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Old 15th March 2007, 09:43 PM   #1
pjpoes is offline pjpoes  United States
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Default Building an HT Amp-paralleling output devices?

Ok I have been playing around with chipamps and finaly gave up on them. Not that I don't like them, but they aren't for me, not for HT. For one thing, after months of changing the grounding scheme as suggested every which way, I still can't get them as quiet as I like. Even with the chips bridged, I can't get the output I want. My biggest issue is that when they clip they have to be one of the worst most ungraceful amps I have ever heard clipping. Movies are just one of those things where graceful clipping is important. Anyway, On to other kits.

I was going to build the Rod Elliot Amplifer which puts out like 130 watts into 8ohm, I believe, and like 200 or so into 4ohm. However, then I was looking at the Aussie amps and Ampslabs kits. I started thinking about it and realized that I'm going to spend about as much to build those Rod Elltiot amps, because of the expensive Hitachi mosfets, as I would to build the ampslab kits. So I have a question about paralleling output devices. Can you do this to any amplifier? Rod Elliot suggested doing that with his kit if you were going to run the amp into 4ohms, wanted greater output current, or wanted to run a higher voltage. If I was to build one of the Ampslab kits, could I also parallel the output devices with a second pair and get the same benefit. Is this done by tying in and adding a second emitter resistor, or increasing the emitter resistors wattage rating? Or will the sinle emitter resistor handle the current just fine?

Another question, I'm yet to find the need to have a 200 watt per channel amp in the rear for effects, even the best HD movies, which I have, don't seem to use the rear channels to such an extent as to justify equal speakers and power in the rear. The only benefit in my experience has been better timber matching, which I do agree is important, but can be achieved I would think through a lower power amp. So I want to run a 100 watt amp in the rear, and 200 in the front, to match my main amp. That way the center channel, which does seem to handle most of the sound in movies, gets its fair share.

Somewhat unrelated to the design of the amp, but another question none the less. Is there a benefit to running an even more power amp in the front than my speakers is rated to handle. I see often guys running amps making 300-600 watts per channel on speaker only rated to handle 150-200 watts rms, and claiming that they handle dynamics so much better. Now my speakers are rated at 92db efficiency and to handle 150 watts. I always figured that 200 watts Rms was more than enough, but one area I think is lacking a bit in my theater is clean dynamics. I often racked it up to the speakers, but wondered if maybe I do need more power, maybe I am clipping my amp. This brings me to the issue of maybe I should build an amp making 400 watts rms per channel, which I think I could do, and use my current main amp for the rear channels. Another idea was to build a 5 channel amp, and biamp the front three speakers. Or a 4 channel amp and just biamp the center, which does still get the majority of the sound. However, I do question if durring the loud dynamic peaks, if that is true, I bet the three front speakers intentioaly share the load pretty evenly in order to give you that loud peak, inwhich case it makes sense for them ot have an equal amount of power.

This of course brings out the issue of, should I maybe be building a much more powerful amplifier, and makes me wonder if something like the UCD700 module for the front three channels would work better, with something else for the rears. Anyway, some opinions would be appreciated.
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Old 18th March 2007, 11:36 AM   #2
dangus is online now dangus  Canada
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If you're after lots of power, have you considered just buying a Behringer or other made-in-China "pro" amp? They're almost priced low enough to be worth buying for the parts alone, especially if you can find one used. Heatsinks, cases, transformers and filter caps add up to a lot of money if you're buying them in small quantities.

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Old 18th March 2007, 01:07 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
you like it loud!
92db & 150W = 113db!!! and you are concerned you have run out of drive voltage.

If peak SPL is that important then consider going fully active.
Lower power amps direct to the drivers produces more clean volume. 10 channels of 50W to 100W connected to all the drivers in the satellites and sufficient power to your low efficiency sub to match the SPL and you will deafen yourself.
50W*10 +100W =600W of active will be louder than passively driven 200W*6.

BTW,
if all the drivers are the same sensitivity then all should be driven to the same maximum voltage. Yes, equal voltage to the sub as the treble IF the sensitivity matches.
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Old 18th March 2007, 02:13 PM   #4
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" ... 150W = 113db!!! ..."

Yes indeed ... and getting close to the threshold of pain.

However when driving certain kinds of speaker loads, power = lots of overhead. I have a stereo 150 watt amp driving a pair Magnepan MMGs and they love it, especially at low volumes and the amp runs nice and cool. If you unload digital DVD - 24 bit / 48K to 96K audio into this setup, the 110 db dynamic range is such that even at low listening levels, the "punches" and roars of a DVD video come through as the music director / producer intended. A good example: in the "Kill Bill #1" DVD movie, the breaking of the glass coffee table is such that, even at a low listening level, you can almost hear the individual pieces falling to the floor ... this is called headroom.

(Most tube types don't ever experience this unless the speakers can reproduce dynamic levels greater than 95 to 100 db dynamic range. Andrew, I know you know all about this ... )
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Old 19th March 2007, 02:39 AM   #5
pjpoes is offline pjpoes  United States
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it really wasn't about reaching those peak levels of 113 decibles, just that I didn't want it clipping when it does reach into those levels. I actually have 200 watt amps for the front speakers right now, but I just feel like sometimes I am hearing compression of the sound tracks.

