Computer technician struggling with electronics: building an amplifier.

[hitech95]

Yea, I know. I need a lower Transformer or a Regulated supply. But HOW?
I need 4.5A/5A at 26V with a linear regulator... I think that it is not so simple...

No, it may not be trivial as you will have to assemble a circuit yourself.

That said, the simplest way to have a linear regulator close to your specifications is to use a UA7824 (24V, 1,5A) tied to an external high power PNP transistor - something similar to what is shown at "page 52" of this page (don't be fooled by the bad web design, as the guy is very experienced).

If you intend to explore switching regulators but still keep the circuit simple, check the LM2679-ADJ.

Interesting even if you do not understand the operation. Unfortunately 24V are few.
I would not use switching components for audio. Otherwise I would have used a ready-made power supplier.

Bye, hitech95.

[mariush]

There are linear regulators which can do high amperage, like LT1083 for example, which can do up to 7.5A .. unfortunately, this particular regulator can only handle up to 30v.

There are linear regulators which can be connected in parallel to achieve higher currents... the one mentioned above (and LT1084 and LT1085, from the same family) can be configured like that.

LT3086 for example can do up to 45v input, but can only do up to 2.1A ... however, it's possible to parallel 2 of those to get over 4A . They're expensive though, as most Linear ICs are (about 6-7$ a piece). There are cheaper linear regulators that can work together sharing the current.

Older audio amplifiers use transistors to regulate the output voltage, somewhat similar to how bench power supplies do it. You could search for an old receiver/amplifier/something schematic on sites like electrotanya and get some inspiration from there. Or, have a look at the schematic attached (basically an opamp and some passives and a few transistors, after you remove the circuitry for relays and lcd display and so on which you wouldn't need)

[hitech95]

There are linear regulators which can do high amperage, like LT1083 for example, which can do up to 7.5A .. unfortunately, this particular regulator can only handle up to 30v.

There are linear regulators which can be connected in parallel to achieve higher currents... the one mentioned above (and LT1084 and LT1085, from the same family) can be configured like that.

LT3086 for example can do up to 45v input, but can only do up to 2.1A ... however, it's possible to parallel 2 of those to get over 4A . They're expensive though, as most Linear ICs are (about 6-7$ a piece). There are cheaper linear regulators that can work together sharing the current.

It is probably the best choice. Although I do not know how to achieve it.
If I understand it, I should find a transformer in which the output voltage is always greater than 26 + 2V. (Depending on the variations of the power grid)
Probably at this point, should I use a switching power supply 28/30V and use a linear regulator to filter the power supply and bring it to 26V. In any case the problem would be is a regulator capable at least 30V and at least 5A.

Older audio amplifiers use transistors to regulate the output voltage, somewhat similar to how bench power supplies do it. You could search for an old receiver/amplifier/something schematic on sites like electrotanya and get some inspiration from there. Or, have a look at the schematic attached (basically an opamp and some passives and a few transistors, after you remove the circuitry for relays and lcd display and so on which you wouldn't need)

This scares me. I am not able to use the transitor. (I've never learned)

Bye, hitech95.

[hitech95]

I just found this: http://www.circuitdiagram.org/24v-5a-power-supply.html
It is an implementation similar to that suggested by rsjsouza, can someone explain the operation?
From what I understand, the transistor is used to adjust the voltage and is controlled by the IC. But beyond that I do not understand each other.

Bye, hitech95.

[Ian.M]

There's really not much point in using a linear regulator to supply a class D output stage.  As long as the switching frequency is well above the audio range and you have enough bulk capacitance to handle the maximum possible ripple current the output stage can pull, simply use a SMPSU.   Run the preamp etc. at a lower voltage via a linear regulator to keep the switching hash out of that and make sure the preamp is well screened and you are most unlikely to be able to detect any difference compared to the same amplifier operating at the same rail voltages with an entirely linear PSU.

[rsjsouza]

I just found this: http://www.circuitdiagram.org/24v-5a-power-supply.html
It is an implementation similar to that suggested by rsjsouza, can someone explain the operation?
From what I understand, the transistor is used to adjust the voltage and is controlled by the IC. But beyond that I do not understand each other.

When the power supply is turned on, the UA7824 will operate as it is intended (a voltage regulator) if the current is low - at this point the transistor is turned off and its voltage between the collector and emitter terminals (V_ce) will be the same as the difference between the output of the rectifier and the output voltage of 24V.

