So ratings differ. Clear example is 100 watt hdmi receiver vs old harman kardon.
Harman kind of rates them as high current 100 watts
Nakamichi for example provide current values..
I've never seen current numbers from other manufacturers
For example re-1 nakamichi is only 80 watts.. but with 4 ohm speakers sound louder than 200 watt yamaha mx1 amp.
How can I find out current values of yamaha mx1 or another amp That only provides watts..
Yamaha is known to inflate power ratings. But I still really like mx1. Sonically and the fact it can handle 2 ohm load rms.
And there are some amps That are rated super conservative. Like 20 watts per channel. But wight 50kg and sound like 200 watts. There is some serbian company or Slovakian. Can't remember That make 25w amps That sound like 200watts.
Real question is I don't want speakers to receive clipped signal.. how can I ensure this.
I like the sound of nakamichi RE-1. But it's only 80 watts ( again that sound like 250watts.. ). And vienna acoustics beethoven (first edition with 2 midrange drivers..not new with one midrange and 3 woofers).
Bit towers That are efficient. Vienna recommends 50-300watts to run these speakers..on paper yamaha mx1 is best I have for them. 260 watts per channel rms
Re-1 runs a little hot. Actually pretty hot on loud volumes.
Anyway to monitor clipped signal?
At the moment I use re1 as pre amp to power yamaha mx1. Mx1 is always at room temperature. A little warm sometimes..
Harman kind of rates them as high current 100 watts
Nakamichi for example provide current values..
I've never seen current numbers from other manufacturers
For example re-1 nakamichi is only 80 watts.. but with 4 ohm speakers sound louder than 200 watt yamaha mx1 amp.
How can I find out current values of yamaha mx1 or another amp That only provides watts..
Yamaha is known to inflate power ratings. But I still really like mx1. Sonically and the fact it can handle 2 ohm load rms.
And there are some amps That are rated super conservative. Like 20 watts per channel. But wight 50kg and sound like 200 watts. There is some serbian company or Slovakian. Can't remember That make 25w amps That sound like 200watts.
Real question is I don't want speakers to receive clipped signal.. how can I ensure this.
I like the sound of nakamichi RE-1. But it's only 80 watts ( again that sound like 250watts.. ). And vienna acoustics beethoven (first edition with 2 midrange drivers..not new with one midrange and 3 woofers).
Bit towers That are efficient. Vienna recommends 50-300watts to run these speakers..on paper yamaha mx1 is best I have for them. 260 watts per channel rms
Re-1 runs a little hot. Actually pretty hot on loud volumes.
Anyway to monitor clipped signal?
At the moment I use re1 as pre amp to power yamaha mx1. Mx1 is always at room temperature. A little warm sometimes..
Last edited:
Perceived volume comes from the gain of an amp, not the watts.
This is in decibels, and is typically 26. Lower power amps can be louder than higher power amps, if they have higher gain, but the tendency to clip is higher.
Amps sold to consumers have various ways to specify watts, and picking one that gives a big number is part of the salesmanship game today.
In the late 60's and seventies there was in the USA a FTC specification for how to rate watts. It involved an 8 ohm speaker, a "soak" time at limited power, and a test time at full power, which was very short - a number of minutes. this led to amps with rediculously inadequate heat sinks being sold. I own one, and when I tried to use it for PA service, melted the solder on some wires as the whole chassis hit the melting temperature at the end of a 3.5 hour rehearsal.
The FTC has gotten out of the business of amp ratings, and vendors are pleased many times now to rate one channel at a time (allowing wimpy transformer or toroid) for only a second at a time (allowing great numbers while violating output transistor SOA limits briefly). there are vendors who use some middle of the road procedure which gives lower and more realistic numbers.
OTOH there is the PA market, which involves amps sold to stadiums and bars. I don't know if the yamaha MX1 is from their consumer or PA line. The watts rating of PA amps tends to be on 4 ohm speakers, which are most common these days, and 24 hours 7 days a week limit. There are only a few vendors that specify this way and they tend to dominate the pro sound market because of the reliability this conservative rating produces.
