Folsom's great little 7297 Chip Amp

Folsom · « **Reply #1100 on:** 15 Mar 2019, 12:57 am »

Nice build!

lacro · « **Reply #1101 on:** 16 Mar 2019, 03:02 pm »

What's the current consensus on transformers that will work? The 16V Hammond in the BOM is really tall (85.6mm) which requires a pretty tall chassis with limited choices available. The 1218 Antec 100VA, 18V and is much shorter in height allowing for many more chassis choices. Is the 18V Antec a viable choice even though the recommended input voltage for the Antipole is 16V?

Folsom · « **Reply #1102 on:** 16 Mar 2019, 04:18 pm »

Its fine

limits · « **Reply #1103 on:** 16 Mar 2019, 04:29 pm »

Quote from: lacro on 16 Mar 2019, 03:02 pm

What's the current consensus on transformers that will work? The 16V Hammond in the BOM is really tall (85.6mm) which requires a pretty tall chassis with limited choices available. The 1218 Antec 100VA, 18V and is much shorter in height allowing for many more chassis choices. Is the 18V Antec a viable choice even though the recommended input voltage for the Antipole is 16V?

Nice build, indeed borism

Larry, I had the 15 volt Antek (200 VA, an2215) in one of my Folsom amps that I recently replaced with their an2218 transformer, and prefer the 18 volt one in there. I also drilled out most of the metal between the binding post for each channel when I had everything apart. I'm liking my 'new' amp...it doesn't seem like having the higher Vout transformer is doing anything detrimental. In fact, there were a few times with the 15 volt transformer in the amp that my speakers bottomed on me, which hasn't happened after the replacement.

I wonder if the 100 VA version would be adequate, as the Hammond is spec.'ed at 130 VA, I believe?

limits

lacro · « **Reply #1104 on:** 16 Mar 2019, 06:03 pm »

Quote from: limits on 16 Mar 2019, 04:29 pm

Nice build, indeed borism

Larry, I had the 15 volt Antek (200 VA, an2215) in one of my Folsom amps that I recently replaced with their an2218 transformer, and prefer the 18 volt one in there. I also drilled out most of the metal between the binding post for each channel when I had everything apart. I'm liking my 'new' amp...it doesn't seem like having the higher Vout transformer is doing anything detrimental. In fact, there were a few times with the 15 volt transformer in the amp that my speakers bottomed on me, which hasn't happened after the replacement.

I wonder if the 100 VA version would be adequate, as the Hammond is spec.'ed at 130 VA, I believe?

limits

Limits, thanks for the heads up. The reason for needing the 1218 over the higher VA 2218 is the size. The 2218 would't fit with the planned chassis. The BOM lists that the trans must be a minimum of 80VA. My concern was whether 18V was too high.

borism · « **Reply #1105 on:** 16 Mar 2019, 09:14 pm »

For what it's worth, I measured my wall outlet voltage at 118V, the Antek 1218 out was 18.5V and the Antipole out was 23.8V DC. It seems to be working just fine.

rockdrummer · « **Reply #1106 on:** 17 Mar 2019, 02:27 pm »

Hi everyone. Happy St Patty's Day!

Couple rookie questions today.
I imported the bom into mouser last night. I would like to replace the caps. Question 1, those would be the input caps correct? The 1.5uF ones?
My 2nd question is related to the first one. Eventually this amp will run mains with servo subs having the bass duty. If I was to give this amp only input signal the subs won't be playing, is that the bypass caps job? Not even sure that those caps in this amp function that way...see? Rookie.

I guess it makes sense to run this amp full signal because i dont even know what my mains will be yet anyway.

And finally, are the power socket cutouts usually the same dimensions if I was to have the enclosure company cut the opening for me? (May save some work by having the diystore cut the back panel for me.)

This thread has been so helpful, but I have bounced around reading it so much, I have defaulted to just asking...

Thanks for any advice.
Ben

Folsom · « **Reply #1107 on:** 17 Mar 2019, 04:46 pm »

1.5uf are the input caps.

You could use smaller ones to limit low frequency extension. You would calculate what you need basedxon 25-30k resistance for the corner frequency with a capacitor.

