Etching a board set for my HRM build...

[martin manning]

I think the main use for this laminate now is as a veneer for office furniture, and so it doesn't need to be as thick or durable as it once was.

Here's some feedback from my experience making a board with the Pulsar “PCB Fab In A Box” system and etching it:

Note I have not run any 1/16" board material yet; only the 1/32" G-10/FR4 with 1/2-oz single-sided copper cladding that came with the kit. I did use the GBC pouch laminator recommended by Pulsar as a heat source instead of a clothes iron, and my test case was a 25mm x 95mm board for a fuzz pedal.

Before transferring the toner to the copper surface, the instructions suggest mechanical cleaning using a green Scotchbrite® pad and detergent, and then dipping the board in Tarn-x (a metal cleaning product for silver and copper available at hardware and grocery stores). I cleaned the board with Scotchbrite as directed, then wiped it with a cotton ball soaked in Tarn-x several times, then rinsed it in water and dried it with a paper towel.

The Pulsar toner transfer paper and laminator combination works great. The image is transferred to the copper surface flawlessly, and the paper releases completely after soaking in water for about 30 seconds. The easy removal of the paper is due to the toner image being fused to a water-soluble coating which, when dissolved, allows the paper to separate from the toner image and come off easily in one piece.

The green film, which is intended to seal the toner image, is a little trickier to apply. The carrier is very thin and it tended to wrinkle as it passed through the laminator, leaving small gaps in the coverage when the carrier was peeled off. With a couple of tries, I got better at it. It is recommended to apply a little tension on the film as the board is drawn through the laminator, both length-wise and width-wise. My test board was so small that I couldn’t really do this very well.

I etched the board with a solution of two parts 3% H202 to one part 31% HCL. I really like this etchant! It’s readily available, cheap, clear (so you can see it working), and fast- it took about two minutes to etch the 1/2-oz copper at room temperature (70F/21C). After etching, the toner and green film resist is removed with acetone, and the board is again scrubbed with Scotchbrite and detergent.

Finally, I used MG Chemicals’ "Liquid Tin" to tin-plate the copper traces. This prevents oxidation of the surface, and the tinned board takes solder much better than plain copper. Before immersing the board in the Liquid Tin I decided to clean it with Tarn-x again, rinsing it in water and drying as before. It flashed from copper to a uniform tin color just a second or two after immersion in the Liquid Tin. It takes several minutes for the tin coating to reach maximum thickness, though, with both the thickness achieved and the time required being temperature dependent. I placed the tray containing the board and Liquid Tin in a warm water bath (~110F/43C) to speed up the process and increase the final coating thickness.

I think that a cleaning with Tarn-x would be a good practice to follow before loading a plain copper board; it should make the soldering easier.

MPM

[ic-racer]

Finally got the HRM stack board finished. See annotation below.

[Structo]

I was wondering where you were with this build.

[ic-racer]

This is the back of the board.

[ic-racer]

Rectifier and bias board finished. (Cap polarity checked ten times... )

[ic-racer]

I was wondering where you were with this build.

Snail's pace

I got most all the caps and resistors for the power board and will etch and construct that this weekend.

[jelle]

I-racer,

Are you sure those bias caps are oriented OK?

Jelle

[ic-racer]

I-racer,

Are you sure those bias caps are oriented OK?

Jelle

Layout for the board was copied from this. Ground line comes up to the bottom of the caps. The shiny end of the caps is up and words are up-side-down. Both indicating that the (+) end is down. But I'm certainly open to other interpretations as I have seen things wrong in the past.

[ic-racer]

Here is the board with annotations as to what I think things are supposed to do. I'd be interested in others' opinions as to if it looks OK.

[jelle]

Hmmm, internet humour does not really work all the time...'are you sure the polarity is ok'....

I have screwed up polarity of bias caps before...thinking: Why is my bias CKT screwy...

Your board looks great!

Jelle

[ic-racer]

Hmmm, internet humour does not really work all the time...'are you sure the polarity is ok'....

I have screwed up polarity of bias caps before...thinking: Why is my bias CKT screwy...

Your board looks great!

Jelle

I kind of figured that. I do appreciate any comment though.

You know I posted that whole set of HRM etching patterns and no one questioned any of it. So, I don't know if it is just so obvious to everyone that the patterns are fine, or that it is so hard to figure out what is going on without the components in place that it is beyond the experience of most of the viewers to make a judgement on them.

Like that HRM board. Does it really make sense to everyone? I'd be glad to annotate a picture of the board if anyone is interested.

[martin manning]

ic, I doubt that it's because nobody looked... I made copies and (virtually) populated them with parts to figure them out. It all made perfect sense to me.

It would be great to see the HRM board annotated if you don't mind posting it. I'm not focused on HRM amps just now, but I'm interested in the education.

MPM

[ic-racer]

Anatomy of the HRM stack board.

The 250k is the Treble, the 1M is the Bass and the 20k is the Mid.

There is one resistor on the top (100R, optional) and one resistor on the bottom (33k) and one resistor connects this board to the main board (100k).

There are 3 capacitors underneath. A 500p (.0005uf) and two .0022 uf. I used the 715 series, as the PS series seemed too big. I don't know what the 'correct' capacitor would be.

[martin manning]

Great, thanks! Where does the test point connect to?

MPM

[ic-racer]

Great, thanks! Where does the test point connect to?

MPM

I believe it drops straight down to the main board. In that case, the location in the circuit depends on if the last stage is wired as a cathode follower (ala Marshall) or not.
I have a diagram I can post.