Folsom's great little 7297 Chip Amp

Folsom · « **Reply #240 on:** 9 Mar 2016, 06:19 am »

It's just how it ends up due to the size of the Antipole board. I suppose you could reduce it by making the enclosure tall and standing the Antipole up, it would probably be around 8" tall, or more with feet, while having a short depth. I think it'd look weird, sort of a pillar. You could then turn the amp side ways and have the speaker terminals close together. Maybe I'll draw a picture.

KR500 · « **Reply #241 on:** 10 Mar 2016, 11:41 pm »

Just wondering what folks are using as a 90 bracket to attach and support the Antipole PCB upright in the case ?
I just got the 3 X 2.75" heat sink from Heatsink USA , well machined 8 oz. piece of aluminum and have to determine the best way to anchor that to the case so it doesn't put a load on the chip . Best practice for this ?

Folsom · « **Reply #242 on:** 11 Mar 2016, 01:02 am »

I'm not sure I follow with 90* brackets? My builds use standoffs for PCB, and the heatsink is either drilled and tapped on the bottom or on the face so it can be bolted to the enclosure wall (aluminum).

G Georgopoulos · « **Reply #243 on:** 11 Mar 2016, 02:32 am »

Jeremy

you're doing great,your pcbs are great,enclosure layout great,as a finished amp looks great...

all the best Mate...

ps:if you want to make it even better give some time to yourself to do it,"great things take time"

KR500 · « **Reply #244 on:** 11 Mar 2016, 11:01 pm »

Thanks for your reply Jeremy , I do have standoffs for the PCB to lay flat but just haven't stood a PCB on end yet . I just wondered how you attached the vertical PCB to the case when you build .
I'll drill out and tap the heat sink to mount it per your suggestion .
Should the transformer have a rubber washer between it and the case when attaching it with nut and bolt ? or is it not nessa'

Folsom · « **Reply #245 on:** 12 Mar 2016, 01:13 am »

The transformer does do well with some rubber washers. EI cores have less noise but like to hum a little bit.

The Antipole PSU PCB mounting can be done with using couplers that receive an end of a bolt from each side, and several nuts to secure everything: against PCB board, against coupler, and against chassis wall. In fact two and washers may be advisable for the ones against the chassis wall and PCB board. You can lock them together.

sorinv · « **Reply #246 on:** 14 Mar 2016, 11:15 am »

Hey Folsom, do you still sell these boards? If you do, how can I get one?

Thanks

Folsom · « **Reply #247 on:** 14 Mar 2016, 04:23 pm »

PM (as you did)

matt_garman · « **Reply #248 on:** 16 Mar 2016, 10:31 pm »

Quote from: Folsom on 7 Mar 2016, 12:57 am

Also it's best to have some distance from transformer and amplifier board.

I recently performed an experiment, albeit unintentionally, that demonstrated the effects of transformer EMI leakage...

I'm building a DAC based on the Soekris dam1021 board. I'm powering it with a 15W R-core transformer and +/- 12V DC supply. But the shipping on that R-core was painfully slow, and the dam1021 will also run directly off a fairly wide range of AC power. So I borrowed the Hammond 185E16 from my Folsom tda7297 build, using it's parallel 8V AC outputs to power the DAC board.

It worked, but I had random dropouts in the music. In particular, the DAC board's status LED would occasionally flash to indicate loss of signal lock.

I posed this question to the big diyaudio thread about this board, and the designer suggested i2s signal integrity issues. My on-desk implementation of this board had wires coupling my Amanero (usb to i2s device) to the dam1021 board. This coupling is via the i2s protocol, and it's really designed for super-short wire runs (generally on board traces, or wires no longer than 10cm in length). My wires were indeed exactly 10cm in length, and I saw plenty of other people with effectively the same setup (but not reporting these drops).

Well, I finally got the R-core transformer, and replaced the Hammond with that plus the DC supply. I ran the thing non-stop all weekend without a single drop or signal loss! (I have the DAC logging to a serial console so I can check for issues even if I'm not listening to it.)

The distance between the Hammond transformer and i2s wires, versus the distance between the R-core and i2s wires is basically the same. The wires I had running from the Hammond to the dam1021 weren't long enough to see how far away the transformer needed to be to stop affecting signal integrity.

Bringing this back on topic: I don't know how sensitive the tda7297 is to EMI, but based on my recent experience, some distance between the psu+amp PCB and transformer can't hurt. Or maybe a mu-metal cover (if you can find one)? Or perhaps an R-core transformer? (If you can even find a big enough one and are willing to pay!) Dunno if a toroid is appropriate for this amp or not?

