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Old 4th October 2004, 12:19 AM   #11
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It's an interesting thought... I will build some cables tomorrow with the ground disconnected and see which is best (easier than disconnecting the ground on the amp now it's all soldered up)

I thought a ground loop was usually something which would pickup the 50Hz mains hum though?
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Old 4th October 2004, 12:21 AM   #12
mattjk is offline mattjk  United States
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yes, usually hum, but that is the biggest difference in our two amps that I can see.

P.S. I like the case you used for you amp. Very nice. Do they make them in custom sizes? I need it in Inches.
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Old 4th October 2004, 12:46 AM   #13
JohnW is online now JohnW  Hong Kong
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With only one channel running (right), then there was only normal background hiss, hardly any high pitched whine, and a tiny bit of "AM tuning" type noise (you know the kind of wheee-awww kind of noise that you get when you tune an am radio). It was just lightly in the background and moving slightly in pitch
It’s really worrying to hear (no pun intended) about “Crackles, Pops, Whines & AM tuning radio type noise”.

Your construction seems very neat, but I would have placed the modules further apart – rather then closer, but this would not explain why a single module still makes noises.

If a single module does it by itself, then it would suggest that the modulator is intermodulation with IT'S SELF! If this is in fact the case, then this is a VERY poor design.

Gut reaction says your always going to have intermodulation issues with multi channel hysteresis type modulators – but that said, UCD owners don’t seem to have an issue.

Do you still hear noises with ONLY one channel operating and its inputs shorted? If so it, really points to internal modulator noise.

I hate to think what affect the RF leakage from a CD / DVD player will have on the sound. The fact that the units have a very “harsh” treble is a SURE sign of High Frequency RF issues.

John
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Old 4th October 2004, 05:31 AM   #14
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Default Uh, huh.......

Just as I suspected. I think John W is on the right track. One midlue making antything other than a very quiet hiss is disheartening.

Jocko
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Old 4th October 2004, 10:36 AM   #15
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Hi, Indeed JohnW might be onto the right idea. But although I haven't tried the modules with the inputs shorted, the noise does go away if I simply unplug the interconnects (as I said in that earlier message).

The noise seems to shift to the other module if there is only one inteconnect on the left channel. Right left hanging

The noise seems to go away on the right channel if I turn off the left channel...

I think this points to some kind of radio RFI interference, and it could well be picking up something nearby. I have a computer, TV, mains filter, 802.11a network and all kinds of nasty stuff within a couple of meters. However, quick tests of turning off most of it and moving the amp around have not shown it to be related to that. I have noted a slight tendency for the noise to change freq if I tilt the whole amplifier at an angle though (lift up one side)

Any thoughts on tracking this down would be appreciated. What order of tests should I try now:

- grounding on the input lines?
- Adding in the LCAudio amp clock module to bring the modulator up to 1Mhz?
- different modules in the amp...

Thanks

P.S. To anyone thinking of copying the layout shown in the photo... Be careful there is not enough cooling in this case if you just strap the module to the steel cooling area at the base of the case. I guess the heat does not run far enough away from the modules and the case above and below the modules gets hot enough to burn you... I will have to add an aluminium plate to it today...
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Old 4th October 2004, 10:42 AM   #16
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You input wires are very close to the output filter AND they are not shieled either. Try to separate input and out and also to twist the output cables in order to minimize the "antenna".

BTW: Steel is not a good heat conductor...
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Old 4th October 2004, 10:45 AM   #17
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Doesn't the level of noise induced follow an inverse square law rule? Distance is key.
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Old 4th October 2004, 11:13 AM   #18
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Hmm, interesting discovery. When I was testing it before I had it plugged into the wall socket directly. Since building it in its box I had it plugged into one of these Kemp mains filters:
http://www.hificollective.co.uk/acce...er_source.html

Unplugging it from the Kemp unit and plugging it back into the wall gets rid of the high pitched whine! Just the normal hiss remains and the crackle goes back to being the usual soft hiss that an amp seems to make at idle.

However, curiously if I bring the mains cable anywhere near the mains conditioner, or inline with the middle of it's axis even quite far away, then the whine comes back. (ie the conditioner is standing upright and if the cable is on the floor it can be quite close, but as soon as I raise the cable near the center of the conditioner then it makes the whine no matter how close it is....

I had assumed that this conditioner was a decent transformer device (looking at the size of it), but clearly something is causing it to act as a radio transmitter that the Zappulse power supply is picking up. I have a Schnaffer medical mains filter fitted (on advice from Lars), but I notice that some people like Bruno Putz dont agree with these things, could there be any interaction there...?

So we seem to have cleared the Zappulse from being the culprit in this case (which is great). However, I wonder if someone can advise me how to adjust my powersupply to be immune to this kind of radiated junk? Is it going to be earth pollution causing this problem?
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Old 4th October 2004, 12:00 PM   #19
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However, curiously if I bring the mains cable anywhere near the mains conditioner, or inline with the middle of it's axis even quite far away, then the whine comes back. (ie the conditioner is standing upright and if the cable is on the floor it can be quite close, but as soon as I raise the cable near the center of the conditioner then it makes the whine no matter how close it is....
As far as I understand this mains conditioner is fully passive. In this case there must be something external causing a stray-field from this mains conditioner. Is there anything else plugged into it when the whininh happens ?

BUT if this mains conditioner isn't working passively at all (i.e. like some UPS do by the use of another class-d amp !) then it's RF hash might INTERFERE with the ZAP amp's own carrier frequency.
Have you got a scope that you could use to check for any RF stray-field from the conditioner by using a pickup-coil ?

The main reason why Bruno P dislikes those RF filters is their caps connected to mains ground.

Apart from Peranders' suggestion of using shielded input cable there are other possibilities to reduce internally generated EMC problems. The modules offer the possibility of synchronisation. They also feature symmetric inputs AFAIK.
Make use of these intrinsic features !

Regards

Charles
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Old 4th October 2004, 01:48 PM   #20
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Hi Phase_accurate. Thanks for the suggestions

As you can see from the pictures I am using a balanced input already, and although it's not clear, and they are too close to the output coil, the input cables are actually braided

The mains conditioner is an unknown, but I would have *assumed* that it was just a large 1:1 transformer? It's very heavy and quite chunky, which tends to confirm this...? I wonder if because I have tilted the thing so it stands up, the center of the transformer is now firing out into the room. Is there likely to be a ton of magnetic/rf junk on the center line of a big tranny? (going out quite far away from the tranny?)

I unplugged everything else from the conditioner during testing, except the preamp (Meridian 502, decent commercial design). Still the whine persists.

Even now with the conditioner just sitting there, bringing the mains cable for the digital amp, either inline with the middle of the conditioner, or very close at the edges, causes the whine to restart. Waving the mains cable around makes a noise like tuning an AM radio (as the cable passes near the conditioner).

Curious...
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