?? dB=<88 loudspeaker and SET like Aries Cerat Diana Forte; how does this match?

RdW

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Probably brought up somewhere else in WBF but I am still puzzled to understand, theoretically vs reality, how a 40 to 60-isch Watt SET would not get the best out of a low sensitive 85-88 dB loudspeaker?

Mathematically, and if one like to listen to let's say a sound pressure of 88dB(A) on average at a listening position that is 3 mtr away from the loudspeakers, applying p=pn + 10*log(P) - 20*log(d) , where p=dB(A) SPL listening position, pn=dB sensitivity loudspeakers, d=distance listening position to loudspeakers and P is Amp power, one would theoretically only need 30 Watt to arrive at a 91dB average loudness (88dB + 3dB headroom; doubling the power need to prevent distortion or fatigue) with 86dB sensitive loudspeakers.

Why is it that there is so much debate that relatively low power SET's would not be able to drive low sensitive loudspeakers?
 

asiufy

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It's not about the average SPLs, it's about peaks, and instantaneous power to properly convey the dynamic swings in the music.
 

RdW

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It's not about the average SPLs, it's about peaks, and instantaneous power to properly convey the dynamic swings in the music.

Thanks. I doubled the power of the amp output (+3 dB) assuming this would be sufficient for the peaks. But that assumption is probably to simple :rolleyes:.

My TAD CR-1's are rated 86dB @ 4ohm with a recommended maximum input power of 200 Watt, but what about minimum power required? I have read on this forum that these TADs need power to get the best out of them, but I also read that this would count for a pair of Sonus Faber Aida 2s rated @ 92 dB that can handle up to 1K Watt. Hence the confusion, not having the full picture how this works.

One way of the other my ears like amps based on SET technology and am simply trying to understand if a 60 Watt Aries Cerat Diana Forte would be an options. I also had the opportunity to listen to the 40 Watt Trafomatic Pandora's, although push-pull, they were good to my ears as well.

But I guess the answer is as usual that one need to audition, which is not always that simple.
 
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DeadWax

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but what about minimum power required?
Meeting minimum power requirements on paper is unlikely to meet you other stated goal:
get the best out of a low sensitive 85-88 dB loudspeaker?
As @Atmasphere has pointed out many times here. it's important to have substantial headroom with SETs. Rather than focusing on the sensitivity rating I'd be more worried about the load. From my pretty limited experience I don't think you're going to get the most out of your speakers using a SET if your speakers drop below 8 ohms along the frequency range.
 

RdW

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Meeting minimum power requirements on paper is unlikely to meet you other stated goal:

As @Atmasphere has pointed out many times here. it's important to have substantial headroom with SETs. Rather than focusing on the sensitivity rating I'd be more worried about the load. From my pretty limited experience I don't think you're going to get the most out of your speakers using a SET if your speakers drop below 8 ohms along the frequency range.

Thanks, I understand I need to improve my search skills here on WBF. Found the thread that indeed explains a lot.
 

Aries Cerat

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Hello
Not all SET as designed the same.A SET can drive down to 1 ohm if the output transformer is configured at that load.

The Forte has impedance selector switches,with which you can select impedance range for your speakers,so as the amplifier is always working optimally. Standard range on the switch mapping is 1-2 , 2-4 and 4-8 ohms.
The impedance selector system reconfigures the secondary windings of the transformer on the fly, so that the reflected load back to the tubes stays withing optimal range.

SETs not driving anything below 8ohm is misquided old news.

Where are you located, maybe a trial will go a long way. Our UK distributor has big Tad and Concero 65 (same output as Forte).

Cheers
Stavros
 
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RdW

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Hello
Not all SET as designed the same.A SET can drive down to 1 ohm if the output transformer is configured at that load.

The Forte has impedance selector switches,with which you can select impedance range for your speakers,so as the amplifier is always working optimally. Standard range on the switch mapping is 1-2 , 2-4 and 4-8 ohms.
The impedance selector system reconfigures the secondary windings of the transformer on the fly, so that the reflected load back to the tubes stays withing optimal range.

