Computer technician struggling with electronics: building an amplifier.

[hitech95]

Hello everyone.
I am new. I just registered to solve a doubt ...

Beginning with presentations, hoping not to bore you.
My name is Nicolò (Nicholas) and I studied electronics at school. Now I realized that we were not taught much. I just realize that i'm not able to make  a simple thing as an small power supply.
Unfortunately, at school I have only studied theory and many things remain on paper...

At this time I would like to build (to start) an audio amplifier .

The idea for this amplifier was to use some boards and "merge them" to achieve an working amplifier.

The features that I would like to achieve are:

• Tone control (High and Low)
• Volume control
• Source Selection
• amplifier for headphones
• IR remote control

The boards that I'm going to use are powered at 24V-30V. I thought to use 26V. They have an maximum absorption of 5A. (Before entering protection)

Being a "dual mono" I opted to use two toroidal transformers (one per channel). With a quick calculation I found what I need 24V AC and 5A. So are two 120VA transformer.

As boards have neither the rectifier nor the filter capacitors, I have to realize the board for the power. The cards are supplied with s single rail 26V-0V.

Here, however, it makes it difficult. to achieve the functions described above, I need use a micro controller to manage everything. (I opted for a ATMega, so I can use the Arduino IDE)

To realize the control tone, volume, etc. I was thinking of using a TDA7468; to achieve the headphones amplifier I thought of using a LM4880.

To complicate matters, in the box I would put a DAC and a Raspberry. (The DAC is one of those made specifically for the Raspberry, the raspberry is one of the audio sources)

I need to implement a system which allows to turn them on remotely (IR remote), and then the control electronics must always be powered. So there will also be a line of standby power.

After filling you with all the necessary information you're probably wondering what the problem is.

The problem is how make the power rails,calculate the capacitors, and design a security system (polyfuse, fuses, etc.) to power the whole.

To the delight of many, I attach some scheme, hoping it can help you to understand. Many things are still in development and so many things could not be right.

On attachments, you will find:

• The power supply section for power amplifiers. (those values I have been recommended in another forum), is one for each transformer.
• The board with electronics for the audio and its power.

For 5V standby and to power the raspberry thought of using something like this:

Whereas to power on and off the amplifier I thought of using a relay card.
Who knows if they hold the 220V AC ....


Thanks, hitech95.

[hitech95]

It's nice to see how a trivial problem as my is completely ignored just because there is a looong description. 
I only tried to give much detail as possible about what I'm doing.

The problem is simple:

• how to realize the safety systems for the supply lines.
• Is good to use relays to control the two transformers? (220V)
• How do you recommend to turn on/off the power of raspberry? Relay or MOSFET or other? (I do not know how to use transistors and their derivatives)

Bye, hitech95.

EDIT: striped a sentence, it could be interpreted negatively.

[Zero999]

Why use two transformers? One transformer should be able to power both channels.

What are you using for the main power amplifier?

It's probably best to design each component separately first.

[Refrigerator]

If you're doing an analog audio amp there's many designs on the web how to do it, tone control can be easily done with an op-amp ( google "opamp tone control" ) TL082 datasheet has a simple tone control schematic.
Class D amps are much more efficient but they also have some quirks ( output filtering, output noise, interference, EMI ).
The headphone output can be fed directly from the op-amp tone control.
If you're making your own power supply then don't forget to put big caps and make proper star-ground to further improve sound quality and overall stability.
Also don't forget to do proper air flow in your amp enclosure so that hot air does not pass over any electrolytics to improve their life and keep the ESR low.
Relays are good for switching the output of the amp on and off, for DC it is better to use transistors or FETs since relays have contact bounce and the raspberry might not like it.

[hitech95]

Why use two transformers? One transformer should be able to power both channels.

What are you using for the main power amplifier?

It's probably best to design each component separately first.

The main aplifier is a board based on a sta508 by ST. (I buy it already made like this) (The voltage in the description is wrong according to the datasheet) <-- Wrong different IC
I would use two transformers because I want to separate as much as possible the two channels.

My "real problem" is that at school I worked only with digital electronics and a few on operational. (Inverting, non-inverting, differential)
I've never made anything with "power".  All I did is read some guide on the internet.

One other thing is how to implement protection circuits for arduino and the raspberry.
For example in HAT specification it is written that it takes in "ZVD" system and I do not even know what it is.

Bye, hitech95.

EDIT: Fixed some mistakes.

