C2/3/5/6 make sense. I've read quite a bit about R2 elsewhere.
What do R1 and C1 accomplish once the signals are all relative to the same ground? Is a high pass necessary without any dc offset?
What do R1 and C1 accomplish once the signals are all relative to the same ground? Is a high pass necessary without any dc offset?
R1 allows a route for input bias current to flow.
C1 is a DC blocker to ensure the input is never exposed to damaging voltages.
RF attenuation is missing.
C1 is a DC blocker to ensure the input is never exposed to damaging voltages.
RF attenuation is missing.
Hi Marshaul,
how is your DS1882 based preamp?
I am also looking to build one preamp with volume and tone controls using DS1882 digital pots. What opamps are you using finally and how are you powering them up.
how is your DS1882 based preamp?
I am also looking to build one preamp with volume and tone controls using DS1882 digital pots. What opamps are you using finally and how are you powering them up.
From the datasheets DS1882 can be supplied up to +/-7V of supply. But most of the preamp circuits I have seen and thinking to build are using at least +/-9 to +/-15v of power supply.
So do we need to have separate power supply for DS1882 and preamp following it or can we use the same power supply for both?
So do we need to have separate power supply for DS1882 and preamp following it or can we use the same power supply for both?
It depends what you mean by "preamp". Personally, I'm a passive preamp kind of guy. So, I supplied my circuit from ±5V and left it at that.
I ended up using LM4562 opamps, powered by the ±5V rails.
Most of the preamp circuits you've seen probably have an active amplification stage, and this is why they want 9-15Vdc. But you should ask yourself what you need an active preamp for. Unless you need a RIAA curve, the primary function of a preamp is to provide switching and volume control (attenuation).
±5V is more than enough overhead to avoid clipping line-level signals, and all the chips you could possibly need in a "passive" preamp circuit will work just fine at ±5V.
I ended up using LM4562 opamps, powered by the ±5V rails.
Most of the preamp circuits you've seen probably have an active amplification stage, and this is why they want 9-15Vdc. But you should ask yourself what you need an active preamp for. Unless you need a RIAA curve, the primary function of a preamp is to provide switching and volume control (attenuation).
±5V is more than enough overhead to avoid clipping line-level signals, and all the chips you could possibly need in a "passive" preamp circuit will work just fine at ±5V.
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could you please tell how dual rail +/-5v is obtained from the single 12v available in the box. Also do we need to use capacitors on the signal path when using dual rail +/-5v power supply for the opamp?
There are a number of ways to get the rails. Generally, the negative is a little more complicated than the positive rail.
Personally, I elected to use an isolated switching regulator. About $10, but nearly 75% efficient, and aside from a little ripple at the switching frequency it's pretty quiet. Since it's isolated and it switches at 200kHz, it doesn't need an obscene amount of filtering. It also simplifies the segregation of the digital and analog components of the design, since the analog ground is physically separated from the noisy main ground.
Here are some basic approaches:
Design ideas: Ten best ways to split a voltage rail | Electronics Weekly
Whether you need capacitors in the signal path depends on the rest of your system. Such capacitors serve two primary functions: they block dc bias which might exist between the preamp and amp, and they serve as a high-pass filter which, properly designed, is a convenient place to attenuate infrasound before the amp.
Generally, if you know that your amp has series capacitors on the signal inputs, you can omit them in the preamp. In my case, I'm hoping to leave the design flexible, and so I'm not making too many assumptions about the downstream configuration. Hence, I used series caps.
Note that a common trick is to parallel two caps, each of half the desired capacitance, which will achieve the desired capacitance with less than half the ESR of either cap (or the equivalent double-value cap). I used bipolar electrolytics, because my research indicates that for these sort of line-level signals they offer distortion comparable to PET caps, which are the next closest thing to an economical choice.
I should also add that many preamps provide tone control, and doing this without attenuating the signal overall is another reason that preamps with a greater-than-unity-gain stage are often used. However, I don't really know anybody who uses tone controls (fortunately). I continue to think "passive" is the way to go.
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Could you please tell which isolated switching regulator have you used.
And also could you please share the schematics of the preamp and its power supply section.
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