clear that this was a B200 as the PCB designation underneath had been neatly obscured by a Musical Fidelity inspection sticker revealing 'B200' when removed - see photo below.
It had the lower voltage mains transformer of the original A1 however thus ensuring the output remained at approx 20W into 8 ohms. Who knows how many of these models proudly sporting 'Class A amplifier' on the fascia are something entirely different inside!
The recent resurgence in listening to vinyl in recent years has led to plenty of dusty late 70's early 80's amplifiers being brought down from the loft after a couple of decades of hibernation. Today's amplifiers don't have a phono stage and often the modern stand alone units available are rather expensive for what is often just couple of cheap op amps inside a plush looking box. Fortunately the old amplifiers usually have a very high quality phono stage inside often built entirely from discrete components(e.g NAD3020) Sadly most owners discover they don't work when resurrecting them after 25 odd years! Most of the amplifiers repared by ARS contain a phono stage and these are all fully overhauled and tested whether or not an owner uses the input. In fact the cost of overhauling the entire amplifier is often less than an seperate modern phono stage usually put together in the Far East for a tiny fraction of that paid by the end user.
On the majority of these models the motorised Alps input selector switch will have become annoyingly noisy/intermittent on most inputs if not all. The culprit is mainly down to the effects of long term sulphation of the silver plated contacts. This is despite evidence of a contact lubricant having been originally used which with time appears to have thickened or dried out thus losing it's self healing film properties. The end result when viewed under high magnification is a fine line of sulphation on the fixed contacts where they mate with the moving ones where any protection afforded by the original treatment is now non existent (if indeed it provided much in the first place) This can just be seen as fine dark lines in the first picture below. Small traces of sulphation are normally removed by the mechanical wiping action of the moving contact but clearly the Alps switch has degraded well beyond the scope of this.
Proper refurbishment is not for the faint hearted, takes several hours and requires complete removal from the circuit board. This can be time consuming to desolder with 40 or so plated through holes and all need to be completely cleared of solder before even attempting to lift the switch assembly away from the PCB otherwise you risk breaking legs off the wafers. The 4 individual sets of switch wafers can then be removed and as with the Alps switches in the Cyrus models are chemically cleaned to remove tarnishing followed by careful polishing and thorough cleaning with solvent to leave the plated contact surface in a pristine and as new condition. In an effort to improve the longevity of these switches further the contact surfaces are now gold electroplated which offers a far superior resistance to tarnishing compared to silver. This is finally topped off with a treatment of Caig DeOxit Gold which is a very high quality industry proven product and should provide long term protection and lubrication to the contact surfaces to extend the usable life of these amplifiers. As these switches are no longer available new this is the only option if you wish to prolong the life of these two models. Forum 'rumours' detailing cost saving attempts by some to squirt switch cleaner through holes in the casing are an absolute waste of time as the contacts are fully enclosed until removed as the lower photo shows (similar to attempting to wash a car locked inside a garage whilst poking the hose through the keyhole!)
If you wish to have your switch refurbished then visit the Arcam pricing page for further information.
You will often see second hand amplifiers for sale with the rather bizarre description of having been 'serviced' as if it were an engine or something with oil, filters and belts that need changing! Depending on the seller this can mean a variety of possibilties from the list below:
1. It was plugged in and it worked, then dusted it clean.
2. Took the lid off and all looked ok inside.
3. A lot of perfectly functioning components have been needlessly replaced with new ones of inferior quality
4. It was blown up but has now been repaired.
5. Or it has been fully tested in acordance with the manufacturer spec and a number of out of tolerance components have been replaced, and all common failure points with this model checked and rectified where necessary.
Hence the seller can then often advertise at an extortionate price once the magic word 'serviced' is applied! Quite which one of the above list applies is anyone's guess - buyer beware! An amplifier either works or it doesn't. If it doesn't then it needs repairing - simple!
