Folsom's great little 7297 Chip Amp

rtate · « **Reply #1000 on:** 6 Dec 2017, 12:31 am »

Yes , there are slots below and the cove is completely vented as well.
I built 2 identical amps just because they were not very expensive and I just like to build stuff.
I have lined the inside of the chassis with duct seal just to deaden it a bit. I will take more pictures later.

I repurposed the heatsinks from some equipment at work. I have had the amp on for about 6 hours and the heat sink still feels like room temperature. Although I am in the garage and it is cooler out here.

Is there a circuit drawing of the amp out there that I could look at ?
I really would like to see what is causing the hum.

Once again a Big Thanks to Folsom for putting this out there for us !!

Folsom · « **Reply #1001 on:** 6 Dec 2017, 01:16 am »

It's just from an incomplete circuit. At that point it is very vulnerable to outside fields like 60hz. With interconnects attached you just have bigger antennas when the circuit isn't complete. Don't worry about it.

Check out the TDA7297 data sheet. There just isn't anything in particular. As long as you followed my instructions for isolation, you're all good.

mlundy57 · « **Reply #1002 on:** 17 Jan 2018, 01:15 am »

The BOM calls for .022uF by-pass caps on the input caps. Would other values like .01 or .047 work? If so, what would the trade offs be?

Mike

Folsom · « **Reply #1003 on:** 17 Jan 2018, 11:01 pm »

Any will work. I wouldn't call any a "trade off" exactly. The value of the capacitance only ultimately matter in the sense that the total amount needs to be high enough to not cut off bass. Once you're there it doens't matter if you have 2 million uf or just 2 uf.

But what you can do is calculate the corner frequency to see where the bypass capacitor will effect. The R value is 25k - 30k, you can try both. The 7297 chip lands somewhere in that range.

mlundy57 · « **Reply #1004 on:** 17 Jan 2018, 11:58 pm »

I’m wondering about the value of the by-pass caps that go under the board.

Folsom · « **Reply #1005 on:** 18 Jan 2018, 10:01 am »

They are in parallel to the ones on top. The capacitance is cumulative. Signal will be split between the two except where one has rolled off and the other has not.

mlundy57 · « **Reply #1006 on:** 18 Jan 2018, 01:48 pm »

Ok. Thanks

WC · « **Reply #1007 on:** 21 Jan 2018, 06:01 pm »

Is there an issue with only using the 7297 to power one of the two channels? I am building way more amps than I have speakers to power, so I was thinking of using only one channel of a stereo amp to power my center channel. Wasn’t sure if the amp would have an issue with it.

Folsom · « **Reply #1008 on:** 21 Jan 2018, 07:07 pm »

That's fine. You can also connect it so both channels provide their current, to the single signal.

zek · « **Reply #1009 on:** 21 Jan 2018, 08:26 pm »

Quote from: Folsom on 21 Jan 2018, 07:07 pm

That's fine. You can also connect it so both channels provide their current, to the single signal.

And how to connect speaker terminals - in parallel (L+ and R+, L- and R-)?

WC · « **Reply #1010 on:** 21 Jan 2018, 09:07 pm »

Ok, can you send the + and - from a balanced signal to the amp and combine the speaker outputs to get a single channel output to the speaker?

Folsom · « **Reply #1011 on:** 21 Jan 2018, 10:15 pm »

Yes the speaker outputs go in parallel. The inputs would be too, but you can use only one set of caps if you tie the channels together after the caps. (look carefully, may not be the holes your think)

Not sure what you mean balanced signal to the amp, it cannot take balanced inputs.

Folsom · « **Reply #1012 on:** 23 Feb 2018, 08:31 pm »

http://www.diyaudio.com/forums/group-buys/309860-folsom-diy7297-amp-antipole-psu-16.html#post5351397

BRN · « **Reply #1013 on:** 5 Mar 2018, 04:28 am »

Finally finished my second Folsom. It only took me 5 months. That’s what happens you have a young child in the house. It takes longer to put things together.

