One component I forgot to mention: RG should be a low value 1/2W resistor, either 0R or 1R. If you would rather take the signal ground directly to your chassis star ground, you can simply run an additional ground wire from the RG hole closest to the LM4702 chip (which is the signal star ground on the PCB) to your ground. Since the signal ground and power grounds will now be separated, I don't think you should have any problems.
I haven't had any problems using a 1R resistor for RG, but if you experience any hum this would be my first suggestion.
David
I haven't had any problems using a 1R resistor for RG, but if you experience any hum this would be my first suggestion.
David
Brett, and others:
I am putting together a few brief comments and suggestions regarding the board and I should be done sometime this weekend. I'll put in some suggestions as to my favorite component configurations and a simple darlington output stage. Most of what I have been playing with lately has been based off of the new information from the National AN-1490 application note. Most of the suggestions they have in the note are easily implimented in these boards, but a couple of things aren't too obvious, so I want to make sure everything works before I tell others to try things!
I am putting together a few brief comments and suggestions regarding the board and I should be done sometime this weekend. I'll put in some suggestions as to my favorite component configurations and a simple darlington output stage. Most of what I have been playing with lately has been based off of the new information from the National AN-1490 application note. Most of the suggestions they have in the note are easily implimented in these boards, but a couple of things aren't too obvious, so I want to make sure everything works before I tell others to try things!
My logic on the ground plane was pretty specific: I wanted the signal grounds in a star configuration connected to a power ground plane via a resistor to avoid any hum while keeping the benefits of a ground plane. In my testing I haven't noticed anything goofy in terms of hum or anything. I still haven't done critical tests, but nothing has shown up on the scope.
David
David
Star ground
I'm certainly no guru and no next to nothing about electronics, but I have always used a 1ohm and a 100nf cap from signal to power ground and never had any noise problems. I think it's really imortant just to make it that little bit more difficult for any dirty power to go through into any of the audio section.
Brett
I'm certainly no guru and no next to nothing about electronics, but I have always used a 1ohm and a 100nf cap from signal to power ground and never had any noise problems. I think it's really imortant just to make it that little bit more difficult for any dirty power to go through into any of the audio section.
Brett
Boards
David
Thanks for that link. It's good for plebs such as myself and interesting reading about grounding issues.
I think the biggets issue for me is also output stage as I'm no wiz. So this will be the scary point.
And also a good idea to have a group buy maybe. As for some of us it may be very difficult to obtain power transistors needed to get this puppy up and running.
And also, thanks for all the work you have put in so far. This project was on the brink of dying until you gave it a new lease of life
Cheers
Brett
David
Thanks for that link. It's good for plebs such as myself and interesting reading about grounding issues.
I think the biggets issue for me is also output stage as I'm no wiz. So this will be the scary point.
And also a good idea to have a group buy maybe. As for some of us it may be very difficult to obtain power transistors needed to get this puppy up and running.
And also, thanks for all the work you have put in so far. This project was on the brink of dying until you gave it a new lease of life
Cheers
Brett
Quick update:
I have a few more boards left as an FYI since people have been asking.
On the building front, after spending half a day tracking down a variable hum that didn't make any sence and then realizing that my board was too close to my transformers on my bench (duh), I have a few observations to share with folks working on the boards.
If I set the gain too high, I get pretty awful clipping that shouldn't be happening, but it definitely is. I haven't found the sweet spot, but I will let you know when I get there.
Bypassing the input caps hasn't caused me any problems yet.
A simple darlington output pair is extremely easy to wire up p2p, but I haven't tried parallel output stages yet. That's on my to do list.
The descrete stages will have have to wait for a little bit, but I think I have a CFP/Sziklai-Pair that will work well. I'll let you know when I get something solid up and running.
David
I have a few more boards left as an FYI since people have been asking.
On the building front, after spending half a day tracking down a variable hum that didn't make any sence and then realizing that my board was too close to my transformers on my bench (duh), I have a few observations to share with folks working on the boards.
If I set the gain too high, I get pretty awful clipping that shouldn't be happening, but it definitely is. I haven't found the sweet spot, but I will let you know when I get there.
Bypassing the input caps hasn't caused me any problems yet.
A simple darlington output pair is extremely easy to wire up p2p, but I haven't tried parallel output stages yet. That's on my to do list.
The descrete stages will have have to wait for a little bit, but I think I have a CFP/Sziklai-Pair that will work well. I'll let you know when I get something solid up and running.
David
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