good afternoon,
my appologies if this question has already been answered, i was unable to find an appropriate-sounding thread on the forum.
how do i find the "RMS" value for digital amps? i've noticed in general they provide ratings for the THD, at given watts, but i haven't yet found any that will list a RMS value. is this something due to the nature of digital amps?
i am planning on driving a pair of small FLUANCE SV10S speakers, which have a confirmed RMS value of 25 watts, and a peak rating of 50 watts.
there are a million different opinions of how to match up the power needs of your speaker to the capacity of your amplifier, but i am aiming to match the RMS value of my amp and of my speaker. so ideally i would like to find an amp that can push 25 watts at 8Ω with as low THD as possible.
currently i am looking at two potential amps :
1. 2 x 50 tda7492
2. 2 x 100 tk2050
the tda7492 feels like a more appropriate amp, and claims 0.1% THD, when pushing 20 watts to 8Ω speakers.
the tk2050 feels like overkill, but claims an amazing 0.007% THD, when pushing 30 watts to 8Ω speakers.
is a scale of THD the closest i'll get to a stated "RMS" on digital amps? is the THD a new and preferred description for the available power of an amp?
if i decide on the larger (tk2050) amp, in the quest for lowest THD, do i run a severe risk of the speakers being damaged if somebody turns the volume too high? i suppose that there are methods to prevent too much power from the amp reaching the speakers.
thanks.
my appologies if this question has already been answered, i was unable to find an appropriate-sounding thread on the forum.
how do i find the "RMS" value for digital amps? i've noticed in general they provide ratings for the THD, at given watts, but i haven't yet found any that will list a RMS value. is this something due to the nature of digital amps?
i am planning on driving a pair of small FLUANCE SV10S speakers, which have a confirmed RMS value of 25 watts, and a peak rating of 50 watts.
there are a million different opinions of how to match up the power needs of your speaker to the capacity of your amplifier, but i am aiming to match the RMS value of my amp and of my speaker. so ideally i would like to find an amp that can push 25 watts at 8Ω with as low THD as possible.
currently i am looking at two potential amps :
1. 2 x 50 tda7492
2. 2 x 100 tk2050
the tda7492 feels like a more appropriate amp, and claims 0.1% THD, when pushing 20 watts to 8Ω speakers.
the tk2050 feels like overkill, but claims an amazing 0.007% THD, when pushing 30 watts to 8Ω speakers.
is a scale of THD the closest i'll get to a stated "RMS" on digital amps? is the THD a new and preferred description for the available power of an amp?
if i decide on the larger (tk2050) amp, in the quest for lowest THD, do i run a severe risk of the speakers being damaged if somebody turns the volume too high? i suppose that there are methods to prevent too much power from the amp reaching the speakers.
thanks.
Based on supply voltage it is quite easy to estimate the RMS power of a D amp. Calculate with alittle lower supply to account for a) weakness of PSU (the lower ohmic speaker the more) and b) MosFET Rdson.
"if i decide on the larger (tk2050) amp, in the quest for lowest THD, do i run a severe risk of the speakers being damaged if somebody turns the volume too high? i suppose that there are methods to prevent too much power from the amp reaching the speakers. "
risk: yes
methods: limiters
best practice is to use overpowered amps and have them limited to match the speakers RMS as well as peak capability. Not so easy to setup. Thats what sound engineers are paid for (among other related things)
thanks.
"if i decide on the larger (tk2050) amp, in the quest for lowest THD, do i run a severe risk of the speakers being damaged if somebody turns the volume too high? i suppose that there are methods to prevent too much power from the amp reaching the speakers. "
risk: yes
methods: limiters
best practice is to use overpowered amps and have them limited to match the speakers RMS as well as peak capability. Not so easy to setup. Thats what sound engineers are paid for (among other related things)
thanks.
good evening, thank you for your reply 
in what can only be a testament of my own ignorance, i find your answers simultaneously too specific, and too vague:
how am i supposed to know what supply voltage to use for this calculation, if the amp itself accepts a fairly wide range of input voltage? and if we're already guessing at that number, how much more vague does this calculation become if i need to judge a "little lower" than that? where do i even find the MosFET Rdson for either of the two amps i listed? am i to believe it's common for users on DIYaudio to find and read the entire whitepaper for every component of the amps they use?
i have some technical background, but any math using the MosFET Rdson is far beyond what i've ever been involved with.
i'm still not certain where in this figuring of estimated estimated power supplies and MosFET Rdson i would be able to get the resulting % of THD. which is what the goal, as stated in my OP, is to know.
