Sunday, January 19, 2014

Sony TA-88 Mini Component Stereo Amplifier

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Somewhere, in the beginning of the genesis of HiFi, under mini component systems, you would find the Sony TA-88. Along with its complimentary ST-88 AM/FM Tuner, SQA-100 Surround Adapter and a pair of SS-5088 bookshelf speakers. This wonderful set is the forerunner of future of mini component systems. The TA-88's power output is rated at 13 watts per channel, so this is no room shaker but its not meant to be. With its small footprint you can have it practically anywhere and where ever you put it, it's going to look good!

The TA-88 paired with its ST-88 and SQA-100 counterparts:
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These petite units each measure 13cm across, 23cm high and 16cm deep. This particular TA-88 has been in my collection for quite some time, over the past year I had managed to acquire the matching components as well as another TA-88 with a blown power supply- a move that has proven to be quite useful as described later on.

In its original condition.
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Covers off and exposed!
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Although small in size, the layout is well thought out. The power transformer is located at the bottom of the unit, it is shielded by the heatsink, which forms an upside down 'L' shape. On the left hand side, you have a single PCB which the bottom half contains the power circuit, including bridge rectifier and filter capacitors, the top half is the power amplifier board. Eight wires go across the unit to the right side, where the pre-amplifier section is located, shielded also by the heatsink and a lattice metal cover from outside interference.

Power supply board and power amplifier section. Can be easily taken out without the need to cut into any cabling for maintenance.
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Heatsink shown aswell as preamplifier board towards the rear. The interconnecting signal wires are easily taken off the mounting pins of the power amplifier board. The 45 years of dust is a bonus!
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As always, all capacitors were replaced with Panasonic capacitors. The original thermal paste was also removed and new paste applied, the original mica film which stops conductivity from the output transistors to the heatsink were cleaned rather than replaced to maintain some originality.

Power amplifier board before:
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After cleanup:
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Original Mica film cleaned:
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Heatsink cleaned and prepared for re-assembly:
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Power amplifier board re-installed into the unit:
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Now onto the underlying issue, I bought this unit faulty, the left output didn't work. My first assumption was that the speaker fuses had blown. But they had not. Next was that the output transistors had blown, a common occurrence if you accidentally short the speaker terminals which was common with the design, but this was not the issue either. Next up, capacitor replacement, and although the unit did sound significantly better the left channel was still dead. Through the convenient design of the unit, I switched the preamp outputs around going to the power amplifier, which could definitively prove that the issue was occurring from the pre-amp side.

The preamp board looked good too, no bad transistors, some were a bit leaky but still working. Those two were replaced with modern day counterparts. So it must not be on the board! But where is it!?

The culprit:
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It was actually a crack in the left volume slider! If you click on the above image you can see a larger image and the crack on the left hand side, just before the the terminals. Now the problem we have is, that this is a 45 year old slider, with no markings, identification or standardisation at the time. Which means I needed to work out, what the resistance range was, if it was a logarithmic or linear resistance scale, measurements and to fit it in the case.... or...

The the "Part out" spare amplifier! Ironically, the more complete looking unit in the below picture!
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I don't like using a second unit to scavenge parts from, I'd rather save both. But there are times when its just too far gone. Among its issues of causing small fires when powered on, this parts unit had the wrong selector knob, no power transformer, no voltage junction block, almost every transistor was replaced.. with the wrong ones.. and missing mounting brackets.

However with a quick switch of the sliders, we were back in business! In the end there were not that many parts replaced, but there was a fair bit of work cleaning it up and bringing it back up to scratch.

Only a few parts, but that's all it takes to make a huge sound difference:

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After all that work, its sound is pretty good! Nice and clear, its best setting is neutral. As mentioned earlier, this is only a small unit and at 13 watts you would want to pair it with a nice set of small efficient speakers. An amplifier suited more for a study than a larger listening room, or as a dedicated headphone amplifier it is a pleasure to listen to.

Some modeling pictures to wrap this up, the wood case was also given some TLC with orange oil to bring it back to life.

As always, you can click on all the images for a larger view, and be sure to have a look at my other writeups! Enjoy!



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3 comments:

  1. My TA88 is currently in use by my daughter at Uni, it has been in almost continuous use since I bought it new for £75 in 1975, couple of fuses replaced but no repairs - the black round the switches is marked. I think 45 years is a bit too long; I think it was the latest thing in '76. It may only be 13 watts (advertised as 10w rms in '75) but it still managed to destroy a pair of 20w speakers when it was turned up full at a student party.

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