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Chip Amps Amplifiers based on integrated circuits

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Old 10th July 2010, 09:58 AM   #121
AndrewT is offline AndrewT  Scotland
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Hi,
the power amp, if working correctly, should have no audible noise at the output.

If you connect a source that becomes noisy as the volume is turned up then the noise is coming from the source not the power amp.

Adding a pre-amp with gain will multiply the signal and the noise and send all of this to the volume control. The added pre-amp will increase the noise, slightly, rather than reduce it.
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Last edited by AndrewT; 10th July 2010 at 10:01 AM.
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Old 10th July 2010, 12:31 PM   #122
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Well, instead of 30k at the amp input, there's an additional load of 18.2k, (10k~8.2k) bringing the amp input close to line level. I'm not sure why the rest of the preamp circuit is necessary, but it also features a line level input of its own. This (these) stronger load(s) may reduce noise.

Some digital VCA volume controls can clip at 60% output, and this would be my only guess at how a preamp could be necessary.
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Old 10th July 2010, 12:41 PM   #123
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Quote:
Originally Posted by kroto View Post
I was rebuild my oldy TDA1554Q, and I more like the TDA1554 sound compared to LM1875 whan playing oldies song... smooth performance, not too much detail. . .
As for LM1875 being "too detailed" there may be two causes:
1). An un-optimized power circuit can make un-level frequency response.
2). Your speaker may operate at a flatter response given the losses of a bridged amplifier's output, and this is most likely to happen with sealed box speakers and/or mid-level retail store speakers.
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Old 12th November 2012, 05:19 AM   #124
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Default Cheap Thrills!

Hey Wahab, I finally did it: TDA8561Q
This one is easy. The mode and ddd pins connect to v+ via 10k, the input loads are also 10k, and the rest is in the datasheet, but very similar to the other Philips chips. Previously I had used the onboard cap for input load attachment, but not accessible this time, so I put the input loads at the input of the 33n wima caps. This chip doesn't "NAAR!" if you unplug the audio cable. Noise floor is zilch. Hooray!!
Tone:
Unlike the older models that were slightly dull, this one has bright, if not slightly sibilant treble (airy but slight overdo) that may need 4 output RC's (bridge amp style) and 2 input RF filters. I think it was designed to use with baxandall in a car radio. However, this thing is clear and powerful. I think Philips hid a loudness contour in here somewhere. On-chip nightclub? The bass is astonishing. I gave it some output caps and got it up to almost plaster cracking output. In about an hour run in, it did a fairly open sound and doesn't draw attention directly to the speaker. No weird ear pressure sensation like Class D, no shout, no static, just easy. SMPS doesn't dull it either--the power noise rejection actually works on this chip. The gain is slightly low for my mp3 player, but I built this one for the TV, so that's fine.

I'm sore at Chevrolet because they didn't put some of these in my car radio.
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Old 27th November 2012, 07:37 PM   #125
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I looked over mouser and digikey and TDA8561Q is not available.
:-(
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Old 28th November 2012, 09:20 AM   #126
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Quote:
Originally Posted by D Bohique View Post
I looked over mouser and digikey and TDA8561Q is not available.
:-(
Here's some alternatives:
TDA7292
TDA7265B
TDA7265
TDA7269
TDA7576
TDA1521Q
TDA1554Q
TDA8561Q
TDA1560Q
TDA1562Q
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Old 29th November 2012, 01:12 AM   #127
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tda1554
tda1554q
tda1557
tda1557q
tda7386_07
tda8563aq
tda7377
tda7560_05
tda1563q
tda1516bq
tda7389
tda8564q
tda7375a

pa7375
nte7163
la47202p
la4905


i think you will find at least one of them.
i can't name more from memory, but if You need i can get a vastly longer list.
I might not commit a mistake if i would say there has to be least 100 different ic that can be used.
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Old 29th November 2012, 10:13 PM   #128
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Thanks a lot
I'll start looking around.
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Old 1st December 2012, 01:46 AM   #129
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I've been wanting to try a pair of TDA7265 or TDA7256B as a bridged amplifier for 12v single rail use. This might also require one transistor for operating the mute feature. The bridged application in the datasheet doesn't make sense, so the prospect seems to imply a trimmer party for discovering optimal resistor values. That's a bit of a workout, but possibly entertaining.
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Old 4th February 2013, 02:53 PM   #130
JMFahey is online now JMFahey  Argentina
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Mmmmhhhh.
I got curious about what you posted, so I had a look at 7265 datasheet.
Weird.
I *think* I understand how it works, but I'm busy now, just stopped 5 minutes for a cup of tea and back to work.
Tonight I'll write longer.
Cheers.
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