As the current flows from the in to the out pins of the UA7824, the resistor connected between the transistor's base and emitter pins will have a voltage across its terminals (ohm's law).

As the current increases at about 0,65~0,7A, the voltage across the resistor's terminals will be 0,65~0,7V (1 ohm resistor), thus also increasing the voltage between the base and the emitter (V_be) pins of the transistor. At that V_be voltage, the transistor then starts to let current flow between the emitter and the collector terminals, which shares the current output with the UA7824. The way the transistor lets more current flow through these terminals is to reduce its collector emitter voltage or V_ce.

As the current increases, most of it is flowing through the transistor but the UA7824 still performs its intended function of regulating the voltage output. For example, if the transistor starts letting too much voltage go through its terminals (by reducing too much its V_ce), the UA7824 will sense the voltage increase in the output and reduce its own current flow, which reduces the current flowing through the resistor, thus decreasing the V_be voltage and consequently increasing the V_ce voltage.

One important detail to consider is the fact this topology will dissipate a lot of heat (or power), thus reducing the available power to the PA itself. For example, if the output of the rectifier is around 30V at 5A, the transistor will have the voltage difference (30-24V) across its terminals and about 4~4,5A will flow through it, which means it will convert 27W (6V * 4,5A) to heat that will be dissipated through its case. This is more than 20% of 120W that the transformer can deliver and is the only reason why folks are suggesting to use a switching power supply.

There's really not much point in using a linear regulator to supply a class D output stage.

Although I agree 100% with this due to efficiency, I have seen in the past severe intermodulation noise between the SMPS and the class D output, especially when both switchers are out of sync. Keep in mind that intermodulation noise can happen even when the switchers are operating at very high frequencies, but close enough to reach the audible range. That can be fixed by syncing both switchers, but it may not be trivial. 

[Ian.M]

There's really not much point in using a linear regulator to supply a class D output stage.

Although I agree 100% with this due to efficiency, I have seen in the past severe intermodulation noise between the SMPS and the class D output, especially when both switchers are out of sync. Keep in mind that intermodulation noise can happen even when the switchers are operating at very high frequencies, but close enough to reach the audible range. That can be fixed by syncing both switchers, but it may not be trivial. 

Which is why I emphasised that there *MUST* be enough bulk capacitance to handle the ripple current with sufficiently small ripple voltage to minimise any intermodulation.  Adding a large high current choke between the PSU and the reservoir capacitor bank will also be helpful. 

[hitech95]

OK, you convinced me.
You have explained a lot of things.

So in summary, a linear regulator is out of the question for the cost and the energy dissipated. (Lost)

At this point there are two choices: (At least the ones I know)

• A switching power supply
• Switching regulator. In this case I can keep the two toroidal transformers and stabilize the voltage.

(I think, but I'm not sure) that the best choice is the second one, because that way I can design the section of the capacitors in relation to my use.

Does anyone have any recommend schematic or IC?

@rsjsouza
Thanks for the explanation, I had not considered the function of resistor (1Ohm). 
Hello, hitech95

[rsjsouza]

Does anyone have any recommend schematic or IC?

As I mentioned before, the LM2679 may work for you. Also, they have a ready-to-assemble PCB board if you want to have some fun. You will have to check the device's datasheet to see the values of the components, though.

You can also get an assembled development kit (I found this other one based on the TPS54541) and modify it to suit the specs you need. To do these calculations, you can simply put the values in their online simulation/circuit design tools online (called webench).

I did a quick test and got this design - schematics also attached. I used V_in = 30~36V, V_out = 26V, I_out = 5A

I am pretty sure there are complete modules around on Alibaba, eBay, etc, but the info above is on the spirit of learning and assembling with practical tools. 

[hitech95]

Does anyone have any recommend schematic or IC?

As I mentioned before, the LM2679 may work for you. Also, they have a ready-to-assemble PCB board if you want to have some fun. You will have to check the device's datasheet to see the values of the components, though.

You can also get an assembled development kit (I found this other one based on the TPS54541) and modify it to suit the specs you need. To do these calculations, you can simply put the values in their online simulation/circuit design tools online (called webench).

I did a quick test and got this design - schematics also attached. I used V_in = 30~36V, V_out = 26V, I_out = 5A

I am pretty sure there are complete modules around on Alibaba, eBay, etc, but the info above is on the spirit of learning and assembling with practical tools.

WTF?     


