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Old 24th September 2012, 05:55 PM   #31
bcmbob is offline bcmbob  United States
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Bare,

Your comments appear sound and logical. I would ask however, if you can comment on a point of diminishing returns for "Us Poor-folk" for speaker selection/building . I see a two sided coin here where either the speakers or the amplification needs to stay the same in order to hear differences in the other leg.

I would also appreciate your experienced view of using discrete equalizers and/or active XOs to shape the sound of any amp into "sweet" or any other character.
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Old 24th September 2012, 09:32 PM   #32
cc00541 is offline cc00541  United States
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Quote:
Originally Posted by danielwritesbac View Post
The new RS180 4 ohm alloy cone woofer is higher resolution part at the cost of a greater reactive load.
Quote from Jim Holtz (circa 2008~2009): "The RS180-4 version was selected after evaluation. We found the 4 ohm version of the RS180 had extended bass just like the 8 ohm but with a higher sensitivity which allowed more flexibility in amp selection." How unfortunate. First, that bit about the amp is backwards (or maybe they were talking about a t-amp). Second, the old RS180-4 is discontinued and the new substitute sucks at efficiency--there's no advantage to the 4 ohm load in this case. The fix for both errors is new, unshielded, RS180-8. There will be some crossover work, but, supporting 8 ohm amplifiers, like MyRef-FE is seriously overdue for the Statement Monitor.
We interrupt this regularly scheduled chip amp thread for fact clarification:

Daniel,
If you are comparing the T/S parameters of the old/new RS180-4, there is no difference in the load seen by the amplifier. Le and Re are nearly identical, and the complex impedance of either, modeled in a vented enclosure, indicates low phase angles at the impedance minima. If you intended to compare the impedance of the 4 ohm to the 8 ohm version, then of course you are correct.

-In addition: I calculate the USPL of the current RS180-4 to be 2.4 dB higher than the RS180-8, based on the published parameters. –No suckage here…
-I use USPL as SS amplifiers are by nature voltage gain devices.

-Finally: Since the vast majority of quality amplifiers are 4 ohm capable, I see no reason to fix my ‘error’ in the Statement series designs. –I’m sure that was just an unfortunate choice of words on your part. Certainly I have 8 ohm designs on my site. The Singularities are a high sensitivity 8 ohm full range design, and would work very well within the electrical constraints of a chip amp, as would the TriTrix design. Unfortunately all the Statement series are 4 ohm designs.

Sorry for the interruption, and may I suggest any further discussion on this topic should be taken to another thread…

Curt C

We now return you to your regularly scheduled chip amp discussion…
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Old 24th September 2012, 09:44 PM   #33
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The original poster did specify a level frequency response and very spacious sound stage. He also gave an example of a singleton input amp that is very difficult to beat on those two features (if one is also using regulated power). He also mentioned that LM1875 was insufficient in comparison.

Now he wants a more powerful amplifier to sound just like his 6 watt singleton input amp (except much more powerful) and he wants it to be a chip amplifier. Tallest order ever. MyRef-FE is a close match to this request, if one has 8 ohm speakers. Driver Chip Amp with a buffer or pre is a close match if one needs to drive 4 ohm speakers.

However, most other options are in or near prototype stage thus low availability.
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Old 24th September 2012, 10:18 PM   #34
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Quote:
Originally Posted by cc00541 View Post
Since the vast majority of quality amplifiers are 4 ohm capable, I see no reason to fix my ‘error’ in the Statement series designs.
Thank you for the response.
To drive a 4 ohm speaker, you're looking at double the transformer amperage, double the heatsink size, and double the thermal interface via doubling the output devices. This meets your "Quality" clause and thus, your statement is not actually erroneous. My apologies. However good your idea is, there is low availability of home amplifiers that drive 4 ohm loads gracefully, safely And in high fidelity. My thoughts were about availability. I also worry about amplifier shoppers being informed or not, since overload risks can be problematic.

Since we're discussing chip amplifiers, how do you feel about an 8 ohm Statement Monitor for the MyRef-FE? Now, that would be an excellent solution. Please?


I support your 4 ohm designs, especially the effective double-woofer designs for moving compromise out of the loudspeaker and into the amplifier where it can be easily dealt with by sturdy design. For me, personally, that's not a problem since I have changed to entirely 4 ohm capable design.
However, breakage or even fire could result if the amplifier is not especially prepared for 4 ohm loads, and therefore, assuming that 4 ohm loads are usually okay for most amplifiers could be hazardous. Unexpectedly pulling double the current for 2.4db will not go well with a random choice of home amplifier, since the standard spec (and builds) are 8 ohms.

P.S.
Earlier wasn't comparing difference in load between old/new RS180, but stating an EMF difference between high resolution alloy cone woofers versus more ordinary woofers. The LM3886 is borderline to drive a cheap 4 ohm woofer, but RS180-4 kills the chip. Neither would work for very long term (unless given 4 ohm specific re-design), and both loads end in destruction so perhaps that point literally fizzled.

