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Musical Fidelity M8 500s power amplifier
Henley Audio
Musical Fidelity
M8 500s power amplifier
test conculsion

Musical Fidelity M8 500s power amplifier

Click an image to enlarge.

...After suffering various documented panel failures to my MartinLogan Scenario ESL speakers, it is only natural to keep a suspicious finger pointed directly at these very sensitive speakers. Instead of enjoying my record collection, I have spent many months swapping various components, interconnects, mains cables and even going all the way back to the electricity consumer unit to test the dedicated hi-fi circuit breaker, desperately trying to isolate the cause of sound degradation.

I can now confirm that issues such as distortion, smearing, loss of dynamics have been caused by multiple failures in the component chain. To make matters worse in respect of identifying and isolating the issues, these multiple component failures were slow to reveal themselves due to their intermittent nature. The above issues have been caused by speaker panel failures at various points (but now resolved with panel replacements) as well as a slow and intermittent amplifier issues.

My Musical Fidelity M8 500s amplifier was shipped to Henley Audio (Musical Fidelity UK Distributor) via Audio Venue dealership Ealing in June 2020 for a final fault diagnosis and fix…

Henley Audio Test Process
We tested the M8 500s on a test bench and also extensively on soak test with different speakers. In both environments it performed within specification and delivered the expected sound quality. We also carried out an internal check and found all componentry to still be operational and generally surmised that the overall condition and performance of the amplifier was very good. Considering the major drawback of our testing was that we have no access to electrostatic loudspeakers, we then theorised over your experience and established the following feedback...

Presumed Issue with ESLs
Generally speaking, Musical Fidelity power amplifiers over 350W will typically be bridged, which effectively means each speaker has two amplifiers in its drive-path. Although the output impedance of our amplifiers is very low (< 0.02?), this configuration will effectively double the output impedance of the power amplifier as a whole. This could affect higher current outputs under very difficult loads.

It's appropriate to say at this time that Musical Fidelity have not had any problems with this configuration when using even the most "difficult" dynamic speaker systems, according to their own experience and the feedback they receive from many of their global distributors and retailers. But, equally, they have also not received any reports from customers with the same type of system configuration as you (i.e. Martin Logan and high-power MF).

It's the opinion of Musical Fidelity that any very reactive speaker needs good current drive capability to drive it, rather than the brute force of volts. In theory this is basically true for both electrostatic and dynamic speakers, but it's appropriate to highlight that ESLs will also have a larger than normal inductance on the driver transformer in the speaker and a relatively huge reflected capacitance in the panel itself. That makes this logic certainly more relevant for ESLs.

So, Musical Fidelity would summarise that their high power bridged amplifiers are not the optimal choice for ESLs, or any other lower-impedance (or "dippy impedance") speakers (typically < 2?), as they would typically "waste" the power they're generating on excess heat rather than the current you need. The company would instead recommend a lower powered amplifier with higher current capability, such as the M6s PRX. That explains why Michael Valentine Studio found no performance issues when they tested the M6 PRX. Amplifiers like this model will give the lowest possible output impedance, and therefore the best panel control with an ESL.

We at Henley understand the frustration of your journey to this point and regret you were not able to get this feedback in the past, but we strongly hope this gives some clarity to your situation. The amplifier is boxed and can be sent back to you with no service charge applied.

Michael Valentine Studio Response
…You have done all you can do, however, this still leaves me with an amplifier that does not work with my system. The only strange entity is the time it has taken to reveal such flaws (or weaknesses) for want of a better term. The system sounded great for quite a while and was seen by many as ‘the level of transparency to aim for’. We will need to have discussions with Audio Venue at some point to see how we move forward. I cannot think of anything else right now.

Response from Henley Audio
… I understand your comments about why the issue seemed to develop, rather than appear from new. I don't know if length of time or exposure has “stressed” either the amplifier or the speakers at all. We have seen that with valve amplifiers, where they sound lovely through a set of speakers, but actually those speakers are too heavy a load and eventually the amplifier just can’t stand it anymore. But I cannot say if such a thing has happened here.

All I can say is this amplifier seems ok in every way, and we have a technical reason for the issue you're experiencing.
All the very best with what comes next, and if you ever need anything else from me don't hesitate to ask.

Kind regards,
Simon Powell
Operations Director

The discussion continues
The discussion regarding how we are going to move forward continues, however, at this point it is important to acknowledge the cooperation of Henley audio’s Operations Director Simon Powell for his assistance to date. We have come a long way in the last month, especially when we consider the painful journey over the last few years…

Update 13 August 2020
After much discussion and further investigation We began the process of testing The Musical Fidelity Nuvista 800 integrated amplifier & Musical Fidelity M8s 700m Monobloc (x2) in our system…

Robin Francis
© Michael Valentine Studio
July - August 2020


Use the links below to read the Musical Fidelity M8s 700m monobloc power amplifier
Experience Review 1,
or the Musical Fidleity Nu-Vista 800, 2020 Experience Review,
or the Musical Fidelity M6 PRX power amplifer Experience Review,
or MartinLogan Scenario Owner Experience 2,
or MartinLogan Scenario Owner Experience 1,
or The System Upgrade 2015...

Musical Fidelity M8s 700m monobloc power amplifier Experience Review 1 (click to go to this page) Musical Fidleity Nu-Vista 800 2020 Experience Review (click to go to this page) Musical Fidelity M6 PRX power amplifer Experience Review (click to go to this page)
MartinLogan Scenario Owner Experience 2 (click to go to this page) MartinLogan Scenario Owner Experience 1 (click to go to this page) The System Upgrade 2015 (click to go to this page)

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