$6 TDA7297 Chip Amp

wushuliu · « **Reply #20 on:** 21 Nov 2013, 02:34 am »

Quote from: rhing on 21 Nov 2013, 02:05 am

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.

Yes the TPA is the real deal. Basically a more powerful, but less optimized (talking about the ebay versions) TBI Millenia.

Folsom · « **Reply #21 on:** 21 Nov 2013, 04:59 am »

Use modified WIMA's, not the stock ones. That or the Silmic II's are popular and very good.

I've used Obbligato Gold's for a cheaper but extremely good film. Some people think the bass is slightly boring, but I haven't found anything to be an issue.

There is no shame in expensive parts with cheap ones. I know some people say there is no replacement for engineering, but I haven't always seen that to be the case. Frankly the power quality just usually isn't around for a cheaper device to perform well, where as a very nicely designed amp doesn't appear dependent on that factor. Besides someone designs the chips in these amplifiers.

I ordered one, why not?

rhing · « **Reply #22 on:** 21 Nov 2013, 06:30 am »

Quote from: Salis Audio on 21 Nov 2013, 04:59 am

Use modified WIMA's, not the stock ones. That or the Silmic II's are popular and very good.

I've used Obbligato Gold's for a cheaper but extremely good film. Some people think the bass is slightly boring, but I haven't found anything to be an issue.

There is no shame in expensive parts with cheap ones. I know some people say there is no replacement for engineering, but I haven't always seen that to be the case. Frankly the power quality just usually isn't around for a cheaper device to perform well, where as a very nicely designed amp doesn't appear dependent on that factor. Besides someone designs the chips in these amplifiers.

I ordered one, why not?

Thanks for the additional tips. I'm learning new terms from you today. What are modified Wima's? As for the Elna Silmic II's, I agree that these are special electrolytic capacitors that can be used for signal coupling. I've found that bypassing them with Sonicap Gen 2 (e.g., 0.01uF Sonicap Gen 2 with 2.2uF or 4.7uF Elna Silmic II) yields clearer highs and a larger soundstage.

I do have a pair of Obbligato Gold 0.22uF metallized Polypropylene film caps, and I intend to try those out as well. My friend convinced me to try the Mundorf Supremes first since he had a positive experience replacing Obbligato Golds with Mundorf Supremes in some speaker crossovers.

Folsom · « **Reply #23 on:** 21 Nov 2013, 06:23 pm »

Well of course Mundorf's are better for the $ difference I'd hope!

The Silmic's and Mundorfs etc aren't designed for low ESR specifically (power caps are). In fact based on people's listening opinions, you don't want that for signal capacitors. That being said, the modified Wima's are still very good. Hell even Panasonic FC's work, they just aren't ideal. Unfortunately the good old non-polar Black Gates aren't around anymore, as they are choice when you lack the money for say Teflon caps. Luckily I pulled all of mine from every project I've retired, so I can put a few in my $6 amp.

No mention of adding more power capacitors? I'm telling you, I think you'll be surprised. A bit ago I made a post on it, no one paid attention. You can literally make hot-glued-together group of them, attach wires, and run them into the same terminals as the power from the wall. Just don't let the metal of the cans touch metal anything else other than hot glue. Aside from this mod I don't think you'll get a lot more out of your unit. But it might be plenty! (especially after bad volume pot removal)

rhing · « **Reply #24 on:** 21 Nov 2013, 06:34 pm »

As a matter of fact, I do have a stash of 1uF / 50V and 4.7uF / 50V Blackgate N (non-polar), and I am thinking of trying out the 1 uF caps in a second TDA7297 amp that should be arriving soon from eBay seller homemart.usa. I love these caps, but they take so long to break in. However, once they do, they have a rich, detailed presentation from top to bottom.

I am definitely going to try the power supply stiffener cap array as you recommended. I am traveling on business this week, so I am not sure what I have in my collection of Panasonic FC or FM electrolytic caps. I have some perf board, I can use to arrange the caps in a neat bundle. Thanks for the reminder.

