[walkern]

I've got my Class D amp powered by an SMPS, and there is no hum (that I can hear) generated by that.  I don't remember the model number (I think maybe 500R?), or much in the way of details about it (I ordered it from somewhere in Europe I think, quite a while back), but it was easy to install and hook up.  Maybe that would solve your issue?

[steve k]

Do you have any fluorescent lights nearby? Sometimes when the ballast goes bad, the ballast hums and introduces hum into the circuit. My SDS amps were humming and Tom brought this up as a possibility. I typically don't use my fluorecscent lights while listening to music. About a month later, I have a small flurorescent lit sign over my turntable that started to mum audibily. When I shut it off, the amp hum hasn't been back since. The sign wasn't making any noise shen I talked to Tom but I have to bellieve the ballast was going bad and addiing noise to the amps anyway.

[roscoeiii]

Could also be dc on your line. Some amps and toroids are more sensitive to this than others. Maybe take it to a buddy's place. There are devices that treat this.

[wim1983]

I've got my Class D amp powered by an SMPS, and there is no hum (that I can hear) generated by that.  I don't remember the model number (I think maybe 500R?), or much in the way of details about it (I ordered it from somewhere in Europe I think, quite a while back), but it was easy to install and hook up.  Maybe that would solve your issue?

So my one is linear PSU? How much you bought? Is it this one?
http://connexelectronic.com/product_info.php/products_id/118

[wim1983]

Do you have any fluorescent lights nearby? Sometimes when the ballast goes bad, the ballast hums and introduces hum into the circuit. My SDS amps were humming and Tom brought this up as a possibility. I typically don't use my fluorecscent lights while listening to music. About a month later, I have a small flurorescent lit sign over my turntable that started to mum audibily. When I shut it off, the amp hum hasn't been back since. The sign wasn't making any noise shen I talked to Tom but I have to bellieve the ballast was going bad and addiing noise to the amps anyway.

Yup there is one fluorescent light on the wall, on top of the amp. I'll do some experiment when the hum coming back again, coz I have no idea when it come, it takes a while for the hum to goes away. Thanks!

[wim1983]

Could also be dc on your line. Some amps and toroids are more sensitive to this than others. Maybe take it to a buddy's place. There are devices that treat this.

To me an amp should not be treated like that. It should just work with a simple power chord. To buy other treatment products, I also not sure whether it works, could end in give more problems than solving it.

[srb]

I'll do some experiment when the hum coming back again, coz I have no idea when it come, it takes a while for the hum to goes away. Thanks!

It might also be related to an appliance with a motor that cycles on and off, like a refrigerator or an air conditioner.

Steve

[firedog]

To me an amp should not be treated like that. It should just work with a simple power chord. To buy other treatment products, I also not sure whether it works, could end in give more problems than solving it.

Lots of appliances are known for causing DC offset: computer printers, blow driers, refrigerators, lighting. It can also originate with a neighbor. In the Van Alstine forum there's a thread that discusses it a little bit, since they make a DC Blocker called the "Humdinger".  If you have enough DC offset on the line, lots of well made amps will be susceptible.

[walkern]

So my one is linear PSU? How much you bought? Is it this one?
http://connexelectronic.com/product_info.php/products_id/118

Yep... that's the one.  I don't know which Class D amp module you have, so make sure the  output voltage of that SMPS is correct for your module (I think mine is the SDS 254).  It is adjustable from a low of + or - 24 V (which is too little) up to 72V (which is too much).  I believe I have mine set at + and - 45V.


[/img]

[roscoeiii]

To me an amp should not be treated like that. It should just work with a simple power chord. To buy other treatment products, I also not sure whether it works, could end in give more problems than solving it.

Problem is your power, not the amp. Maybe another household device is putting dc on the line, or it is something from your home's wiring or the power coming into your house. If everything is up to spec, DC should not be on the line.

Have you tried it on other outlets in your house, or at a friend's house?

Also make sure the toroid is sufficiently tightened down.

[wim1983]

Problem is your power, not the amp. Maybe another household device is putting dc on the line, or it is something from your home's wiring or the power coming into your house. If everything is up to spec, DC should not be on the line.

Have you tried it on other outlets in your house, or at a friend's house?

Also make sure the toroid is sufficiently tightened down.

Guess I can live with it. It's not happening so often, very rare, just that someitme pop up disturb my near field critical listening and judgement. Actually is it all Class D Audio power amp using that toroidal transformer? I thought I heard sth like SMPS from Class D Audio Website?

[roscoeiii]

Something like the Humdinger from Van Alstine can fix the problem. If it doesn't work, there is a 30 day return policy.

[wim1983]

Something like the Humdinger from Van Alstine can fix the problem. If it doesn't work, there is a 30 day return policy.

Now that when I complain, the hum problem does not happen again

Guess it's ok now, thanks for you guys, I see that Class D Audio Web site got some revamp, still look no further but Class D Audio power amp, the price just so nice

[.Marcus.]

I want to share a mod which i done recently.

I highly recommend this mod, it's a real improvement in more music details

Technical :
The input stage (balanced line receiver) is supplied by an on-board power supply. This supply is an very basic concept by using and Resistor and Z-Diode to generate +-15V.

