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3.2 ohm Radio Speakers

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Lucan01

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I am looking to restore those speakers. I just need 5-10w amplifiers that has input sounds to be heard from the devices through amplifier to these speakers.

It's 5w 3.2ohm speakers, and I cannot find the datasheet for the sound ranges and frequencies to help with my project. The box will be custom made in small MDF woods or plywoods. Looking to make it loud, but it don't need much bass. it's radio speakers.

I am eyeing on TDA2030 in my hand, and the power source will be 120VAC at 60Hz, single-phrase in Canada. I am only expecting less than 15 watts for the whole projects. some power left over will be going to a powered 5VDC USB @ 500mA or more. I also have large heatsink to use with TDA2030 if it required.

I have several kinds of transformers, and some rectifiers I can make the new power supply, but other than that I am not sure where I can start.
 

Lucan01

New Member
I am still learning the electronics, but using the calculator to decide the impedance for these speakers don't makes any sense to this project without knowing which to start the appropriate amplifier.

In Series, the calculator says for 10W, it will be 5W each at 6.4 ohm together.
In Parallel, the calculator says for 10W, it will be 5W each at 1.6 ohm on the same channel.

There are sources that says making the stereo will takes two sets of the same circuit. ( Heck, I am not sure if this apply to my project. )

Does this means I need 8 ohm amplifier and pair a set of resistors to each speakers?

I have so much to learn....

Edited, and Yes, I am sorry for double posting.
 

spec

Well-Known Member
Most Helpful Member
Hi Lucan,

Can I get your aims right:

(1) You have two loudspeaker chassis of 3.2 Ohms 5W
(2) You want to put the loudspeaker chassis in your own made custom cabinets.
(3) You want to make a stereo amplifier to drive the two speakers with.

If that is correct, just go ahead and make the cabinets and mount the speakers in the cabinets. That is the speakers taken care of

(4) You want to make an amplifier to drive your speaks
(5) You want to make a power supply to power the amplifier.

If that is correct the first thing you need to do is to find a case, preferably metal, to house your amplifier and the power supply.

Then you need to decide what controls you want.

Then build the power supply and get that going

Then build the amplifier

Test the amplifier and speakers with some music input and you are done.

Don't get into a tangle with voltage, impedance, and power- we can sort that- it is not as critical as you seem to think.

If you treat the above areas logically and progressively, there is no reason why you should not suceed. But you must divide your tasks.

The saying is divide and conquer.

spec
 

spec

Well-Known Member
Most Helpful Member
I am still learning the electronics, but using the calculator to decide the impedance for these speakers don't makes any sense to this project without knowing which to start the appropriate amplifier.

In Series, the calculator says for 10W, it will be 5W each at 6.4 ohm together.
In Parallel, the calculator says for 10W, it will be 5W each at 1.6 ohm on the same channel.
This is rather a jumble and does not make much sense- sorry. The calculations are much simpler than you think

There are sources that says making the stereo will takes two sets of the same circuit. ( Heck, I am not sure if this apply to my project. )
Yes you will need to build two amplifiers but just one power supply. One amplifier is for the left stereo signals and the other amplifier is for the right stereo signals.

Does this means I need 8 ohm amplifier and pair a set of resistors to each speakers?
You will need two amplifiers. Each amplifier must be capable of driving the 3.2 Ohm speakers at the power that you want. No resistors are needed.

Just a few points:
(1) A stereo amplifier is made from two totally separate mono amplifiers. There is no connection between the amplifiers, except that they may share a common power supply.
(2) All audio amplifiers have a zero Ohm output impedance regardless of what impedance speakers they are designed to drive.
(3) It is not necessary to match the amplifier power to the speaker power. In fact to get the best sound from a speaker it is best to have an amplifier with more power than the speaker.

So it would be perfectly acceptable to have a 10W amplifier driving a 5W speaker.

The other thing is that an amplifier designed to drive a 3.2 ohm speaker will be quite happy driving speakers of any higher impedance.

The above is a greatly simplified and shortened version of the whole story, but it will give you a good start and hopefully dispel some of the confusion.:)

spec
 
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Lucan01

New Member
This comes down to last question, so I thank you very much for going through the troubles with my mind.

Is there any circuit that I can use to build an amplifier to work with these speakers I mentioned?
 

spec

Well-Known Member
Most Helpful Member
This comes down to last question, so I thank you very much for going through the troubles with my mind.

