Any interest in GC input buffer and power supply regulator pcb's?

[randytsuch]

Originally posted by Sheldon


If boards do not become available, I'll probably try etching some. I know nothing about it, but if you can etch one side, why not two? Aren't the only extra requirements be that one side is protected while the other etched and that the respective patterns be reasonably well mated? Can't be that hard for a small board? I like the idea of compact layouts (just because).

Sheldon

I have not etched before, but I would think you would just etch both sides at once.

The thing you can't do at home is make plated through holes (at least I don't know how) This means the pad on the top side won't be connected to the pad on the bottom, unless you run a wire through the hole.

For lining up top and bottom, there should be registration holes in the corners of the board (at least three of the corners). This should make it pretty easy to line up.

Randy

[Sheldon]

Originally posted by Sheldon

I still have a little tuning to do. I'm getting about 90mv offset in one channel and some hum, about 75mv in the other but very low hum. Maybe a bad joint or grounding arrangement to chase down. Time for a break before I tackle those.

Sheldon

So time to tune. The setup as described earlier is one of Brian's non-inverted boards with Pedja's jfet buffer and his discreet reg. p.s. I'm getting a little more hum on one channel, though not bad (I have to be within a foot or so on 90 db speakers, as compared to a few inches for the quieter channel). And I'd like to reduce the DC offset, though I'm not sure it's essential. The max I see is 100mv which at 8 ohms is still only 1.25 mw. The table below is self explanatory, except for the "buffer grounded" column. Here I have the buffer output shorted to the signal ground on the amp board. Here's the data:

Normal Operation ... Buffer Grounded

....L ........ R ......L....... R
AC 0.4mv 1.1 mv 0.4mv 12 mv
DC -75mv -100mv -10mv +140mv

One other note: When I touch the buffer output in the right channel with the multimeter probe, it get's a little quieter in normal mode, but the hum get's louder in the "buffer grounded" mode. Anything obvious I should look for?


Sheldon

[moving_electron]

Originally posted by Sheldon


Aren't the only extra requirements be that one side is protected while the other etched and that the respective patterns be reasonably well mated?

The degree of difficulty is higher on a double sided board but not prohibitively so.

1) the masking for the two sides needs to be aligned so that the pads etc. will be in the right place on each side. For most boards this has to be done pretty accurately.

2) You have to mask, expose, develop and etch each side seperately and as you mentioned each side has to be protected as the other side is worked on.

3) you need double sided medium which is somewhat more expensive, especially if you are using presensitized boards.

4) your chance of success on a double sided board is lower - on the order of the square of the chance of success on a single sided board. So if you have a success rate of .75 on a single side, your success rate on a double sided board will be on the order of .75x.75= 56% If your rate is 50% on a single sided board then your success rate on a double sided board will be something like .5x.5= 25%. [Of course if your chance of success on single sided is .99999 then your chance on a double sided is very high .]

So it probably comes down to the goal:
If the goal is to have a board artwork that can enable the most people and facilitate the most success for first time etchers then single sided is the way to go.

If the goal is to have the most compact board with no jumpers then double sided has the advantage. Quite a few people could make this work but some will be left out or unsuccessful.

[Sheldon]

Originally posted by Sheldon



So time to tune. The setup as described earlier is one of Brian's non-inverted boards with Pedja's jfet buffer and his discreet reg. p.s. I'm getting a little more hum on one channel, though not bad (I have to be within a foot or so on 90 db speakers, as compared to a few inches for the quieter channel). And I'd like to reduce the DC offset, though I'm not sure it's essential. The max I see is 100mv which at 8 ohms is still only 1.25 mw. The table below is self explanatory, except for the "buffer grounded" column. Here I have the buffer output shorted to the signal ground on the amp board. Here's the data:

Normal Operation ... Buffer Grounded

....L ........ R ......L....... R
AC 0.4mv 1.1 mv 0.4mv 12 mv
DC -75mv -100mv -10mv +140mv

One other note: When I touch the buffer output in the right channel with the multimeter probe, it get's a little quieter in normal mode, but the hum get's louder in the "buffer grounded" mode. Anything obvious I should look for?


Sheldon

Fixed the hum problem. Discovered that I has miswired one of the LP filter caps. Hum from either side is now inaudible from 10-20 cm away. Last issue is the DC offset. Sorry for the wasted bandwidth.