Mod :
Replace this R/Z-Diode Supply Stage by an external low noise +-12V or +-15V power supply board. If the ClassDAudio Kit Transformer (Antek) is used than the unused 12V and 18V winding of the transformer could connected to supply the external board, so no extra transformer is required.

Regards
Marcus

[wgscott]

Has anyone changed over from unbalanced to balanced input, and if so, was the improvement audible and significant? Is it just a matter of removing the two jumpers next to the input terminals (and using XLR inputs)?

Also, has anyone directly compared the SDS to Hypex NC-400?   

[.Marcus.]

Has anyone changed over from unbalanced to balanced input, and if so, was the improvement audible and significant? Is it just a matter of removing the two jumpers next to the input terminals (and using XLR inputs)?

Well, i had changed from unbalanced to balanced.. but i my case i also changed some other things, so it is not meaningful.
The input Stage of the SDS Board (THAT1200, Balanced Line Receiver) will do a nice job with balanced and unbalanced input signals. So it depends mainly on your source. As first approximation i would chose the connection depend on your source build, is it balanced or not, to eliminate additional converting.

May be you are interessted to do some mod's. I do a lot of mod's on the SDS Boards, here is my list starting with most audible mod :

1. Replace R/C Power supply of input stage by external low noise power supply !
2. Replace couple capacitor between Input Stage and IRS2092 by Audio Caps (Elna Silmic II)
3. Replace Bootstrap Capacitor of THAT1200 by Audio Caps (Elna Silmic II)
3. Upgrade all on-board supply capacitors by Low ESR Types with higher capacitor values (Panasonic FC /FR)
3. Replace all Resistors in Signal Path (4x 100 Ohm / 2x 3.3KOhm) by high graded resistors (Texas Components ASM2575)

(Yes 3x position 3 )

Also, has anyone directly compared the SDS to Hypex NC-400?

There are some people who comared both, most say NCore is better.. i brood over buying ncore's for a year now, but I'm actual very impressed by my SDS254 include all the mod's so ..

But I'm also interested about reports / reviews about comparing both systems directly..

[.Marcus.]

Bellow a picture of my latest setup with external Power Supply, additional Transformer and motorized ALPS Pot as Volume Control :
I highly recommend an external Power Supply, it's not that much difficult to implement. I could never live without again 

[matt_garman]

Looks awesome, Marcus, thanks for posting!  Kinda makes me wish I hadn't sold my ClassDAudio amps! 

[.Marcus.]

Looks awesome, Marcus, thanks for posting!  Kinda makes me wish I hadn't sold my ClassDAudio amps! 

Why do you sold the ClassDAudio Amps ? What's your actual amps ?

[matt_garman]

Why do you sold the ClassDAudio Amps ? What's your actual amps ?

I had two SDS-470 amps, one was a DIY job that I put together myself, and the other was purchased finished from ClassDAudio.

I only needed one.  I got the pre-made one so I could have a known good/working one while I tinkered with the DIY one.  But eventually my DIY one reached a good working state (where I wasn't compelled to constantly tweak it), so I sold the pre-made one.  (Note: I never did anything nearly as fancy as what you've done, as at this time, I was literally just getting started with DIY.)

Later, I started building amps based on the tpa311x chip.  While my SDS-470 was working just fine, I built a dual-mono tpa3116 amp that was smaller, lighter, and more energy efficient than the SDS-470 (see here for pics).  I didn't really do any extensive A-B testing for sound quality, but with a quick check, I didn't hear any obvious downgrade.  This was for my living room, and by this time, I wasn't really doing any "serious" listening on this rig anyway.

A little more rambling info: I believe the SDS-470 is ClassDAudio's most powerful amp, and in hindsight, I realize it was ridiculous overkill for my needs.  There was a thread on AVS Forums talking about using super high power pro power amps for improved sound quality, and I jumped on the bandwagon with a QSC RMX2450, in all its big, heavy and power-hungry glory.  Then I read about class d amps (in general, not ClassDAudio specifically), and how they were far more energy efficient.  That plus this thread right here, led me to ClassDAudio.  At that time I still thought I needed ludicrous wattage, so that's why I bought the SDS-470.

I tried to cram my DIY SDS-470 into a case that was just big enough for the amp board plus a Connex SMPS800R power supply.  I think there are pictures buried in this thread somewhere.  But that caused me to run into overheating issues.  Eventually, Tom (at ClassDAudio) gave me a new revision of the SDS-470 board with a bigger, fancier heatsink, and I moved everything in a larger enclosure with better ventilation.  That cured the heating issues.

But then I became so enamored with the tpa311x amps that I felt compelled to build one to replace the SDS-470, mainly for size and power-efficiency reasons.

So, in short, I really only sold them due to "new toy syndrome".  I wish I realized back when I first got into those ClassDAudio amps that I didn't need so much power, and probably would have been better served with something like an SDS-254.  Lower power means less heat and less wasted electricity.

Having said all that, I'm tempted to build another irs2092-based amp using the LMJ boards (example: L15D), as these are cheaper than the ClassDAudio boards ($80 for a mono pair on ebay) and have a good reputation on diyaudio.