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gargoor • Jan 30, 2009

Measurment on amplimo amplifier with oscillator\function generator\multimeter

hello ,,, well i'm a 1st year student in electrical & electronic engineer its my 2nd quarter now ,
i had a class that i should do measurment on amplimo amplifier with oscillator\function generator\multimeter\resistors , and we had to measure those : (to know wich amplifier(amplimo or velleman) produces better sound )
-output power
-input impedence
-output resistor
-rise time
,, after doing the measurment we should do presentation about it ,

well on monday i got the presentation , i need ur help ppl in illustrating for me the bandwidth , rise time and efficency i mean like i got few questions that m not certain about thm :
well , 1st ... what is exactly bandwidth ? what's it for ? why we must measure it? is it necessary ? how to measure it ?
2nd .... also about rise time and effeciency the same questions .
plz plz pl ppl i need ur help cause i dont have time the presentation is after two days and i need to draw the graphs and prepare my speech for presentation and do powerpoint slides , 😕
Rifaa • Jan 30, 2009
Re: need ur help ppl (measurments)

Hi gargoor, u came to the right place, no worries for I am here . 😉

The only way i can help you is if you asked questions and a lot of them, and you should be the one doing the practical, based on your observation I can only guide you, get my point.
So for now I'll just answer your current q?, I explain each one by one and if you need to measure them I have to know what equipments you have.

Output Power
Out put power is defined in WATTS ( W ) which means basically V X I which is delivered to the load in this case the speaker.
Power can be defined in as Average power, PMPO ( peak music power output) and RMS power ( Root mean square ) or True power.
The most important thing is the RMS power which is the true power delivered to the speaker by the amplifier before clipping, and U will here power as music coming from the speakers, the more power the louder it will sound.
Note that Maximum power is measured before the output clipping Occurs, If the output clips the amp will deliver DC to the load instead of AC, which will sound as distortion, and it dangerous to both the speaker and the amplifier

Input Impedance
This is the input resistance that a typical amplifier will load to any source which is connected to the amplifier input, Impudence is same as resistance but it is the AC resistance which is abbreviated in Z. So u can say impedance is AC resistance.

Output Resistor 😕
This is a mistake, output does not have a resistor, but output impedance. I think you meant to say tht U are using a resistor instead of a speaker, I need more info on this part

Bandwidth is the range of frequencies which the amplifier will amplify without dropping the output power by 70.7 % of it's rated power.
In short mostly it is the range we humans can hear but most of them goes way over 25 kHz of effective bandwidth. Hi class ones have a power bandwidth of around 25K to 35k Hz even though most of us cannot hear beyond 16 kHz.
The lower range is mostly around 30Hz, but better ones can go below as much as 10 Hz, but to produce 10 Hz an amplifier will need a lot of Power and a large Woofer to drive

Rise time
This is the slew rate of an amplifier, which is defined by ho fast the out put signal changes when an input signal change occurs and is measured in milli sec or micro secs.

This is the how good the amplifier delivers power compared to the power that is supplied by the Mains voltage. ( input power VS output power ) Amplifiers produce heat which it dissipates. This is the power that is lost.
So hight efficiency amps will produce less heat at full power, Low efficiency ones will produce a lot of heat even at low volumes.
;-) Pls note tht the input signal is not measured as power but rather in milli Volts. Amplifier power is defined by the power it's power supply produces compared to the out put power the amp delivers. Mostly this is around 75 %.
Class A amps have around 50% efficiency is it produce a lot of heat but the sound is awesome
Class B is around 80 to 85 % but produces a lot of distortion, which is not good for audio.
The one mainly used in consumer items are class AB which has an efficiency of 75 % and gives good sound
there a re class C and D which is above 90 % but is not suitable for Audio.

But as technology increase, PWM (Switch mode )Amps are coming which has around 95% efficiency and can sound pretty good.