Is there any circuit that I can use to build an amplifier to work with these speakers I mentioned?
Yes, there are litterly hundreds of suitable circuits.

Presumably, you want an amplifier that is easy to build and gives a good performance.

But here is the question: do you just want an amplifier or do you want the experience of building an amplifier from scratch.

Because, if you just want an amplifier and are not really interested in the experience of building an amplifier, by a along way, the best thing to do is to buy an amplifier ready made; it will be quicker, cheaper, and you will be guaranteed of success.:)

spec
 
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Lucan01

New Member
I am looking to make from scratch if its possible to be better than schematics found online.

Beside I learn better when I do this way, but yes, I know its cheapest and higher quality to buy the smaller and premade boards.
 

spec

Well-Known Member
Most Helpful Member
I am looking to make from scratch if its possible to be better than schematics found online.

Beside I learn better when I do this way, but yes, I know its cheapest and higher quality to buy the smaller and premade boards.
Ah yes- you have an interest in electronics, just like all of us on ETO.:)

Can I now make a suggestion, that you buy a bare purpose-designed printed circuit board for your amplifier and then build your amplifier using the printed circuit board.

The reason why I suggest this is that the layout of an audio power amplifier is critical and if this is your first electronics project it would be very difficult to succeed any other way.

You will still be building the power supply from scratch and the amplifier case so that will give you plenty of experience in the technical and mechanical aspects of electronics.

spec
 

Lucan01

New Member
This is why I came here hoping to pick up a circuit that is better than those 4/8ohm amplifiers that can power my 3.2 ohm speaker.

The original reason of my post is to endeavor my learning experience with electronic. Telling me to buy the premade boards for my electronic projects just don't make me feels good knowing I did learn something first before this project.

If it helps, I did built regulators and I did learned something from it. I have also built the motor controller, SSTC, HVT Driver to make jacob's ladder, and a plenty of power supplies.

Recently I recovered an abused microwave near the restaurant, and I just uncovered few awesome parts from it, especially with microwave oven transformer.

I learns new things everyday, not just from internet circuits but from you, but not just you, but from everyone. (Yes I purposed the "But" three times on purposes, lol) However, into audio field is something I have not gone into yet.

Now, please, help me with the circuit so I can build the amplifier. :)
 

Les Jones

Well-Known Member
Most Helpful Member
Am I correct in understanding that you want a mono (Single channel ) ampifier and NOT a stereo (Two channel.) amplifier ? Using the TDA2030 IC that you have (I am asuming you will be happy to use that as you did not say it had to be built from individual transistors or even valves.) To use the TDA2030 with the two speakers they would have to be connected in series so you would be driving a 6.4 ohm load. for 10 watts into a 6.4 ohm load you would require the square root of 10 x 6.4 = the square root of 64 = 8 volts rms. 8 volts RMS would have peak voltages of +/- 1.414 x 8 = +/- 11.3 volts
You would need to allow a couple of extra volts so the output transistors did not sturate. So I would aim for +/- 13 to 14 volts. Using standard mains transformers 9 volts would be about right (9 x 1.414 = 12.7 V) So you could use a 9 - 0 - 9 transformer for both a single supply or split supply version. An 18 volt transformer could be used for the single supply version. I assume the circuits you found on the internet are the ones on the TDA2030 data sheet. What is it that you find wrong with them ? I have built amplifiers in the past using audio amplifier ICs using the circuits from manufacturers data sheets and have not had any problems.

Les.
 

spec

Well-Known Member
Most Helpful Member
This is why I came here hoping to pick up a circuit that is better than those 4/8ohm amplifiers that can power my 3.2 ohm speaker.

The original reason of my post is to endeavor my learning experience with electronic. Telling me to buy the premade boards for my electronic projects just don't make me feels good knowing I did learn something first before this project.

If it helps, I did built regulators and I did learned something from it. I have also built the motor controller, SSTC, HVT Driver to make jacob's ladder, and a plenty of power supplies.

Recently I recovered an abused microwave near the restaurant, and I just uncovered few awesome parts from it, especially with microwave oven transformer.

I learns new things everyday, not just from internet circuits but from you, but not just you, but from everyone. (Yes I purposed the "But" three times on purposes, lol) However, into audio field is something I have not gone into yet.

