'Underwater' sound from valved amp. - UK Vintage Radio Repair and Restoration Discussion Forum

musonick · 1st Dec 2011, 2:18 pm

Very quick question. Am I correct in thinking that an 'underwater' ripple sound on a valve amp is likely to be caused bad electrolytic smoothing caps?

Thanks,
Nick.

Station X · 1st Dec 2011, 4:00 pm

I wouldn't think so. Bad smoothing capacitors give rise to a loud low pitched hum, which is unmistakable.

You problem is more likely down to leaky paper dielectric capacitors, dirty switch contacts, dirty valve pins or dirty potentiometer tracks.

Michael Maurice · 1st Dec 2011, 9:34 pm

Sounds like motorboating or instability.

ms660 · 1st Dec 2011, 9:43 pm

He could be trying to describe hum....induced before the volume control and modulating the signal. Maybe the poster can be a little more specific of the symptons.

Lawrence

Station X · 1st Dec 2011, 10:31 pm

"Under water ripple sound" could be many things, but I don't think hum is one of them.

maninashed · 1st Dec 2011, 10:37 pm

Not quite sure what underwater sound means, but it may be that one of the pre-amp valves has gone microphonic causing hollow sound. More information would help.
Bill

ms660 · 1st Dec 2011, 10:50 pm

Quote:

Originally Posted by Station X

"Under water ripple sound" could be many things, but I don't think hum is one of them.

It might or might not be in this case but a hum modulated signal can sound remarkably like someone having a gargle underwater in many instances...hum modulation in a Freq Changer/Mixer for instance or a signal level dropping to a level which is approaching the level of any residual hum in a circuit. Like I said in my previous post, more information from the poster might give us a better idea.

Lawrence.

musonick · 2nd Dec 2011, 12:27 am

hi, the signal modulates. there is no hum

Station X · 2nd Dec 2011, 1:30 am

What is being modulated by what?

Amraduk · 2nd Dec 2011, 2:51 am

Hello Nick,

Quote:

Originally Posted by musonick

Very quick question. Am I correct in thinking that an 'underwater' ripple sound on a valve amp is likely to be caused bad electrolytic smoothing caps?

Can you make a short recording of the effect and post it on the forum as an MP3 file?

Regards,

Dave.

musonick · 2nd Dec 2011, 5:36 am

Hi, it's probably too subtle to do a recording but it's 'there'. It's the actual audio signal fluctuating.

mrmagnetophon · 2nd Dec 2011, 5:43 am

Push pull amp? Give me technical aspects, and i'll attempt to give you the things causing the problem/
-Chris

crackle · 2nd Dec 2011, 7:55 am

It would be useful to know the make and model, it's not an Ashdown by any chance?

Andy Doz · 2nd Dec 2011, 9:47 am

Motorboating?

SeanStevens · 2nd Dec 2011, 11:47 am

Is this valve amp a guitar amp or audio amp?

If it is a guitar amp it might have a tremelo (effect)

SEAN

PJL · 2nd Dec 2011, 3:25 pm

Maybe it's because you are up at 4:36AM?

I would stop using it as it could be signs of a fault that could cause damage. Let's have a model number and pics.

ITAM805 · 2nd Dec 2011, 8:17 pm

Does it sound like this?

musonick · 2nd Dec 2011, 10:53 pm

Cheers Mick

jokes aside, it does sound a bit like that but not as exagerated.

Amp details here P.30
http://thearcadeboneyard.com/Jukebox...0Combined).pdf

Moderator's note. Warning - if you have a slow internet connection you might want to be aware that this file is 28M and will take forever to load.

PJL · 3rd Dec 2011, 12:22 am

Has the amp been restored recently? If not I would want to give it a full health check:
- Test output valve grids are 0V (leaky audio coupling capacitors)
- Check individual anode currents as it uses shared cathode bias arrangement
- Check voltages against schematic

As it's stereo, the obvious question is does it do the same on both channels? are the noises present when there is no input or is it just distortion of the sound? does the amount of distortion change with increased volume?

musonick · 3rd Dec 2011, 7:44 pm

hi, yes the sound is on both channels and it is only apparent with audio input. i have ordered a cap kit and will do the necessaries.

thanks, nick

1st Dec 2011, 2:18 pm	#1
musonick Retired Dormant Member Join Date: Feb 2011 Location: Sudbury Hill, Middlesex, UK. Posts: 200	'Underwater' sound from valved amp. Very quick question. Am I correct in thinking that an 'underwater' ripple sound on a valve amp is likely to be caused bad electrolytic smoothing caps? Thanks, Nick.