is there no simple "rule of thumb" a common layperson, like myself, can rely on to derive a RMS value when generally the only information provided in the item description is a single watt rating?
now i'm a bit lost for the generalities of the terms used...
what do you mean by limiters?
is this something to do with the input power?
a polyswitch on the output to cut the connection to the speakers if the signal is over a certain amperage?
do you mean a bolt that keeps the volume knob from being turned too far?
i will again assume (and we know the risk that entails) that the DIYaudio forum is full of people who have successfully figured a way to prevent their speakers from being over-driven, without outsourcing the task to sound engineers.
thank you again for your reply, and your obvious wealth of knowledge... but they are a bit too specific, and then too enigmatic for me to quite understand them. any rephrasing would be greatly appreciated. i would love to have an amp that matches my speakers in both RMS and peak wattage!
in what can only be a testament of my own ignorance, i find your answers simultaneously too specific, and too vague:
how am i supposed to know what supply voltage to use for this calculation, if the amp itself accepts a fairly wide range of input voltage? and if we're already guessing at that number, how much more vague does this calculation become if i need to judge a "little lower" than that? where do i even find the MosFET Rdson for either of the two amps i listed? am i to believe it's common for users on DIYaudio to find and read the entire whitepaper for every component of the amps they use?
i have some technical background, but any math using the MosFET Rdson is far beyond what i've ever been involved with.
i'm still not certain where in this figuring of estimated estimated power supplies and MosFET Rdson i would be able to get the resulting % of THD. which is what the goal, as stated in my OP, is to know.
is there no simple "rule of thumb" a common layperson, like myself, can rely on to derive a RMS value when generally the only information provided in the item description is a single watt rating?
now i'm a bit lost for the generalities of the terms used...
what do you mean by limiters?
is this something to do with the input power?
a polyswitch on the output to cut the connection to the speakers if the signal is over a certain amperage?
do you mean a bolt that keeps the volume knob from being turned too far?
i will again assume (and we know the risk that entails) that the DIYaudio forum is full of people who have successfully figured a way to prevent their speakers from being over-driven, without outsourcing the task to sound engineers.
thank you again for your reply, and your obvious wealth of knowledge... but they are a bit too specific, and then too enigmatic for me to quite understand them. any rephrasing would be greatly appreciated. i would love to have an amp that matches my speakers in both RMS and peak wattage!
Generally speaking its better to have an amp that is higher rated power wise than the speakers. Its easier to damage a speaker with low powered amp that's clipping and running into distortion rather than overdriving a speaker with a "clean" signal.
As with most things, its a balance and common sense. A 100watt RMS amp would fine with speakers of a nominal 30 watt rating if used sensibly. A 20 watt amp could just as easily damage those same speakers if it were turned up to high and the signal (the voltage applied to the speaker) was clipped and distorted.
Limiters... yes a bolt on the volume control Common sense is your best limiter. Polyswitches are a no no. Far too non linear and unpredicatable. Electronically, limiters can be constructed to "level out" the volume as you turn it up and up... remember the old AGC feature on cassette decks that acted like a soft clip. That's not really something you should be doing these days.
You might be really surprised how little power (or more correctly voltage) you need across a speaker for your normal listening levels.
Have a read and try at this
http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html
As with most things, its a balance and common sense. A 100watt RMS amp would fine with speakers of a nominal 30 watt rating if used sensibly. A 20 watt amp could just as easily damage those same speakers if it were turned up to high and the signal (the voltage applied to the speaker) was clipped and distorted.
Limiters... yes a bolt on the volume control
Common sense is your best limiter. Polyswitches are a no no. Far too non linear and unpredicatable. Electronically, limiters can be constructed to "level out" the volume as you turn it up and up... remember the old AGC feature on cassette decks that acted like a soft clip. That's not really something you should be doing these days. You might be really surprised how little power (or more correctly voltage) you need across a speaker for your normal listening levels.
Have a read and try at this
http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html
Its a common fairy tale that speakers are more in danger from too weak amps - that may be true for tweeters, but for woofers it is the RMS power that cooks the voice coil and the peak voltage (together with enclosure design / frequency...) that determines the excursion. Both excursion and temperature will destroy the speaker. An underpowered but clipping amp cannot produce as high total RMS voltage value or as high peak voltage value as an overpowered amp can do. So it is less likely to damage a woofer (that does not really care about distortion btw.) than an overpowered one.
a Limiter is typically a software encoded part of a DSP which is used for X-OVR, EQ, Delay and *guess what* limiting the signal. I think there have existed some analogue small signal limiters, but no one would use this today any more. Tweaking attack / release and level is best done per software...
a Limiter is typically a software encoded part of a DSP which is used for X-OVR, EQ, Delay and *guess what* limiting the signal. I think there have existed some analogue small signal limiters, but no one would use this today any more. Tweaking attack / release and level is best done per software...
