Starke Sound Fiera4 4CH Amplifier Does It Meet Power Spec?

[gene]

The Starke Sound AD4.320 was recently discontinued and replaced by the Fiera4. We wanted to see IF this new amp could meet power spec as we were assured by Starke Sound that it would. This amp has a completely redesigned power supply. The old amp had a linear supply and this new model has SMPS which has some advantages discussed in this test report.

The Starke Sound Fiera4 is a four channel Class D amplifier. It provides plenty of power to juice your home theater (130wpc x4 into 8 ohms, 250wpc x 4 into 4 ohms) in a light weight and energy efficient package. Build quality is among the best in the business for this price class and performance is respectable as well. Check out our quick review to see our take on this amplifier and to decide if it's for you.

Read: Starke Sound Fiera4 Bench Test Results

Labor Day Sale: the Fierra4 is currently on sale for $1,299

 

[shadyJ]

Good stuff, Matthew, nice review! This one looks like a big improvement over the AD4.320. I should probably look at something like this since I am having problems with my current amplifier.

 

[ryanosaur]

Good write up; thank you @Matthew J Poes !

 

[Kvn_Walker]

That's a good rebound after the last PR disaster. Very nice looking amp too.

 

[TLS Guy]

It is interesting to see Class D amplifiers coming of age. I suspect they will continue to improve.

The issue that concerns me most about that amplifier compared to Hypex and Purifi amps is the increased output/source resistance. This is a key parameter in my experience, and does not show its ill effects on bench tests. However the issue becomes, is that the higher the source resistance/impedance, the higher the likelihood the frequency response will tend towards the impedance curve of the speaker it is driving. The is one of the biggest limitations of tube amplifiers.

This becomes important, as people who have speakers with problem difficult to drive loads including, but not limited to adverse impedance curves, are in general the first to want external power amplification. So my concern is that there may very well be, and probably is, an audible difference between this amp and a Hypex or Purifi amp driving a speaker with impedance and phase angle curves that look like a mountain range.

Of course this highlights a big advantage of active speakers, because it is the passive crossovers that are the cause of these difficult loads. In active speakers the load is less complex and therefore the source impedance is of lesser importance.

This issue is at the crux of the issue of divergence of bench and listening tests of amplifiers.

That is one of the reasons I have stuck with Quad amplification, the other being reliability. But it really does require, in my opinion, that designers move low source resistance/impedance well to the top of their design goals.

 

[Matthew J Poes]

It is interesting to see Class D amplifiers coming of age. I suspect they will continue to improve.

The issue that concerns me most about that amplifier compared to Hypex and Purifi amps is the increased output/source resistance. This is a key parameter in my experience, and does not show its ill effects on bench tests. However the issue becomes, is that the higher the source resistance/impedance, the higher the likelihood the frequency response will tend towards the impedance curve of the speaker it is driving. The is one of the biggest limitations of tube amplifiers.

This becomes important, as people who have speakers with problem difficult to drive loads including, but not limited to adverse impedance curves, are in general the first to want external power amplification. So my concern is that there may very well be, and probably is, an audible difference between this amp and a Hypex or Purifi amp driving a speaker with impedance and phase angle curves that look like a mountain range.

Of course this highlights a big advantage of active speakers, because it is the passive crossovers that are the cause of these difficult loads. In active speakers the load is less complex and therefore the source impedance is of lesser importance.

This issue is at the crux of the issue of divergence of bench and listening tests of amplifiers.

That is one of the reasons I have stuck with Quad amplification, the other being reliability. But it really does require, in my opinion, that designers move low source resistance/impedance well to the top of their design goals.

While I understand what you are saying, you picked on the wrong amps. The output impedance of the Purifi amplifier is extremely low. 65 micro-ohms at 1khz. While it does rise with frequency, it does so far less than others. That’s why the amplifiers frequency response changes so little with load. It’s the lowest I’ve ever seen. It’s damping factor is over 2000. There are very few if any Class AB amplifiers doing that.

 

[Verdinut]

While I understand what you are saying, you picked on the wrong amps. The output impedance of the Purifi amplifier is extremely low. 65 micro-ohms at 1khz. While it does rise with frequency, it does so far less than others. That’s why the amplifiers frequency response changes so little with load. It’s the lowest I’ve ever seen. It’s damping factor is over 2000. There are very few if any Class AB amplifiers doing that.

