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Cambridge Audio 840A amp erratic volume fix


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Hi

I've had the pleasure of using my Cambridge Audio 840A for about 4 years now.

In the past year when using the volume control on the amp the volume has behaved in a random/erratic manner.

Volume increasing when turning it down, especially when turning it down quickly. Volume does behave normally when using the remote.

 

Recently the volume started increasing without input from me on the volume control.

I could hear the relays clicking when the amp was on with no music playing.

Sometimes when listening to music it would get noticeably louder.

 

The volume going up without input is potentially speaker damaging.

I read on another forum where someone had blown a pair of B&W speakers due to this problem.

(They left music on and went out for an hour or so)

 

After researching, the potential fixes where:

1. Replace all the relay switches that control the volume. One person had replaced all the relays with upgraded ones. 

Only to have the same issue reappear a few years later.

 

2. Access the volume control and spray some Deoxit D5 contact cleaner onto the contact area of the volume control.

This fix was in relation to some other makes of amplifier.

 

I chose potential fix number 2 and purchased a can of Deoxit D5 from Jaycar Electronics for $29.95

 

After removing the top cover and the front control panel of the amp I discovered the volume control contact area was a sealed, so no way of spraying directly onto the contact area of the control.

Instead I covered the surrounding area with paper towelling and sprayed where the rotating spindle enters the volume control.

I then rotated the spindle back and forth for a couple of minutes.

As I repeated this procedure 3 times the spindle became easier and easier to rotate. 

 

After putting the amp back together the volume was once again responding appropriately to up and down movements of the volume control.

 

It's been a few weeks and all is well, I now have the confidence to listen at a reasonably high volume without fear of it increasing randomly.

 

In hindsight this fix is possible by simply removing the volume control knob and spraying where the spindle enters the volume control with Deoxit and rotating.

Now a 5-10 minute job.

 

Hope this is of some help 

Cheers, Phil

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If your pot is sealed and you did not unseal it to get to the resistor wafer element and the point of contact, I hate to say it there is a high possibility you didn't fix your issue.  Rotating the pot physically and winding it from one end to the other may have done it some good.

The 1st point of degradation on any amplifier is 1st the volume pot and then any switches, especially the ones that select between sources.

Over the years I found that doing exactly what you did had made it worst and it start to have a scratchy sound through the speakers as you rotate that pot, that's because certain pot manufacturers use conductive grease on the resistor element and the contact point, spraying things like contact cleaner or detox removes this grease and makes it worst.

i hate mechanical volume pots with a passion, they are so dinosaur!  it doesn't matter if it's a gold plated DACT or an Alps Rk50. They will all degrade the SQ.  

The best you can do is go back to the manufacturer and have it replaced.

We are in 2017 and there are many different ways to control volume, any preamplifier using old mechanical pots ticks the box to stay away!  Period!  

 

 

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does the 840A even have a vol pot for volume control ? 

 

can you post of the pics of the innards as all once have seen show no volume pot. and especially if talking relay switches. sure its not a ladder style ?with no volume pot ? its an amp with a ht bypass as well as far as i know and software implemented am pretty sure like cyrus, arcam and the like employ and is done not using a volume pot. 

 

you sure not more a case of some other gremlins sending things haywire with random volume gymnastics happening... without rhyme or reason ?

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4 hours ago, :) al said:

does the 840A even have a vol pot for volume control ? 

 

can you post of the pics of the innards as all once have seen show no volume pot. and especially if talking relay switches. sure its not a ladder style ?with no volume pot ? its an amp with a ht bypass as well as far as i know and software implemented am pretty sure like cyrus, arcam and the like employ and is done not using a volume pot. 

 

you sure not more a case of some other gremlins sending things haywire with random volume gymnastics happening... without rhyme or reason ?

 

Good point @:) al

 

if there are relays involved it means the pot that he just sprayed detox on is highly possible a rotary encoder.  Looking at the post he does say that the volume increases without input. The Rotory encoder is either physical switch or optical type, that sends a coded pulse to a microprocessor to control a set of relays to resistors to attenuate volume.    Generally speaking these encoders  are very reliable but like all things I have heard they do pay up.   Regardless whether it's an optical or a switch,  check the solder joints for dry joints or replace the encoder.  It's rare and won't be the microprocessor, but if it is you cannot replace that chip and expect that to be the fix, it won't as these chips are programmed specifically to control that function by the manufacturer.

Edited by Addicted to music
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I had the same problem with my 740 before it became a boat anchor.

The volume pot was replaced (under warranty).