1st Dec 2011, 4:00 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: 'underwater' sound I wouldn't think so. Bad smoothing capacitors give rise to a loud low pitched hum, which is unmistakable. You problem is more likely down to leaky paper dielectric capacitors, dirty switch contacts, dirty valve pins or dirty potentiometer tracks. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

1st Dec 2011, 9:34 pm	#3
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: 'Underwater' sound from valved amp. Sounds like motorboating or instability.

1st Dec 2011, 9:43 pm	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: 'Underwater' sound from valved amp. He could be trying to describe hum....induced before the volume control and modulating the signal. Maybe the poster can be a little more specific of the symptons. Lawrence

1st Dec 2011, 10:31 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: 'Underwater' sound from valved amp. "Under water ripple sound" could be many things, but I don't think hum is one of them. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

1st Dec 2011, 10:37 pm	#6
maninashed Rest in Peace Join Date: May 2011 Location: Preston, Lancashire UK Posts: 955	Re: 'Underwater' sound from valved amp. Not quite sure what underwater sound means, but it may be that one of the pre-amp valves has gone microphonic causing hollow sound. More information would help. Bill

2nd Dec 2011, 12:27 am	#8
musonick Retired Dormant Member Join Date: Feb 2011 Location: Sudbury Hill, Middlesex, UK. Posts: 200	Re: 'Underwater' sound from valved amp. hi, the signal modulates. there is no hum

2nd Dec 2011, 1:30 am	#9
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: 'Underwater' sound from valved amp. What is being modulated by what? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

2nd Dec 2011, 5:36 am	#11
musonick Retired Dormant Member Join Date: Feb 2011 Location: Sudbury Hill, Middlesex, UK. Posts: 200	Re: 'Underwater' sound from valved amp. Hi, it's probably too subtle to do a recording but it's 'there'. It's the actual audio signal fluctuating.

2nd Dec 2011, 5:43 am	#12
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: 'Underwater' sound from valved amp. Push pull amp? Give me technical aspects, and i'll attempt to give you the things causing the problem/ -Chris

2nd Dec 2011, 7:55 am	#13
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: 'Underwater' sound from valved amp. It would be useful to know the make and model, it's not an Ashdown by any chance?

2nd Dec 2011, 9:47 am	#14
Andy Doz Hexode Join Date: Feb 2011 Location: Gloucestershire, UK. Posts: 376	Re: 'Underwater' sound from valved amp. Motorboating?

2nd Dec 2011, 11:47 am	#15
SeanStevens Octode Join Date: Sep 2009 Location: Bath, Somerset, UK. Posts: 1,033	Re: 'Underwater' sound from valved amp. Is this valve amp a guitar amp or audio amp? If it is a guitar amp it might have a tremelo (effect) SEAN __________________ There are only 10 types of people, those who understand the binary system, and those who don't.

2nd Dec 2011, 3:25 pm	#16
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 'Underwater' sound from valved amp. Maybe it's because you are up at 4:36AM? I would stop using it as it could be signs of a fault that could cause damage. Let's have a model number and pics.

2nd Dec 2011, 8:17 pm	#17
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: 'Underwater' sound from valved amp. Does it sound like this?

2nd Dec 2011, 10:53 pm	#18
musonick Retired Dormant Member Join Date: Feb 2011 Location: Sudbury Hill, Middlesex, UK. Posts: 200	Re: 'Underwater' sound from valved amp. Cheers Mick jokes aside, it does sound a bit like that but not as exagerated. Amp details here P.30 http://thearcadeboneyard.com/Jukebox...0Combined).pdf Moderator's note. Warning - if you have a slow internet connection you might want to be aware that this file is 28M and will take forever to load. Last edited by Brian R Pateman; 3rd Dec 2011 at 10:01 am. Reason: Moderator's note added.

3rd Dec 2011, 12:22 am	#19
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: 'Underwater' sound from valved amp. Has the amp been restored recently? If not I would want to give it a full health check: - Test output valve grids are 0V (leaky audio coupling capacitors) - Check individual anode currents as it uses shared cathode bias arrangement - Check voltages against schematic As it's stereo, the obvious question is does it do the same on both channels? are the noises present when there is no input or is it just distortion of the sound? does the amount of distortion change with increased volume?

3rd Dec 2011, 7:44 pm	#20
musonick Retired Dormant Member Join Date: Feb 2011 Location: Sudbury Hill, Middlesex, UK. Posts: 200	Re: 'Underwater' sound from valved amp. hi, yes the sound is on both channels and it is only apparent with audio input. i have ordered a cap kit and will do the necessaries. thanks, nick