SETs not driving anything below 8ohm is misquided old news.

Where are you located, maybe a trial will go a long way. Our UK distributor has big Tad and Concero 65 (same output as Forte).

Cheers
Stavros

Thanks Stavros. Always nice to have feedback from the master himself :)

Interesting to learn that your amps have taking into account difference speaker impedance loads. I’m not an expert but assume this means your amps can provide peak current when driving more challenging speaker. My TADs btw seem to operate above 7.5 Ohm all the time and only drops to 4 or below between 40 and 225Hz.

I am in the Netherlands which makes auditioning a challenge.
 

Atmasphere

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SETs not driving anything below 8ohm is misquided old news.

It does not matter what sort of amp you have, it will be compromised in some way when asked to drive a lower impedance load. If solid state, its likely to make more distortion, which will be audible as brightness and harshness since the distortion will be mostly higher ordered harmonics. If an output transformer is involved, you will get less power (since driving lower impedances makes the transformer less efficient) and often less bandwidth for the same reason. Usually the bottom octave is the one that suffers the most, but that is a compromise worked out by the designer of the output transformer.
 
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DeadWax

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Well I''m always the expert when it comes to delivering old news :confused: But honestly, I was suggesting just from my own layman's experience that driving speakers with lower loads may not get the most out of a SET amp. It's nice to hear that the "new" news indicates the technology and designs have evolved.
 

Aries Cerat

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It does not matter what sort of amp you have, it will be compromised in some way when asked to drive a lower impedance load. If solid state, its likely to make more distortion, which will be audible as brightness and harshness since the distortion will be mostly higher ordered harmonics. If an output transformer is involved, you will get less power (since driving lower impedances makes the transformer less efficient) and often less bandwidth for the same reason. Usually the bottom octave is the one that suffers the most, but that is a compromise worked out by the designer of the output transformer.


I am sorry but, no. If the output transformer is specifically designed to drive low impedances,it will have full power at low impedances.

If the same amplifier is equipped with OPT to drive 0.1 ohm ,it will drive 0.1 ohm, period.And at full power.Been there done that.( but that amplifier will NOT be optimal for 8 ohm as you can imagine)

What is an actual issue,is varying impedance,and depending on output impedance of output stage,the power vs freq response will "follow" the impedance vs freq response.
A speaker which is 3 ohm flat, is better handled, than a speaker that varies from 5 to 20 ohm ,to a non feedback amplifier.Given that the OTP is designed for that load that is.

More so with higher output impedance of output tubes,less so with low OI.

The impedance selector on our OPT can deliver full power to 1 ,2, 4, or 8ohm ,assuming you use the configuration switches.

Also nothing to do with efficiency of OPT. Copper losses are always the same with this system.


Cheers
Stavros
 

DeadWax

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@Aries Cerat Hi Stavros - just trying to learn a little here, hence my question. I've always been under the impression that amplifiers produce less distortion when driving a higher impedance load. Are you saying there are design approaches that overcome that? Perhaps my understanding isn't a even a true generalization?
 

Aries Cerat

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@Aries Cerat Hi Stavros - just trying to learn a little here, hence my question. I've always been under the impression that amplifiers produce less distortion when driving a higher impedance load. Are you saying there are design approaches that overcome that? Perhaps my understanding isn't a even a true generalization?

Hello there.Happy to answer.

Tubes in general have lower distortion , the higher the load is.Correct.
In OTL designs, the tube "sees" a load (the speaker load),divided by number of tubes. If the load is halved,then the number of tubes must be doubled, if we want for each of the tube in the output stage to see the same impedance as before.

However
A transformer is an impedance matcher.The load that each of the tube "sees" is the impedance of the load multiplied by step down ratio squared.

For example, a tube in a SET output stage, will "see" a 8 ohm load as 5000ohm if a 25:1 step down is used. If the load becomes 4ohm, and if we keep the same step down ratio of 25:1, the reflected load will be 2500ohm.