IMO Cambridge audio products are not built to last and are expensive to repair due to the modular design.

Spare parts availability IME is very poor.

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It is likely the fault lies with the 'volume encoder'. The control on the amp is not a pot. It is a multi-contact rotary switch, with as many as 50 or more contacts. These devices are cheap and nasty and often cause problems. Solution? Clean it or replace it. In reality, they are not designed to be cleaned. Seen it many times.

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On 18/02/2017 at 8:49 PM, Addicted to music said:

If your pot is sealed and you did not unseal it to get to the resistor wafer element and the point of contact, I hate to say it there is a high possibility you didn't fix your issue.  Rotating the pot physically and winding it from one end to the other may have done it some good.

The 1st point of degradation on any amplifier is 1st the volume pot and then any switches, especially the ones that select between sources.

Over the years I found that doing exactly what you did had made it worst and it start to have a scratchy sound through the speakers as you rotate that pot, that's because certain pot manufacturers use conductive grease on the resistor element and the contact point, spraying things like contact cleaner or detox removes this grease and makes it worst.

i hate mechanical volume pots with a passion, they are so dinosaur!  it doesn't matter if it's a gold plated DACT or an Alps Rk50. They will all degrade the SQ.  

The best you can do is go back to the manufacturer and have it replaced.

We are in 2017 and there are many different ways to control volume, any preamplifier using old mechanical pots ticks the box to stay away!  Period!  

 

 

But he did fix it;):party.........your angry 'audio intelligentsia' waffle is no help at all.....Period!!:emot-bang::wacko:  BTW, that's actually 'full stop' in real English.;)

Edited by stevoz
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  • 11 months later...

I think I just "fixed" my original version 840a. It never had a warranty. It was purchased north of Boston when Tweeter was going out of business and has a clear acrylic top to show off the innards.

 

It had the volume goes up either way you turn the knob issue for years, but it never increased volume by itself until tonight.

 

My wife was watching TV (yes, we do our home theatre 2 channel) when pretty soon our whole apartment building was listening to what she was watching. I'm lucky by B&W 603s3's survived.

 

She said it turned up on its own. She wasn't sitting on the remote. Then, it did it again while I was standing there. And again. It wanted to rock and we wanted it "reasonable."

 

I had a can of D5 around and may have used too much. Switched the amp back on and there was nothing. Turning it up more, it was crackling. Several power cycles (and some time waiting) later, it's fine. Maybe I used too much D5.. I don't know. Maybe the main power switch in the back should have had D5 because it was only ever used once since I've had it...

 

Here's hoping..and thanks for the help!

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Glad to be of help Seth.

 

Good to hear you ignored some of the more knowing contributors to this thread and gave it a go.

 

After 12 months I haven't had any issues with the volume control since using D5, it is still working perfectly and sounds fantastic.

 

The 840a is a great amp and can be an absolute bargain bought second hand.

 

All the best.

 

Cheers

Phil :) 

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  • 1 year later...
On 18/02/2017 at 4:49 AM, Addicted to music said:

If your pot is sealed and you did not unseal it to get to the resistor wafer element and the point of contact, I hate to say it there is a high possibility you didn't fix your issue.  Rotating the pot physically and winding it from one end to the other may have done it some good.

The 1st point of degradation on any amplifier is 1st the volume pot and then any switches, especially the ones that select between sources.

Over the years I found that doing exactly what you did had made it worst and it start to have a scratchy sound through the speakers as you rotate that pot, that's because certain pot manufacturers use conductive grease on the resistor element and the contact point, spraying things like contact cleaner or detox removes this grease and makes it worst.

i hate mechanical volume pots with a passion, they are so dinosaur!  it doesn't matter if it's a gold plated DACT or an Alps Rk50. They will all degrade the SQ.  

The best you can do is go back to the manufacturer and have it replaced.

We are in 2017 and there are many different ways to control volume, any preamplifier using old mechanical pots ticks the box to stay away!  Period!  

 

 

Hey ATM: I love the passion;

 

(RE: " ...i hate mechanical volume pots with a passion, they are so dinosaur!  it doesn't matter if it's a gold plated DACT or an Alps Rk50. They will all degrade the SQ.")

 

Just wondering if that holds true today; perhaps a volume 'pot' like that of Spectral is an exception ?

(I believe it too uses a typical 'wiper' type analog potentiometer design.)

 

Yet, your comments are worth noting; volume attenuation is not as simple as it may appear, the finest modern designs employing resistor ladder/relay's  in effort to maintain excellent channel balance,  bandwidth and low noise. 