Folsom · « **Reply #249 on:** 16 Mar 2016, 11:03 pm »

R cores are good. They cost more and aren't available from Mouser. I tried to make everything from mouser, for ease of use.

KR500 · « **Reply #250 on:** 16 Mar 2016, 11:27 pm »

Jeez , I feel like Captain Obvious after asking above about rubber insulation when mounting the transformer ( it's addressed early in this thread ) and size of the heat sink ( it's listed in the construction page from Folsom that came )
Too many hours at work this month dimming my bulb
Anyway when mentioning the term 90 in my last post .....I meant the right angle mounting brackets to attach the Antipole board vertically . I can see them in the photo of the board when I zoom in on the amp insides .
The 90 is a holdover term from my previous job.

Folsom · « **Reply #251 on:** 17 Mar 2016, 12:35 am »

You don't have to use 90° . As I was saying, you can mount it off a vertical panel as well.

Odal3 · « **Reply #252 on:** 17 Mar 2016, 01:58 am »

Matt - curious the learn more about your Soekris DAC build. How does the 7297 sound with it?

To not get off topic here, do you have another thread on AC somewhere explaining your build? I started to read the DIY thread a while ago but coming late to long threads is a bit overwhelming sometimes...

matt_garman · « **Reply #253 on:** 17 Mar 2016, 04:29 pm »

Quote from: Odal3 on 17 Mar 2016, 01:58 am

Matt - curious the learn more about your Soekris DAC build. How does the 7297 sound with it?

I actually haven't heard Folsom's 7297 with any DAC, as I think I made some mistake when building it. Haven't put in enough time to fix it yet (though Jeremy has been quite generous with his time giving tips and suggestions).

Quote from: Odal3 on 17 Mar 2016, 01:58 am

To not get off topic here, do you have another thread on AC somewhere explaining your build? I started to read the DIY thread a while ago but coming late to long threads is a bit overwhelming sometimes...

I don't have any build thread (here or anywhere else), as my "build" is still just boards and wires in a mess on my desk.

And my plans are pretty pedestrian (i.e. nothing fancy). That said, I'll try to do a little writeup here when the project is farther along, as I think the finished product will be "Cheap and Cheerful". (Similar to what I did with the tda1387 x8 dac.)

But the short version is: so far I really like what I hear, though I haven't had an opportunity for a long critical listening session (and the "build" is too messy to easily switch between other DACs for comparisons). But the most basic config is almost trivial to assemble (if you can do the Folsom 7297 board, you can do a dam1021 build). Perhaps the biggest selling point is that it presents so many options (i.e. make it as simple or fancy as you want).

Oh, the diyAudio thread is a bit long. See glt's blog for a more accessible overview of the dam1021. Near the bottom of the linked page, he gives links to other posts he's done on it.

Apologies for the off-topic digression!

Odal3 · « **Reply #254 on:** 17 Mar 2016, 04:49 pm »

Thanks for the info - you need to hurry getting it fixed because it's really good.

I'm actually thinking of ordering a second one.

Folsom · « **Reply #255 on:** 17 Mar 2016, 05:10 pm »

I've seen some pics of Matt's. Best guess is an arc fried a transistor, from connecting a charged PSU capacitor.

He did a nice job soldering, so I sent him a new small transistor to check with before anything drastic could be looked at (shipping/chip replacement for example)

lacro · « **Reply #256 on:** 18 Mar 2016, 05:00 pm »

What is the ideal voltage for SMPS's I haven't yet committed to building the Antipole PS, so I have a couple of 24V SMPS (bricks) one is delivering 24v, the other is 24.4V. So... is a 24v SMPS too high voltage to use?

Folsom · « **Reply #257 on:** 18 Mar 2016, 05:21 pm »

Those will be fine.

lacro · « **Reply #258 on:** 20 Mar 2016, 03:27 pm »

A couple of Chassis questions:

One: Do the standoff holes in the board have to be insulated from an earth grounded metal chassis? My chassis has PCB slide-in grooves (115mm) so I won't be using stand-off's, but the holes in the board could make contact with the chassis groove unless I isolate them.

Two: If I mount the Transistor that has the heat sink to a bulkhead divider to act as a heat sink, does it have to be insulated with a ceramic washer and mica sheet if this metal divider is grounded?

Folsom · « **Reply #259 on:** 20 Mar 2016, 05:58 pm »

1. No, not less you tried to drill them out or something odd.

2. No, it has connection between tab and any of its legs.

3. Please post a pic when you're done, I'm curious.