Hi,
Please tell me I'm wrong, I'm beginning to think this is the Elephant that we dare not speak of with Class-D.
Having just bought a cheap ebay TDA7492 Class-D pre-built board, it
HISSSSSSSSES.
I've read the design guides, the weighty dos and do nots and they all say that this is POOR layout, switching radiation finding it's way into the input, bad decoupling of the rail and this can be dealt with.
But I'm not so sure, it seems every cheap Tripath amps, hissss, every cheap PC speaker hisses. Trevor in his design guide to improve the "Sure Electronics" amp on this very forum said "I stuck my earlobe in the speaker cone and could barely detect the hissss".
I'm NOT at all keen on this 'pink noise' generator aspect, coming from the world of warm FETs at dawn, it seems like a very good idea to save power, but I don't want to know the amplifier is powered on, unless there's a bulb alight telling me.
So, can anyone reassure me, and point me to a ready-made Class-D board ideally, that is genuinely properly silent. 🙂
Cheers,
E.T.
Please tell me I'm wrong, I'm beginning to think this is the Elephant that we dare not speak of with Class-D.
Having just bought a cheap ebay TDA7492 Class-D pre-built board, it
HISSSSSSSSES.
I've read the design guides, the weighty dos and do nots and they all say that this is POOR layout, switching radiation finding it's way into the input, bad decoupling of the rail and this can be dealt with.
But I'm not so sure, it seems every cheap Tripath amps, hissss, every cheap PC speaker hisses. Trevor in his design guide to improve the "Sure Electronics" amp on this very forum said "I stuck my earlobe in the speaker cone and could barely detect the hissss".
I'm NOT at all keen on this 'pink noise' generator aspect, coming from the world of warm FETs at dawn, it seems like a very good idea to save power, but I don't want to know the amplifier is powered on, unless there's a bulb alight telling me.
So, can anyone reassure me, and point me to a ready-made Class-D board ideally, that is genuinely properly silent. 🙂
Cheers,
E.T.
Entirely different price class, but my Hypex NC400's are totally silent. Just showing that class D as such isn't noisy - it is always the implementation.
Are there poweramplifiers, that do not mute input when there isn't any signal, that do not have noise from speaker with ear in speakercone ? I haven´t owned one
Hi Julf,
Well, that is reassuring. Thanks for the rapid response.
I'm still coming to terms with 300Khz of shash on the output and 200mV of 2MHz on the supply rail of this 'design'.
ET.
Well, that is reassuring. Thanks for the rapid response.
I'm still coming to terms with 300Khz of shash on the output and 200mV of 2MHz on the supply rail of this 'design'.
ET.
I meant output btw, some switch off output with relais for example when no signal comes in, no hiss then ...
Trevor was quoted saying, ear in cone, there is little hiss, which was taken as example classD has hiss. ClassA and AB have hiss too, or just all I owned and heard did.
Trevor was quoted saying, ear in cone, there is little hiss, which was taken as example classD has hiss. ClassA and AB have hiss too, or just all I owned and heard did.
Keyword here is "cheap". They are cheap for a reason. You want quality. Pay for it.
A guy I knew put his **** in the vacuum cleaner hose. His wife had to come turn it off, he was insensible with pain. So I guess ear-in-the-speakercone is not that obscure a form of masochism.
This hisssssssss I can hear 1 metre away, I don't have to have my "ear in the cone", Baby !!
irribeo: - Good point about the Mute function. I not sure if this thing is muting, other than on power up. Might be an option, a kind of VOX (Voice Activated Switch) circuit, might be an idea, I'll play with that.
re. RF Shash. @ HF - I hadn't expected to have to bolt this thing down in a metal box with through-line power RF filters to ensure it doesn't wipe out BBC Radio 4 Long Wave ....or Hilversum, ....ahhh that dates me.
I hoped to run this in "bridge-mode" ie, use both amps in the stereo chip to feed a single speaker, and feed the input(s) from a balanced line. The idea is to create an active speaker, by placing this Class-D amp inside an old mediocre (not that cheap, please) bookshelf speaker cabinet, physically where the 4mm speaker terminals are currently on a plastic panel.
You'll love this for 'cheap' - I was thinking, maybe use Cat5 (100baset) LAN cable and an RJ45 as the way to connect to it, one twisted pair (110 Ohms) as the audio and the remaining 2 or 3 pairs for the dc supply kinda like simple (mode-1 ?) POE (Power Over Ethernet). I thought feed the cable from a 600 Ohm audio transformer (Unbal-bal) at line level 775mV. I can see now, that to make that work the dc is going to need severe decoupling and filtering at the amp.
