I was recently repairing an old amplifier that contained a specialized IC. The amplifier as a whole worked well, but had some problems with the effects switching. I tracked it down to a defective IC, the TL604 / SN99661. Unfortunately, this IC had been obsolete since sometime in the 1990s. Peavey once made a kit that allowed the use of another current production IC, but that kit has also gone obsolete. While the kit can still be found, it was MUCH larger than the original part, requiring custom work to install. That’s assuming there’s room inside the amp.

Rather than waiting for another solution to appear, and not satisfied with scrapping another otherwise good amplifier, I decided to make my own replacement solution. I found a modern part that would do the task. With the magic of miniaturization, the new IC is so small that it can fit within the space of the original IC! In order to make this as future resistant as possible, I designed the PCB to accommodate two different package styles of the same new IC. Not only that, I included space to put an entirely different modern IC on the other side of the board (not visible). This too has two different package styles. In all, there are now 4 modern ICs that will fill the role of this long unobtanium IC. I call it the TL604JDP.

The TL604JDP brings new life to old Peavey and Gallien-Krueger amplifiers by providing an alternative to “Obsolete” and “unavailable”. Below is my adaptor board in place, sitting next to the failed TL604 that I removed. It is plug and play with this adaptor! Here the TL604JDP is giving new life to the phaser circuit on a Peavey Classic VT-212.