To all current/budding audiophiles; take note of the volume "control" design of any Preamp, Int., CDP,  DAC, Streamer  -or any other device that offers up volume attenuation- and give it more than passing consideration; it plays a vital role in defining high performance.

 

pj        

Edited by allhifi
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9 hours ago, allhifi said:

 

Hey ATM: I love the passion;

 

(RE: " ...i hate mechanical volume pots with a passion, they are so dinosaur!  it doesn't matter if it's a gold plated DACT or an Alps Rk50. They will all degrade the SQ.")

 

Just wondering if that holds true today; perhaps a volume 'pot' like that of Spectral is an exception ?

 

Find 2 identical Preamp with a typical mechanical volume pot,  rotate the volume pot up for at least 500 times and then compare it to one that hasn’t had any use and you’ll find that there will be degradation.  

 

No idea what the “Spectral “ is all about.

 

9 hours ago, allhifi said:

 

Yet, your comments are worth noting; volume attenuation is not as simple as it may appear, the finest modern designs employing resistor ladder/relay's  in effort to maintain excellent channel balance,  bandwidth and low noise. 

To all current/budding audiophiles; take note of the volume "control" design of any Preamp, Int., CDP,  DAC, Streamer  -or any other device that offers up volume attenuation- and give it more than passing consideration; it plays a vital role in defining hig performance.

 

Absolutely,

Volume control implementation is a big deal in high quality electronics,  speaks loudly when it comes to improvements where audiophiles bang on about other things such as mains cable etc.  Changing the implementation of volume control has major impact in SQ that’s far greater than any mega dollar cable change.

Resistor/relay is a very imported leap forward,  encoder microprocessors controlled like what the OP has in his CA  reduces wear on a contact point during use, and becuase resistors are used the channel/balance is almost identical right throughout the range of the control maintaining almost perfect balance.  

The other way to do it is use volume control chips, these maintain balance within +/- 0.5db throughout the entire volume range which takes accuracy even further and becuase there are no relays used and contactless means there will be zero degradation,  so what you get brand new will stay brand new for the life of the product.  

You’ll find most Preamp manufacturers will use any BS excuses why they didn’t use them and stuck to prehistoric times,  but if you look at Nelson Pass top of the line Preamp, he uses a Muses volume control chip!    

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5 hours ago, Addicted to music said:

Find 2 identical Preamp with a typical mechanical volume pot,  rotate the volume pot up for at least 500 times and then compare it to one that hasn’t had any use and you’ll find that there will be degradation.  

 

No idea what the “Spectral “ is all about.

 

Absolutely,

Volume control implementation is a big deal in high quality electronics,  speaks loudly when it comes to improvements where audiophiles bang on about other things such as mains cable etc.  Changing the implementation of volume control has major impact in SQ that’s far greater than any mega dollar cable change.

Resistor/relay is a very imported leap forward,  encoder microprocessors controlled like what the OP has in his CA  reduces wear on a contact point during use, and becuase resistors are used the channel/balance is almost identical right throughout the range of the control maintaining almost perfect balance.  

The other way to do it is use volume control chips, these maintain balance within +/- 0.5db throughout the entire volume range which takes accuracy even further and becuase there are no relays used and contactless means there will be zero degradation,  so what you get brand new will stay brand new for the life of the product.  

You’ll find most Preamp manufacturers will use any BS excuses why they didn’t use them and stuck to prehistoric times,  but if you look at Nelson Pass top of the line Preamp, he uses a Muses volume control chip!    

 

Excellent reply.

 

Thanks for sharing.

 

pj

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5 hours ago, Addicted to music said:

Find 2 identical Preamp with a typical mechanical volume pot,  rotate the volume pot up for at least 500 times and then compare it to one that hasn’t had any use and you’ll find that there will be degradation.  

 

No idea what the “Spectral “ is all about.

 

Absolutely,

Volume control implementation is a big deal in high quality electronics,  speaks loudly when it comes to improvements where audiophiles bang on about other things such as mains cable etc.  Changing the implementation of volume control has major impact in SQ that’s far greater than any mega dollar cable change.

Resistor/relay is a very imported leap forward,  encoder microprocessors controlled like what the OP has in his CA  reduces wear on a contact point during use, and becuase resistors are used the channel/balance is almost identical right throughout the range of the control maintaining almost perfect balance.  

The other way to do it is use volume control chips, these maintain balance within +/- 0.5db throughout the entire volume range which takes accuracy even further and becuase there are no relays used and contactless means there will be zero degradation,  so what you get brand new will stay brand new for the life of the product.  

