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Old 25th December 2005, 08:27 PM   #1
boxedin is offline boxedin  Canada
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Talking What is input sensitivity?

hi,

I got basic question.

When people say their amp does 100 watts in 8 ohms, what does that mean?.

is it 100 watts at peak time?. what is average watts? can you do average wattage of amp based on sound signal?

What is the input voltage (maximum) for an amplifier? is it the sensitivity?.

Is it around 1.5 volts or in 200 mv?.


I am designing amp with 10 mv, not getting enough power for that low input. (225ma,8 ohm load).

Let me know.

Thanks
Alexk
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Old 25th December 2005, 09:56 PM   #2
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input sensitity is the max input signal voltage that drives the amp at max output
power it depends on the internal circuitry and gain of the amp, most amp are
designed to work with sensitivities in the range of o.7v to 2v higher sensitivites
mean lower levels of input signal the voltage levels and power are most often
rms values, higher sensitivies mean that the amp can be driven from sources with lower level

hope this help

happy days mate
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Old 25th December 2005, 10:13 PM   #3
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Sorry to bug you ,

Is the amplification is same at low voltage?. Is it linear? Like 30 times input signal voltage?. If the amp is not linear what is the use of Output power?.

I simulated my first am design with 10 HZ 10 mv and 1000HZ 10 mv , 20000 HZ 10 mv.

What is the output of common Mp3 player at max sound volume?.

Because my amp clips after 1V input signal. Hahhaaha.

Its all in simulation though, so i have n't lost any money.

How do you measure THD?. How do you measure input impedence of an amp and output impedence?. Will it vary with input frequency?.

More questions follow.

Thanks
Alexk
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Old 25th December 2005, 10:31 PM   #4
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what is the input signal range ? How much input , high end amp can take?. 1v?
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Old 26th December 2005, 07:05 AM   #5
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Quote:
Originally posted by boxedin
Sorry to bug you ,

1 Is the amplification is same at low voltage?. Is it linear? Like 30 times input signal voltage?. If the amp is not linear what is the use of Output power?.

I simulated my first am design with 10 HZ 10 mv and 1000HZ 10 mv , 20000 HZ 10 mv.

2 What is the output of common Mp3 player at max sound volume?.

Because my amp clips after 1V input signal. Hahhaaha.

Its all in simulation though, so i have n't lost any money.

3 How do you measure THD?. How do you measure input impedence of an amp and output impedence?. Will it vary with input frequency?.
1 Yes, the amp is linear and amplifies voltage and normal gain is 20-30 times.

2 Don't know but no fantasy voltages. I'll guess 0.5-1 volts.

3 You can use an ordinary soundcard and a freeware from http://audio.rightmark.org The output from the program look like this Input and output impedance are normally rather uninteresting as long as they are "normal" and not to extreme.
Quote:
Originally posted by boxedin
what is the input signal range ? How much input , high end amp can take?. 1v?
Normal input signal is 0.1-1 volt and a good power amp can take several volts at the input without break down.
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Old 26th December 2005, 07:56 AM   #6
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Thanks P-A.

I did the simulation with 500 mv.

http://www.diyaudio.com/forums/showt...935#post798935

You can comment on it.

All i see i sine wave both side without distortion. So it is working. I think.

How do you reduce noise in single ended class A amp without adding Feedeback or using too many capacitors.

Thanks
Alexk
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Old 26th December 2005, 11:45 AM   #7
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Quote:
Originally posted by boxedin
How do you reduce noise in single ended class A amp without adding Feedeback or using too many capacitors.
With feedback or not:

1 Reduce the output impedance of the signal source.

2 Use currents in the first stage which gives you the lowest noise in combination with your signal source (0.1-1 mA, depending of situation.)

... but noise is hardly any issue in a power amp.
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Old 26th December 2005, 08:43 PM   #8
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Thanks.
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Old 27th December 2005, 09:08 AM   #9
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Hi,
it is normal to quote sensitivity in either of two alternative forms.

1. the input voltage to produce maximum rated output power.

2. the input voltage to produce a standard output voltage.

The manufacturer can sometimes also specify the amplifier gain.

The gain should be constant for all input voltages between noise only and maximum power output and for all frequencies from a low limit of between DC and 20Hz upto an upper limit from 20kHz to 150kHz.

Since you are designing this amp you choose your limits.
I suggest you aim for a high sensitivity to make it compatible to a wider range of sources. Try a gain between 30 (+29.5db) and 60 (+35.5db) times.

For type 1. and 20W output (single ended amp) the minimum input to produce maximum power is 12.6Vac/30 = 420mVac. This may sound a bit quiet and require a preamp from low level sources. That's why I suggest a higher gain. If it's too loud you can either reduce the source signal or add an analogue volume control to attenuate the signal.

For type 2. and 1Vac output the input would be 1Vac/30 = 33mVac. This is more like the average level coming from sources with normal music content. Since the 1V is well below maximum compared to 20W you have a headroom for loud peaks. The headroom is 12.6/1 = 12.6 times and converted to decibels = +22db.

Hope this helps.
I have included a range of concepts here and if you need clarification please ask.
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Old 28th December 2005, 03:16 AM   #10
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I still don't understand it. But i think i find which particular resistor changes of sensitivity of the amplifier. Input gainstage. Mainly Ac Current path. If i can vary the Resistor it vary the gain of AC current(amplified). By making it low i can increase the sensitivity by increasing the gain of amplifier but it will clip after some stage. To be wide band sensitivity , i had to increase the resistance for ac current path and decrease the gain of Amplifier first stage.

My simulation works good as i do not get my Input do not distort with 0-1 V input. I can get same output with 0-100 mv also by increasing the sensitivity.

Sensitivity do not affect overall performance of amplifier except with higher sensitivity noises also get amplified.

I will work on noise part later.

Now back to my power stage. I don't see anyone uses darlington pair for Current gain stage? why? There is no good darlighton pair transistor suitable for audio?

Thanks
Alexk
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