Whereas amps sold to consumers will have one number, the PA amps sometimes have six watts ratings. There are 1 % HD ratings, which are the advertised values, and there are the minimum HD ratings, which are a little less, maybe 90% of the first. On top of this, each comes in a 8 ohm, 4 ohm, and 2 ohm rating. I was going to link to the owners manual of a Peavey amp I own with the six power ratings, but they have quit distributing it.
1% HD ratings necessarily include a little clipping. In the class AB days, 4 ohm ratings could be 20% higher than 8 ohm, and 2 ohm ratings could be higher still, which might be the effect of what you say a "current" rating is. 2 ohm ratings involve more current than 8 ohm ratings. I don't have the owner's manual available on this computer, but I believe my PA amp has a 400 W/ch 8 ohm rating at .02% HD, 650 W/ch at 4 ohms, and 1000 W/ch at 2 ohms. Thus the 2 ohm rating is more than double the 8 ohm rating. this is a class AB amp with 25 lb power transformer, heat sinks weighing a pound, an 8" fan, and 5 pairs of TO3 transistors, Motorola/On semi's best.
Some pro level amps have a clip indicator lamp on the panel, some top end consumer amps have a VU meter with a red zone. Of course with a meter, transient clips lasting milliseconds will not be shown. You can also build such a device, see for example certain parts IC threads.
Personally I find heavy clipping makes sine waves, which normally sound like a flute, sound like an ambulance siren, the mechanical kind with a slotted rotor and an electric motor.
People find tube amps "louder" than equivalently rated solid state amps, in part because tubes clip gently with round edges, making the sound rather pleasant rather than the annoying sound of a SS amp flattening the tops of the sine waves. Also tube watts come from a very efficient radiator, a hot vacuum tube, so the heat sinks don't cost more than the tube in the first place.
I have an amp with the high power supply voltage required to produce modest wattage in the days when power transistors had a gain of 5 at high currents. By installing power transistors with a gain of 25, I've made it very clip resistant, as long as I listen to classical music with brief volume peaks. If I used it in PA service as I did previously when it melted the solder, again the heat sinks would be inadequate. But as is in my living room, where my base volume is 1/8 watt, 1V into 8 ohm speakers, this 60W amp is quite as loud as my PA amp with a 260 w/ch 8 ohm rating. One of the benefits of high gain. One channel has original 1970 input & driver transistors, and hisses slightly with no signal. The other channel has modern input & driver transistors and hisses not at all. The power of progress, that $.35 transistors are dead quiet at high gain. Of course, using modern metal film resistors instead of the original 1970 carbon comp resistors help the modern channel hiss less.
Current is calculated from a power rating at I=sqrt(P/Z) where I is current, P is power, and Z is the speaker impedance. Note speaker impedance is typically 4/3 times the resistance you can measure with a DVM ohms scale. Thus my 8 ohm speakers read about 6.5 on the meter, when the battery is fresh.
Have fun shopping or even more adventurous, building an amp.
This is in decibels, and is typically 26. Lower power amps can be louder than higher power amps, if they have higher gain, but the tendency to clip is higher.
Amps sold to consumers have various ways to specify watts, and picking one that gives a big number is part of the salesmanship game today.
In the late 60's and seventies there was in the USA a FTC specification for how to rate watts. It involved an 8 ohm speaker, a "soak" time at limited power, and a test time at full power, which was very short - a number of minutes. this led to amps with rediculously inadequate heat sinks being sold. I own one, and when I tried to use it for PA service, melted the solder on some wires as the whole chassis hit the melting temperature at the end of a 3.5 hour rehearsal.
The FTC has gotten out of the business of amp ratings, and vendors are pleased many times now to rate one channel at a time (allowing wimpy transformer or toroid) for only a second at a time (allowing great numbers while violating output transistor SOA limits briefly). there are vendors who use some middle of the road procedure which gives lower and more realistic numbers.
OTOH there is the PA market, which involves amps sold to stadiums and bars. I don't know if the yamaha MX1 is from their consumer or PA line. The watts rating of PA amps tends to be on 4 ohm speakers, which are most common these days, and 24 hours 7 days a week limit. There are only a few vendors that specify this way and they tend to dominate the pro sound market because of the reliability this conservative rating produces.
