Noise & Tripping AMP - I am ay my wits end

[smarkgee]

I have a PC, Musical Fidelity X24 DAC and an arcam 9 pre and power amp with two sets of speakers on the power amp (celestion A and some other brand). For about 3 years I have had the problem of the AMP tripping. Usually first thing in the morning and mostly in winter (its in a cupboard under the stairs but that's not that cold) I have had my arcam serviced by the manufacturer, i have replaced every cable (including speaker cable that was channeled in wall and run under floor boards. I have done everything. I even at one point got the amp to trip with just the amp and speakers connected (then got the amp serviced and ran a new set of speaker cables and tried different speakers). So it MUST be the ampo...and yet it can't be the amp. Arcam said it was OK apart from a knob that they replaced ... all for £150.I have tested the speaker cables for continuity. They are OKI have replaced the high quality interconnects.I have a mains filter. I have tried powering from a different ring mains via an extension lead.(I have just bought soem ferritin things that go around the cables) I have a high quality SB sound card and also a lower quality inbuilt soundcard that luckily has an infrred port (using the latter doesn't solve the problem either!)SOHINT: It seems to trip when there is quite a bit of hummingIf I fiddle with the interconnects and/or the speaker wire then I can get the humming to stop (although it will come back the next day)So because there is hummning then there must be some sort of interferenceAm I right that if there is a lot of humming this can create a DC current and that is what trips the amp? Anyway. What can I do to resolve this apart from moving house and buying a new hi-fi?ANY SUGGESTIONS however stupid will be apprecaited especially if it solves the problem.

 

[The_Lhc]

I have a PC, Musical Fidelity X24 DAC and an arcam 9 pre and power amp with two sets of speakers on the power amp (celestion A and some other brand).

Please be more specific, from what little I can find about the Celestion A-series on the net they appear to be 4 Ohm speakers, the manual I found for the Arcam 9 power amp specifically states that if you're connecting two sets of speakers they MUST be rated between 8 and 16 Ohms, otherwise you're forcing the impedence way below what the amp can handle (if the other speakers are 8 Ohms the combined impedance will be less than 3 Ohms), guess what that'll make it do? Unplug the "other brand" speakers and see how the amp gets on, it'll probably be ok.

 

[smarkgee]

hey! thanks for that. I've cut and pasted the info I have both speakers are 4ohms and the amp seems to be 8ohms per channel.

It doesn't necessarily trip when SP2 is on. I cna have it connected and off and it can trip.

So the speaker ohms has to be lower than the amp ohms?

Should I move the SP2 speaker onto the second AMP's SP2? (I don't use either that much rarely both of these together - like 4 times a year!)

SP1: Celestion Compact A Series 4 ohm

SP2: A KEF SP3235 4Ohm

Second amp SP1 driving: B B&W LM1 8Ohm - don't know what the amp's Ohms are

Second amp SP2: empty

-------------------------------------------------------------------------------------------
Continuous Power Output, per channel

Both channels, 8ohms.....................70 Watts (20Hz-20kHz) Single channel, 8ohms, 1kHz...........85 Watts Single channel, 4ohms, 1kHz...........140 Watts Peak current rating..........................+/-12A

Distortion....................................... 0.02% (8 ohms, 80% rated power, 1kHz)

 

[The_Lhc]

hey! thanks for that. I've cut and pasted the info I have both speakers are 4ohms and the amp seems to be 8ohms per channel.

It doesn't necessarily trip when SP2 is on. I cna have it connected and off and it can trip.

And what happens if you don't have the second pair connected?

So the speaker ohms has to be lower than the amp ohms?

NO, absolutely not, the amp Ohm rating is telling you what impedance of speaker it can handle, you should remain within the boundaries given by the amp, as I said the amps manual clearly states that if you are using both sets of speaker terminals the speakers MUST (MUST, not should!) be between 8 and 16 ohms. Both of your speaker pairs are FOUR ohms, combined that gives an impedance of just TWO ohms, I'm pretty surprised the amp hasn't gone bang in a quite spectacular way.

