Hi all, I've got spare time off work, so I've built up a few JHL1969
I've looked at a previous thread on here that was done back in 2017. The discussion on the power supply regarding the correct voltage/wattage that would be safe to use. It went over my head, and was a higher voltage supply.
So the amp I bought only needed soldering up and I thought I'd be good to go. I didn't realise that I would need a specialist power supply, the kind I don't have, and a 3 pin audio in cable/plug.
I'm now looking to use a 3.5mm jack plug with 3 lose ends. I've also ordered a 15-0-15, 50va, 240v Toroidal transformer. along with similar 50va 230v 2x15v Toroidal mains transformer. In my rush to buy a transformer I didn't full read the ebay listing on the first unit, it states that is new but old Maplin's stock and the 2nd voltage only appears to be 7v off load.
With the amp board having the capacitors already on, does this mean I don't need to worry about supply any to added. I'm a total newbie with this.
If anyone has any simple links for the working out if I need to add any extra components to the supply before trying it out, that would be a big help.

 

It is not clear what you are trying to do. Let's get down to specifics.
What are the current and voltage requirements of your board?
What is it that you are trying to do with the transformer?

We cannot read the label properly because of the glare.

A search on RS site for 91236-P2S2 brings up RS Part No. 257-4890, 2 x 9VAC 15VA
The datasheet is confusing.
RS part number 257-4890 is shown as Nuvotem 91223-P2S2 on the datasheet.

 

Toroidal transformers are usually the easiest to modify, i.e. add or subtract windings, keep in mind that you will have 1.4x the voltage after rectification & smoothing..

 

Ok, so my plan is to build the power supply with the 15-0-15 transformer to power the amp. With the requirements advised on the board being 12-0-12, I've gone slightly higher to compensate for any voltage drop. I didn't get any info regarding the power required other than what's printed on board.
So I was wondering if I pretty much make a mains input to the transformer, then connect the other leads into the power input on the board. With the capacitors on the board dealing with the voltage ripple effect, and any other unwanted effects from the voltage/power supply.

 

Your board requires 24VAC centre-tap transformer. That is why it is written as AC 12-0-12 on the board.
The board has rectifiers and reservoir capacitors on board to convert AC to DC.

The board may have some voltage tolerance but we don't know what is the maximum voltage that it can accept.
15VAC is going to give about ±20VDC and probably some more. Transformer manufacturers have already designed in losses so you are likely going to go beyond ±25VDC.

Can you post a link to where you purchased the amplifier?
Or tell us the part number of the amplifier ICs and we can look up the maximum supply voltages.

What you need to pay attention to is how to wire the toroidal transformer for 240VAC input and how to connect the secondaries for centre-tap configuration. It is critical that you get the phase right.

 

Hi Mr chips.
Does this help-
Description:


PCB Size: 121mm * 108mm * 35mm

Job Type: Single-ended Class A

Operating voltage: AC 12V-0V-12V

Frequency characteristics:

12Hz~50KHz(+0dB,-1dB)
12Hz~120KHz(+0dB,-3dB)

Voltage gain: 21dB

SNR:> 101dB

Conversion rate:> 35V / μS

Quiescent Current: 240mA



Note：


Diy kit：all parts need buyer to solder

 

Ok. I see now that the board uses +12V and -12V three-terminal voltage regulators rated at 1A.
The 15-0-15 transformer will be fine. Expect the regulators to run hot.

What is the capacitance and voltage rating on the large black capacitors right next to the power input connector?

 

Glad to hear the 15-0-15 was ok to use. Wasn't sure so also ordered an 18-0-18. That will be for a more powerful board if I ever get one, thank you for the help Mr Chips, Capacitors are- 25v 2200uf.

 

Just to make sure I'm giving the correct info.

 

Hi,

Let's see the heatsinks on the 12v, 1 amp voltage regulators. That's important too.

 

I see 2200μF/25V on the capacitors farthest away from the power input connector.
We need the values on the capacitors closest to the connector.

As I said, 15VAC input could very well end up with 25VDC. You will be pushing a 25V capacitor to its limit.
A 18VAC transformer will definitely go over the limit.

 

Hi,

Let's see the heatsinks on the 12v, 1 amp voltage regulators. That's important too.

They are shown in the first post.

 

They look ok. Fingers crossed they work ok, just have to keep an eye on the temps.

