Folsom's great little 7297 Chip Amp

1108 · « **Reply #280 on:** 6 Apr 2016, 01:03 pm »

I'm having the same problem. How can I check the mute/standby?

Folsom · « **Reply #281 on:** 6 Apr 2016, 06:05 pm »

mute/stdby won't affect the voltage at the capacitor, it just turns the chip off.

Have you checked where your voltage stops?

limits · « **Reply #282 on:** 6 Apr 2016, 06:29 pm »

I didn't get the email about adding the two additional caps. What are the values for each location?

Trying to figure out a path forward to try to get my amp working...do the readings I mentioned earlier seem ok? I measured 19.2 VAC out of the transformer, 25.2 VDC through the antipole to the input of the amp board, and 1.7 volts (assume this is DC also) from Oscon positive leg to ground. I would like to eliminate things that are likely ok, so I can hopefully narrow in on the problem.

My plan tonight is to re-solder the middle leg of the TL431, which looks a bit suspect, and solder in a new 7297, as I think I fried the one on the board last night.

Folsom · « **Reply #283 on:** 6 Apr 2016, 06:39 pm »

1.7 from an OSCON means the power is not getting through. It is not related to mute/stdby.

Set your DMM to ohm reading and check between the ground wire coming in and several OSCON ground legs (the side with marking). And then check to chip tab.

Your soldering looks like you needed to wait just a moment longer to get enough heat on the board, in several locations, because the solder tended to pool up first on the leads. Hopefully there's no cold joints. A light wiggle can often identify them.

The TL431 does look like it needs the center leg touched up.

I don't know if the chip is bad, could be. Do you have solder wick? You'll need that. I'd suggest cutting the chip off and then pulling the legs out when heat is applied, and solder wicking to clean. If you have a heated desolder tool you might get a good clean spot on the legs once chip is removed. It's certainly not the easiest task with 15 pins, but it's doable (I did it with the first PCB I had, before anyone knew that SG and PG had to be connected outside of the chip for it to turn on; all boards are correct this way now).

limits · « **Reply #284 on:** 6 Apr 2016, 06:59 pm »

Hi Folsom...thanks for the reply. Yeah--my impatience in using the crappy solder iron tip that I should have replaced before I started the board really cost me...I will pick up some supplies today.

So, I am assuming the check from Oscon neg. to ground should give the same reading (or similar) as touching the two leads of the DMM together, right? What reading should I get between the chip tab and ground?

Do you know of any way to check if I fried my 7297 before I remove it?

Thanks! Very much appreciated.

Folsom · « **Reply #285 on:** 6 Apr 2016, 07:21 pm »

Correct the reading should be close to touching the meter tips together. That goes for the chip tab too.

I do not have a clear way to test the chip besides turning it on and checking for voltage on the outputs; but it might turn itself off without a load. The good protection qualities in the chip are a double-edged sword you might say.

sorinv · « **Reply #286 on:** 7 Apr 2016, 04:58 am »

Quote

I didn't get the email about adding the two additional caps. What are the values for each location?

I didn't get that either. I have in the BOM 220uf, speced for primary use with battery supply. Should I install those with the altipole in a different enclosure with one foot DC cable to the amp?

Folsom · « **Reply #287 on:** 7 Apr 2016, 05:25 am »

Yes, I would. The inductance is too much otherwise.

matt_garman · « **Reply #288 on:** 10 Apr 2016, 11:17 pm »

Quote from: matt_garman on 26 Mar 2016, 08:25 pm

Here's the chassis layout I'm thinking about...

It's becoming a reality:

I need to have the back panel cut for RCA, speaker terminals, and IEC. I'll probably have that done by Front Panel Express.

I'll shorten those AC leads in and out of the transformer before it's all done.

For the front panel, I'll go with a power LED and maybe on/off switch (or the on/off switch will be integrated into the IEC, haven't decided on that yet).

