Folsom's great little 7297 Chip Amp

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drew_t

  • Jr. Member
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Re: Folsom's great little 7297 Chip Amp
« Reply #1320 on: 20 Jul 2020, 01:36 am »
Newbie problems....

Haven't run mine in a while, and when I started it, it has a nasty ground hum. It is somewhat under control when playing music from my macbook pro unconnected, but gets worse if I touch the metal of the computer and much worse if I plug it in to the wall.
Where do I search and what do I search for..?

Since it worked OK previously, I would suspect it's just something simple like a plug or jack that isn't making good contact, or a flaky cable.

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #1321 on: 20 Jul 2020, 02:03 am »
Since it worked OK previously, I would suspect it's just something simple like a plug or jack that isn't making good contact, or a flaky cable.

That's pretty typical. A bad connection somewhere is very commonly behind such noise.

vilding

  • Jr. Member
  • Posts: 94
  • Musician. Audiophile on a budget.
Re: Folsom's great little 7297 Chip Amp
« Reply #1322 on: 20 Jul 2020, 09:04 am »
You guys have any good tips on searching for it? Where to measure and what to look for? :) Can't find any cold joints or visually flaky cables.


ostvald

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Re: Folsom's great little 7297 Chip Amp
« Reply #1323 on: 23 Jul 2020, 05:21 am »
Hi guys, I have some build-related questions.

First, I have these type of RCA connectors:
.
Does it still make any sense to drill a hole in the chassis between them, as was advised to do here in this thread?

Another thing is - what would be your recommended way of mounting the pcb to the chassis, specifically the type of stand-offs?
Is it OK to use metal standoffs and bolts ("grounding" the pcb to the chassis, is there any grounding layer in the pcb connected to mounting holes?), or
is it better to isolate the PCB from chassis with plastic (shoulder) washers, or mount on plastic stand-offs? Both PSU and the AMP PCBs are the subject.

Thanks!

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #1324 on: 24 Jul 2020, 03:40 am »
You'd have to cut through the connector housing as well all the way to the plastic.

7297 and psu holes don't connect to ground.

ostvald

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  • Posts: 12
Re: Folsom's great little 7297 Chip Amp
« Reply #1325 on: 24 Jul 2020, 10:11 am »
You'd have to cut through the connector housing as well all the way to the plastic.

7297 and psu holes don't connect to ground.

Ouch.. Don't have suitable tools, will probably just destroy them, so will leave it like this for the build

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #1326 on: 25 Jul 2020, 03:10 am »
Use different RCA’s?

ostvald

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Re: Folsom's great little 7297 Chip Amp
« Reply #1327 on: 25 Jul 2020, 11:09 am »
Use different RCA’s?

Neutriks where kind of one of your recomendations from the Construction Notes, Furutechs were a bit more expensive and not supplied by Mouser.
Could you please maybe recommend any other RCAs (to be ordered from Mouser)?

HT cOz

Re: Folsom's great little 7297 Chip Amp
« Reply #1328 on: 25 Jul 2020, 03:39 pm »
Hi guys, I have some build-related questions.

First, I have these type of RCA connectors:
.
Does it still make any sense to drill a hole in the chassis between them, as was advised to do here in this thread?

Another thing is - what would be your recommended way of mounting the pcb to the chassis, specifically the type of stand-offs?
Is it OK to use metal standoffs and bolts ("grounding" the pcb to the chassis, is there any grounding layer in the pcb connected to mounting holes?), or
is it better to isolate the PCB from chassis with plastic (shoulder) washers, or mount on plastic stand-offs? Both PSU and the AMP PCBs are the subject.

Thanks!

We might be able to help but it's hard to understand your question.  Why not use these as designed?

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #1329 on: 25 Jul 2020, 05:16 pm »
Neutriks where kind of one of your recomendations from the Construction Notes, Furutechs were a bit more expensive and not supplied by Mouser.
Could you please maybe recommend any other RCAs (to be ordered from Mouser)?

I admit it needs an update. You'll still be happy with those. But if you were wanting to go for the slots, I wanted to help.

NYS367-2
and
NYS367-9

would be compatible with a slot/hole.

ostvald

  • Jr. Member
  • Posts: 12
Re: Folsom's great little 7297 Chip Amp
« Reply #1330 on: 8 Aug 2020, 10:19 am »
More photos from my build!


24 mm hole for a push button switch


PSU board power up


Packed


Bottom up



Front view, still no decals. On the background:
NORD NC500 SE MKII mono block,
RME ADI-2 DAC,
DIY Discowery-12W speakers

It turned up I messed 100uF cap polarity and I need to re-assemble / resolder the amp board (thanks 2 Jeremy for instant reply with the solution!) -
currently the amp plays for several minutes and then goes to mute, so no listening impressions yet.
I am to compare it vs my NC500 mono blocks, btw  :roll:

ostvald

  • Jr. Member
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Re: Folsom's great little 7297 Chip Amp
« Reply #1331 on: 9 Aug 2020, 08:47 pm »
Ok, so it's a hi-fidelity quality, that's for sure :icon_surprised:

Compared to the NCore, it's more musical - with its downsides, but pleasant to listen to :)
Continuing the burning-in - it gets better.

Jeremy, could you give an idea what are the burning in timings for the amp?