In that case,obviously the tube will suffer from reduced power and higher distortion level.
Now,if we increase the step down ratio by a factor of 1.4 ,the reflected load will be again 5000ohm.Tube is happy again,delivering same power and same distortion as in the 8ohm load.

Now,how this is done( the increase in step down ratio of the OTP) , is where the whole game is.Sub par solutions end up with lower bandwidth and/or higher copper losses.But there are some techniques/solutions then bend around these issues.

A tube stage loaded with a step down transformer has absolutely no problem delivering extremely low distortions and high power even down to 0.1ohm, if the transformer is designed for that purpose.

Cheers
Stavros
 

DeadWax

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@Aries Cerat Incredibly helpful! You explained that in terms even I could understand. Much appreciated :)
 

RdW

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Hello there.Happy to answer.

Tubes in general have lower distortion , the higher the load is.Correct.
In OTL designs, the tube "sees" a load (the speaker load),divided by number of tubes. If the load is halved,then the number of tubes must be doubled, if we want for each of the tube in the output stage to see the same impedance as before.

However
A transformer is an impedance matcher.The load that each of the tube "sees" is the impedance of the load multiplied by step down ratio squared.

For example, a tube in a SET output stage, will "see" a 8 ohm load as 5000ohm if a 25:1 step down is used. If the load becomes 4ohm, and if we keep the same step down ratio of 25:1, the reflected load will be 2500ohm.

In that case,obviously the tube will suffer from reduced power and higher distortion level.
Now,if we increase the step down ratio by a factor of 1.4 ,the reflected load will be again 5000ohm.Tube is happy again,delivering same power and same distortion as in the 8ohm load.

Now,how this is done( the increase in step down ratio of the OTP) , is where the whole game is.Sub par solutions end up with lower bandwidth and/or higher copper losses.But there are some techniques/solutions then bend around these issues.

A tube stage loaded with a step down transformer has absolutely no problem delivering extremely low distortions and high power even down to 0.1ohm, if the transformer is designed for that purpose.

Cheers
Stavros

Thanks Stavros for the details. Readers might appreciate this.

To come back to your earlier remark, Is it an option to auditioning your fine amps in NL?
 

Atmasphere

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I am sorry but, no. If the output transformer is specifically designed to drive low impedances,it will have full power at low impedances.
This statement is false. It essentially presumes that you can get something for nothing. The challenge that any transformer manufacturer faces is that the more windings you put on the device, the greater issues getting it to perform. A typical example is a transformer with 4,8 and 16 ohm windings. The simple fact is that it will perform best on the 16 ohms tap (always assuming that it is properly loaded for my comments here); it will have wider bandwidth and actually make a slightly greater amount of power since less of the amplifier power is being converted into heat in the transformer since it is able to operate more efficiently. Operating on the 4 ohm tap it may well lose an octave out of the bass response.

Now if the transformer has taps for 1,2,3 and 4 ohms the same is true- the 4 ohm tap will have the best performance. But its also easy to show that if that transformer also had an 8 ohm tap that its performance on 8 ohms would be better than on the 1 ohm tap. This should come as no surprise to anyone! As the winding impedance is reduced, there is something called 'IsquaredR' losses that increases, so to compensate you have to use heavier wire. This makes the winding harder to conform to the core and you get less efficiency- more amplifier energy is converted to heat.

When you are dealing with low impedance loads you have a number of serious obstacles to overcome. One is the speaker cable- as the load impedance is reduced, the speaker cable becomes far more critical and should be kept absolutely as short as possible. Another is the output impedance of the amplifier itself since that amplifier will offer less damping to the speaker. Most of the low impedance speakers I'm aware of seem to be designed for amps that have a rather high damping factor, although no speaker I'm aware of needs more than about 20:1. So matching between the amp and the speaker might become an issue despite having taps to do the job.

