Radio Road Which tuner to get and getting the most from it. Thank God, for the radio!

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Re: Binggggg! bonggggg! That's how tantalum capacitors go, when you GIVE them a flick,.....

Posted by Dave Kingsland on January 4, 2007 at 21:41:13

In Reply to: Binggggg! bonggggg! That's how tantalum capacitors go, when you GIVE them a flick,..... posted by Timbo in Oz on January 2, 2007 at 23:49:56:

George is our resident Accuphase evangelist, but he doesn't know the T-101. I've given the MPX/audio board a good look over and I'm impressed when it comes to design by not so impressed when it comes to parts quality.

From a circuit design POV, things look really good, especially considering when it was designed. De-MPX is handled in an IC, but after that I think the output stages are all discrete. There are low pass filters in little boxes following the de-emphasis stage which I haven't opened, but everything else is discrete. De-emphasis appears to be a simple passive RC, which is nice. There is a Euro/US de-emphasis switch, but at least it's used to switch different caps to ground. Muting is via relay shunting the output to ground, so it's out of the circuit path. The audio board is grounded on the perimeter and the whole thing is shielded.

But when it comes to details like parts selection, the T-101 is a bit dated. For example, there are no less than 5 tantalum caps in the audio path for each channel. Most or all of them are +/- 20%. Resistor tolerances aren't great either. The signal path is also excessively long, thanks to locating the audio board on the opposite side from the IF board, and the output RCA jacks over on the opposite side again.

It seems that parts replacement alone could improve audio quality a noticeable degree, and the size & layout of the audio board makes it really easy to work on.

But -

I'm going to hold off on any mods until I can figure out the source of the noise problem we discussed below. I haven't had much time to investigate, but a few follow-up experiments confirmed that the source of the noise is external and directional. It also varies by day and time of day. And it's definitely strongest towards the low end of the FM band. I think the first task should be confirming that the antenna pattern is what I expect and/or confirming that all elements are connected properly.

Dave

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