![]() And I separated out the info specific to an amp into a number of "technical supplements" more specific to one amp per supplement than the general stuff in the Safety Net. Grew to about 180 pages.Īt this point, I thought, why not tell every Vox owner how to fix the rest of the amp, as not all the problems were related to the repro PCBs, so I word-processed out the "how to fix the rest of the amp" into what has become "The Vox Owner's Safety Net", being a compendium of what I know about Thomas Vox amps. to work if it's not the board?" meant that I needed to write up "how to fix the rest of the amp, too". Then I started getting commentary that this or that didn't work after the board was in the amp, and it slowly dawned on me that the questions on "well, how do I get this. As the first adopters fed back info, that grew to about 85+ pages per board. Originally I did the docos for a board as simply as possible, just parts list, schematic, and some helpful advice. I got one trace in the wrong place, and reversed a TO-220 but they do work. I forgot to say - checkout period is over. They all work properly, sound like the original, but I get a comment from each builder - there's none of the hiss I remember. The recommended sink is $0.23 in ones at Mouser.Īs a bit of review, there are now about 8-10 (I'd have to go count) of the Vox preamp works-alike boards out in the world now. The reverb driver(s) were even cooler, but still warm, so I suggest that any builders use sinks there. Only the 7824 really needed it, and that was marginal. Then I tested the temperature rise on them without heat sinks on the first populated board. I actually laid the board out for heat sinks for all the TO-220 parts, just so there would be space. It was handy and more reliable, and only $1.00 more in parts for a big board, so I went with three.Įliminating heatsinks was a welcome side effect. But three lets you de-power a section during debug to see what's wrong. It is likely that one 7818 would have done it. I wanted to make sure that the works-like-a-Vox boards didn't have grounding or interference problems, so I checked to see if the extra board area for separate domains for each circuit section would fit it would, so I did. They were as quiet and hum free as any tube amp I've ever heard, so I knew it worked. I did on-PCB star grounding for the Visual Sound Workhorse amps, and it worked really well. The original Thomas Vox amps had individual power and ground domains, each star-wired back to decoupling caps. The question behind that is why one? I originally split the power sections for what may turn out to be silly reasons. Ordinary three terminal regulators don't need a minimum load, so why not use the higher-power parts and let them loaf. I did start with TO-92s and was reminded when I started looking up parts that the TO-220 and the TO-92 voltage regulators are very nearly the same price. ![]() It was a compendium of those, plus some star grounding. I have about half a dozen from the first proto batch. I was holding off on letting anyone use them until someone other than me had taken a board, built it, and successfully put it into an amp. The ICs are CD4052 CMOS switches that replace the old hard-wired 4P3T switching so that the signal doesn't have to go off the board on six wires to get to the switch, which was its own nest of wires.īut except for that, it's the same circuit schematics. I did fix the power circuits, subbing in linear regulators (those to-220 packages) for the resistor/capacitor voltage supplies in the originals. The signal circuits are verbatim the same as the old ones, just new resistors, caps, and 2N5088 transistors instead of the old special-part-numbered 2N2925 types. No tracing wires through the bundle and breaking other wires by flexing the bundles. ![]() The general idea was to make "fixing" one of these amps be to clip off all the wires at the controls and jacks, then wire in the new board. I only know of four techs *in the USA* that will. It was so bad to work on the old boards that pretty much no amp tech will work on them.
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