Folsom's great little 7297 Chip Amp

AKLegal · « **Reply #1340 on:** 21 Dec 2020, 06:06 pm »

Quote from: Folsom on 21 Dec 2020, 03:31 pm

That will not work because the outputs are balanced of the 7297. You can't combine them.

One could do this with four of your 7293 boards correct?

Folsom · « **Reply #1341 on:** 21 Dec 2020, 08:44 pm »

I would not go as far as to make a claim that something could be possible that is untested thus far... (and if possible how much modification it would take)

The easier thing to do is just use an input transformer that turns balanced to single ended, and eliminates the need for an input capacitor.

AKLegal · « **Reply #1342 on:** 21 Dec 2020, 11:02 pm »

Thanks. I'm not really interested in further modding my amp anyway. Just trying to learn a bit more.

vilding · « **Reply #1343 on:** 23 Feb 2021, 04:16 pm »

Quote from: vilding on 15 Oct 2020, 08:41 pm

Ok. So i put the amp on a board, went over all joints and connections and all seemed fine and it made the music. Happy moment!

I then moved the amp to a new case, connected everything and started listening. It held up fine and sounded great at low levels for maybe two hours. At that point I turned it up a bit, maybe halfway on the pre, and it started to distort badly, then flail back and forth between distorted and quiet music and after maybe ten seconds of this going silent. No more music... The chip was cool to the touch. One of the resistors (big one) was a little warm but nothing bad. I measure 22.4 vdc in to the amp, zero volts at speaker output. No speaker posts or connectors touch the chassi.
I'm starting to give up on this DIY thing at this point... :´(

So I almost gave up and did other stuff for a while, after being quite discouraged by the struggles of amp building. I still have the big EC7293 waiting for me as well...

I´m posting a few pics. My suspicion is that I might have fried a transistor or so, but I´m not sure how to measure for it. My biggest scare is that I somehow damaged the chip, which would really, really suck. I'm hoping for you guys experience and patience to help med put this together.

Cheers!

Folsom · « **Reply #1344 on:** 23 Feb 2021, 04:50 pm »

Where are the two capacitors that go next to the DC input?

vilding · « **Reply #1345 on:** 23 Feb 2021, 05:33 pm »

Feeling stupid now, but were they not optional for rf screening, or have I burnt my chip to crisp....

Folsom · « **Reply #1346 on:** 23 Feb 2021, 05:37 pm »

Sorry, what are symptoms again?

They are not optional.

Can you see a gap between all the chip pins? It's pretty hard from the pictures to tell.

BTW I can't reply to noreply emails. My email is folsom.jeremyh@gmail.com

vilding · « **Reply #1347 on:** 23 Feb 2021, 05:42 pm »

Ok. I'll mail you.

No, there are no solder bridges. It looks a little messy but thats mostly flux... It played for a few hours on low volume, and when I turned it up, it started to distort badly and then went real quiet fo a few secs before it went silent.

vilding · « **Reply #1348 on:** 10 Mar 2021, 05:42 pm »

It's alive!
Thank you Jeremy!
Now time for listening...

S Clark · « **Reply #1349 on:** 10 Mar 2021, 06:11 pm »

That's good news. It's a very nice little amp, and you're going to enjoy it.

Folsom · « **Reply #1350 on:** 10 Mar 2021, 06:39 pm »

Quote from: vilding on 10 Mar 2021, 05:42 pm

It's alive!
Thank you Jeremy!
Now time for listening...

Awesome, I'm glad it wasn't too difficult.

vilding · « **Reply #1351 on:** 10 Mar 2021, 09:24 pm »

Quote from: Folsom on 10 Mar 2021, 06:39 pm

Awesome, I'm glad it wasn't too difficult.

Quote from: S Clark on 10 Mar 2021, 06:11 pm

That's good news. It's a very nice little amp, and you're going to enjoy it.

Listening through it right now. So glad I finally fixed it. Deep soundstage, tight bass, sweet top end. Planted in the chair...

Yatsushiro · « **Reply #1352 on:** 12 Mar 2021, 07:26 am »

What was the fix?

vilding · « **Reply #1353 on:** 12 Mar 2021, 10:21 am »

Quote from: Yatsushiro on 12 Mar 2021, 07:26 am

What was the fix?

Stupid noob misunderstanding of instructions.... Omitted the 220Uf caps at the DC intake and fried the big transistor. Very easy fix, very happy noob. Strange thing is that the transistor held up pretty well earlier. It died after I had changed chassis to sort out a ground loop issue (after lying in the closet for a few months).

Nahuelitsn · « **Reply #1354 on:** 15 Mar 2021, 03:17 am »

Hi guys. I don’t know if this is the place and you can help me. I make all the changes to the Chinese tda7297. First build guide 1 amazing sound. Put to Shame some vintage amplifiers of friends. And now build guide v2. I have big problems. I put more capacitance off the board (8500uf ) and bypass the 1.5uf dc input caps. But when i connect my amp to 12v battery i see a spark and the amp stays mute. Then if i connect again start playing only in left channel and the right doesnt produce sound at all but i can see the speaker stay stuck forward like if receive DC power. Please help!!

Thanks for your time and sorry for my english. Best regards.

Folsom · « **Reply #1355 on:** 15 Mar 2021, 05:56 pm »

Pretty hard to tell from pictures. You didn't put a switch for turn on?

Nahuelitsn · « **Reply #1356 on:** 15 Mar 2021, 07:17 pm »

I did not install a switch because I am an anxious person

and wanted to test if it worked before continuing to assemble the rest of the things. I have a switch to install that would allow me in its on state to connect the battery to the amplifier and when I turn it off, connect the battery to its charger, leaving the amplifier without power.

I recently discovered that between the ground and the left channel I have a very low impedance and sometimes the tester beeps indicating continuity. In the right channel I have about 1200ohms of impedance between ground and R Line In But I can't find the problem on the board. Could the chip be damaged by turning it on without a switch? Prior to these problems the amplifier was working on the battery correctly but it started to distort easily if I increased the signal from my DAC. Before that with the potentiometer this did not happen and it achieved higher SPL without distortion and with a very bad and precarious power supply. The battery is a 12v 7ah SLA.

Folsom · « **Reply #1357 on:** 17 Mar 2021, 10:52 pm »

I think you might be on your own little quest here to figure out what's going given the amount of variables. The input impedance is suppose to be 25-30k I believe in the spec sheet. You can test by removing cables and checking with multi-meter on each channel. When everything is attached there's no way to really know.

Nahuelitsn · « **Reply #1358 on:** 17 Mar 2021, 11:08 pm »

Thanks Folsom. I desolder everything except the chip and happen exactly the same. Between R and ground Líne in have :duh:5 ohms and between L and ground 1200ohm. If i put a 1k resistance between the R in and ground nothing change. I think that i screw it up the chip.

Folsom · « **Reply #1359 on:** 18 Mar 2021, 12:37 am »

Well order a couple this time