[Folsom]

Mine must fried. But it might have been the non-polar 10uf.

Maybe a surge in AC. Can't get a peep out of it.... This has to be solved because the diode kills performance. But maybe a couple would bring it back instead of none.

Ugh, 2 week shipping.

[Folsom]

It says you can use AC for power on another sellers deal. I'm not so sure the diode mattered, maybe mine died just randomly... Diodes leak more AC than my smps makes, directly connected.

Other designs have it directly connected, no diode. I must have bad luck.

[S Clark]

I've been listening to Sting's Brand New Day and James Taylor's Hourglass, both excellent cd's that I know in and out.  Sometimes you hear extra detail because something else is taken away, and in this case the lack of bass clearly accentuates the upper mids.  But, it doesn't change the fact that there is a special ability to split instruments, duets, different drums within the drumset, etc. into their separate spaces.  Pretty dang cool at this price point.

[Folsom]

If the bass can be attained, it's crazy good for price.

[rhing]

I've been listening to Sting's Brand New Day and James Taylor's Hourglass, both excellent cd's that I know in and out.  Sometimes you hear extra detail because something else is taken away, and in this case the lack of bass clearly accentuates the upper mids.  But, it doesn't change the fact that there is a special ability to split instruments, duets, different drums within the drumset, etc. into their separate spaces.  Pretty dang cool at this price point.

Missing bass? One of the reasons I like these amps is that they do produce bass. Are you running the amp stock?

[Folsom]

From what I gather poking around.

Diode can be replaced by wire if you use DC power. But perhaps bypassing it with wire is a mistake; it has to come out.

The 10uf cap isn't necessary but a wire has to replace it. It just reduces the on pop, not a big unless your speakers blow easy.

And my luck sucks. Did anyone order several two weeks ago so I can get one off them?    I am hooked on not only the detail, imaging, but the sonic qualities in certain areas are just.... heh, something else.

p.s. Blackgates literally take 200 hours.

[S Clark]

Missing bass? One if the reasons I like these amps is that they do produce bass. Are you running the amp stock?

Absolutely stock.  Just got it today and got it running a couple of hours ago.  Where would you mod first to improve bass? At least it's on batteries, so no power supply issues.

[Folsom]

Absolutely stock.  Just got it today and got it running a couple of hours ago.  Where would you mod first to improve bass? At least it's on batteries, so no power supply issues.

Toss the diode, add lots of parallel power caps, and get a good one for the board. (The stock is probably like 20 speed). Generally robust power allows bass.

[rhing]

Toss the diode, add lots of parallel power caps, and get a good one for the board. (The stock is probably like 20 speed). Generally robust power allows bass.

I am satisfied with the audio quality having the diode in place, but I may try taking it out later on.

As for improving the bass, I am not sure the stock 2,200uF / 25V power supply tank cap is really a 2,200uF / 25V cap. Matsushita (a.k.a. Panasonic) and Nichicon make some of the most compact low ESR, low impedance electrolytic caps, and their caps of the same rating are taller than the stock cap. I would replace this part first. You must use a cap with a diameter of 12.5mm or less for it to fit on the board. If you only made this part upgrade with the amp, you would notice a significant improvement in bass and dynamic slam, not to mention a larger, deeper soundstage. As Salis Audio mentioned before, you can assemble a cluster of 4-6 parallel-wired caps like 2,200uF / 25V Panasonic FM electrolytic caps (EEU-FM1E222L) and connect them to the DC input of the TDA7297 board.

A good power supply is also important to good bass response. As I posted earlier, I use a slightly modified Power One MAP110-S148 SMPS capable of outputting 110 watts. These are no longer available. In fact, I bought mine for $15 from a surplus electronics Web store years ago. A good SMPS suitable for experienced DIYers to add connections is the Mean Well RS-100-12 SMPS. This is a 100 watt-capable SMPS that generates over 7A current and 12V DC. Battery power is also a good, clean power source as long as the battery is rated for 12V DC or higher (up to 18V DC). Car booster (starter) batteries seem to be capable of delivering plenty of current on demand. Myself, I am considering an Astron RS-12A regulated linear power supply that can deliver 13.8V DC and 12A current. These cost about $80 new retail.

For other improvements, I would replace the stock input capacitors. On my amps from eBay seller homemart.usa, these are the two little Orange-colored Epoxy-encased 0.22uF / 63V Polyester film. I would either use 1uF / 50V Elna Silmic II electrolytic caps (RFS-50V010ME3#5) or Wima 0.22uF / 250V MKP2 metallized Polypropylene (MKP) film caps (MKP2F032201K00JSSD). All of these parts including the Panasonic FM electrolytic caps are available from Mouser Electronics, a reputable online electronic components distributor/reseller (www.mouser.com). These caps are compact enough to fit on the amplifier circuit board and they are reasonably priced. If you want to use "boutique" input coupling caps, you can use whatever your heart desires.

For those new to DIY and who want to know how to wire up one of these $6 wonders, I've attached a diagram.



I think some of the newer TDA7297 boards available through eBay now incorporate DC power connectors on the board, but if you need a suitable DC power connector, get the Switchcraft 722A DC power connector (722A) from Mouser or other online electronics parts stores.

[mboxler]

For those of us still learning 

This amp follows the "Stand-alone low-cost application" schematic in this datasheet

http://www.st.com/web/en/resource/technical/document/datasheet/CD00001048.pdf

D1 (the p-n diode) is only there to protect against the DC power supply failing or being hooked up backwards.

