Multi-purpose amp circuit

xxRockOnxx

Member
2016-06-15 11:23 am
Hi, I'm looking for something easy to build. I have an interface here and a pair of speakers. The problem is I don't have a power amp.

Even low watt circuit would do as I only have small room. 1w is suffice and 9v-12v powered if possible. At first, I just thought of making one just to make the speakers work, but I hope it could be use for monitoring too. Transparent and neutral sounding if possible. I looked on google for a circuit but all I could find is for Cmoy.

The AD8066 I found here: Flavors of Audio Op-Amps - SGHeadphones seems pleasing and looks like it's what I want, the problem is it's for headphones.

Is there any AD8066 circuit there I could use for speakers or something similar?

Hoping I could use it for monitoring and/or room playing with amp modellers.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Have a look at circuits using the LM386 and TDA2050

The data sheets give typical circuit applications and for battery use you need the TDA2050 configured for 'single rail operation'. The TDA2050 is very much like a powerful opamp and is used in the same basic configurations as small signal opamps such as the headphone amp uses.

You can get the data sheets from here:
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
These are the basic circuits:
 

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xxRockOnxx

Member
2016-06-15 11:23 am
I thought of the LM386 too cause that's the very common one. But while I'm searching for some circuits, they say LM386 is just for test amps only or experiments.

I tend to avoid it now because of that. Is that true? Of course I'll be using this for a lot of stuffs so I would like it to sound good.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
The LM386 is a found in commercial equipment (radios etc). It does what it says on the tin within the constraints of its modest specification.

The CMOY is a popular minimalist circuit that you could lift out of any text book. If you added a buffer then it becomes a simple opamp gain stage + unity gain buffer. What would you use as a buffer to drive a low impedance speaker load ?

The TDA2050 has real 'drive' ability and is rated into 4 ohm loads.
 

farley

Member
2011-10-22 11:22 pm
Texas
The TDA7266 is pretty easy to use. This is the same amplifier used in the Tivoli Model 1. I use it to play music in my office streamed from a raspberry pi.

My implementation is essentially from the datasheet with an extra decoupling cap and connections added to the PCB for volume adjust pots. Any standard 10k dual (audio taper) pot will work.

Be aware that this is a BTL configuration. Do not allow any of the speaker output connections to connect to ground or common. Doing so will damage the TDA7266.
 

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xxRockOnxx

Member
2016-06-15 11:23 am
The TDA7266 is pretty easy to use. This is the same amplifier used in the Tivoli Model 1. I use it to play music in my office streamed from a raspberry pi.

My implementation is essentially from the datasheet with an extra decoupling cap and connections added to the PCB for volume adjust pots. Any standard 10k dual (audio taper) pot will work.

Be aware that this is a BTL configuration. Do not allow any of the speaker output connections to connect to ground or common. Doing so will damage the TDA7266.

Hmm, this looks good based on your experience. How does it sound? Is it good? Sounds natural? No harsh trebles and not too dark? I want balance as possible tho I know there is no perfectly flat (Lol).

The CMOY is a popular minimalist circuit that you could lift out of any text book. If you added a buffer then it becomes a simple opamp gain stage + unity gain buffer. What would you use as a buffer to drive a low impedance speaker load ?

I thought that was what buffers are used for. I'm new to this stuffs, don't know what buffers/impedance do in this context then. I started from making guitar fx stuffs so everything I know about audio circuits came from those.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Speakers are a low impedance load which means they take lots of current to drive them. An opamp can not do this. The CMOY gets away with it because headphones, although lowish in impedance also require only a little voltage to make a big noise... so it works up to a point.

Buffers normally refer to low power devices, and for various technical reasons you don't see opamps + buffers to drive speakers. Opamps + transistors yes, but that is not really a buffer in the true sense.
 

xxRockOnxx

Member
2016-06-15 11:23 am
Speakers are a low impedance load which means they take lots of current to drive them. An opamp can not do this. The CMOY gets away with it because headphones, although lowish in impedance also require only a little voltage to make a big noise... so it works up to a point.

Buffers normally refer to low power devices, and for various technical reasons you don't see opamps + buffers to drive speakers. Opamps + transistors yes, but that is not really a buffer in the true sense.

I studied a bit about speaker impedance and now know a bit of background about it. But I wonder, why does lower impedance needs more current to drive it?

Either higher or better if equal should be used. Hmm, I wondered cause in simple circuits low resistor value means more current can pass through compared to the one with higher resistance. Does that apply also to the speaker impedance as well? Hope you get what I mean.

-- EDIT --

Ok I found an analogy, but it's a bit ironical compared to how you say that low impedance load take a lots of currents. Here's the analogy I found:

Ohms are the units that impedance is measured with. You can kind of think of impedance as the measure of how hard the amp has to push to get current to flow. The lower the impedance, the more power will be output from your amp. Unfortunately, the amplifier circuit wants to push against something, so that if the impedance is too low, the amp can perform badly, and even overheat and burn out.

From: https://www.sweetwater.com/forums/archive/index.php/t-2193.html

That is a bit connected to this analogy too:

Understanding Ohms and Impedance:
In order to understand the reasons for the rules for speaker connection, we need a bit of electrical theory. You probably had this as a lesson in high school at some point, but were more interested in other things at the time. In order to relate it to something you are more familiar with, let's consider the ordinary garden hose. Print this off and go outside, hook up the hose (no nozzle) and turn on the water. Pretty soon, water should start flowing out the end of the hose. This flow of water through the hose is similar to electric current, which is usually described as the flow of electrons through the wire and is measured in Amperes.