This time I used a Galaxy 4U chasis and an AnTek 18v 200va transformer. I would have purchased the 100va transformer but they were not in stock at the time. I also, ordered the transformer with the steel case.

Everything came together nicely and the amp fired up the first time. I had no mechanical noise like I got with Hammond transformer. The chassis was nice, but not the quality of Landfall Systems.

I really missed having this amp in my system. Even without break in it sounds good.

TrungT · « **Reply #1014 on:** 5 Mar 2018, 04:54 am »

Very nice and clean build

Thanks for sharing.

Folsom · « **Reply #1015 on:** 5 Mar 2018, 06:00 am »

Very nice! I have one small suggestions that is a minor upgrade. It shouldn't take you 5 month...

Between the binding posts of each channel, cut out either a slot between them, or drill a hole large enough between them that there is a clear opening between them. The idea is not to open it up far enough to sacrifice the integrity of the hole, but just enough to stop a turn in the grounding from the balanced outputs by allowing the two fields to touch.

lacro · « **Reply #1016 on:** 5 Mar 2018, 02:53 pm »

Quote from: BRN on 5 Mar 2018, 04:28 am

Finally finished my second Folsom.

Looks really well done... congrats!

lacro · « **Reply #1017 on:** 5 Mar 2018, 02:55 pm »

Quote from: Folsom on 5 Mar 2018, 06:00 am

Between the binding posts of each channel, cut out either a slot between them, or drill a hole large enough between them that there is a clear opening between them. The idea is not to open it up far enough to sacrifice the integrity of the hole, but just enough to stop a turn in the grounding from the balanced outputs by allowing the two fields to touch.

Huh?

limits · « **Reply #1018 on:** 5 Mar 2018, 03:04 pm »

Nice job, Brad--really well done!

Before using this amp, I was never much of a believer in 'improving your source gear'. I was in the 'but they're just ones and zeros' camp, pass the digits and let the DAC do its thing. Well, not anymore! I hear a huge difference when using a usb attached hard drive loaded with flac files/raspberry pi 2/volumio/allo DigiOne/BNC SPDIF/iFi 5 volt SMPS versus spinning discs through my Oppo BluRay (coax SPDIF) to the Folsom 7297. Sorry for the aside, but this is quite a testament to this amp, I think!

Enjoy, Brad

BRN · « **Reply #1019 on:** 5 Mar 2018, 08:54 pm »

Quote from: limits on 5 Mar 2018, 03:04 pm

Nice job, Brad--really well done!

Before using this amp, I was never much of a believer in 'improving your source gear'. I was in the 'but they're just ones and zeros' camp, pass the digits and let the DAC do its thing. Well, not anymore! I hear a huge difference when using a usb attached hard drive loaded with flac files/raspberry pi 2/volumio/allo DigiOne/BNC SPDIF/iFi 5 volt SMPS versus spinning discs through my Oppo BluRay (coax SPDIF) to the Folsom 7297. Sorry for the aside, but this is quite a testament to this amp, I think!

Enjoy, Brad

Limits,

Yes a good amp does put other components in a system under the microscope. The amp I was using is a very nice sounding Decware ZKIT1 with some upgrades. It does have a very clean and sweat midrange sound, but does not have the extension of the Folsom or the imaging. I use a BH Quickie preamp that is very clean. I find that I like a preamp that has gain, as opposed to a buffer or passive control, even though I can't move the volume control much. It adds just a little more in dynamics to the sound. My next is a new preamp kit.

Quote from: Folsom on 5 Mar 2018, 06:00 am

Very nice! I have one small suggestions that is a minor upgrade. It shouldn't take you 5 month...

Between the binding posts of each channel, cut out either a slot between them, or drill a hole large enough between them that there is a clear opening between them. The idea is not to open it up far enough to sacrifice the integrity of the hole, but just enough to stop a turn in the grounding from the balanced outputs by allowing the two fields to touch.

Jeremy,

What is the purpose of cutting a space between each binding post? I assume you mean between the plus and minus of each post.

Thanks,
Brad