Whereas amps sold to consumers will have one number, the PA amps sometimes have six watts ratings. There are 1 % HD ratings, which are the advertised values, and there are the minimum HD ratings, which are a little less, maybe 90% of the first. On top of this, each comes in a 8 ohm, 4 ohm, and 2 ohm rating. I was going to link to the owners manual of a Peavey amp I own with the six power ratings, but they have quit distributing it.
1% HD ratings necessarily include a little clipping. In the class AB days, 4 ohm ratings could be 20% higher than 8 ohm, and 2 ohm ratings could be higher still, which might be the effect of what you say a "current" rating is. 2 ohm ratings involve more current than 8 ohm ratings. I don't have the owner's manual available on this computer, but I believe my PA amp has a 400 W/ch 8 ohm rating at .02% HD, 650 W/ch at 4 ohms, and 1000 W/ch at 2 ohms. Thus the 2 ohm rating is more than double the 8 ohm rating. this is a class AB amp with 25 lb power transformer, heat sinks weighing a pound, an 8" fan, and 5 pairs of TO3 transistors, Motorola/On semi's best.
Some pro level amps have a clip indicator lamp on the panel, some top end consumer amps have a VU meter with a red zone. Of course with a meter, transient clips lasting milliseconds will not be shown. You can also build such a device, see for example certain parts IC threads.
Personally I find heavy clipping makes sine waves, which normally sound like a flute, sound like an ambulance siren, the mechanical kind with a slotted rotor and an electric motor.
People find tube amps "louder" than equivalently rated solid state amps, in part because tubes clip gently with round edges, making the sound rather pleasant rather than the annoying sound of a SS amp flattening the tops of the sine waves. Also tube watts come from a very efficient radiator, a hot vacuum tube, so the heat sinks don't cost more than the tube in the first place.
I have an amp with the high power supply voltage required to produce modest wattage in the days when power transistors had a gain of 5 at high currents. By installing power transistors with a gain of 25, I've made it very clip resistant, as long as I listen to classical music with brief volume peaks. If I used it in PA service as I did previously when it melted the solder, again the heat sinks would be inadequate. But as is in my living room, where my base volume is 1/8 watt, 1V into 8 ohm speakers, this 60W amp is quite as loud as my PA amp with a 260 w/ch 8 ohm rating. One of the benefits of high gain. One channel has original 1970 input & driver transistors, and hisses slightly with no signal. The other channel has modern input & driver transistors and hisses not at all. The power of progress, that $.35 transistors are dead quiet at high gain. Of course, using modern metal film resistors instead of the original 1970 carbon comp resistors help the modern channel hiss less.
Current is calculated from a power rating at I=sqrt(P/Z) where I is current, P is power, and Z is the speaker impedance. Note speaker impedance is typically 4/3 times the resistance you can measure with a DVM ohms scale. Thus my 8 ohm speakers read about 6.5 on the meter, when the battery is fresh.
Have fun shopping or even more adventurous, building an amp.
Last edited:
OK, here are the objective facts, according to the service manuals:
Nakamichi RE-1
Voltage gain: 28.2db
Rails voltage: +/-53.6V
OPS: 1 pair of C3856/A1492
Output power @ 8 ohm: 80W per channel
Weight: 11.5Kg
Yamaha MX1
Voltage gain: 28.4db
Rails voltage: +/-75.3V
OPS: 3 pairs of C3856/A1492
Output power @ 8 ohm: 200W per channel
Weight: 24Kg
Voltage gain is almost the same, although Yamaha has got the volume trimmers at the input
Output current capability - MX1 is roughly 3 times "stronger". This Yamaha is actually a high-class design, built for high performance even at 2 ohm load (up to 320W RMS).
PSU - 2 big transformers, 4 reservoirs (2 x per channel), regulated rails, even for OPS - 2 separate PSUs in fact.
With all respect to Nakamichi - this receiver is just in a different league, one grade down. Much smaller transformer, 2 smaller reservoirs - one PSU for both channels. 1 pair of outputs instead of 3 pairs, lower rails.
In fact, RE1 is just 1/3 of MX1 in terms of current capability.