[hitech95]

If you're doing an analog audio amp there's many designs on the web how to do it, tone control can be easily done with an op-amp ( google "opamp tone control" ) TL082 datasheet has a simple tone control schematic.
Class D amps are much more efficient but they also have some quirks ( output filtering, output noise, interference, EMI ).
The headphone output can be fed directly from the op-amp tone control.
If you're making your own power supply then don't forget to put big caps and make proper star-ground to further improve sound quality and overall stability.
Also don't forget to do proper air flow in your amp enclosure so that hot air does not pass over any electrolytics to improve their life and keep the ESR low.
Relays are good for switching the output of the amp on and off, for DC it is better to use transistors or FETs since relays have contact bounce and the raspberry might not like it.

Oh an other reply. Sorry for the double post.

Yes, as you'll see from the previous answer, I use a board that is already made.
My problem is how to power the whole.
For the management of the tones I've already written that I will use an IC because I need the remote control. (I have a lazy brother)

Bye, hitech95

EDIT: striped a sentence, it could be interpreted negatively.

[Grapsus]

Hi hitech95,

Do I correctly understand your problem ?
  - You need 5V standby power to keep the RPi running
  - You need a bigger PSU for the audio circuit that could turned on and off by software in the RPi

I think you're right about getting a small ready to use 230 VAC => 5 VDC module for the RPi. You can even take an entire USB charger if it fits in your enclosure.

Regarding the big main PSU, you have several options, but since you're not familiar with power supply design I would advise you against building your own. That would be too dangerous without any gain in the final device. Just take an industrial power supply with the voltages you need and have the RPi to connect and disconnect it from mains with a suitable relay. Some PSUs even have a control signal so you'd only have to do the wiring.

As a super cheap alternative, why don't you use an ATX PC PSU? It already has 5 V standby, 12 V outputs with plenty of power and the main power can be controlled with a logic /PS_ON signal.

[Refrigerator]

If you're doing an analog audio amp there's many designs on the web how to do it, tone control can be easily done with an op-amp ( google "opamp tone control" ) TL082 datasheet has a simple tone control schematic.
Class D amps are much more efficient but they also have some quirks ( output filtering, output noise, interference, EMI ).
The headphone output can be fed directly from the op-amp tone control.
If you're making your own power supply then don't forget to put big caps and make proper star-ground to further improve sound quality and overall stability.
Also don't forget to do proper air flow in your amp enclosure so that hot air does not pass over any electrolytics to improve their life and keep the ESR low.
Relays are good for switching the output of the amp on and off, for DC it is better to use transistors or FETs since relays have contact bounce and the raspberry might not like it.

Oh an other reply.
Yes, as you'll see from the previous answer, I use a board that is already made.
My problem is how to power the whole.
For the management of the tones I've already written that I will use an IC because I need the remote control. (I have a lazy brother)

Bye, hitech95

But plugging ready made modules into a whole, at least to me, sounds like no fun.

[Ian.M]

Your PSU design is borked to start with.  In the EU, the specification for the nominal 230V AC mains supply is +10%, -6%.   If the transformer secondary is a nominal 24V RMS, the peak voltage on the reservoir capacitor can exceed 36V if the mains voltage is at its high limit and the load current is small.  I doubt your 30V max modules will like that much.

[Grapsus]

I think our duty here is to discourage hitech95 from building his own PSU. It's way to dangerous with absolutely no gain. It's too early for someone starting with analog stuff to play around with the primary side of something. Without even talking about fuses, line filtering, inrush current limining, wire gages, PCB tracks width etc.

[hitech95]

Your PSU design is borked to start with.  In the EU, the specification for the nominal 230V AC mains supply is +10%, -6%. If the transformer secondary is a nominal 24V RMS, the peak voltage on the reservoir capacitor can exceed 36V if the mains voltage is at its high limit and the load current is small.  I doubt your 30V max modules will like that much.

Could you be more specific? I would like to learn. The values that you have seen me have been suggested without explaining.
It is for this reason that I decided to write here.

Hi hitech95,

Do I correctly understand your problem ?
  - You need 5V standby power to keep the RPi running
  - You need a bigger PSU for the audio circuit that could turned on and off by software in the RPi

I think you're right about getting a small ready to use 230 VAC => 5 VDC module for the RPi. You can even take an entire USB charger if it fits in your enclosure.

Regarding the big main PSU, you have several options, but since you're not familiar with power supply design I would advise you against building your own. That would be too dangerous without any gain in the final device. Just take an industrial power supply with the voltages you need and have the RPi to connect and disconnect it from mains with a suitable relay. Some PSUs even have a control signal so you'd only have to do the wiring.

