Folsom's great little 7297 Chip Amp

limits · « **Reply #300 on:** 19 Apr 2016, 06:19 pm »

Hi Everybody;

I finally got back to troubleshooting my build. I re-did some of my really bad solder joints, and now get 17.7 VDC from positive Oscon leg to amp board ground. Does this sound right?

I might have a blown 7297 chip (touched it against the amp case and it went 'pop' in an earlier troubleshooting attempt), but I would rather not replace it until I know what voltages the caps should see.

Not being familiar with the circuit, I don't know what to check next...

Thanks for any help you may be able to provide.

limits

limits · « **Reply #301 on:** 19 Apr 2016, 06:22 pm »

...Also checked continuity of Chip tab to negative on amp board and that was OK...

Folsom · « **Reply #302 on:** 19 Apr 2016, 06:24 pm »

The voltage is correct. Can you take pics? That helps us tremendously.

limits · « **Reply #303 on:** 19 Apr 2016, 06:45 pm »

Certainly...not pretty, I know...

lacro · « **Reply #304 on:** 19 Apr 2016, 09:54 pm »

Thanks for the kind words guys.....

Quote from: shadowlight on 19 Apr 2016, 04:46 pm

@lacro, where did you get the case from?

Shadowlight:
http://www.aliexpress.com/snapshot/7493007269.html?

Quote from: matt_garman on 19 Apr 2016, 05:03 pm

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!

Matt: The SMPS is one that was talked about on DIY Audio. I did the suggested mods replacing all electrolytics, and adding a couple of ceramic SMD caps on the secondary outputs. It doesn't produce any audible noise (hiss/hum), and stays pretty cool. The main reason I used it was it is the same length as the amp board (115mm) so it fits the PCB groves in the case. It just slides into the case without mounting hardware being needed. The Antipole would have required me to install it in a separate case as it's 7" long. I do feel Linear PS are superior, and the Antipole is probably the best choice for this amp, but so far I am pretty happy with this one.

The heatsink is a separate piece; got it from PE. It is mounted with screws from the back (5 total). The back panel was sand blasted to remove the powder coating where the HS mounts; then bedded in thermal grease. The chip is bolted through the back to the HS (sandblasting/thermal grease again on the inside)

Quote from: Odal3 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.

Odal3: The heatsinks, both the chip and transistor are sandwiched with the back plate, and bulkhead. The heatsinks are bolted to the chip and transistor through the back plate and bulkhead creating a secondary heatsink. At high listening levels the case stays only slightly warm when driving 89db speakers; when driving 84db speakers, it gets a lot warmer. There are a lot of ventilation holes I drilled in the top, bottom and back to aid in cooling.

What else do you want to know about my build specs?

Folsom · « **Reply #305 on:** 19 Apr 2016, 10:16 pm »

Quote from: limits on 19 Apr 2016, 06:45 pm

Certainly...not pretty, I know...

I don't see anything obvious about it that's wrong. You've got correct voltage. You might have fried the mute/stby section somehow (that's in the chip), if you get zero sound.

limits · « **Reply #306 on:** 19 Apr 2016, 11:31 pm »

Ok. I will try hooking it up again, hopefully tonight. Unless I read the meter wrong on my first try (1.7 VDC is what I noted before-- Oscon positive leg to board ground), I should at least have more power running through the board. Really hoping I don't have to replace that chip...Fingers crossed...

matt_garman · « **Reply #307 on:** 20 Apr 2016, 02:20 am »

Quote from: lacro on 19 Apr 2016, 09:54 pm

Thanks for the kind words guys.....

They are well-deserved. Just when I think my builds are starting to look half-decent, you come along and post that!

Quote from: lacro on 19 Apr 2016, 09:54 pm

Matt: The SMPS is one that was talked about on DIY Audio. I did the suggested mods replacing all electrolytics, and adding a couple of ceramic SMD caps on the secondary outputs. It doesn't produce any audible noise (hiss/hum), and stays pretty cool. The main reason I used it was it is the same length as the amp board (115mm) so it fits the PCB groves in the case. It just slides into the case without mounting hardware being needed. The Antipole would have required me to install it in a separate case as it's 7" long. I do feel Linear PS are superior, and the Antipole is probably the best choice for this amp, but so far I am pretty happy with this one.

Do you happen to have a link to the DIYAudio thread discussing that SMPS?

I keep going back and looking at the pics of your build, Lacro. It's really nice. Since you made such efficient use of space, did you find it hard to get everything in place?

Odal3 · « **Reply #308 on:** 20 Apr 2016, 02:23 am »

Thanks for the info!

lacro · « **Reply #309 on:** 20 Apr 2016, 01:38 pm »

Quote from: matt_garman on 20 Apr 2016, 02:20 am

I keep going back and looking at the pics of your build, Lacro. It's really nice. Since you made such efficient use of space, did you find it hard to get everything in place?

Matt: The case is bigger than the photos make it look. It's 4-1/2" Wide; 3" high, and 6" long. I made everything to be modular. The PS module, and amp module can be removed from the case in less than 5 minutes. Everything either unplugs or is held with screws. The modules slide into the grooves provided in the case.

