Optimal Toroid for multi channel power amplifier

Thread Starter

kwikas

Joined Jul 29, 2018
16
Hello All,

I have signed up to this forum after spending some time lurking. I certainly feel I have come to the right place for assistance.

I want to build a 6 channel power amplifier for my home cinema. I have the amplifier modules, chassis/case and heat sinks etc as well as a toroid. Here are the modules I am using (and I hope the link works):

https://www.ebay.com.au/itm/L15-MOSFET-Amplifier-Board-2-Channel-AMP-IRFP240-IRFP9240-Angle-Aluminum/192138675527?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

The toroid I have is 625kVA with 2 x 35Vac.

My question is whether this toroid is going to be suitable for use with multiple amp boards. I have googled extensively (and I have used the search function for this site), but can't really seem to find a suitable answer. So, I am unsure whether a toroid with a single secondary is considered workable. I notice that some amp builders recommend using a toroid with multiple secondaries as the only way to go for multi channel amps.

I have a bunch of other questions related to the power supply design for my amp but I think I should seek an answer to this question first before going further.

Many thanks
 

ericgibbs

Joined Jan 29, 2010
8,733
hi kwikas,
Welcome to AAC.
Looking at your link, the power supply required is +/-55V and your transformer secondary is 2 * 35Vac
E

L15 MOSFETAmplifier Board 2 Channel AMP IRFP240 IRFP9240 + Angle Aluminum


Parameters:
Frequency response range: 5 HZ - 3 db, 250 k HZ - 3 db
Power: 150 w r, 4 r 300 w, 600 w 2 r. (+ - 55 v power supply)
The SR > 20 v/US
THD < 0.02% 150 w 8 r.
SNR > 97 db
VOLTAGE GAIN = 36 times
PCB size : long= 150 MM , wide = 40 MM
 

AlbertHall

Joined Jun 4, 2014
8,358
I am confused with the transformer power rating - 625kVA. That would be an enormous transformer and must be a misprint.
The obvious would be to eliminate the 'k', making it 625VA but that wouldn't supply 6 channels at 150W.
 

Thread Starter

kwikas

Joined Jul 29, 2018
16
Hi Albert,

Yes, sorry 625VA (don't know why I hit the 'k' button) and from what you and Eric have just said, the toroid i have wont do the job in any event.

Time for me to look for something more suitable. And that brings me back to my original question I guess...
 

bertus

Joined Apr 5, 2008
20,051
Hello,

Reading the specs, the amplifier can supply the following powers:
150 Watts @ 8 Ω
300 Watts @ 4 Ω
600 Watts @ 2 Ω

What is the impedance of the speakers to be used?

Bertus
 

bertus

Joined Apr 5, 2008
20,051
Hello,

So 6 times 150 Watts, that is 900 Watts.
To have some spare power, use a 1200 Watts transformer.
(you can also use 2 transformers given, each for 3 channels).

Bertus
 

ericgibbs

Joined Jan 29, 2010
8,733
hi,
So you are using 6 channels at a nominal 150Watts, requiring a +/-55Vdc supply.?
E
 

Thread Starter

kwikas

Joined Jul 29, 2018
16
Thanks Bertus.
I could use 2 transformers (1 each for 3 channels) - no reason why not. I do have 2 of these trannies but as Eric has pointed out they don't appear to be suitable for my amp boards unfortunately.

Hi Eric,
Yes that is correct. 6 channels at a nominal 150Watts requiring a +/-55Vdc supply. What are your thoughts here?
 

ericgibbs

Joined Jan 29, 2010
8,733
hi,
As the Spec does not state 150Watts RMS and it is from China, I would say thats it is a peak power rating is 150Watts, so the power supply requirement could be less.
E
 

Thread Starter

kwikas

Joined Jul 29, 2018
16
So maybe I can use 1 transformer for 3 amplifier boards...tks - Andrew
 

ericgibbs

Joined Jan 29, 2010
8,733
hi,
That PSU link states Using original 25A bridge rectifiers, which suggests the rectifier is on the PCB.??
It could be that vertical FWB at the end of the PCB.?
You say 2 * 35Vac are you planning trying rectify to peak DC on the cap PCB. ie 35v * 1.414 ie ~ 47Vdc .??

E

EDIT:

This data link is a guide to audio power specifications.
http://www.rocketroberts.com/techart/powerart_a.htm
 
Last edited:

Thread Starter

kwikas

Joined Jul 29, 2018
16
Yes Eric......peak 47Vdc.

Thanks for the link. I will have a good read of it.

Andrew
 

ericgibbs

Joined Jan 29, 2010
8,733
hi,
Is the 2 * 35V secondary a centre tap or two isolated windings.?

The 47Vdc peak will sag/drop under load during high audio output periods.

E
 

Thread Starter

kwikas

Joined Jul 29, 2018
16
Thanks and that's good to know re sag/drop. I am really beginning to think I will need to get toroid(s) that are better suited to this purpose.

Centre tap or two isolated windings? I will have to go and find out as I'm not sure.

Andrew
 

ericgibbs

Joined Jan 29, 2010
8,733
hi,
As you are trying to generate a +47Vdc and a -47Vdc from the same transformer, where the + and - share the same 0V its important we know the exact connections.
Also how are the terminals marked on the power/rectifier PCB that you have on the bench post #13.?

E
 

Thread Starter

kwikas

Joined Jul 29, 2018
16
I will have to get the PCB out of the box and have a look. It's currently stored away but I'll come back to you on this soon...likewise as regards the centre tap/windings question. Meantime, thanks for all the help you're giving me....
 

Thread Starter

kwikas

Joined Jul 29, 2018
16
I have an answer as regards the toroid....it's a standard 240V primary.

The devices are supplied with two separate secondary windings.

The device can be configured as per diagram attached.

· two separate windings

· paralleled windings

· centre tapped version

upload_2018-7-31_21-3-22.png

PCB answer shortly........
 
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