This amp came in for repair after the client stated his girlfriend had been connecting up the speakers and had managed to short the speaker cables. There’s at least a couple of morals in that tale, the most important being ‘switch off ‘ before you connect or disconnect speakers-and inputs in fact as the resulting transient can easily damage speakers too.
Despite sophisticated protection circuitry the amplifier had blown its output transistors. Once replaced the amplifier is singing away sweetly again.
Another Yaqin 13s on the workbench for the usual upgrades: upgraded coupling capacitors, upgraded grid stopper resistors and fitting of cathode bypass capacitors. These mods worked their usual charms and gave a very decent performance, even with the stock tubes. This time tho, I tried the amp with negative feedback removed. The difference was dramatic, and so a small switch was installed on a plate to replace the mains voltage switch which was re-mounted inside the chassis. In my set up, I never switched the feedback back on and both myself and my regular ‘golden-eared’ mates considered it way better. Here’s what the owner had to say:
‘Just collected my MC13S following David’s mods and I’m stunned! In addition to the mods described above David also fitted a feedback bypass switch and with the negative feedback switched off the resolution of this amp is incredible. I keep wanting to try another track to test the improvements but find myself having to hear the whole track before switching, which is not something that usually happens when I buy new kit. All in all I’m very pleased with these mods….’
I’m constantly amazed by the results of upgrading Yaqin amps of which I’ve now completed quite a few. I remember my nervousness upgrading the first one as the received wisdom was ‘Chinese transformers are no good’. Yaqin’s transformers are made in house and they claim, are made of Japanese steel.Whatever the ingredients the result is an amplifier that sounds very decent as standard but which can easily be improved with some simple upgrades.
Circuit wise the amp is a fairly standard ultra linear output stage with input and phase splitter. The upgrades this time were to add improved Mundorf coupling caps, to change the grid stopper resistors on the output valves and to add Elna Silmic bypass capacitors to the output valves.
Once installed the amplifier performs at a new level. The light graininess of the sound disappears, vocals become more breathy, and bass and dynamics improve. All these improvements were heard with the stock Chinese valves and of course these too can be swapped for improved Western designs or NOS types.
The Onix Melody is an Australian design made in China and runs 6L6 valves or equivalents. It had a pretty decent sound for the money when released in early 2000 and one of its main claims to fame was the use of a stepped attenuator.
Another feature is its use of Russian military paper in oil capacitors (in the green cans in the picture above). These are not bad in terms of sound quality, but can be bettered with a decent audio grade capacitor. So, after discussion with the owner, we agreed we would upgrade the cathode bypass capacitors with Elna Silmics and the coupling capacitors with Musicaps. I also installed an earth lift system to stop the amplifier interacting with other equipment.
Overall the result was a very decent uplift in performance.
This iconic little amp came in to the workshop for some TLC. Not much wrong really. A blown internal fuse but bias and every other parameter measured fine. So once checked and the fuse replaced the amp works fine and sounds good. There is a noticeable thump on switch on, which is typical for an amp of this age as capacitors and transistors age. A recap and change of transistor would cure this but for an amplifier of this age, I often simply install a slow start module as a cheaper fix for switch on thump. It really depends on how much the owner likes the amp and wants to invest in its future.
These two Canary CA303 mono blocks came in for re-biasing and an open-ended ‘could I do anything in terms of upgrades?’. Like a lot of high end American gear, the componentry is top notch, so there’s no easy wins in terms of upgrading capacitors, resistors, or rectifiers for example. But what I did do was to install a switch for the negative feedback. With feedback switched off, with my speakers, these amps really hit their stride, open up and become seriously dynamic performers.
Those with keen eyesight will notice an Audio Innovations 700, and an LFD integrated solid state amp, both of early 90s vintage I believe.
This LFD integrated amplifier came to the workshop for some TLC. This little amplifier is now 26 years old. A capacitor had spilled its guts inside, and the input selector switch and source/mute/monitor switch were very noisy. The input selector switch stopped being noisy after being stripped and cleaned, and the monitor/source/mute switch was taken out of circuit.
Following that work the amplifier is now sounding great again, and ready for a new lease of life.