| Electronics > Beginners |
| Just how bad is it? Audio mixer with headphone amp. |
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| Bassman59:
--- Quote from: paulca on February 28, 2018, 06:52:45 pm ---Apparently you can buy cheap digital 8 channel desks for £600, but most of the stuff I have seen is pubs, clubs, bands and bedroom musicians are using things like Mackie's and Soundcraft spirits. So maybe they are getting cheap enough for smaller venues, but the only digital mixing I have seen has been using PC/Mac sound card style solutions with USB remotes. Those are just the electronic musicians though. --- End quote --- Right, it’s the EDM kids “mixing” on laptops, but doing that is completely unworkable for mixing a live band with even a modest number of inputs. Your standard two-guitars/bass/drums/vox rock band fits into 16 channels, I’ve been using 26 of late, but remember, there are people playing the instruments, and even the most well-rehearsed band varies their performances. And with that, the person out front behind the faders has to, well, mix the show! And that’s why you won’t see computer-based mixing for live shows, because we need a user interface. And as the Mackie 24*8 and the Soundcraft Spirit and Allen and Heath GL-series desks wear out and become unreliable, they’re being replaced by Behringer X-32 and the Soundcraft Si and other small digital mixers. Hell, the X-32 costs US$2000 and it has 40 inputs, 22 outputs, USB for recording and playback, and it sounds better than it should. (I am no fan of Behringer.) You’d be stupid to use an analog console instead. |
| paulca:
Theory question... Why does increasing the load ohms on the output effect the opamp gain? So if for example I am measuring 4.5V peak to peak on the output and then connect my headphones the output voltage drops to around 800mVpp. The amp would be driving 136 Ohms. Is this likely to be current limiting? I think I answered my own question here. I = 4.5V / 136Ohm = 0.033A. The output current limit is 10mA. I = 800mV / 136Ohm = 0.007A When driving the scope which will have at least a 1M impedance it doesn't current limit as the current is minuscule. I might just be getting some small understand of impedance. So given these are pre-amps and I shouldn't really be driving headphones off them anyway, I should test them driving a line level input instead. When connected together onto the "MIX_BUS" I intend to use 2.2Ks on each which will allow them to run to max Vpp without current limiting. |
| BrianHG:
Buy 1 x 8 pin dip 1 amp x2 ON-Semiconductors op-amp for £1 to drive your headphones. Run it in voltage follower mode for the best response. Use a series 8 ohm resistor to protect output short. Get rid of the series caps if you trust your circuit to have 0v average DC out. Careful, it has a non-standard pinout. I thinking of making a cheap 30 watt stereo amp, 1hz to 100Khz using 2 of them with an IC heat-sink ontop of them with a 4amp AC out wallwart, not that Amp power ICs dont already exist, it's just going to look cute getting linear 30 watts stereo, ie 60 watts out of 2x 8 pin dip devices for under 5$ total circuit including PCB... |
| Audioguru:
--- Quote from: Bassman59 on March 01, 2018, 02:59:23 am --- --- Quote from: BrianHG on February 28, 2018, 07:46:34 pm ---try the TCA0372BDP1G at 0.48$ each --- End quote --- Wow, I had no idea that guy even existed. The data sheet advertises “No deadband crossover distortion provides better performance for driving coils,” and of course headphones are coils. Sounds (pun intended) good to me. Gonna order a few and test. --- End quote --- It is fairly noisy (5 times as much as an audio opamp) and has its distortion listed at only 0.5V, 50 ohms like two ordinary opamps I'm parallel. Its slew rate is very low like an old 741 or LM324 so it might not produce the top octave of audio. |
| paulca:
I do like the idea of the OPA551 for the output stage. How does it thermally handle the higher current? Not that I could drive it's full output into headphones without killing them, but even at lower currents will it not get hot? That would allow me to finish the design of the amplifier section and get back to the DAC and BT stages. Still need to prototype two pre-amps to mix amp and... I still need to get get proper square wave response scope shots. |
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