EDIT:
I gave it a quick read to the datasheet.
Many things I have not clear. (Stupid deficiencies)
Someone is kind enough to explain? (PWRGD is a output? Why there is a generator?, same for the Load... )
 Another question: how the hell do I can solder that thing? It is tiny!
Doing a quick calculation, I noticed that I should do the tracks 3mm width, but now the entire IC is 3mm; how the hell do I do?

Thanks, hitech95

[hitech95]

UP?

[hitech95]

Does anyone have any recommend schematic or IC?

As I mentioned before, the LM2679 may work for you. Also, they have a ready-to-assemble PCB board if you want to have some fun. You will have to check the device's datasheet to see the values of the components, though.

You can also get an assembled development kit (I found this other one based on the TPS54541) and modify it to suit the specs you need. To do these calculations, you can simply put the values in their online simulation/circuit design tools online (called webench).

I did a quick test and got this design - schematics also attached. I used V_in = 30~36V, V_out = 26V, I_out = 5A

I am pretty sure there are complete modules around on Alibaba, eBay, etc, but the info above is on the spirit of learning and assembling with practical tools.

Third UP.
I think it's better the LM2679. I'm not sure but it is easier to solder and should be even easier to dissipate.

Unfortunately I lose the ability to know if the power has some problems. (PWRGD)
I have read the datasheet but I did not understand how to calculate the values of some components. (Diode, condensers, etc.)

Bye, hitech95.

[hitech95]

It seems the topic is dead. No one can answer my questions ...
In short, I do not ask a scheme but would like to understand how to do.

rsjsouza gave an example, with everything I need, but I did not understand what he did to find that solution. It seems difficult to achieve because of the IC package.
I have no way to solder "dense" SMD components.

Bye, hitech95

[mariush]

rsjsouza gave an example, with everything I need, but I did not understand what he did to find that solution. It seems difficult to achieve because of the IC package.
I have no way to solder "dense" SMD components.

Then pick another IC with an easier to use package.  Same with the SMD components, for probably 95% of the basic smd components out there (capacitors, diodes, inductors) there are through hole alternatives out there.
Just go to an online store like digikey.com , farnell.com, mouser.com , tme.eu  and go through their list of parts and find parts that match (or exceed) the specifications you need.

That ti webbench software can give you circuit examples and for each part in the circuit, they usually offer alternate parts or suggest other parts if you change the slider (on the page) to trade between performance and used pcb area for example. You just have to be curious and interested enough to do some research and play around with that software.

Look up at the parts they recommend, see what key specifications must be met, then look up the component code at the online stores I mentioned, or look up suggested alternatives if you don't find that exact part, or if you're really out of luck search for similar components that meet or exceed those specifications.  It's really not hard, just annoying process, takes time.

It seems the topic is dead. No one can answer my questions ...

People answer when there's something worthwhile to answer to.

[Ian.M]

Simply get some suitable switching regulator modules and get it up and running.

Your mistake was getting both the amplifier modules and the incompatible  transformers.

If you want to design it yourself, don't order any parts before you have checked the whole design.   If you are working around some part or module that was too good a deal to miss, don't get any other parts until you have worked out how the good deal parts requirements constrain the rest of the design. 

If you want to assemble this from loose components, why did you even buy amplifier modules rather than assembling them yourself?

If you want the experience of assembling it yourself from individual components, start with a design published in a magazine for which a kit is available.   The parts will have been chosen to work together and have appropriate voltage ratings.

[hitech95]

I decided to start from scratch.
Then. I chose the new components, using some SMD resistors and SMD capacitors.
I noticed a discrepancy in the datasheet of the LM4880 that I would use. I therefore ask you more experienced if it is so and how can I fix the possible problem.

Reading the electrical characteristics it appears that it (LM4880) accept as input signal only a voltage ranging from -0.3V to Vdd + 0.3V
If I understand correctly it means that if I send a AC signal the chip can be damaged because it can't handle negative values.
The reasoning that I just made is correct?

I decided to use as a preamplifier, TDA7439DS apparently there may be a DC component up to 4V (VOUTDC, look onthe Datasheet). If I have not misunderstood I can use a capacitor for eliminate it.
Remaining on TDA, I noticed there is a capacitor on the CREF Pin, but not understand which type should be.

This question applies to all instead chip: The decoupling capacitor of that material feeds should put it? I've seen various solutions: ceramic, polyester, electrolytic, tantalum. You can explain how to choose the type of capacitor? I need to figure out what to put for the TDA and the LM.