Now put your thumb over the end of the hose and try to stop the flow of water. Feel the pressure? This pressure is similar to Voltage. It is the force of electricity that pushes the electrons through the wire. Notice that if you succeed in plugging the water flow, (no current) the pressure is still there. This is like an amplifier with no speakers attached, or an AC outlet with nothing plugged in. Voltage is present, but there is no current flow.

From: http://www.prestonelectronics.com/audio/Impedance.htm

That makes more sense compared to how you said it.

1st analogy said amps wants to push against something, I guess because of the voltage present stated in the 2nd analogy. So if the impedance is low there's just a little current passing through and voltage is pressuring the amp. (That's how I understand it. Did I get it right? Or did I miss something?)

-- EDIT --
But low impedance speaker is louder, why would low impedance then have low current? Hmm this is all quite confusing hahahaha and why would it draw a lot more current?

I read the 2nd reply on the 1st analogy link
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Think of ohms law. For any given voltage you apply across a resistance (we will call impedance resistance for now), the current that flows depends on the value of that resistor.

eg.

10 volts applied across 1000 ohms causes a current of 0.01 amps to flow.

10 volts applied across 10 ohms causes a current of 1 amp to flow.

We could describe the 1000 ohms as a high resistance or impedance and the 10 ohms as low.

Speakers are low impedance because it takes serious power to move the air and produce sound. If we made them high impedance then we would need to apply many volts to generate the same power. We could do it but it would not be convenient. Who wants an amplifier running on a 1000 or 10,000 volts driving a 10,000 ohm speaker when we can do the same with a 10 volt supply and low impedance speaker.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
I see you edited your post :) and I picked my numbers 'out of the air' :D

At the end of the day you need to arrive at a given 'power' to do the job in hand whether it be driving a speaker or turning a motor.

We can achieve the same 'power' by a combination of different resistance and voltage levels. A car starter might draw 200 amps at 12 volts. That's 2400 watts. Ohms law tells us the motor has a resistance of 0.06 ohms. LOW !

Supposing we had to make the motor so that it had a much higher resistance, say 100 ohms. To generate 2400 watts of useful energy we would need to apply nearly 500 volts to the motor.

With speakers 'efficiency' is the big decider on how loud one vs another is.

And ALL normal type speakers are 'low impedance loads'. 4 ohms, 8 ohms, 16 ohms, they are all classed as 'low' compared to the loads that opamps and so on work with.
 

farley

Member
2011-10-22 11:22 pm
Texas
How does it sound? Is it good? Sounds natural? No harsh trebles and not too dark? I want balance as possible tho I know there is no perfectly flat
It sounds fine. It's a small stereo amplifier on a board mounted heat sink running off a 12V wall wart and is capable of about 3-4W per channel. I don't know how to classify it based on "harsh trebles" or "too dark." Those terms are apparently uniquely defined by each individual. The LM3886 amplifier I have in my living room sounds better.

The data sheet for the TDA7266 shows its capabilities:
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00000203.pdf
 

xxRockOnxx

Member
2016-06-15 11:23 am
It sounds fine. It's a small stereo amplifier on a board mounted heat sink running off a 12V wall wart and is capable of about 3-4W per channel. I don't know how to classify it based on "harsh trebles" or "too dark." Those terms are apparently uniquely defined by each individual. The LM3886 amplifier I have in my living room sounds better.

The data sheet for the TDA7266 shows its capabilities:
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00000203.pdf

Thanks for narrowing down circuits I have on my list. What do you favor most? LM3886 or the TDA7266? Describe it based on what you hear or just compare the two then I'll based on that.

And ALL normal type speakers are 'low impedance loads'. 4 ohms, 8 ohms, 16 ohms, they are all classed as 'low' compared to the loads that opamps and so on work with.

That line summarizes it up xD I thought you mean by low is 4 ohms or anything lower than that and the rest is high or normal ones. Still have a lot to learn but I don't have the time currently. I learn by doing things and experiencing them btw, not by reading tho it helps but still you won't learn just by reading it.

But still I'm confused to why low impedance would draw a lot of current or stress the amp? Shouldn't it be just drawing what it could from the amp? That's how I understand it, similar to how the phone charging works... it would just draw what it can (if low mA charger) or what is enough for itself (if high mA charger)... it doesn't stress the charger to give more.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
But still I'm confused to why low impedance would draw a lot of current or stress the amp? Shouldn't it be just drawing what it could from the amp? That's how I understand it, similar to how the phone charging works... it would just draw what it can (if low mA charger) or what is enough for itself (if high mA charger)... it doesn't stress the charger to give more.

Amplifier are thought of as 'constant voltage devices'. This means that they maintain their output voltage irrespective of the load. It is the load that determines how much current will be drawn from the amplifier.

A 12 volt battery maintains its voltage whether its a tiny bulb connected to it or a 55 watt headlamp bulb. It is the load (the bulb) that is determining the current.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
And your charger analogy...

A battery such as a mobile phone or laptop type isn't anything like a resistive load that obeys ohms law, they work very differently. Those type of batteries are electronically managed internally (they are 'smart batteries' with complex onboard circuitry).
 

farley

Member
2011-10-22 11:22 pm
Texas
What do you favor most? LM3886 or the TDA7266?
For easy and quick to build the TDA7266. Power it with a 1A to 2A 12V DC wall wart. It more than meets the criteria you identified in your original post:

1w is suffice and 9v-12v powered if possible.
The LM3886 is a different beast. Its typical configuration will require 2 of them, a large transformer, large heat sinks, connection to mains, etc... It's more complicated and, considering mains wiring is involved, dangerous and lethal if you don't know exactly what you're doing.