Hi, I'm recycling some recycled material to build a small 2.1 amp for the desk. I will use a TDA7375 with a simple preamp input to have more gain for the phone. The proposed scheme contains a preamp based on TL072 and a filter for the subwoofer cut at around 100 Hz based on TL081. All powered at around 12V or maybe 15V. Being a beginner, can you give me directions and/or corrections, but above all would it work?
The sub low-pass function does look rather non-standard. I simulated it in LTSpice and found the turnover frequency is in the region of 2Hz, so over all the LF band it has a falling response, there's no flat passband. Normally a sub turnover frequency will be in the region 40-160Hz and below that the frequency response will be generally flat. You might consider replacing your sub filter part (the TL081) with a 2nd order Sallen-Key low pass, it still only needs a single opamp. Such circuits are very commonly used in a subwoofer application.
Thanks, do you think this might work? it is a tool found online
http://sim.okawa-denshi.jp/en/OPseikiLowkeisan.htm
http://sim.okawa-denshi.jp/en/OPseikiLowkeisan.htm
Wanting to insert the Sallen-Key filter calculated with a 100Hz cut-off, I would like to power the Tl 081 op with a single 12V power supply, is a single capacitor on V+ and V- to ground ok or is something else needed? I'm a beginner and have never powered an op amp with a single power supply. Thank you
If you arrange the pot (POT-PRE) to connect to ~+6V rather than to GND that can provide the necessary bias point for the TL081. So a 5.6V zener (anode to GND) and 1k resistor from +12V to the zener cathode will give you a mid-rail point at the zener cathode. Then move the left terminals of POT-PRE from GND to that mid-rail point and delete C-F1 to give DC coupling to the TL081.
I think I understand, but doesn't the DC on the POT-PRE disturb the input of the TDA7375? Inputs 1 and 2 only have polyester capacitors and therefore not polarised. I attach the modified circuit. Thank you
No, it would if there weren't coupling caps prior to those inputs, but you have 4.7uFs there. You got the zener idea perfectly!
Incidentally if your 5.6V zener turns out a little noisy then maybe some filtering between the zener and the pot will be in order. But try it without first. Oh and also the 0.47uF caps on the inputs aren't at all a good idea, best remove them (C-PRE3 and C-PRE4).