About the power final I got some 90W, 8 ohm speakers.
Would that then the final can safely drive: 80W.
Then V = sqrt (80 * = 25.3. So are the usual 26V.
IMAX = (80W + 25%)/26 = 3.8 to so we can fit them in 4A.
(The 25% is caused of inefficience, switch regulator, D class, other)

Then again doing the sum I need at least 105VA.
But this will be assessed later. For now I want to focus on the controller board.

Thanks, hitech95

[bson]

Make sure your rail caps are dimensioned for the worst case, which is the absolute max rail-to-rail voltage times some safety margin.  This is needed because your ground will be coupled to safety earth, to the chassis, and if one of the rails shorts to the chassis this means half your caps will sit between the rails until the fuse or something else (like a rectifier) blows.  You don't want this under any circumstance while you have the lid off and are poking around inside it to see what's going on (it may be a progressive failure you're trying to diagnose on a live supply that suddenly fails completely on you).

[hitech95]

Make sure your rail caps are dimensioned for the worst case, which is the absolute max rail-to-rail voltage times some safety margin.  This is needed because your ground will be coupled to safety earth, to the chassis, and if one of the rails shorts to the chassis this means half your caps will sit between the rails until the fuse or something else (like a rectifier) blows.  You don't want this under any circumstance while you have the lid off and are poking around inside it to see what's going on (it may be a progressive failure you're trying to diagnose on a live supply that suddenly fails completely on you).

I must apologize but I do not know some words in English and therefore do not understand the explanation:

• rail caps
• rail-to-rail voltage

In theory there should be a safety fuse.
I "know" that the voltage rating of a capacitor is approximately three times the voltage.

Bye, hitech95

[Richard Crowley]

"rail" refers to the main positive and negative voltage supply wires. It is like the two steel rails that train cars run on. A rail on each side.  When you look at a typical electronic schematic diagram you can see one wire ("rail") having the main positive power supply (typically at the top of the diagram).  And then typically along the bottom of the diagram, the main negative supply "rail".

When bson refers to "rail caps" he means the big filter capacitors on the main power supply "rails" (the positive power node, and the negative power node).
The term "rail-to-rail" refers to the total voltage from the negative rail up to the positive rail.  For example if you had -15V negative rail, and +15V positive rail, you would have 30V "rail-to-rail".

Electrolytic capacitors are made in rather "standard" voltages like 10, 16, 25, 35, 50, 75, 100, 150V, etc. Of course you should always use a capacitor of higher voltage rating than the circuit is designed for. But I have never seen anybody use capacitors that are 3x over-rated. It is rare to see even 2x over-rated except at very low voltages.  And many observe that using large electrolytics at a fraction of their rated voltage actually may be a disadvantage because they require something near the design voltage to develop the rated capacitance value.

[hitech95]

"rail" refers to the main positive and negative voltage supply wires. It is like the two steel rails that train cars run on. A rail on each side.  When you look at a typical electronic schematic diagram you can see one wire ("rail") having the main positive power supply (typically at the top of the diagram).  And then typically along the bottom of the diagram, the main negative supply "rail".

When bson refers to "rail caps" he means the big filter capacitors on the main power supply "rails" (the positive power node, and the negative power node).
The term "rail-to-rail" refers to the total voltage from the negative rail up to the positive rail.  For example if you had -15V negative rail, and +15V positive rail, you would have 30V "rail-to-rail".

Electrolytic capacitors are made in rather "standard" voltages like 10, 16, 25, 35, 50, 75, 100, 150V, etc. Of course you should always use a capacitor of higher voltage rating than the circuit is designed for. But I have never seen anybody use capacitors that are 3x over-rated. It is rare to see even 2x over-rated except at very low voltages.  And many observe that using large electrolytics at a fraction of their rated voltage actually may be a disadvantage because they require something near the design voltage to develop the rated capacitance value.

Thanks for the explanation, now I understand.
I do not remember who told me this thing of "multiply by 3".
Now need to know which material for the cap.

To power the headphone amplifier I found a LT1763-5. It seems to be easy to use and does what it needs. But also it had no need of many external components.
Instead to provide 9V to the TDA I have found a L78L09.
I'd say they are perfect for my needs.
What do you say?

Bye, hitech95.

[oldway]

Why not to begin with an audio kit ?