D2 (the LED) and it's currect limiting resistor (R1) are for looks only.

D1 could be replaced with a wire, and the amp would get an extra .7 volts (big deal, I know, but...)

D2 (the LED) could be removed.  Not sure of the advantage.

Am I close?

Thanks, Mike

[rhing]

For those of us still learning 

This amp follows the "Stand-alone low-cost application" schematic in this datasheet

http://www.st.com/web/en/resource/technical/document/datasheet/CD00001048.pdf

D1 (the p-n diode) is only there to protect against the DC power supply failing or being hooked up backwards.

D2 (the LED) and it's currect limiting resistor (R1) are for looks only.

D1 could be replaced with a wire, and the amp would get an extra .7 volts (big deal, I know, but...)

D2 (the LED) could be removed.  Not sure of the advantage.

Am I close?

Thanks, Mike

Sounds right to me. Attached is a schematic that is similar to the one referenced by mboxler, and it seems to be almost identical to the circuit on the module from homemart.usa. The DO-41 diode is non-essential to the operation of the amplifier. I left it in there, and I'm fine with the sound quality.

[Folsom]

Nice job Mike.

The 10uf cap is only for the event in which a turn on peak from this amp could blow your speakers. If your speakers couldn't handle a peak of low frequency at something like 30w or whatever, keep it.

The diode is so you can hook up an AC source. Pretty sure it'd sound bad... Capacitors stock or not wouldn't be able to compensate well enough, not without adding a full bridge rectifier.

But I came up with a stupid simple added protection from left over AC on your DC, that I don't think should add notable noise. Just put a diode (stripe end) across the DC wires pre amp board and capacitor bank if you got one. You could parrallel a few even. Technicaly the power caps should do this, problem is they are charged a lot of the time, and they have a limit for how much they'll attenuate. I'm sure someone will think "hey just use an RC network" but I'm fairly positive it'd rob some quality. They're cool for constant current power, but not this style.

[Folsom]

LEDs make erratic noise, so I am told.

The input impedence is better matched with 1-2.2uf input caps than .22uf. They knew this and uses 2.2uf in data sheet.

Nichicon ES might be a nice uber cheap input cap option.

I'll measure the Chang "2,200uf" that I pull out of my next one.

Later I'll try to make a new schematic for you guys playing around the first time. I'll see what I can so about pictures.

[S Clark]

Thanks for the suggestions for upgrades.  I've ordered a few of the Panasonic FR 2200uf caps and have them on the way.  I've got several values of Sprague orange drops and may have some Panasonics laying around that I can use for the .22 cap.... or I have some Russian teflons that are bigger than the whole amp.    I have extras of the Panasonic coming if anyone needs one.

[randytsuch]

So I don't see D1 on these schematics 

From the description, must be connected to VCC.

If I had one of these, I would jumper out D1, and see if it makes a difference.

[S Clark]

Just for grins I hookeditup to my huge ls9's.  Sounds pretty good if you don't ask to much volume from it. It will most likely end up on a TV that has crappy sound.

[Folsom]

So I don't see D1 on these schematics 

From the description, must be connected to VCC.

If I had one of these, I would jumper out D1, and see if it makes a difference.

Correct, but just incase entirely remove it. Also only do this for DC power. You could reuse D1 the way I described too.

[rhing]

Salis Audio,

Have you checked the output of your SMPS? How stable is it? If the output momentarily exceeded the voltage input limit of the TDA7297 chip, it might have fried something in the chip. If you don't want to wait two weeks for a new replacement amp, you might want to order a new TDA7297 chip from Mouser. However, note that a single TDA7297 amp costs about the same as a complete amp module from China.

You are correct in that a reverse polarity protection diode (D1) is not required. I haven't removed mine yet, but since it is wired in series with the DC power to Vcc, a jumper wired is required to replace the P-N diode. I don't believe this diode offers any over-voltage protection, so if a power supply could run over 18V DC, it wouldn't do anything to help.

I am not sure why these manufacturers would silkscreen "AC/DC" voltage input on the power rail since that diode is not there for rectification. The small 0.1uF cap and the larger 2,200uF cap are not sufficient for filtering an incoming AC power voltage. With that much ripple on Vcc, I would expect that the sound would be heavily distorted.

So I don't see D1 on these schematics 

From the description, must be connected to VCC.

If I had one of these, I would jumper out D1, and see if it makes a difference.

D1 is not on the schematic but it is wired in series between the power supply and Vcc. This is a low-cost method of protecting the circuit from errant reverse polarity connections.

[Folsom]

A generous member is sending me a unit that had a damaged pot. My supply is 16v but puts out close to 17v. Perhaps I'll switch it to another lower voltage unit. I'll look about town for a decent one.

AC would work with a diode and cap but you'd lose everything that makes it good because the chip would see constant significant voltage drops unless it had absurd capacitence, like 30kuf or something.

I ordered some new capacitors from Mouser that'll serve as a standard for modifications since they are avaliable to all. I'll post part numbers when I take pictures of the process. (And measure the Chang cap)

I choose Muse ES caps for this next build, cheap enough it's cheaper to order 10 than 2! They are considered bass oriented (good for this amp) and know to be more transparent than many caps at higher prices, to naturally show of the extreme detail in this amp. My experience is they are pretty smooth to. It's going to be good; and docmented. Sometime next week..

[mboxler]

A generous member is sending me a unit that had a damaged pot.

Yea...both units I received had damaged pots.  The "mummy" wrapping was so tight it bent both pots.

On the bright side, my de-soldering skills are improving  .