Folsom's great little 7297 Chip Amp

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lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #840 on: 10 Jul 2017, 11:50 pm »
In case anyone wants some boards, this just started.

That's great news! Anybody that has been interested in building one of these great amps, better jump on the group buy.

jmc207

Re: Folsom's great little 7297 Chip Amp
« Reply #841 on: 11 Jul 2017, 11:25 pm »
That's great news! Anybody that has been interested in building one of these great amps, better jump on the group buy.


I'll second this great news!  http://www.diyaudio.com/forums/group-buys/309860-folsom-diy7297-amp-antipole-psu.html#post5128286

WC

Re: Folsom's great little 7297 Chip Amp
« Reply #842 on: 12 Jul 2017, 03:26 am »
Haven't even finished mine current amp build, but I put in for another set of boards. I bought two of the amp chips, so I guess I should be able to use them both now.

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #843 on: 12 Jul 2017, 09:17 pm »
Pro tip:

The 7297 can be light in the bass if a speaker is ported/vented with too low of QES (too much physical dampening is bad too). The simple solution is to take the speaker impedance (4 , 6 , 8 ohm) and divide by 5.45 and get a resistor of that value to insert in series with the speaker. At least as of so far that's the conclusion. If you know the spec's on the driver, and QES is in the .30's range, try a resistor and less stuffing for ported/vented.

Odal3

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Re: Folsom's great little 7297 Chip Amp
« Reply #844 on: 12 Jul 2017, 09:36 pm »
Great to see that you have a group buy going.  :thumb:

indosmokejon

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Re: Folsom's great little 7297 Chip Amp
« Reply #845 on: 13 Jul 2017, 06:31 pm »
For ebag4. The antek toroidal transformers that I bought and used for my two builds work flawlessly and produce not the slightest hum. I am pretty sure I used the as-1215 I believe???  Here is a link.
http://www.antekinc.com/as-1215/

Also, I think it was KR500 that complimented me on my finished build a page or two back, thanks for the praise!!!

ebag4

Re: Folsom's great little 7297 Chip Amp
« Reply #846 on: 14 Jul 2017, 12:29 am »
For ebag4. The antek toroidal transformers that I bought and used for my two builds work flawlessly and produce not the slightest hum. I am pretty sure I used the as-1215 I believe???  Here is a link.
http://www.antekinc.com/as-1215/

Also, I think it was KR500 that complimented me on my finished build a page or two back, thanks for the praise!!!
Thanks for that, much appreciated.  I see they have a 15v and 20v, I wonder if there is any reason to go above the recommended 16v since it appears he is taking it to 23 V:

Battery power use 24v, SMPS can be as low as 21v, and transformer should be 16v to get rectified around 23-24v.

Best,
Ed

BRN

Re: Folsom's great little 7297 Chip Amp
« Reply #847 on: 14 Jul 2017, 07:17 pm »
Thanks for that, much appreciated.  I see they have a 15v and 20v, I wonder if there is any reason to go above the recommended 16v since it appears he is taking it to 23 V:

Best,
Ed
You need to be careful about how much voltage you are providing the amp, because the regulators my not be able to handle the higher voltage.

indosmokejon,

Thanks for the link to the power tansformer. I think that I will use it for my next build. From my calculation it should provide over 21.7VDC.

Brad

Plund

Re: Folsom's great little 7297 Chip Amp
« Reply #848 on: 16 Jul 2017, 01:36 pm »
Lacro,  earlier you posted about completing your fourth Folsom amp and how noticeably better sounding it was compared to the previous three.  What do you attribute most of the improvement to...the large Lundahl xformer?  ...the Clarity input caps?

Looking forward to my 1st Folsom amp build,
Pete

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #849 on: 16 Jul 2017, 02:24 pm »
Lacro,  earlier you posted about completing your fourth Folsom amp and how noticeably better sounding it was compared to the previous three.  What do you attribute most of the improvement to...the large Lundahl xformer?  ...the Clarity input caps?

Looking forward to my 1st Folsom amp build,
Pete

Pete,
If you read my post, you will see that ALL previous builds were powered by SMPS's, not the Antipole PS. I feel the single greatest improvement is the Antipole PS, but powering it with the overkill Lundahl transformer has to be working some magic too. The input caps upgrade  are probably adding something as well. There are dozens of choices for the input and bypass caps to experiment with, limited only by your wallet.

Plund

Re: Folsom's great little 7297 Chip Amp
« Reply #850 on: 16 Jul 2017, 10:35 pm »
Thanks Lacro...so, the Antipole is the magic.  Good to hear that the "cheap and cheerful" version of the Antipole is also magical.   I am not sure my ears are golden enough to hear or appreciate any added benefit that the rolls royce-esque components might add anyway.

ebag4

Re: Folsom's great little 7297 Chip Amp
« Reply #851 on: 22 Jul 2017, 10:29 pm »
For ebag4. The antek toroidal transformers that I bought and used for my two builds work flawlessly and produce not the slightest hum. I am pretty sure I used the as-1215 I believe???  Here is a link.
http://www.antekinc.com/as-1215/
Thanks again indosmokejon/BRN, I recieved the Antek as-1215, it is now installed.  It is dead quiet, the amp is completely quiet .  This one is for my son but I have another set of the boards on order from Folsom.  Happy camper!

Best,
Ed

Quick question for anyone, the LED in my switch is rated at 12VDC, it is the automotive type. I put the recommended 680 ohms resistor in  series  with the positive lead, I am picking up the power to the switch from the output of the Antipole.  The LED is incredibly bright, what are my options to reduce the brightness?



