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 ...
- 9,749
25
votes
Accepted
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 ...
- 17.6k
21
votes
Accepted
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 ...
- 38.5k
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 ...
- 100k
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 ...
- 315k
16
votes
Accepted
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,...
- 81.8k
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 ...
12
votes
Accepted
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 ...
- 473k
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 ...
- 57.3k
11
votes
Accepted
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 ...
- 180k
10
votes
Accepted
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}\$
...
- 78.7k
10
votes
Accepted
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, ...
- 47.1k
9
votes
Accepted
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 ...
- 23.5k
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 ...
- 47.3k
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.
...
- 473k
8
votes
Accepted
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 ...
- 174k
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 ...
- 16.4k
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 ...
- 30.6k
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 ...
- 473k
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 ...
- 47.1k
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 ...
- 7,933
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 ...
- 178k
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 ...
- 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).
...
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 ...
- 315k
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 ...
- 989
7
votes
Accepted
Dependence of transistor current gain on operating conditions
"On the Variation of Junction-Transistor Current-Amplification Factor with Emitter Current," by W. M. Webster, Proc. IRE, Vol. 42, pp. 914-920, June 1954, is the seminal paper on this topic.
...
- 78.7k
7
votes
Is there an easier alternative for finding the gain of this operational amplifier?
The possible option I see for this circuit is to use the extra-element theorem or EET forged by Dr. Middlebrook some decades ago. You first identify an element that complicates the analysis. Here, it ...
- 23.5k
7
votes
Is there a programmable variable resistor
There are a few ways this can be implemented without specialized chips.
1. Using GPIO pins as a rudimentary DAC
Design the amplifier circuit so that gain can be varied with a resistor connected to ...
- 9,666
Only top scored, non community-wiki answers of a minimum length are eligible