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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Preamp between DSP(ADAU1701) and TPA3255 AMP
Preamp between DSP(ADAU1701) and TPA3255 AMP
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Old 6th July 2018, 01:42 PM   #1
KidCe is offline KidCe
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Default Preamp between DSP(ADAU1701) and TPA3255 AMP

Hello there,

im currently building my frist speaker, its gonna be a Battery powered PA-Speaker. i have some problems and some ideas to solve them but i would like your confirmation that this is working


The well known ADAU1701 DSP has a Output voltage of 0.9Vrms, the TPA3255 board by Nobsound ( Amazon.com: Nobsound TPA3255 Digital Power Amplifier Class D Audio Amp Assembled Board 300W+300W HiFi: Home Audio & Theater ) states to have 2Vrms inputs.

So that means when the DSP is running at full Volume, the TPA3255 wont even run at half its maximum power?

As i want to design the Board for the ADAU1701 by myself i have following idea to solve the problem:

at the Output of the DAC's i have to connect OP-AMP which is good for Audio. The Resistors around the OPAMP should then make it to have Amplification of 2,2(Vout/Vin) ... or 6,94dB

Is my thinking correct that the DSP would be bottleneck for the AMP?
And would the OpAmp curcuit solve the problem ?

Thanks for your help

KidCe
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Old 7th July 2018, 08:14 PM   #2
KidCe is offline KidCe
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Nobody there who can help me ? :/

Just a little "Yes tha would work"
or
"No its not that easy"
would help me alot
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Old 8th July 2018, 08:30 AM   #3
doctormord is offline doctormord  Germany
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Yes that works, but opamp output filter is normally not needed, simple RC-filter will also do. You can set the gain on the TPA3255 boards as well by changing the resistor values at the opamps in the front input stage.
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Old 9th July 2018, 03:42 AM   #4
PRR is offline PRR  United States
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Yes tha would work
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Old 9th July 2018, 06:46 AM   #5
KidCe is offline KidCe
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Quote:
Yes that works, but opamp output filter is normally not needed, simple RC-filter will also do.
Im not planing to do Filtering with the OPamps, just using the Amplification.

Quote:
You can set the gain on the TPA3255 boards as well by changing the resistor values at the opamps in the front input stage.
Good point
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If im right this should be the Input stage of the Nobsoundboard.
So i would just have to find out how these OPAMPs are wired and then i can replace the Resistors to my needs by desoldering and soldering in new ones with other values.

I Couldnt find high res Picks of the 3e Audio TPA3255 board to look how the Inputstage is made there but it should be somewhat similar but with jumpers for Single ended / Differential input.
Maybe ill go with the 3e Board when its available again.

Last edited by KidCe; 9th July 2018 at 06:53 AM.
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