Switch Specs
Specifications:
Head diameter: 7/8" (22mm)
Mounting hole size: 3/4" (19mm)
Depth inc contacts: 1.5" (38mm)
Switch combination: 1NO1NC
Operation types: Latching
Switch rating: 5A/250VAC
LED voltage: 12V DC
LED color: Red
Head shape: Flat
Enclosure material: Stainless Steel
Protection level: IP67, IK10

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #852 on: 23 Jul 2017, 12:04 am »


Quick question for anyone, the LED in my switch is rated at 12VDC, it is the automotive type. I put the recommended 680 ohms resistor in  series  with the positive lead, I am picking up the power to the switch from the output of the Antipole.  The LED is incredibly bright, what are my options to reduce the brightness?


Switch Specs
Specifications:
Head diameter: 7/8" (22mm)
Mounting hole size: 3/4" (19mm)
Depth inc contacts: 1.5" (38mm)
Switch combination: 1NO1NC
Operation types: Latching
Switch rating: 5A/250VAC
LED voltage: 12V DC
LED color: Red
Head shape: Flat
Enclosure material: Stainless Steel
Protection level: IP67, IK10

Ed,
 I have the same or similar switch, and I used a 10 or 15K trim pot (variable resistor) to fine tune the illumination I liked, then checked the pot's resistance with my DMM. I ended up with 8k resistance needed, and I didn't have that value resistor so I used 2 resistors in series to get to 8K. Also, I wired my push button switch so power ON is with the switch out, and OFF is in. I liked the way the light looks when it's in the out position. Hope this helps....

ebag4

Re: Folsom's great little 7297 Chip Amp
« Reply #853 on: 23 Jul 2017, 12:09 am »
Thanks Lacro, exactly the info I needed.

Best,
Ed

limits

Re: Folsom's great little 7297 Chip Amp
« Reply #854 on: 16 Aug 2017, 03:52 pm »
Hi Folsom:

Remarkably quiet around here lately...everyone must be building up their new boards  :D

I had a couple questions about changes you made in the BOM from the first run of boards to the current round:

1) The OSCON cap bank change from 330 to 560 uf--does this affect the sound of the amp at all, or does it simply provide a little more headroom/reserve capacitance to the 7297?

2) In the DIY Audio thread (announcing the new batch of boards http://www.diyaudio.com/forums/group-buys/309860-folsom-diy7297-amp-antipole-psu.html#post5128286) you wrote:
'These next print of boards will feature a BOM with an updated TL431 that's even lower noise. The old TI one sounds a little warmer for who's ever interested.' I ended up ordering both the old TI part and the ON part, and am not sure which one I will use...I know you described the change in the BOM pretty well, just wondering if you have any further insight into this change?

3) For my second Folsom 7297 build (with the new boards), I am going to use a different transformer (Antek AS-2215) and incorporate a Felix line conditioner in the amp case in front of the primaries of the transformer. The ones I have built in the past did not use the 1.8 kOhm 3 watt resistor bypassing the coils of the CMC, which you mention in your construction notes. What is the function of adding this resistor?

Thanks for any insight you may have on my ramblings  :lol:

limits

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #855 on: 17 Aug 2017, 05:43 pm »
1. Not sure anyone will hear the difference, just a little more headroom.

2. TL431.. one sounds a little warmer, one sounds a little more clear. Thats it.

3. Don't put any caps post CMC. What size CMC are you going to use? 1.8k may not be a good value. The resistors stop the CMC from struggling with capacitence on the AC mostly, but help it with other problematic stuff riding on it that can filthy up the CMC too much.

limits

Re: Folsom's great little 7297 Chip Amp
« Reply #856 on: 17 Aug 2017, 06:28 pm »
Hi Folsom:

Thanks for the response. I was planning on using the Bourns 8120 RC. Do you think the 1.8kOhm/3 watt resistor would be suitable with this CMC? I was planning on using 1 uf, 0.1 uf, and 0.01 uf x-caps in front of the CMC.

So...kind of a half Felix (no caps past the CMC)? Interesting. Most of the examples I have seen where people have incorporated a felix into a case have used the audiocircle pcb's and have caps after the choke, but I could certainly leave these out.

Thanks again;
limits

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #857 on: 17 Aug 2017, 09:07 pm »
Those are good R values for that CMC.

I know about having the following caps on the CMC's, seems like a good idea on the 115v AC side, but really isn't.

BRN

Re: Folsom's great little 7297 Chip Amp
« Reply #858 on: 18 Aug 2017, 04:22 am »


Ed,

The chassis looks nice. Where did you get it?

Thanks,
Brad

rtate

Re: Folsom's great little 7297 Chip Amp
« Reply #859 on: 18 Aug 2017, 10:59 am »
Got my boards here in Canada yesterday , thanks Jeremy !!   :green:
I have a couple of decisions on parts selection and would like some opinions if I may.

1) for the antipole transformer, some have used a toroid with 18V secondary's, is there any advantage to this or any risk with the higher voltage ? Is there a performance loss with the 15V secondary's instead of the spec'd 16V ?

2)In pictures I have noticed 2 different styles of chokes, one more square and one round. Is one better than the other?

3)I would like to hear from those who have upgraded their caps to see what people are using.
I realize that it's a personal/subjective thing only limited to ones wallet...  :wink:

Keep those build pictures coming, they are really helpful and inspiring !!