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January 26, 2012

Most Repairs are Easy – Fixing an Old Hitachi Receiver

Filed under: repair,Uncategorized — Tags: , , , , — admin @ 1:34 pm

As you can see throughout this blog, I do a lot of repairs of durable goods ranging from cars to electronics. I’m writing a book on closely related topics now (stay tuned here for publication news). One of my contentions is that most repairs are quite easily accomplished with only a small set of tools and rudimentary expertise. In addition, often, the source of the problem can be found by simple visual inspection. Here is one such example.

The Failed Switch

The Failed Switch

I had in my electronic “junk pile” an old Hitachi SR-5150 stereo receiver that a neighbour had discarded in the fertile back lanes of Vancouver, BC. The SR-5150 is roughly early 1970′s vintage; it is all solid state and has all discrete transistors (the power transistors are even Hitachi’s own), and an analog FM tuner driven mechanically with pulleys and a flywheel. Nothing high end, maybe 20-30W per channel judging from the power supply. The receiver was dead to the world; it would not show any signs of life when turned on. I was motivated to fix the thing because I was looking for a decent amp to use as part of a new sound system centred on a home computer. (more…)

July 12, 2011

Reducing audio frequency electrical noise in a PC sound system

Kinter Amplifier in PC Case

Kinter Amplifier in PC Case

I recently built a new PC that I use for multimedia and other purposes. It’s Intel “Sandybridge” 1155 -based, with a Gigabyte P67 series motherboard and Realtek onboard sound. Unfortunately, like so many other recent PC audio systems, it doesn’t have sufficient output power to drive unamplified speakers directly. I have some unpowerd bookshelf speakers that I wanted to keep using. So, I added a cheap audio power amplifier to the Realtek output. The resultant system had slightly annoying audio frequency noise, not 60Hz noise but various other noise from misc. stuff in the PC.  Here are some details re the amp and what I did to fix the noise problem.

The audio amplifier is one I found on eBay from a Chinese manufacturer, with labeling “Kinter 500W”.  Price was about $10 including shipping, cheaper than I could build one for myself. I knew what was in the amp from some googling: an LM-series audio amp IC and typical supporting parts, providing a few watts per channel. Not the claimed 500W :-) , but adequate for what I wanted. I run the amp from the PC 12V supply, which is far enough beyond spec for the other stuff in the PC that it’s fine to power the amp with it too. I started with a generic 1/8″ stereo to RCA patch cord about 3ft. long to connect the amp to the PC audio output. (more…)

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