The output impedance of the Purifi amplifier being at 1 kHz is only 65 micro-ohms, then what is it between 20-100 Hz which are in my opinion the most critical frequencies for good transient response with loudspeakers having a higher Qts and other hard to drive ones.

 

[gene]

The output impedance of the Purifi amplifier being at 1 kHz is only 65 micro-ohms, then what is it between 20-100 Hz which are in my opinion the most critical frequencies for good transient response with loudspeakers having a higher Qts and other hard to drive ones.

wow lots of mysticism here surrounding class D amps. The Purifi amp has ruler flat frequency response from 10Hz to 20kHz regarding loaded or unloaded. Anyone claiming the output impedance of a good Class D amp isn't low enough, is spurting dogmatic views or poor understanding of new technologies.

 

[Verdinut]

wow lots of mysticism here surrounding class D amps. The Purifi amp has ruler flat frequency response from 10Hz to 20kHz regarding loaded or unloaded. Anyone claiming the output impedance of a good Class D amp isn't low enough, is spurting dogmatic views or poor understanding of new technologies.

No, it is just by curiosity that I was asking the figure for the low frequencies. I never doubted about the Purifi amplifier's output impedance at low frequencies.

Most Class AB amp manufacturers usually publish damping factor for their products at 1 kHz, but that doesn't clearly specify what it is at lower frequencies. Also, if the damping factor is published, they seldom specify for what impedance load. We know that for a 4 ohm load, the damping factor specified at 8 ohm is halved. Of course, well designed SS amplifiers have a low output impedance.

 

[gene]

No, it is just by curiosity that I was asking the figure for the low frequencies. I never doubted about the Purifi amplifier's output impedance at low frequencies.

Most Class AB amp manufacturers usually publish damping factor for their products at 1 kHz, but that doesn't clearly specify what it is at lower frequencies. Also, if the damping factor is published, they seldom specify for what impedance load. We know that for a 4 ohm load, the damping factor specified at 8 ohm is halved. Of course, well designed SS amplifiers have a low output impedance.

Damping factor is a meaningless spec beyond a value of 50 or so. Cable impedance swamps it out. The only time I ever see output impedance being an issue is with older tube amp designs and some poor behaved Class D amps. Load invariant amps are pretty common these days with good designs.

 

[lovinthehd]

Definite improvement over that first Stark amp tested!

 

[TLS Guy]

The output impedance of the Purifi amplifier being at 1 kHz is only 65 micro-ohms, then what is it between 20-100 Hz which are in my opinion the most critical frequencies for good transient response with loudspeakers having a higher Qts and other hard to drive ones.

I have looked to see what the damping factor of these class D amps actually is. For other members damping factor is the load impedance (speaker impedance) divided by the amplifier source impedance. So for example my Quad 909 amps have a source impedance of 0.05 ohms. So driving an 8 ohm load that gives a damping factor of 20, which for a Class AB amp is considered very good.

If we look a what has been measured for class D amps they stack up well.

This is the Hypex N-core.

This is the damping factor for the Fiera4

You can see that their is significant drop starting above 2000 Hz, and by 20K it is poor. Again this is with an 8 ohm load. With a four ohm load the damping factor will be halved.

On that parameter the Hypex shows excellent performance. The Fiera4 I think might well not be a stellar performer with four ohm speakers presenting complex loads above 5K.

So on that parameter the Hypex scores higher. It is not clear to me why the source impedance appears to be rising with frequency in the Fiera4. As of yet I have no experience with class D amps. I am not aware of class A or AB amps, having a frequency dependent source impedance. Although the Quad performs as class A, the output transistors are biased class B, and a small class A amp provides a feed forward error correction, resulting in spec. that is like a class A amp, but without the inefficiency of class A biasing. That is unique to Quad current dumping amps.

 

[Verdinut]

Damping factor is a meaningless spec beyond a value of 50 or so. Cable impedance swamps it out. The only time I ever see output impedance being an issue is with older tube amp designs and some poor behaved Class D amps. Load invariant amps are pretty common these days with good designs.

