TDA7297 Build Guide V.2 Updated SG Change

Folsom · « **on:** 13 Jun 2015, 08:22 pm »

Hey Guys!

Here's an updated one with some better parts and a nice change to the Chinese TDA7297. You can ignore the little black cap being moved to the bottom, I did that trying to find room for the input capacitors. As far as power supplies I highly recommend a nice linear unit. The Astron's are hard to beat so long as you only need 12~ volts, which is below the safety threshold of the second rate chips that come on the units from eBay. Also make sure your chip screw is tight!

First remove all the junk. (Diode, LED, bypass DC capacitor, pot, big DC capacitor, crappy input capacitors, 1/8th in mini Jack)

Bridge the diode vias

Bridge the signal paths you took out.

Now here comes an interesting part, solder in the PHE426 caps (you need 2x). They may not fit without being off the board a little bit, you may want to zip tie them together and bend the leads in as best as possible.

You can put in your DC cap, such as a Nichicon FG 470uf. I put one on the bottom as well, so that's up to you. Don't forget the stipe (indicates ground/negatives on caps) on the capacitors goes to the striping silk screen on the board, represtening the ground. This step can be done before the PHE426's, doesn't matter. I'd still recommend more capacitance off the board for better sound; one of these would work.

Here's how to make your incoming connections. SG = Signal ground. ***I recommend twisting your SG with R and L, up until the capacitor, then running one line to the 9th pin (4rth in from farthest out on bottom row, 9 on data sheet). I just realized on closer inspection that the PG (power ground) runs directly through the path of SG (signal ground) and it sure to cause unwanted noise! But you can correct it with this method. Just be careful nothing is touching that shouldn't be.

snake69fast · « **Reply #1 on:** 17 Jun 2015, 06:41 am »

How does it sound now compared wit the previous version?

Folsom · « **Reply #2 on:** 22 Jun 2015, 12:24 am »

These input caps are superior. It took awhile to land on them trying a bunch of them. Also having the large cap to backup the small ones is good. I've found the Nichicon KG series to be sonically superior to using several Panasonic FC's.

matt_garman · « **Reply #3 on:** 27 Jun 2015, 09:15 pm »

What happened to the 120pF caps across the inputs?

Folsom · « **Reply #4 on:** 27 Jun 2015, 09:28 pm »

Quote from: matt_garman on 27 Jun 2015, 09:15 pm

What happened to the 120pF caps across the inputs?

Skip em.

Folsom · « **Reply #5 on:** 30 Jun 2015, 04:24 am »

Hey guys, word of caution.

Someone on the DIYAudio site got a board where the polarity is incorrectly marked on one side. Pin 1 and Pin 15 are the + for speaker outputs. They're easy to spot because they are the two pins farthest from the center.

Odal3 · « **Reply #6 on:** 11 Oct 2015, 01:02 am »

Folsom - Thanks for sharing all the build instructions for the TDA7297. I have a couple of non-modified TPA3116 amps, and they all sound nice, but I'm missing something on the low-end, so I'm going to give this a try. I may be mistaken on this, but I think I remember that you mentioned the umph the TDA7297 has over the whole frequency width.

This will be my first attempt to solder on a board so it will hopefully be a good learning experience as well. What wire do you use for the bridging?

Also, what's a good source/seller for the boards?

Folsom · « **Reply #7 on:** 11 Oct 2015, 03:16 am »

Make sure you have 1.5uf input caps (film) for bass. Your speaker efficiency will greatly contribute to the amount of bass too.

If you're running only 12v all of the eBay sellers are reasonable. This looks the same as the one in this guide.

If you want to run 18v you should use a chip from Mouser. You'd have to desolder the one on the board, and I'd recommend a desolder tool.

I'm seriously thinking I need to print up some PCB's soon however. People keep contacting me. They cost more to build, but they pay off is awesome; especially if you use some nice Furutech copper connectors and a good PSU.

Odal3 · « **Reply #8 on:** 12 Oct 2015, 04:41 am »

Same day free (prime) delivery via amazon is nice - ordered the board in the morning and got it by dinner!

Tried it out briefly in stock condition powered by an Astron, and I can hear the potential. Now I need to order all the parts for the mods. Any recommendations on wire?

Folsom · « **Reply #9 on:** 12 Oct 2015, 04:55 am »

I'd use solid core because of more current available. I often order from Parts Connexion.

Odal3 · « **Reply #10 on:** 4 Dec 2015, 06:01 pm »

Finally had a chance to do the mods, and success!!!! Thank you again for the good instructions. This was my first attempt ever to mod and my skills with the soldering iron definitely needs some practice. Well, soldering wasn't too hard (if I ignore the fact my solders looks like a kid did them), but desoldering the volume pot was the tough part.

The board after my attempt looks like someone has dragged it over rocks and then ran over it with a car, but somehow, it worked on the first attempt.

I did a quick comparison with a couple of unmodded tpa amps combined with an astron both before and after the mods.