Your speakers are entirely unsuited to the amp, you should either change the amp to something that can handle that load or change the speakers to ones that are between 8 and 16 Ohms, as the manual requests.

Should I move the SP2 speaker onto the second AMP's SP2? (I don't use either that much rarely both of these together - like 4 times a year!)

SP1: Celestion Compact A Series 4 ohm

SP2: A KEF SP3235 4Ohm

Second amp SP1 driving: B B&W LM1 8Ohm - don't know what the amp's Ohms are

Second amp SP2: empty

What second amp would that be?

 

[MajorFubar]

It's a basic process of ellimination. Try one set of speakers connected via a couple of short lengths of known-good cable and work from there.

 

[smarkgee]

@major - ty for helping. I have spent DAYS trying to eliminate all the various components. so it's something unusual or I've missed something obvious (eg the ohms - which perhaps should be obvious to me!!!!) or done something stupid (oike buying the wrong speakers)

@lhc: If the second pair is NOT conencted it can still trip. on reflection it happens most when i press the sp2 on with a second set connected (but definately NOT always)

I haven't got the money (or a willing wife) to buy more stuff - those glory days are long gone!!. Could I use sp1 and sp2 to bi-wire a single set of 4ohm speakers. Does that affect the calculation? I do really want the arcam to drive that set of speakers if at all poss.

the other amp is a sony ta f211 which i think is also 8 ohm. That was a £50 ebay job

Before I moved to this house (years ago) it was fine ie the arcam+celestion combo NEVER tripped. Today it's fine because it's relatively warm and then i don't get the problem (I never get it in summer).

thanks again guys i seem to be getting further with this forum than several years of trying on my own!!

 

[The_Lhc]

@lhc: If the second pair is NOT conencted it can still trip. on reflection it happens most when i press the sp2 on with a second set connected (but definately NOT always).

I'd guess that amp really doesn't like 4 Ohm speakers then. Either that or there are frequencies where the speakers dip well below 4 Ohms (the impedance quote is only for a given frequency, many speakers will dip well below their quoted impedance at certain frequencies.

I haven't got the money (or a willing wife) to buy more stuff - those glory days are long gone!!. Could I use sp1 and sp2 to bi-wire a single set of 4ohm speakers. Does that affect the calculation?

Probably not, you're then just splitting the two sections of the speakers, both of which are possibly 4Ohms and wiring them in parallel again, ending up with 2 Ohms. Not entirely sure about that though.

Before I moved to this house (years ago) it was fine ie the arcam+celestion combo NEVER tripped. Today it's fine because it's relatively warm and then i don't get the problem (I never get it in summer)

Err, right, not sure why being warm would make a difference, if the amp's overheating I'd have thought that would make it worse, unless there's a component not getting up to operating temperature when it's cold, although I'd be surprised if an ambient temperature change would make that much difference. Does it usually trip from cold? What happens if you leave the amp running for an hour before you play anything through it?

 

[Andrew Everard]

Could I use sp1 and sp2 to bi-wire a single set of 4ohm speakers. Does that affect the calculation?

Probably not, you're then just splitting the two sections of the speakers, both of which are possibly 4Ohms and wiring them in parallel again, ending up with 2 Ohms. Not entirely sure about that though.

No, biwiring using either one or two sets of output terminals won't affect the problem: if the amp runs OK with just the one set of speakers connected to one set of amp outputs, it'll be fine when biwired like this.

But I agree with the impedance problem being the main cause of the tripping, though it sounds like something else is at play, too. The hum should be sortable by re-routing the cables, or changing to some interconnects with better shielding, but the random tripping with only one set of speaker in harness is more confusing if the amps have been checked over by Arcam.

I'm just wondering whether if there are such temperature fluctuations there may be some condensation problems if the amps get really cold, and are allowing some moisture from the air to settle somewhere. Just a thought...