Any other questions
gargoor • Jan 31, 2009
that is perfect i couldnt expect any1 to answer me ,
practically, me and my classmate who worked on the amplifier had in hand :
*function generator (all-in-one instrunment XELTEK DOA-141)
*oscilloscope (PM3050 60 MHZ)
*4 ohm two resistors
*digital multimeter (fluk 45)
we didnt use any speaker , we did the measurments for each specification (the ones i gave u), the point of this class is to get us used to work on those stuffs . and after getting the measurments we compare them to the other amplifier (velleman) to see wich one is better but!!! ? for now we did all the measurments but we dont know how to determine wich amplifier is better (is it by checking the effeciency? ?! and the presentation is all about telling the audience wich one is better ?!

this is my 1st time in my life working with those instruments well i did all the practical thingy but still m not certain about anythin all my informations are not complete that can make me be able to explain everything ,,

about the output restance i ment output impedence i had this thought that impedence is the same as resistance for each cases AC and DC.

i still have more questions i hope u can answer it for me ,
output power :
u said it can be defined in as Average power, PMPO ( peak music power output) and RMS power ( Root mean square ) or True power. ... is it all the same meaning and the same way to measure?! i got the output power: by measuring the output volts through the multimeter for each frequency then calculating P=V^2/Rtotal
for each step then get the total power and divide it by 2 to get the output power .. i guess that way is for average power as u meantioned but i am woundering if it is the same as PMPO ( peak music power output) and RMS power ( Root mean square ) or True power ? or they got different measuring ways , just want to know for my own knowledge ...
but what is important for my presentation now that i should know perfectly the work of bandwidth\risetime\effeciency .. i still have more questions on my mind because i did alot of researchs but still i cant get it :
_the range where humens can hear is between 16 to 16 khz right?? i read in some books its 15Hz to 20Khz, i donno now what is the right answer? and in school i'v been told its between 20Hz and 20Khz.. ? wich one is the right answer ?!
*in speakers it will always be between this range ?
_u mentioned that : it is the range of frequece that the amplifier amplifies without dropping the output power by 70.7%.. i didnt really understand what u mean by saying "without dropping the output power by 70.7% of its rated power " ?? does the range of frequencies affct the output power or smthin els ? m lost ...

let me tell u the steps i followed to measure , after i hardly found the way how to measure the bandwidth and plz correct me if i said\did something wrong cz as i told u m not certain about every concept
1- i measured the dB(decibal) for each frequency 1Hz, 10 Hz , 100 Hz , 1Khz , 10Khz , 100 Khz , 1Mhz .. so i got from 10Hz to 10Khz mostly the same value like 26,7 26,9 26,9 26,1V ( is it because 10hz to 10khz is the range where the speaker can produce sound that can be hurd by humanz?) also i want to know why it was necessary to measure the dB why not something els ? what decibal stands for ?
after gettin the db values i took 26,7 and 26,9 and subtract it by 3 ( i donno why 3 ? if u can tell me why i would be more then happy at least i can explain in my presentation)
so i checked wich frequency that gives 23,9 and 26,9 and that gives me f1 and f2
thus the bandwidth= f2-f1 = 25000-3=24997 Hz
does that make sence ?
rise time
for the rise time we were suppose to measure slew rate but we didnt have the instruments so we just neglect that part ,the rise time can be calculated by this formula
rise time = 0.35 / bandwidth
but what 0.35 stands for ? why not 0.45 or any other number?
((RISETIME)) its not the same as the rise time in pulse waveform that is between 10% to 90% of the pulse leading edge

the effeciency=output power/input power
is that right?
Rifaa • Feb 1, 2009
U are one confused kid? 😉
Well to me it seems that u totally lost with amplifier, actually it is child's play once you understand it. No worries.

The Instruments u have is good to find how well an amp works or sounds. :music: Now I presume "amplimo" is the model of the amplifier you have, since amplimo is something I never heard of :shock:
As I thought U are using resistors as the load for the amplifier and the function generator to input a sine wave which is the source.. and using the multimeter to measure the output voltage, plus a scope to see the waveforms. good. u have everything.
First of all never confuse with impedance and resistance. All though they denote the same thing they are not same. Resistance is measured in ohms and impedance in Z. Impedance will only exist for varying frequencies. Like Audio, it is a range of frequencies, or the Audio spectrum contains any and all the values from 20 Hz to 20 KHz. This "20Hz to 20kHz" is called the audio spectrum which is the range we humans can only hear. the value changes because everyone's ears are not perfect. I don't think there is a human who can here down to 20Hz and up to 20 Khz, even I can't hear above 16K. It is this imperfection tht creates the different figures of frequencies. Babies have the most acute hearing, they can hear what we can't. So basically it is from 30 Hz to 16 KHz which is the range which most of us can hear.
So an amplifier should perform well with in this range to be of a quality one, most of the amps are designed to be from 20Hz to 20Khz of power bandwidth, but Really good quality ones bandwidth can go down to 15Hz ( even though we can't hear ) and goes way beyond 30Khz. This range with which an amplifier can produce and gives a constant amount of output is known as the power bandwidth or just the "Bandwidth" of the amplifier

