Big difference in amps - tag/rotel has me confused - diyAudio
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Old 31st May 2012, 09:13 AM   #1
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Default Big difference in amps - tag/rotel has me confused

Hi,

Been a long time since I was here, my hifi got good with your tips so no longer needed help.

However something has changed and I am curious, and would appreciate some expert advice.

I am very happy to say I just saved a pair of Tag Mclaren 125ms from a skip.
Seriously!

I have plugged them in to my hifi and i am amazed with the change in sound.

That is the thing that perplexes me, why is there such a significant change in sound; I thought all high end amps sounded kinda similar?

My set up is as follows:

AAA5+ CDP
Rotel RC-995
Rotel RB-991 --> 2xTag 125m
Acoustic Energy 309
All cabling Black Rhodium.

With the Rotel Amp the bass and treble were VERY forward, with midrange a bit relaxed. With the Tags the treble and mid is forward and bass more relaxed.

The sound change is significant, even my wife could notice the difference (and that is saying something).

On paper the amps are very similar. High damping factor, 145/200w similar gain. Distortion is under o.o3%.

So finally to the question.



If the distortion is so low, and stats so similar, how can the sound be so different?

P
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Old 31st May 2012, 08:06 PM   #2
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Quote:
Originally Posted by inteificio View Post
If the distortion is so low, and stats so similar, how can the sound be so different?
Either one of the amps is not performing to spec, or you got fooled by significantly different voltage gain (and thus output volume) between the two.

Now I checked the specs of the 125Ms, and voltage gain is stated as 29.0 dB, while for the Rotel it calculates to 28.9something dB from its schematic - close enough, I say. Oddly, however, Stereophile measurements for the RB-991 indicate a gain of 31.8 dB when using the unbalanced inputs, almost 3 dB more than specified. That may already explain the differences you were hearing.

Other than that the Rotel makes a pretty good "wire with gain". It also contains fairly little that could impair performance with age (including no protection relay; the only kind of protection is provided by rail fuses, for better or worse).
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Old 1st June 2012, 05:32 AM   #3
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It could be concluded that bass was weak on The Tag McClaren amplifiers.
Does that go for both channels - equally?
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Old 1st June 2012, 07:58 AM   #4
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Hi, all hifi's sound different
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Old 1st June 2012, 08:20 AM   #5
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Argh just spent 10 mins writing a nice detailed answer, and then page lost it, typical!

Either one of the amps is not performing to spec, or you got fooled by significantly different voltage gain (and thus output volume) between the two.

That was first thought.
I tried Rotel with both balanced and unbalanced and could not notice any difference.
Then compared left right channels on both amps, identical.

So as the Tags are monos that pretty conclusively puts them as functioning perfectly. The Rotels are not far off monos, think they only share transformer, think that is working too!

"It could be concluded that bass was weak on The Tag McClaren amplifiers. "
You could say that the mid was lacking in the Rotel just as fairly.

Unless I get out an oscilascope I not sure what to check.

Think J might had hit it on the head.
Although the stats suggest perfect reproduction, they don't, they all add their own character. So much for "wire with gain" theory!
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Old 1st June 2012, 08:26 AM   #6
PChi is offline PChi  United Kingdom
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Do the amplifiers sound different using an AB comparison test?
It's amazing how different the bass and treble sounds when levels aren't the same. The gains have to be well matched to within a fraction of a dB for amplifiers to sound similar.
I used some scrap relays along with some standard potentiometers to build a switching box to compare units. The conclusion was that amplifiers sound pretty much the same.
Certainly not true for Loudspeakers.
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Old 1st June 2012, 08:32 AM   #7
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Quote:
Originally Posted by PChi View Post
Do the amplifiers sound different using an AB comparison test?
It's amazing how different the bass and treble sounds when levels aren't the same. The gains have to be well matched to within a fraction of a dB for amplifiers to sound similar.
I used some scrap relays along with some standard potentiometers to build a switching box to compare units. The conclusion was that amplifiers sound pretty much the same.
Certainly not true for Loudspeakers.
Hi, Exposure's sound different to Linn's which sound different to Ferrograph's.
The list is endless, even resistors sound different, ask the modders
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Old 1st June 2012, 08:52 AM   #8
PChi is offline PChi  United Kingdom
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It's possible to make an amplifier that does sound different. Just a fraction of dB diference in frequency response is detectable in an AB comparison test though I don't know if that really matters

Is the Ferrograph amplifier old? Some of the early semiconductor amplifiers would sound different.
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Old 1st June 2012, 08:59 AM   #9
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Hi,
Yes, but all amps are different ages.
My point is that it is no good telling anyone that all amplifiers sound the same as then there is no need to audition them, just buy one off the shelf, any colour, they all sound the same anyway.
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Old 1st June 2012, 09:28 AM   #10
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Didn't realize this would be such a contentious issue!
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