New LM4702 Build

[Boscoe]

Originally Posted by redjr

Hi Boscoe, Thanks. I got it from an eBay vendor in China. Here's a link to the amp module and his site. I've been very pleased with the quality of stuff he offers and his store is full of DIY kits, amps, DACs, enclosures, parts, etc. Some are full kits, others partially assembled, and still others ready to go right out of the box! I've written him several times via email, and he's very helpful and has even allowed me to order some key parts in larger quantities - just for asking. Shipping is expensive, but he has worked with me to combine items for shipping and sent airmail (DLH).

I did visit the xd218.com site once, but found it is mostly in Chinese - even with the help of Google translate. Don't know if he's associated with xd218, or if it's his brick & mortar company in China. Most of what he quotes on his website is in USD, but I have seen a few items listed in pounds.

I've still got a little work to do on the amp, but for the most part it's complete. It took awhile, but I've been in no hurry, and had to wait for several shipments to show up from China. I'm still stocking up on some of the everyday DIY parts, as I hope to build some other things along the way. They're definitely not the Heathkits I used to put together years ago, but it's all fun. - Rick

Edit: One other thing... I believe this amp module can also be purchased in full kit form for a few less $.

Thanks for the info but I'm always cautious when buying from china, I've had a lot of crap in the past.

[redjr]

Originally Posted by Boscoe

Thanks for the info but I'm always cautious when buying from china, I've had a lot of crap in the past.

I have to say I've been impressed with the quality of most of the pieces I've purchased from his site. Except for a recent DAC PCB I purchased (and it wasn't all that bad), the PCBs are top quality, and components appear to be genuine(?). And the assembled modules I've bought seem to be meticulously crafted. I'm sure there's plenty of junk out there, but I see that from other places too. I didn't buy this stuff on a whim, but carefully studied what I wanted, looked at the specs and inspected the pictures. I even emailed the vendor when I had questions, or wanted more clarification. He's actually been very good about following up with tech support from time to time. I'm willing to take a gamble on some things, and so far I'm pleased.

[redjr]

Hi all - Finalizing my build and wanted to include a few more pictures. The final wiring was to bring the power LED out to the front panel. Done! Now with the amp completed I can finally see it with the case close. Rather bland, but overall it will work nicely. I'm satisfied.

I did more testing the past couple of days and today I hooked up a new DAC unit I've built. I used the optical out of my aging Sony D-303 portable CD player. Not any critical listening per se, but wanted to hear a digital signal as the source input. I'm very happy with the sound. And I'm even happier that I can't audibly hear any ground loop hum. Even with several external pre-amps and sources I've tested with it, the amp is dead silent.

[SoIL4x4]

Looks good! How about a pic of the inside.

[redjr]

Originally Posted by SoIL4x4

Looks good! How about a pic of the inside.

Check posts #13 and #26.

I've also posted many more pics here.

[redjr]

Update.....

I later discovered I had a ground loop hum. Not sure how I missed that. It turned out to be how I had wired up the RCA inputs and how they were grounded. I re-did the wiring using both leads from the RCAs to the amp input connectors. I ended up using some standard unshielded, twisted pair from a CAT5 cable. This virtually eliminated all hum. Good results.

[redjr]

Originally Posted by AndrewT

Redjr,
One of the green wire connections to the Main Audio Ground mounted to the chassis floor looks to me to be a link to the Mains PE.

That is wrong.

Change it.

Question...

(1) At some point in the design and layout do all 'grounds' come together - either through a star reference point, star of stars, or buss arrangement - as Dave Davenport illustrates in his excellent article here? Is that a true statement? While his article covers the topic in a much broader sense, he does discuss grounding strategy within a single component.

And I quote,

"4.1 - Grounding Rules

Here are some rules to help you plan your grounding structure. The first four rules are from what we learned about interconnecting equipment.

Rule 1: Each of the following must be connected to the system star ground by one and only one route.
All signal references
All power commons
Shields of non-galvanically isolated single-ended inputs and outputs
Safety ground and chassis. The safety ground and chassis should be thought of as a single entity.
The connection may be direct, or indirect through a star-of-stars or buss. This is expanded upon below.
The safety ground and chassis may be connected to the system star ground through a Safety Loop Breaker Circuit.
The “one and only one” part of this rule precludes ground loops. There is no excuse for a ground loop within a single component...."

I have reworked my grounding strategy to help better isolate my PSU ground and audio signal ground. I'm assuming, because some terminology is loosely used, and Dave often refers to 'system ground'. Is this the ground path between the PSU, amp and other modules that may be inter-connected inside a chassis, and then tied to the star ground at a single point? My audio signal ground from input to the speaker out remains isolated on the amp PCB and speaker protection PCB. They are only connected to the star ground at a single point. I have virtually eliminated all detectable hum that I can noticeably hear, or see without using equipment. I did not employ a Safety Loop Breaker Circuit.

I have included a pic of one of Dave's illustration and believe my grounding topology supports this method.

[AndrewT]

The problem that appears to show in the pic is that the chassis to PE connection is mixed in with all the other returns forming the Main Audio Ground (MAG).
There is nothing wrong with locating the MAG on the chassis.

One of the green wire connections to the Main Audio Ground mounted to the chassis floor looks to me to be a link to the Mains PE.

That is wrong.

It is the long PE to Chassis connection !

I see the Chassis to PE connection as a SAFETY connection and by my reckoning it should be a permanent fixing at the mains input socket. For lowest impedance it must be a short wire. It should not have any other connection tied to it, otherwise there is temptation to dismantle the "permanent" connection that is mandatory.

[redjr]

Originally Posted by AndrewT

The problem that appears to show in the pic is that the chassis to PE connection is mixed in with all the other returns forming the Main Audio Ground (MAG).
There is nothing wrong with locating the MAG on the chassis. It is the long PE to Chassis connection !

I see the Chassis to PE connection as a SAFETY connection and by my reckoning it should be a permanent fixing at the mains input socket. For lowest impedance it must be a short wire. It should not have any other connection tied to it, otherwise there is temptation to dismantle the "permanent" connection that is mandatory.

Ok. I understand what you're saying now. You are correct, there is a long green lead from the IEC connector (PE) to my star point. That's an easy fix. I can simply tie it to the chassis using a much shorter lead. Problem solved!

[SoIL4x4]

If you had a shorter length to the PE can you still connect your return points to the same point? My understanding of what I read in the grounding article is that you could as long as your safety earth to chassis point was secured under its own dedicated nut on the stud. I think part of the issue is that all of your ground points share the same securing nut. It is a safety issue, but should function the same?
I used a similar ground scheme in my amp. All my pcbs have star ground on board and one reference from each board to the chassis. These two references are connected to the ground stud above the dedicated PE connection. My PE ground is a third of the length of my other ground references. This is the method recommended by Peter Daniel. I have not looked at your pcbs but would hope they have a similar on board star ground.