 

[smarkgee]

hmmm...interesting. thank you again guys.

Am i using the bi-wiring term correctly. My speakers do have 4 terminals each. However at present they are bridged by a metal thingy meaning i am only using one set of the terminals each.

what i meant to say was if i have SP1 and SP2 driving only 2 terminals (in total) per speaker then wouldn't that make it series not parallel? (my 'o' level physias was a long time ago)

I have a LOT of cables and wires in my cupboard!! (mostly pc network cables )

my interconencts are good quality. they weren't cheap at the time. i'm not sure if they are shielded though. cambridge audio yellow plastic sheethed. Is there any TEMPORARY way that I can see if shielding is a cause? eg covering in tin foil. ie the question is what will provide an effective temporary shield

When I turn the amp on first thing in the morning in winter it is immediately DEFINATELY at its worst. The humming could be quite loud (alomst a buzzing) and sometimes it will die down within a minute or so to a lower level of humming (as it is now!).

Condensation: I don't think that is an issue.

 

[eggontoast]

It sounds like you have a dodgy connection somewhere, if you have varying degrees of hum by moving the cables around it would suggest a broken earth somewhere. It might be at the source end and nothing to do with the power amps and every now and again it's going unstable and oscillating, hence the amp trips out. Is your preamp an alpha 9C of just an alpha 9 that your using as a preamp ? Can you try a different source ?

EDIT

what i meant to say was if i have SP1 and SP2 driving only 2 terminals (in total) per speaker then wouldn't that make it series not parallel? (my 'o' level physias was a long time ago)

If you remove the jumpers from your speakers, connect two runs of wires to each speaker from SP1 & SP2 you effectively just move the jumpers from the speakers to the amplifier, same load.

 

[Andrew Everard]

Am i using the bi-wiring term correctly. My speakers do have 4 terminals each. However at present they are bridged by a metal thingy meaning i am only using one set of the terminals each.

what i meant to say was if i have SP1 and SP2 driving only 2 terminals (in total) per speaker then wouldn't that make it series not parallel? (my 'o' level physias was a long time ago)

Yes, you're using the term correctly, but there's no point in using both sets of terminals on the amp commoned into one set of terminals on the speaker: the only possible advantage may be found by removing the linking bars on the speakers, and running separate cables from the amp terminals to the treble and bass connections on the speakers.

Worth a try, but it won't change the fundamental problems here.

And as far as the condensation thing is concerned, I wasn't suggesting water settling such that you could see/feel it – if something is amiss, either in a cable or inside one of the amps, it would only take a small amount of atmospheric moisture to compund the problem. As I said, bit of a long-shot...

 

[smarkgee]

It sounds like you have a dodgy connection somewhere, if you have varying degrees of hum by moving the cables around it would suggest a broken earth somewhere. It might be at the source end and nothing to do with the power amps and every now and again it's going unstable and oscillating, hence the amp trips out. Is your preamp an alpha 9C of just an alpha 9 that your using as a preamp ? Can you try a different source ?

EDIT

what i meant to say was if i have SP1 and SP2 driving only 2 terminals (in total) per speaker then wouldn't that make it series not parallel? (my 'o' level physias was a long time ago)

If you remove the jumpers from your speakers, connect two runs of wires to each speaker from SP1 & SP2 you effectively just move the jumpers from the speakers to the amplifier, same load.

thank you. it is a pre-amp, proper. so i think the 9c

i'm saying leave the jumper connected but on the amp side have sp1 and sp2 driving it...wouldn't that half (double?) the effective ohmage?

it's hard to find a 'true' different source, the musical fidelity x24 dac is the analog source - which at one stage i thought was the problem. if i turn that off the hum goes...but then it would wouldnt is at that is the source .

 

[eggontoast]

thank you. it is a pre-amp, proper. so i think the 9c

i'm saying leave the jumper connected but on the amp side have sp1 and sp2 driving it...wouldn't that half (double?) the effective ohmage?