As a super cheap alternative, why don't you use an ATX PC PSU? It already has 5 V standby, 12 V outputs with plenty of power and the main power can be controlled with a logic /PS_ON signal.

Yea I need:
5V to supply the arduino/atmega (standby and controls)
5V for the PI
12V to supply the tone IC (with a linear regulator down to 7V)
26V to supply amplifiers

I think our duty here is to discourage hitech95 from building his own PSU. It's way to dangerous with absolutely no gain. It's too early for someone starting with analog stuff to play around with the primary side of something. Without even talking about fuses, line filtering, inrush current limining, wire gages, PCB tracks width etc.

I understand that is not easy to design something like that, but I want to learn.
Unfortunately (in Italy) electronics is disappearing. There are more magazines, shops, specialized websites. Forums people (in italian) do not explain and throw me random numbers.

Bye, hitech95.

[hitech95]

But plugging ready made modules into a whole, at least to me, sounds like no fun.

Unfortunately draw a PCB and put all the SMD components is complicated.
I've already tried, the result was not bad. But my pockets are empty. 5PCB € 140.

What you see here is the only thing I did "seriously" with electronics.

[mariush]

The power supply schematic is a bit weird.  I see there 2 x 10.000 uF + 1000uF which seems like a huge amount. When you plug that power supply into the mains with the capacitors discharged, the capacitors may pull so much power that you'll blow the fuse.
So much capacitance isn't normally necessary, it's often cheaper/easier to just use a transformer with higher output voltage in the first place.

As others mentioned, since the mains voltage can vary so much, the voltage on the secondary side can be a bit higher than the advertised value, by a few volts. Your 230v->24v has a 9.58 ratio, with 240v on the mains you suddenly have 25v AC.

In addition, when a transformer is "idling" ( there's little power pulled from it), most transformers but especially < 50-75VA transformers will again output a much higher voltage, typically 5-10% more... so this will also add a few volts to the output.  If you combine this with high mains voltage you wake up with 26-27v AC on the output of a transformer.

The bridge rectifier converts the AC to DC, and the result is DC with peak voltages up to 1.414 x Vac, minus the losses in the bridge rectifier (2 x voltage drop on one diode)... knowing that we may have up to 26v AC at the output, this means you may have 1.414x26 = 37 volts, minus about 1.5-2v in the bridge rectifier, so about 35v.
Therefore, you have to consider your peak voltages as anything between about 32v and 35v, depending on your mains voltage.

Capacitors come here to smooth out the DC output and make sure the minimum voltage is always above a certain threshold. You can use a formula to approximate how much capacitance you need to keep the voltage above a minimum :  C = current / [ 2 x AC mains frequency x (Vdc peak - Vdc min)]  ...

In your case, since your amplifier needs maximum 26 volts (and for the sake of an example let's say maximum 1.5A current), you can think of using a linear regulator to make sure the amplifier always gets only 26v.  Linear regulators typically need a couple of voltages above the output voltage to work properly, so you need to make sure the linear regulator always has at least 28v to work, so now you can figure out how much capacitance to use ... C = 1.5 A / [2 x 50 Hz x (32v - 28v)] = 1.5 / 400 = 0.00375 Farads or 3750 uF ... any more capacitance will just raise the minimum voltage above 28v, so 4700uF will be safe and more than enough for this particular example. 
A cheap and simple linear regulator that would do this would be LM317 http://www.ti.com/lit/ds/symlink/lm317.pdf ... works with up to 40v DC so it won't mind 28-35v at input, will output 26v at 1.5A, all's good in the world.


As for 5v and 12v for everything else, first of all make sure you don't need positive AND negative voltages for the opamps and tone ic or whatever else your circuit needs.

You may want to use a smaller transformer with two secondary windings to get +12v and -12v, using the same techniques, lm317 and lm337 as linear regulators for +12v and -12v. For 5v, you could use a ready made usb charger or you could use an ebay bought dc-dc buck converter like the ones with xl4015   or LM2576, lm2577, lm2596,  just search these words on ebay and you'll find plenty of ready made boards for a few dollars.
 

[hitech95]

Thanks for the reply.
I'm analyzing, and trying to understand your reasoning.

The power supply schematic is a bit weird.  I see there 2 x 10.000 uF + 1000uF which seems like a huge amount. When you plug that power supply into the mains with the capacitors discharged, the capacitors may pull so much power that you'll blow the fuse.
So much capacitance isn't normally necessary, it's often cheaper/easier to just use a transformer with higher output voltage in the first place.

