Audio preamp question

157

02:39:38

I'm working on a breadboard audio preamp for learning purposes. I'm trying to figure out if I have the gain of the op amps set correctly for a LM741. I would likely relocate the volume pot but it seemed fine like this so the output has a ground reference. Thanks

published 4 years ago

GLaDOS

4 years ago

I don't recommend you to use a LM741 for sound, it can cause noise because it's not a good op amp. I recommend you a 4558 or a TL061

benmo

4 years ago

Good circuit, the EQ control is my first audio pre-amp practice circuit .

gorgut00

4 years ago

I'll have to order some of those. Thanks for the suggestion. I initially set out to work with what I have on hand. That turned out to be LM741 and LM317 voltage regulator. It has issues I need to work out and I haven't added the tone circuit yet but it is working as an amplifier.

fatcat2

4 years ago

Never use LM741 opamps in audio circuits. It has a very low slew rate along with a poor THD-frequency curve. This opamp is an old model. The noise density is also high in the case of this model. Use NE5532 instead. For a better noise performance, use an LM4562 opamp. I don't prefer using FET opamps as they have a higher voltage noise. Also, distortion and driving capabilities are limited in the latter case.

fatcat2

4 years ago

Check this out http://everycircuit.com/circuit/5876264471363584

gorgut00

4 years ago

Ok. Thanks fatcat2. I'll put those on order too. For the original purpose of just seeing how well I can drive a speaker with the minimal parts i had on hand it's turned out well so far and I've learned a lot. I have just a single op amp stage feeding a LM317 to provide the current. It makes amplified sound anyways. I'll definitely be taking your suggestions and create more complex circuits. I like that tone stack.

gorgut00

4 years ago

My question was about the gain setting on this app. Is the default 100kV/V typical and can just be left art default in mist cases? I tried to Google and read datasheets but didn't find a clear answer

fatcat2

4 years ago

Yeah; I also didn't find useful information on the correct gain of the LM741 opamp. The closed-loop gain changes very little when the open-loop gain is very high; there is no problem if it is 90k or 110k. I have cascaded 2 stages coz in this way, we are eliminating the Johnson noise from the 68k resistor as well as improving the BW and all those stuff.

gorgut00

4 years ago

I finally had time at work to implement the tone circuit you suggested. Can't wait to power it up tomorrow. Prior to that I swapped out the 741 for 4558 and adjusted the gain to accommodate my phone output plus headroom. So far it sounds fantastic through a 6.4R speaker load. Move and clean.

gorgut00

4 years ago

Nice and clean

gorgut00

4 years ago

Pretty sure I've reached the limit of the power section using 317 as a power amp and 317 at 1.3a as a current sink

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