Chip amp power supply- a beginners guide

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A

AndrewT

R.I.P.
Joined 2004
Yes the CT current is not zero. That is because the +ve currents are not exactly equal to the -ve currents. But more importantly the +ve current flows at a different TIME from the -ve current.

When you set up your simulation the model did not know that the currents could be different and did not know that the currents would flow at different times.

The model gave the wrong answer because you asked the wrong question.

That is very important when simulating with a model.
The model is your "question", the answer is the prediction given out by the simulator.
A CT current of Zero is the wrong answer. Can you now see why I asked you to change the load so that the model could show a non zero CT current?
 
N

NaveenPunnana

Member
Joined 2014
AndrewT said:
Yes the CT current is not zero. That is because the +ve currents are not exactly equal to the -ve currents. But more importantly the +ve current flows at a different TIME from the -ve current.

When you set up your simulation the model did not know that the currents could be different and did not know that the currents would flow at different times.

The model gave the wrong answer because you asked the wrong question.

That is very important when simulating with a model.
The model is your "question", the answer is the prediction given out by the simulator.
A CT current of Zero is the wrong answer. Can you now see why I asked you to change the load so that the model could show a non zero CT current?
Click to expand...

Yes... Thanks I got you.
 
A

AndrewT

R.I.P.
Joined 2004
30W or 30VA is too low for a competent Power Amplifier.
Some will use 80VA and upwards. I recommend 160VA and upwards.
The DC output voltage of the PSU is very roughly 1.5times the secondary AC voltage.

A dual or centre tapped secondary that is 20Vac will give ~30Vdc at the supply pins.
20Vac > ~30V
30Vac > ~45V
40Vac > ~60V.
50Vac > ~75Vac
Not many chipamps can manage with supplies above 70V.
The 3886 has an absolute max of 84V when a signal is present.
26+26Vac to 27+27Vac is roughly the absolute max secondary voltage that you could feed into a 3886 & 4780.
 
ranhaber

ranhaber

Member
Joined 2013
AndrewT said:
30W or 30VA is too low for a competent Power Amplifier.
Some will use 80VA and upwards. I recommend 160VA and upwards.
The DC output voltage of the PSU is very roughly 1.5times the secondary AC voltage.

A dual or centre tapped secondary that is 20Vac will give ~30Vdc at the supply pins.
20Vac > ~30V
30Vac > ~45V
40Vac > ~60V.
50Vac > ~75Vac
Not many chipamps can manage with supplies above 70V.
The 3886 has an absolute max of 84V when a signal is present.
26+26Vac to 27+27Vac is roughly the absolute max secondary voltage that you could feed into a 3886 & 4780.
Click to expand...

I forgot to mention that it's for LM1875 amp.
Does that change you answer?
 
A

AndrewT

R.I.P.
Joined 2004
Check the datasheet.
The absolute maximum supply voltage will be in there.
YOU must select a transformer that for worst case conditions NEVER exceeds the abs max V.

How much does your electricity supplier vary your mains voltage?

Here in the UK we have a nominal 240Vac supply, but they call it 230Vac and the maximum is 253Vac. That makes a BIG difference to the worst case supply voltage.
 
ranhaber

ranhaber

Member
Joined 2013
AndrewT said:
Check the datasheet.
The absolute maximum supply voltage will be in there.
YOU must select a transformer that for worst case conditions NEVER exceeds the abs max V.

How much does your electricity supplier vary your mains voltage?

Here in the UK we have a nominal 240Vac supply, but they call it 230Vac and the maximum is 253Vac. That makes a BIG difference to the worst case supply voltage.
Click to expand...

The LM1875 spec say the max voltage is 60V.
If I wish do a better design I could use transformer with 24V output and a 18v regulator.
Still my question remain, will it work with the LM1875? :D
 
mravlca

mravlca

Member
Joined 2009
ranhaber said:
This is a newbie question.
Can I use only this transformer without the PT and PSU ? (one for each channel)
VTX-214-030-118 - VIGORTRONIX - PCB Mount Power Supply, Fixed, 90 V, 265 V, 30 W, 18 V, 1.666 A | Farnell element14

I just have some at my work (even 12V and 15V)
Click to expand...

Hi ranhaber,

yes, you can make it work, but there are some limits. You'll need two of these PSUs to create symmetrical power supply (+ / 0 / -), I doubt that you are running them from a single PSU. +-18V won't give you as much power as recommended voltage in datasheet. In short, you won't be able to throw a party with it, but it will play loud enough in the office.

Best Regards,
Aleš
 
B

bwolf

Member
Joined 2015
powering my amp board suggestions

Hello All
Im new here. Im doing my first diy project.

purchased
Sure Electronics AA-AB32231 2x8W at 4 Ohm TPA3110 Class-D Audio Amplifier Board

I want to power this with 16v 2amp with step down transformer <=30V
Give me Circuit Diagram. components needed.

or any other way to power my amp board with good stable 16V or greater @ 2A Current ?

Thank You very much :)
 
L

leRooie

Member
Joined 2015
Hi all!

Also a newbie I'm afraid, and working on my first chipamp. I've build a couple of mic pre's in the past though (Soundskulptor, so quite easy with all the instructions).

So I've been wondering how to go about my PSU in my 1875 amp. I've ordered a pcb set from chipamp.com (2x 1875 amp + 1 psu) and I'm planning to build a simple amp mainly for my record player. This means I'll need a phono amp stage as well. This is where I've got a question about. I'd really like to build the phono stage and 1875 amp in the same case, but I'm trying to figure out how to go about the psu for both. Can I use 1 toroid for the two or is it better to split these? Is there any way the phono stage can share the same rectifier bridge with the amps or is that a bad idea?

I've been looking at various phono pcb's, like the Muffsy and the Very Simple Phono Stage. Both run on different V's. The rectifier bridge that comes with the 1875 output's 25v, when connected to an 18v secondary. However, the Muffsy needs 15v. Is there anyway to match these? One can also order a psu with the Muffsy, which runs on a simple AC adapter 15-18v's. In that case it might be possible to run both psu's on the same toroid outputting 18v's on it's secondaries?

Thanks for any advice, I'm kinda in the dark here, just short on knowledge I guess.

Regards,
Sietse
 
A

AndrewT

R.I.P.
Joined 2004
Use the AC from the main transformer. Rectify that and then smooth and regulate down to ~±15Vdc.

Alternatively, you can tap into the main DC supply rails and regulate down from there. But this puts more supply rail modulation onto the regulators and makes them work harder. You could use a JLH hum buster or a capacitance multiplier between the DC supplies and the regulator to help attenuate the ripple.

By using the same AC windings, you must share a common voltage reference for Main Audio Ground. Do not pass any large, or variable, current through any of the voltage reference wires that link to the voltage reference.

read Decibel Dungeon and the Forum:
Audio Component Grounding and Interconnection - diyAudio
 
L

leRooie

Member
Joined 2015
Thanks Andrew for the quick reply.

AndrewT said:
Use the AC from the main transformer. Rectify that and then smooth and regulate down to ~±15Vdc.
Click to expand...

This seems like the best option to me. If I understand correctly, you'd have to connect (I guess just parallel) 2 rectifier bridges: one that rectifies and smooths the 18vac to 25dc rails for the chipamp (the psu board thats already in the kit) and another separate one to get it down to 15dc for the phono amp.

Any advise on kits or simple circuits that I could look at to do this? I'm reading through the Decibel Dungeon and this forum as much as I can to learn more about this, but your advice is more than welcome ;)
 
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