 

All the capacitors are the same value 25v 2200uf

 

Is there any information books, PDFs you guys can advise me of. I'm working my way through, The art of electronics. And a practical introduction to electronic circuits. It's not easy reading and I'm got getting the info I'm looking for skimming through the books, for toroidal transformers.

 

From the pic shown of the toroid's, if they are dual winding (4 ends) instead of center tap, (3 leads) then it may be easy to remove a few turns off each, as often they are wound bifilar, if so, that means that all four ends come out and each winding ends up on the outside of the toroid,
This type of Tfmr is ~ 2 turns/volt.

 

They look ok. Fingers crossed they work ok, just have to keep an eye on the temps.

Hi,

To me the heat sinks look a little small. That means they wont work well if there is a large input to output differential.
If the input is 15v and the output 12v and the current 1 amp, the power dissipation is 3 watts. They might take that.
If the input is 18v and the output 12v and the current 1 amp, the power dissipation is 6 watts. Not sure they are big enough for that.
So the input to output voltage and the max current is the key to figuring out if the heatsinks are big enough. If you can get data on the heatsinks we can calculate the temperature rise. I wouldn't want the temperature to rise too much more than 60 degrees C.
You can look around the web to find a heatsink that is similar to the ones you have. We would want to know the power handling capability of the heatsink in degrees per watt.

There are other issues that come up though. The ripple dips cannot go too low, and that means significant capacitor filtering, yet that also means higher average DC voltage which means higher average power dissipation in the regulators. Thus the transformer secondary voltage and filter capacitors influence the total power dissipation at full load.
The peak DC voltage is about 1.4 times the RMS voltage of the secondary, plus a little more perhaps depending on how the transformer is wound. If there is very significant filter capacitance the average DC voltage could be close to the peak value. The peak value for a 15vrms wave is about 19.5 volts after we subtract a little for the diode drops.

 

Hi,

To me the heat sinks look a little small. That means they wont work well if there is a large input to output differential.
If the input is 15v and the output 12v and the current 1 amp, the power dissipation is 3 watts. They might take that.
If the input is 18v and the output 12v and the current 1 amp, the power dissipation is 6 watts. Not sure they are big enough for that.
So the input to output voltage and the max current is the key to figuring out if the heatsinks are big enough. If you can get data on the heatsinks we can calculate the temperature rise. I wouldn't want the temperature to rise too much more than 60 degrees C.
You can look around the web to find a heatsink that is similar to the ones you have. We would want to know the power handling capability of the heatsink in degrees per watt.

There are other issues that come up though. The ripple dips cannot go too low, and that means significant capacitor filtering, yet that also means higher average DC voltage which means higher average power dissipation in the regulators. Thus the transformer secondary voltage and filter capacitors influence the total power dissipation at full load.
The peak DC voltage is about 1.4 times the RMS voltage of the secondary, plus a little more perhaps depending on how the transformer is wound. If there is very significant filter capacitance the average DC voltage could be close to the peak value. The peak value for a 15vrms wave is about 19.5 volts after we subtract a little for the diode drops.

I was looking at slightly bigger copper heat sinks, but they do not have the same form factor as the ones on the board. I would have needed to stick them to backs with thermal adhesive pads. I've done something similar on my old GTX1080ti, playing star citizen and DCS really heats the old boy up.
I'll research the heat sinks. Thanks for the info MrAI.

 

I was looking at slightly bigger copper heat sinks, but they do not have the same form factor as the ones on the board. I would have needed to stick them to backs with thermal adhesive pads. I've done something similar on my old GTX1080ti, playing star citizen and DCS really heats the old boy up.
I'll research the heat sinks. Thanks for the info MrAI.

Hello again,

If it is not a problem, you can introduce one or more fans. Forced air cooling works a lot better than convection cooling. That may make this possible if they get too hot.

 

So all my items have arrived. I've used the 15-0-15 transformers, I don't have anything plugged into mains yet, still waiting on my bulb holder to arrive so I can test it using this first.
So I've got this as both red wires are the 230v inputs, leaving 4 secondary wires, the two in the centre, blue, black get joined up for the 0v, leaving the outer black as the 15v, the other outer blue as 15v (15-0-15) so the bit I'm unsure of is I'm left with the two 230v inputs and the three cables on the mains rocker switch. I know the red cable on the rocker is the power lead, am I right in thinking I can't plug the two red cables in to the mains rocker, as it's normally red power, blue accessories, yellow ground-open.
Do I need another type of mains socket?
Or is the left side red being 0v in this configuration used as the accessories input, the right as the 230v power lead....