In the vast majority of cases this is usually down to the failure of either output or driver semiconductors or electrolytic capacitors. In particular heat is the enemy of such devices and poor layout by the designer is often a contributary factor. For instance a number of manufacturers mistakenly locate electrolytic capacitors alongside heatsinks or power resistors. An average quality 85C capacitor probably has an estimated lifetime of 3000 hours at that temperature. This is generally accepted to double for every 10 deg C reduction in temperature. In a well known Class A amplifier from the 1980's the heatsink is happily running at just over 65C with several capacitors within a few mm of this meaning lifetime is probably 12000 hours or so before they are outside the specified tolerance. If the amplifier is used for 3 hours daily then 12000 hours equates to about 11 years before such components are nearing end of life. Of course that is an extreme case afflicting only a few particular models.
Even worse are those parts of amplifiers that are left powered 24/7 when owners think a standby switch is turning it off. Several capacitors in a popular range of subwoofers are probably subject to an ambient temperature of at least 45C but with a 3000 hour life and unwittingly left powered 24/7 by owners this leads to just over a 1 year lifespan (and I believe there were many warranty repair claims thus confirming the maths!)
At the other extreme the very high quality main PSU smoothing capacitors (Slit Foil - presumably BHC) used in a Cyrus One or Two almost certainly had a specified life of at least 12000 hours plus. Located far away from any heat source they probably endure an ambient temperature of no more than 45C even taking into account any ripple current heating leading to a 48000 hour anticipated lifetime or ~ 45 years at 3 hours use daily. This is not as unreasonable as it sounds as a 40 year old Quad 303 in the workshop recently had it's original smoothing capacitors removed and tested fine for capacitance and ESR.
By their design electrolytic capacitors do have a finite lifetime. They are basically two rolled up aluminium foils usually etched to increase surface area with a paper dielectric in between impregnated with an electrolyte and then all sealed in a can. The electrolyte typically consists of ethylene glycol with aluminium borate as the main ingredients and a small percentage of water. The main difference between expensive long life capacitors and budget hobbyist ones is mainly the quality of the foil, seals and electrolyte. More heat means the electrolyte dries out over a shorter time scale and eventually capacitance falls and ESR rises. Several well respected manufacturers still routinely use some really nasty brands in their equipment probably knowing that 10 years on failure is not an issue when any warranty is long gone.
Semiconductor junctions although rated at quite high temperatures (e.g 150C and that is the junction - not heatsink!) will eventually break down under conditions of excess heat whether by poor design or owner abuse. The latter is often through placing other equipment on top of vents, hiding amplifiers away in enclosed cabinets combined with sustained running at high volume levels. Some failures are caused by those owners that accidentally short loudspeaker terminals together usually through poorly terminated speaker cables and exposed conductor strands - for those amplifiers without protection it usually spells instant death to an output device.
Frequently failure of a single transistor (output or driver) will lead to burnt out resistors and other failed transistors upstream or downstream (resistors usually cause the smoke you will see rising through vents as your amplifier is on it's death bed). It's no good replacing one failed device without having properly checked the others unless you wish to be quickly back at square one. It's a fact of life and probably always will be that your amplifier will be one of the least reliable parts of your HiFi setup (closely followed by cd players which can also be regarded as consumables!)
One of these has just left the workbench after arriving faulty on one channel. Clear signs that the owner had attempted repair and given up however in the end it was simply a dead driver transistor with an internally arcing main power switch also found faulty, the latter causing a unusual burst of noise for a few seconds until it settled down every time it was powered on. Once a few dry joints were attended to with some power cabling below the pcb properly sleeved (sharp component leads were chafing it!) and biasing set up it was back to earning it's keep once again.
For a cheaply built Taiwanese amplifier now close to 30 years old for the early models these are a real shock (audibly of course!) if you have never heard one and are more used to what you would consider much higher end equipment. Quite simply they are fabulous amplifiers and sound far better than their plastic utilitarian design and 25W would suggest and they will certainly give a Cyrus One a good run for it's money and many others which sell for considerably more. Part of it's magic must lie in the preamplifier stage as when substituted with an old Linn Wakonda (kept in the workshop for testing) driving the NAD power amp stage the whole setup was immediately rendered bland and lifeless and the Wakonda soon went back to it's shelf! Most 3020's sell between £40-£100 secondhand and the simple design means it should be possible to keep these running almost indefinitely unlike modern equivalents with their unnecessary microprocessor 'bells and whistles' which add nothing to the listening experience! In terms of audiophile performance per £ spent these can easily be regarded as being close to the very top. A repair service for these is available from ARS and a comprehensive NAD3020 upgrade service too for those owners who wish to know that all will be well 'under the lid' for another 25 years.
