Hey Guys,
I am looking to build a 5.1 channel chip amp to go with my decoder/DAC that I am also building. It is all for a surround system for my TV. I think that I will be using the LM3875, but am open to suggestions. I have a few question and hope that you guys can help me as I begin to design the amp. I hope to breadboard at least one channel before designing a PCB. Here are my questions:
1. What output power is appropriate for each channel of a surround system? I don't need to rattle the house, but I want sufficient power.
2. Does the sub need a different type of amp?
3. Should I power the whole amp with one transformer/psu?
4. How should I decide on a heat sink and where should I get it?
5. Is the sample circuit in the datasheet a good place to start for the circuit?
6. I would rather not have a preamp if I can. I the volume control on my DAC (CS4360) sufficient?
I want to build a nice amp, but I don't want to spend a fortune.
Thanks in advance for all your help!
I am looking to build a 5.1 channel chip amp to go with my decoder/DAC that I am also building. It is all for a surround system for my TV. I think that I will be using the LM3875, but am open to suggestions. I have a few question and hope that you guys can help me as I begin to design the amp. I hope to breadboard at least one channel before designing a PCB. Here are my questions:
1. What output power is appropriate for each channel of a surround system? I don't need to rattle the house, but I want sufficient power.
2. Does the sub need a different type of amp?
3. Should I power the whole amp with one transformer/psu?
4. How should I decide on a heat sink and where should I get it?
5. Is the sample circuit in the datasheet a good place to start for the circuit?
6. I would rather not have a preamp if I can. I the volume control on my DAC (CS4360) sufficient?
I want to build a nice amp, but I don't want to spend a fortune.
Thanks in advance for all your help!
the required output power of the amplifier is determined by the sensitivity of your speakers and what volume you require (hear and fill).
If you find 100mW (800mVac to 1000mVac into 8ohms) is sufficient for your average listening needs then an amp with a maximum power output between 50 and 100times your average will cover much of your use except loud.
If your speakers are too quiet with 100mW, then you have to turn up the volume until you have found your comfortable average level and then apply the 50 to 100times to find your amplifier power.
The cheapest way is one transformer and one PSU and one chassis to power all six channels.
The dearest way is one transformer and one PSU and one chassis to every channel.
If you find 100mW (800mVac to 1000mVac into 8ohms) is sufficient for your average listening needs then an amp with a maximum power output between 50 and 100times your average will cover much of your use except loud.
If your speakers are too quiet with 100mW, then you have to turn up the volume until you have found your comfortable average level and then apply the 50 to 100times to find your amplifier power.
The cheapest way is one transformer and one PSU and one chassis to power all six channels.
The dearest way is one transformer and one PSU and one chassis to every channel.
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1) Speaker efficiency matters a LOT. A small change in this number has the same effect on loudness as doubling or more the power. Adds watts is a poor way to make a system play louder. Speaker design matters a LOT more. For example I have a 5W guitar amp and a very efficient speaker (abot 100 db/W 1M) People across the street can hear it. But the same 5W amp driving a 4: diameter 84db speak is not loud at all
2) For pactical purposes yes.
6) Volume controls -- yes. Even if these are just trimmer pots inside the case. You will need a way to adjust the relative volue of each speaker. You will need to balance the system some how. Of cource your amp may have these controls But still I'd want to be able to adjust relative volume
7) heat sink info is on the spec sheets.
Thanks for the info guys ... keep it coming. I guess I will need to look at what speakers I will use to determine what kind of amplifier I need. Can someone tell me what kind of speakers are generally used for each channel on a 5.1 system? I am totally new to this. Also, what type of ceramic SMD caps do you guys use for bypassing? I have never done surface mount before and I could use some help. Thanks!
It depends on the goal. If this is for action films and you are listening to car crashes and explosions then you can get by with small speakers and a huge sub-woofer. But if for music then you want at least the two front L and R speakers to look and sound a lot like conventional home stereo speakers and if a sub is used to cross it over "way low"
And then pratical conciderations, what's the budget and how large can the speakers be
The design of any sound system should begin with writing down the size of the room, a floor plan and then what it is you'll be listening to. The floor plan tell you things like how far th rear wall is from the listener's head Floor plan will also say if you can use little satilite speakers ot floor standing ones. In terms of sound you want the listener in the cente of the room and speakers all pull in off the walls. Practically people prefer everything to be alow the edges of the room
Any kind of speakers are used. Your choice depends on the SPL you want and the sizes of your listening room and wallet. Some people are quite happy with five 3" full-rangers and a 6" subwoofer. Others have five 2- or 3-way speakers with 12" woofers and several even bigger subwoofers strategically placed around the room plus body-shakers below each seat. Usually you have two big main speakers accompanied by a center speaker that should be as similar to the mains as the space allows and smaller effect speakers. The sub should cover 20..80 Hz, mains and center 80..20.000 Hz and the effect speakers depending on the surround specification either 125..20.000 (ProLogic) or 80..20.000 Hz (Digital or DTS). If you additionally want to cover THX specs all speakers must reach 105 dB at the listening position with low distortion.
The types of bypass caps are often determined by their size. The most recommendable NP0 or C0G are only available in small values or at extreme prices, which limits your choice to X7R, because the remaining ceramics don't provide sufficient quality for that purpose.
The types of bypass caps are often determined by their size. The most recommendable NP0 or C0G are only available in small values or at extreme prices, which limits your choice to X7R, because the remaining ceramics don't provide sufficient quality for that purpose.
I am currently building my own system which has been coming along over a long time.