Assuming both devices are running according to specification - all the rest is just your perception. Most likely, you drive Nakamichi to the limit - at the beginning of clipping, because of extra distortion, the sound seems louder and brighter.
For Yamaha, the same level of power is just roughly 1/3rd of what it can deliver - so no quality degradation.
Cheers,
Valery
Nakamichi RE-1
Voltage gain: 28.2db
Rails voltage: +/-53.6V
OPS: 1 pair of C3856/A1492
Output power @ 8 ohm: 80W per channel
Weight: 11.5Kg
Yamaha MX1
Voltage gain: 28.4db
Rails voltage: +/-75.3V
OPS: 3 pairs of C3856/A1492
Output power @ 8 ohm: 200W per channel
Weight: 24Kg
Voltage gain is almost the same, although Yamaha has got the volume trimmers at the input
Output current capability - MX1 is roughly 3 times "stronger". This Yamaha is actually a high-class design, built for high performance even at 2 ohm load (up to 320W RMS).
PSU - 2 big transformers, 4 reservoirs (2 x per channel), regulated rails, even for OPS - 2 separate PSUs in fact.
With all respect to Nakamichi - this receiver is just in a different league, one grade down. Much smaller transformer, 2 smaller reservoirs - one PSU for both channels. 1 pair of outputs instead of 3 pairs, lower rails.
In fact, RE1 is just 1/3 of MX1 in terms of current capability.
Assuming both devices are running according to specification - all the rest is just your perception. Most likely, you drive Nakamichi to the limit - at the beginning of clipping, because of extra distortion, the sound seems louder and brighter.
For Yamaha, the same level of power is just roughly 1/3rd of what it can deliver - so no quality degradation.
Cheers,
Valery
Wow. Thanks a lot for your time to answer..would have taken me a loong time to at least find out FTC way of rating amps is not used these days.. I'll be calling yamaha to try to get current output per channel. Was thinking of selling it. But looks like I must keep it.
Re-1 outputs 18a per channel with 8ohm speskers.
Waiting for nakamichi ta-4a to arrive.. supposed to output 28a per channel
Re-1 outputs 18a per channel with 8ohm speskers.
Waiting for nakamichi ta-4a to arrive.. supposed to output 28a per channel
18A is not possible for RE-1 just because is uses one pair of C3856/A1492 - one of them works at a time. Those are excellent Sanken transistors. According to the datasheet, maximum current it can handle is 15A - that's the breakdown value, at higher current is will start melting. That's the maximum value. RMS current limit will be lower - roughly 10.7A
MX1 has got three pairs of those in parallel and much bigger PSU, so it can handle roughly 3 times higher currents at the output.
We have to bear in mind - all those systems are voltage-driven, meaning they provide as much current, as demanded. You need to use lower ohm loads to achieve higher currents.
Example calculation. RE-1 - rails are 53.6V, maximum amplitude at the output is, say, 53Vpp = 53 / 1.4 = 37.9V RMS.
At 8 ohm load that gives us I = V/R = 37.9 / 8 = 4.7A
That's the maximum that will ever demanded from RE-1 before clipping.
MX1 can drive more at 8 ohm load, as it's got higher rails - 75.3V, maximum amplitude at the output is, say, 74.7Vpp = 74.7 / 1.4 = 53.3V RMS.
At 8 ohm load that gives us I = V/R = 53.3 / 8 = 6.7A
However, this one can drive up to 2 ohm load, providing 53.3 / 2 = 26.7A in this case. Well, at this power the rails will sag a bit, so the real value will be slightly less - but still a lot.
RE-1 will die at 2 ohm... output stage will burn.
MX1 has got three pairs of those in parallel and much bigger PSU, so it can handle roughly 3 times higher currents at the output.
We have to bear in mind - all those systems are voltage-driven, meaning they provide as much current, as demanded. You need to use lower ohm loads to achieve higher currents.
Example calculation. RE-1 - rails are 53.6V, maximum amplitude at the output is, say, 53Vpp = 53 / 1.4 = 37.9V RMS.
At 8 ohm load that gives us I = V/R = 37.9 / 8 = 4.7A
That's the maximum that will ever demanded from RE-1 before clipping.
