[rhing]

At the recommendation of some people on the diyAudio.com Class D amplifier forums (http://www.diyaudio.com/forums/class-d/231988-what-heck-its-less-than-lunch.html#post3409339), I decided to purchase a TDA7297 Class AB chip amp from an auction seller, homemart.usa. The amp only cost $4.99 plus $1.00 shipping from Hong Kong. Several people claimed that this amp sounds better than the TA2020 Tripath Class D (i.e., Class T) amp I was already using. I've wasted $6 on bad lunches before, so I figured what could I lose.

Within a week, the amp module came in a padded envelope from Hong Kong. It was wrapped in Saran Wrap and bubble wrap. The amp has a 2" x 2" footprint. The heat sink, which is the largest component on the printed circuit board is a bit less than 2" high. This amp is tiny. I wired it up in a makeshift test bed with 5-way binding posts and good quality RCA connectors. I hooked up my Klipsch Forte IIs, my Sony SACD/CD player and powered up the amp with the same modified power supply I used with T-amp. I've been listening to music the last two evenings using this tiny amp, and I am amazed that this amp really does sound better than ma Tripath TA2020 T-amp. It digs deeper in the bass and sounds clearer than the T-amp. The tonality is balanced, the timbral detail is nice, and the amp has plenty of headroom despite its low power spec. I've listened to rock, classical and jazz, and I am impressed with the size of the soundstage and well defined imaging.

The funny thing is the data sheet from STM, the chip's manufacturer, states that applications for this chip include televisions and portable audio.

[S Clark]

Very cool.  Do you have a link to where you bought it?

[WireNut]

Groovy man. If I can build an amp for 6 bucks I'm hip to that 

[Guy 13]

Hi rhing and all Audio Circle members.
On January 2014
I am going to Hong Kong for business and if I can get the link I could find their address
 and buy that 6 USD amp. and at the same time see what else interesting worth buying they have.

Guy 13

[rhing]

I hate to post links to the famous auction site, because they expire and become dead links so quickly. Go to the auction site and search for seller "homemart.usa" or search for "tda7297f" and you'll find a bunch of these tiny TDA7297 amps. If you find one that looks like the one in my posted photo, you should be okay.

Please keep in mind, I am using 98dB sensitive Klipsch Forte II speakers with this amp that probably puts out around 10 watts. I've compared this amp to my combination of Audio Research LS7 line stage and restored/modified Dynakit Stereo 35 EL84 power amp, and this little amp does a respectable job. In the photo below, I have my restored Kenwood PC-400U idler/belt drive turntable feeding my Audio Research PH5 phono stage connected to the little TDA7297 amp.

[S Clark]

I couldn't pass it up.  Got one on the way.

[persisting1]

I'm sure Guy 13 can buy the $6 amp in HK for much less than that. Group buy anyone? 

[Guy 13]

I'm sure Guy 13 can buy the $6 amp in HK for much less than that. Group buy anyone? 

Hi persisting1 and all Audio Circle members.
Group buy, no cannot !
I cannot ship them from Vietnam to the USA for 1 $ as per stated by rhing.
Sorry.

Guy 13

[jparkhur]

How are you powering it?   Some detail if possible.  I see the 12v leads......??

Thanks

Jon   

[rhing]

How are you powering it?   Some detail if possible.  I see the 12v leads......??

Thanks

Jon

I currently use a Power One MAP110-S148 110W Switch Mode Power Supply (SMPS) that I purchased as a close-out item from All Electronics in Van Nuys, CA. I replaced the second stage power supply filter caps with 2,200uF / 50V Panasonic FM low ESR electrolytic capacitors. which reduced DC ripple and transient response of the various T-amps that I could power with nominal 12VDC power. Others are using a similar Mean Well RS-100-12 SMPS, 12VDC car starter batteries with up to 900A peak and 600 A cranking currents, and LM338-regulated linear power supplies available through eBay. Based on what I've read, this amp likes current, so you can go beyond the recommended 2A current -- 5A or more. I tried the little desktop, brick-sized 12VDC / 2A power supply that came with a Sonic Impact 5065 TA2024-based T-amp I bought from Parts Express and even though it could power the TDA7297 chip amp, the sound was thin with weakened bass, loss of detail and depth of soundstage compared to the warm, rich sound I get from my higher powered Power One SMPS. I am now considering an Astron RS-12A regulated linear power supply that is often used to power CB and HAM radios.

I've also upgraded the onboard power supply filter cap on the TDA7297 amp module with a 2,200uF / 25V Panasonic FM electrolytic capacitor and a pair of 0.22uF / 1200V Mundorf Supreme non-inductive metallized Polypropylene capacitors. I have purchased a low cost, but effective, 50k log tapered SMD resistor-based stepped attenuator from auction seller tube_buyer to replace the 50k volume pot that has a slight channel imbalance at low volume settings. The upgrades to date allow this little amp to present a big sound with my speakers. If you have inefficient speakers with <90dB sensitivity, this amp probably will not work as well for creating room-filling sound.