As others mentioned, since the mains voltage can vary so much, the voltage on the secondary side can be a bit higher than the advertised value, by a few volts. Your 230v->24v has a 9.58 ratio, with 240v on the mains you suddenly have 25v AC.

Ok

In addition, when a transformer is "idling" ( there's little power pulled from it), most transformers but especially < 50-75VA transformers will again output a much higher voltage, typically 5-10% more... so this will also add a few volts to the output.  If you combine this with high mains voltage you wake up with 26-27v AC on the output of a transformer.

Could you be more specific? I don't understand.

The bridge rectifier converts the AC to DC, and the result is DC with peak voltages up to 1.414 x Vac, minus the losses in the bridge rectifier (2 x voltage drop on one diode)... knowing that we may have up to 26v AC at the output, this means you may have 1.414x26 = 37 volts, minus about 1.5-2v in the bridge rectifier, so about 35v.
Therefore, you have to consider your peak voltages as anything between about 32v and 35v, depending on your mains voltage.

Capacitors come here to smooth out the DC output and make sure the minimum voltage is always above a certain threshold. You can use a formula to approximate how much capacitance you need to keep the voltage above a minimum :  C = current / [ 2 x AC mains frequency x (Vdc peak - Vdc min)]  ...

Ok

In your case, since your amplifier needs maximum 26 volts (and for the sake of an example let's say maximum 1.5A current), you can think of using a linear regulator to make sure the amplifier always gets only 26v.  Linear regulators typically need a couple of voltages above the output voltage to work properly, so you need to make sure the linear regulator always has at least 28v to work, so now you can figure out how much capacitance to use ... C = 1.5 A / [2 x 50 Hz x (32v - 28v)] = 1.5 / 400 = 0.00375 Farads or 3750 uF ... any more capacitance will just raise the minimum voltage above 28v, so 4700uF will be safe and more than enough for this particular example. 
A cheap and simple linear regulator that would do this would be LM317 http://www.ti.com/lit/ds/symlink/lm317.pdf ... works with up to 40v DC so it won't mind 28-35v at input, will output 26v at 1.5A, all's good in the world.

I was advised to don't use a stabilized power supply. So as not to shackle the sound.

As for 5v and 12v for everything else, first of all make sure you don't need positive AND negative voltages for the opamps and tone ic or whatever else your circuit needs.

You may want to use a smaller transformer with two secondary windings to get +12v and -12v, using the same techniques, lm317 and lm337 as linear regulators for +12v and -12v. For 5v, you could use a ready made usb charger or you could use an ebay bought dc-dc buck converter like the ones with xl4015   or LM2576, lm2577, lm2596,  just search these words on ebay and you'll find plenty of ready made boards for a few dollars.

I don't I need a dual power supply.
I would find a switching power supply for 12V, then lower them to 7V with a linear regulator. (for the Tone/Input Select IC)
Instead for 5V always thought of from the 12V but those for the raspberry I would filter so that the signal that comes out of the DAC is cleaner.

Thanks , hitech95.

[mariush]

Transformers are designed for a particular output power and voltage. Due to type, construction, magnetics and other factors, the output voltage is sort of guaranteed to be the one on the label only when devices connected to it pull some amount of power, let's say at least 10-20% of the transformer's rated power. When a device pulls less power from the transformer, the output voltage of the transformer may be higher than the one advertised on the label.
The smaller the power rating of the transformer, the higher the "error margin" on the output voltage.

For example, here's the datasheet for a series of transformers produced by Pro Power : http://www.farnell.com/datasheets/1508683.pdf

You have there a chart with two columns, one saying VA rating and one saying Reg%, that reg% column tells you how much can the voltage deviate from the advertised value. 

As you can see there, a very small transformer rated for only 6 VA, for example a 12v AC 6VA one, may output up to 12v + 24%, which is 12x1.24 = 14.88v AC,and that could screw up things if you don't take this into account.
Transformers rated for higher power, like 50VA or 75VA, are typically at less than 10% as you can see in the datasheet, and that makes things easy.

I was advised to don't use a stabilized power supply. So as not to shackle the sound.

If the amplifier at any point uses maximum 26v at 1.4A or something like that, then using a linear regulator capable of up to 1.5A won't "shackle" the sound in any way. There are amplifiers that may pull more current for small periods of time, in which case I agree, a linear regulator may temporarily enter into a "protection" mode for a few milliseconds to prevent damage... but in this case you can use linear regulators capable of handling more current, like 3 or 5A.

