Category Archives: Hi-fi workshop

We get many repairs into the business and this section documents the faults that occur andhow we fix them.

HifiGear’s Hifi Dictionary

The world of hifi can be a daunting and confusing place at first, especially when looking at different models of speakers and amps and CD players and streamers and the mighty list of technical terms they come with. Hopefully we can help bust some of that jargon here. Are we missing a word or term you’d like to know the meaning of? Leave us a comment below.

Three pairs of output transistors per channel bode well for long term reliability

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What Are MM and MC Phono Cartridges?

ortofon-2m-black-moving-magnet-cartridge-[3]-1829-p

A Moving Magnet phono cartridge is comprised of a tiny magnet, located at the end of the cantilever of the stylus that sits between two coils. One coil caters to the left aspect of the music, while the other is for the right – this allows for the stereo sound. This magnet vibrates between the two coils and induces a small electrical current within them in the process. Because the magnet is so small, it needs less tracking/downward force to correctly manoeuvre between the grooves of a vinyl record. A Moving Iron cartridge makes use of essentially the same construction, but swaps the magnet for a tiny piece of iron or other light-weight and ferrous alloy. The iron is lighter and so reduces the necessary tracking force even further.

Moving Magnet is the most common type of phono cartridge, so many integrated amplifiers now feature a Moving Magnet phono stage and many manufacturers, such as Rega and Ortofon design and construct a wide range of MM cartridges with varying levels of quality. While every MM cartridge makes use of this fundamental construction, the way that this is implemented within a cartridge varies as do the materials used, allowing for differing qualities and a unique sound-signature depending on the brand and model.

Moving Magnet Cartridge Design

Moving Magnet Cartridge design. The Magnet sits between two coils at the end of the cantilever.

Moving Coil cartridges feature an inverted version of the Moving Magnet design. Instead of a magnet sitting on the end of the cantilever between two coils, the coils are attached the cantilever and a magnet is placed near them. Because space within the cartridge at this level is extremely limited, the coils are made from an exceptionally fine wire.

The coils tiny size results in a very low output. While Moving Magnet cartridges tend to offer a more relaxed, warmer sound, Moving Coils are known for offering a better level of detail and a wider stereofield than the Moving Magnet alternatives. Moving Coil Cartridges will often require an external phono-stage specific to their construction.

Moving Coil Cart

Moving Coil Cartridge design. Inverted to MM design, the coil is this time on the cantilever with a magnet located close-by.

 

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Alchemist Forseti APD15A RC Integrated amplifier

We recently had a customer present this faulty Alchemist Forseti integrated amp for repair – I’d guess this dates from the 1990’s and has been well looked after. It’s a bit of a bruiser as you can see from the extensive heatsinking!

 

Alcemist Forseti integrated amplifier

Alcemist Forseti integrated amplifier

Unfortunately it developed a DC fault on the loudspeaker outputs and destroyed the customers speakers, so it’s now in the naughty corner awaiting surgery.

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Repair of Arcam CD73 laser mechanism

This 2004 vintage Arcam CD73 came into us with the reported fault that it would no longer play CD’s, or even read the table of contents. Given that it is over eight years old and had plenty of use in that time, we were not surprised to find that the laser had expired and needed replacing.

Arcam CD73 CD player from 2004

Arcam CD73 CD player from 2004

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Marantz CD63SE laser transport mechanism replacement

An elderly, but still sought after Marantz CD63SE was bought into the shop last week, with the fault reported that CD’s would no longer play. After approximately 15 years of use, this is a common situation, as the laser power will gradually reduce over time to the point where it can no longer focus reliably on the spinning CD disc – however with the easy availability of VAM1202 CD mechanisms for below £20, repair is a viable option over and above the purchase of a new CD player.

A 15 year old Marantz CD63SE with failed laser mechanism

A 15 year old Marantz CD63SE with failed laser mechanism

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How to set up your B&W Zeppelin Air

B&W Zeppelin Air setup

B&W Zeppelin Air setup – you will need access to the rear panel

With the B&W Zeppelin Air being such a popular iPod docking station as well as a fantastic AirPlay compatible device we thought it would be a good idea to write a ‘how to’ on setting up your new Zeppelin Air. Continue reading

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NAD C355BEE with faulty driver and output stage

nad amp

Dead output transistors lurk within!

A NAD C355BEE integrated amplifier came into us for repair last week, with the customer reporting that the amp would remain in standby at all times – this is a common fault when the output stages have been destroyed, usually by short circuit load or high volume use for prolonged period (thermal runnaway).

repaired nad amp

Happily ready to play music again!

Having got hold of the circuit diagram, it was easy to diagnose the problem armed with just a continuity tester – the PNP output transistor on the right channel was short circuit from collector to emitter, which had then blown the DC power supply fuses. His caused the output voltage of that channel to be stuck hard against the negative power supply rail. The TO126 package transistors mounted on the smaller black heatsinks are driver stage transistors, and checking these, the one that drives the failed output device was also short circuit. Removing this transistor was tricky, as NAD mount 3 transistors back to back on this one heatsink – presumably for good thermal tracking and stability, or maybe also for ease of manufacture.
With the two faulty transistors replaced, and after carefully checking the circuit board for any solder bridges where the repairs had been needed, it was time for testing! Rather than power up via the NAD’s own power supply (which carries the risk of uncontrolled current flow if something is still amiss), the amp was powered using a current limited, adjustable voltage regulated power supply, gradually ramping from 0 volts up to about plus/ minus 30V. The output voltage of the repaired channel now sat at 100mV, which is absolutely normal. The amp was then re-biassed and soak tested for 24 hours.

Here is the NAD C355BEE schematic and service manual.

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