[Folsom]

Try 4-6 output filter caps in parallel. But put them next to the amplifier. Use FM's, and any value will probably fine around 800-2200uf. They'll stay mostly charged, and your power supply is plenty big enough.

Trust me, it's nice 

Then put a Felix in front of the SMPS.

You're going to be very pleased once the volume pot is out.

[rhing]

Try 4-6 output filter caps in parallel. But put them next to the amplifier. Use FM's, and any value will probably fine around 800-2200uf. They'll stay mostly charged, and your power supply is plenty big enough.

Trust me, it's nice 

Then put a Felix in front of the SMPS.

You're going to be very pleased once the volume pot is out.

I understand the addition of parallel capacitors off the board, but can you please explain what a "Felix" is?

[randytsuch]

A Felix is a AC power filter/conditioner.  It is basically 6 caps and a Common Mode Choke, with three caps on either side of the choke.  The caps are different values, to provide filtering over a larger frequency range.

There is a long thread on it here somewhere, probably the DIY section.

So you added $25-30 in caps to your $6 chip amp?
BTW, I am not criticizing, I do stuff like that all the time, but you no longer have a $6 amp.

Even when you factor in your mods, and the PS you need to add, still sounds like high bang for the buck.

Randy

[Folsom]

What size (form factor) is the diode on it?

[rhing]

A Felix is a AC power filter/conditioner.  It is basically 6 caps and a Common Mode Choke, with three caps on either side of the choke.  The caps are different values, to provide filtering over a larger frequency range.

There is a long thread on it here somewhere, probably the DIY section.

So you added $25-30 in caps to your $6 chip amp?
BTW, I am not criticizing, I do stuff like that all the time, but you no longer have a $6 amp.

Even when you factor in your mods, and the PS you need to add, still sounds like high bang for the buck.

Randy

Randy,

Thanks for the explanation of what a Felix is. It sounds like something worth investigating.

I know putting $22 of film caps on a $6 amp sounds ludicrous. I did this after auditioning the amp for some time. For the most part, the amp in stock form delivers great audio quality. I heard a bit of upper midrange/treble glare that was really evident when playing classical music with strings and rock recordings that tended to be on the bright side. With jazz and  blues, the stock amp sounded fine, and I think most people would be happy with the amp as-is. However, I am a hacker and I just couldn't help but think that replacing those two little cheap Polyester film caps with some Polypropylene film caps would result in something more to my liking. I had a pair of 0.22uF / 400V Panasonic ECQP Polypropylene film and foil caps in my stash used for my tube amp rebuild projects. I had bought these NOS caps from Jim McShane when I restored a Dynakit Stereo 35 EL84 amp and a Dynaco SCA-35 EL84 integrated amp. I put replaced the stock Polyester caps with these, and found the improvements to be significant. I shared my results with an audio friend who also bought one of these TDA7297 amps, and he suggested to me to try a pair of Mundorf Supremes, so I figured why not.



If I left the Panasonic caps ($3.50 each) in the TDA7297, I would have been very pleased at that, but I had read and heard so many great things about the Mundorf Supreme caps I just had to try them. To my ears, the Panasonic caps give me 90% of what the Mundorfs provide at a fraction of the cost. I am also going to explore the possibilities of Wima MKP2 metallized Polypropylene film caps that cost $1.64 each at Mouser. I like this amp for evaluating caps because the capacitance value is low enough to keep costs somewhat reasonable and because the circuit is so simple. Not counting connectors, there are only the three passive components in the signal path: two input caps and a volume pot. Even if this amp was $20, I'd still mention it on this forum, because it does sound good and it beats many amps costing much more.

What size (form factor) is the diode on it?

I think the diode is in a DO-41 package.

[shadowlight]

can the amp be run off battery?

[randytsuch]

Rhing,
Like I said, I understand the need to mod.  Almost all of my gear has been modded either by me or someone else.

And as long as you get good bang for the buck when you are done, then it makes sense.  If your $30 amp can complete with "real" amps, then it's worthwhile to do.

Is anyone at diyaudio using these for active speakers?  Since they are so cheap, seems like would be a great application.

I was also noticing if can get more power if you run them at a higher voltage, I think they can take up to 18VDC.  Not sure if guys have played with that either.

Randy

[wushuliu]

Rhing, have you not been to the TPA3116 thread at diyaudio? THAT is a hell of an amp and only $16.

[rhing]

That's next on the list to tackle. So many great projects, so little time. A friend suggested that the TPA3116 Class D is a real bargain amp too. That's what's so fun about these chip amps and Class D amps--they're cheap enough to experiment with and try different things.

[*Scotty*]

If your preamp is capacitor coupled at its output you don't need DC blocking capacitors at the input of the amplifier at all.
This could save you some money if eliminated and the sound could be improved.
Scotty