Alternatively, you can use transformers rated for less voltage, for example a 18v AC transformer.

[hitech95]

Transformers are designed for a particular output power and voltage. Due to type, construction, magnetics and other factors, the output voltage is sort of guaranteed to be the one on the label only when devices connected to it pull some amount of power, let's say at least 10-20% of the transformer's rated power. When a device pulls less power from the transformer, the output voltage of the transformer may be higher than the one advertised on the label.
The smaller the power rating of the transformer, the higher the "error margin" on the output voltage.

For example, here's the datasheet for a series of transformers produced by Pro Power : http://www.farnell.com/datasheets/1508683.pdf

You have there a chart with two columns, one saying VA rating and one saying Reg%, that reg% column tells you how much can the voltage deviate from the advertised value. 

As you can see there, a very small transformer rated for only 6 VA, for example a 12v AC 6VA one, may output up to 12v + 24%, which is 12x1.24 = 14.88v AC,and that could screw up things if you don't take this into account.
Transformers rated for higher power, like 50VA or 75VA, are typically at less than 10% as you can see in the datasheet, and that makes things easy.

I was advised to don't use a stabilized power supply. So as not to shackle the sound.

If the amplifier at any point uses maximum 26v at 1.4A or something like that, then using a linear regulator capable of up to 1.5A won't "shackle" the sound in any way. There are amplifiers that may pull more current for small periods of time, in which case I agree, a linear regulator may temporarily enter into a "protection" mode for a few milliseconds to prevent damage... but in this case you can use linear regulators capable of handling more current, like 3 or 5A.

Alternatively, you can use transformers rated for less voltage, for example a 18v AC transformer.

The card is made to work from 12V up to 30V. (It should not exceed 30V DC). For this I chose a voltage of 26V.
According to the datasheet the chip supports a maximum current of 9A, but typical of 6A. I wanted to limit the maximum current to 4A.

I have seen some people use my same transformer to power a similar amplifier. I would like to understand why they did not do all of your considerations.

Bye, hitech95

[Zero999]

As said above, a 24VAC transformer is not suitable for powering an amplifier card with a maximum input voltage of 30VDC.

AC voltages from transformers are specified in RMS voltages. A 24V transformer has a peak voltage of 24*root(2) =34V which is what you get on the filter capacitor, minus the rectifier losses and ripple. As explained above, under light loads, the voltage will be even higher, as transformers are specified under full load conditions, then the mains voltage could also be on the higher end of normal. 

[hitech95]

As said above, a 24VAC transformer is not suitable for powering an amplifier card with a maximum input voltage of 30VDC.

AC voltages from transformers are specified in RMS voltages. A 24V transformer has a peak voltage of 24*root(2) =34V which is what you get on the filter capacitor, minus the rectifier losses and ripple. As explained above, under light loads, the voltage will be even higher, as transformers are specified under full load conditions, then the mains voltage could also be on the higher end of normal.

I have understood, what I do not understand is why they do not have anything fried.

Bye, hitech95.

[rsjsouza]

I have seen some people use my same transformer to power a similar amplifier.

If you are absolutely confident the transformer and the output power amplifier board are identical, it is possible that:
- they are using a voltage regulator to trim the power supply output to the specified value (up to 30V);
- they are relying on the device's specifications and not the board's specifications.

I have understood, what I do not understand is why they do not have anything fried.

The power amplifier (PA) datasheet mentions it can support up to 36V in continuous mode (Table 6, V_CC row), therefore the main device may be working just fine despite the board's specifications. If you asked me, I wouldn't recommend doing this as the PA board may not provision the correct heat dissipation when operating at the 36V voltage level. This will reduce the lifespan of the device.

Therefore, as others have said, if you want to use the PA board's specifications you must either use a voltage regulator or change the transformer.

By the way, mariush's calculations about the capacitor are off. Probably he missed that each PA board can consume up to 5A, which would require at least 12500uF per power supply. (everything else is correct, though)

Instead, if you go along with putting out 35V, also keep in mind the output current each PA will consume. The device datasheet mentions that, in Bridge-tied-load (BTL), it can output up to 160W when V_CC is 35V.

When talking about power, whatever comes out in the loudspeaker must be sourced by the power supply. Also, there are inneficiencies on the circuit (heat, etc) that the power supply must source as well. We don't know the efficiency of the PA board, but given the device is a class D, I would suspect it is high (above 70%, which means that up to 30% is consumed as heat, noise, etc.). In maximum output power and using the worst case scenario (70%), your power supply must source at least:

P_supply = P_out / (^%efficiency / ₁₀₀) = ¹⁶⁰ / _0,7 = 228W
I_supply = P_supply / V_supply = ²²⁸ / ₃₅ = 6,5A

This will require redesigning the power supply and using a different transformer which is not what you probably want...