Coming along nicely I think!

lacro · « **Reply #289 on:** 10 Apr 2016, 11:52 pm »

Looking good, Matt

Folsom · « **Reply #290 on:** 11 Apr 2016, 08:38 am »

Ok guys, it's been random for turn on noise. I sent out two emails. One about the input caps for DC, which Matt has (gold caps). That stabilizes performance and stops turn on noise two people have had. And one or two have a small bump sound during turn on, which I sent the second email about. The 10uf blue cap can be bypassed by a 100uf (or replaced, but I wouldn't try it unless you're very good with a soldering iron, and even then it's risky due to hole size). Here's a capacitor that'll work and fit everyone's budget (I hope).

I tested it this evening in order to make everyone happy. The turn on bump was harmless at 15w max (if you even had it), but hey we can do silent worry free so why not!

1108 · « **Reply #291 on:** 19 Apr 2016, 11:54 am »

I have the Bourns 8120 for the Antipole. Does it need to be oriented in any particular way?

Gopher · « **Reply #292 on:** 19 Apr 2016, 03:13 pm »

I had the opportunity to meet Folsom at AXPONA and give his amp a listen after hours and can say it is coming along quite well. The bass in particular was impressive.

Cool meeting you, man and good luck with this endeavor!

lacro · « **Reply #293 on:** 19 Apr 2016, 03:48 pm »

Well - I finally finished building my DIY TDA7297 Folsom amp. I have been playing around with the Class D amplifier boards (TPA3110/3116/3118) for several years now. Trying different boards,and mods with resulting great sound for cheap.
However, Folsom's implementation of the Class A/B TDA7297 chip amp is definitely a leap forward by a big margin. I finally have a DIY amp that truly meets my expectations without needing further mods to make it sound right. I am listen now at pretty high levels; the bass is just amazing on my GR Research X-LS Encores. These speakers always sounded good to me, but this amp really brings out their best! Good job Folsom

Folsom · « **Reply #294 on:** 19 Apr 2016, 03:54 pm »

Wow! The award for most compact design goes to Lacro!

How funny is it that the Folsom name is on someone else's project before anything of my own?

It looks great Lacro. I'm glad you're enjoying the amp!

Folsom · « **Reply #295 on:** 19 Apr 2016, 03:58 pm »

Quote from: Gopher on 19 Apr 2016, 03:13 pm

I had the opportunity to meet Folsom at AXPONA and give his amp a listen after hours and can say it is coming along quite well. The bass in particular was impressive.

Cool meeting you, man and good luck with this endeavor!

Thank you Gopher.

Odal3 · « **Reply #296 on:** 19 Apr 2016, 04:19 pm »

Lacro - Double wow! That's super nice. Well done. I can't tell from the pics but are the heatsinks mounted on the case/middle plate or do they go straight through to allow direct contact with the chip and transistor? Is it keeping pretty cool in the case?

Please tell us more about your build spec.

limits · « **Reply #297 on:** 19 Apr 2016, 04:41 pm »

Nice, NICE, work, lacro!! My fingers are growing ever big and clumsy when I look at your packaging

Dang--that's tight! Very attractive build...Congrats!

shadowlight · « **Reply #298 on:** 19 Apr 2016, 04:46 pm »

@lacro, where did you get the case from?

matt_garman · « **Reply #299 on:** 19 Apr 2016, 05:03 pm »

Quote from: lacro on 19 Apr 2016, 03:48 pm

Well - I finally finished building my DIY TDA7297 Folsom amp. I have been playing around with the Class D amplifier boards (TPA3110/3116/3118) for several years now. Trying different boards,and mods with resulting great sound for cheap.
However, Folsom's implementation of the Class A/B TDA7297 chip amp is definitely a leap forward by a big margin. I finally have a DIY amp that truly meets my expectations without needing further mods to make it sound right. I am listen now at pretty high levels; the bass is just amazing on my GR Research X-LS Encores. These speakers always sounded good to me, but this amp really brings out their best! Good job Folsom

Lacro, that is super nice! I love how compact it is, yet (to my eyes anyway), I don't see any compromises.

What SMPS are you using? (I know people debate SMPS vs linear, but if space/compactness is a concern, SMPS is the clear winner.)

And is that heatsink in the back (the one for the tda7297 chip) integrated with the case, or did you add it on?

Once again, great work. Nothing short of impressive!