Before mod, order of preference (all powered by Astron psu):
Tpa3116 audiobah (green board) / Tpa3116 dual chip (small diff - dual chip has better punch while audiobah better highs)
Sure tpa3110 - Step down - lost the magic vs the tpa3116
TDA7297 unmodded even further step down - decent oumph and punsh but veiled/compressed sound

After TDA7297 mod,

I will never listen to the Sure TPA3110 umodded ever again! The TDA7297 mod resulted in HUGE improvement in sound. My initial impression (on my gear, my ears, etc.) was that it has better punshy bass then the audiobah (unmodded), very tight, clean and dynamic sound. I need to move it over to listen more in my main rig vs taking it straight from a digital source as I did for the tests, but it didn't have the same "glitterly"/airy highs as the TPA. This may also be due to the fact that I only used a random crappy wire for the mods that I found in the junk drawer as well as a junk rca cable that I butchered to connect to the input. Will change it once I get around to ordering better stuff and I expect that may make it even better. But still, the sound is really good as is. Still can't believe the sound it delivers for ~$10-15 (including all the mods)

Is it better or worse than the unmodded TPA3116 - I don't know. My initial impression is that perhaps different is a better way to put it. The one thing that surprised me when I did the back-to-back testing is that I maybe liked the dual chip TPA3116 better than the green audiobah board.

Now I'm looking forward to getting the higher quality Folsom board!

Folsom · « **Reply #11 on:** 4 Dec 2015, 06:09 pm »

If you bypass the input capacitors with the MKP1837 I've been using with my design, you'll get all the high frequency pleasure you want.

Bypassing means just soldering each end of the new cap to each end of the current cap.

Odal3 · « **Reply #12 on:** 4 Dec 2015, 06:27 pm »

Thanks, and thank you for proactively answering my question about bypassing...

! Will need to try that next. How that does work, will the by-pass only affect a certain frequency band?

Also - is there a good place to read up on the theory.

Folsom · « **Reply #13 on:** 4 Dec 2015, 08:25 pm »

In general smaller caps have more noticeable affects on higher frequencies, and that's why they're common on tweeter crossovers sections.

It gets a bit more complicated from there, so I suggest if you're interesting to start doing a lot of reading.

Odal3 · « **Reply #14 on:** 7 Dec 2015, 02:21 am »

Been listening on it for a while now and i like it more and more.

I'm sure I have already maxed out on questions asked, but here's another one. I want to connect my crown xls for sub duties via the speaker out. In other words, Speaker out from the TDA7297 to line level input

Previously you linked to the following thread as a reply to someone else: http://www.diyaudio.com/forums/parts/79250-speaker-line-level-adapter-circuit-question.html

At the hornshoppe forum, the specific recommendation for the Crown XLS is a 600k ohm 1/4W resistor in line with the speaker cable.

http://thehornshoppeforum.com/index.php?topic=406.135

Some of the circuits on DIY audio looked a bit more complex than the 600k in series to me, so just wanted to double check what's the recommended way to do this with the TDA7297 so I don't burn anything up.

You also mentioned before that the output on the TDA7297 is balanced. Does this mean it would be possible to take a balanced signal out to the Crown?

Folsom · « **Reply #15 on:** 7 Dec 2015, 05:00 am »

What it means is you should use the balanced inputs on the Crown, or something might go wrong. Luckily the Crown has gain settings so you can adjust them based on need. The Crown's balanced inputs are a higher level, so if 600 is right for the single ended, maybe try 1kohm for them.

In fact this might be one of the few amps you can use with the 7297, in this fashion. Match made in heaven?

Odal3 · « **Reply #16 on:** 7 Dec 2015, 06:15 am »

Thank you!

I'm getting excited, and if this will work, I'm going to be more than thrilled!

OK, the 1/4 TRS and XLR are balanced on the crown.
So this is what I will do (unless I misunderstood),
Positive Left speaker out -> resistor -> tip of 1/4 or pin 2 of XLR
Negative Left speaker out -> ring of 1/4 or pin 3 of XLR
Neg power input -> shield -> sleeve of 1/4 or pin 1 of XLR

and then do the same for right output.

Folsom · « **Reply #17 on:** 7 Dec 2015, 06:45 am »

What shield? I wouldn't use pin1 or a shield.

Odal3 · « **Reply #18 on:** 7 Dec 2015, 05:26 pm »

Sorry - should have mentioned it was in reference to your old post about using the shield of a Belden cable (but in that case it was only connected on one end). I notied the post has now been removed.

So how would I then connect ground for the three pin XLR connection?

Speedskater · « **Reply #19 on:** 7 Dec 2015, 05:34 pm »

There is no ground connection on a balanced line level interconnect system.
XLR pin #1 is a shield, but it will only be connected at the Crown amplifier end and then it's just connected to the amp's chassis.
The TDA's speaker output after going through a resistor dropping network (that's three resistors) connects to the XLR's pins # 2 & 3.

TDA7297 Build Guide V.2 **Updated SG Change**

TDA7297 Build Guide V.2 Updated SG Change