After 15 years of completely reliable service from my Magnum I, one day a few months ago I decided to tweak the volume trim pots on the neck pickup a little, and poof - no sound from the A string. After a little testing and contact cleaner yielded no improvement, I knew I was going to have to make an expedition inside this strange and wonderful pickup. (I wasn't thinking it was so wonderful in that moment, but it was before and after that.)

Though there is a lot of random Ovation info on the web, I was kind of surprised to not be able to find anything anywhere on this topic, at least everywhere I searched. So, once I sorted everything out, I wanted to share something here so that future Magnum owners who run into the same issue would have an all-in-one reference that would save them the time and guesswork I had to spend.

First task was to open up the frame the pickups are attached to. The following pic shows what the pickup looks like underneath. The pickup is a sealed case, with the back plate attached very firmly with some quite large globs of solder (with leftover flux still visible).

Removing this solder is fairly straightforward if you're decent with a soldering iron. I recommend using a broad tip and a solder-sucker - it makes melting and removing much faster than with a smaller tip and braided tape. But it still takes a little patience, so take your time.

Once the solder is removed, pickup case opens easily - only the solder around the edges holds it closed - and you are then able to access the full guts of the pickup.

The stock photo of the pickup that's in the Ovation manual is pretty accurate. Here's what mine looked like when opened up:

This gves you a good look at what I believed was the culprit: one of the little trim pots that are used to adjust the volume of each individual pole piece in the pickup. These pots are a great feature to have, because they allow you to balance string volume very precisely. But it also adds another part that can go bad (though one glitch in nearly 40 years of the instrument's life isn't bad!). Fortunately, as you'll see below, it's also very inexpensive to replace.

So how does this pickup really work, anyway? Before going any further, I referred to the patent documentation for the pickup to get a basic understanding of the principles involved in the various parts of the pickup.

Closer inspection revealed the source of the problem. These types of trim pots use a thin conductive carbon ring on a plastic substrate as opposed to a wire resistor. They are not sealed, which makes things a little more vulnerable to debris or other outside factors. As you can see in the following pic, the carbon ring on the A-string trim pot was missing. It had broken off, and I found it in pieces inside the pickup case.

At this point it was clear that replacing the trim pot was needed. 40-year-old unique pickup - how easy would this part be to find? Was it a custom part? I desoldered it and looked for any indication of its resistance or a model number. The part number turned up nothing, but some searching led me to the wiring schematic for the Magnum, which shows 100K resistors in line with the pole pieces.

Some online scouring finally led me to this part, which is the correct replacement trim pot for the Magnum pickup:

https://www.digikey.com/product-detail/en/201UR104B/201UR104B-ND/98353

• Part: CTS Electrocomponents 201UR104B
• Resistance: 100K OHM
• Product series: U201
• Price: $0.56 each
• Image

Removing the pot was a simple matter of desoldering the four contact points:

And then soldering in the new pot. As you can see, the original pots in the pickup had red adjustment dials. I've not seen red ones anywhere, even color versions of the original stock photo linked above (they're blue there, too). But no matter - a little change in color is worth it for everything to be working again:

And that was that! I tested out the new pot, and everything was back to working perfectly - the new pot worked just as well as the old, and it was again possible to balance the volume of the strings. I re-closed the pickup case (using a bit less solder than Ovation had, but still plenty to seal it firmly) and closed it all back up again. It was a little tricky getting the solder to start sticking to the casing - I highly recommend using a paste flux to help get this part of the job going. I bought some at my local Radio Shack that was cheap and did very well.

So if any of you have to take your own journey inside the mysterious Magnum neck pickup, I hope this little guide will prove helpful! If you have questions, feel free to let me know.

Cheers,
Kevin