Class T(ea) with AMP-3

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When using the 41Hz AMP-3 I get a strange whistling noise (like the sound of a kettle boiling) on at least one track of a CD. The CD in question is 'Natural Light' by Eric Bibb and the whistling is most obvious on track 1.

What is this and the whistling down to the amp, the CD, or both? I didn't notice it with the other class-T amps that I ahve here. :xeye:
 

t.

Member
Joined 2003
Hi NUUK

I sometimes get a high pitched whistle with my Amp3
It seems to be when I use either of my NOS dacs most noticeable if theres no cd in the transport or when I'm loading a disc, its only faint but there is a high pitched noise, I've also noticed a few strange whistling noises on HDCD recorded discs:confused:

Leo
 
Nuuk said:
When using the 41Hz AMP-3 I get a strange whistling noise (like the sound of a kettle boiling) on at least one track of a CD. The CD in question is 'Natural Light' by Eric Bibb and the whistling is most obvious on track 1.

What is this and the whistling down to the amp, the CD, or both? I didn't notice it with the other class-T amps that I ahve here. :xeye:
Hi,

I'm not sure if an experience I previously had could be signifiant here, but just in case. A guy at work have a Maranz reveiver and he had some problem with a particulra CD of Nora Jone. At some specific place of the songs, the amp was delivering a suspect noise. I can't tell you exactly how it sounded as I never visited this person. Anyway, he ask me to listen to the CD to see if the CD was bad and I had no such problem. So, he went to his Hi-Fi store and they finally found that the amp was not able to take the load during the "peak" of this CD. I suppose that the CD was recorded to hight as the music was very soft.

Maybe you have some similar problem with the amp3. You have to listen to many CD and see if it always happen and when it happen.

Regards,
 

t.

Member
Joined 2003
Nuuk said:


Hi Leo, I was just going to email you! OK, so I am not alone here!

Now we need to know if anybody else has experienced 'the whistle'! :att'n:

Well I've mailed you anyway:D

The sound of the actual music seems fine and the whistle seems its nothing to do with the actual recording, its like that feeling you get when a tv is on if you know what I mean
Strange:confused:
 
Years ago, when I was contemplating buying my first CD player, almost all the players I heard demonstrated produced a sound similar to a TV line whistle.
None of the dealers I asked about it claimed to be able to hear it, but it was quite audible to me, and made the music almost unlistenable, and put me off CDs for some time. Eventually I decided I'd have to put up with it in order to listen to any newly released music.
These days I don't hear it any more, whether from a good or a bad player, so either I've become 'immune' to it or (more likely) my old ears don't go that high any more.
 
I'm betting it also sounds like a cheap AM radio does when you're tuning stations on it.

http://dictionary.reference.com/search?q=heterodyne

Those difference signals, are your whistle.

Distance and shielding between modules is a good help. Are your modules right next to each other? I don't even know if they're both built on the same PCB so forgive the ignorance.

Is there any kind of low pass on the inputs already?

You could also take measures to attempt to lower the modules EMI, I assume there's some sort of heatsink on it, is it bypassed to ground?

Regards
 

t.

Member
Joined 2003
dnsey said:
Years ago, when I was contemplating buying my first CD player, almost all the players I heard demonstrated produced a sound similar to a TV line whistle.
None of the dealers I asked about it claimed to be able to hear it, but it was quite audible to me, and made the music almost unlistenable, and put me off CDs for some time. Eventually I decided I'd have to put up with it in order to listen to any newly released music.
These days I don't hear it any more, whether from a good or a bad player, so either I've become 'immune' to it or (more likely) my old ears don't go that high any more.

Well I've always had very good hearing:)
Mine is doing similar to NUUK though in that its only noticeable on a few cd's at certain parts of a track and normally if there is no cd in the transport
 
classd4sure said:
I'm betting it also sounds like a cheap AM radio does when you're tuning stations on it.

http://dictionary.reference.com/search?q=heterodyne

Those difference signals, are your whistle.

Distance and shielding between modules is a good help. Are your modules right next to each other? I don't even know if they're both built on the same PCB so forgive the ignorance.

Is there any kind of low pass on the inputs already?

You could also take measures to attempt to lower the modules EMI, I assume there's some sort of heatsink on it, is it bypassed to ground?

Regards

Thank you for the link:)
We both use an amp based on the TA2021 so its stereo on a single chip, my psu is in a seperate case.
There is a 100pf cap on the input and ground which I presume is used for the filtering.
It seems strange that its only mainly noticeable on some cd tracks
 
Hi,

Wow, just had a look at what you're dealing with.

