Despite what most people think, the smaller the amplifier, the greater the
risk of distortion and burned tweeters.
The MS150s are a bit hungry though not extremely so, and they will probably work
fine with a 60W amplifier and as long as you keep the sound clean, you will
not destroy anything.
Actually most speakers will handle a lot more power than their specs suggest as
long as the distortion is kept low.
Distortion contains a huge amount of power in harmonics and that is the dangerous
content in the signal.

Martin

Beovox MS150 has - like the other speakers in this serie - an effective overload protection if they get "to much", - so dont worry.

With these loudspeakers I would go for the Beomaster 6000 with 2 x 75 W (IHF). In different test at the time in 1981/82 it was in many ways better than Beomaster 8000.

arned wrote:

Beovox MS150 has - like the other speakers in this serie - an effective overload protection if they get "to much", - so dont worry.

With these loudspeakers I would go for the Beomaster 6000 with 2 x 75 W (IHF). In different test at the time in 1981/82 it was in many ways better than Beomaster 8000.

I disagree. I've had both (still do, but my 6000 is non-operational for the time being...), and the 8000 is the far superior product. Much more dynamic and powerful.

Jon

Just to clarify, I used Peerless drivers in my S120 before I knew of Recone (who are not active at present sadly) - given what I know now, I would have had the originals reconed. The Peerless drivers were however very good.

Jon wrote:

arned wrote:

Beovox MS150 has - like the other speakers in this serie - an effective overload protection if they get "to much", - so dont worry.

With these loudspeakers I would go for the Beomaster 6000 with 2 x 75 W (IHF). In different test at the time in 1981/82 it was in many ways better than Beomaster 8000.

I disagree. I've had both (still do, but my 6000 is non-operational for the time being...), and the 8000 is the far superior product. Much more dynamic and powerful.

Jon

I've had both too. The 6000 is a great little amp that is very nice to listen to, but if you want to listen to music at serious volume in a big room, then you need a Beomaster 8000 and either some MS150.2s or some Beovox Pentas!

Anybody have an 8000 that they would be interested in selling?  The guy selling the Rotel is asking $150 which is about the most I can do right now.  I tried searching for Beomaster 8000's and only found 1 that was listed for sale (sold though) for $199.  If I don't really get anywhere finding an 8000 then I am going to go check out that Rotel on Saturday.

A fully-working Beomaster 8000 in good condition would set you back between £250-300 (or approx $500ish). Beware though, as older ones on eBay will probably need some repairs now as they are complex machines. They also weigh a ton, so shipping from outside of the US would probably be prohibitive given your budget.

They really are wonderful amps though :)

Wow, that being said I think I'll go look at that Rotel.  It has a high damping factor of 150 and I'm sure it produces really clean, high current capable sound.  There is a TNT Audio review of the Rotel from 2000 so I assume the model is not that old.  Is also cost near $700 in the US when released so $150 is not bad IMO.  I'll keep everyone updated, thanks.

Hey Daniel, a couple of things here.

To me, 60wpc won't be enough.

Audio manufacturers like to be sneaky and say "high-current design" making people think that it's better than a "regular" (???) amplifier design or something.

However, the Beovox MS150's are an 8 ohm nominal speaker. So, you can have a super special "high-current" design all you want, but the amp in question is only going to be able to deliver so much current into the speaker for it's given impedance.

Say you've got two amps, one a quality "regular" amp, and another, "high-current" design, both similar enough in design and layout to be fairly comparable, and both rated to deliver 40 V at the power supply rails. With the MS150's being "8 ohms" (which is a bit of a misnomer, and relates to the whole damping factor thing, which I'll get into in a minute), you're only going to be able to deliver 5 amps max into them (mathematically anyway, not counting losses and inefficiencies, and impedance irregularites), regardless of whether it's a "high-current" design or not. So all that "extra current" goes to waste!😂

No, but, do you see what I mean? Power is voltage times current, and current is voltage divided by resistance. Unless you're looking at wiring up three or four sets of MS150's in parallel, a "high-current" design (one that actually delivers on it's promises, at that) pretty much means nothing.

About the impedance and damping factor thing... Damping factor is simply a numerical value describing the load impedance divided by the amp's output impedance.

An "8 ohm" speaker like the MS150 or almost any speaker on the the planet isn't really a linear 8 ohm impedance. If it were, it would be a resistor. That's why speaker loads are described by impedance, which is basically a reactive resistive load. A speaker's impedance varies with things like frequency, enclosure tuning, voice coil heating, and non-linearities in the motor. It fluctuates just with the movement of the coil in and out of the magnetic gap. It presents the amplifier with a load possessing inductive and capacitive properties.

Even with a decently linear speaker like the MS150, which has impedance compensation networks in it's crossover, it will have a relatively large "double camel hump" in it's impedance graph around it's enclosure tuning frequency. Look at this chart I pulled off the Stereophile's website of a JBL speaker (first one that came up in a Google search):

See how the dark solid line varies between about 3.75 ohms and over 20 above and below the port tuning frequency?

Given Ohm's law, you'd think the amplifier's frequency response would mirror that of the speaker's impedance, and in crappy amplifier designs, it does! But a low output impedance (i.e. high damping factor) means that the amplifier is more of a constant voltage source, not letting the speaker's impedance affect it's frequency response.

And of course, the speaker itself will have a voltage sensitivity that looks a bit like it's impedance plot. This is why you can have a very irregular impedance, and still have a flat response (I don't know if this JBL has a flat response, I'm just saying it's possible in a design). Basically, there's less current delivered to it at certain frequencies, but the frequency response of the speaker doesn't dip because of the higher voltage sensitivity at that frequency.

Combined with an amp having a high damping factor, the final result can be very flat response, despite the impedance being all over the place!

By the way, I'm working on packing your 8" drivers. Hope you find it satisfactory.

Regards!😁

Jon

Hey Jon, thanks for the reply.  I am aware of everything you said, I have my associates in electronics and was a bench tech for a lighting control company for years (now manage the quotes team).  The only thing I meant by high current torroidal XFMR is that the 60 watts it is producing is probably constant RMS value (at louder volumes) and not a peak figure so many manufacturers use.

Damping factor as I have always known it basically means better cone control throughout the available frequency range but even more so at lower frequencies where cone movement is much greater.

I wish I would have one of these speakers complete to bring with and hook up to the amp.  The owner did say he has some larger speakers we could hook up but I know efficiency plays a huge role.

The Beomaster 8000 only did 150W at 4 ohms and only 100W at 8 ohms.  Compared to the Rotel, that is far less than 3dbW.

Thanks again for the 8's, really looking forward to receiving them.  Yesterday I re-soldered a few joints on the crossovers (cold or broken traces/pads) and glued down some of the inductors that became loose.