Gain settings TDA 7498

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   Hi,
Just bought a cheap tda 7498 board on aliexpress: http://www.aliexpress.com/item/Excellent-Quality-TDA7498-100W-100W-Class-D-Amplifier-Board-High-Power-Amplifier-Board-Hot-Sale-Easy/32470916498.html

Nice little board, the only problem the bloody thing doesn't go loud enough!
I'm using a iphone/ipad as source, and I think the ouput voltage of these is to low to drive the amp to max. volume.
Have no idea what the input gain of this board is, but if I look at the data sheet of the 7498 chip it can be adjusted but the info is very limited:

''Four selectable, fixed gain settings of
nominally 25.6 dB, 31.6 dB, 35.1 dB and
37.6 dB

The gain of the TDA7498 is set by the two inputs, GAIN0 (pin 30) and GAIN1 (pin31).
Internally, the gain is set by changing the feedback resistors of the amplifier.
Table 8: Gain settings
GAIN0 GAIN1 Nominal gain, Gv (dB)
L L 25.6
L H 31.6
H L 35.6
H H 37.6''

Anybody know how to find out what the input gain is now? And how I can adjust it?

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jerronimo Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 11 July 2009 Location: Nederland Status: Offline Points: 438	Post Options Post Reply Quote jerronimo Report Post Thanks(0) Quote Reply Topic: Gain settings TDA 7498 Posted: 22 June 2016 at 7:39pm
	Hi, Just bought a cheap tda 7498 board on aliexpress: http://www.aliexpress.com/item/Excellent-Quality-TDA7498-100W-100W-Class-D-Amplifier-Board-High-Power-Amplifier-Board-Hot-Sale-Easy/32470916498.html Nice little board, the only problem the bloody thing doesn't go loud enough! I'm using a iphone/ipad as source, and I think the ouput voltage of these is to low to drive the amp to max. volume. Have no idea what the input gain of this board is, but if I look at the data sheet of the 7498 chip it can be adjusted but the info is very limited: ''Four selectable, fixed gain settings of nominally 25.6 dB, 31.6 dB, 35.1 dB and 37.6 dB The gain of the TDA7498 is set by the two inputs, GAIN0 (pin 30) and GAIN1 (pin31). Internally, the gain is set by changing the feedback resistors of the amplifier. Table 8: Gain settings GAIN0 GAIN1 Nominal gain, Gv (dB) L L 25.6 L H 31.6 H L 35.6 H H 37.6'' Anybody know how to find out what the input gain is now? And how I can adjust it?

studio45 Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3864	Post Options Post Reply Quote studio45 Report Post Thanks(0) Quote Reply Posted: 24 June 2016 at 3:25pm
	Well, you'll want to know what is connected to those pins 30 and 31. Looks like that will mean getting the heatsink off. If the board is designed well, I would hope to find the relevant resistors are some of the ones you can access without removing the 'sink. Have you emailed the manufacturer to ask them? 37.6dB gain would usually be enough to drive the amp to full output power with about 0.775v input signal - iDevices can easily output this level into the 10k typical input impedance of an chip amp board, but in my experience only some source files are actually properly normalised to 0dBFS, and the "Sound Check" function actually just makes the loud files quieter to match the quiet ones (by setting a volume reduction tag in the metadata!!). So these 12v amps sometimes expose a need to organise/encode one's music collection better! I've got an MP3 of Talking Heads "Road To Nowhere" that is at least 3dB louder than anything else on my hard drive, no idea why :) iPad is generally louder than iPhone I have found, but the Macbook and other good laptops can output 1.4V into 10k playing a well-normalised source file or test tone generator. That's a proper line level (+5dBu)
	Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA

radi Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 22 October 2014 Status: Offline Points: 21	Post Options Post Reply Quote radi Report Post Thanks(0) Quote Reply Posted: 16 August 2016 at 11:22am
	That's the board with odd output resistors. From diyaudio: "It turns out that the manufacturer have implemented the RC-damper in the output very poorly. Wrong actually. - or at least in a way I dont understand. The 2.2Ohm resistor is NOT part of the RC, but in series with the output.... This explains the asymmetric output voltages and the lack of bass that some people have reported. So 2 solutions: 1)Short out the 2.2 resistor. 2) pull out the capacitor and the resistor and implement the the RC correct. Both versions work. Approx the same residual noise on the output." post #14 http://www.diyaudio.com/forums/class-d/276187-tda7498-ebay-strange-output-levels.html

radi Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 22 October 2014 Status: Offline Points: 21	Post Options Post Reply Quote radi Report Post Thanks(0) Quote Reply Posted: 16 August 2016 at 3:27pm
	Also this gem: "..And another thing for owners of this board, the speakers will be out of phase if you follow the white lettering. In reality (from the datasheet and listening tests) both the +ve connections are on the outer edge of the board. I did wonder why my proper filter still gave no bass LOL." post #68 http://www.diyaudio.com/forums/class-d/265387-ebay-cheap-tda7498-boards-7.html