I'm looking at the DAC output filter in a Wolfson datasheet (attached). I think this might be a simple question, but where do I connect toe rails for the 6 (3 per channel) op amps? I at first thought obviously to +5V and GND. If that's the case how does the output achieve negative voltage for the analog RCA outputs since the outside of the plug is GND?
Probably a simple explanation here and I'm just overthinking things. Thanks
Probably a simple explanation here and I'm just overthinking things. Thanks
Attachments
Max output level is a vital consideration, the standard 2Vrms is nearly 6 volts pk/pk. In practice anything from -/+9 volts to -/+15 would be OK and those convertors are available in 12 and 15 volt ratings so that makes the decision for you and allows any of the standard opamp types to be used such as LM4562/OPA2134 etc etc.
Alright it looks like DC converter is quickly becoming a good option then. You say "standard 2Vrms", where is that value coming from? My quick look on Wikipedia says consumer audio is 0.316Vrms, professional is 1.228Vrms, and ARD is 1.546Vrms.
In that filter circuit I posted in the first post, wouldn't the output voltage be dictated by the gains and inputs to the op amps? So the only effect the rail voltage would have is to prevent it from saturating at the rails (or max/min output voltages for the op amp)? Thanks again, appreciate your help.
In that filter circuit I posted in the first post, wouldn't the output voltage be dictated by the gains and inputs to the op amps? So the only effect the rail voltage would have is to prevent it from saturating at the rails (or max/min output voltages for the op amp)? Thanks again, appreciate your help.
If you check any CD player the standard tends to be 2 volt RMS for, sometimes a bit higher for SACD so I imagine that's the kind of levels you would see from a DAC like you mention. Post #162, totally unrelated but it shows typical levels,
http://www.diyaudio.com/forums/mult...ower-do-your-speakers-need-9.html#post2883059
Opamps tend to perform best at the higher voltages (lowest distortion) and they have the best drive ability at those voltages too.
http://www.diyaudio.com/forums/mult...ower-do-your-speakers-need-9.html#post2883059
Opamps tend to perform best at the higher voltages (lowest distortion) and they have the best drive ability at those voltages too.
The particular opamp datasheet will specify the max supply current (typically 4-8mA for an audio opamp). To that you'll need to add the signal currents which flow in the resistors around your differencing opamp (the 3rd one). I very much doubt you'll reach even 70mA all told. Be sure to filter the DC/DC converter's output extremely well (LC filters plus ferrite beads) as they're notoriously noisy and opamps are highly susceptible to HF hash.
<edit> The 660R effective input impedance to the 3rd opamp stage looks excessively low and will be something of a current hog - for myself I'd scale up those resistor values by a factor of 3X - to 1k for the 330Rs and the capacitors 3X smaller.
<edit> The 660R effective input impedance to the 3rd opamp stage looks excessively low and will be something of a current hog - for myself I'd scale up those resistor values by a factor of 3X - to 1k for the 330Rs and the capacitors 3X smaller.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.