Sorry you've lost me there, if you leave the jumpers on the speakers the load will never change.

it's hard to find a 'true' different source, the musical fidelity x24 dac is the analog source - which at one stage i thought was the problem. if i turn that off the hum goes...but then it would wouldnt is at that is the source .

Not over familiar with the X-DAC are you feeding it from coax, optical, USB ?

I think the problem is emanating from this though, if your getting hum with it switched on there is either a fault with it or you are getting a ground loop from the PSU. Does this use a double insulated external power supply ?

It would be handy if you could just run an ipod into you gear via a 3.5mm to RCA lead with the X-DAC disconnected from the amp, if you get no tripping out or hum you know where the problem lies.

 

[smarkgee]

[/quote]Not over familiar with the X-DAC are you feeding it from coax, optical, USB ?

I think the problem is emanating from this though, if your getting hum with it switched on there is either a fault with it or you are getting a ground loop from the PSU. Does this use a double insulated external power supply ?

It would be handy if you could just run an ipod into you gear via a 3.5mm to RCA lead with the X-DAC disconnected from the amp, if you get no tripping out or hum you know where the problem lies.

[/quote]

EUREKA - that's it. I'm extremely happy.

Did as suggested no hiss no hum.

the x-dac is on all the time even at night - so i don't know if this is the trip problem. still could be i suppose.

it's the original power supply - nothing fancy but the dac was not cheap so i imagine it ought to be OK?

what should i do - i can run to buying a new PSU if necessary (remember it is on a extension lead that has some sort of line / noise filter in it so not sure if necessary) ideally i don't want to have to buy a new DAC!.

cable: this could be a prob too. I did used to originally have a camb audio coax cable - coax means the core is shielded right? (prob not!!). but i stopped using it for some reason (I still have it i think). I just use a regular interconnect now (obviously just one of the 'strands').

 

[eggontoast]

Easy tiger, not quite there yet. What happens if you plug the dac into the amp and disconnect the coax input, do you get any hum/hiss ?

It's not going to be the power supply unit for the dac as they are just AC supplies (transformer only). It could be a fault with the internal power supply (dried out caps if its permanently on) or an earth loop from the PC since you are using a coax input (disconnecting as suggested above will tell you this) can you try an optical input too ? Also get a proper coax cable.

 

[smarkgee]

Ah sy the co-ax thing was a red herring. the coax is an input to the dac... i used to use that with from a cd player tot he DAC years ago.

the x24 only has one analog output which takes the standard interconnects. which is the one i have to use. only other outputs are digital

i currently have spdif input to the dac and a toslink input to the DAC swithing between the two makes no difference. Each are from a different card on the PC.

i have and use a soundblaster 2 audigy zs with the external bay...but that only has a headphone analog output.

so the DAC is the only place i can get the analog signal from (other than the jacks on the soundblaster PCI card itself)

so it looks like internal PSU on the DAC then?

 

[eggontoast]

I've just re-read some of your posts. If there was a fault with the PSU on the DAC the hum would not vary by moving the cables, it would be constant.

Since you are only using an optical input it narrows down the problem. You need to find out what the source of interference is. Get the DAC away from any power supply bricks, transformer etc, pull it right out from your equipment if need be. Move it around and the analogue output wire until you can find where it is picking the interference from.

 

[smarkgee]

Right i've experimented some more with this.

I've got a lump of roof lead and stuck it next to my DAC (isolated it by so doing) and changed an inerconnect that may have been a contributing factor.

Obviously a lump of lead is going to stop nuclear radiation as well as electrical interference. I've only got so much lead tho!!

For the purposes of testing further; what can i (for example) wrap cables in to stop interference. eg could i run them through a bit of copper tubing or wrap some kitchen tin foil around them?

I've now also noticed some highish volume distortion with video-audio playback, which may or may not be related.

It keeps pointing back to the DAC. But I don't want to fork our >>£100 to get something serviced if it ain't broke.

any more suggestions from you knowledgeable lot gratefully appreciated!