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Old 8th June 2015, 12:25 PM   #1
xrk971 is offline xrk971  United States
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Default TDA7492 Amp

Having been a big TPA3316D2 user and fan for over 2 years now, I am just starting to use the very low-cost TDA7492 amp boards available from China. I recently bought a pair from Aliexpress for about $8 ea shipping included. They arrived in a few weeks and I have since set them up, and even started modifying them in a way similar to the TPA3116D2 with regards to power rail caps and snubbers. I think this amp deserves its own thread to keep the 3116 thread on topic...

Click the image to open in full size.

Datasheet here: http://www.st.com/web/en/catalog/sen...SC983/PF214773

For the purposes of comparison of sound quality between the TPA3116D2 and the TDA7492's (both amps have same mods), I am using rather nice speakers that I just finished building - the ScanSpeak 10F/8424 & Dayton RS225-8 Ref Monitor shown here:

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This is the current monitor's measured response and acoustic XO:

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Group delay for this monitor (sealed Limkwitz transform bass) is +/- 2.5ms above 33Hz:

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Here are the amps now connected to my miniDSP powering my ScanSpeak 10F/8424 & Dayton RS225-8 FAST reference speakers (10F/8424 & RS225-8 FAST Ref Monitor):

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Having shown you the performance of the reference monitors, I can say that using these speakers, compared to the 3116, these amps sounded OK stock, but seemed a bit harsh and edgy on the top end, and lacked some forcefulness in the bass department. So I proceeded to add a pair of Panasonic OSCON 330uF 25V SEPF caps and a Panasonic 560uF 35V FM cap to the single stock 2200uF 25V cap that was there. I also added 330pF and 10R snubbers at the inputs of the inductors. With the mods in place, this amp sounds very very good! I think it has better high frequency resolution that the 3116, and the extra snubber smoothed out the harshness. The OSCON upgrade always helps - a lot better bass authority and the sound stage and imaging improved.

Click the image to open in full size.

Here is how I added 330pF and 10R snubbers to the input side of the inductors, basically same location where the "bootstrap" snubbers would go on the 3116. Note that the TDA7492 does not have external bootstap caps.

Click the image to open in full size.

I pulled the massive heatsink off of the board to reveal a Feixiang pcb - here is a high res layout photo. It looks like the Feixiang board pretty much follows the suggested circuit but as you can see from the photo, they added some stuff like a protection diode on Vcc, and a pair of small SMT by-pass caps after the electrolytics very close to the pins for the best noise suppression - a nice touch. Input and output filter caps are EPCOS films. The input caps have been upgraded from factory suggested 470nF to 1uF EPCOS film caps. The output filters seem to be using a compromise arrangement of 22uH and 220nF and 100nF film caps. Usually this would be with 33uH inductors. :

Click the image to open in full size.

The amps run warmer than the 3116, but one of my amps runs hotter than the other and one of the inductors (far right) runs hot to the touch which is why I am looking at it closely to see what the problem is. It looks like the ferrite shield casing is chipped or cracked.

Here is the datasheet suggested schematic:

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Here are the datasheet pinouts:

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You can get these for circa $7 shipping included:
http://www.aliexpress.com/item/2015-...331617990.html
Attached Images
File Type: png TDA7492-IC-Circuit.png (217.0 KB, 1226 views)
File Type: png TDA7492-IC-Pinout.png (181.9 KB, 1212 views)

Last edited by xrk971; 8th June 2015 at 12:55 PM.
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Old 8th June 2015, 01:53 PM   #2
irribeo is offline irribeo  Netherlands
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Ok datasheet shows it is a little weaker than TI tpa3116, distortion sees steep rise above 20watt, TI above 30watt, so distortion is probably what makes the 7492 appear more powerfull. The output filterfrequency is much closer to audioband so peaking is more audible with 7492, I think you already found that. The filter used is in datasheet for 6 ohm, your SS10F monitor probably above that. Datasheet 7498 shows a little more advanced outputfilter with more damping of peaking probably.
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Old 8th June 2015, 03:10 PM   #3
xrk971 is offline xrk971  United States
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Quote:
distortion sees steep rise above 20watt, TI above 30watt, so distortion is probably what makes the 7492 appear more powerfull
I do not see higher distortion at the speaker frequency response and HD measurement. Speakers are generally limiting factor but HD seems comparable at the acoustic level to 3116.

