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Old 28th December 2010, 03:08 PM   #1
hjf is offline hjf  Argentina
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Join Date: Dec 2010
Default Soundbarclone?

Hi guys, I'm new to this forum. I'm starting a project which is probably going to take several months. So I'll get started:

I like to watch movies, but I don't like 5.1 setups. I really don't care about the 5.1 effect... or more likely, I don't have a room big enough to have a permanent 5.1 setup with all the needed distances. The stereo effect is good enough for me. And I honestly don't believe in the 7.1/7.2 setups available now: they've be telling us for years that 1 big sub is enough to fill a room, and now it turns out we actually need two, to cover the "deaf" spots from a single sub (something we knew all along). But worse yet, they now tell us we need two front "effect" spekers, and two front "voice" speakers, so voice won't be distorted by sound effects or loud music - as if manufacturers put such good amps and drivers that this would be a noticeable effect, let alone that most consumers won't be able to tell the difference.

Anyway, I like 2.1 and I'm sticking with it.

So I have at my shop a Philips HTS6600 home theater, which is, simply put, an amazing piece of consumer audio gear. It's a 2.1 speaker+dvd combo, with HDMI out, SPDIF in, aux, dvd, etc. And a fantastic look:

Click the image to open in full size.

It also sounds amazing - each of the 2 front speakers has EIGHT (!) tiny drivers. The sub is pretty good too, it fills the room quite nicely. I use it to fill my store with great sound. It sounds good at low listening levels but it can sound LOUD when i want to. I just love it. But it's WAY too expensive where I live. Or it was, It's from about 2006 so I doubt it's in production anymore.

But actually there's another one I like best. The HTS8100 "Soundbar", picture here:

Click the image to open in full size.

This one sits below the TV so it suits me better - and looks amazing too. I don't really need the DVD or BD player capacity. In fact, I don't even want it.

So I'm planning to build a clone of that.

So now to the actual project:

The sub I have is already built. It's a 10" sub which I made over 10 years ago. The main question is if 68W from an LM3886 would be enough to drive it (it's 4-ohm). I want it for both movies and music.

The front speakers won't need that much power. Probably, what, 10-15 watts? I haven't even started with them yet.

My idea is to have a setup like this:

The sub box holds the power transformer inside (I'm not buying a toroid, I already have a good transformer), and the amp board+heatsink outside. Then it connects to the "soundbar", which holds the smaller stereo amp and small-signal circuits (stereo-to-mono, lpf, volume... tone control?).

The transformer I have seems to be 24-16-0-16-24 so I think it would be good for both the 68W amp (24-0-24) and the smaller amp (16-0-16).

Here's when I hit my first issue: I would like to have a single, big cable to run both power and audio. Mayble a 5-pin XLR cable. The problem is: it's never a good idea to run the power cables right next to the audio cables. Especially when you're sending low-voltage high-current AC. So I thought about using a balanced line to send the audio signal, which would eliminate any 50Hz hum that could have been induced.

DC could be used too: I'm not sure how much good or bad will that do - AFAIK many connector types don't like high-current DC because of oxidation processes.

I've seen a number of posts regarding the ability of an LM3886 to take a balanced input. Some suggest using a instrumentation amplifier approach, others recommend a balanced-to-SE stage and use the LM3886 as a regular SE input. I've seen just one using a LM3886 taking balanced inputs and converting to SE, which would be great because it would save me for making a separate low-voltage power supply (a TL081 can't take 28+28V).

So what do you guys think about this idea?

Recap:

big box on the floor, holding the big amp and transformer.
Single 5-conductor cable sending audio+,audio-,16V,0V,16V to the "soundbar".
"Soundbar" with small amp and audio processing (inputs, tone control, LPF, SE-to-balanced)
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Old 29th December 2010, 08:35 AM   #2
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Quote:
Originally Posted by hjf View Post
The sub I have is already built. It's a 10" sub which I made over 10 years ago. The main question is if 68W from an LM3886 would be enough to drive it (it's 4-ohm). I want it for both movies and music.
Especially when it comes to bass preferences are different. How much power have you been using on it during the last 10 years?