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #1332 on: 10 Aug 2020, 05:44 pm »
At 20 hours it'll sound a lot like it will continue to sound but the input capacitors might take a fair bit more like 80hrs to really finish.

ostvald

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Re: Folsom's great little 7297 Chip Amp
« Reply #1333 on: 16 Aug 2020, 09:23 am »
As I promised before, I feel like ready to share my listening impressions of Folsom's 7297 chip amp.

First, let's clarify the costs. I reside in Israel, so the following table includes shipment and tax prices for Israel. The overhead is basically costs which are not directly related to the build (like tools, additional parts that were not needed, or solder tin that I bought a lot, cos you can't buy just a bit), or additional costs that could have been avoided, like additional boards components being sent. Here is the table:



Let's say, it's a $600 amp for me in parts (shipped to IL, $440 - no shipment, no tax) + my labor, which was about ~60 hours, as far as I can estimate it.
60 hours is a lot, but this is basically my first amp build, and it was a pleasure to do.

It's about 50 hours of burn-in passed now, and I'm mainly talking about 10-15 last hours of listening. You really need to burn it in at least 20 hours like Jeremy already wrote here, don't even listen to it before that.

SO, what does it sound like?
Well, in short, it's very nice, especially for the price! For me it sounds "sweet", with pretty much apparent solid state signature I was looking for.

My listening setup is DIY Troels Gravesen Discovery-12W speakers: http://www.troelsgravesen.dk/Discovery-12W_Ilia.htm which are very nice 800 EUR alone in parts (no shipment no tax no cabinet no labor) desktop monitors
The source is digital - RME ADI-2 DAC https://www.rme-audio.de/adi-2-dac.html (about $1150)
I also own Audeze LCD-X headphones to "verify" what I hear. Together with the DAC's headphone amp, these are analytical monsters - https://www.audeze.com/products/lcd-x (about $1200)
I'm mainly comparing the build with my Nord ONE SE NC500MB MKII mono blocks, which are class D NCore 500 based power amps - https://www.nordacoustics.co.uk/product-page/nord-one-se-up-nc500mb-mkii-mono-block-single  (~$1000 each - ~$2000 for stereo)

I basically have a desktop setup, so I intend to use the 7297 on my desktop, and the amp has way enough power for this application.

So what do I mean by "sweet"?
I will do measurements later, but it looks like compared to my monoblocks it has those higher 2-nd and 3-rd harmonics, which make the sound rich, pretty dense hence still clear. It has very nice layering. Because of the presentation it's much easier to perceive it, as opposed to my monoblocks, which are sharper. Generally, my monoblocks are much more "analytical", while 7297 is more "musical", so it is pleasant to listen to. It sounds super great with soft rock, jazz, blues. Vocals are also great.

The downsides, well.. There are some. First, highs are (juuuust a bit rolled off?) not that crisp as on NCores. On the Ncores I even put an "SD Slow" filter on my DAC when I want a longer listening and not analytical session. On the 7297 amp I put "SD Sharp", otherwise it starts to be a bit "muddy". The base is not that tight as on NCores, it sounds a bit relaxed, that especially noticed with electronic music tracks. Though, it's not distorted, even on a decent volume. Few times while I was listening to some not thoroughly known tracks I heard a distortion and was like "Ahaa!", but after rechecking with my headphones it always turned out the distortion was in the record itself (and I was able to hear it "as is" with the amp!). I must also say the base improved a lot while the burn in. I was even setting +1.5 Db on the DAC to match my regular base expectation in the beginning, but now it is set back to 0Db, so I kind of expect it to improve a bit more, but the gap is still big. NCores are holding those D12s by the throat. Looks like the NCores have a sharper step response and a greater damping factor. I'm not really talking about the lower lower base cos my speakers don't really produce it. Still, the base is nice.

Summing up again, it's a very decent amp for the money! It sounds sweet on the midrange midbass, which was my main goal, the presentation I lacked with my NCores.
It's clear, the highs are precise hence not analytically bright, the base is pretty strong and also sweet and natural which adds up to the space perception and "drive" when is appropriate.
It's not a loud deep house party amp, but it was not meant to. In general, I'm indeed pretty much satisfied.

I'm looking forward to building Folsoms 7293 chip amp - https://www.diyaudio.com/forums/group-buys/357577-gb-2-folsom-ec7293-pvi-powered-frontend-amplifier-60-120w-8-4ohm-0-0005-thd.html
It was told to be "better in every single way" and I have no reason not to believe it. I suppose I would be able to drive floor standing speakers with inarguable base authority.

Jeremy, thank you very much for everything - your guidance, assistance, responsiveness and a great design!
Also, thanks everybody for the help and a great community we have.
I was very helped and inspired by other people's builds.

Thank you!

 
« Last Edit: 16 Aug 2020, 03:21 pm by ostvald »

Ambio

Re: Folsom's great little 7297 Chip Amp
« Reply #1334 on: 8 Oct 2020, 08:54 pm »
Hi all, I have been having fun learning about this amp via the eBay version, preliminary to build folsoms amp. This thread helping enormously so thanks everyone! Here is a handy tool if you can obtain them. There perfect for cutting circular holes in metal neatly and quickly.




I have my work cut-out for me :lol:

vilding

  • Jr. Member
  • Posts: 94
  • Musician. Audiophile on a budget.
Re: Folsom's great little 7297 Chip Amp
« Reply #1335 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... :´(

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #1336 on: 15 Oct 2020, 09:31 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... :´(


Maybe some hi-res photos would help see what's up.