The input selector on all the Cyrus One and Two models is a high quality Japanese switch made by Alps. However it's open (as opposed to sealed) construction does expose it's silver plated contact surface to atmospheric pollutants, dust and whatever else is in your living room! Eventually a tarnish/dirt layer forms on the more exposed rear most portion of the contact surface primarily made up of not so conductive Silver Sulphide (not oxide as some think) and thus the audio input fails to reach the output.
Although not for the faint hearted this switch can be desoldered, carefully dismantled and chemically cleaned and polished to as new condition (incidentally using much the same techniques used by the author in the broadcast industry for cleaning the silver plated Klystron tuning cavities on high power analogue UHF TV transmitters when they became twitchy and noisy to tune!) This picture shows the contact surface with a 20 year old tarnished one upper and a restored one lower which should have another 20 year lifespan - useful as these now appear to be obsolete......
Newly constructed replacement ARS Quad 303 boards undergoing setting up and testing. By far the easiest way of rejuvenating a tired 40 year old Quad 303 amplifier. Priced at £124 for a pair of driver boards and £25 for the regulator board they are currently on sale in the 'shop' section of the website. High quality components including Wima and Panasonic FC capacitors and 1% tolerance metal film resistorse used (and built to exactly the same design as boards used in Quad 303's above S.N 11500)
For those owners not confident enough to replace and set up purchased replacement boards then an installation service is also offered by ARS Amplifier repair priced at £25 including the cost of shipping your 303 back following the upgrade. Use the 'contact' form to enquire about this service.
(ARS also offer a fixed price Quad 303 repair service at £89 or have your Quad 303 repaired and a complete set of new boards fitted at the same time - please visit the Quad page for pricing on this option)
Along with the Cyrus 1 and 2 amplifiers the compact Musical Fidelity A1 is another very good value excellent sounding amplifier as long as you partner it with reasonably sensitive speakers.
Biased mostly into class A it runs very hot though with the top of the amplifier forming the heatsink which reaches temperatures of up to 60 deg C. Incredibly the earlier examples were a sealed box with no ventilation whatsoever! The end result of this is everything is slowly cooked with the electrolytic capacitors suffering the most.
The picture below shows all the electrolytics removed from a 1987 example . Some are well known respected brands such as Dubilier and Rubycon and others, Sunking, Liyeh and Bennic not so.
Out of the small signal electrolytics pictured below 30% of these were out of spec with low (if any!) capacitance and high ESR. These included all of the orange Sunking ones, the 3 grey Liyeh and a couple of the brown Bennic ones. All of the Rubycon PSU smoothing capacitors were still within Spec but after 25 years they were probably on borrowed time. In fact with the slow deteriotation of capacitors over the years it it probably isn't easy to notice the gradual fall off in performance until they are replaced in one hit as done here.
All small signal capacitors were replaced with 105 deg C Rubycon's (all originals were only 85C rated which does not bode well for a long life in such a hot environment). The PSU caps were replaced with
some nice compact 32mm high axial Epcos 35V ones as the original 25V rating is pushing the boundary a little. More expensive brands are available but at 3 to 4 times the price I doubt the lifetime would scale accordingly.
Once replaced along with a new ALPS blue 50K pot the A1 was returned to it's original smooth sweet sounding personality and for such a basic design and only 20W sounds fabulous once again! The only other drawback with these amplifiers and similar MF equipment of that era is the consistently poor internal build quality more resembling something built from a kit on a kitchen table by a keen amateur! However this is no different to several other UK products from the 1980's so perhaps it was considered acceptable at the time and simply looks rough compared to todays standards.