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Old 10th November 2011, 09:26 AM   #1
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Default Please help me make sense of Trends Bi-amping

Hi, this is only very mild DIY, but I'm hoping someone with experience in bi-amping can help. I have an ME240 integrated amp, and I'd like to run the passive pre-out to power two Trends Micro amps (in power-amp mode) in order to bi-amp my speakers. I have tried talking to Trends and had a good look at their guide to bi-amping, but it's all just too vague to be of any use, and they don't seem too keen on making much sense, which does worry me. In their diagram they show their own pre-amp with 2 sets of outputs powering their TA amps - and no mention of changing the internal jumpers to convert them from integrated to power mode. My amp has Aux and Pre-outs: are these the same thing? - Trends said I can bi-amp as long as my pre has two outputs? I'd ask the builder (Pete Stein) but he doesn't respond to email. I have a guide courtesy of 6moons on how to convert the TA's to power amps, and I understand the Trends wiring diagrams, all I need to know is the Aux/Pre out thing: are they the same? And to beat the first person who asks, to the punch: the point is to 'make louder' as stereo enthusiasts are so fond of saying. My setups is Foobar going into an Audio-GD, into The ME240 to a pair of Adelaide Sentinel speakers. It's a very relaxed, almost luxuriant sound, but it really is a little too relaxed and not 'loud' enough - not forward enough, the soundstage could use a lot more depth. I'll be cross-posting this at stereonet. Any help appreciated.
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Old 10th November 2011, 04:33 PM   #2
AndrewT is offline AndrewT  Scotland
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I think you are going down the wrong alley.
Bi-amping is not intended for making louder.
It is intended for making the load on the amplifiers easier to allow them to perform better.
regards Andrew T.
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Old 10th November 2011, 11:02 PM   #3
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Originally Posted by AndrewT View Post
I think you are going down the wrong alley.
Bi-amping is not intended for making louder.
It is intended for making the load on the amplifiers easier to allow them to perform better.
...which in turn increases the dynamic range, transient attack, reproduction of ambience and therefore perceived 'loudness' or 'liveliness', which is why almost everyone refers to it as 'loudness' - I presume. Quotation marks are for indicating someone else's comments/opinions, and usually used to distinguish them from the writer's own - for indicating verbatim what was said - someone else's comments, not my own. I asked some pretty specific DIY questions, surely someone knows what I'm talking about. Additionally it's pretty obvious I'm going down the right path because I've clearly done a lot of research, and am continuing to do so, if you check out any of the brands mentioned you'll understand that straight away. These are all hand-made customised items at very low prices, items that people do not part with willingly and not the sort of things you find in your local hifi store. Any further hindrance appreciated.
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Old 11th November 2011, 04:20 AM   #4
wwenze is offline wwenze  Singapore
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Old 11th November 2011, 06:16 AM   #5
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Soundfield depth smashed?
More than just dark voiced, it is actually recessed?

That's noise.

A few other (related) errors cause this problem:
Ceramic disc cap for input cap (an error often seen in radios).
Power circuit noise at close proximity to amp (china made kits often do this)
Solid state amp with a gritty sound and no resolution (bias wrong or a part is worn)
Feedback resistor with insufficient current (more than 133k on non-inverting amp)
Instability type in the reverse of acutance (anti-clarity type noise on scope)
Extreme mismatch in parallel amplifier (cancellations also extreme cancels signal)
Insufficient input load (basically a noise issue but worn/omitted pot dial can do it)
Ceramic cap where a silver-mica should go (solid state amp economizing error)
Applying gain to a unity stable op-amp (same as overlarge cap at + to - input)
Error in constructing an inverting amplifier (excess gain on a near-unity stable amp)
Badly made baxandall, eq, buffer, or pre (with any of the above problems)

The hardest things to spot are Negative feedback with insufficient current and baxandall or SLOW preamp (too much gain on near unity rated parts or too much gain on inverting designs).
Feedback: If you have insufficient current, normally you get a tirade unpleasant forwards sound, but if the problem is inverse as would happen inside the Negative feedback loop, you get a recessed amplifier like the Quasar Kits K50 mistaken 180k value (should be within the range of 47k to 114k).
Pre/Baxandall: The number one worst problem with a baxandall is stability band-aided by inserting a unity stable op-amp or using a regular op-amp inverted plus an overlarge resistor at + to - input of the chip, slowing it down and ruining its resolution. . . although there's many ways to ruin resolution with a preamp and then later apply gain to the problem with the power amp. There may also be filtering/tone controls inside the feedback loop doing the inverse of the expected job, thus excessive cancellations.
Yes, all of these issues are really just noise.

As far as dynamics, only really lazy amplifiers actually need bi-amp, but there are plenty of hi-charge designs that exaggerate dynamics. Almost all of the power cheat designs and reduced feedback designs are extremely dynamic, pushing for power with variance to seem louder but without exceeding their limited resources. There is also the lavish sound of high current capacity builds like parallel amplifiers (with hand-matched resistors!) and of course the huge soundfield of the howland current pump.

One popular chip-amp based howland current pump is the MyRef series. I'm actually not quite smart enough to determine if it is a composite/nested or actually a current pump; however, the practical news is that it will do the job that you desire. With the parallel version still unavailable, it has become popular to bi-amp using the MyRef for midrange and tweeter, but a BPA200 or BPA300 for the woofer.

The MyRef won't go either recessed or forwards because it is governed by the "pilot" amp, the little opamp (a sort of predrive) that controls the whole thing and isn't struck by big current. The same is true of any sort of nested/composite design if the power circuit of the pilot (predrive) is on shunt regulated power. Many discrete solid state, STK and TDA7294 designs can be upgraded to the same audio performance of a nested design by simply running the predrive section on shunt regulated power.

Deep forwards rearwards soundfield projection from a monophonic speaker is a simple matter of low noise amplification. The re-iteration of adding a speaker for stereo cannot reproduce this effect although the effect of low noise high resolution is generally beneficial to any amplifier.

Wide soundfield projection from a monophonic speaker is most like to occur from a bridge amplifier that accomplishes the bridging via input transformer; but, otherwise, I have absolutely no idea how to cause that effect from a high fidelity analog amplifier.
Although the re-interation of adding a speaker for stereo cannot reproduce this effect, it can partially cover up the absence of the "wide" sound. However, a dark voice amplifier at hard center monophonic (carefully voiced so that its not actually dull) plus a rather forwards stereo pair (that combo is called TRIO amplifier) can indeed reproduce the "wide" sound even if the individual amplifiers cannot do so with their individual speakers. The Trio is something to consider for busy people and/or weird seating arrangements whereby listening isn't confined to just one chair at centerpoint of a stereo pair.

The easiest answer: MyRef

Last edited by danielwritesbac; 11th November 2011 at 06:36 AM.
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Old 11th November 2011, 06:26 AM   #6
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The sound you describe has a name. It is called the "stars fall" sound. That is extremely rare. There's much not available production examples of replay with both forwards and rearwards character plus a wide presentation all simultaneously to cause the music to swarm about. Linkwitz has some ideas on bi-amping and the stars fall sound. He doesn't mention that by name, but look at his equipment examples and you'll see it for sure.
Linkwitz Lab - Loudspeaker Design <---link
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