New set up annoying buzz / hum I can't get to the bottom of......

[Weeman1973]

I've just set up a new system using pre-loved items mostly procured from this parish - WLM La Scala Speakers, Croft 5c Power & Gate Pre Amps.

No matter what I do, I cannot stop background hum, or buzz through the speakers when there's no source playing which I can't help thinking isn't right?

I've tried different cables (speaker, interconnect & power), different wall sockets & although I can find some improvements depending on combinations, the hum is still audible with no source (magnified when using the TT input).

I thought it may have been the speakers as they are super efficient at 93db but it also happens when I've used the amps with my Naim Allae's (for sale actually....)

Sometimes the speaker cones actually move in & out if I turn the volume about half way (with no source playing of course) which does worry me if I'm doing damage to them? The hum is still there even with the pre off & just the power is on feeding the speakers as well.

I can live with it as obviously most times when the amp is on there is music playing but would prefer it not be there of course but I also worry if it is damaging the speakers at all?

Any thoughts?

[Stratmangler]

Do pre and power amps have connection to ground on the power side of things?
You could have a ground loop.

[Weeman1973]

Hi Chris,

Not really sure to be honest - electrics aren't my strong point.....

How would I check?

[Stratmangler]

You mention using different power sockets.
Have you tried using just one mains socket with an extension board?

https://images-na.ssl-images-amazon.com/images/I/51Mz6Aiiw7L._SX425_.jpg

[Weeman1973]

Yes, have tried that Chris & still the same.

I did make up my own lead using Belden cable & tried hat but no good.

Interestingly, the Belden cable has another strip of wire inside the casing outside of the regular live, earth & neutral - what should i do with this? I just cut it off!

[Ali Tait]

https://www.psaudio.com/ps_how/how-to-find-and-fix-hum/

[hifi_dave]

It would be helpful to know what the equipment concerned is.

First you need to narrow things down. Unplug everything from the amp except the speakers and check if the hum is still there. Don't turn the amp up to where you see the cones move because that is bad.

[Edward]

Hum is one of the most annoying things to eliminate. Going through the PS Audio process is definitely recommended to establish if there is a ground loop issue and if so how to cure it.

Sometimes I've found that hum is caused by EMI interference where the shielding on interconnects is not sufficient to eliminate such interference. If EMI is the cause then usually (i.e. not always) moving interconnect cables marginally (for example away from amp transformers or from power lines or not running parallel to power lines) can eliminate hum.

On your TT are you running a grounding wire back to your preamp/amp?

[Weeman1973]

https://www.psaudio.com/ps_how/how-to-find-and-fix-hum/

Thanks for the link - I'll have to run through all the checks at lunch & see what I can conclude

[Weeman1973]

It would be helpful to know what the equipment concerned is.

First you need to narrow things down. Unplug everything from the amp except the speakers and check if the hum is still there. Don't turn the amp up to where you see the cones move because that is bad.

Thanks Dave - kit is Gate Valve Pre Amp, Croft 5C Valve Amp, WML La Scala Speakers.

I've disconnected everything except PowerAmp to La Scala Speakers - hum is still there but very feint.

If I connect any leads at all to the Input on the Power Amp, the hum gets louder (even if not connected to Pre amp at the other end).

If I then connect the Pre & Power Amps together, hum gets louder - even if Pre is not switched on.

Louder still once Pre is switched on & then louder again when using the MM Phono input on the Gate pre.

Seems to me like an issue with the Power amp?

[Ali Tait]

Yes worth doing, means you can isolate it to a source or the amp, we can then proceed from there.

[Weeman1973]

I've now uploaded some video of the hum & cones flapping on both my La Scala's & Naim Speakers (easier to see on the Naim's):

https://www.youtube.com/watch?v=9JBn8A8WFzU

https://www.youtube.com/watch?v=j9DtfjsJziM

[struth]

could be dc from amp. can you try another amp?

[Ali Tait]

Also try moving the amp around, see if the hum changes/goes. Could be picking up RF from another component.

[hifi_dave]

Thanks Dave - kit is Gate Valve Pre Amp, Croft 5C Valve Amp, WML La Scala Speakers.

I've disconnected everything except PowerAmp to La Scala Speakers - hum is still there but very feint.

If I connect any leads at all to the Input on the Power Amp, the hum gets louder (even if not connected to Pre amp at the other end).

If I then connect the Pre & Power Amps together, hum gets louder - even if Pre is not switched on.

Louder still once Pre is switched on & then louder again when using the MM Phono input on the Gate pre.

Seems to me like an issue with the Power amp?

