Crawls Backward (When Alarmed)

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The Saga Continues - More Dynaco PAS

Now ve start on zee list of zee bullet points, yes?


I just cleaned up the old contacts on the input board, or as Joe Curcio calls it, the "I/O" board (aka "Input/Output").  That sounds too modern for me, but it is accurate.  This is the row of RCA jacks on the back of the PAS where the various components you are preamplifying connect to (inputs) as well as the outputs from the PAS to the power amp and tape my case CD recorder.

I had previously snipped off and partially desoldered all the wiring that goes to the board and now I need to go back and clean up the old connections.  You can see some old solder, bits of old wire and even some insulation still on there.  I take my trusty soldering iron, wire snips and desoldering wick and, armed with some patience, I go through and clean up the connectors.  This leaves little bits of junk on the bottom of the chassis, which winds up dumped onto the workbench and from there into the trash.

The end result is pretty clean.  These are the same terminals you see in the first picture.  Whoever put this together did a good job to start with - they didn't use an excess amount of solder.  A lot of times on old radios, especially where several components connect to one point, there is a lot of solder and it takes a while to clean up.  But not this time.  Good deal.

Now, you may recall my mini-soapboxes about cleaning the older solder and wire bits when doing restorations.  I would like to think that this picture proves my point.  Why would you want to tack a new component onto old solder blobs?  It's so much easier to put net leads on nice clean connectors, don'tcha think?

I gave some thought to building up a new board with new connectors, but these aren't in bad shape, so I'm going to reuse this one.  Maybe when I rebuild my other one I'll do that.

The other thing I cooked up were some changes to the phono board, PC-6.  Joe Curcio, who I mentioned earlier, has a "fix" for the RIAA circuit, which I incorporated here.  Turns out he original Dynaco phono circuit is off the RIAA curve by plus or minus 4 db.   When you consider that a difference in gain of 3 db is perceived as "twice as loud," you realize that 4 db is substantial.

As an aside, the "RIAA" curve is the Record Industry of America equalization curve that was applied to records when they were mastered.  Certain frequencies were boosted when the records were mastered, and then the same frequencies were cut (by the playback equipment) when played back.  You can read more about it here.

The Curcio mods bring the difference down to 0.2 db.  Pretty close indeed.  The mods are very easy, they involve changing the value of 2 capacitors and two resistors and doubling up a couple of caps and resistors.  You can pretty much see them on the board.  I also jumpered the first stage coupling caps per his suggestion, and I replaced the Illinois capacitors that came with the board with Orange Drops (you can probably spot ' for two other signal caps.

I have two top secret caps that I'm going to replace the output stage caps with - those are the two remaining yellow caps.  But I'm holding off on that until the board is in the preamp and I'm wiring up the selector switch.  Hopefully it will be clear at that point why I held off.


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