I don't think there's anything you can do aside from live with it or get rid of it.

I can't help but wonder how it would work if one of the channels was routed to the other side of the board with a ground plane in between...

I don't believe tripath's CLASS D (snicker) amps are clocked, they're self oscillating from what I know. That means there's bound to be some level of frequency modulation. With two stereo channels side by side like that.... you will get a heterodyne effect as they'll have a different frequency modulation at any given time while working with different signals. I'm sure they correct for frequency modulation, but when is anything ever perfect? So this makes "only certain parts of certains songs/certain CD's" pretty believable to me at least.

You see why it's only a 25W chip.

All I can think of, but it seems overlycomplex for what it's worth, you'd have to force both modulators to switch at the same time by mixing both inputs with the same clock signal.

PS: Maybe higher quality bypass caps would make a difference? If you can find such a thing.
 
Well AFAIK, there are quite a few of these amps in use around the world so it would be strange indeed if Leo and I are the only ones experiencing the whistle! I would still like to herar if anybody else with an AMP-3 (or other class-T amp) has heard it.

Fortunately, I don't have to live with it! ;)
 
I must admit these amps do sound very good for such a compact unit.
The sound is different to my other amps, if its better than my tube amp is hard to say but it is good for sure:)

I think the noise I get when no cd's are in the transport is something to do with the CS8412's in both my dacs or possibly my transport:confused:
I've never noticed it on my other amps though.

NUUK, just out of interest is your Eric Bibb cd HDCD, the ones where I noticed the whistle on some tracks have HDCD stamped on the cover, strange really because both my dacs are not HDCD compatible so its probably nothing to do with it
 
Ex-Moderator
Joined 2005
Nuuk, do you get the whistling sound at all volume levels or only certain volume levels? and do you still hear the sound if only one channel is driven? from what you've said so far it seems like it has to be the program material on the couple of tracks that you mentioned that is causing the amp to produce an undesirable output.
 
NUUK, just out of interest is your Eric Bibb cd HDCD,

No it's not Leo.

Nuuk, do you get the whistling sound at all volume levels or only certain volume levels?

At all volume levels but the level of whistle seems to be constant, ie independent of the volume control setting.

and do you still hear the sound if only one channel is driven?

Well I removed one lead from the DAC and left only the left channel connected (that's the side I notice the whistling most) but I got nothing at all. It seems the DAC only works with both leads connected!

I'll play around tomorrow some more when I am not so tired. I'll also try the other class-T amps with that particular track (Too much stuff).

I should add in fairness that the AMP-3 sounds very good! :)
 
Hi guys,

I think it might be worth experimenting with bypass caps, if you find ones with lower ESR and better all around, mounted right over the pins if you have to, it might lower EMI just enough to keep the heterodyning down.

I think with only one channel going it will still whistle, unless you can actually disable/mute just the one channel.. doesn't look like it has that ability though. The other channel will still be oscillating, only at a more less constant frequency since it's not modulating anything.

I'd let the guys at 41hz know about it... maybe they'll rework the PCB or have some other tips for you to try?

Best of luck with it,
Chris
 
Hi guys,
I know what I've experienced with SI t-amp is not the same but it may have some bearing - when I substituted input section of t-amp (consisting of res & cap to ground & inductor & cap in series) with just 2.2uF cap in series, I noticed the mid range lost some life & sparkle. I tried on 2 different t-amps with the same result. When 2.2uF cap just substitued t-amps 0.3uF cap with all other input components in circuit life & sparkle restored.

I surmissed this might have to do with high freq signals on input section coming from t-amp??

Could this have any relevance?

John
 
classd4sure said:
Hi guys,

I think it might be worth experimenting with bypass caps, if you find ones with lower ESR and better all around, mounted right over the pins if you have to, it might lower EMI just enough to keep the heterodyning down.

I think with only one channel going it will still whistle, unless you can actually disable/mute just the one channel.. doesn't look like it has that ability though. The other channel will still be oscillating, only at a more less constant frequency since it's not modulating anything.

I'd let the guys at 41hz know about it... maybe they'll rework the PCB or have some other tips for you to try?

Best of luck with it,
Chris

Hi Chris,

I use 680uf Blackgate NX type cap on each of the voltage decoupling which are a couple of mm from the chips pins so there is a pair of these on the pcb.
The pcb of the Amp3 is tiny but I can't see any bypass caps on the main supply lines for the chip
 
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