Seems to me more like the pre. The power-amp will usually produce a very slight hum through sensitive speakers, audible close up to the speakers, with nothing connected.

If the hum gets louder with pre connected and louder still with the pre switched on, it is likely to be the pre. Also, that thing with the volume control is worrying.

[Weeman1973]

After lots of fettling, I think I can narrow it down to the Power Amp...

I set my Croft Integrated (active pre & power sections) to the speakers & powered up with nothing connected - very low hum but only if i put my ears very close to speakers - this hum doesn't go up & down with volume.

Connected my X40 Streamer and powered up, all is good no extra hum there.

I then connected a SS Power Amp (Cympol CPA3) to my speakers with no source connected to that - absolute silence. Same when I use my X40 as the pre so all is good there.

I then connected the Gate Pre Amp to the Cymbol PA & used the X40 as a source then. With nothing playing there is silence except when I tun the volume on the Gate up & down - no hum but a sort of white noise sound but again very low. When playing a source this way there's no hum either.

So I think it must be the PA - trouble is how do I solve it?

[struth]

I would get it checked out by an engineer.. may be the start of dc getting onto the speakers, or it could be something else. You have said your not comfortable with electrics so getting it checked by someone that is is important in case it gets worse.

[Weeman1973]

I would get it checked out by an engineer.. may be the start of dc getting onto the speakers, or it could be something else. You have said your not comfortable with electrics so getting it checked by someone that is is important in case it gets worse.

Think I will thanks Grant.

It was originally Alan's (Firebottle) & he said he noticed nothing untoward when he had it.

Any recommendations of who I could see with it (I'm in Cambridgeshire). Thanks.

[struth]

the amp could still be ok, and it is something that is affecting that amp but not your others, but getting it checked and either fixed or cleared of having a fault is the first step. Until that is done its difficult to be sure about anything else. :)
Alas everything is not always straightforward on these occasions

[Light Dependant Resistor]

The usual cause of hum like this in a unbalanced audio system is a cable with a ground connection missing or broken - like a RCA cable looking OK externally but actually having a
broken connection for its ground. Suggest disconnect input cables to power amp... does hum disappear ? If Yes then fault is a input cable.requiring repair or replacement.

Opto coupling with a LDR attenuator enables total silence for audio attenuation- which is a amazing feature of LDR's that other preamps cannot match.

[Weeman1973]

The usual cause of hum like this in a unbalanced audio system is a cable with a ground connection missing or broken - like a RCA cable looking OK externally but actually having a
broken connection for its ground. Suggest disconnect input cables to power amp... does hum disappear ? If Yes then fault is a input cable.requiring repair or replacement.

Opto coupling with a LDR attenuator enables total silence for audio attenuation- which is a amazing feature of LDR's that other preamps cannot match.

Thanks Chris & although the hum does disappear when no cables are connected to the input, just speaker cables to the speakers, as soon as I attach any cables (tried about 6 different ones) , the hum comes back so don't think it's cable related in this instance.

[struth]

maybe they are picking up electrical/radio interference?.. ive seen this before too and its difficult to find.. can come from mains leads near the cables. I had one am that was very bad for this.
as i say, if amp is checked over, then it can be looked at after... if you have another system to try amp in, then see if you get the same happening.

[Light Dependant Resistor]

Thanks Chris & although the hum does disappear when no cables are connected to the input, just speaker cables to the speakers, as soon as I attach any cables (tried about 6 different ones) , the hum comes back so don't think it's cable related in this instance.

But is indicating there is at least one cable missing its ground upward from the power amp. You just need to find which one.

[Ali Tait]

If there is no hum with all inputs disconnected then the problem does not lie with the amp, unless you still get the cone movement with the volume control turning which will be a separate issue if so.

[Weeman1973]

If there is no hum with all inputs disconnected then the problem does not lie with the amp, unless you still get the cone movement with the volume control turning which will be a separate issue if so.

That's what I thought as well, however whichever cable I use to connect the pre to the power enhances the hum (even just adding cables to the input of the Power amp without connecting the other end to the pre amp)

The pre works silently with another power amp (SS one) which is why I'm ruling out the pre amp.

Can't tell if the cone flapping is power or pre related as obviously can only turn volume up & down once the pre is connected to the power then the power connected to the speakers.

[Ali Tait]

...which proves the cables are ok lol, so it’s a problem with pre when it’s connected to that amp.

Does one of your other amps have a pre out so you can try that as the preamp into your main amp.