We used to make an outboard matching autoformer for our amps, and since we have Magnaplanar in our back yard so to speak, a lot of our customers wanted to put our amps with their speakers. The autoformer was our solution- it offered taps down to 1 ohm (which historically made us likely the first tube amplifier manufacturer to be able to effortlessly drive a set of the old Apogee Full Range loudspeakers, which are 1 ohm). As any transformer designer probably knows, to make a successful transformer design you 'wind' up building a lot of prototypes and the same was true with us. The thing is, we like bandwidth (our amps are full power to 1 or 2Hz depending on the model; this is to prevent phase shift at 20Hz so to maintain impact). So low frequency bandwidth below 10Hz was very important in our design and we went through a few. We got it to go to 2Hz. Most transformers can't do this simply because the turns ratio gets too high (inductance takes its toll in a number of ways!), but in our case we could get away with it because our amps already have a fairly low output impedance compared to 300bs, KT988s and the like- our amps had a value low enough to drive speakers directly. So we had a very close up and personal experience with this.

I will concede that if low frequencies are limited to a cutoff several octaves higher, it may seem that there is little difference in low frequency bandwidth when lower impedance taps are employed. But the simple fact is that will happen, and the other simple fact is that if you really want to get the most out of your amplifier (if sound quality is the goal) your amplifier dollar investment will be best served by a speaker of higher impedance. This is true regardless of the amplifier you run (tube, solid state, classD) and its easy to see in the distortion specs. Its also audible; the ear uses higher ordered harmonics to sense sound pressure (so is keenly sensitive to these harmonics). When any amplifier makes higher distortion, it will include the higher orders, which the ear interprets not only as loudness but also as harshness and brightness. High end audio is usually all about getting the music to sound real. If some other goal is desired, such as sound pressure, then you have a weak argument (perhaps only 3dB) for lower impedances if you have solid state amp that can drive them.
 
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RdW

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And I though I was asking a simple question :eek:.

But great to see that two movers and shakers in this industry are having this conversation. My assumption however is that both of you are manufacturing great products as Aries Cerat and Atmasphere have found there way to the homes of happy customers.

But to be honest, I’m a bit lost now ...
 

Aries Cerat

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Hello

You assume i am speaking about tapped designs.I know that OTP are not your main thing so i could understand your assumption,which leads you to very wrong conclusions.
Tapped secondaries is, as it seems ,the industry norm in tube amplifier designs, a choice which carries the correctly pointed faults.We do not use this technique.

We are not talking about tapped secondaries though.For example,the 2 ohm configuration has 8 times less DCR than the 8 ohm configuration. That being said, the copper (heat losses) will be trivial.No higher power losses in lower impedance.
The inductance however in 2ohm is lower by 1.4 , so LF cut off is higher, but if 8ohm is flat at 5Hz then it is of no real consequence for the 2ohm.
The solution we use takes use of the same layers of secondaries, leakage inductance is same and lower than 8ohm,so HF does not suffer as in tapped designs.

There is no free meal in all designs,as you pointed out.
This is either we are talking OTL vs transf designs, SS VS tube.
If you want to use tubes and have useful DF without feedback, a healthy reflected load to the tube so you can have lower distortion,again without feedback then an OTP with enough step down ratio is the way to go.No free launches but you choose you poison.


This is the same give and take ,as when talking transformer design.The 8ohm tap does sound and measure better.But if some one has to have low impedance speakers,to be able to drive them ,deliver the needed current,then a higher step down ratio must be used. How this is designed,is the key,and the significant factor why some SET sound dull and dead and some shine.
Generally speaking in OPT design, you will sacrifice some HF for lower LF or some LF for higher HF. This is unavoidable.How much you sacrifice depends on the design.Fortunately not all are designed the same.Higher step up ratios are much more difficult to design. For example a 10k:8 OPT for a 211 tube can never be as good as a 1k:8 transformer,all techniques used being equal. Some of our designs use 2:1 step down ratios.Our higher powered class A amp was a 40tube per channel OTL strapped to a 3:1 transformer.It idled at 6A per channel.Proper furnace of an equipment.

I 100% agree on the lower impedance speakers.Usually multidriver cone speakers with absurd crossovers.Who needs them:)

About higher damping factor, and the fact that in a 2ohm speaker,the speaker cable will ruin the DF, you are preaching to the Pope here. After all, the best drivers ever made up to date , are overdamped by design,they not only do not need high DF, from the amplifier, but high DF kills their performance.