For example, a K4003 Velleman stereo amplifier kit.
 2 x 15Wrms in 4ohm or 2 x 10Wrms in 8ohm.
Short circuit proof.
You only need a 2x12V 80VA transformer.
http://www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k4003_rev1.pdf

For tone control, you can use a K8084 Velleman volume and tone control preamplifier kit.
http://www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k8084.pdf

[hitech95]

Why not to begin with an audio kit ?

For example, a K4003 Velleman stereo amplifier kit.
 2 x 15Wrms in 4ohm or 2 x 10Wrms in 8ohm.
Short circuit proof.
You only need a 2x12V 80VA transformer.
http://www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k4003_rev1.pdf

For tone control, you can use a K8084 Velleman volume and tone control preamplifier kit.
http://www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k8084.pdf

Why should I? I want to learn how to make circuits, no soldering.
Bye, hitech95.

[Richard Crowley]

Now need to know which material for the cap.

I do not understand the question?  Most conventional larger power-supply filter capacitors are "aluminum electrolytic".  I see no reason to use anything other than the most common kind of capacitor there.

To power the headphone amplifier I found a LT1763-5. It seems to be easy to use and does what it needs. But also it had no need of many external components.

Please remind us which headphone amplifier you are using?  And why you need a regulator for it?

Instead to provide 9V to the TDA I have found a L78L09.
I'd say they are perfect for my needs.
What do you say?

Yes, 78L09 is probably a good regulator for the TDA7439 audio processor chip.

Bye, hitech95.

We typically say "bye" only at the END of a conversation, when we don't expect any further response.
It seems strange for you to say "Bye" every time in the middle of this conversation.

[hitech95]

I do not understand the question?  Most conventional larger power-supply filter capacitors are "aluminum electrolytic".  I see no reason to use anything other than the most common kind of capacitor there.

I do not understand what type of capacitor to use for each type of use.
For example for the rail cap we use the electrolytic. For the decoupling capacitors are used instead of a lot of different types and I do not understand the "rule".

Please remind us which headphone amplifier you are using?  And why you need a regulator for it?

I invite you to read this post:

I decided to start from scratch.
Then. I chose the new components, using some SMD resistors and SMD capacitors.
I noticed a discrepancy in the datasheet of the LM4880 that I would use. I therefore ask you more experienced if it is so and how can I fix the possible problem.

Reading the electrical characteristics it appears that it (LM4880) accept as input signal only a voltage ranging from -0.3V to Vdd + 0.3V
If I understand correctly it means that if I send a AC signal the chip can be damaged because it can't handle negative values.
The reasoning that I just made is correct?

I decided to use as a preamplifier, TDA7439DS apparently there may be a DC component up to 4V (VOUTDC, look onthe Datasheet). If I have not misunderstood I can use a capacitor for eliminate it.
Remaining on TDA, I noticed there is a capacitor on the CREF Pin, but not understand which type should be.

This question applies to all instead chip: The decoupling capacitor of that material feeds should put it? I've seen various solutions: ceramic, polyester, electrolytic, tantalum. You can explain how to choose the type of capacitor? I need to figure out what to put for the TDA and the LM.

About the power final I got some 90W, 8 ohm speakers.
Would that then the final can safely drive: 80W.
Then V = sqrt (80 * = 25.3. So are the usual 26V.
IMAX = (80W + 25%)/26 = 3.8 to so we can fit them in 4A.
(The 25% is caused of inefficience, switch regulator, D class, other)

Then again doing the sum I need at least 105VA.
But this will be assessed later. For now I want to focus on the controller board.

Thanks, hitech95

The amplifier is a LM4880.

Yes, 78L09 is probably a good regulator for the TDA7439 audio processor chip.

At least one thing I have chosen correctly. 

We typically say "bye" only at the END of a conversation, when we don't expect any further response.
It seems strange for you to say "Bye" every time in the middle of this conversation.

I apologize for the mistakes. It is probably best a "thanks".


Thanks, hitech95.

[Richard Crowley]

For larger value capacitors (generally over 1uF) we typically use aluminum electrolytic because of the space (and cost) efficiency.
And for smaller value capacitors, there is a wider variety of types to choose from. Poly film are favorites of audiophiles.

The LM4880 is specified for: "2.7V to 5.5V". WHY do you need ANY kind of voltage regulator there?
That chip is made for portable applications so that it will continue to operate within spec while the battery discharges.
Regulating the supply voltage for that chip appears to have no motivation here.