Now, please, help me with the circuit so I can build the amplifier. :)
OK

spec
 

Lucan01

New Member
Am I correct in understanding that you want a mono (Single channel ) ampifier and NOT a stereo (Two channel.) amplifier ? Using the TDA2030 IC that you have (I am asuming you will be happy to use that as you did not say it had to be built from individual transistors or even valves.) To use the TDA2030 with the two speakers they would have to be connected in series so you would be driving a 6.4 ohm load. for 10 watts into a 6.4 ohm load you would require the square root of 10 x 6.4 = the square root of 64 = 8 volts rms. 8 volts RMS would have peak voltages of +/- 1.414 x 8 = +/- 11.3 volts
You would need to allow a couple of extra volts so the output transistors did not sturate. So I would aim for +/- 13 to 14 volts. Using standard mains transformers 9 volts would be about right (9 x 1.414 = 12.7 V) So you could use a 9 - 0 - 9 transformer for both a single supply or split supply version. An 18 volt transformer could be used for the single supply version. I assume the circuits you found on the internet are the ones on the TDA2030 data sheet. What is it that you find wrong with them ? I have built amplifiers in the past using audio amplifier ICs using the circuits from manufacturers data sheets and have not had any problems.

Les.
Thanks for your reply,

Speaker to Amplifier at 3.2 ohm impedance matching is my problem. Thank you, Les, for coming to me with this writing. Something I can answer to. Radio speakers was mono; i think, that I gutted the radio before. Picture will be tweeted and I hope this will help you better understanding. (Edited: Apparently i forgot I had two tweeters on it, so that i think changes some thing here. )

Circuits I have found for 10W amplifiers pretty much limited to 4 or 8 ohm, does uses TDA2030, and used range of input voltage of 12 to 28V ( vary from the circuits). Giving it juices are not problem, but how can I have it to work with 3.2 ohm?

The power supply you mentioned is what I have in my hand; old radio power supply which do offer 15.70V at no load. It has own rectifiers and fuse. i think center tap start after rectifiers so it will be yellow wire. Red and black is you know what. Multimeter test returns from this set:
Voltage before rectifier and transformer is 120V at 60hZ
Voltage after rectifier and transformer is 15.70V
The word written on the board is 4.5W
- Diode is FR202 x 4. (DATASHEET: http://pdf1.alldatasheet.com/datasheet-pdf/view/190600/WTE/FR202.html)
- Transformer is EI 57; 12V AC.
- Resistor is just pink 1/4w 2.2K ohm at 2%
- Fused with T2.5A 250V

Picture Tweeted: https://twitter.com/TheLucanPer/status/820705003434373124

Picture of Speakers Tweeted: https://twitter.com/TheLucanPer/status/820706617100472320
 
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audioguru

Well-Known Member
Most Helpful Member
Good home speakers are 8 ohms. Speakers that are 4 ohms used in cars. Poor quality speakers with poor sound are 3.2 ohms and are usually too small to produce low frequency bass sounds in music.
Speakers have a low frequency resonance like a bongo drum that messes up low frequencies in music and speech. The output of the amplifier "damps" the resonance. But speakers in series ruin the damping and you have bass at one frequency like a bongo drum. Is 5W the maximum average power rating or is it the maximum peak power rating which is double the average rating?

Use a TDA2030A amplifier IC. Its datasheet shows 10W into 4 ohms when its power supply is 24V which might be 11W into 3.2 ohms. Simply reduce the power supply voltage so that the little 5W speaker does not blow up.
5W into 3.2 ohms is a signal voltage that is 11.4V p-p which requires a power supply that is about 16.4VDC. The minimum supply voltage for the TDA2030A is 12V so 16.4V is fine. 5W is not much power so the heatsink can be fairly small.

A transformer that is 13V RMS at 1.5A will be fine for the stereo amplifier. It feeds a full wave bridge rectifier module then a pretty large (4700uF) filter capacitor.

The datasheet for the TDA2030A shows an amplifier with a single supply. Make two amplifiers for stereo.

Half-decent speakers have a datasheet that shows a recommended enclosure design. Usually a woofer is used for low frequencies and a tweeter is used for high frequencies. Sometimes a midrange speaker is also used. A crossover network divides the frequencies.
 

