The DIY 2.1 amplifier. Should I build it? Would you buy it?

[NickJ]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

I have been lurking and following this (and promising myself that, no in fact I don't need another amp), but I just wanted to say that you are doing awesome work.

[tyger23]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Using the amps for different frequency bands as you do in this 2.1 amp might eliminate any potential "beating". I've just read what it says in the datasheets, but I don't know how much you can actually get away with in real-world designs. Also, I'm not clear on whether the "beating" is a power supply issue or an artifact of the residual switching frequency in the outputs.

So I was wondering whether you have been able to experiment with the stock amps or whether you went ahead and tried to synchronize the clocks.

Hey Neil - Beat tones are real. Very, very real and very, very ugly. Oddly enough, though - they're showing up in a manner I did not expect. I was expecting the issue to be power supply related, but it's showing up as a magnetics issue on these TDA7492 boards. If you look at the picture where the two boards are mounted, you'll notice the magnetics are all in a line and all very close together. This is a big no-no in class-D world (as I'm sure you know) because of coupling. I could prove it was coupling just by moving one of the boards away from the other.

Sure enough, the switching frequency between the boards is not sync'd and the magnetics are coupling, showing up as a high frequency whine. Fortunately, the revision of TDA7492 boards I have (rev 3.1) has a test point pulled out for the SYNC pin, and the rework was straightforward and relatively easy. Better yet - it fixed the issue ;).

I'm not sure if the TPA3116 boards will need to be sync'd or not - their magnetics layout is different. I'll have to check that later.

[neildavis]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Hey Neil - Beat tones are real. Very, very real and very, very ugly. Oddly enough, though - they're showing up in a manner I did not expect. I was expecting the issue to be power supply related, but it's showing up as a magnetics issue on these TDA7492 boards. If you look at the picture where the two boards are mounted, you'll notice the magnetics are all in a line and all very close together. This is a big no-no in class-D world (as I'm sure you know) because of coupling. I could prove it was coupling just by moving one of the boards away from the other.

Interesting. I really didn't expect power supply issues with a switching supply and decent decoupling, so I was wondering why the spec sheets had the warning about syncing multiple chips. But I hadn't thought about magnetic coupling between the filters. Those little bobbin inductors are supposed to be fairly well shielded, so I'm surprised that you had that much coupling. Bourns lists 3 different type of SMD inductors --unshielded, semi-shielded and shielded, and the type on the board (according to the picture at PE) are the "shielded" variety.

I'm glad you found a quick and easy solution.

[djg]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

OK, so how easy/hard/impossible would it be to do a 2.2 version? Not necessarily stereo sub outputs, just two of them.

[tyger23]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

OK, so how easy/hard/impossible would it be to do a 2.2 version? Not necessarily stereo sub outputs, just two of them.

Depending on the sub, there's no reason you can't just wire the subs in parallel. The beauty of supporting a parallel mono scheme on the amplifier is that you can support loads of 2-ohms or less on the TPA3116. The TDA7492 doesn't specifically call out a minimum supported load for the parallel mode, but I believe 2-ohms should be possible.

With the mono amp, though - both the left and right channels are producing the same signal, so it's possible to just connect one sub to the left channel and one sub to the right. You'll just have to figure out how to fit that many connectors on the back plate of the case.

[tyger23]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

The beast is complete. The pots are backwards, and reworking them is a bear - but it can be done.

I imagine I'll do a lot of the rework on the pots before I ship out any of the boards (at least as much as I can), which will make life much easier for the recipient.

It sounds pretty darned good. There's a bit of noise floor hiss, but I don't have enough experience with these amps to know if it's an amp issue or a baseboard issue. Plus, you really don't hear the hiss unless you're putting your ear up to the speaker.

There's a small turn-on tick, but hardly noticeable. There is a heinous turn off pop. I don't think I'll be able to do anything about that, and I'm not sure if the TPA3116 will have the same issue. Don't turn the amp off? ;).

Now it's onto the mechanical integration. Drill a couple holes out of the back panel and I should be done ;).

[tyger23]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Here's the built up photos:







I've got to trim the length on the pot arms, but she looks pretty good!

[tyger23]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

All,

I've started shipping out these boards to those who helped with the project funding. Hopefully they'll get them over the Christmas break. I've started on some build instructions, but they're not totally complete. There's still a lot of images to add - I'm just running out of time before Christmas.

For now, I can't recommend the TPA3116 boards because they've been a bear to get going. I damaged my subwoofer amp trying to rework it, and I've got another on order but it will be after Christmas and CES before I can get back to it. The TDA7492 boards are MUCH easier to get going, but I'll admit that I think the TPA3116 boards sounded slightly better.

This document will get updated as I get around to it, and hopefully I'll get most of it done before I leave for the holidays. Anyways, enjoy!

https://docs.google.com/document/d/1fdcWq2ciOpgk7S_qVRXFXlXuAW0L47PYmrXTTrtSrVw/edit?usp=sharing

[djg]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Here's some bad pictures of the 2.1 amp and speakers I made for it. sounds pretty darn good. The outputs have not been relabeled yet. Just sitting on my computer desk, the little NRNP sub is weak. I haven't put it down in a corner yet. Possibly might have to upgrade to Wolf's sub with the PRs . Plugged into one of my Anarchy tapped horn subs, serious bass is experienced.

[djg]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

I took this 2.1 amp out to the living room and listened to some CDs through some better speakers. It is a very nice sounding unit. Curt and Wayne's Singularities and BFM Table Tuba. Both fairly sensitive. Starting at 7 O'clock, 9 O'clock was a good level, 10 was getting loud. The one concern I see would be if you have a real sensitivity mismatch with very sensitive mains and a low sensitivity sub, you could not "turn up" the sub output sufficiently for a balanced result.

[tyger23]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Sub sensitivity is definitely a concern. In the instructions, I'm recommending everyone change the gain to have a +6db difference between the subs and the main speakers. This difference can be increased even further if necessary, but having a more sensitive sub is definitely a good thing. Sensitivity can also be obtained by using a low impedance sub, which would increase the power to the sub as versus the mains.

[Wolf]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

I took this 2.1 amp out to the living room and listened to some CDs through some better speakers. It is a very nice sounding unit. Curt and Wayne's Singularities and BFM Table Tuba. Both fairly sensitive. Starting at 7 O'clock, 9 O'clock was a good level, 10 was getting loud. The one concern I see would be if you have a real sensitivity mismatch with very sensitive mains and a low sensitivity sub, you could not "turn up" the sub output sufficiently for a balanced result.

Caught the "On Every Street" sitting there...
Great recording!!

Later,
Wolf

[djg]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

The imaging on a couple of tracks through the Singularities and that little amp was downright spooky. Really "earcatching".

[Pete Basel]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Have you seen this about the TPA7492 do you know of a source for boards
that already use the correct type of output caps?

http://www.trevormarshall.com/class-d-tutorial/

[neildavis]

Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

Have you seen this about the TPA7492 do you know of a source for boards
that already use the correct type of output caps?

http://www.trevormarshall.com/class-d-tutorial/

The PE boards that Ty specified use stacked poly capacitors for both the input and the output filter--you can see the blue components in the picture on the PE product page. There are a lot of different low-cost TDA7492 boards available on eBay, but from what I saw from a quick look, the Sure version seems to be the only one that uses those ceramic caps in the output filter.