Help with Hum?

elnorte

New member
Mar 6, 2016
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Hello Everyone

First time posting here so thanks in advance to anyone who may be able to help with my query.

Recently I inherited a Garrard AP 76 turntable and Armstrong 521 amplifier (both originally purchased in the early 1970s I believe). Excited that I finally had some classic vintage equipment to play my vinyl collection on I first took the two items to a specialist repair shop as I figured since they had not been used in years they would at least require a little fixing up.

The shop quoted me £90 each for the two pieces of equpiment and later communicated to me that the service had involved a full replacement of many of the corroded components within both systems.

Unfortunately after setting up at home I quickly noticed the volume was particuarly low (even when turned up close to maximum) along with a noticeable hum emanating from the speakers when no music was playing.

After contacting the shop again the owner speculated it could be a further cartridge issue but to bring both iterms back for a further look.

The first problem regarding the volume level was solved when it was clarified that the turntable cable was plugged into the wrong port on the amp (may sound a little silly but I had orginally been told this was the correct connection!). However, I was told that the hum was still present but this was simply down to the build of the amp and not any further issue that needed or could be addressed.

However, this last explanation concerns me. From a brief bit of research I've carried out online it would seem that a hum almost always points to some form of technical fault and not a natural occurance unless it's particularly cheap equipment which I don't believe in this case they are.

More optimistically it could be that what I'm being told is the truth and that both items have been restored as best as they possibly can be. If so I'd be happy, and truth be told relieved, to carry on using the turntable and amp as they are right now.

Either way I would sincerely appreciate any advice or insight before considering my options or going back to the shop a second time which ideally I would very much like to avoid.
 
elnorte said:
Hello Everyone

First time posting here so thanks in advance to anyone who may be able to help with my query.

Recently I inherited a Garrard AP 76 turntable and Armstrong 521 amplifier (both originally purchased in the early 1970s I believe). Excited that I finally had some classic vintage equipment to play my vinyl collection on I first took the two items to a specialist repair shop as I figured since they had not been used in years they would at least require a little fixing up.

The shop quoted me £90 each for the two pieces of equpiment and later communicated to me that the service had involved a full replacement of many of the corroded components within both systems.

Unfortunately after setting up at home I quickly noticed the volume was particuarly low (even when turned up close to maximum) along with a noticeable hum emanating from the speakers when no music was playing.

After contacting the shop again the owner speculated it could be a further cartridge issue but to bring both iterms back for a further look.

The first problem regarding the volume level was solved when it was clarified that the turntable cable was plugged into the wrong port on the amp (may sound a little silly but I had orginally been told this was the correct connection!). However, I was told that the hum was still present but this was simply down to the build of the amp and not any further issue that needed or could be addressed.

However, this last explanation concerns me. From a brief bit of research I've carried out online it would seem that a hum almost always points to some form of technical fault and not a natural occurance unless it's particularly cheap equipment which I don't believe in this case they are.

More optimistically it could be that what I'm being told is the truth and that both items have been restored as best as they possibly can be. If so I'd be happy, and truth be told relieved, to carry on using the turntable and amp as they are right now.

Either way I would sincerely appreciate any advice or insight before considering my options or going back to the shop a second time which ideally I would very much like to avoid.
Welcome to the forum. Hums are a bugbear of some older equipment and difficult to trace. Does the amp hum with nothing at all connected at the back?

Does your turntable cable have an earth lead along with the Left/Right phono cables? It could very well be an earthing problem. Does the mains plug on your amp have an earth wire?
 

elnorte

New member
Mar 6, 2016
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Thanks for such a quick response.

After I unplugged the turntable connection from the back of the amp there was no longer any noticeable hum. Complete silence as far as I could tell.

I'm not sure about earth leads (definition-wise I mean) but for the meantime I will try to describe the set-up as best I can.

The turntable has a five pin connector at the back to which the corresponding cable is plugged in. At the other end of this cable are dual red and black pins (adaptors) which plug into the back of the amp.

Both the amp and the turntable have their own separte mains cables. I'm using a multi-socket adaptor to plug these into the mains.

If you like I could always attach a photo (or two) of the set up if you feel it would help at all.
 

brownz

New member
Apr 9, 2015
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0
Earthing Hum by the sounds of it.
If your equipment has a two pin figure of 8 mains plug then it will be a floating earth.
If your equipment has a three pin kettle lead style plug then it will have a direct earth.
99% of earth hum can be eliminated by connecting a ground wire between the turntable and the amplifier, both "should" have a little thumbscrew somewhere to allow this.
In some certain extreme circumstances you may also need to call on the help of an extra earth from both to mains socket using something like this :


If you still have a hum after trying these then it's normally down to having a floating shield on the RCA cables between turntable and the AMP. You'll need to check how the cables are terminated in the plugs.
 

elnorte

New member
Mar 6, 2016
4
0
0
Hi

Thanks for all the advice. Very much appreciated.

I was originally going to give some additional information that I thought might be helpful to anyone interested in this issue. Unfortunately the whole situation has now become more complicated.

As I said in my previous post I was under the impression that with the turntable unplugged from the back of the amp there was no hum to be heard. However, part of the shop's original service also involved having one of the ports at the back of the amp adapted for an iPod or MP3 Player.

Now I tried using this for the first time tonight. In this instance I was certain I had it plugged into the correct connection (there is also corresponding button that needs pushed at the front with the matching symbol) but once again I noticed serious issues regarding the volume level.

Having no idea what the problem could be this time around I thought perhaps like before that the iPod adaptor was actually in the wrong port and therefore I instead plugged it into the same one I use for the turntable. At this point the volume did increase somewhat but still not nearly as loud as it should be in my opinion.

But most worrying of all is that since attempting that experiment (and I'm almost certain this is what has happened) I now do have a hum being emitted from the amp WITHOUT anything plugged into it! And the hum that was there previously WITH the turntable plugged in sounds different to how it did before. Not massively so perhaps but it's definitely changed a little.

So I guess what I'm asking is have I effectively damaged the amp (further) by having the iPod adaptor plugged into the turntable port?

Sorry if I sound like such a useless idiot in this thread by the way. At this point I really don't know if I can face going back the shop. I'm close to being too embarrassed to do so but I guess I almost need to for no other reason than to discuss the MP3 player volume problem.

If anyone wishes to take pity on me for this latest round of stupidity I would be very grateful.
 

brownz

New member
Apr 9, 2015
5
0
0
elnorte said:
Hi

Thanks for all the advice. Very much appreciated.

Snipped....

Having no idea what the problem could be this time around I thought perhaps like before that the iPod adaptor was actually in the wrong port and therefore I instead plugged it into the same one I use for the turntable. At this point the volume did increase somewhat but still not nearly as loud as it should be in my opinion.
I'd pay a visit back to the dealer who carried out the modifications. If you don't get anywhere there are some useful contacts on this page http://www.audiomisc.co.uk/Armstrong/armstrong.html

Potentially, plugging in a source that is already amplified into a Phono Input can lead to damage as your introducing a twice amplified signal into the mix. But most amps will protect against this.
 

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