Folsom · « **Reply #25 on:** 21 Nov 2013, 07:30 pm »

I was going to use 4.7uf's. The burn in time is painful, but mine are used so I don't have to go through that (but they may not last forever).

It's important to put them in reverse orientation. They sound better that way despite being non-polar.

rhing · « **Reply #26 on:** 27 Nov 2013, 09:41 pm »

I built a second unit on another makeshift chassis using some scrap wood I had in the garage. I started with this unit in stock form and compared it with my first unit upgraded with better caps like Mundorf Supreme film caps. As nice as the stock unit sounds, the upgraded unit sounded significantly better with better frequency extension, a deeper soundstage, more focused imaging and greater detail. Of course, the upgraded unit should sound better.

So I decided to upgrade the second amp using the following:

1uF / 50V Black Gate N non-polar electrolytics on the inputs
2,200uF /25V Panasonic FM low ESR cap as the power supply filter cap
47uF /50V Panasonic FC low ESR cap on the mute and standby circuit
Directly wired the RCA chassis connectors to the board using 20AWG Silver-plated solid core Copper Mil-Spec wire

I know the Black Gates will require a lengthy burn-in, but it sounds much better than the stock version.

Folsom · « **Reply #27 on:** 27 Nov 2013, 11:08 pm »

Getting that volume pot out will be rewarding

rhing · « **Reply #28 on:** 28 Nov 2013, 12:45 am »

Actually, the volume pot in this unit has good balance and doesn't color the sound like most cheap volume pots. Nonetheless, I have a 100k Alps Blue Velvet volume waiting in the wings when I feel like installing it. I'm going to let the Black Gate input coupling caps settle in a bit more.

I also need to order more Panasonic FM electrolytic caps to make that off-board stiffener array.

Folsom · « **Reply #29 on:** 28 Nov 2013, 02:56 am »

Really? I don't even like vlue velvets. Maybe my ears are sensitive.

Folsom · « **Reply #30 on:** 4 Dec 2013, 12:31 am »

Well I received mine. HOLY SHIT.

In the first few minutes I knew this thing out classed my current amplifier. I didn't bother to turn it on stock.

4.7uf non-polar BlackGates on input (reverse orientation), the 10uf was replaced with 10uf non-polar BlackGate (because I had one around, it's not actually the best cap for the job). The big cap is now a 220uf FM cap because nothing else I had would fit. The diode is my beloved MUR860.

I'm hoping a little more playback will make it slightly softer on the ears, and maybe a little more bass (oogles of quality treble spill out of my 4in Fostex). But it gives music a presence already. My 3875 amplifier modeled directly after Peter Daniel's own, Blackgates and all, couldn't touch this thing with a ten foot pole. I'm hearing things I've never heard before! How is this possible? The solder is barely passable, not the solder job, the solder itself is almost so sub-par that the unit can easily have cold solder joints (my pot had one).

Whatever... I'll let you know if I think of anything else. I'm powering mine with a 4.5a IBM thinkpad charger that's actually kinda nice inside, and 6x 1500uf FC capacitors on the line going in (maybe the most important part, but I'm debating if they'd be good for post diode, which would mean bypassing tracings to allow for more current to them).

The best part of the packaging,

Folsom · « **Reply #31 on:** 4 Dec 2013, 12:51 am »

My friend's Bryston AB class is boring compared to this thing. You can't touch it with commercial stuff I've heard. The only thing that I remember doing things this does was some old DIY guy with a beard that had silver wire strung to his air motion transformer or something, and maybe some Lowethers, I forget.

There isn't the slightest bit of shame in spending any amount of money on capacitors for the inputs. Use copper foil V-caps without shame. NONE. I don't know where the limit is for this chip. Usually I don't think tricking out some fancy caps on a little inferior amplifier to something like a Pass unit could really do a lot but... whatever. Whoever is designing these chips is a god damned ninja, you just have to open it up.