Quote:
Originally Posted by hjf View Post
The front speakers won't need that much power. Probably, what, 10-15 watts?
That should be enough most of the time. Depends on the speakers and your listening habits, though.

Quote:
Originally Posted by hjf View Post
The transformer I have seems to be 24-16-0-16-24 so I think it would be good for both the 68W amp (24-0-24) and the smaller amp (16-0-16).
24-0-24 could already be too much for the LM3886 with a 4 Ohm woofer. The datasheet specifies 68 W into 4 Ohm at ±28 V. 24-0-24 will give somthing like 32-33 V. You will probably have to use two ICs in parallel to share the heat dissipation among them provided the transformer can deliver the corresponding current.

Quote:
Originally Posted by hjf View Post
So I thought about using a balanced line to send the audio signal, which would eliminate any 50Hz hum that could have been induced.
You can achieve the same effect with twisted wires. The RE-2Y(ST)Yv PiMF is available with 0,5 mm˛ (3 A) or 1,3 mm˛ (13 A) shielded twisted pairs. That would save the additional complexity of balancing the signal.
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Old 29th December 2010, 12:13 PM   #3
hjf is offline hjf  Argentina
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Quote:
Originally Posted by pacificblue View Post
Especially when it comes to bass preferences are different. How much power have you been using on it during the last 10 years?
I haven't actually measured it - I always used a mini-component system to power it, a Sony GRX80. What I do remember is that this system is STK411-240E based, and according to datasheet it's 150W max. I don't really know how much power it actually delivers, but I do know that the volume knob goes to 30 and only in rare occasions I've used it past 25, because of room size and woofer excursion.

Quote:
24-0-24 could already be too much for the LM3886 with a 4 Ohm woofer. The datasheet specifies 68 W into 4 Ohm at ±28 V. 24-0-24 will give somthing like 32-33 V. You will probably have to use two ICs in parallel to share the heat dissipation among them provided the transformer can deliver the corresponding current.
Maybe I should switch to a TDA7294 amp? That one seems to be rated to higher power and voltage.

Quote:
You can achieve the same effect with twisted wires. The RE-2Y(ST)Yv PiMF is available with 0,5 mm˛ (3 A) or 1,3 mm˛ (13 A) shielded twisted pairs. That would save the additional complexity of balancing the signal.
Unfortunately I can't get that where I live (Argentina). I guess I could make something similar out of Cat5 twisted pairs and some power cables, and stuff all that into a heat shrink tube.
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Old 30th December 2010, 10:49 PM   #4
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Quote:
Originally Posted by hjf View Post
Maybe I should switch to a TDA7294 amp? That one seems to be rated to higher power and voltage.
The specs for the LM3886 are
Supply Voltage (No Signal): 94 V
Supply Voltage (With Signal): 84 V
Output Power 0,1 % THD: 68 W into 4 Ohm

The specs for the TDA are
Supply Voltage (No Signal): 100 V
Supply Voltage (With Signal): 80 V
Output Power 0,5 % THD: 70 W into 4 Ohm

Not much difference. The difficult thing when you combine chip amps and 4 Ohm speakers is heatsinking. The LM3886T has a slight edge there. Either way it is recommendable to use 2 ICs in parallel for the woofer.
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Old 30th December 2010, 11:23 PM   #5
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Hi,

A 2.1 system has nothing to do with proper "soundbars".

You might as well build all circuitry into the sub and run speaker leads.

For the main bar, I'd forget about that, its not a driver array, two simple boxes
on stands either side will work far better, suggest : Zaph|Audio - 4" Bargain Mini
Smaller (less depth) sealed is possible with proper active
high pass filtering built into the active amplifiers feedback.

Done well subwoofer power should not be an issue, the
lower the sub/speaker point, less sub power is needed.

rgds, sreten.
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Last edited by sreten; 30th December 2010 at 11:38 PM.
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