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LOL after checking out your links I see that using a $500+ DSP to protect $99 speakers is somehow pointless ... ;-)
But since this amps are w/o power supply, it is youself who has to supply the amps with DC - so you should know exactly what is the supply rail and can therefore easily determine max output by selecting an appropriate power supply.
But since this amps are w/o power supply, it is youself who has to supply the amps with DC - so you should know exactly what is the supply rail and can therefore easily determine max output by selecting an appropriate power supply.
Not quite right here!
If you overdrive any amplifier, the amplifier will produce square waves. A square wave at a low frequency will in turn look like DC across the speech coil as the amplifier will tend to lock up to one or other supply rail and heat the coil up. Too many square waves for a prolonged period of time will destroy the speech coil subject to the power supply limits. Too much power from a large amplifier will damage the loudspeaker also by breaking the paper cone, cambric edge or cook the speech coil.
"Not quite right here!
If you overdrive any amplifier, the amplifier will produce square waves."
-> Agreed, though you 'd need to overdrive quite hard to reach what is close to square wave signal. Typically you get cutted peaks.
"A square wave at a low frequency will in turn look like DC across the speech coil as the amplifier will tend to lock up to one or other supply rail and heat the coil up."
-> It will look like positive DC only during one half wave, negative during the other. Result will still be AC voltage w/o real DC component. Real DC component = offset.
"Too many square waves for a prolonged period of time will destroy the speech coil subject to the power supply limits."
-> Too many of EVERY signal will destroy the coil. Can be DC, sine AC or square AC, sawtooth, ....what you like.
BUT keep in mind that every signal an overdriven amplifier can or will produce will ALWAYS have less RMS voltage than the signal that would come out of a more powerful but unclipped amp (assume same input signal, same gain of course). Cutting the peaks off of a sine wave will reduce total RMS voltage.
"Too much power from a large amplifier will damage the loudspeaker also by breaking the paper cone, cambric edge or cook the speech coil. "
-> Exactly that is the main problem today as multi kW amps are now in reach for kids $$-wise like iNukes or LG fp14k clones from china and the like, but good powerful speakers are always 4 figure.
If you overdrive any amplifier, the amplifier will produce square waves."
-> Agreed, though you 'd need to overdrive quite hard to reach what is close to square wave signal. Typically you get cutted peaks.
"A square wave at a low frequency will in turn look like DC across the speech coil as the amplifier will tend to lock up to one or other supply rail and heat the coil up."
-> It will look like positive DC only during one half wave, negative during the other. Result will still be AC voltage w/o real DC component. Real DC component = offset.
"Too many square waves for a prolonged period of time will destroy the speech coil subject to the power supply limits."
-> Too many of EVERY signal will destroy the coil. Can be DC, sine AC or square AC, sawtooth, ....what you like.
BUT keep in mind that every signal an overdriven amplifier can or will produce will ALWAYS have less RMS voltage than the signal that would come out of a more powerful but unclipped amp (assume same input signal, same gain of course). Cutting the peaks off of a sine wave will reduce total RMS voltage.
"Too much power from a large amplifier will damage the loudspeaker also by breaking the paper cone, cambric edge or cook the speech coil. "
-> Exactly that is the main problem today as multi kW amps are now in reach for kids $$-wise like iNukes or LG fp14k clones from china and the like, but good powerful speakers are always 4 figure.
good afternoon
ah... i don't yet have the power supply.
what i meant was, in reference to the TK2050, the description says it will accept between 12v-30v with a maximum of 32v. if i am interested in driving this amp at its lowest distortion, it claims to deliver 0.007% THD+N driving 8Ω speakers at 30 watts
but it doesn't tell me anywhere whether this is 30 watts RMS, or 30 watts peak? i assume its not peak, as the amp is advertised as "2x100 watt", and i can only assume it means "2x100 watts peak", since i've never seen an amp listed by its RMS value.
or are these questions getting specific enough to the TK2050 i should start a thread particularly about this amp?
ah... i don't yet have the power supply.
what i meant was, in reference to the TK2050, the description says it will accept between 12v-30v with a maximum of 32v. if i am interested in driving this amp at its lowest distortion, it claims to deliver 0.007% THD+N driving 8Ω speakers at 30 watts
but it doesn't tell me anywhere whether this is 30 watts RMS, or 30 watts peak? i assume its not peak, as the amp is advertised as "2x100 watt", and i can only assume it means "2x100 watts peak", since i've never seen an amp listed by its RMS value.
or are these questions getting specific enough to the TK2050 i should start a thread particularly about this amp?
