In our former home, my Beomaster 4500 was pressed into service standing in for my McIntosh 2255 that was in for service at the factory. The sound was unbelievable; to the extent that I believe this amplifier produces the best sound quality of any amplifier I have ever owned.

 

One drawback, when the volume was turned up with the 4500 powering several highly inefficient speakers, the 4500 balked and dropped the volume level. I accepted this at face value, in spite of the fact that my Beomaster 2400 had NO problem doing the same thing with 6 inefficient speakers as opposed to 4. But OK, you can’t ask more than it possible.

 

Now in our present home I have the Beomaster 4500 powering a set of S-75 speakers and was surprised when the 4500 again turned back the volume above “75.”

 

Is this normal, or a case of the dreaded bad caps? From my understanding, if this 4500 had bad caps the sound would be distorted, which it most certainly is not.

 

My Beomaster 2400 can play music at distinctly higher volume…. Make that MUCH higher volume but the fantastic sound of the 4500 is missing. Of course I am powering the 2400 with three-way S-45’s which I deemed a good match.

 

What are your thoughts?

 

Jeff

Jeff,

We've had this up a couple of times.

The Beomaster 2400 and 4500 are two very different machines.
The 2400 has a discrete DC coupled amplifier that will accept a lot, though without any safety circuits to avoid distortion etc.
whereas the 4500 has an integrated hybrid IC, one chip that holds both channels with some safety circuits.
The 4500 is a beautiful machine and probably more linear and all that but I'd still prefer the discrete amplifier anytime.
Maybe not a very high volume player (the 4500 aren't either) but a wonderful sound, a surprising dynamics response and just pleasant to listen to where I tend to get a bit tired listening to the hybrids almost sterile sound.

Martin

Hi Martin,

 

I hope that I was not being totally redundant, however I was under the impression that the volume “pull back” was in response to my overloading the Beomaster 4500 with my Linn Isobaric and McIntosh ML-2 speakers.

 

The Beomaster 2400, as mentioned a couple of time had NO problem powering those speakers plus a set of Fishers. It got toasty doing so, so I turned down the volume as a precaution.

 

My real surprise and disappointment was when I swapped speakers and gave the S-45’s to the 2400 and the S-75’s to the 4500 figuring a better match for both. The S-45/2400 combination is alright, but those speakers simply can not handle the power of this amp.

 

The reverse is true of the S-75/4500 combination, whereas the sound is quite wonderful; the volume is flat out not there.

 

While I understand and admire your vast expertise, I really prefer the sound quality of the 4500 over all my other amps. I especially enjoyed the 4500 paired with the Linn Isobaric speakers acting as my “home theater.” The McIntosh 2255 with its 500 watts does a commendable job, but I have to turn the bass way up for it to approach the fullness of the 4500.

 

The 2400 sounds a tad anemic by comparison; however this little 60 watt amp can power speakers with the best of them.

 

My goal “had” been to provide the Beomaster 4500 with a set of S-120 speakers, but at this point I question the advisability of this match.

 

Jeff

I don't have the 'seat time' with the 2400 and 4500 that I'd like to have, but perhaps the issue lies elsewhere.  I know that the BeoCenter 9500 had a protection circuit which behaves precisely as you describe when driven into a shorted cable or speaker.  If you are wiring your speakers to the 4500 in such a way as to drop below 2 ohms impedance, I would suspect that the 4500 is protecting itself.  You might also wish to check the cables and the woofers in the speakers, as dying 'motors' may only 'short' at high excursions.

Russ 

Hi Russ,

 

When I originally wired this Beomaster 4500 to my Linn speakers, both B&O connectors were shorted out….. a sloppy job by the eBay seller. This undoubtedly contributed to the protection feature kicking in a bit early.

 

I have since purchased new plugs and had them professionally soldered.

 

So now with new plugs I was greatly surprised that the protection feature comes on with S-75 speakers. Surely the S-75’s and the Beomaster 4500 should be a good match.

 

I was thinking of purchasing S-120 speakers, but now feel “why bother” as this Beomaster can’t handle the more modest demands of the S-75’s.

 

Adding to my frustration is the fact that my low-power Beomaster 2400 is clearly over-driving the S-45 three-way speakers that I thought would be a decent match for it. As such I have to use care to not raise the volume too much fearing doing real damage to these speakers.

 

Point of fact the Beomaster 2400 also over-drove the S-75’s when they were so attached.

 

Although it doesn’t make any sense, this 2400 seemed perfectly happy powering my big inefficient speakers. (Linn Isobaric & McIntosh ML-2) Both Martin and Peter assured me that the 2400 could “take it,” but I was concerned to be asking too much and wired up the S-75 speakers.

 

The speakers are wired direct. So there is no danger of them working at 2 ohms.