Anyway in the end I have decided just to build a few more 200 watt amp channels. Should be loud enough.
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Old 19th March 2007, 03:49 AM   #6
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" ... I just feel like sometimes I am hearing compression of the sound tracks. ..."

You may now join those of us who have the same feelings about most modern CD recordings. ("CDs suck" - Bob Dylan)

16 bit CDs just don't do it for me anymore, either (85 db at best). ... and it takes plenty of headroom (dynamic amp power) to listen to the better stuff, the 24 bit DVD-A / SACD recordings (100 db or more). Likewise for enjoying listening to LPs (90 db or more).
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Old 19th March 2007, 02:57 PM   #7
pjpoes is offline pjpoes  United States
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well I have definatly felt that way abotu cd's for a long time. I honostly don't understand how anyone was ever able to listen to a large orchestra or a pipe organ on CD and say, Hey this sounds more real than on Vinyl. Which isn't to say Vinyl gets it right either, but its a lot closer IMO. I think some of it is format, but I think anymore most of it is the mastering engineers. I don't listen to a ton of classic, but its the one type of music where I found it so obvious that the engineers managed ot turn a huge sound into something very small, destroying any sense of "you are there" realism.

As for movies, I picked up an HD DVD player from Toshiba, and using the analogue outputs is letting me listen to the new "Lossless" surround formats, which I would be remiss if I didn't say improved the dynamics thing some, but still don't fully cut it. I have heard somewhat more dynamic theaters than my own. I will say, I recently finished my center channel, got things resituated, and the other day I watched Ghost Rider at the Theaters. My GF and I both said, man now having a home theater that rivals the movie theater makes this seem unimpressive. I sorta wanted them to turn it up. Not that I couldn't hear, the movie was plenty loud, but the dynamics were just weak sounding by comparison. I also think in general that movie theater speakers sound bad, they sound bright and overly forward. That's coming from a guy with a Focal based hometheater. I don't have room or money for the 2 story 1080P projection setup, but that would be a nice next step towards bettering the theaters. Then I just need some sort of inside source for first run movies, no?

Part of why I asked about adding an extra pair of output devices or two, and various other things to increase output was because of headroom. It was purely wanting to make sure that when a big dynamic peak hit, I wasn't hearing amplifier distortion.
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Old 19th March 2007, 04:34 PM   #8
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pjpoes: " ... As for movies, I picked up an HD DVD player from Toshiba, and using the analogue outputs is letting me listen to the new "Lossless" surround formats, which I would be remiss if I didn't say improved the dynamics thing some, but still don't fully cut it. ..."

You are on the right track with that one. I notice that Toshiba also has a quite inexpensive player that will play DVD-A with an output to (optical or coaxial = unclear which) ports @ 24bit / 192K resolution (plus Dolby 5.1, etc.) ... http://www.tacp.toshiba.com/dvd/prod...?model=sd-7990 ... it also does the 1080p "upconvert" ~= HD display. This is the right direction, but having two or six RCA analog ports would be an improvement (ala the Oppodigital.com 981 player), even if the Toshiba DAC was trivial or anemic. (For a few $$ more: http://www.tacp.toshiba.com/dvd/prod...?model=sd-6980 ... also has "Super Audio CD Multi-Channel Playback", but apparently NOT the DVD-A ?? ) ... The (quite high priced) Toshiba XA2 ( http://www.tacp.toshiba.com/dvd/prod...p?model=hd-xa2 ) , but it cdoesn't play DVD-A ... or does it, can't really tell from the hype on line.

The good thing is that there are several majors and a whole bunch of minor manufacturers who are scrambling to give us what we want ... DVD-A & SACD without the BS. That Oppodigirtal.com 981 is interesting in that it does upconvert to 1080p, SACD & DVD-A (+ CD) playback with "gold plated" 6 port analog DAC ... and with a magic command, it will play all that great European PAL Zone 2 videos and audio = ... which Toshiba, Marantz, Oinkie, Mitsubishi, etc. etc. et al can't seem to get into North America without grief from Sony ... ... the only thing wrong with the Oppo is its DAC is rather poor, but at least it plays just about everything
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Old 19th March 2007, 08:54 PM   #9
pjpoes is offline pjpoes  United States
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I have the Oppo 971, which does DVD-A but not SACD. I have a pioneer that does SACD, all of which are hooked up to my system, and modified a little bit. THe HD DVD player is an Xa1 and I am using the gold played analogue outputs from it for sound. It has suprisingly good sounding dac's, whatever they are, but far from the best I have heard. I haven't even opened it to find out what is inside. I understand it to be some sort of computer basicly, so I am guessing a switching power supply, flash memory, processor, etc. I may need to get in and clean up the power supply some, see what that does.

I designed a power supply today on PSUD2 that uses some 18mh inductors to make a Pi filter, and has remarkably low ripple in the 300microvolt range.
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Old 20th March 2007, 08:12 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi Pj,
it's easy to achieve low ripple with a Pi filter.
What peak current can you get out of it to power the amplifier is a much more important quaestion.
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