Typical 5 minute dis-assembly:

Remove wooden front panel; unplug LED, and remove switch
Slide top off case
Disconnect wires from power supply (all held with screws)
Slide out power supply. No hardware, held in with rubber springs
Remove bolt from center bracket/star ground, remove screws from back panel
Slide Amp out as one unit with back panel, and aluminum divider bulkhead attached
The bulkhead, and heatsink can be removed from the Transistor with one screw if needed.

This is pretty much how I put it together; treating it as a case, and two separate modules. There wasn't any tight, difficult assembly, or wiring. The hardest part for me was laying out the back panel so everything fit since the heat sink took so much space. Compared to my stuffing a TPA 3110 into an Altoids mint tin, this build has lots of room:D http://www.audiocircle.com/index.php?action=profile;u=74671;area=showposts;start=140

1108 · « **Reply #310 on:** 20 Apr 2016, 04:18 pm »

Quote from: 1108 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?

Anyone?

limits · « **Reply #311 on:** 20 Apr 2016, 04:32 pm »

Hi...I believe it was discussed earlier, but the Bournes can go either way on the antipole board.

I tried hooking my amp up again last night, and it still doesn't work. I guess I will try cutting off the 7297 and fitting in a new chip. If that doesn't work, it might be closet-city for this project

1108 · « **Reply #312 on:** 20 Apr 2016, 04:38 pm »

Thanks. I thought I read that someplace but couldn't find it again.

Folsom · « **Reply #313 on:** 20 Apr 2016, 04:40 pm »

Quote from: limits on 20 Apr 2016, 04:32 pm

Hi...I believe it was discussed earlier, but the Bournes can go either way on the antipole board.

I tried hooking my amp up again last night, and it still doesn't work. I guess I will try cutting off the 7297 and fitting in a new chip.

That might be the best option for right now, since you clearly have enough voltage. Do you have any solder wick? I suggest using it after cutting the chip, then pulling the legs out one by one. It's a little bit of a tricky operation but I've done it, so I know it's possible.

limits · « **Reply #314 on:** 20 Apr 2016, 04:48 pm »

I picked up some solder wick the other day, so yes--I will give it a shot. Fifteen teeny-tiny holes...ugh

lacro · « **Reply #315 on:** 20 Apr 2016, 05:08 pm »

A word of caution on removing the chip: If you soldered the legs so the solder flowed from the bottom to the top in excess; solidly anchoring the legs at the top of the via as well as bottom, you will need to be careful to remove as much solder with the wick from both sides of the board before trying to pull the leads out. If you try to just heat one side, and pull on the lead with tweezers, the solder on the opposite side may not have melted, and you risk tearing the via.

This tool works pretty good for removing solder:
http://www.amazon.com/Tenma-21-8240-Vacuum-Desoldering-Iron/dp/B008DJRYIG/ref=sr_1_4?s=hi&ie=UTF8&qid=1461171099&sr=1-4&keywords=electric+solder+sucker

limits · « **Reply #316 on:** 20 Apr 2016, 05:23 pm »

lacro -- Brilliant! Just ordered this. Thank you!

I'll spend 16 bucks for less frustration any day. I used some of the solder wick I had to clean up some of my bad/globby joints earlier this week with only so-so success, so I definitely wasn't looking forward to the chip replacement.

Appreciate the suggestion...

matt_garman · « **Reply #317 on:** 20 Apr 2016, 07:48 pm »

Quote from: Folsom 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).

Hi Jeremy, sorry I didn't follow-up on this sooner. I got your recommendation for the 100uF cap to replace the 10uF as a solution to the power-on thump. I didn't want to place a Mouser order for just one cap, so I rummaged through my parts collection. I found a small 22uF cap that I put in place of the 10uF. There's still a thump, but it's substantially quieter. In fact, it's practically silent. I can still see the speaker drivers moving a bit, but I really don't think it's nearly as bad as it was before. So even 22uF is noticeably better, at least in my case. (I'll order the 100uF cap when I have a critical mass of parts I need.)

Also: when I installed the 22uF cap, I also changed to the heatsink shown in the picture back a page or two. My previous heatsink was not electrically isolated from the tda7297 chip. But I took the time to do it with the new heatsink (exactly per your recommendation, with the rubber screw isolator and mica film). I highly doubt that had anything to do with the power-on thump, but it's an additional change.

Folsom · « **Reply #318 on:** 20 Apr 2016, 07:52 pm »

Yes, you should have less RF with the mica and shoulder washer.

Again the turn on sound was only 15w max, so it was never a harmful thing. It just isn't as pleasant as nothing at all.

lacro · « **Reply #319 on:** 20 Apr 2016, 10:27 pm »

Quote from: matt_garman on 20 Apr 2016, 07:48 pm

Hi Jeremy, sorry I didn't follow-up on this sooner. I got your recommendation for the 100uF cap to replace the 10uF as a solution to the power-on thump. I didn't want to place a Mouser order for just one cap, so I rummaged through my parts collection. I found a small 22uF cap that I put in place of the 10uF. There's still a thump, but it's substantially quieter. In fact, it's practically silent. I can still see the speaker drivers moving a bit, but I really don't think it's nearly as bad as it was before. So even 22uF is noticeably better, at least in my case. (I'll order the 100uF cap when I have a critical mass of parts I need.)

Matt, Did you bypass the existing cap on the bottom as Jeremy suggested or removed/replaced it?