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Old 23rd February 2014, 01:12 PM   #1
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Default TDA1524A IC Pre-Amp

Hello, I have built a pre-amp based on the TDA1524A Philips IC (the kit is a 'SmartKit'). It sounds very good as the front-end of a Velleman 4040 Valve amp but I'd like a brighter treble response. The specsheet states 15dB +/- @ 16khz and I'd like to increase this a little. I have wired in a 'loudness' circuit which does increase both bass and treble but also greatly increases hiss thus I'd rather 'tweek' the TDA1524 circuit if possible. Any ideas please?
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Old 23rd February 2014, 01:34 PM   #2
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Moved to analogue line level.
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Old 23rd February 2014, 01:44 PM   #3
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We would have to know the circuit to advise but I suspect your problem could be that the tone controls are operating at the ends of the audio range. 16kHz is getting toward the limits of audibility, you really need to boost frequencies from much lower down, say from 6 or 7kHz.

Here is the data sheet. There are caps connected to pins 5,6 and 7 (other channel above these) that look as they could be the frequency determining components.

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Old 24th February 2014, 08:35 AM   #4
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Default Pre-amp

Thanks for the reply, I agree that 16khz is too high (I'm 60 years old and I doubt that I can hear that frequency!) The capacitors C4 and C8 (attached to pins 7 & 12 are 15nF and C5 and C10 (attached between pins 5 & 6 and pins 14 & 15 are 56nF.
The official Philips data sheet for the IC show a modification to improve "D.C. feedback with filter network for improved signal handling." Quite what this means I'm unsure of.
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Old 24th February 2014, 10:11 AM   #5
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I think all you could do is experiment with different cap values tbh to see if that alters the turnover points. The data sheet doesn't give any real clues.

The mod you mention looks like an external feedback loop with a cap to remove audio above certain frequencies. Again, without actually having one of these devices to play with, its difficult to give definitive advice.

Maybe have a determined web search looking for designs using this chip and see if any clues appear.
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