Re-Jigging the jig: Speaker testing device for Arta, Speaker Workshop & HOLMImpulse

[Variac]

Never seen that front panel idea with the illumination. Looks great and makes it easy to get tough lettering. You may become famous for it!

There is a lacquer specifically for copper and brass that chemically makes them very resistant to corrosion It is called Incralac:

TalasOnline.com - Incralac - Solvent Based

Incralac

[MJL21193]

Thanks
I originally had the idea to use it on an LED VU meter and I'll eventually get around to doing that also. It makes a very clean, neat looking panel.
I have had excellent results from Watco spray lacquer. It isn't specially formulated for copper but I think that making sure that the piece is absolutely clean makes a big difference. I clean it with steel wool then wipe it off with lacquer thinner, being careful not to touch it with my fingers.

I finished putting the latest board layout together:

NPX_038.JPG

And did some testing - everything looks good. I can finally call this the last revision.

I like to make sure that everything is operating as it should be, therefore I ran the internal amp through Right Mark audio analyzer to gauge its performance. The results:

RightMark Audio Analyzer test _ [MME] Wave mapper.pdf

Not too shabby for this very simple implementation and certainly more than adequate for speaker testing purposes.

[tsmith1315]

Leave that Jolly Roger on there!

[MJL21193]

Originally Posted by tsmith1315

Leave that Jolly Roger on there!

That's a given.

118.PNG

I have the board finalized and out for a quote. Updates soon.

[smokinghot]

A question about the All in One you're auctioning off...

Will your implementation of the LM1875 remain stable if driving a 4ohm load...?

[MJL21193]

Hi Jarrett,
Yes, no problem with any load really. The design is based on the idea that you will be testing at ~ 1 watt (2.83V output).

[mcmahon48]

how is the pricing on the pcb and how is the impedance determined at bp 3-4

[MJL21193]

Originally Posted by mcmahon48

how is the pricing on the pcb and how is the impedance determined at bp 3-4

Hi,
The boards will be $12 each plus shipping. I don't have them yet but expect they will arrive this week. I only ordered 10, mostly to see the quality of the board house who I haven't used before.
The boards have a full printed silkscreen layer that shows all of the component values for ultra easy assembly. They also have soldermask, so are truly pro boards, not like my homemade stuff.

Impedance at BP 3, 4, do you mean during operation of the jig to measure a speaker free air impedance? If so, you just plug in the jig to your soundcard (the software you are using needs to be calibrated for it, same as for the Wallin jig except simpler) and connect the driver to BP 3, 4 and run the measurement.
The jig has 2 external switches, one for amp power/frequency response, the next for impedance measurement/direct (direct is for channel difference calibration only) There is a third switch, it is internal to the mic input jack - it takes R13 out of circuit and routes the mic input directly to the "line in" jack.

[anatech]

Hi John,
As usual for you, an excellent job!

Your back-lit PCB front panel is very creative, and I love it! Many, many years age, a friend of mine did something similar, but without a back-light. He built an amplifier and used an etched PCB as the face plate. It looked really good also.

-Chris

[MJL21193]

Thanks Chris,
It's fun to find new and interesting ways to waste copper clad board.
Usually they wind up in my trash can with some parts still holding on for dear life.
I've taken this design to where I want it to be, so no more prototyping.