 

As for issues with the S-75’s…. I am no expert, however they play well enough overall that I do not suspect a speaker related problem.

 

Jeff  

Hi Jeff,

I would still advise checking the speakers, mainly because of the combination of symptoms/characteristics you're describing.  It seems to me possible that the 2400, lacking the same protection circuitry isn't really 'overdriving' the speakers so much as it is driving a bad woofer or midrange to the point where it begins to short, which the 4500 is refusing to do.  In this case I am perfectly happy to be proven wrong, but it is worth investigating.

A quick-and-dirty method of checking is to (with the system off) gently push straight in on the woofers and midranges (each in turn), and check for any scratchiness or roughness in the movement. 

Russ 

Hi Russ,

 

I will try your “quick and dirty” test on these speakers. Both sets (S-45 & S75) were gifts from a good friend, but their “history” is completely unknown.

 

Currently I have the S-45’s connected to the 2400 and it is clearly NOT a happy combination. I turned up the volume and the speakers really protested. So I turned the bass down and that helped. This Beomaster was probably happiest powering the McIntosh ML-2’s, but I have them on other “duty.”

 

In any case, I will check them all out and report back on what I find.

 

Thanks for the useful tip!

 

Jeff

I reckon the 4500 needs servicing - I suspect the variable resistors in the power supply are out. A 4500 should be able to drive S75s to full volume no problem!

Peter :

I reckon the 4500 needs servicing - I suspect the variable resistors in the power supply are out. A 4500 should be able to drive S75s to full volume no problem!

 

I totally agree Peter, assuming that the speakers are good.

Russ 

Yikes!

 

I am in the process of packing up my Beogram 4000 to have serviced…. on top of the non-functional Beogram 8000, and recently dead Beocord 9000.

 

I would never but NEVER “shoot the messenger,” however the idea that my Beomaster 4500 needs service is not exactly welcome news at this moment in time. (No matter how true.)

 

The Beomaster 2400 is simply far and away too much for either set of speakers; however this is particularly true of the S-45’s. This should not be the case. These 4 speakers (S-45 & S-75) were very kind gifts, but come from an assortment of sources.

 

I just tried Russ’ “down and dirty” test and the midrange on one of the S-75’s sounds like you are crunching cardboard when you press in on it. The woofer is fine, but the midrange sounds like something is dragging, if that makes any sense.

 

As I turned up the volume the speaker in question really began to sound bad, to the point that I was about to turn the volume down from “80” on the Beomaster 4500 when it SHUT OFF.

 

This has not happened before, and I was afraid that the 4500 was seriously damaged or at the very least blew a fuse. Not so, a press of the phono button and the 4500 resumed its playing at the preset level. I turned it up to 72 which is more than loud enough and just under the maximum for the S-75’s.

 

So now what do you guys think?

 

Jeff

I think there's nothing wrong with your beomaster 4500.  It uses the exact same amplifier as the Beocenter 9500 and 9000.  Also the exact same amplifier as the Beolink passive.

Well, all my units do exactly the same thing on certain speakers, in particular 6ohm speakers.  They will either throttle back to prevent clipping, which they are supposed to do, or shut off.  I thought this odd at first, but it IS by design.  I have a 2400, 4500, 9000 and 9500.  All have the SAME amplifier except the 2400.

 Yes, my Beomaster 2400 will drive into distortion and clipping.  It will probably blow it's output transistors if overdriven.  The 2400 does not have the protection built in as the STK Chip amps in the others.

The ONLY other thing I can think of would be the main filter capacitors getting weak.  It could reduce the max voltage available to the AMP and cause it to throttle back at lower power.  It's possible.  But it is still doing what it's supposed to do, and that's to prevent clipping.

Clipping can blow your speakers, so the protection is a good thing.  By the way, the soft clipping circuit is described in one of the manuals... I don't recall exactly, but it's a "feature".

Marc

Agree with the above - the 4500 has a protection circuit as do all the later amplifiers. However I have used my 9500 to drive S75s for years and it never once backed off the volume. In fact the only time any protection circuit has ever cut in on any of my amplifiers was when I was power testing them - the Beomaster 7000 shut off as the load was 4 ohms. Only got about 50W out of that one. The 2400 would produce nearly 40W and the 8000 went off the scale (100W) and started smoking! To be fair, I didn't test the 9500 but would not be surprised if it shut down on that test. However it drove S120s and S45s with no problem at all.

Given the results of your 'test', I feel that the 4500 is seeing the bad mid-range driver and 'throttling back' to protect itself.

Hi Russ,

 

I am no expert, but I feel that you are right. I went for the speaker which does not like high volume and the mid-range really sounded crummy moving in and out. Just like I was dragging cardboard back and forth.

 

So the 4500 protecting itself makes perfect sense.

 

Thanks for the great tip.

 

Jeff