It gives more of a sound stage then my last amp, which gave more of a giant instrument type of display. But that's cool, since it's doing some 3D stuff. Shame my turntable isn't up to snuff for this little devil.

Folsom · « **Reply #32 on:** 4 Dec 2013, 01:08 am »

Don't expect the same results necessarily without power conditioning**** Yes I have about a $5k conditioner (mine) backing this Devil. I'm calling The Devil from now on.

mboxler · « **Reply #33 on:** 4 Dec 2013, 01:49 am »

Quote from: Salis Audio on 4 Dec 2013, 12:31 am

4.7uf non-polar BlackGates on input (reverse orientation), the 10uf was replaced with 10uf non-polar BlackGate (because I had one around, it's not actually the best cap for the job). The big cap is now a 220uf FM cap because nothing else I had would fit. The diode is my beloved MUR860.

Can't tell from the picture, but it appears the only original parts are R1, R2, R3, C4, and D1?

Mike

shadowlight · « **Reply #34 on:** 4 Dec 2013, 02:17 am »

Request for folks who are modifying the amp. Can you post closeup pictures of the changes that you have made so newbie like me can learn

Folsom · « **Reply #35 on:** 4 Dec 2013, 02:23 am »

The original parts are the resistors and one mini film cap (yellow one).

I bypassed the diode. Now I am just going to cut it out. Imagine went up 3x just bypassing it. Bass improved. It's only purpose is safety. Any noise rejection isn't really a concern.

Folsom · « **Reply #36 on:** 4 Dec 2013, 02:40 am »

Well mine just quit haha. Maybe something to do with diode not being removed while bypassed, probably just random though.

rhing · « **Reply #37 on:** 4 Dec 2013, 02:50 am »

Quote from: Salis Audio on 4 Dec 2013, 02:23 am

The original parts are the resistors and one mini film cap (yellow one).

I bypassed the diode. Now I am just going to cut it out. Imagine went up 3x just bypassing it. Bass improved. It's only purpose is safety. Any noise rejection isn't really a concern.

Salis Audio,

Thanks for sharing your observations. With the Black Gate N caps in my amp, the frequency response seemed to favor the treble at first, but they have smoothed out with time. I knew that using the Black Gates, the break in period would require patience, but everything is now settling in and the sound is rich and detailed. The Black Gates are similar to the Mundorf Supremes in that I hear things in recordings I haven't noticed before.

I would recommend a 2,200uF / 25V Panasonic FM low ESR electrolytic cap in that power supply tank cap position. That really brought low end balance to the amp's sound. I ended up installing a 21-step 50k log tapered stepped attenuator from eBay seller tube_buyer. The nice thing is that this stepped attenuator and the Black Gate N caps all fit on the board nicely.

My understanding is the the Mute and Standby keep the amp from passing through a power-up thump. I have not confirmed this. I do know the two resistors and 10uF electrolytic cap have no bearing on sound quality.

For the diode bypass, did you just remove it and replace it with a wire jumper? It sounds like you obtained some improvements doing this. Maybe it is a necessity. Please keep us posted on your recovery.

Folsom · « **Reply #38 on:** 4 Dec 2013, 03:12 am »

I ran a wire across it's leads

, just for testing.

I'm getting zero sound now though, it just utterly turned off. I'll check the 10uf cap. After staring at the schematic I do think you need the 10uf and resistors.

I took the the R1 and LED out of mine.

The input impedance would favor 1-2.2uf. My 4.7 are big, I don't think I have any others, have to check.

I'll report again if mine turns back on. Perhaps for safety sake just parallel several diodes to see if imaging turns up (it's very noticeable).

My smps puts out less AC than the input is rated for though, not sure what happened yet.

S Clark · « **Reply #39 on:** 4 Dec 2013, 03:16 am »

I got mine today. Tried it with a burned out power supply... surprise, it didn't work!. However, robbed the cord and hooked it to an 18 AH battery and Voila! music. Sounds pretty damned detailed just stock. $6. Impressive. It's light in bass, but that's what mods are for.