Folsom's great little 7297 Chip Amp

Folsom · « **Reply #380 on:** 22 Jun 2016, 09:00 pm »

The mica is electrically insulating, not thermally. It has about the same thermal properties as the chip. There are some higher performing versions other than mica, but they're very hard to source and wouldn't change much here.

KR500 · « **Reply #381 on:** 23 Jun 2016, 09:23 pm »

for the amp board are there polarity issues on the provided BC337 chip or the TL431 regulator, or can they be installed in either direction ?
Also , the unmarked capacitor spot in front of the 470pF slot is for the 1uF cap, right ?
I see others pictured their boards showing a green cap there like the 1uF but just wanted to make sure since it isn't labeled

thanks

Folsom · « **Reply #382 on:** 23 Jun 2016, 09:48 pm »

You're correct on the little green cap. It's labeled just it got moved over a little

And no you can't orient the TL431 and BC337 anyway you want - good god no. There's a very specific orientation correctly shown on the PCB board. Look at their datasheets, "polarity" doesn't even really apply.

KR500 · « **Reply #383 on:** 23 Jun 2016, 11:10 pm »

Thanks Jeremy ,
Yes the orientation was hiding in plain sight with the little white outline for the 2 , I was so intent on reading numbers to match up I blew by the little outline. Better slow down and look more closely next time

limits · « **Reply #384 on:** 29 Jun 2016, 10:24 pm »

Hi all...Amp is sounding quite awesome...thanks, again Folsom!

So, I had this evil thought, and was hoping somebody would stop me. Or not...how 'bout a felix-hammond transformer combo in the shielded chamber of the amp case I previously built (a new one, of course http://www.surplussales.com/Cab-RacksHardware/encl_2.html). There is plenty of room in the case. It ain't pretty, but is roomy.

Then the antipole, which would power (easily) both the Folsom 7297 board, and a Nelson Pass B1 buffer. The 19+/- VDC output from the antipole is about right for the B1. I love my buffer, but wonder how it would sound sans my crappy PC SMPS that it is currently using. And maybe put some fancy caps in it, too

I think this would be a KILLER combo. And I have a spare B1 board and matched JFETs...

Jeremy, do you have any more antipole and amp boards?

...best Jim Carey voice 'Somebody stop me'

Folsom · « **Reply #385 on:** 29 Jun 2016, 11:10 pm »

Yes I have some boards.

1. I can't tell you what will happen if you use the 7297 and B1 off the same power supply. It should work but because they're not isolated via the transformer there's a potential you'll have to fiddle with it. You could run a separate Antipole just for the B1 and choose smaller version of the transformer for size, weight, and $, that'll give a lower output that's safer for the B1 transistors.

2. If you use a "felix" you can use the same Bourne's CMC with it, but I probably wouldn't use caps on the side towards the transformer.

snake69fast · « **Reply #386 on:** 2 Jul 2016, 03:43 am »

How about TDA7379? Any chance to be better than TDA7297?

Folsom · « **Reply #387 on:** 2 Jul 2016, 04:53 am »

It's very different. It doesn't have balanced outputs is a real big difference. Could it sound good? Probably, but as good? Who knows... I wouldn't expect it to.

If someone starts talking real big about another chipamp maybe I'll start a path with it. I may have a 7293 in the works, as a much more powerful DIY option.

snake69fast · « **Reply #388 on:** 2 Jul 2016, 09:05 am »

Speaking about balanced it is possible an TDA7297 amplifier with balanced inputs?

Folsom · « **Reply #389 on:** 2 Jul 2016, 04:39 pm »

If you use transformer inputs, yes. They would convert the balanced into single ended once inside the amp. This way you get the benefits of the noise rejection. But there's no true balanced possible.

moremoremore · « **Reply #390 on:** 8 Jul 2016, 08:26 pm »

I've got a theoretical question (or more) for you guys. I bought two sets of amp/power boards from Folsom in anticipation of building an active bi-amped version of his 7297 using a miniDSP, which has worked well when I used a couple of cheap class D stereo amps.

But I'm wondering if I ought to cobble together an Econowave XO for my Large Advent Econowaves that use the original Advent woofers and Dayton polyimide compression drivers. The reason for this about-face is lower parts cost and for simplification's sake. Basically I'm wondering if 15 watts will be enough for the woofers for my not-so-demanding listening requirements. Obviously 15 watts is more than plenty for the horns, but I think the Advent woofers are only about 89 dB/w/m sensitivity. Anybody running a roughly equivalent setup?

Also, I have a Meanwell 24-volt 350-watt SMPS. I've used it to power my miniDSP. Will it work okay as the power source for the 7297 board?

Pre-emptive no-no.

Folsom · « **Reply #391 on:** 8 Jul 2016, 08:52 pm »

The SMPS will work to power an amp.

How big is your room? In a small room the 7297 is plenty for 87db speakers, so 89db would be fine in a room that isn't too big.

moremoremore · « **Reply #392 on:** 8 Jul 2016, 11:44 pm »

About 2500 cubic feet. My little SMSL amps use TPA3118D2 chips, which put out about 20 watts per channel.

Hmm, I think you just made me focus on the essentials, and now I have the answer.

I'll probably experiment with using the Mean Well and see if in the end I Meant Well.

Folsom · « **Reply #393 on:** 9 Jul 2016, 01:48 am »

That's probably small enough.

S Clark · « **Reply #394 on:** 11 Jul 2016, 02:03 am »

It finally got too hot to run my Dodd tube amp, so my 7297 amp came out of storage for the summer. I'd forgotten what great detail it has. It's running 24V of battery power and sounding good.

mlundy57 · « **Reply #395 on:** 11 Jul 2016, 02:41 am »

Quote from: S Clark on 11 Jul 2016, 02:03 am

It finally got too hot to run my Dodd tube amp, so my 7297 amp came out of storage for the summer. I'd forgotten what great detail it has. It's running 24V of battery power and sounding good.

Are you running it with a single 24 volt battery or two 12's?

S Clark · « **Reply #396 on:** 11 Jul 2016, 02:46 am »

Actually, it's a cobbled together set of two 5 AH's in parallel, connected to a 18 AH in series to get to 24.
Right now I don't even have a charger on it- used the battery tender off my Goldwing. I'll look at getting another 18AH asap.

nik.d · « **Reply #397 on:** 27 Jul 2016, 02:33 pm »

Here's another (almost) finished amp, need to install mica insulator (not wanted silicon one) and some feets that will have
double role here: They are also used for fastening sub-chassis carrying Alu bracket(s) / PCB boards / heatsink etc.
Enclosure is 220 x 100 x 300 mm WHD.

George

lacro · « **Reply #398 on:** 27 Jul 2016, 06:08 pm »

Wow! that's superb work!!!

wushuliu · « **Reply #399 on:** 27 Jul 2016, 06:48 pm »

Quote from: nik.d on 27 Jul 2016, 02:33 pm

Here's another (almost) finished amp, need to install mica insulator (not wanted silicon one) and some feets that will have
double role here: They are also used for fastening sub-chassis carrying Alu bracket(s) / PCB boards / heatsink etc.
Enclosure is 220 x 100 x 300 mm WHD.

George

Impressive.