You’ll find most Preamp manufacturers will use any BS excuses why they didn’t use them and stuck to prehistoric times,  but if you look at Nelson Pass top of the line Preamp, he uses a Muses volume control chip!    

ATM: Spectral Audio -a long-standing premium (USA) hifi manufacturer; peramps, power, CDP.

 

pj 

Edited by allhifi
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On 24/02/2017 at 8:39 PM, stevoz said:

But he did fix it;):party.........your angry 'audio intelligentsia' waffle is no help at all.....Period!!:emot-bang::wacko:  BTW, that's actually 'full stop' in real English.;)

I tell everyone not to physically touch the volume knob and use the remote only. It's when someone touches the actual knob that it starts acting up again. Otherwise, even aggressively turning the knob up and down while the power is shut off from the rear switch clears it up well enough.

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54 minutes ago, Seth Albaum said:

I tell everyone not to physically touch the volume knob and use the remote only. It's when someone touches the actual knob that it starts acting up again. Otherwise, even aggressively turning the knob up and down while the power is shut off from the rear switch clears it up well enough.

 

Seth: I sure hope that your reply was more a 'tongue-in-cheek' comment as opposed to some 'real' advice ?

 

Seriously: 

 

"....I tell everyone not to physically touch the volume knob and use the remote only. It's when someone touches the actual knob that it starts acting up again."

 

Gimm'e a break. CA has a disturbingly long history of well-documented erratic volume-control issues; including one of my own 840E's. Remarkably, after I received my second 840E -and connected, I opened up my original/existing preamps top-plate (and above beyond admiring the beautifully laid out/constructed build quality), I noted actual burn-marks (discoloration) on the inside of the top plate that lines-up with the positioning of a fairly large heatsink just to the left of the volume control.

In other words, the thing got so bloody hot it discolored/burned the metal top plate ! The 840E is  has NO ventilation vents on the top cover -completely sealed. Great design ! CA should be ashamed.

 

The successor (851E) is not nearly as well-built/designed or constructed as its predecessor -but does offer up the required ventilation holes on its top-plate -5-years after the introduction of the 840-series!

 

Such a manufacturing/design oversight is difficult to comprehend: Cambridge Audio recently "celebrated" their 50-year anniversary.  It's sensible to assume another 5 years (60 months) is not assured if it continues to manufacture defective designs -and then refuses to acknowledge, or accept either responsibility or offer up a sensible "fix".         

 

pj

 

Edited by allhifi
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  • 3 years later...

I realise this is an old thread, wondered if the “cleaning” still remains a fix for the volume control. My Azur840A is now at the stage where it randomly turns the volume to maximum daily, I have to be there ready to turn it off.

 

I’d moved it from my main speakers for fear of damage some time ago as this randomly happened. Now I’m concerned my secondary speakers will suffer so no longer using it at all. Shame because the sound is excellent - if you are game!

 

So boat anchor or repair? My Hi-Fi shop who I trust recommended a fishing trip…. My repairer recommended about a $250 investment.

 

Tony

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  • 1 year later...
On 14/02/2017 at 5:40 AM, earthwoodphil said:

Hi

I've had the pleasure of using my Cambridge Audio 840A for about 4 years now.

In the past year when using the volume control on the amp the volume has behaved in a random/erratic manner.

Volume increasing when turning it down, especially when turning it down quickly. Volume does behave normally when using the remote.

...

Hope this is of some help 

Cheers, Phil

Got this problem today. Volume suddenly went to MAX, nearly blowing up the speakers. Only slight response from changing volume with encoder or remote, but could not control it.

Used WD-40 cleaning as you suggested, and it worked.
What seems to happen is that the encoder gets stuck on sending 'volume up' signal continously. 
I also have the other type of volume control issue whith warm and erratic relays, but I can live with that. This however could have been a terminal problem without this fix. Thanks for sharing your experience.

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Hello

Very glad to hear you tried this easy fix on your 840A and did not give up on what is a really impressive amp.

 

For me the problem reappeared after about 12 months, that being four and a half years ago now. I sprayed it again and it's still going strong. 

However I do not use the volume knob at all and rely on the remote only for volume adjustments.

 

I enjoy listening to my 840A for hours every day of the week as it has the TV hooked up to it, home theatre front main speakers, as well as my music system.

 

Now into it's eleventh year of ownership and I could not be happier with it. 

 

Hope you have many more years of listening enjoyment from your 840A.

 

Cheers

Phil

  

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