I have reduced the internal gain on the TDA7492 to the minimum of 20dB using the gain setting pins, didn't help with the hissssssss.
Any other "no-hiss" good experiences with Class-D designs off-the-shelf ?
ET.
irribeo: - Good point about the Mute function. I not sure if this thing is muting, other than on power up. Might be an option, a kind of VOX (Voice Activated Switch) circuit, might be an idea, I'll play with that.
re. RF Shash. @ HF - I hadn't expected to have to bolt this thing down in a metal box with through-line power RF filters to ensure it doesn't wipe out BBC Radio 4 Long Wave ....or Hilversum, ....ahhh that dates me.
I hoped to run this in "bridge-mode" ie, use both amps in the stereo chip to feed a single speaker, and feed the input(s) from a balanced line. The idea is to create an active speaker, by placing this Class-D amp inside an old mediocre (not that cheap, please) bookshelf speaker cabinet, physically where the 4mm speaker terminals are currently on a plastic panel.
You'll love this for 'cheap' - I was thinking, maybe use Cat5 (100baset) LAN cable and an RJ45 as the way to connect to it, one twisted pair (110 Ohms) as the audio and the remaining 2 or 3 pairs for the dc supply kinda like simple (mode-1 ?) POE (Power Over Ethernet). I thought feed the cable from a 600 Ohm audio transformer (Unbal-bal) at line level 775mV. I can see now, that to make that work the dc is going to need severe decoupling and filtering at the amp.
I have reduced the internal gain on the TDA7492 to the minimum of 20dB using the gain setting pins, didn't help with the hissssssss.
Any other "no-hiss" good experiences with Class-D designs off-the-shelf ?
ET.
What loudspeakers are you using? If they are high sensitivity, sometimes you really do need to design the system carefully.
Been there, done that, back in the 1990s. With 24AWG cable and three pairs for power you can go quite a few (ten or more) metres, depending on the voltage you run (I used +/-24V) and the speaker impedance. 24AWG runs 84mohm/metre so with 3 pairs that's 28mohm/m. From memory, for a 100W active speaker I think I had 4700uF between the rails in each speaker.
I have a range of different class D amplifers from the cheapest of the cheap, to some OK quality - the background noise varies between them all.
Also the gain has an effect - some boards implemented with low gain, some with high gain.
Some I can use on my active system (103 & 98 dB sensitive drivers), some I can't.
The quieter ones - Hifimediy T2 (tk2050), TPA3116
medium : Connex TA3020 chipset, tweaked Lepai
noisier: irs2092 L20D (though still fine with passive crossover system & 94dB sensitive)
etc
..this is just from memory.
Also the gain has an effect - some boards implemented with low gain, some with high gain.
Some I can use on my active system (103 & 98 dB sensitive drivers), some I can't.
The quieter ones - Hifimediy T2 (tk2050), TPA3116
medium : Connex TA3020 chipset, tweaked Lepai
noisier: irs2092 L20D (though still fine with passive crossover system & 94dB sensitive)
etc
..this is just from memory.
No need for the transformer. A differential balanced input doesn't care if the source is balanced or not - all it cares about is the voltage difference between the inverting and non-inverting input.
There is no elephant in my room. My class d audio cda 258 is dead quiet. My system is on 15 hours a day and the amp handles it easily. Performs far above the $300 price. Now I just need to get it into a case of some kind........
Erm:
"a cheap ebay TDA7492 Class-D pre-built board"
Pretty well sums it all up neatly 😉
Buy cheap.. buy twice, or even worse: repeatedly
"a cheap ebay TDA7492 Class-D pre-built board"
Pretty well sums it all up neatly 😉
Buy cheap.. buy twice, or even worse: repeatedly
Thanks everyone..
Hi Everyone,
Thanks for the feedback (ho ho), I may jump ship to Class-A/B chip amps.; this project is not about ultimate fidelity, or as my colleague refers to it "damped miniature leaf-springs widening the sound stage". It's merely an attempt to re-use some speakers intelligently.
I'll order up a selection of ready-made Chinese boards, compare them, double check my PSUs, decoupling, mute etc.. and report back. The hissssss must be defeated !
Cheers,
ET.
Hi Everyone,
Thanks for the feedback (ho ho), I may jump ship to Class-A/B chip amps.; this project is not about ultimate fidelity, or as my colleague refers to it "damped miniature leaf-springs widening the sound stage". It's merely an attempt to re-use some speakers intelligently.
I'll order up a selection of ready-made Chinese boards, compare them, double check my PSUs, decoupling, mute etc.. and report back. The hissssss must be defeated !
Cheers,
ET.
You can start with like 5cm twisted inputwire and see if it still hisses when connected to a source or preamp
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