Les Jones

Well-Known Member
Most Helpful Member
Speaker to Amplifier at 3.2 ohm impedance matching is my problem.
With audio amplifiers you do not match impedances in the same way as you do a radio frequencies. An audio amplifier will have a very low outpur impedance. (Much less than 1 ohm.) All you need to wory about is not exceeding the ratings of the components in the amplifier. The TDA2030 has a maximum supply voltage of 36 volts. (You would normally aim to make sure it was a few volts below this value.) The TDA2030 also has a peak current rating of 3,5 amps so you would not want to use a load with such a low impedance that this value was exceeded. (The TDA2030 has built in limiting for this so it would not damage the chip but it would cause severe distorsion.). The question of mono or stereo depends on the source of the audio signal that you plan to amplify. Most equipment these days is at least stereo.

Les.
 

Lucan01

New Member
... The TDA2030 also has a peak current rating of 3,5 amps so you would not want to use a load with such a low impedance that this value was exceeded. (The TDA2030 has built in limiting for this so it would not damage the chip but it would cause severe distorsion.)...
This is why I started the thread, because I am not able to understand how I can match my speaker to an amplifier that can be driven in this impedance.

Once again, this continue to confuse me. This meant to me for an example using 4 ohm amplifier with TDA2030A will not be able to drive 3.2ohm correctly [Or if in parallel, it would be 1.6 ohm, or in series, will be at 6.4 ohm.]. This stop me from searching any further for circuits from 4 ohm or 8 ohm ampifier that can't indicate it's ability to drive from my impedance.

With your helps, I will be able to understand better.

Audioguru, thank you for being helpful too.
 

audioguru

Well-Known Member
Most Helpful Member
A TDA2030A IC can drive a 3.2 ohm speaker at only 5W easily because the peak current will be only 1.77A but its maximum allowed current is much more at 3.5A. The power supply should be about 16.4VDC. Since the power and output current is low then it can also drive 1.6 ohms since the peak current will be at about its maximum of 3.5A if the two 3.2 ohm speakers use 5W each. Don't connect speakers in series.

The largest electronic parts distributor (Digikey) in the USA says that the TDA2030 and TDA2030A are obsolete and they do not have any.
 

Les Jones

Well-Known Member
Most Helpful Member
Both myself and ag have explained the options you have. The voltage values we have given have been slightly different as we have made slightly different allowances. Such as I had been a bit more cautious on the maximum voltage that you may get from a lightly loaded transformer. ag has shown you that you have the option of using the speakers is series or parallel. (I had initially discounted the parallel option without actually doing the calculation.) As you do not seem to have understood the calculations I will make the assumption that you have no electrical knowledge.
First "ohms law" This is the relationship between voltage (V), current (I). and resistance (R) I = V/R Which can also be rearranged as V= I x R or R = V/I
Next the relationship between power (P), current (I), and voltage (V) P = I x V
By substituting for V or I using ohms law we can work out the voltage and current for a value of power dissipated in a resistor. (The resistor represents your speakers)
If we want to know the voltage for a known power into a known resistance. We know P = I x V so if we rearrange it V = P/I So by using ohms law we can substitute V/R for I
This gives us V = P/(V/R) we can rearrange this to V = (P x R)/V If we again re arrange it we get V^2 = P x R so V equals the square root of P x R
We can do a similar thing to get I in terms of P and R and we get I = square root of P/R
We also need to know the relationship between the RMS voltage of a sine wave and it's peak value. The peak value is the RMS value times root 2 (1.414)
We will now use these facts to calculate the current and voltage required to give 10 watts into a 1.6 ohm load using the above equations.
V = root (P x R so V = root (10 x 1.6) = root 16. The square root of 16 is 4 So we need 4 volts RMS The peak voltage will be 4 x 1.414 = 5.7 volts
The waveform will go from - 5.7 volts to + 5.7 volts so the peak to peak voltage required is 11.4 volts (We need a few volts more than this to avoid the output transistors going into saturation.)
We now know the voltage and the resistance so we can now calculate the peak current. I = V/R So I = 5.7/1.6 = 3.56 amps This is only very slightly more than the peak current rating (Which is internally limited) So you should only get the start of distortion if you drive the amplifier above 10 watts output.

I can't think of a more basic way of explaining the calculations.

Les.
 

Lucan01

New Member
Guys,

Thank you so much for the help lately. I have been super busy this week.

Actually, I have gotten enough idea what I need to build the circuit, so thank you all for your calculations. it's very useful. Yes, again, I'll say this again, I am still learning.

Unfortunately, with my time beings, I'll have to return this post later if i needed some more help if my circuit wouldn't work out correctly. Also, when I built a working circuit, I'll also post back here with the results.

Deeply in my heart, I thank you all for your help.

Lucan
 
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