C-19 preamp "MICROPHONICS"

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lives country ( carver )
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C-19 preamp "MICROPHONICS"

Post by lives country ( carver ) » Sat Aug 30, 2008 8:51 pm

anyone experience this problem?

.....the c-19 powers up and plays fine, after 10 to 20 minutes (sometimes varries) of playing the preamp becomes "very microphonic"....it looses the lower mid, and bottom frequency band, and the amp is definetly microphonic in sound output, and if you touch, or gently tap, the case or even the rack system it's compares to tapping a dynamic microphone. ???

anyone have this experience...could it be as simple as any of the front control pots or switches, needing cleaning....tubes check fine and have tried other brands of 6dj8's.....no change...never did locate the service manual for the C-19, any help here, maybe the schematics would be a start, will request in manuals section as well.....thanks everyone!

david
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BillD
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Re: C-19 preamp "MICROPHONICS"

Post by BillD » Sat Aug 30, 2008 9:53 pm

Well, I was going to suggest the tubes, as they do become microphonic. So do capacitors, so you might want to check them. With the lid off, I'd go gently tapping things with something non-conductive.
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tfm75
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Re: C-19 preamp "MICROPHONICS"

Post by tfm75 » Sat Aug 30, 2008 9:57 pm

David check you in box O:)
Between FrankieD and I we have logged in over 12,000 miles going and coming from Carverfest's. Don't let the miles in between play with your mind. Get over it, jump on a plane get to the fest and have a great time !

lives country ( carver )
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Re: C-19 preamp "MICROPHONICS"

Post by lives country ( carver ) » Sat Aug 30, 2008 10:21 pm

thank you Tim,....mega much....
I received it and sent u a pm as well....

david
country's...pure sole...

lives country ( carver )
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Re: C-19 preamp "MICROPHONICS"

Post by lives country ( carver ) » Sat Aug 30, 2008 10:29 pm

hi BillD

thank you for suggestions, I will do some probing, carefully, and any other member suggestions are welcome, I just received the schematics from TFM 75, and though I'm no tech, I can read somewhat schematics, will see what occurs and will keep you and the forum posted, this is an interesting one eh! Would like to hear Rich's thoughts...

david
country's...pure sole...

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snarffydoggy
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Re: C-19 preamp "MICROPHONICS"

Post by snarffydoggy » Sun Aug 31, 2008 7:25 am

Good luck lives country, keep us posted..
snarffydoggy

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Re: C-19 preamp "MICROPHONICS"

Post by RichP714 » Sun Aug 31, 2008 9:48 am

lives country ( carver ) wrote:anyone experience this problem?

.....the c-19 powers up and plays fine, after 10 to 20 minutes (sometimes varries) of playing the preamp becomes "very microphonic"....it looses the lower mid, and bottom frequency band, and the amp is definetly microphonic in sound output, and if you touch, or gently tap, the case or even the rack system it's compares to tapping a dynamic microphone. ???

anyone have this experience...could it be as simple as any of the front control pots or switches, needing cleaning....tubes check fine and have tried other brands of 6dj8's.....no change...never did locate the service manual for the C-19, any help here, maybe the schematics would be a start, will request in manuals section as well.....thanks everyone!

david
The usualy suspects, tubes and caps, have already been mentioned, but I'm wondering, from what you said in red, are you using the technical or colloquial term?

Technically, a tube subject to vibration will experience fluctuating distance between the elements, which will produce a fluctuating current flow, or noise added to the signal; changing vibration to voltage. This can happen with tubes, caps, sometimes coils

Colloquially, the vibrations are actually transduced into an audible sound that can be heard when playing at high power into dummy loads, for example. Same likely culprits, but at higher frequencies can even be poor solder joints (especially solder joints with sharp points in flyback sections of TV's; makes that high pitched squeal)

If you've got BOTH kinds of gremlin, and the audible aspect is as sensitive as touching the rack the unit is mounted on, it almost HAS to be approaching a feedback condition, and is likely the tubes or the socket's they're mounted in. Anyone use Cramolin on tube sockets to reduce this?

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