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Is buying these Sure Class D boards a bad idea?

andreasmaaan

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#1
I'm designing a budget 3-way active system for the living room atm as we've been surviving off a €100 Creative 2.1 satellite system since early this year. The system is mostly made up of odds and ends that I've had sitting around for a while, but the one aspect that I haven't got sorted is the amplifiers.

I need 6 channels in total, with at least 50 clean watts into 4 Ohm per channel for the bass drivers, and a little less than that for the mids and tweeters. I don't want to spend more than around 200€ on amplification (including power supply).

These new-ish Sure Class D boards seem to fit the bill.

However, the datasheet looks very suspect to me. Words like "typical" in front of the measurements, discrepancies between the claimed specs and the graphs, and disclaimers like "subject to change without notice"... Also, although distortion and noise measurements are excellent for a €33 board, the frequency response is pretty wonky (not a problem in itself as the system will be EQ'd with DSP, but... concerning).

Looking at the information that's available, can anyone tell me if buying these would be an unwise decision? Or perhaps someone could recommend some better alternatives?

Help much appreciated :)
 

restorer-john

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#2
The rated A-weighted, shorted input, residual noise is a huge 270uV.

Consider decent power amplifiers have numbers of 25-35uV. And D/A converters have residuals down to a few uV.

You will hear hiss/noise from the speaker drivers IMO.

I'll look into some options for you. You want to build yes?
 
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andreasmaaan

andreasmaaan

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Thread Starter #3
The rated A-weighted, shorted input, residual noise is a huge 270uV.

Consider decent power amplifiers have numbers of 25-35uV. And D/A converters have residuals down to a few uV.

You will hear hiss/noise from the speaker drivers IMO.

I'll look into some options for you. You want to build yes?
Good to know, thanks :) Had overlooked that spec. None of these drivers are more sensitive than about 90dB, but the high noise level is just another thing about these boards that looks a little suspect.

Tbh, I'd rather avoid soldering together an entire board as I have a lot on my plate atm and am not a skilled solderer. So I'm keeping it to pre-assembled boards (but would be fine to solder on connectors and put in a case etc).

I also considered Hypex UCD36 since it's a cheap pre-assembled 6-channel unit with on-board power supply from a trustworthy manufacturer, but it's not quite powerful enough and the measurements are just so-so. Also it's apparently just gone out of production which gives me pause.
 
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amirm

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#4
Specs are not good as John mentioned but I am impressed with the measurements provided. The fan is problematic too. Amazing what you can get for $35 though.
 
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andreasmaaan

andreasmaaan

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Thread Starter #5
Specs are not good as John mentioned but I am impressed with the measurements provided. The fan is problematic too. Amazing what you can get for $35 though.
Yeh the fan is another reason not to get these!

@restorer-john and @amirm, am I right in thinking residual noise of 270uV gives about a 70dB SNR?
 

bigx5murf

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#6
I have both the single and dual chip version of this, I did the gain lowering mod on both of them, and really like them. You can power them with spare laptop power supply bricks.

 

restorer-john

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#7
@restorer-john and @amirm, am I right in thinking residual noise of 270uV gives about a 70dB SNR?
The issue is that residual noise is quite likely to be a relatively constant level, regardless of output. Where that comes into play is at typical listening levels of a few watts or so where the noise will be a much greater proportion of output. As most listening is done at normal domestic levels, low level noise can ruin the listening experience IMO.

I have had situations where I bridged two big power amplifiers and the residual noise doubled and I could hear it in my tweeters from across the room (sensitive speakers). They were amplifiers with a 120dB S/N.

The THD seems reasonable at low-medium powers, but we really don't know at what point it starts to skyrocket to the 10% quoted figure. As such the S/N is hard to predict, but at 1 watt (assuming all things are equal), it'd be a paltry 80dB approx.

As Don pointed out, the fan is also a physical signal to noise wall too, but if it's a temperature controlled one, it could be off or running very slow at low outputs.

It is amazing what you can get for so little money however.
 

March Audio

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#8
To put these noise levels into context, 3 of the Hypex based amps I am about to introduce have residual noise levels of 30uV, the top end one is 9uV. Thats an SNR of 112 dB(A) for 2.8Vrms (nominal 1 watt into 8 ohms) or 137dB(A) into full power.
 

restorer-john

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#9
...the top end one is 9uV...
9uV residual on a power amp is absolutely incredible. My best big power amplifiers are 25uV-35uV rated residual, so your 30uV is excellent.
 
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andreasmaaan

andreasmaaan

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Thread Starter #11
FWIW, I tracked down some independent measurements from German site Klang und Ton, which show the amps measure significantly worse than the datasheet suggests - although still by no means terribly (top graph measured into 4 Ohm):
1544485782403.png


And factory measurements of the other ultra-cheap amp (Hypex UCD32) I was looking at for comparison:

1544486010913.png
 

DWPress

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#12
For what it's worth - I'm running a 3.2 active system with MiniDSP2x8 and have used the Sure 4x100 watt (TK2050) board for just the mids and tweets in the past with more powerful class D amps for the woofers and subs. It sounded fine and I got no hiss or other audible sounds coming from the drivers even when total SPL was around 90dB+, I replaced the fan with an oversized heatsink from an ancient graphics card and mounted a smaller fan on top - it never comes on. The amount of power you actually need to drive the smaller speakers pails in comparison to the larger drivers and even at high listening volume is maybe only pulling 35 watts for mids and 12 for the tweets going into a 8omh load. At this level of being driven the THD seems acceptable.

I will say that I no longer use this set up, prefering (self delusion?) class AB amps to take care of the upper frequencies. Ideally, and a new post I am formulating, I'd like to go digital from the MiniDSP into digital inputs on a new set of small class D or AB amps for the mids and tweets but measurements and reviews leave me content to stay where I am right now.
 
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