I am also happy to see that you agree that ,the only way to match tubes with really low impedances is through auto/transfromers. Now, why would anyone go to the trouble of using such a low impedance/sensitivity speaker,like you imply on your last sentence, again you are preaching to the choir.

Thank you for the chat
Stavros
 

Atmasphere

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The inductance however in 2ohm is lower by 1.4 , so LF cut off is higher, but if 8ohm is flat at 5Hz then it is of no real consequence for the 2ohm.
The 8ohm tap does sound and measure better.But if some one has to have low impedance speakers,to be able to drive them ,deliver the needed current,then a higher step down ratio must be used. How this is designed,is the key,and the significant factor why some SET sound dull and dead and some shine.
About higher damping factor, and the fact that in a 2ohm speaker,the speaker cable will ruin the DF, you are preaching to the Pope here. After all, the best drivers ever made up to date , are overdamped by design,they not only do not need high DF, from the amplifier, but high DF kills their performance.

Hm. This really reads to me as if we are on the same page- you've supported all my comments.
 
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Alrainbow

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Hello

You assume i am speaking about tapped designs.I know that OTP are not your main thing so i could understand your assumption,which leads you to very wrong conclusions.
Tapped secondaries is, as it seems ,the industry norm in tube amplifier designs, a choice which carries the correctly pointed faults.We do not use this technique.

We are not talking about tapped secondaries though.For example,the 2 ohm configuration has 8 times less DCR than the 8 ohm configuration. That being said, the copper (heat losses) will be trivial.No higher power losses in lower impedance.
The inductance however in 2ohm is lower by 1.4 , so LF cut off is higher, but if 8ohm is flat at 5Hz then it is of no real consequence for the 2ohm.
The solution we use takes use of the same layers of secondaries, leakage inductance is same and lower than 8ohm,so HF does not suffer as in tapped designs.

There is no free meal in all designs,as you pointed out.
This is either we are talking OTL vs transf designs, SS VS tube.
If you want to use tubes and have useful DF without feedback, a healthy reflected load to the tube so you can have lower distortion,again without feedback then an OTP with enough step down ratio is the way to go.No free launches but you choose you poison.


This is the same give and take ,as when talking transformer design.The 8ohm tap does sound and measure better.But if some one has to have low impedance speakers,to be able to drive them ,deliver the needed current,then a higher step down ratio must be used. How this is designed,is the key,and the significant factor why some SET sound dull and dead and some shine.
Generally speaking in OPT design, you will sacrifice some HF for lower LF or some LF for higher HF. This is unavoidable.How much you sacrifice depends on the design.Fortunately not all are designed the same.Higher step up ratios are much more difficult to design. For example a 10k:8 OPT for a 211 tube can never be as good as a 1k:8 transformer,all techniques used being equal. Some of our designs use 2:1 step down ratios.Our higher powered class A amp was a 40tube per channel OTL strapped to a 3:1 transformer.It idled at 6A per channel.Proper furnace of an equipment.

I 100% agree on the lower impedance speakers.Usually multidriver cone speakers with absurd crossovers.Who needs them:)

About higher damping factor, and the fact that in a 2ohm speaker,the speaker cable will ruin the DF, you are preaching to the Pope here. After all, the best drivers ever made up to date , are overdamped by design,they not only do not need high DF, from the amplifier, but high DF kills their performance.

I am also happy to see that you agree that ,the only way to match tubes with really low impedances is through auto/transfromers. Now, why would anyone go to the trouble of using such a low impedance/sensitivity speaker,like you imply on your last sentence, again you are preaching to the choir.

Thank you for the chat
Stavros


Your last question is easy , people use them because they can be made to sound better than over damped , high distortion shouty high sensitivity speakers with no sense of space and timing ...

Errr , just saying ... :)
 

Alrainbow

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Two sides to this audio coin , one mans euphoria is another's anathema , every discussion is becoming the same , getting tired of all this Horns for All WW2 stuff as if everyone else is stupid ....
 
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