Repair job bounce

Phil Allison · 2019-11-08T01:34:25+00:00

Hi to all my loyal followers, ----------------------------- The term "bounce" is applied when an item that has been recently repaired is brought back for a similar or repeat failure. Mostly it's a false alarm, a new problem or just once in a while the same failure involving the new parts. This is the worst scenario and for me very rare. One that comes to mind was a MusicMan hybrid guitar amp - the RD50. The circuit is all solid state except for a pair of 6L6GC tubes for output. One came to me with the input op-amp ( IC1) having it's output stuck to a DC rail. Fitted a new TL072 and away it went, good as new. Unusual failure, but shit happens sometimes. It was back in a week with the new IC blown, just like before. Another TL072 fixed it again, but I smelt a big fat rat. Since the op-amp interfaced with the external world of musicians and their assorted paraphernalia - it must had failed due to abuse, twice. But what exactly ? To stop the nonsense, I fitted 1N4148 diodes from pin 3 to each rail as a precaution. Walter C. Jung's "IC Op-Amp Cookbook " gave support for fact that such inputs were vulnerable. The customer was not happy, he insisted on speaking with me and was very aggressive. I had understood he was a school teacher but it turned out he was in fact a *Taekwando* instructor !! He expected the new repair to be covered by warranty, but I was not budging. He insisted that guitar amps were built very tough to take all sorts of abuse. I assured him he was mistaken: "I make my living because that's not true" - I stated firmly. After extracting a few details from him, it all became clear. Any guess what seemingly innocent act he had performed done, twice ? -------------------- Question 2: The same amp has a shameful design problem with the output stage. Wilful stupidity. Bet nobody gets it. .... Phil

Repair job bounce

Nov 08, 2019 43 Replies

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bitrex 6 years ago

Generally by playing stairway to heaven as the test case

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bitrex 6 years ago

the first few bars of Stairway are acoustic, Van Halen's "Ain't Talkin' 'Bout Love" are more appropriate if you're going to play the first few bars of something

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bitrex 6 years ago

Van Halen 1 is a weird album it's like whomever mixed it decided that the guitar should live mostly in the left channel, and the reverb on the guitar should live in the right channel and that's just how it is

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Phil Allison 6 years ago

-------------------------------------

** There are no guitar cables on that list.

Guitarist buy ready made, 5m &r 7m leads in packets from retail stores. Most of them from China. Not 100m reels of expensive cable that exists only on maker's web pages.

You tedious wog wanker.

.... Phil

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