Help with Class D amp measurements and XLR input wiring

[isophase]

Hello Group DIY,

Actually building a 16 channel class D amplifier (with FX Audio D amp cards) and switching power supply.

50 Watt/4 ohms per channel.
Power supply requirements is 10 to 26 VDC - 3 Ampere per stereo card.

I’m using a mean well 750Watt 24VDC capable of 31.3 Ampere.

How can i measure the total power consumption? Is it possible with resistive loads on each output ?
There is a volume pot on each card and I would like determine a « maximum volume position » for each cards in order to stay within reasonable range of power supply capacity.
How can I do that?

Also, the card inputs are unbalanced three pins connectors > Left/Right and common ground for both channels. i’m intending to use XLR input connectors on the unit and the sources will come from Yamaha RIO3224 stage box. The manual doesn’t specify what type of balanced output, only says “balanced output”.

Should I short pins 3 of XLR input connectors to chassis ?
Or should I NOT short pins 3 to chassis?

Thank you in advance for your help

 

[JohnRoberts]

Hello Group DIY,

Actually building a 16 channel class D amplifier (with FX Audio D amp cards) and switching power supply.

50 Watt/4 ohms per channel.
Power supply requirements is 10 to 26 VDC - 3 Ampere per stereo card.

I’m using a mean well 750Watt 24VDC capable of 31.3 Ampere.

How can i measure the total power consumption? Is it possible with resistive loads on each output ?

An ammeter in series with +24V. Alternately a small resistor (like 0.1 ohm and a voltmeter could impute current.

There is a volume pot on each card and I would like determine a « maximum volume position » for each cards in order to stay within reasonable range of power supply capacity.
How can I do that?

you can't, volume pots alter the voltage gain but power is a function of load impedance and input voltage.

Also, the card inputs are unbalanced three pins connectors > Left/Right and common ground for both channels. i’m intending to use XLR input connectors on the unit and the sources will come from Yamaha RIO3224 stage box. The manual doesn’t specify what type of balanced output, only says “balanced output”.

Should I short pins 3 of XLR input connectors to chassis ?
Or should I NOT short pins 3 to chassis?

ideally a differential or balanced input circuit could combine both the + and - signals and reject ground potential issues.

Thank you in advance for your help

good luck...

JR

 

[isophase]

Thank you John for your help,

you can't, volume pots alter the voltage gain but power is a function of load impedance and input voltage.

Is this specific to class D amplifiers with single rail power supply ?
Sorry in advance for very basic question, and I believe you! However, I’m thinking (and so most probably wrong!) that depending on the average level of the program material and the volume pot set to the middle, sure enough, the speaker or transducer would not be as exited as with the pot set to fully CW. And so the consumption should be less ?

Also, the (very basic) description for this amplifier card only mention “50 Watt/4 Ohms” is it 50 Watt RMS?

Concerning the unbalanced input wiring, I tested the cards feeding from the balanced output of my sound card, and I wired both pin 3 from left and right XLR connectors together and connected to ground on the card. Pin 1 is left unconnected at the moment, I will connect them to chassis when I finish the metalwork. is it better to short pin 3 to pin 1/chassis or not?
Knowing that all inputs would be coming off of the same unit (RIO3224 stage box)
I know this is not ideal and a proper balanced input would be better…

Thank you again for your help !

 

[ccaudle]

Is this specific to class D amplifiers with single rail power supply ?

No, that is a basic feature of amplifiers used with speakers. Speakers are complex impedance. The mathematical details are not important at the moment, but in this context that means that the current drawn by a speaker depends on the frequencies being reproduced, and even more so if it is a multi-way speaker with crossover (as opposed for example to using line level crossovers and one amp channel per driver).
You can get in the ballpark if you know the details about the impedance of the speaker you will be using. You have a little bit of margin already, you said the amp cards are rated at 24A total and you have a 31A power supply.

Should I short pins 3 of XLR input connectors to chassis ?