[struth]

I thought it was still humming by itself?
Maybe at cross porpoises here so will drop out. Ali will tell u all you need to know

[Audio Al]

Have you looked closely at the speaker cables / terminations ?

[Stratmangler]

I've now uploaded some video of the hum & cones flapping on both my La Scala's & Naim Speakers (easier to see on the Naim's):

https://www.youtube.com/watch?v=9JBn8A8WFzU

https://www.youtube.com/watch?v=j9DtfjsJziM

The tone of the noise is around about G, which roughly translates to 49Hz ish. It could be the octave harmonic I'm picking up more, so 100Hz ish.
It's mains frequency noise.

[walpurgis]

Is the signal neg common with the amp chassis/case? It could be worth running a wire between the metal casework of the power amp to the case of the pre-amp to see what happens. It may go quiet, get worse or do nothing.

[montesquieu]

Just to say that Russ bought both of these from me (at different times - the power amp had been on loan to Jake).

They worked together really well here with no hum beyond the minimum ear up to the speaker noise that's normal with valve amps. I had them running together in the study for a while with a Garrard 401, latterly with a Technics SL10 (into the phono input), an Arcam iBlink and a Sony ES CDP, into Tannoy DC6's - this was actually a stunning combo. I ran them both separately into the main rig as well driving the big Tannoys with no problems and the pre driving my Radford STA100 at the time. All no issues.

The pre-was driven north by Petrat and collected, so wasn't shipped - it would definitely have arrived undamaged. The Croft was shipped to Jake's (where it was fine for several weeks) and on to Russ. Prior to me getting it it was fettled by Alan (Firebottle) and sounded stunning here. Behaved fine for Jake too.

Unless something has damaged the power amp in transit (which I guess is possible) then this is most likely to be a local mains hum issue. @Russ can you show the layout? It's still most likely to be a ground loop in my view, though it's also possible that it or the attached interconnect is picking up transformer noise from something too close. The speaker flap is a bit odd though and looks a bit like DC.

[STD305M]

Hi
Had the very same issue with my power amps
Turned out to be a loose connection in the amp.

Get it checked

Steve

[Weeman1973]

Thanks All for the comments - have just spent the best part of an hour trying all various combo's & have massively reduced the hum...

I now have the power plugged into to a different mains socket to the rest of the kit. Also using some Van Damme studio interconnects with locking connectors & have tightened the input connections on the back of the power amp as noticed these were easily spun round by hand.

There is no only a very slight hum when ear is next to the speakers which is usual with Valve amps when using a normal line, however when using the Phono (MM) input on the Gate pre amp, the hum gets louder as I increase volume (no source playing of course) & also noticed the speakers flapping again???

Beyond bemused!!!

[Light Dependant Resistor]

Thanks All for the comments - have just spent the best part of an hour trying all various combo's & have massively reduced the hum...

I now have the power plugged into to a different mains socket to the rest of the kit. Also using some Van Damme studio interconnects with locking connectors & have tightened the input connections on the back of the power amp as noticed these were easily spun round by hand.

There is no only a very slight hum when ear is next to the speakers which is usual with Valve amps when using a normal line, however when using the Phono (MM) input on the Gate pre amp, the hum gets louder as I increase volume (no source playing of course) & also noticed the speakers flapping again???

Beyond bemused!!!

If available attach the separate ground lead of your phono RCA cable to dedicated ground post on the preamp. But it looks like You may also have some acoustic feedback creeping in, which is where the turntable
is not isolated well enough on its stand, and is converting feet movement vibration, or indeed just the speakers nearby to become very low frequency energy.

Jimi Hendrix used to make direct use of feedback with guitar , amp and speakers but in your case its an annoying artifice.

Look carefully at how the turntable attaches to its stand, and seek to cure any vibration as picking up and being re-amplified.25578

[Ali Tait]

Is the signal neg common with the amp chassis/case? It could be worth running a wire between the metal casework of the power amp to the case of the pre-amp to see what happens. It may go quiet, get worse or do nothing.

Yeah that would have been my next suggestion. Looks like he has it sorted though.

[Audio Al]

I assume you have a earth connected from the TT onto the pre and then onto the power amp ?

[Weeman1973]

Is the signal neg common with the amp chassis/case? It could be worth running a wire between the metal casework of the power amp to the case of the pre-amp to see what happens. It may go quiet, get worse or do nothing.

Thanks but this was the 1st thing I tried - did nothing. Even stripped the paint away from the case of the Power Amp & attached a piece of speaker wire to the grounding connection of the pre amp - nada!

[Weeman1973]

I assume you have a earth connected from the TT onto the pre and then onto the power amp ?