I'll be get back to u, and continue ( sumthin has come up )
gargoor • Feb 1, 2009
thanks alot ,appreciate the corporation ... so far so good
Rifaa • Feb 1, 2009
Okay... Hi.
Now for the actual thing which defines an amp. The POWER.
This is what amp delivers as current and voltage to the load. V X I = P
varies equations are derived when we introduce ohm's law into it, ex:
P=VI ------ using IR instead of V ( V=IR) we get P= I ^2 X R
P=VI-------using V/R instead of I ( I=V/R) we get P= V^2/R
and so an so.... hope u understood.

Note: Keep in mind that amps are tested for power, harmonic distortion, and clipping by using a 1 KHz sine wave at a value of approx. 775mV at it's input and the load is matched to output impedance of the amplifier it self, which means to drive a 8 Ohm load the output Z ( impedance ) of the amp shud be 8 ohms too. A mismatch will reflect power back in to the out put stage of the amp and causes overdrive, clipping, heating and finally if driven long enuf BAAM!! 😁 blows the out put stage.
man, I just luv the sound of it!!!! 😁

So...An AC power can be defined in many ways.
1. Peak power (PMPO) this is the amplitude of the wave ( either +ve or -ve half cycle ) that u measure using the scope. the Peak voltage value from round times the current delivered to the load gives the peak power, which in fact is a useless for any purpose since peak power does not develops at the load, it is just to understand how the things work.
U can see at the stores where a Hi fi will be advertised saying "5000W PMPO" 😲. WOW!!! what lot of power for such a small D***N Hi fi.
This so called 5000 watts is to get u to by the stupid thing. Keep tht in Mind.
2. Is the Average power which can also be measured using the scope. Here you should take the peak value and multiply it by 63.6%. You can say that it is 63.6% of the out put peak power and holds no actual figure tht we can use in real world when it comes to music. it is just for calculation and complex mathematics when using AC circuits.

3. Now this is what we really want, the True power or the apparent power or for us CE's the real power known as the RMS Power.
This value defines an amplifier. It is the value that you get from using a DMM to measure the Voltage and current that an amp gives to the load. this is the real power or the effective power and it is always 70.7% of the Peak power.

If you are using a scope than u get everything, but with a DMM you only get true or RMS Values, using a scope u can see the waveform and from it u can calculate the Peak voltage and Peak to Peak voltage too. and from that you can use the 63.6% or 70.7% figures to get what ever u want.

The RMS power should be stable through out the whole bandwidth.
let's take an example ... An amplifier has a true power of 100W to an 8 ohm load, the bandwidth is 15Hz to 15 kHz. The input sensitivity is 775mV and THD is .004%. These are a typical figures of an amp and I will summarize them to u.
First u should consider the load which is 8 ohms, and u should not go below or above this value if u want the amp to produce it's max output.
Now comes the power, the figure clearly states RMS Power so it is the effective power the load will see, and from it u can get the true voltage and current by using ohm's law. A rough calculation gives me a V = 28.3V
and I= 3.5A. these two figures are the values u can see from you DMM, when u measure across the load of the amp at an input of 775mV AC @ 1Khz sine wave to it's input.
This is the maximum power it can produce without distorting the sound, or clipping the out put.
Clipping can be heard as very harsh or very loud music, it can be like when u crank up the volume of a heavy metal song and all u can hear is Blah blah blah and u don't understand s***t about the song.
And it can also be seen from the scope, After u get a clean sine wave from the scope, try increasing the input voltage not the frequency, and see the peak value of the wave rising, and at some point in will not go but instead it will flatten, same will happen from the other half cycle too. This is clipping or overdrive. from this point the amp cannot produce any more power or voltage instead it is giving DC to the load and this can be dangerous to an amp.
Next point is for u to measure the exact peak value right before clipping occurs, this the maximum safe level that this amp can handle to 8 ohms load, and this value should be stable through out the entire bandwidth, this value should not drop in it's stated bandwidth and if it does then there is something wrong either with the amp or the design.
But power will drop at both ends since a typical bandwidth is given and the minimum value to and from both slopes is 70.7% of the peak voltage. any value below this is not true power.
If the amp out put stays above 70.7% of it's peak voltage through it's stated bandwidth then the amplifier will pass, it's power bandwidth measurements.