MX1 can drive more at 8 ohm load, as it's got higher rails - 75.3V, maximum amplitude at the output is, say, 74.7Vpp = 74.7 / 1.4 = 53.3V RMS.
At 8 ohm load that gives us I = V/R = 53.3 / 8 = 6.7A
However, this one can drive up to 2 ohm load, providing 53.3 / 2 = 26.7A in this case. Well, at this power the rails will sag a bit, so the real value will be slightly less - but still a lot.
RE-1 will die at 2 ohm... output stage will burn.
Being more precise - the real speaker, rated as 8 ohm, always has got some lower R at low frequencies, demanding more current at these frequencies. That's where higher current capability really "plays its role".
More current -> more power without reaching the limits - that's what a good amplifier provides with no hustle
More current -> more power without reaching the limits - that's what a good amplifier provides with no hustle
Thank you very much Mr Vlad (I guess) зайченко..
Is there any chance for u to help me approximate max current on nakamichi ta-4a.
I attached service manual page with transistor pairings.
2SA1492
2SC3856
2 pairs on each channel it looks like.
So far RE--1 max current per channel is around 10 amp? That's like maximum with 4ohm speakers..
Mx1 max current per channel around 30 amp? With 2 ohm speakers
I would guess for ta-4a it's around 18-20 amp per channel. With 4ohm speakers
Basically It would be helpful to kind of aproximate max current of each of these receivers /amplifiers at 8 and 4ohm loads.. I've seen these transistor pairings on many Japanese amps. .Pretty sure onkyo used them. In future this may be very helpful to approximate power of an amp by looking at your sample calculations
I understand that yamaha mx1+cx1 are superb amps) I actually shuffled through all m series and left this mx1/cx1 combo. Serious build quality. . And sonics. Of course it's all personal. )
Glad you both mentioned gain.. was confused about watts vs volume level..
Ive had amps with power meters before. And my loud listening volumes on average are around 50watts (based on onkyo m504 readings, and yamaha m85, both sold )
I don't play concert stadium volume levels..
Only worry is that I don't damage these beautiful furniture /great speakers by vienna. Long time ago I powered power hungry polk SDA-Crs speakers with hdmi /Bluetooth ready receiver.. and few times at loud volumes I've smelled some nasty smell from speakers. I'd guess it was ferrofluid in tweeters or insulation. Speakers played fine. I upgraded tweeters and sold speakers later. Just don't want this gradual clipping damage to these viennas.
Any chance to send clipped signal to these 4 ohm speakers with nakanichi TA-4a at 9-11 o'clock volume knob position? Or with RE-1 at 9 clock position
Is there any chance for u to help me approximate max current on nakamichi ta-4a.
I attached service manual page with transistor pairings.
2SA1492
2SC3856
2 pairs on each channel it looks like.
So far RE--1 max current per channel is around 10 amp? That's like maximum with 4ohm speakers..
Mx1 max current per channel around 30 amp? With 2 ohm speakers
I would guess for ta-4a it's around 18-20 amp per channel. With 4ohm speakers
Basically It would be helpful to kind of aproximate max current of each of these receivers /amplifiers at 8 and 4ohm loads.. I've seen these transistor pairings on many Japanese amps. .Pretty sure onkyo used them. In future this may be very helpful to approximate power of an amp by looking at your sample calculations
I understand that yamaha mx1+cx1 are superb amps) I actually shuffled through all m series and left this mx1/cx1 combo. Serious build quality. . And sonics. Of course it's all personal. )
Glad you both mentioned gain.. was confused about watts vs volume level..
Ive had amps with power meters before. And my loud listening volumes on average are around 50watts (based on onkyo m504 readings, and yamaha m85, both sold )
I don't play concert stadium volume levels..
Only worry is that I don't damage these beautiful furniture /great speakers by vienna. Long time ago I powered power hungry polk SDA-Crs speakers with hdmi /Bluetooth ready receiver.. and few times at loud volumes I've smelled some nasty smell from speakers. I'd guess it was ferrofluid in tweeters or insulation. Speakers played fine. I upgraded tweeters and sold speakers later. Just don't want this gradual clipping damage to these viennas.
