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Old 24th August 2005, 08:43 PM   #1
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Default DIY Class D Amp using TDA8939 or similar

I'm new at the whole Class-D scene, but I've been reading a lot about it to get the hang of it. I want to try to build one for myself, but I don't want to use the ready-made UcD or ZapPulse modules. They're too expensive for my taste. Especially if you want to build a 5 channel amplifier.

A highly regarded amplifier like the "van Medevoort MA240" uses the Philips TDA8939 with very nice results according to the reviews. I've looked up the
specsheet at the Philips Website and it looks pretty simple to build. It even has protection circuits and standby/reset circuits.

I tried searching for information about it on the internet, but so far I came up blank. So for my question: Does anyone know of a website or person who is active is building these kind of amplifiers? Or do you have any tips or hints?

Thanks!

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Old 24th August 2005, 09:28 PM   #2
IVX is offline IVX  Russian Federation
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You know, i think that 8939(van Medevoort MA240 have other chip in use) it's a very strange history..no appnote, no modulator offered even, but available, and samples too.. So what i'll do with 8939 if i'll buy it, connect to the TAS5518? Strange..
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Old 25th August 2005, 02:39 AM   #3
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Hi,

I don't know if you're decided on a chip based amp... you could look into tripath stuff, there's a number of threads on them around here, you must have seen some of them.

You could wait aaand wait, before www.mueta.com has any to offer.

Good thread with good links:

http://www.diyaudio.com/forums/showthread/t-36528.html

You could also try scrolling through old threads here there's a reference design thread that's got some good info for anyone wanting to build their own amp.

What do you expect out of it in the end? If you expect ultra quiet and high power with excellent everything the cost of DIY is beyond most and your best bet is to look towards where you said you dont' want to go with the modules, which makes it more than possible.

If it's about a learning experience you can build a worthwhile amp with alot of work and alot of compromise. End result there is, great sounding amp of low to moderate power (efficient speakers helps) and you'll no doubt learn alot. It will be forever fun to listen to, even if only for you.

Regards,
Chris
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Old 25th August 2005, 01:15 PM   #4
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Thanks for the info, but when I look at the specsheet and the proposed schematics therein, it looks very simple to build. Van Medevoort does use the TDA8939, but in a different package than described on the Philips website. Here's a picture of the inside of the VM240:

Click the image to open in full size.

The picture in my first post is also of the VM240. You can see the TDA here from behind.

So it should be as simple as connecting a PWM controller to the TDA8939 and you're ready to go. The TAS5518 is a nice module, but maybe too complex for my project. But there must be simpler modules, which accept analog signals instead of or besides digital ones.
Or am i thinking too simple and is there more to this?
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Old 25th August 2005, 01:15 PM   #5
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I just noticed a huge mistake in the type of chip. I was talking about the TDA8939, but VM uses the TDA8938. Slight oversight, but big difference. And I can't find any information about the 8938 on the Philips website. But the 8938 is supposed to accept an analog signal directly, according to the review where these pictures come from. Unfortunately the review is in Dutch, so I don't think you'll understand...
But when looking at the picture closely I don't see a chip next to the TDA8938, which can be a PWM controller...
So I have a mystery on my hands here... What are the specs of the TDA 8938 and where can I get one?
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Old 25th August 2005, 09:49 PM   #6
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TDA8938 is (as far as I heard) a Philips products IC only, probably developed as a "counteraction" to the guys that did the (discrete components) UCD amplifier for the DFR9000. And that one can very well compete with the Van Meedevoort amplifier .....
Maybe Van Meedevoort was allowed to use it because of good connections with the Philips developers .....


I expect that in the coming months/year we will see a public type powerIC that can act as a UCD amplifier. And that makes life simple for the diy'er.
Some expect however that for top-quality UCD(like) amps we still have to go for discrete components some time as some components are quite critical and still binded to specific manufacturers.
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Old 28th August 2005, 06:58 PM   #7
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I asked Philips about the TDA8938 and I got this response:

Quote:
Re: Japp,

Thank you for writing to the Philips Technical Support Center and for your interest in our products.

We stopped development on the TDA8938 just under two years ago due to techncial difficulties in designing and implememnting the IC.

You can view our other Class D offerings at the following link:

http://www.semiconductors.philips.co...dex.html#31627

Regards,

Jim K.
So according to this information is the 8938 not available. That's too bad...
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Old 29th August 2005, 10:15 AM   #8
Kenshin is offline Kenshin  China
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How could discreet gate drivers be faster than IC?
Quote:
Originally posted by marconist
Some expect however that for top-quality UCD(like) amps we still have to go for discrete components some time as some components are quite critical and still binded to specific manufacturers.
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Old 29th August 2005, 05:49 PM   #9
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Quote:
Originally posted by Kenshin
How could discreet gate drivers be faster than IC?
Fast is not the only criterium.
But I meant mainly that fi. the sota powerFets technology is not in everybodies hands.
That may mean that Philips is not able yet to make topnotch IC class D amplifiers in one package.

If you look at the schematic of the DFR9000 UCD power output amp you will see that it is component build!
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Old 15th November 2006, 05:12 PM   #10
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Is there a pcb available to test this Philips chip ?
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