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35 votes

Is there a programmable variable resistor

The term you are looking for is digital potentiometer. Search for parts to find one that fits your needs. You can get them with up to 10 Bits of resolution. Be aware that on power-up the value might ...
jusaca's user avatar
  • 9,609
25 votes
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Why do (microphone) preamp designs tend to limit opamp gain to max 60 dB?

Gain/Bandwidth product, you want maybe 50KHz bandwidth at 60dB (1,000 times), so you need somewhere around 50MHz, gain/bandwidth product (And more would lower HF distortion)... Make it 80dB and now ...
Dan Mills's user avatar
  • 17.6k
20 votes
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Single supply non-inverting amplifier using op amp

Your schematic should be as following: simulate this circuit – Schematic created using CircuitLab Since you're using a single-supply non-inverting amplifier, the non-inv input of the opamp ...
Rohat Kılıç's user avatar
20 votes

Is there a programmable variable resistor

It seems you're trying to build a programmable gain amplifier. Programmable resistors, as jusaca says, exist in the shape of digital potentiometers. However, there's also programmable gain amplifiers ...
Marcus Müller's user avatar
17 votes

Reduce audio amplifier output power

Don't bother. 2.5 W is unlikely to hurt a 2 W speaker. It will just cause distortion. Somewhere in your audio chain there must surely be a volume control. Turn down the volume to the point where ...
Olin Lathrop's user avatar
16 votes
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What is noise gain, really? And how is it determined in the general case?

Okay, after a lot more research, I think I've gotten to the bottom of this. Actually I'm certain it's only approaching the bottom, as I've found this topic area quite deep, but I think I've gotten ...
scanny's user avatar
  • 7,172
16 votes
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Op-amps, why do they have such low output currents

It's simple: manufacturers make what customers will buy! It's the same reason why Ferrari won't put a trailer attachment at the rear of their cars... Price is a very important part of this, of course,...
bobflux's user avatar
  • 79.5k
14 votes

Why do (microphone) preamp designs tend to limit opamp gain to max 60 dB?

There is the matter of GBW(gain-bandwidth product), so a single stage is improbable with good performance. It's not enough to just squeak through in bandwidth you also want enough gain to reduce the ...
Spehro Pefhany's user avatar
12 votes

What is the largest gain configurable with an opamp?

Short: No!!!! Longer: Without a very specific description of a real world requirement this sort of question is useful at best as a thought experiment. Single stage: So - yes - it can be configured, ...
Russell McMahon's user avatar
  • 151k
12 votes
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Why is open loop gain important in an op amp?

Why should someone measure or even care about the open loop gain when op-amps are always used in closed loop with feedback only? Some relevant stuff about op-amps: - The open-loop gain you are ...
Andy aka's user avatar
  • 464k
11 votes

How does opamp open-loop gain affect closed-loop gain in a circuit?

From Texas Instruments "Stability Analysis of Voltage-Feedback Op Amps Including Compensation Techniques" http://www.ti.com/lit/an/sloa020a/sloa020a.pdf A is the open loop gain (the gain of the ...
DKNguyen's user avatar
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11 votes
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In an amplifier, does the gain knob boost or attenuate the input signal?

It could be either when determined by marketing. Two common configurations are shown below. simulate this circuit – Schematic created using CircuitLab Figure 1a: Fixed gain pre-amp with ...
Transistor's user avatar
  • 177k
10 votes
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Common emitter transistor amplifier working in simulation but not in reality

Let's start with some simple calculations based only upon a few starting points: \$R_{_\text{C}}=6\:\text{k}\Omega\$ \$A_v=100\$ \$V_{_\text{CC}}=12\:\text{V}\$ \$v_{_\text{PP(IN)}}=20\:\text{mV}\$ ...
jonk's user avatar
  • 78.3k
9 votes
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DC Gain of the System

What you need to stabilize your converter is the control-to-output transfer function: if a stimulus is applied to the duty ratio input, how does it propagate through the converter and create a ...
Verbal Kint's user avatar
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9 votes
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Will a bipolar transistor have gain, even if the collector has no curent?