You want to get the white paper with dimensions to give to the machinest for whatever IEC socket you use.

lacro · « **Reply #1108 on:** 17 Mar 2019, 05:15 pm »

I like to use Neutrik Powercons for AC input instead of the standard IEC connector. The hole for the chassis connector is an easy to make 15/16" round hole. You will have to make your own cord for the power plug. The Powercon offers a very secure connection compared to IEC connectors.

https://www.mouser.com/ProductDetail/Neutrik/NAC3FCA?qs=sGAEpiMZZMtiRBiUbHlRZXrdchW6pJUT93uYqN%2FSFGw%3D

https://www.mouser.com/ProductDetail/Neutrik/NAC3MPA-1?qs=sGAEpiMZZMtiRBiUbHlRZaspORIhCQLubgktMdJEqK0%3D

Here's the hole(s) cut layout for the chassis connector:

lacro · « **Reply #1109 on:** 17 Mar 2019, 06:44 pm »

Quote from: borism on 16 Mar 2019, 09:14 pm

For what it's worth, I measured my wall outlet voltage at 118V, the Antek 1218 out was 18.5V and the Antipole out was 23.8V DC. It seems to be working just fine.

Would you please measure the exact diameter of your Antek 1218. I know the data sheet states 3.9" Just want to know if it's actually larger.

lacro · « **Reply #1110 on:** 17 Mar 2019, 08:59 pm »

Jeremy,
In your build photos I see you used shorter capacitors for the big ones on the Antipole PS. Are they something that you would recommend? They would help gain a lot of room in the chassis. If so part # please.

Folsom · « **Reply #1111 on:** 18 Mar 2019, 03:49 pm »

No, they're too small. I painfully added more to that amp after the fact.

rockdrummer · « **Reply #1112 on:** 18 Mar 2019, 10:57 pm »

Hey there, I'm still coming up with questions.

Taking the neutrik connector approach.
I see the ratings on those connectors is 20A and 250v. I can't find an AC plug for the other end of the power cable with those same ratings. I need to stay affordable. I see lots of 15A and 125v, and I'm sure the answer is obvious but not to me. Also any advice for the actual cable brand some use would be great.
Thanks
Ben

Also, I certainly am likely over-thinking some of this. I appreciate it.

lacro · « **Reply #1113 on:** 18 Mar 2019, 11:10 pm »

15A plug is all you need. I used 14ga wire for my cord.

rockdrummer · « **Reply #1114 on:** 18 Mar 2019, 11:12 pm »

Terrific, thank you lacro!
Ben

borism · « **Reply #1115 on:** 18 Mar 2019, 11:46 pm »

Lacro, I measured the diameter of my Antek 1218 to be between 3 3/4 and 3 7/8".

Here is my amp with vinyl lettering.

lacro · « **Reply #1116 on:** 19 Mar 2019, 04:22 pm »

Thanks for getting back. Tell me more about the vinyl lettering. When I built my first Folsom amp I printed my front panel lettering on tissue paper, and buried it in varnish, but the vinyl letters look good on aluminum.

borism · « **Reply #1117 on:** 19 Mar 2019, 05:37 pm »

Lacro, I was looking for a quick and inexpensive solution. The vinyl letters come in different sizes and colors. I chose 1/4" black and white.
Here is a link:
https://www.amazon.com/gp/product/B000GP08K6/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

rockdrummer · « **Reply #1118 on:** 25 Mar 2019, 05:13 pm »

Hey everyone. I am waiting on some parts to be delivered, and will need to start layout planning soon. But I am still asking questions.

Up front, I appreciate all the help.

1. Can my divider wall have holes in it? I was going to order a chassis from DIYstore, and use the riser walls to separate the boards. They have a grid of holes pre drilled in them. Will those play the role of divider or do I need a solid sheet of metal for it to do it's job?

2. I see some people are using terminal blocks inside the amp to connect transformers to the boards. Also, I think that maybe where some switches are attached. I wasn't aware of those and wonder if I need to try to use one.

3. Can I use solid core 16 gauge wire everywhere in the amp? Or do i need to use signal wire and power supply wire that is different gauges? Also, I wouldn't know how to choose since I don't know if it matters or not.

Antek transformer wiring and switch/LED questions to come later

Thanks for any advice,
Ben

WireNut · « **Reply #1119 on:** 25 Mar 2019, 06:55 pm »

Hi Jeremy,

Just wondering what the 2 black looking parts are that are connected to the RCA's? Bleed resistors maybe?

I didn't see them in the BOM.

See Pic.

Thanks.