Old Colony Zen circuitboard warning

[Mike L.]

Hello all,

I recently finished an original Zen amp using the circuit board obtained from Old Colony Sound Laboratory. It came with photostatic copies of the Zen articles from Audio Amateur 2/94 and 3/94.

The board is very nicely done and the articles provide a nice parts list complete with Digikey catalog numbers. I happily completed stuffing the board last weekend but when I plugged the amp into the wall outlet, nothing happened. I was rather perplexed. At first I thought that maybe I had zapped the mosfets with esd. So I removed all the transistors from the board and tested them. They are all good. Unfortunately, I had to snip the leads of the mosfets to remove them, rendering them useless for this project.

Yesterday, I sat down with the board and the articles to try and figure this thing out. Now the article from the 3/94 Audio Amateur notes that the two figures included in the 2/94 article showing each side of the board were swapped; the top layer is mislabeled as the bottom layer and vice versa. No error is noted concerning the stuffing guide figure. Well, you know what they say about assuming things.

The circuit board as received has the silk screening applied to the top layer. The stuffing guide figure shows the silk screening over the top layer circuitry. The mosfet plated through holes are labeled "S", "D" and "G". I blithely oriented my mosfets as per the stuffing guide without carefully examining the circuit traces shown underintensified in the figure. As it turns out, the circuitry in the stuffing guide is the mirror image of the top layer circuitry. I had installed the mosfets backwards.

I have ordered replacement mosfets and should have the amp working by this weekend. I just thought I would pass this along so others may avoid this pitfall.

Thanks for letting me ramble.

Mike L.

[Nelson Pass]

Sorry about that. AE should have included a
little note about the error.

[vdi_nenna]

They did, I got one.