Just an observation, that last parts-express link for the TK2050 does state the power output is RMS not peak
In general I run an amp with enough gain to output about 3 to 6dB above my max listening level. With the amps +/- power rails [or just +Vdc] high enough that clipping doesn't occur even at full output. The amps power output [Watts] can be worked out with the source output level, the amps gain and speaker impedance.
(input x gain)^2/impedance... (2Vrms x 10 gain)^2 / 8 = (20Vrms)^2 / 8 = 400 / 8 = 50Watt
A quick way to work out the amps gain... divide the amps gain [in dB] by 3... 30dB / 3 = 10 [x10 gain] or 26dB / 3 = 8.6...
Paul
In general I run an amp with enough gain to output about 3 to 6dB above my max listening level. With the amps +/- power rails [or just +Vdc] high enough that clipping doesn't occur even at full output. The amps power output [Watts] can be worked out with the source output level, the amps gain and speaker impedance.
(input x gain)^2/impedance... (2Vrms x 10 gain)^2 / 8 = (20Vrms)^2 / 8 = 400 / 8 = 50Watt
A quick way to work out the amps gain... divide the amps gain [in dB] by 3... 30dB / 3 = 10 [x10 gain] or 26dB / 3 = 8.6...
Paul
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yes, indeed.
i have an impossible dream of building the whole machine for around $250. numbers which i'm sure will make all of the enthusiasts on this forum wince and shake their head. but essentially i'm looking at building something instead of buying an Onkyo CS-445, so i have a pretty low price-point to compete with.
so far i'm figuring :
$100 for speakers
$50 for the D-amp
$75 for the PSU
$25 for connectors
i'll be building the enclosure myself.
but i'm still (obviously) in the learning phase about what architecture is even the best option: so far on this adventure i've discovered digital amps, and now am sorting through switching VS linear power supplies. on and on $50 for the D-amp
$75 for the PSU
$25 for connectors
i'll be building the enclosure myself.
i'm giving myself another couple weeks to get the best and most practical method figured out, and the prices for the parts. then it will be time to decide if it's going to be better to just buy instead of build.
i have no doubt that the Fluance speakers will out perform the ones from the little Onkyo system... but the vote is still out - so to speak - on whether the total cost of building even a small receiver/amp will outweigh the potentially superior sound production. or whether i will be able to make something close to the convenient user experience of the Onkyo... this is destined to be a birthday gift.
Just an observation, that last parts-express link for the TK2050 does state the power output is RMS not peak
In general I run an amp with enough gain to output about 3 to 6dB above my max listening level. With the amps +/- power rails [or just +Vdc] high enough that clipping doesn't occur even at full output. The amps power output [Watts] can be worked out with the source output level, the amps gain and speaker impedance.
(input x gain)^2/impedance... (2Vrms x 10 gain)^2 / 8 = (20Vrms)^2 / 8 = 400 / 8 = 50Watt
A quick way to work out the amps gain... divide the amps gain [in dB] by 3... 30dB / 3 = 10 [x10 gain] or 26dB / 3 = 8.6...
Paul
i swear they must have added that RMS info since i first linked to that amp!
it would appear that the RMS has a varying value based on the power you provide the amp? please pardon my ignorance, i'm trying to learn as much as i can... but i've never seen a value range listed as the RMS. all of my experience is with receivers that already have their own PSU, so maybe that's why they only list one RMS value on the plate.
this seems to list two different "types" of RMS?
could you further explain how you adjust the gain on your amp?
it sounds like that may be exactly what i need... a way to keep the amp within the safe watt range of the speakers. the threads i've seen here, referring to gain always describe it as an impedance to signal. as in, "the input from my ipod is too quiet, because the gain on my receiver is too high". is this a correct definition of gain?
ah... i think something just clicked for me.
i was looking again at the description for the TK2050, and fretting over the fact that it lists a supply voltage requirement, but no suggested amperage. and then it clicked that the only place where watts is described, is in the output for the amp.
sooooo, if P (watts) = I (amps) x V (volts), then P / V = I
does this mean i adjust the output wattage of the amp by how much power i supply it? that seems to be what ViennaTom has been trying to explain it to me
if i want 100 watts of RMS output, i supply the TK2050 3.3amps of 30v
if i want 40 watts of RMS output, i supply the TK2050 1.3amps of 30v
assuming perfect conversion...
