If you need to control the output that well, you'll have to set up a limiter/compressor of sorts... Or as janneman says, AGC (Automatic Gain Control).
One way of doing this is to have a detection curcuit at the output of the audio amplifier that is set to 2.83V. The output of this curcuit could control a VCA (Voltage Controlled Amplifier) stage which drives the main amplifier.
This way, you set a limit output voltage in the detection circuit and use that to vary the gain of the input amp so that the output always stays at your set voltage.
(This might be useful if you want to do 1W into speakers with impedance other than 8 ohms.)
16 ohms = 1W @ 4.000Vrms
8 ohms = 1W @ 2.828Vrms
4 ohms = 1W @ 2.000Vrms
2 ohms = 1W @ 1.414Vrms
1 ohm = 1W @ 1.000Vrms
Just take the root of the impedance if you like to find required voltage to get one watt. And if you need the voltage required for a different wattage, multiply watts and ohms and then take the root of that product.
One way of doing this is to have a detection curcuit at the output of the audio amplifier that is set to 2.83V. The output of this curcuit could control a VCA (Voltage Controlled Amplifier) stage which drives the main amplifier.
This way, you set a limit output voltage in the detection circuit and use that to vary the gain of the input amp so that the output always stays at your set voltage.
(This might be useful if you want to do 1W into speakers with impedance other than 8 ohms.)
16 ohms = 1W @ 4.000Vrms
8 ohms = 1W @ 2.828Vrms
4 ohms = 1W @ 2.000Vrms
2 ohms = 1W @ 1.414Vrms
1 ohm = 1W @ 1.000Vrms
Just take the root of the impedance if you like to find required voltage to get one watt. And if you need the voltage required for a different wattage, multiply watts and ohms and then take the root of that product.
if you have some money to spend consider a Thaler SWR200 and an attenuator -- 7.071 VRMS +/-0.05%, 3ppm stability -- Thaler will sell parts over the phone.
elsewise -- (and I have used this) -- use a precision rectifier to sample the output and compare to a reference -- you need a good rail-to-rail opamp for this. the error signal controls the bias of a voltage controlled amplifier -- this is how the very acurate signal generators from HP and Boonton do it. if you need some SSM2018's let me know.
elsewise -- (and I have used this) -- use a precision rectifier to sample the output and compare to a reference -- you need a good rail-to-rail opamp for this. the error signal controls the bias of a voltage controlled amplifier -- this is how the very acurate signal generators from HP and Boonton do it. if you need some SSM2018's let me know.
Most amplifiers are fairly stable wrt voltage out and simply deliver the needed current while maintaining a constant voltage.
All you really need then is a 'volume' control. A linear potentiometer would be easiest to adjust.
If you need 1 watt at each of the waveshapes (~2.83 for sine waves) you might want a switch so that each wave can be set differently/appropriately for 1 watt.
All you really need then is a 'volume' control. A linear potentiometer would be easiest to adjust.
If you need 1 watt at each of the waveshapes (~2.83 for sine waves) you might want a switch so that each wave can be set differently/appropriately for 1 watt.
Can i do this Way, first I would make a Regulated +_12V and regulate it with 7812 & 7912.
Then each outputs (i.e. Sine / Tri / Squ & Pink Noise) would have a Pot.
Would that do the job as i have a well regulated PS & a chip amp have +- 12V would have a decent & non distorted 1W Output.
I hope this would ba a good idea, suggest me a good chip amp for +- 12V.
Then each outputs (i.e. Sine / Tri / Squ & Pink Noise) would have a Pot.
Would that do the job as i have a well regulated PS & a chip amp have +- 12V would have a decent & non distorted 1W Output.
I hope this would ba a good idea, suggest me a good chip amp for +- 12V.
crissty said:
OK, that makes it more clear. In that case, distortion is a boring issue, most reasonable amps distort less than 0.1% especially at 1W. Regulated supplies are also overkill. You may want to keep an eye on bandwidth if you really want to test your speakers with triangle and square waves. Keep in mind that if you send out a 10kHz square wave, you have quite strong odd harmonics out to 100k or so. (Similar with triangles, but there you have even harmonics). In the interest of keeping both the amp and the tweeter alive, you probably want to low-pass filter your amp input at 20kHz or so.
On the fr measurements, recall that even the latest & greatest speakers have more than 1dB response irregularities, sometimes 5dB or more, so a reasonable amp with 0.1 dB between 20Hz and 20kHz is more than adequate, and it would take a really incompetent amp design that would not meet that.
My advice: start measuring rather than worring about your amp.
Jan Didden
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