Muting the audio on a Jukebox - UK Vintage Radio Repair and Restoration Discussion Forum

vinrads · 28th Nov 2021, 10:22 am

I need to mute the audio during the record changing ,there is a mute relay in the pre amp stage ,it works but there is still motor noise ,due to part of the amp still working , I think switching the ht could cause a pop/ click which would be as bad , my thoughts were shorting the speaker out ,with another relay, thoughts please, Mick.

vidjoman · 28th Nov 2021, 10:37 am

Which Jukebox - what make etc. Sounds like it could be bad earthing somewhere. It's a fault - not good to short the speakers although some makes did.

Tractorfan · 28th Nov 2021, 10:57 am

Hi,
I have a domestic Garrard autochanger. It shorts the pick up cartridge during the change cycle, then opens the contacts again just when the stylus lands on the record. I presume the mute relay does the same.
Hope this helps.
Cheers. Pete

PaulR · 28th Nov 2021, 11:52 am

If possible, might screening the valves in the power amp help?

vidjoman · 28th Nov 2021, 4:40 pm

I don't think any suggestions are going to help until we know what jukebox it is. There have been many different muting systems applied to different boxes and as original they all worked when new, so therefor there is a fault that has occurred. If the motor noise is from a DC motor, then maybe the carbon brushes are bad and that has nothing to do with the amplifier.
More info needed otherwise we are chasing a wild goose.

ben · 29th Nov 2021, 10:52 pm

I'd imagine that shorting the speaker out would be a very bad idea!

What happens when you short the input from the cartridge to ground?

Analogue man · 30th Nov 2021, 12:41 am

Quote:

Originally Posted by ben

I'd imagine that shorting the speaker out would be a very bad idea!

What happens when you short the input from the cartridge to ground?

Shorting the cartridge to ground is the way that Wurlitzers mute the deck during record change.

vinrads · 30th Nov 2021, 11:23 am

Hi thanks for the replies chaps, the amp is from a Rock-ola 1488 the mute relay is connected to the balance control earthing the sig at both ends, it does mute the signal , but as stated the rest of the amp is left open so to speak and prone to pick up interference, it is possible the the motor is a bit tired , suppressor capacitors have been tried on the motor to no effect, more thoughts on shorting out the speakers, I don't see a problem as there is no sig ,so the output valves are just sat there all dc conditions correct Mick.

Analogue man · 30th Nov 2021, 12:52 pm

Quote:

Originally Posted by vinrads

Hi thanks for the replies chaps, the amp is from a Rock-ola 1488 the mute relay is connected to the balance control earthing the sig at both ends, it does mute the signal , but as stated the rest of the amp is left open so to speak and prone to pick up interference, it is possible the the motor is a bit tired , suppressor capacitors have been tried on the motor to no effect, more thoughts on shorting out the speakers, I don't see a problem as there is no sig ,so the output valves are just sat there all dc conditions correct Mick.

As your jukebox has a valve amplifier then shorting the speaker terminals will mute the noise through the speaker but it might put the amp into oscillation if there is negative feedback taken from the secondary side of the output transformer, you won't hear it but it will do the amp no good at all.

vinrads · 30th Nov 2021, 4:03 pm

I see from the cct there is neg feedback, I will put it to the test ie scope it when I get the amp , Mick.

28th Nov 2021, 10:22 am	#1
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Muting the audio on a Jukebox I need to mute the audio during the record changing ,there is a mute relay in the pre amp stage ,it works but there is still motor noise ,due to part of the amp still working , I think switching the ht could cause a pop/ click which would be as bad , my thoughts were shorting the speaker out ,with another relay, thoughts please, Mick.

28th Nov 2021, 10:37 am	#2
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,324	Re: Muting the audio on a Jukebox Which Jukebox - what make etc. Sounds like it could be bad earthing somewhere. It's a fault - not good to short the speakers although some makes did.

28th Nov 2021, 10:57 am	#3
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,182	Re: Muting the audio on a Jukebox Hi, I have a domestic Garrard autochanger. It shorts the pick up cartridge during the change cycle, then opens the contacts again just when the stylus lands on the record. I presume the mute relay does the same. Hope this helps. Cheers. Pete __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

28th Nov 2021, 11:52 am	#4
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Muting the audio on a Jukebox If possible, might screening the valves in the power amp help? __________________ Paul

28th Nov 2021, 4:40 pm	#5
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,324	Re: Muting the audio on a Jukebox I don't think any suggestions are going to help until we know what jukebox it is. There have been many different muting systems applied to different boxes and as original they all worked when new, so therefor there is a fault that has occurred. If the motor noise is from a DC motor, then maybe the carbon brushes are bad and that has nothing to do with the amplifier. More info needed otherwise we are chasing a wild goose.

29th Nov 2021, 10:52 pm	#6
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Muting the audio on a Jukebox I'd imagine that shorting the speaker out would be a very bad idea! What happens when you short the input from the cartridge to ground? __________________ Regards, Ben.

30th Nov 2021, 11:23 am	#8
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: Muting the audio on a Jukebox Hi thanks for the replies chaps, the amp is from a Rock-ola 1488 the mute relay is connected to the balance control earthing the sig at both ends, it does mute the signal , but as stated the rest of the amp is left open so to speak and prone to pick up interference, it is possible the the motor is a bit tired , suppressor capacitors have been tried on the motor to no effect, more thoughts on shorting out the speakers, I don't see a problem as there is no sig ,so the output valves are just sat there all dc conditions correct Mick.

30th Nov 2021, 4:03 pm	#10
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: Muting the audio on a Jukebox I see from the cct there is neg feedback, I will put it to the test ie scope it when I get the amp , Mick. Last edited by vinrads; 30th Nov 2021 at 4:12 pm.