the description includes :
i was looking again at the description for the TK2050, and fretting over the fact that it lists a supply voltage requirement, but no suggested amperage. and then it clicked that the only place where watts is described, is in the output for the amp.
sooooo, if P (watts) = I (amps) x V (volts), then P / V = I
does this mean i adjust the output wattage of the amp by how much power i supply it? that seems to be what ViennaTom has been trying to explain it to me
if i want 100 watts of RMS output, i supply the TK2050 3.3amps of 30v
if i want 40 watts of RMS output, i supply the TK2050 1.3amps of 30v
assuming perfect conversion...
the description includes :
- High output power:
30W @ 6Ω, < 1% THD+N
40W @ 8Ω, < 3% THD+N
100W @ 4Ω, < 10.0% THD+N - High efficiency:
86% @ 60W 8Ω
82% @ 46W 6Ω
90% @ 100W 4Ω - Audiophile quality sound:
0.007% THD+N @ 30W 8Ω
0.005% THD+N @ 70W 4Ω
if i want 100 watts of RMS output, i supply the TK2050 3.3amps of 30v
if i want 40 watts of RMS output, i supply the TK2050 1.3amps of 30v
assuming perfect conversion...
it is not that easy but depends on speaker impedance.
To make it easier: Tell me your speaker impedance, your desired RMS wattage and how much headroom for burst power you d like to have, so I can gueestimate the best supply voltage for you.
if i want 40 watts of RMS output, i supply the TK2050 1.3amps of 30v
assuming perfect conversion...
it is not that easy but depends on speaker impedance.
To make it easier: Tell me your speaker impedance, your desired RMS wattage and how much headroom for burst power you d like to have, so I can gueestimate the best supply voltage for you.
good evening,
very kind of you to help me try and figure this out
the exact speakers i am planning for this project is the SV10S from Fluance.
they are listed for 25 to 50 watts, and are 8Ω.
according to the manufacturer, 25 watts should be the RMS, and 50 watts the peak.
although i'm sure they could handle more than 50 watts, if i could get a 25-50watt range with the extremely low 0.007% THD, i would be delighted.
Let's go through the basics once again. Power depends on voltage and current. Current depends on load impedance (in this case your speaker impedance) and voltage. Thus, power is the square of the voltage divided by the load impedance, P = U^2 / R.
The supply voltage determines at what point the amp runs out of voltage margin and starts to clip. The actual output voltage (and thus power) below the clipping point depends on your input signal voltage - output voltage is input voltage times voltage gain.
The supply voltage determines at what point the amp runs out of voltage margin and starts to clip. The actual output voltage (and thus power) below the clipping point depends on your input signal voltage - output voltage is input voltage times voltage gain.
Both ICs are 2ch (stereo) full bridges - only one PSU rail required.
Good.
They use feedback before the lowpass - not so good.
THD: Don't worry about the THD too much, since the speaker is always 10x - 1000x worse than even a cheap amp like this.
Powers supply: To get 50W of unclipped sine wave power into 8 Ohms, at least about 29VDC are required in a full bridge. TDA7492 can t do this.
Guess it can do about 36 into 8 ohm at 25VDC supply.
If the power supply can sustain current >=Output power / (average efficiency x supply voltage), then the power would be continuous. If you only want 25W continuous RMS power to not cook your speaker, use a weaker / current limited power supply. To be still able to get short higher musical peaks (bursts) to the speaker, use electrolytics in parallel to the amp supply. The bigger the capacity, the longer bursts can be sustained. The lower the current limit of the PSU, the lower the RMS power limit. Cheap skate limiter (C) 2014 by ViennaTom
Good.
They use feedback before the lowpass - not so good.
THD: Don't worry about the THD too much, since the speaker is always 10x - 1000x worse than even a cheap amp like this.
Powers supply: To get 50W of unclipped sine wave power into 8 Ohms, at least about 29VDC are required in a full bridge. TDA7492 can t do this.
Guess it can do about 36 into 8 ohm at 25VDC supply.
If the power supply can sustain current >=Output power / (average efficiency x supply voltage), then the power would be continuous. If you only want 25W continuous RMS power to not cook your speaker, use a weaker / current limited power supply. To be still able to get short higher musical peaks (bursts) to the speaker, use electrolytics in parallel to the amp supply. The bigger the capacity, the longer bursts can be sustained. The lower the current limit of the PSU, the lower the RMS power limit. Cheap skate limiter (C) 2014 by ViennaTom
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