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babadono

Another (my first) Class D DIY amp

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Finally getting going on this........

Based on TI's 3255 Eval board. I'm going to try to do some extra tricks on it. Gain control for one. And some kind of level indicator. Rear panel fab'd and prelim guts layout:

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Mine's still in the box, ordered before the infamous Class D thread disappeared a couple years ago. I'm interested in all the tweaks you're installing, please describe them as you progress with the build.

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Yea, was disappointed when WDEcho left and took all his threads:(

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Very nice!

 

This is a very good way to get some serious amplification for not much investment in time and money. I've been furloughed twice for the pandemic, and each time I took an old power amplifier that had a good power supply but was otherwise dead and not worth repairing, stripped-out all of the circuitry, and substituted a Class-D module from 3E Audio. The results have been excellent, and now I have two working amps that were previously just gathering dust.

 

Or, of course, you can do as @babadono did here, and start from scratch. Either way, it's worth the effort.

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2 hours ago, babadono said:

Based on TI's 3255 Eval board. I'm going to try to do some extra tricks on it. Gain control for one. And some kind of level indicator.

Nice work.

 

After borrowing/listening to a Schiit Loki for a week, I'm going to purchase a Loki for my TI 3255 eval board.

I'm using a SYS passive volume control at the moment.

 

Mike

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@mike stehr so obviously you have a linear unregulated P.S. on that one. Curious what is the voltage when amp is at idle? And then when its cranking?

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3 hours ago, Edgar said:

Very nice!

 

This is a very good way to get some serious amplification for not much investment in time and money. I've been furloughed twice for the pandemic, and each time I took an old power amplifier that had a good power supply but was otherwise dead and not worth repairing, stripped-out all of the circuitry, and substituted a Class-D module from 3E Audio. The results have been excellent, and now I have two working amps that were previously just gathering dust.

 

Or, of course, you can do as @babadono did here, and start from scratch. Either way, it's worth the effort.

I'm still furloughed under the pandemic excuse. It sux. Those 3E boards look to have some potential, especially the 3 channel. I'm not reluctant to ordering a switching power supply, but I'm wondering what current the TI 3255 board needs? I've got a NOS Stancor 24VCT 4Amp transformer that I was wondering about making into a linear supply. 

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4 hours ago, babadono said:

Based on TI's 3255 Eval board. I'm going to try to do some extra tricks on it. Gain control for one.

I'm going to do the same thing...................after other projects.

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7 hours ago, Davecv41 said:

I'm not reluctant to ordering a switching power supply, but I'm wondering what current the TI 3255 board needs? I've got a NOS Stancor 24VCT 4Amp transformer that I was wondering about making into a linear supply. 

 

Well, the PS that I used with a single TPA3255-2CH-260W board delivers 15.5A at 37.5VDC, and the one that I used with two TPA3255-1CH-480W boards delivers 22.5A at 46.5VDC. Mine may be a bit of overkill but, regretfully, I don't think your Stancor is up to the task.

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23 hours ago, babadono said:

@mike stehr so obviously you have a linear unregulated P.S. on that one. Curious what is the voltage when amp is at idle? And then when its cranking?

 

William and I had some personal message correspondence with the 3255 TI regarding power supplies. I was going to go with a Meanwell switching supply, but built a linear supply to save a few bucks. The supply is the same as what William uses with his. He went with a 300VA (32 or 34) Antek transformer, I'm using a 400VA Antek 34 volt transformer. It was only three bucks more...

 

A 35 amp bridge rectifier is used. Overkill, but a good price. And two 15,000uF capacitors.

 

I recall measuring 49.5 volts from the supply unloaded. How much voltage drop at idle or cranked up I have no idea, because I've never measured the supply loaded.

It could be easily measured, however...now that you've sparked my interest. I doubt there would be much voltage sag with 30,000uF for the supply, and the capacitance from the (multiplier?) capacitors on the eval board.

 

If you don't use the RESET switch, the circuit will DC couple and de-couple through the speakers upon power-up and power-down. William didn't have an issue with it, and quite a few others don't seem to mind the mild thump as well. I've been using the switch recently, because I am not very fond of the thump/pop through my spendy Faital pro drivers.

 

The 3255 evaluation board seems to sound best after an hour of use.

 

Mike

 

 

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Thanks Mike. I was concerned that if one designed an unregulated supply that put out the voltage that the 3255 wants at full power say nominally 48 volts @ 12 to 15 amps that at idle the voltage would surpass the max allowable input voltage.

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The 3255 evaluation board also "improves" if you bypass the whole input section and connet a set of transformers where the ceramic caps are (they need to be removed) that run directly into the chip itself - for me that has been the most worthwhile mod.

Cheers, Wolfram

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5 minutes ago, dubai2000 said:

The 3255 evaluation board also "improves" if you bypass the whole input section and connet a set of transformers where the ceramic caps are (they need to be removed) that run directly into the chip itself - for me that has been the most worthwhile mod.

Cheers, Wolfram

 

I’m curious.  Is this modification compatible with running the amp in balanced mode?   

 

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That's what I asked a friend today as well - and the answer seems to be yes - one only has to connect balanced sockets to the input side of the transformer (a datasheet might say how) - I am using Lundahl 1540 btw.

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My first go at this will have a balanced input receiver I.C. http://www.thatcorp.com/datashts/THAT_1200-Series_Datasheet.pdf

The output from this will feed a pot so level (gain) can be adjusted. The pot output will feed a differential driver I.C. http://www.thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf

Differential drive is required by the 3255. These circuits will bypass all the front end on the eval board. I had been procrastinating because of having to build the board with these I.C.s. Then I happened upon these break out boards from SparkFun that is making it much easier https://www.sparkfun.com/products/14002

and https://www.sparkfun.com/products/14003

 

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But won't these boards add another IC into the signal? - sorry for the ignorant question. The beauty of transformers is - to my ears - that they often sound quite good.

Cheers, Wolfram

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Yes actually 2 I.C.s. But will remove the ones on the eval board. They are the best line receivers/ drivers on the planet IMHO. The guys at THAT Corp and Bill Whitlock of Jensen Transformers(inventor and patent holder of the InGenius I.C.) know their stuff. The proof will be as they say in the pudding.

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Cool - good luck with your project btw.

Cheers, Wolfram

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Wiring progressing, decided to turn P.S. 90 degrees and keep AC wiring on one side of chassis. Any of you guys that have built one of these, do you install any protection on the AC input? Fuses? Transzorbs? Filters?

 

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All righty then, wiring is completed. Amp works on bench but only if an extra wire is added from the input buffer board to the Ground on the EVM3255 board. This wire connects the 2 grounds together but they are already connected without it. Really does not make much sense to me yet. Without the added wire I get a fault (fault red LED) on and it shuts down the C and D outputs.

This is my first Class D amp, so let me ask this. I see about 2 volts peak to peak signal @450 kHZ with no signal being output. This is the residual switching frequency that makes the amp work? Or is my amp really screwed up?

And oh yea still waiting on some LED meters from Ebay/China/Taiwan/Hong Kong.

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