Sure TPA3110 signal input voltage - diyAudio
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Old 17th September 2013, 11:12 PM   #1
Thor Ra is offline Thor Ra  Denmark
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Default Sure TPA3110 maximum signal input voltage

Greetings gentlemen (of both sexes),

Reading the Sure TPA3110 manual (found here) I'm getting a little confused by these specifications:

High-level input voltage: Min. 2V
Low-level input voltage: Max. 0.8V

Can anyone explain to me what the difference is between high-level and low-level input? Is it some sort of mode you can choose between ? One might get the idea that only input voltages between 0.8V and 2V are a no go but I take it that's not the case.

What I'm trying to establish is whether a 5V input signal will fry the chip.

Specifically I am planning on using 3 of these little amps in my car with a Clarion CZ702E head unit which has 6-channel audio pre-outs rated 5V. Can I safely connect these to the 3.5mm stereo input jacks on the amplifier boards or would I need pots or some sort of voltage divider in between? Or could I just keep the volume low on the head unit at all times?

In case pots/voltage attenuation is necessary your thoughts on what would be the best/easiest/cheapest solution (with the least influence on sound quality) would also be welcomed (keep in mind I'm a noob).

Last edited by Thor Ra; 18th September 2013 at 07:27 PM.
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Old 19th September 2013, 07:45 PM   #2
John8 is offline John8  United Kingdom
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The high level input voltage and low level input voltage refer to the voltage applied to the SD Pin to mute the chip. It is not the audio level.
If you don't need the mute facility then just leave the SD open. According to the TI data sheet the SD input is a 5V logic level input but can withstand the supply voltage as high level. A 0V on the pin will mute the chip.
The board has a sensitivity of 0.283V so if your pre-amp has an output of 5V then you will need to attenuate by a factor of 5/0.283 which is about 17 times. A voltage divider with a ratio of 15 or thereabouts should be OK.
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Old 20th September 2013, 01:00 AM   #3
Thor Ra is offline Thor Ra  Denmark
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Join Date: Nov 2012
Thanks a lot John, makes sense.

Sounds like the strong output of the pre-amp may be a poor match for the TPA3110 amps if the signal needs this much attenuation. I wonder how that will affect sound quality?

By the way I found more detail on how the pre-amp output voltage is rated: 5.0V (CD play mode: 1kHz, 0dB, 10kΩ load)
Even more interestingly I also found out that gain is adjustable on all the pre-out channels from -20-----0dB.

Now, if the pre-amp output voltage is 5.0V at 0dB but I can lower it -20dB this equals a factor 0.1 (10 times attenuation or 0.5V) if I'm not mistaken.

According to the Sure TPA3110 specs these amps have a typical input impedance of 30kΩ. In order to calculate how much changing the load from 10kΩ to 30kΩ will affect the input voltage I believe I would have to know the output impedance of the pre-amp - which I don't - but it should be fair to assume that it's so much lower than the input impedance of the amp that this again ought to make this difference negligible, correct?

To sum up it seems I only have to attenuate a further 0.5/0.283 = 1.77 times in order to reach optimal input voltage (if I turn gain all the way down on the head unit), correct? Maybe 0.5V input voltage is even close enough to leave out attenuation if I don't dial up the volume button too much?
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Old 20th September 2013, 06:29 AM   #4
John8 is offline John8  United Kingdom
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I don't think you will have any problems if you can reduce the output levels from the pre-amps by 20dB. All it will do is overload at really high volume settings which probably will not be an issue.
The impedance mismatch will make no difference as the output impedance of the pre-amp will be very low compared with the 10kΩ input of the amplifier.
As you say, try it and see before you do anything else, you will probably find it works well.
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Old 20th September 2013, 09:41 AM   #5
xrk971 is offline xrk971  United States
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TPA31xx chips are highly protected with built in circuitry to protect against just about every overage condition (except power supply rails). They are pretty much bulletproof. I would not worry if you can adjust gain on preamp by -20 dB. That is the point of preamps is to have sufficient signal to drive loads, you will be fine.
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Old 21st September 2013, 06:25 PM   #6
Thor Ra is offline Thor Ra  Denmark
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Thanks guys. I'll post my findings once I've had my Fiat Panda do pop, polka, punk and post-disco.
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