I have the TT grounded to the pre amp but then nothing onto the Power amp.

Do you think I should run another cable from the pre amp to the case of the power amp then?

[walpurgis]

Do you think I should run another cable from the pre amp to the case of the power amp then?

I suggested that. You have nothing to lose by trying it. If there are eath terminals use those, if not just loosen a case screw on each unit and slip the bare wire end under it. Don't do this with anything switched on and make sure the pre-amp volume is right down.

[Audio Al]

I have the TT grounded to the pre amp but then nothing onto the Power amp.

Do you think I should run another cable from the pre amp to the case of the power amp then?

YES

[Weeman1973]

YES

So I ran some cable from the grounding connection on the pre amp (still with the TT also grounded but not on) to the case of the power amp (undid a screw & removed the paint) and.......


It’s worse!!!

I give up - then I’ll stick to integrated’s!

[andyrlb]

You’re welcome to try it here mate if that might help


Sent from my iPhone using Tapatalk

[Weeman1973]

You’re welcome to try it here mate if that might help


Sent from my iPhone using Tapatalk

Thanks Andy - appreciate it.

As it stands I’ve got the hum to a very bare minimum by using various power sockets & cables etc.

I’m also picking up a new TT tomorrow so will how it all behaves then & go from there. [emoji1695]

[sumday]

Is your WiFi modem positioned anywhere near your amps perchance?
Tubes are remarkably sensitive to WiFi emmisions.....a tube preamp I ran recently was placed near my modem and picked up all sorts of nasties.

[Weeman1973]

Is your WiFi modem positioned anywhere near your amps perchance?
Tubes are remarkably sensitive to WiFi emmisions.....a tube preamp I ran recently was placed near my modem and picked up all sorts of nasties.

I did think that so turned the router off - no discernible difference.

It’s about 10ft away from the amps & around 2ft from one of the speakers.

Had a play around yesterday with everything again & still the hum - worse on the Phono stage which tends to go up & down when I increase / decrease volume.

Today I’m going to clean all the valve seats etc with contact cleaner & reposition them - see if that helps.

Also will try different lengths / types of speaker cable & interconnects however I fear it won’t have much impact.

Thinking down the route of going back to my Integrated as this was more or less silent through my speakers.

[hifi_dave]

The pre is faulty.

[montesquieu]

I already suggested the other day that Russ get it checked over and I'll cover any repair. The original manufacturer is back in business and not that far from him. https://www.vintagevalveandvinyl.co.uk/about-us/

It has been behaving fine for me this past year or so right up till I stopped using it a few weeks ago when the Croft went to Jake, but it does seem that there's some kind of issue appeared on the phono stage. I doubt it can be anything too serious.

[Weeman1973]

OK, after lots of fettling & cleaning etc. I think I can safely say it is the pre at fault.

I've taken both pre & power apart & cleaned all valves, pots etc. with contact cleaner.

Put it back together & powered up - hum still there, louder on the Phono input, increases with volume (& speakers flap).

Used my Croft integrated paired to WML speakers - a lot quieter, hardly any background noise at all. This doesn't have a phono input however I used my Schiit Mani to hook up the TT. This is sligthtly noisier than a regular input but I would expect that with the extra gain. Still not as loud as the Gate pre.

I then used a SS Power Amp I have (Cymbol CPA3) & used the Gate as the Pre - background hum is there again, louder on phono stage.

Used the Cymbol as the Power with my X40 streamer as the pre - virtually silent with no source playing, even whacking the volume up.

Last permutation is using the Gate as a Phono Stage only, coming out of the tape outs into the input on the X40 & using that as the pre. Noise is back which increases with volume, using the Croft Valve & Cymbol SS Power Amps.

This makes me think it is the Pre which is loud, particularly on the phono stage, however what I still can't understand is why my Croft Integrated (active pre & power sections) is still quieter than the Croft 5C Power Amp - I guess it's different gain 7 the way it's set up?

[hifi_dave]

Hallelujah, see post 15.

The Croft 5C is all valve and now old. The Croft Integrated is hybrid and very quiet.

[Weeman1973]

Hallelujah, see post 15.

The Croft 5C is all valve and now old. The Croft Integrated is hybrid and very quiet.

Appreciate that the Croft 5C is relatively old - maybe new valves required & that might quieten it down a bit.

The Croft integrated is newer but still valves on pre & power stages - was adapted by Glenn himself & upgraded power supply at the same time

[hifi_dave]

The Croft Series 7 Integrated is a hybrid with valve input and MosFet output. Usually as quiet as a mouse.