Not without verifying what type of output circuit the Yamaha stage box has. The safest would be to just use pin 2, or build a differential receiver like John suggested.
You did not link the model of amp card you bought, but it looks like the rest of FX Audio devices are consumer focused, not pro, so you will probably have to attenuate the input to match normal consumer line level anyway.

the (very basic) description for this amplifier card only mention “50 Watt/4 Ohms” is it 50 Watt RMS?

That would be the typical way to rate an amplifier. Post a link, maybe there are some details mentioned that you did no recognize (like reference to a particular industry specification for test conditions).

I wired both pin 3 from left and right XLR connectors together and connected to ground on the card

You need to know the type of output circuitry to know whether that is safe to do or not. If the output circuit just has an op-amp driving pin 3, then you just shorted the op-amp output to ground.
If the output circuit has an old-style cross-coupled output, like the SSM and TI devices, then there is a possibility of oscillation if the cold output is connected to the receiver input ground rather than to ground directly at the output.
Newer ThatCorp output drivers do not have that problem.

is it better to short pin 3 to pin 1/chassis or not?

Since you have to attenuate the input anyway, I would recommend do not short pin 3 to chassis, that should get you 6dB attenuation right away, and then you do not have to worry about what type of output circuit you have.

Are these the modules you are using?
D-Amp module at audiophonics.fr

That is very sparse information. Did the vendor provide any more detailed connection diagrams in the packaging? That particular page is absolutely useless for determining anything about the module.

 

[isophase]

Thanks a lot for your help.

The link you posted is exactly the amplifier cards I am using. Unfortunately, no more details or information comes with these pcbs. All info is on the link you provided. Very basic indeed.
You can see on the photos of the PCB there is another 3 pin connector with mute/ground and “SD”, I’m thinking this is suppose to connect to an toggle switch to provide a mute function to prevent “plocking” the speakers on power on. But what the hell does “SD” stands for? “Super distortion”? “Signal disintegration” ? I would like to know…

BTW, this amplifier is intended to be used exclusively with 4 ohms exiters/transducers, it is for an artist with plastic arts background I’m helping out for a special project.

Not without verifying what type of output circuit the Yamaha stage box has.

Yes, I cannot find this information from the Yamaha RIO manual. Also I suppose the analog outputs must be differential balanced?

Since you have to attenuate the input anyway, I would recommend do not short pin 3 to chassis, that should get you 6dB attenuation right away, and then you do not have to worry about what type of output circuit you have.

That’s what I’m thinking.
Thank you!

There isn’t very much space left inside the chassis for adding balancing cards for the inputs. A perfect solution would be to use small Neutrik audio transformers on all XLR inputs that would provide a balanced input with the added benefit of also providing galvanic isolation in case noise would be an issue. I think there is a 10:1 version that would also provide adequate attention to “consumer level”. That would be perfect and I would love to transformer balance all the inputs, but that comes at a cost (do you know an artist with money?)
Let’s see if noise will be an issue or not when the unit will be tested in real conditions…

Again thank you for the help!

 

[ccaudle]

there is another 3 pin connector with mute/ground and “SD”

Perhaps "signal detect" so you mute or power down when there is no signal present.

Also I suppose the analog outputs must be differential balanced?

I think highly likely that the Yamaha has symmetric outputs, the maximum output is 24 dBu which is over 12V RMS, or over 17V peak. Being able to drive that level from pin 2 only would be unusual in modern designs which usually power the buffers from bipolar 12V to 15V supplies.

Let’s see if noise will be an issue or not when the unit will be tested in real conditions…

How far away will the amplifier chassis be from the Yamaha interface? If both are powered from the same or nearby outlets with short cables it will likely be OK. The Dante interface is inherently isolated by the Ethernet transformer, so locating the interface remote from the Dante source and closer to the amplifier would be the ideal from a noise concern.

 

[isophase]

The amplifier would sit right next to the RIO stage box and connected with x2 “short” XLR octopair cables.
Fingers crossed about any noise issue.
And thanks a lot for your help!