Any chance to send clipped signal to these 4 ohm speakers with nakanichi TA-4a at 9-11 o'clock volume knob position? Or with RE-1 at 9 clock position
Last edited:
So one thing I noticed is that when powering these speAkers with yamaha mx1 highs are more airy/ "splashy?" ) more volume or 3d effect in highs. Same speakers with say luxman r115 don't sound as airy. Flatter duller highs. But with re1 similar airyliness.. 3Dness.
Not sure if harmonic time alignment on Re1 is a gimick or a real deal.
Basically another question is .. would ta-4a or re-1 have sufficient current to bring full potential of these viennas at moderate volumes.. )?9-11 o'clock volume knob. If i need louder volumes Id no doubt use mx1
Not sure if harmonic time alignment on Re1 is a gimick or a real deal.
Basically another question is .. would ta-4a or re-1 have sufficient current to bring full potential of these viennas at moderate volumes.. )?9-11 o'clock volume knob. If i need louder volumes Id no doubt use mx1
I don't know the characteristics of your particular speaker. You may download a datasheet, but if sold to consumers it is likely to not say much useful. My 1/8 watt habit is using horn speakers of high efficiency, 101 db @ 1W 1 M. Most acoustic suspension speakers are much less efficient, often being about 84 db @ 1W 1M.
Ordinarily in PA service, bands buy an amp with about twice the watt rating of the speaker. This is to avoid clipping damage. Of course your home speakers may not have a watt rating published. But guitar/bass/singer bands are prone to use the "crunch" pedal which produces a lot of flat top waves with heavy high freq components, which tend to toast tweeters and stress the woofer too. See the Hartley Peavey white paper on speaker design where this practice caused a lot of warrenty returns in his company's early days. His company designed a patented "DDT" circuit for their PA amps, that detects when the signal has excessive high frequency component, and turns down the input gain during that time. Also lights a lamp on the front panel.
Some extremely professional PA grade speakers have current limiters on the tweeters, usually an incandescent light bulb or PTC resistor in series after the crossover network.
Bands also employ "limiters" between the mixing board and the amp, to keep from sending a out a signal of dangerous content to the amps.
This tweeter problem is one I've had. I've blown two tweeters in two different speakers, with a tube amp of 35 W/ch which is not known for oscillating ultrasonically very frequently. That state of an amp will blow tweeters. I didn't smell anything, just I noticed my highs were missing on one side, and found the tweeter open on the ohms scale.
PA line Yamahas are one of the four brands recommended by a repairman on here as being competent, and are conservatively rated for watts. How one sorts out the consumer market products sold under the same name I don't know. Others are QSC, Crown, & Peavey.
You can approximate the current limit of output transistors by looking at the datasheet, at the "SOA" spec. This is a plot of the absolute maximum the transistor can put out if the case is at 25 deg C, at a range of voltages. One assumes the voltage on the table are lower for 2 ohm speakers for example, than 8 ohm speakers. This makes the SOA bigger for 2 ohm speakers. You'll notice the current goes up as the voltage decreases. State of the art TO3 transistors tend to be 2.5 to 3 amps max SOA, with the Sanyo MT200 package ones just a little higher. Datasheets for most transistors are on datasheetcatalog.com
The max current available from a given receiver may also be limited by the rail voltage, particularly on the 8 ohm rating. Receivers may also have a limited power transformer, which limits the amount of current available itself, once the rail caps are discharged. PA line speakers with 8 ohm 4 ohm and 2 ohm power ratings are rated for that by test, not some theoretical datasheet calculation. Most consumer products don't have a 2 ohm rating.
Ordinarily in PA service, bands buy an amp with about twice the watt rating of the speaker. This is to avoid clipping damage. Of course your home speakers may not have a watt rating published. But guitar/bass/singer bands are prone to use the "crunch" pedal which produces a lot of flat top waves with heavy high freq components, which tend to toast tweeters and stress the woofer too. See the Hartley Peavey white paper on speaker design where this practice caused a lot of warrenty returns in his company's early days. His company designed a patented "DDT" circuit for their PA amps, that detects when the signal has excessive high frequency component, and turns down the input gain during that time. Also lights a lamp on the front panel.
