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Musmy a75 clone (not a review)
- Thread starter ryan74701
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In the realm of home theatre, the recordings are based on a peak headroom of 20db - so one can play safe by providing 25db of headroom - but that still results in a peak SPL of only 100db for a typical domestic environment average SPL of 75db....
With an 86db @1Wm speaker - that means circa 0.25W for 74db (@3m) continuous, and 128W for 101db (with excess headroom of 5db) - actual peak would be 95db which is achieved at 32W
So in theory, assuming that you listen at 75db average (from a single speaker - I have not calculated the impact of multiple simultaneous speakers - which substantially reduces the required power per speaker in actual use!- and note that my typical average SPL is 72db - which halves the power requirements!)
What you actually need is an amp capable of circa 1W into whatever load your speaker provides, and 32W peak / dynamic capability...
If you want additional margin ... 128W peak provides for 25db dynamic peaks.
Having said that, some of the more excessive "bass heads" in our community target 130db SPL peaks for their bass... and it is worth noting that on an 86db/wm speaker, 130db would require circa 65,000W - so obviously if such SPL's are desired, it will require subs with substantially higher efficiencies and / or a multitude of subs to aggregate to the required SPL's.
From my own experience and my own power utilisation measurements... I don't believe my setup has ever used more than 16W peak
note: my speakers are reactive with a capacitive tweeter, and impedance dropping down to 1.63ohm - amps that are unstable into that kind of load are audibly impacted, and immediately identifiable... the amps need not be overly powerful - although I have used Crown XLS2500's for some years - but much less powerful amps have shown themselves to be audibly identical to the very powerful crowns... such as Quad 606/707 - but those amps are "unconditionally stable into any load" as per specs!
So yes reactive loads have an impact, and powerhouse amps often can handle those reactive loads (and are specified down to 1ohm) - but there are also less powerful amps that can handle reactive loads without any trouble.
Indeed ... and Amir's measurements here on ASR often include reactive load tests (indcuctive / resistive / capacitivy impedance). Some of these measurements are rather revealing. E.g. check out his Topping B200 results (output power varies between 140 and 210 Watts depending on load's phase.
For my situation, this is most relevant in the 100 Hz bass region where my Sonus Faber Cremona speakers drop below 3 Ohms. E.g. my home theater AVR (NAD T778) is struggling with these; bass sounds muddy even at moderate volume. Not so the Mumsys A75: output power remains constant within 0.1 dB down to 10 Hz with Cremonas connected, tested between 0.1W and 10W and measured using digital signal generator plus Fluke 8060 A RMS multimeter. A75 bass slam accuracy is also (subjectively) a lot better than that of T778. Thinking of getting rid of that ugly active 12" subwoofer I have for movies...
As per earlier quoted Amir tests, Topping B200 drops from 210W (at 4 Ohm) to 84W (at 2 Ohm) for purely resistive loads. This is about 4 dBs in logarithmic terms. I suspect this is is due to critical sizing of output stages and/or power supplies. Not a good match for my speakers, although I can see why other folks love these amps.
For my situation, this is most relevant in the 100 Hz bass region where my Sonus Faber Cremona speakers drop below 3 Ohms. E.g. my home theater AVR (NAD T778) is struggling with these; bass sounds muddy even at moderate volume. Not so the Mumsys A75: output power remains constant within 0.1 dB down to 10 Hz with Cremonas connected, tested between 0.1W and 10W and measured using digital signal generator plus Fluke 8060 A RMS multimeter. A75 bass slam accuracy is also (subjectively) a lot better than that of T778. Thinking of getting rid of that ugly active 12" subwoofer I have for movies...
As per earlier quoted Amir tests, Topping B200 drops from 210W (at 4 Ohm) to 84W (at 2 Ohm) for purely resistive loads. This is about 4 dBs in logarithmic terms. I suspect this is is due to critical sizing of output stages and/or power supplies. Not a good match for my speakers, although I can see why other folks love these amps.
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There are 2 pots on the board/pcb, is one bias/other dc-balance?
Yes, and bias is the top one. I have measured the bias voltage between the transistor source pins (rightmost pin) and speaker out. In my case, the voltage variance between transistors was about +/-10%, i.e. the transistors are reasonably well matched. Pick the one with the highest bias to adjust. DC needed only small adjustment after increasing bias.
This is a somewhat famous study. The statistically valid overall conclusion, is that across all listener types and all amplifier pairs people could not reliably tell the difference between amplifiers. However there is a lot of "devil in the details" that hard-core "All amplifiers sound the same" proponents would rather ignore.
In the details it's clear the for certain pairs of amplifiers, listeners could hear differences at statistically significant levels. See page 83. For instance as betten the Futterman and Pioneer amps, skeptical listeners called the correct amplifier 78 out of 128 trials which we are told has a statistical change of being random of only 0.046.
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... which is cutting it really fine for p < 0.05
Bare in mind that's the chance of the positive result being random.
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Exactly. The result is right on the edge of the typically defined significance level.
OK sure, I.e. generally 95% +/-2% 19/20 times, (blah yada
).Come to that, I'm pretty sure I could 19/20 times tell a Futterman (OTL, "Output transformerless" tube amp) from the Pioneer (conventional s/s design of time) under fair test conditions, (prove me wrong
... I have no idea which I'd prefer)
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If there were two amplifiers that were demonstrably different, those two would be it; I'll give you that!
Still, that level of significance cries out for a substantially bigger value of n before one could take it to the bank.
They're probably easily different by robust quantitative analytical methods, too -- e.g., THD and/or the HD spectra themselves.
Those quantitative assays are way easier to apply. They're also far more accurate and precise, and would allow for much more robust and significant statistical comparison, with a lot less work!
I mean, you could do the listening test with trained mice, but you would need a lotta mice.
Still, that level of significance cries out for a substantially bigger value of n before one could take it to the bank.
They're probably easily different by robust quantitative analytical methods, too -- e.g., THD and/or the HD spectra themselves.
Those quantitative assays are way easier to apply. They're also far more accurate and precise, and would allow for much more robust and significant statistical comparison, with a lot less work!
I mean, you could do the listening test with trained mice, but you would need a lotta mice.
Just for fun , I've just ordered THIS DartZeel knock-off from AliExpress. Delivery is expect, (i.e. hoped for), in the next few days Price including shipping was Cdn$800; I expect to pay some taxes, brokerage, and maybe duties.
The vendor asserts ...
"The main amplifier circuit is derived from the Dartzeel-NHB-108, a famous machine with a price of around $50,000. The circuit matches the original 1:1. The selected components also correspond to the original at the key points in the sound and therefore no compromises have to be made in terms of sound compared to the original."
We shall see. I'll get back about this unit.
, I've just ordered THIS DartZeel knock-off from AliExpress. Delivery is expect, (i.e. hoped for), in the next few days Price including shipping was Cdn$800; I expect to pay some taxes, brokerage, and maybe duties.
The vendor asserts ...
"The main amplifier circuit is derived from the Dartzeel-NHB-108, a famous machine with a price of around $50,000. The circuit matches the original 1:1. The selected components also correspond to the original at the key points in the sound and therefore no compromises have to be made in terms of sound compared to the original."
We shall see. I'll get back about this unit.
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