There's only one relationship between currents in the transistor which is always true; it's an application of Kirchhoff's Current Law (KCL): $$I_E = I_C + I_B$$ Everything else is conditional, ...
Simon Fitch's user avatar
  • 38.3k
8 votes
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Non-inverting and inverting gain of differential amplifier

First we must start with some basic assumptions, we assume that the inputs of the circuit are fed from ideal voltage sources and that the op-amp is an ideal op-amp. The latter means that the circuit ...
Peter Green's user avatar
  • 22.7k
8 votes

Why do (microphone) preamp designs tend to limit opamp gain to max 60 dB?

Many op amp circuits are designed so that they would yield a known finite gain if constructed using ideal components including an infinite-gain op amp. In practice, such circuits will always be ...
supercat's user avatar
  • 47k
8 votes

Why do (microphone) preamp designs tend to limit opamp gain to max 60 dB?

Why (microphones) preamps designs tend to limit opamp gain to max 60 dB? A good overall picture of the whole range of what microphones and other audio devices produce: - Picture taken from here. ...
Andy aka's user avatar
  • 464k
8 votes
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Understanding what is meant by the magnitude of an Op-Amp's gain?

The gain is defined as the output signal divided by the input signal. The amplifier has a voltage output. It's a virtual ground input configuration, the input will stay at 0v by feedback action. The ...
Neil_UK's user avatar
  • 169k
8 votes

How does opamp open-loop gain affect closed-loop gain in a circuit?

The formula you quote is not the gain of an opamp. It is the gain of a circuit containing an opamp and several resistors. That formula only holds when the open loop gain of the opamp is much larger ...
Barry's user avatar
  • 16.1k
8 votes

How does opamp open-loop gain affect closed-loop gain in a circuit?

Let's start with the definition of the op amp: $$e_{out}= A_{OL}(e_+ -e_-)$$ This is true for every op amp. The device is a differential amplifier, with a very high gain. Now, given that the ...
Scott Seidman's user avatar
8 votes
Accepted

Why is there a resistor in the feedback section of this buffer circuit?

Why is there a resistor in the feedback section of this buffer circuit? If the op-amp has significant input bias currents (rather than offset currents) then making \$R_F = R_1||R_2\$ has some DC ...
Andy aka's user avatar
  • 464k
8 votes
Accepted

Do we always take the corner frequency of a filter at exactly -3dB?

It's not 3dB absolute, it's 3dB down from the peak, or some sort of nominal attenuation. So in your case, where the passband is -3dB, 3dB down is at -6dB. Note that some filters (e.g. Chebychev) have ...
TimWescott's user avatar
  • 46.6k
8 votes

Is there a programmable variable resistor

As well as the solutions given above, you can use a voltage controlled resistor and drive it from a D to A. One way is to use an FET, a more obscure one is to use a light dependent resistor which is ...
danmcb's user avatar
  • 7,287
8 votes

Why use gains on an ADC

ADCs typically have a fixed number of bits. If the signal of interest does not cover the full natural range of the ADC input, then some of those bits get "wasted", reducing the effective ...
Dave Tweed's user avatar
  • 175k
8 votes

Will a bipolar transistor have gain, even if the collector has no curent?

When there is no collector current all the emitter current is from the base and all base current flows "out of" the emitter. If you define current gain as Ic/Ib then there is by definition ...
ATCSVOL's user avatar
  • 795
8 votes

Multistage amplifier voltage gain

You can use 1V in all situations. You'll get the same results as with different voltages except the gain will be correct (at least the gain will be correct for small inputs, not necessarily for 1V). ...
Spehro Pefhany's user avatar
7 votes
Accepted

Gain-bandwidth product proof for open loop/closed loop opamp

Could you please tell me that if the wikipedia proof is wrong? I don't see any thing wrong with it. The so called "proof" itself is wrong simply because they are using the Open Loop Gain to ...
Victor S's user avatar
  • 889
7 votes

Why do (microphone) preamp designs tend to limit opamp gain to max 60 dB?

60 dB means 1 mV from the mic becomes 1 V out. That's about the maximum you want to amplify a microphone and feed into a "line level" input. Most microphones produce a few mV out for normal sound ...
Olin Lathrop's user avatar

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