EDIT:
Most shoppers and builders are assuming that Overture series and some other chip amplifiers are entirely quality design because the chips DO contain top-notch predive units; however, most people seem to have ignored the fact that the tiny enclosed outputs aren't stronger than something like a BD911 for example (strong output devices can't fit inside the chips). Even with larger transistors, consuming the insides of BJT output devices is exactly what heavy loads will do. When enough of the interior insulating layer is eaten away, a spark is conveyed and then the stench of burning electronics. Some amplifiers may last 6 months to a year before the damage of corrupted output devices becomes severe enough for burnout. That is more likely to happen to a chip's small output devices, but any size can be damaged, including discrete amplifiers made for home use.

Ultimately, it is your choice as a designer to determine how much trouble 2.4db is worth.
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Last edited by danielwritesbac; 24th September 2012 at 10:41 PM.
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Old 24th September 2012, 11:00 PM   #35
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Compare:
Waste heat in the transfomer
Waste heat in the CRC resistors
Waste heat in the ballast resistors
Waste heat in the heatsink
Using RS180-4 and RS180-8 for the comparison, output power has been crippled by the RS180-4's load causing output power to go many places other than the speaker and this waste may result in much more clipping. Given the many losses, surely the 2.4db advantage is not in effect during maximum output, and thus the 4 ohm version has uselessly abused the amplifier. At maximum output, you'll find the 2.4db worth of watts has been outputted to the heatsink, not the speaker.
The above is regarding single woofer speakers.
I have no complaint about double-woofer speakers requiring more current to move twice the cone area.
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Last edited by danielwritesbac; 24th September 2012 at 11:03 PM.
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Old 24th September 2012, 11:34 PM   #36
bcmbob is offline bcmbob  United States
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Hey Curt, For me - this discussion is too interesting to just drop. Are you aware of an appropriate existing thread that addresses the topic? My interest is centered on the MR FE/LM3886 but the 4 Ohm/8 Ohm information in the last few pages appears a logical next step to optimize the marriage between the MyRef family and speakers at the quality of the Statements family.

If nothing exists, I'll gladly volunteer space on the FE integration thread.
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Old 25th September 2012, 09:01 AM   #37
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Default Actually love Curt's speaker designs.

As a matter of public record, I love Curt's double-woofer designs, and a diyaudio.com search will confirm that I have a long history of recommending the Statement speakers. . . and usually as motivation for building extra sturdy amplifiers. For this reason, my 4 of NOS LM3886T's are still waiting on MyRef-EVO2 boards. It has been a long wait.

On topic. . .
This thread is basically about soundstage of audio amplifiers:
Invalid compensation produces "pancake" pattern (not long, not wide)
NatSemi chip amps produce "alley" pattern (long, not wide)
TDA7293/4 chip amps produce "stage" pattern (wide, not long)
High Fidelity Class produces "arena" pattern (both long and wide)
The above can be observed with one/each speaker. The chip amps can be nested, composite or current pump to incorporate a small signal amp in the feedback loop, and if the small signal amp has the opposite pattern, then the result is a high fidelity class soundstage, (both long and wide). It is also possible to alter soundstage at the power circuit, which is working with the speaker negative instead of the speaker positive. Or, a very faithful Driver Chip Amp can be used with a high fidelity preamp for somewhat similar results.

Now, match the available excellent speakers to the Available excellent and extra sturdy chip amplifier. Oh dear! Well, the other way to put an end to the long wait is an 8 ohm Statement Monitor to support the MyRef-FE.
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Last edited by danielwritesbac; 25th September 2012 at 09:06 AM.
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Old 27th September 2012, 05:26 PM   #38
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sweet? go with OPA549
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Old 27th September 2012, 06:10 PM   #39
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Can you consider LME49830 + external pair of fets as chipamp? If yes - then it is a go. When I p2p-ed it, I was surprised with the excellent sound. I run it with IRFPs, 2 pairs per ch, 700mA bias. About OPA549 - it sounds sweet with additional gain stage, and the chip running at low gain, like 3x.
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Old 27th September 2012, 06:35 PM   #40
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Maybe 12AX7 in front of OPA549 or LM3886 used with low gain could make it sounds "sweet".

However good amp (and preamp) for quality stereo should be fully transparent without no coloration at all with a decent BW and what has to be "sweet" is your audio source.

Wadia are making "sweet" DACs. Pioneer Legato Link is not so advanced but might be an inexpensive item to get (it's using simple cubical spline for interpolation). Lampizate it with 12AX7 that is it.

LPs do not suffer dither & interpolation artifacts sounds clean and natural with good tube phono. But NOS LPs priced insanely noways thanks to Philips aggressive (if not call it bloody) marketing of "superb CDs" in the recent past.
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