Also all expensive McIntosh SS amplifiers with transformers in their output stages have a published wideband damping factor under 50, while some of their tube amps have a DF of only about 25. They don't specify for what load, I would assume that it represents figures for an 8 ohm load.

 

[Matthew J Poes]

The output impedance of the Purifi amplifier being at 1 kHz is only 65 micro-ohms, then what is it between 20-100 Hz which are in my opinion the most critical frequencies for good transient response with loudspeakers having a higher Qts and other hard to drive ones.

It would be dead flat there. It rises at higher frequencies.

 

[lovinthehd]

It would be dead flat there. It rises at higher frequencies.

How important is damping factor at higher frequencies, tho?

 

[gene]

How important is damping factor at higher frequencies, tho?

All that matters is the amplitude response under various load conditions which we show in the Starke amp and my soon to publish NAD M23 amp. The NAD is completely load invariant. The Starke output impedance is affected by load at 20kHz but it's not jarring and likely inaudible as most audiophiles can't hear close to 20kHz especially if they are over the age of 40.

 

[Matthew J Poes]

I have looked to see what the damping factor of these class D amps actually is. For other members damping factor is the load impedance (speaker impedance) divided by the amplifier source impedance. So for example my Quad 909 amps have a source impedance of 0.05 ohms. So driving an 8 ohm load that gives a damping factor of 20, which for a Class AB amp is considered very good.

If we look a what has been measured for class D amps they stack up well.

This is the Hypex N-core.

This is the damping factor for the Fiera4

You can see that their is significant drop starting above 2000 Hz, and by 20K it is poor. Again this is with an 8 ohm load. With a four ohm load the damping factor will be halved.

On that parameter the Hypex shows excellent performance. The Fiera4 I think might well not be a stellar performer with four ohm speakers presenting complex loads above 5K.

So on that parameter the Hypex scores higher. It is not clear to me why the source impedance appears to be rising with frequency in the Fiera4. As of yet I have no experience with class D amps. I am not aware of class A or AB amps, having a frequency dependent source impedance. Although the Quad performs as class A, the output transistors are biased class B, and a small class A amp provides a feed forward error correction, resulting in spec. that is like a class A amp, but without the inefficiency of class A biasing. That is unique to Quad current dumping amps.

The low damping factor at high frequencies relates to how the feedback is handled and is the same reason that the 8 ohm load peaks. I griped about it in the review.

I still doubt it to be all that audible. The Hypex and Purifi stuff clearly measure a lot better. They Are SOTA. But this one isn’t all that bad. It’s damping factor is high where it’s needed most.

 

[Matthew J Poes]

How important is damping factor at higher frequencies, tho?

I wouldn’t think it’s all that important. Both speakers that I used don’t have a great response at 20khz. The Gedlees use a compression driver with a dip at 20khz or so that causes the response to be only flat to around 15khz. It then peaks followed by a dip. If you measure it out to 40khz you can see that what looks like the response falling off past 15khz is actually this cancelation dip. So I didn’t hear anything but then the Gedlee doesn’t produce 20khz either. I also can’t hear 20khz.

the Def Tech tweeter has a a phase plug and I’ve noticed in measurements some on-axis peaking in that range that I suspect the phase plug causes in the name of a smoother power response. So they have something at 20khz but it might be not the best way to hear any issues. I will look for another speaker I have laying around that might be a better test. But I don’t imagine this is audible. It’s so small a difference at such a high frequency that I can’t imagine being able to hear it.

the usual description of damping factor is the amps ability to control the motion of the driver. It’s usually said to be most important in the bass range. If that is true, then this amp fits the criteria fine. It has a high damping factor at the bass range.

 

[Matthew J Poes]

By the way. I also measured the output impedance of the amp and plotted it. I was reluctant to publish it because I had forgotten to remove the effect of the cable. My measurement was lower than what Soundatagr got, but the cable is likely the cause. I want to remediate with a shorter cable and to zero out the cable first.

 

[Verdinut]

By the way. I also measured the output impedance of the amp and plotted it. I was reluctant to publish it because I had forgotten to remove the effect of the cable. My measurement was lower than what Soundatagr got, but the cable is likely the cause. I want to remediate with a shorter cable and to zero out the cable first.

Just use a short AWG 0 gauge wire and you will get very accurate results.