Sheldon

[Pedja]

Originally posted by cjd
Here we go again. Bypass caps are not on-board at all, though holes are provided if you choose to mount under the board, or you can mount straight to the pins or whatnot.

Maybe: R2 above R1; then the output bypass cap right of this new R2 position; the reg itself maybe moved a bit down, so R1 becomes closer to it; previous R2 position stays empty so this place may be used for the input bypass cap.

The 1M resistor is rear-mounted. There's room to slide it over and mount above the two resistors if that would be preferable.

What I was initially about was:




Then I thought it can be done this way:




Then I thought about the strayed capacitance from the output to the input:




But I thought also the cascode can be made tighter, though the V- supply path pays the price…

"Incoming and outgoing traces around the reg itself are narrowing" - if this refers to the traces getting narrow to clear the other reg pins, a question: Is it better to have smaller traces that are consistent in size vs. thicker and narrow right at the reg?

It is OK now, previously they were getting narrow too early. Btw, you are not supposed to use just one track width, you may combine a few tracks of less width to get better results.

Do not be too upset about anything of these notices, take them as a final thoughts…

Two more important things at the moment... Where the filter is supposed (if the filter is supposed) to be mounted? And, on the amps boards, the cap from the mute pin to ground is missing.

Pedja

[Sheldon]

Originally posted by Sheldon


Last issue is the DC offset. Sorry for the wasted bandwidth.

Sheldon

Did a bit of searching, which I should have done before I asked about the offset. As I understand it, the DC offset, assuming it isn't a function of DC input (which shouldn't be the case here, as the buffers are coupled to the amp boards via a 4.7uf cap) is caused by bias current in the amp chip. So, as Carlos pointed out in another thread(http://www.diyaudio.com/forums/showt...843#post438843), it's somewhat of an inherent problem with the NI versions. And its magnitude depends at least partly on manufacturing variation. So how about injecting a little DC offset as suggested here: http://www.diyaudio.com/forums/showt...198#post385198

Anyone see problems with this approach? I could use the output from the regulated supply or from the buffer regulators.

Sheldon

[Pedja]

Sheldon,

You may put 10k instead of 22k input resistor on the non-inverting input (ignore filter’s frequency for the moment). You may go also somewhat below 10k. I’d expect this to solve the issue in certain degree. No idea if it will be sufficient (for you at least).

Pedja

[cjd]

Hmm...

why hadn't I considered moving the pins to allow more space?!

FWIW, I've only found any posts to be quite helpful. I have no illusions about being a great designer in this arena, as I know I'm missing too many rules and standard practices (all of which have solid reasons for existing).

Then again, it could just be that none of you have suffered through an art critique (which, I must say, are incredibly harsh and demanding).

I'll continue pondering these. Every few days I give them a fresh look over and invariably find things to tweak.

Pedja, your illustration sequence is amazingly helpful in ways beyond just providing layout suggestion. Thanks!

C

[Pedja]

Originally posted by Pedja
Btw, you are not supposed to use just one track width, you may combine a few tracks of less width to get better results.

one track width should be one track of the given width

Originally posted by Sheldon
So how about injecting a little DC offset as suggested here: http://www.diyaudio.com/forums/showt...198#post385198
Anyone see problems with this approach? I could use the output from the regulated supply or from the buffer regulators.

To answer the question, I think it won't work. Even in your case of defined DC resistance seen by the non-inverting input.

Pedja

[Sheldon]

Originally posted by Pedja
Sheldon,

You may put 10k instead of 22k input resistor on the non-inverting input (ignore filter’s frequency for the moment). You may go also somewhat below 10k. I’d expect this to solve the issue in certain degree. No idea if it will be sufficient (for you at least).

Pedja

Thanks Pedja,

I tried 9.5K and 6.6K. It does indeed lower the offset, as would be expected if the offset is a result of bias current. I assume that would raise the LP filter cutoff some? As the offset is under 50mv, I can't imagine that it would be a problem. Even at 100mv it may not be a problem. Just the ordinary quest for perfection, I guess.

Originally posted by Pedja

To answer the question, I think it won't work. Even in your case of defined DC resistance seen by the non-inverting input.

Pedja

Would the injected offset affect the LP, even if a fairly high value resistor is used? Or does it create a feedback issue? I assume that when you say it won't work that it would have an adverse affect on sonics? National looks like they do something similar when using positive power supply.

This continues to be an excellent learning experience, thanks to you and all the experienced users that are willing to share.

Sheldon