Interesting that distortion makes it sound more powerful? The gain is higher than 26dB so things are just louder by about 6dB or so. However, turning input gain on miniDSP down by -6dB it still sounds very dynamic.

For $6 to $8 though, they are an absolute deal. How can you lose?

Why do they run hotter though even though same 90% quoted efficiency?
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Old 8th June 2015, 06:55 PM   #4
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i subscribe this thread and suggest anyone who likes that board/chip to try its bigger brother the 7498.
the black 7498 board is a steal for only 10€ - 11€ shipped from china.

what i miss on those boards is the possibility to easily mod it to differential inputs.
would be super easy with only throgh hole caps on the negative inputs, too.
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Old 8th June 2015, 11:04 PM   #5
xrk971 is offline xrk971  United States
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Do you have a link for the 7498 that you like?
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Old 9th June 2015, 12:37 AM   #6
Lo_Tse is offline Lo_Tse  Canada
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Just curious, is there any special reason that you used 10R for the snubber instead of 22R? Thanks!
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Old 9th June 2015, 12:55 AM   #7
xrk971 is offline xrk971  United States
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The snubber used on the input of the inductor for the TPA3116 was 330pF and 10R. I just used same one because that was what I had on hand. I don't even know if it is right for the 7492. It does seem to have similar values for the inductor and output capacitor values.

Do you see 22R used somewhere? Oh I see what you are saying as there is a 330pF and 22R connecting the two inductor inputs together. I don't know if that is a snubber as it doesn't go to ground - just between the positive and negative legs.

Last edited by xrk971; 9th June 2015 at 12:58 AM.
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Old 9th June 2015, 01:07 AM   #8
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Quote:
Originally Posted by irribeo View Post
Ok datasheet shows it is a little weaker than TI tpa3116, distortion sees steep rise above 20watt, TI above 30watt, so distortion is probably what makes the 7492 appear more powerfull.
I doubt that higher distortion on a sinewave is the reason that an amp sounds more powerful. In my experience its dynamics that are associated with the perception of more power - so I'd reckon that the TDA has a more constant noise floor, less dynamic variation with signal.

I've not tried this chip yet but its possible it shares some heritage with NXP's classD offerings and the TDA8932 was definitely subjectively more dynamic in the bass to my ears than the TPA3116.

If the chip's running hot, I'd firstly look at the output inductors - perhaps they're too lossy at the switching frequency. Certainly they look rather small ones.....
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Last edited by abraxalito; 9th June 2015 at 01:10 AM.
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Old 9th June 2015, 02:11 AM   #9
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by xrk971 View Post
The snubber used on the input of the inductor for the TPA3116 was 330pF and 10R. I just used same one because that was what I had on hand. I don't even know if it is right for the 7492. It does seem to have similar values for the inductor and output capacitor values.

Do you see 22R used somewhere? Oh I see what you are saying as there is a 330pF and 22R connecting the two inductor inputs together. I don't know if that is a snubber as it doesn't go to ground - just between the positive and negative legs.
Yes. You are right. This part is absent in the TPS3116 schematic. In the TPA3116, there are pins from the chip (BSNX) that are specifically for connecting to a snubber, that I do not see in the TPA chip. Anyway, comparing the schematics side by side, it seems that the out filter sections of the two chips are different. I need to look up the TI paper on Class D amp output filter design to get more details.

Regards,
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Old 9th June 2015, 02:13 AM   #10
xrk971 is offline xrk971  United States
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Sound clip with 10F ref speaker

http://www.diyaudio.com/forums/attac...492-amp-01.asc

Change extension to .mp3 to listen.
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