Now for the slew rate, this just how fast an amp can operate, meaning how long the output takes to changes when the input does. It's the delay in time measured in milliseconds that the amp responds to any given input..
This can be only measured using the scope, and by giving the in out signals, that is using two channels. one for the input and one for the output, give a 1Khz 500mV sine wave, connect the load and the scope and overlap the two sine waves and measure the time difference of both waves any given point. Simple. say 100ms or 50 micro sec. something like tht.
The faster the amp respond the better it is. got it.

Now for the decibel.
this is the unit which sound is measured in like ohms for resistance.
Decibel defines how loud the sound sounds.
Typically it is 3 decibels because it is the same way as RMS ( 70.7% of the peak)
decibel counts from -ve to +ve and zero is the middle value or the nominal value. anything below -3db is below like 70.7%, get the idea.
decibel is a weighted factor...look it up in googles
and any value above + 6 db is too much for audio and sound will clip.
but gain of the amplifier is also given in decibels too, funny though.

Bandwidth can also be stated together with decibels, like any frequencies below -3db is not included in the power bandwidth

and as for f1 and f2
f1 should be the lower frequency and f2 should be the higher end, any value in between should be above -3 db or above 70.7 % and falls in the bandwidth.

Efficiency is Output power / input power

As for Distortion (THD= 0.004%) this how good the amp imitates it's input signal. Not every amp has low THD ( total harmonic distortion ) some even has 1% which is yuck!!! for music.
the lower the THD the quieter the amp and the cleaner the output and there will be little or no difference in the input to output wave forms.

😳 ever wonder an amp producing a square wave out put with a sine wave input...think of the THD Value 😕😕
So taking all these things and values , we can compare any amp to any other.
The RMS power with a wider bandwidth, lower THD and input sensitivity ( rarely counts) and how low the load can go ( SAY LIKE 2 TO 4 OHMS ) defines an Amplifier

PS: Still the output stage also count when defining the quality of the sound it will produce since it is related to THD and power. But these are design features one can change to make an amp better and badder, and to Rock the nuggets out of the neighbors...tht's me !!!

Gargoor,rifaa had really explained well,i hope everything will be cleared,just make it simple what exactly you want to do??? it will help us CEans to solve and answer your query in simplest of form!!!!
gargoor • Feb 4, 2009
m feeling good right now after understanding the whole idea , jst i need to practise it more practicly
thanks alot rifa thats far to kind , electronix field is intresting and m looking forword to be a qualified engineer , i'll be always posting my questions in this forum i couldnt believe my eyes when some1 replayed me with whole this knowledge its just amazing ,
till later , god bless ya all
Kaustubh Katdare
Kaustubh Katdare • Feb 4, 2009
i'll be always posting my questions in this forum i couldnt believe my eyes when some1 replayed me with whole this knowledge its just amazing ,
till later , god bless ya all
😀 You've just had a taste of the spirit of CEans. Do not forget to help others whenever you can. [​IMG]
Rifaa • Feb 4, 2009
m feeling good right now after understanding the whole idea , jst i need to practise it more practicly
thanks alot rifa thats far to kind , electronix field is intresting and m looking forword to be a qualified engineer , i'll be always posting my questions in this forum i couldnt believe my eyes when some1 replayed me with whole this knowledge its just amazing ,
till later , god bless ya all
No pro buddy!!
Remember that practice makes perfect.
I tell u nothing will beat what you have learned by your self. Only you can make you better.
One more this field the more you fail, the more you blow things up, the closer you will get to your goal. Failing is a part of doing it better.
Ask, Ask, Ask. from those who know. do not hesitate. whether it is the dumbest thing you have ever asked or done, you'll always find some one dumber 😁 Everyone has an advice, every time. it never fails.
And I or from now on never gives up. 😎
Rifaa • Feb 17, 2009
Hey gargoor, how did u do in your presentation?

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