Some extremely professional PA grade speakers have current limiters on the tweeters, usually an incandescent light bulb or PTC resistor in series after the crossover network.
Bands also employ "limiters" between the mixing board and the amp, to keep from sending a out a signal of dangerous content to the amps.
This tweeter problem is one I've had. I've blown two tweeters in two different speakers, with a tube amp of 35 W/ch which is not known for oscillating ultrasonically very frequently. That state of an amp will blow tweeters. I didn't smell anything, just I noticed my highs were missing on one side, and found the tweeter open on the ohms scale.
PA line Yamahas are one of the four brands recommended by a repairman on here as being competent, and are conservatively rated for watts. How one sorts out the consumer market products sold under the same name I don't know. Others are QSC, Crown, & Peavey.
You can approximate the current limit of output transistors by looking at the datasheet, at the "SOA" spec. This is a plot of the absolute maximum the transistor can put out if the case is at 25 deg C, at a range of voltages. One assumes the voltage on the table are lower for 2 ohm speakers for example, than 8 ohm speakers. This makes the SOA bigger for 2 ohm speakers. You'll notice the current goes up as the voltage decreases. State of the art TO3 transistors tend to be 2.5 to 3 amps max SOA, with the Sanyo MT200 package ones just a little higher. Datasheets for most transistors are on datasheetcatalog.com
The max current available from a given receiver may also be limited by the rail voltage, particularly on the 8 ohm rating. Receivers may also have a limited power transformer, which limits the amount of current available itself, once the rail caps are discharged. PA line speakers with 8 ohm 4 ohm and 2 ohm power ratings are rated for that by test, not some theoretical datasheet calculation. Most consumer products don't have a 2 ohm rating.
Last edited:
Yes, for Richard - it's important to understand, that the maximum current at the output of an amplifier is a "potential capability".
The load is driven by the voltage from the amplifier's output.
Let say, the amplifier gives 10V RMS at the output. The load is 8R.
In this case, the power W = V * V / R = 100/8 = 12.5W
Output current I = V / R = 1.25A
So, as far as the load R is constant (8R), the current only depends on the voltage at the amplifier's output. The current is "demanded" by the load. It will not increase by itself.
It will only increase if:
- the output voltage goes up;
- the load R goes down.
Speaker's impedance is rather complex thing - it's never really 8R, it also depends on the frequency, especially in the lower range of frequencies. This is where the currents will be higher because of lower impedance.
I also agree with Indianajo on the limiting factors - normally, first of all it's the power supply (receivers always get smaller supplies than required - power amps are better in this department). Then - the output transistors' SOA comes in, resulting in overheating, explosions and other unpleasant effects
Thinking about how "tightly" the amplifier controls the speaker, we also have to consider the output impedance of the speaker - imagine it as a resistor equivalent in series with the load. The lower the value of this resistor - the less its influence - the tighter the amplifier controls the speaker. However, in the feedback amplifiers, this value is significantly decreased by the feedback, typically coming down to less than 0.01 ohm.
The load is driven by the voltage from the amplifier's output.
Let say, the amplifier gives 10V RMS at the output. The load is 8R.
In this case, the power W = V * V / R = 100/8 = 12.5W
Output current I = V / R = 1.25A
So, as far as the load R is constant (8R), the current only depends on the voltage at the amplifier's output. The current is "demanded" by the load. It will not increase by itself.
It will only increase if:
- the output voltage goes up;
- the load R goes down.
Speaker's impedance is rather complex thing - it's never really 8R, it also depends on the frequency, especially in the lower range of frequencies. This is where the currents will be higher because of lower impedance.
I also agree with Indianajo on the limiting factors - normally, first of all it's the power supply (receivers always get smaller supplies than required - power amps are better in this department). Then - the output transistors' SOA comes in, resulting in overheating, explosions and other unpleasant effects
Thinking about how "tightly" the amplifier controls the speaker, we also have to consider the output impedance of the speaker - imagine it as a resistor equivalent in series with the load. The lower the value of this resistor - the less its influence - the tighter the amplifier controls the speaker. However, in the feedback amplifiers, this value is significantly decreased by the feedback, typically coming down to less than 0.01 ohm.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.