[hitech95]

I have seen some people use my same transformer to power a similar amplifier.

If you are absolutely confident the transformer and the output power amplifier board are identical, it is possible that:
- they are using a voltage regulator to trim the power supply output to the specified value (up to 30V);
- they are relying on the device's specifications and not the board's specifications.

I have understood, what I do not understand is why they do not have anything fried.

The power amplifier (PA) datasheet mentions it can support up to 36V in continuous mode (Table 6, V_CC row), therefore the main device may be working just fine despite the board's specifications. If you asked me, I wouldn't recommend doing this as the PA board may not provision the correct heat dissipation when operating at the 36V voltage level. This will reduce the lifespan of the device.

Therefore, as others have said, if you want to use the PA board's specifications you must either use a voltage regulator or change the transformer.

By the way, mariush's calculations about the capacitor are off. Probably he missed that each PA board can consume up to 5A, which would require at least 12500uF per power supply. (everything else is correct, though)

Instead, if you go along with putting out 35V, also keep in mind the output current each PA will consume. The device datasheet mentions that, in Bridge-tied-load (BTL), it can output up to 160W when V_CC is 35V.

When talking about power, whatever comes out in the loudspeaker must be sourced by the power supply. Also, there are inneficiencies on the circuit (heat, etc) that the power supply must source as well. We don't know the efficiency of the PA board, but given the device is a class D, I would suspect it is high (above 70%, which means that up to 30% is consumed as heat, noise, etc.). In maximum output power and using the worst case scenario (70%), your power supply must source at least:

P_supply = P_out / (^%efficiency / ₁₀₀) = ¹⁶⁰ / _0,7 = 228W
I_supply = P_supply / V_supply = ²²⁸ / ₃₅ = 6,5A

This will require redesigning the power supply and using a different transformer which is not what you probably want...

I am writing here just to learn and to understand.

What I do is what you suggest me to do. The only thing I "worry" is having to put a linear regulator. I found none of >5A for the voltage that I need.
The boards that they use is based the same of mine but mine is mono:
.
This is fed with a 300VA 20V, that according to the calculations previously made are too many: [20 + (20 * 0.20)] * sqrt (2) = 33.94
And 4 cap 10000 uF 50V.
I start to think that they are crazy ...

Bye, hitech95.

[Ian.M]

Looking at the datasheet for the STA516B chip your supplier claims is on the modules, http://hifimediy.com/amplifiers/diy-amplifiers/T3-mono, S.T. recommend operation from a 50V rail.   The module derates that to 48V.   A good quality 240V primary 30V secondary transformer will give about 44V max on the reservoir cap.  If you are using a 220V primary transformer you need a 28V one.   That gives you an adequate margin for high mains conditions.     If your preamp  and other modules have a 30V max rating, use a linear regulator to feed them as their current consumption will be much lower.   A low current negative rail can be provided from a capacitively coupled bridge rectifier.  Make sure that all linear regulators have a high enough input voltage rating and are adequately heatsinked.

[hitech95]

Looking at the datasheet for the STA516B chip your supplier claims is on the modules, http://hifimediy.com/amplifiers/diy-amplifiers/T3-mono, S.T. recommend operation from a 50V rail.   The module derates that to 48V.   A good quality 240V primary 30V secondary transformer will give about 44V max on the reservoir cap.  If you are using a 220V primary transformer you need a 28V one.   That gives you an adequate margin for high mains conditions.     If your preamp  and other modules have a 30V max rating, use a linear regulator to feed them as their current consumption will be much lower.   A low current negative rail can be provided from a capacitively coupled bridge rectifier.  Make sure that all linear regulators have a high enough input voltage rating and are adequately heatsinked.

Yes but mine has a sta508 not a STA516B, I have the old version.

Bye, hitech95.

[Ian.M]

In that case, you need a lower voltage transformer or a commercial DC output regulated PSU module.  If your design cant withstand 230V +10% (253V) AC input, it isn't fit for use in the EU.

[hitech95]

In that case, you need a lower voltage transformer or a commercial DC output regulated PSU module.  If your design cant withstand 230V +10% (253V) AC input, it isn't fit for use in the EU.

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...

[rsjsouza]

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.