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Old 11th July 2010, 12:55 PM   #1
zog666 is offline zog666  Australia
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Default inexpensive YuanJing TDA8920 board from ebay

I recently got a YuanJing brand low cost TDA8920 based board from ebay. This is a fairly basic low frills build but worth documenting for those interested.

I'd already wired up the case for my second ConnexElectronics TDA8920 board when I managed to fry the board. Out of curiousity I decided to check out this lower cost board that was going cheap cheap ($19USD + $9USD postage), as I could use the transformer I'd already mounted in the case as they are similar units.

This is the board on ebay:
TDA8920 Class D Amplifier board/ audio Power AMP 2X100W - eBay Power Amplifiers, Amplifiers, Home Audio, Electronics. (end time 19-Jul-10 02:14:45 AEST)

Click the image to open in full size.
It has a smaller heatsink than the connex module, and smaller PSU 4700uF caps.

Initially it sounded OK, but not as good as the Connex module, quite a bit more grainy.. also interestingly it uses 5W power even when silent, and hence (with the smaller heatsink) runs a lot hotter.

Tracing out the circuit it appears it is pretty much the reference implementation of the TDA8920 circuit, with a volume control tacked on. Though the PCB mentions 0.680uF caps, they have used values 0.470 as per the reference circuit

Some minor tweaks I have made to the unit include:
  • remove the input capacitors, and put the inputs where the capacitors were. This cuts out the 0.47 coupling caps, the volume control, and some 5.6K resistors. Also means I have to make sure anything I plug into it doesn't have any DC offset! This has really cleared up the amps sound quality a lot.
  • took the 10000uF caps from the connex amp and wired them in parallel with the existing 4700uF caps. Seems to have more solid bass... but hard to say.
  • took the 11uH inductors from the Connex amp and replaced the 33uH inductors (which are in metal cans). After comparing the circuits and discussing with Col also replaced the 0.470 caps output filter caps with 2 in parallel (0.95uF) to match the values as per the Connex amp. Hard to tell if this helped either.

Click the image to open in full size.

The overall result now sounds better. Not incredible but quite OK for a modded cheapy. Interestingly this unit doesn't seem to have what I call the "Diana Krall" bug (faint fizz audible on very soft piano notes) thats been noted on other TDA8920 based modules. I'm using a basic plastic enclosure from Altronics, 160VA toroidal transformer, and have the ESP groundloop protection in there as well.

Click the image to open in full size.

Last edited by zog666; 11th July 2010 at 01:00 PM.
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Old 2nd August 2010, 08:59 PM   #2
JoelM81 is offline JoelM81  United States
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Quote:
Originally Posted by zog666 View Post
remove the input capacitors, and put the inputs where the capacitors were. This cuts out the 0.47 coupling caps, the volume control, and some 5.6K resistors. Also means I have to make sure anything I plug into it doesn't have any DC offset! This has really cleared up the amps sound quality a lot.
In what way does it sound "cleared up"?

Is the input differential? Split supply with one input tied directly to ground and the other directly to signal?

Quote:
Interestingly this unit doesn't seem to have what I call the "Diana Krall" bug (faint fizz audible on very soft piano notes) thats been noted on other TDA8920 based modules.
Do you happen to know why it doesn't?
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Old 3rd August 2010, 01:49 PM   #3
zog666 is offline zog666  Australia
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Quote:
Originally Posted by JoelM81 View Post
In what way does it sound "cleared up"?
When I first fired up the amp it just sounded a bit "grainy", though not in an unpleasant way. It just sounded clearer I think.. though this could be my perception bias of course after investing the effort fiddling with it.

Quote:
Originally Posted by JoelM81 View Post
Is the input differential? Split supply with one input tied directly to ground and the other directly to signal?
Inputs are differential (can be tied together BTL?)
I didnt trace the whole circuit, but the parts I did trace indicated to me it is pretty close to the reference circuit as per : http://www.eurica.ru/sound/TDA8920TH.pdf


Quote:
Originally Posted by JoelM81 View Post
Do you happen to know why it doesn't?
No.

also.. a few weeks ago I killed it.. sent a blast of full amplitude noise into it while fiddling with a pre-amp and fried the TDA8920 chip. Although I could attribute removing the input capacitors, I did have it buffered via a behringer Xenyx1204 mixer.

re-using the case for an AMT2050 board, as the toroid is the right voltage.
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Old 3rd August 2010, 05:37 PM   #4
JoelM81 is offline JoelM81  United States
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Originally Posted by zog666 View Post
also.. a few weeks ago I killed it.. sent a blast of full amplitude noise into it while fiddling with a pre-amp and fried the TDA8920 chip. Although I could attribute removing the input capacitors, I did have it buffered via a behringer Xenyx1204 mixer.
Yeah, these chips seem to fry easily. From what I know, the PROT cap on pin 13 determines the trade-off between short circuit protection and audio drop-outs at high volumes.
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Old 10th August 2010, 06:53 PM   #5
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These little boards caught my eye also, it looks like a lot of bang for the buck.

Do you think that they be any good for subwoofer use or would the heatsink struggle to keep things cool enough? I guess bridged into an 8 ohm load will be pushing things somewhat!
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Old 11th August 2010, 11:16 AM   #6
zog666 is offline zog666  Australia
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Hi,
yes the heat sink is pretty small, though it didnt get much hotter when I was using it, but then I didnt crank it that much (or bridge it). It did have pads on the board for soldering thr bridges in.

The ConnexElectronics units run a lot cooler, and have a lot more options, and are smaller.. though cost a few bucks more - and harder to mount, depending on your case layout.
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Old 12th August 2010, 01:20 AM   #7
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Quote:
Originally Posted by zog666 View Post
Hi,
yes the heat sink is pretty small, though it didnt get much hotter when I was using it, but then I didnt crank it that much (or bridge it). It did have pads on the board for soldering thr bridges in.

The ConnexElectronics units run a lot cooler, and have a lot more options, and are smaller.. though cost a few bucks more - and harder to mount, depending on your case layout.
Thanks, I'll think I'll check out the ConnexElectronics modules, I don't mind spending a little more really. I'm tempted to check one of these board out though, mainly out of curiosity really, if I don't use it for the subwoofer I have plenty of other uses for it.
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Old 13th August 2010, 01:20 AM   #8
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How to control the voice?????
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Old 13th January 2011, 10:34 AM   #9
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HI! Do you use 4 or 8 ohms speakers?
I just bought one kit and a boost converter and i will use the PC power supply to power it.
I also want to buy a pair of Kenwood 17cm car speakers that are 4 ohms and about 35w RMS (180w peak) and I'm not sure what result I'll have.
Thank you!:|)
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Old 27th January 2011, 01:21 PM   #10
zog666 is offline zog666  Australia
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I used 8 ohm speakers.
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