 

[isophase]

I forgot to ask about the fuse.
The Meanwell switching power supply has all sorts of self protections but I’m thinking I should still install a fuse? how do I calculate its rating?
Thank you

 

[ccaudle]

I’m thinking I should still install a fuse?

Yes, good practice.

Is this a 120V North America system, or a 230V European system?

Assuming you want to be able to handle the full output of the power supply without blowing a fuse:

750W output/90% efficient -> 834W input power
834W input power / 230V input voltage -> 3.6A input current

Get a 4A or 5A slow blow fuse and it should be OK.

 

[isophase]

Thank you ccaudle!

 

[Mr. Moscode]

You could safely connect the unused input through a 1k resistor to ground just to keep it quiet.

I've seen Class D ratings assuming a 20% duty cycle based on music use.

My guess is you may need fan cooling.

 

[cyrano]

You might want to take a look at Ti's spec sheet for the TPA3116D2.

https://www.ti.com/lit/ds/symlink/tpa3116d2.pdf
This thing does a hellofalot more than the average class D chip.

 

[Mr. Moscode]

You might want to take a look at Ti's spec sheet for the TPA3116D2.

https://www.ti.com/lit/ds/symlink/tpa3116d2.pdf
This thing does a hellofalot more than the average class D chip.

I like the 1.2mhz switching frequency. At that rate it probably has good resolution.

100 watts on a postage stamp. Jeez!


How do they sound? Inquiring ears and all that . .

 

[Mr. Moscode]

I searched for FX Audio D amp cards but didn't see cards. Where can I see one?
Thanks

 

[ccaudle]

I searched for FX Audio D amp cards but didn't see cards.

I linked to them earlier, but it was way down in my post:
amp card at audiophonics.fr

 

[Mr. Moscode]

Thank you. Like I said 100 watts on a postage stamp.
Under $20. Jeez! Cool.
What's your judgement on the sound?

 

[Mr. Moscode]

I think with 8 cards and the PS in a box a fan of some sort would be in order. Cheap and plentiful.

I can't imagine that even with the built in AM suppression that 16 channels, a switcher for a PS and long speaker wires won't put a lot of RF EMI in the air. Hopefully it's not a problem in the installation.

 

[isophase]

Hi,

I finished the assembly yesterday and did some testing this afternoon. Boy was it a mechanical challenge! but of course, i had lots of fun doing it !
The most time conssuming part was the multiple assembly/disassembly i had to do many times to get it right.

I can't imagine that even with the built in AM suppression that 16 channels, a switcher for a PS and long speaker wires won't put a lot of RF EMI in the air. Hopefully it's not a problem in the installation.

Yes i hope it will be ok in real conditions... if not, then i will try to convince the artist to buy the 10:1 neutrik transformers.

What's your judgement on the sound?

I did some listenig tests with my cheap Sony three way speakers, and i must admit i am quite impressed with the sound! Most of all, the power these cards deliver is quite very impressive!
To my ears, these cards sound "better" than my cheap sony HiFi amplifier with the same speakers. Transients do sound "sharper" and overall nice clear sound, to my ears anyway... But then mabe its just my 25+ years old cheap sony amplifier that really sounds a bit dull...

You could safely connect the unused input through a 1k resistor to ground just to keep it quiet.

All inputs are intended to be used, sorry i don't get it ? do you mean in case an input would not be used its good to solder a 1K resistor to ground? you mean between pin 2 and ground?

Actually, all channels are very quiet and no noise issues whatsoever during the tests at home this afternoon.
Unbalanced XLR input connectors are wired like this :
-All pin 1s are soldered to chassis directly on the connectors.
-XLR Left and right pin 3s are jumpered together and connected to common ground on the amplifier card input.
-Pin 2s from XLR left and right are connected to L&R inputs on the amplifier card respectively.
The amplifier cards are NOT referenced to ground inside the box (no continuity) "ground" on the cards are only connected to power supply 0 volt.
I hope "real conditions" will be as quiet as during my test, especially that there will be some light dimmers all around :-/ fingers crossed !

I will try to upload some photos

 

[isophase]

 

[isophase]