BrianGT, first timer w/ radio (accidentally) - Page 2 - diyAudio
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Old 13th December 2004, 08:31 PM   #11
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Thanks, I'm about to go hunt down a 220pF ceramic cap, is there anything else than can help improve SQ/ get rid of static or hum?

How can I speed up the burn in process, its been about 15hrs burn in and it doesn't sound better than my dad's 7 year old Sony reciever or my Denon.
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Old 13th December 2004, 11:28 PM   #12
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Well I talked to Brian and he gave me some more good advise, then I had a friend over to do some history work with. He turned down the volume when his phone was ringing, and had the phone in the same hand that he turned the volume down with and I heard mayjor interference! I took off my B&W speakers from the amp and connected raw drivers that I first tested the amp with, and moved the pol downwards and towards the toroid and rectifier, to see what it would be like if my volume knob was not floating, and hisssss in the left speaker, sizzle, and pop! left speaker blown, guessing DC power was going to it, then 1 minute later the same happened to the right speaker, then I was about to test DC voltage from the speaker terminals when POP went a cap when my face was less than a foot away.

I'm working on a project right now so I cant inspect the problem yet but it looks like I just ruined the panasonic cap and nothing else.

Unfortunately the smell of 2 burnt voice coils and the smell of a blown cap do not smell good at all and I have to use the computer to do the project for history.

Was I getting DC voltages going to the speakers?
Why would moving the pot make the speakers have DC?
Do you think everything on that board is ruined or just the cap?

Thanks,

please help,

Josh
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Old 14th December 2004, 01:13 AM   #13
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Can someone give me some advise please?
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Old 14th December 2004, 04:03 AM   #14
kneadle is offline kneadle  United States
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Bump.

I'm following. Have no advice. Here's hoping you get an answer.

Dave
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Old 14th December 2004, 08:25 AM   #15
Nuuk is offline Nuuk  United Kingdom
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I'm not sure that I can follow what you are saying.

When you say 'moved the pot', do you mean physically moved it or adjusted the volume?

What do you mean by 'floating pot'?

My advice is to start from scratch. Take everything out of the case and assemble it on a piece of wood. Start by measuring the AC voltages from the transformer., then connect the bridge and measure the DC rails.

If they are correct, replace the blown cap and connect power to the amp. Measure the DC offset and report back here.

BTW - you had a cheap lesson with that cap! A pair of safety glasses may be a very cheap investment!
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Old 14th December 2004, 12:55 PM   #16
kneadle is offline kneadle  United States
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Quote:
Originally posted by Nuuk
BTW - you had a cheap lesson with that cap! A pair of safety glasses may be a very cheap investment!
Some prominent contributors here (Peter Daniel?) have some horror stories to tell and old war wounds to show, like permanently damaged eyes.

Dave
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Old 14th December 2004, 09:31 PM   #17
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I physically pushed the pot itself down into my case, as you can see in my pictures it was either on a peice of wood or it was held up by the wires about 3 inches above voltage lines.

I had my amp working properly for more than 24 hours, I checked Dc and Ac voltages (It was like 26.9 and 38).

I live in Atlanta and BrianGT offered to rebuild it with me. I have come to the conclusion that maybe when forcing the pot down, wires touched or something or maybe an arc. This was a test box to make sure everything was working alright but Brian helped me come to the conclusion that my design was pretty good but could be better.

Nuuk I've read your site many times and it has been very helpful, are there any suggestions you have that can help me for the next build and the next design?

I'm very open to anny suggestions and especially ones to help increase SQ with Brian's basic kit.


About the safty glasses, I use them when working on my table saw, but at the time that this happened I was doing homework I just pushed the pot down thinking about what it might sound like if it were in it's "to be" location but I am very glad I had the amps facing eachother because I'm sure that burns really bad!

Thanks,

Josh
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Old 14th December 2004, 09:36 PM   #18
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Another place to check for DC voltage is at the speaker outputs. If you have an excess of DC offset (more than 100mv), there may be something wrong somewhere else.

It's a bit of fortune that you live next door to the designer of the product, isnt' it?

Dave
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Old 14th December 2004, 09:45 PM   #19
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I was going down to check the DC voltage of the speaker outs when it blew, (I keep my multimeter handy )

About an hour away but yea I would say its pretty nice, and he has been more than helpful. He probably gets a little annoyed but I'm able to call him and ask him questions (ones that I might be ashamed to ask on here) But he hasn't seemed to mind too much so far.

Unfortunately I dont know anyone else that knows enough about electronics to even think about being able to answer my questions. And I havent't taken Physics yet, thats next year.
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Old 15th December 2004, 07:53 AM   #20
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Josh, I haven't actually completed a Brian GT kit yet but I would guess the usual advice holds true for any GC.

Check that you have made the best possible solder joints.
Keep all wiring as short as possible.
Pay attention to your grounding arrangement.

It seems that you didn't do a bad job of building your GC and that your problems were mainly due to moving that pot. So I hope you will remember to power down before making any such 'adjustments' in the future!
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