# motorboat sound on idle



## markxander (Oct 24, 2009)

My old Carmen Ghia has developed a thrumming kind of motorboat sound as soon as you power it on -- it still works as it should, but the sound is always there. 

I've also noticed over the last few months that the amp has taken longer and longer to warm up when I turn it on. Not sure if it's related or not. The amp is over 30 years old.

I haven't done any amp maintenance myself so I'll likely find a tech to do it (although I don't really like the well known one that lives near me), but does anyone have any recommendations on what it could be and if it's something I could tackle myself?

I'm comfortable soldering and using a multimeter but I don't have any relevant experience here.


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## greco (Jul 15, 2007)

FYI..
*Derek Lawrence* is doing the amp repair locally for Sherwood Music
Tel: 519-745-6154
He also owns "Anodyne Audio Service" in Cambridge
Tel: 519-239-8880
anodyne audio service amplifier repair


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## Wardo (Feb 5, 2010)

I was thinking vacuum leak; until I got to the second paragraph…lol


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## jb welder (Sep 14, 2010)

Wardo said:


> I was thinking vacuum leak; until I got to the second paragraph…lol


That's where I was going too. The Karmann Ghia had the pancake 4 banger same as the other VW's didn't it? 

Motorboating in amplifiers can sometimes be caused by loss of filtering in the power supply (filter caps).


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## laristotle (Aug 29, 2019)




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## Latole (Aug 11, 2020)

jb welder said:


> Motorboating in amplifiers can sometimes be caused by loss of filtering in the power supply (filter caps).



Right !


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## Verne (Dec 29, 2018)

Wardo said:


> I was thinking vacuum leak; until I got to the second paragraph…lol


Ditto. Carmen Ghia. Cool car..............wait, an amp?!? I'm out. HAHAHA


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## Verne (Dec 29, 2018)

jb welder said:


> That's where I was going too. The Karmann Ghia had the pancake 4 banger same as the other VW's didn't it?


Carmen Ghia is basically a flat Beetle. That whole range. Squareback, Notchback and the hatchback style. /hijack


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## Verne (Dec 29, 2018)

Motorboating............is that like a surging? Like fluctuating power?


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## Paul Running (Apr 12, 2020)

Hoping you have balls of steel, here you go:








Main filter caps and decoupling caps is the number one failure mode for squegging (the technical term for motorboating).


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## markxander (Oct 24, 2009)

Here's a video if anyone is interested: New video by Mark Carter

It comes on right away when the amp warms up and isn't related to the volume in any way, so I kind of guessed power supply -- filter caps are part of that zone right?

I'm going to just be a grown up and bring it to a tech. I've had 13+ years of worry-free operation with this great amp, and it deserves a spa day more than it deserves a 250 pound chimp poking it with a pencil and a knife.


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## Paul Running (Apr 12, 2020)

markxander said:


> Here's a video if anyone is interested: New video by Mark Carter
> 
> It comes on right away when the amp warms up and isn't related to the volume in any way, so I kind of guessed power supply -- filter caps are part of that zone right?
> 
> I'm going to just be a grown up and bring it to a tech. I've had 13+ years of worry-free operation with this great amp, and it deserves a spa day more than it deserves a 250 pound chimp poking it with a pencil and a knife.


I believe that your guess is correct; yeah, if you do not feel comfortable poking around then, it would be wise to have a pro look at it...doesn't hurt to eye-ball the caps though, sometimes they will reveal a physical anomaly such as a bulge in the can or oozing electrolyte.


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## tomee2 (Feb 27, 2017)

...


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