Over the years, I’ve managed to accumulate a few more cards than I need for repair inventory purposes. Specifically, I have several Equalizer cards for sale. They are fully restored, tested, and guaranteed. While I have some other cards as well (to be offered at a later date), they are not yet refurbished.

Trying to be fair, I’ve set a price of $30 each plus shipping, which is about what I charge to refurbish one. If you need one, please send me an email at admin at dap310.com. First come, first served.

While I wasn’t looking, all major manufacturers have discontinued the 8-pin DIP plastic version of the ubiquitous LM301 op amp. When such a popular part is discontinued, there’s usually a years-long supply in multiple warehouses. I have had little luck finding any 301s in stock at an affordable price. While I don’t need any at the moment, they are used extensively in the DAP 310. Sure, there are many chips that will work as a replacement, but a lot of my customers ask that their units be maintained as close to stock as possible.

For some reason, I’m seeing an increasing number of LM741 failures. I cannot imagine 741s being discontinued, but I also never imagined the 301 being discontinued. It’s possible to get an SMD version and solder it to an adapter board that plugs into the 8-pin socket, but that solution adds time and money to a refurb. I just bought a lifetime supply of 741s.

The potentiometers on DAPs (Bourns 3386H-1-202LF, primarily) are now over $1.00 each in quantity. While that doesn’t seem like much, I typically don’t charge extra for minor parts when I refurb a DAP. I have a pretty good supply of those pots that will last a while, but it looks like I may have to charge regular labor plus parts for a refurb. Everything is getting more expensive.

A lot of people over the years have removed Expander cards from their 310s, and they’ve apparently discarded them. I regularly get requests for them, and I don’t have them. I’m seriously considering producing one. If you’re interested in getting some, please let me know.

Recently I acquired a new stock of parts for the DAP 310. My inventory now includes most parts EXCEPT the meter bezels or the FETs. If you have a DAP that needs repair, let me know. Most repairs are $200 or less. You’re also welcome to send me an email if you’re having a problem with a repair. admin at dap310 dot com.

The trimmer potentiometers on the 310 are not very robust. They are not designed to be turned many, many times. If a pot is in an audio circuit, it’s easy to hear when it is going bad. When it is in a control circuit, like the FET BIAS pot in a DAP, it can be difficult to diagnose as a source of a problem.

Recently, a 310 that I refurbished would periodically slam the low frequency meter downscale. The problem was very intermittent. As I was going through the final alignment, the FET BIAS control was very touchy. At that point, I decided to replace the pot. When I did, both problems disappeared. It was immediately obvious that the pot had failed.

Most of the pots in the 310 are Bourns 3386H-1-202 or equivalent. If you’re replacing caps and bringing a DAP back to life for long-term use, you might want to go ahead and replace the pots. They’re very easy to replace thanks to the single-sided printed circuit boards.

It’s somewhat axiomatic that replacing all electrolytic capacitors in a DAP should be the first step in a refurb. They’re about 43 years old, and they deteriorate over time. Axial capacitors are still available, but they’re getting expensive, and the selection is not what it used to be.

It’s possible to eliminate three electrolytic capacitors on the Equalizer board. The output of each of the three channels is capacitively coupled to the next stage, which is a 2K pot followed by another cap. While there is a possibility that there could be a little DC voltage on the output of one of the 301 op amps, it’s not likely.

That being said, it has been recommended that you can remove C20 on Z1 (shown as 6uF), and you can. However, there will probably be an offset voltage on the output of Z1 if you do. That offset voltage will vary with the 301 in the circuit. While the offset is very low and not of much consequence, it will put DC on the 2K pot in the Compressor card that follows. DC on a pot can cause some nasty scratching noises. You decide.

The ground screw of the input/output barrier strip on a 310 that I’m refurbishing had a seized thread that caused someone to twist the head off. After a little research, I found that the Cinch 5-140-Y barrier strip is an exact replacement. If you need to order one, be aware that many of the pictures that sellers use for these parts are incorrect. The “Y” terminal is a solder tail that feeds through back panel into the case.

Cinch 5-140-Y

The original on this one was made by Kulka, but the Cinch fits perfectly. Cinch may have been used by the factory in some models.

Remove the existing strip by removing four screws. Let the strip hang away from the back of the DAP. Gently remove the heat shrink tubing around each wire. Thread each wire into a short piece of 1/8″ heat shrink tubing before sweating it back onto the proper Y solder tab. Shrink the tubing so that none of the wiring can short against the metal case. Re-install the strip. Good as new.