| Electronics > Beginners |
| Negative version of LP2951 LDO |
| << < (3/8) > >> |
| ZeroResistance:
--- Quote from: edavid on September 10, 2019, 03:28:24 pm ---1. For a simple design like this, a rail splitter would be as good as split supplies --- End quote --- How does one do that? --- Quote ---2. Unless you know exactly what will be connected to the inputs, it's better to AC couple them --- End quote --- The inputs would be headphone outputs from other devices. What is the advantage of AC coupling, isn't it better to DC couple and get rid of the DC offset. --- Quote ---3. Don't you need a buffer after your volume control? --- End quote --- Since the outputs are phone outputs, I didn't consider it necessary. --- Quote ---4. For the negative supply, why were you thinking you needed an LDO? Would an extra volt drop really be significant? --- End quote --- I'm currently considering the good old 317 / 337 combo but was interested in the LP2951 due to its low dropout and thought it would be easy to find the negative version of it... Also i'm currently generating the negative supply with a charge pump, because I wanted to keep noise low and didn't go in for the switched inductor power supplies. |
| MagicSmoker:
--- Quote from: edavid on September 10, 2019, 03:28:24 pm ---1. For a simple design like this, a rail splitter would be as good as split supplies --- End quote --- Functionally, sure - it just turns the mid-point of a positive supply into the 0V reference - but this also elevates the "supposed to be grounded" shell of shielded interconnects to the mid-point voltage which can cause problems when connecting to other devices, especially if they share a chassis ground and/or are earthed. --- Quote from: edavid on September 10, 2019, 03:28:24 pm ---2. Unless you know exactly what will be connected to the inputs, it's better to AC couple them --- End quote --- Agreed, though with proper bipolar supplies it is perfectly acceptable - and even preferred - to just use a coupling capacitor on the input, where even a small capacitance will still allow for a low frequency 3dB point in the single Hz range. The output coupling capacitor can - and should - be dispensed with. Always keep in mind that wiring 3 or 4 RC networks in series with overall gain present is a great way to make an oscillator... --- Quote from: ZeroResistance on September 10, 2019, 05:31:51 pm --- --- Quote from: edavid on September 10, 2019, 03:28:24 pm ---1. For a simple design like this, a rail splitter would be as good as split supplies --- End quote --- How does one do that? --- End quote --- With just a voltage divider, technically, but it's better to buffer the divider output with an op-amp follower so you don't have to use inconveniently small value resistors. Note that this circuit works best when the current drawn from each rail with respect to 0V is balanced, but that is pretty much always the case with audio. |
| ZeroResistance:
--- Quote from: MagicSmoker on September 10, 2019, 07:43:17 pm ---Agreed, though with proper bipolar supplies it is perfectly acceptable - and even preferred - to just use a coupling capacitor on the input, where even a small capacitance will still allow for a low frequency 3dB point in the single Hz range. The output coupling capacitor can - and should - be dispensed with. Always keep in mind that wiring 3 or 4 RC networks in series with overall gain present is a great way to make an oscillator... --- End quote --- So If I have 2 stages, 1 Summing amplifier and 1 Power amplifiers DC blocking caps at the Summing amplifier is sufficient? Is there No need to add it further down the line? Won't the summing amp stage add a dc offset at its output? |
| MagicSmoker:
--- Quote from: ZeroResistance on September 10, 2019, 09:24:32 pm ---... So If I have 2 stages, 1 Summing amplifier and 1 Power amplifiers DC blocking caps at the Summing amplifier is sufficient? Is there No need to add it further down the line? Won't the summing amp stage add a dc offset at its output? --- End quote --- No, I was saying that as long as bipolar supplies are used you don't need a coupling cap at the output of each stage. In other words, the output of one stage doesn't need a coupling cap if the input of the following stage has a coupling cap (which it should, for reasons already pointed out). For interstage coupling in an amplifier string with modest overall voltage gain* you can usually dispense with the DC blocking capacitor, but since you will only need a few uF to maintain a low-end frequency response down to a few Hz why not use one there, too? It's getting rid of the DC blocking capacitor between the power amplifier and speaker that is the real benefit** (for distortion, reducing "thump" at turn on/off, and cost). * - for example, you need 20Vrms to drive 8R speakers at 50W, and the standard line level signal is 1Vrms (0dBV), so that requires a voltage gain of 20; even relatively high offset op-amps like the NE5534 (5mV worst case) will only subject the speaker to a DC bias of 0.1V here. That's about 1.25mW of DC dissipation, which is basically negligible. ** - as well as the DC biasing resistors needed for every op-amp if a single supply is used. |
| ZeroResistance:
So I know impedance of at least one of the outputs that will connect to my Audio Mixer input. Its output impendance is 200ohms with max 4V rms. So would I need to match the impedance for this source. The circuit which I had posted earlier had just a 10K audio taper to attenuate the phone output followed by a 1uF dc blocking cap? |
| Navigation |
| Message Index |
| Next page |
| Previous page |