MY current system:
5.1 DAC = rotel 985 rsp (bought from a guy who thought it was broken)
5 Main amplifiers (already built):
Powersupply: 500VA 25-0-25V transformer with 40000uf per voltage rail.
amplifier: 5 x lm3886 with 100uF per voltage rail close to each rail on chip, using standard national circuit
Fotos: Heinrich Spreeth's Photos - My eerste amplifier | Facebook
subwoofer currently building:
bpa300 with 500VA with 2 x 12" drivers
the linkwitz tranform circuit is done and speaker enclosure but still need to built the amplifier itself.
fotos:
Heinrich Spreeth's Photos - Home cinema .1 channel in the making | Facebook
MY current system:
5.1 DAC = rotel 985 rsp (bought from a guy who thought it was broken)
5 Main amplifiers (already built):
Powersupply: 500VA 25-0-25V transformer with 40000uf per voltage rail.
amplifier: 5 x lm3886 with 100uF per voltage rail close to each rail on chip, using standard national circuit
Fotos: Heinrich Spreeth's Photos - My eerste amplifier | Facebook
subwoofer currently building:
bpa300 with 500VA with 2 x 12" drivers
the linkwitz tranform circuit is done and speaker enclosure but still need to built the amplifier itself.
fotos:
Heinrich Spreeth's Photos - Home cinema .1 channel in the making | Facebook
Hi nightanole
For a DAC you have 3 options in my opinion.
1) look for mainstream namebrand 5.1 decoder that has line level analogue output that support all the codecs you want (dts , dolby digital) with a few analogue inputs ,does it need phono input?
2) look for a kit on ebay , a quick search and I found something like this:
DTS AC3 5.1 DIGIT AUDIO DECODER dac mocha JY-M2 SKU39 - eBay (item 330347698128 end time Apr-22-10 18:01:54 PDT)
3) Use a pc based system with a decent sound card.
For a DAC you have 3 options in my opinion.
1) look for mainstream namebrand 5.1 decoder that has line level analogue output that support all the codecs you want (dts , dolby digital) with a few analogue inputs ,does it need phono input?
2) look for a kit on ebay , a quick search and I found something like this:
DTS AC3 5.1 DIGIT AUDIO DECODER dac mocha JY-M2 SKU39 - eBay (item 330347698128 end time Apr-22-10 18:01:54 PDT)
3) Use a pc based system with a decent sound card.
So, I have decided to build one channel using an LM3886 as an experiment. I would like to get 50W into 8 ohms. I think this would require 35 volt rails, so I would need a transformer with 25 volt secondaries. Are my numbers correct and will they work ok with the chip? Will 150VA per channel be enough?
Thanks!
Thanks!
I like the idea of one transformer. However, would there be any issues with inrush current when it is turned on? Would one transformer cause crosstalk between channels?
If you are concerned about this then build a distributed filter. But that is the way gainclones are typically built. You have one transformer, rectifier and set of caps then from there power leads go to each channel. On each channel is another set of filter caps.
What this does is divide the power supply into 5 channels by cutting the capacitor bank. This is the lowest cost and simplist thing to to and also the most common.
But with more effort you can divide the power suply in 5ths at some other point. The extream case is right after the on/off switch by using five transformers.
There are compromise solutions that involve dividing the power supply at other points and you get more or less isolation. One simple one is to place a resistor in series with each power lead. this in effect places a CRC low pass filter between each channel. The R drops some volts but you can select a transformer that supplies the extra volts.
Much more expensive but providing near perfect isolation is a regulated power supply with 5 regulators. This is complex but I think cheaper then buying five 150VA transformers.
But the true audiophile "nut" would insist on putting each channel in it's own chassis and not even sharing a power switch.
What would I do? Simply buy an over-spec'd transformer. The oversize will provide very good load regulation and mostly eliminate the need for isolation. It's worth it to just spend a few extra $$ and keep the power supply very simple.
If you go with inverting i hope you have a good preamp, it has a lot lower input impedance then the non inverting (10x or more) and requires a bigger input cap to compensate. both Chipamp.com and audiosector.com use non inverting and no one complains.
This could open a whole coke vs pepsi debate.
This could open a whole coke vs pepsi debate.
both chipamp and audiosector have there designs and easy build sheets on pdf on there sites.
Here is an inverted one:
Building a Gainclone chip amp
I went with the chipamp.com pcb, which you can get for dirt cheap if you dont want to mess with the air wiring.
db dungeon has alot of inverted gainclone stuff to read over. I would start there because ive only been doing this for a year and only used the pcb sets and only traditional non inverting.
Here is an inverted one:
Building a Gainclone chip amp
I went with the chipamp.com pcb, which you can get for dirt cheap if you dont want to mess with the air wiring.
db dungeon has alot of inverted gainclone stuff to read over. I would start there because ive only been doing this for a year and only used the pcb sets and only traditional non inverting.
In my opinion:
a 500VA would probably be more than enough ( if you take the rule of thumb of 2x your amplifier output watt) bigger will be better though , how much time is not sure.
One thing to remember is that for a 5.1 system it is VERY rare for all 5 speakers to run at the same time at high levels.
For music you only use two channels anyway.
My 500va makes the house lights dim when I switch it on.
For a 750VA I would suggest a slow start circuit like the one on ESP pages:
Soft-Start Circuit For Power Amps
I am currently building one for mine but I am using a lm555 monostable for a delay of around 130ms.
a 500VA would probably be more than enough ( if you take the rule of thumb of 2x your amplifier output watt) bigger will be better though , how much time is not sure.
One thing to remember is that for a 5.1 system it is VERY rare for all 5 speakers to run at the same time at high levels.
For music you only use two channels anyway.
My 500va makes the house lights dim when I switch it on.
For a 750VA I would suggest a slow start circuit like the one on ESP pages:
Soft-Start Circuit For Power Amps
I am currently building one for mine but I am using a lm555 monostable for a delay of around 130ms.
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