Update on Parts Availability

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.

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  1. Even Mike himself, said that the better method of aligning the unit is to use the 2db drop in level, then trying to balance against the expander card. The expander cards were never that linear. And when biased enough to function, they act more like a squelch than an expander. Also the lm301 is available in an equivalent of nte. They probably bought $100,000 of them and re-labeled them under their own part number. That’s why you can use the nte 113, and replace of the fet. But the current cross reference for the fet will not work. The 113 is out of a 1970s cross reference. a much softer characteristic than the current substitution.. being at the 301 and the 741 are interchangeable. The only difference with a slight reduction in the noise level. However if the unit is aligned using 12 volts instead of 15 volts from the power supply. The noise floor drops by approximately 8 db. Also the unit runs cooler overall. The fancy bordens trim pots are not necessary. The ones I’m buying off of eBay that are 10 for a dollar. Blue white plastic things. The only difference is they operate backwards of the boarding spots. So everywhere in the manual that it tells you to turn it whichever direction you have to remember that that’s now been reversed. Yes if you want to do a real restoration you do need to use the factory part. But if you’re just trying to make it work. The blue and white cheap ones work just fine. If you’re really sadistic about it there is a 10-turn version available. If you want to rip your hair out while trying to adjust the fet. I tried it it’s a bad idea. You’ll never get it close enough using a 10 turn. The voltage will slowly increase in avalanche. You need the quick voltage rise and drop of a standard pot rotation for that to work. Also I found out that biasing the fet on harder, so that you see more of a 3 to 6Db drop. Instead of 2 DB, will help keep the gain reduction of the fet more linear. It is possible to bias them so that the fet has a gain reduction of 30 DB linear across its entire range. With the standard 2db drop alignment. The gain reduction is not linear. It will jump in ratio as it increases. Sounding something like a dbx compressor but not in a good way.

  2. Jeff, you helped me out with a 310 several years ago. I was away from that unit until recently. Not any more, and I have a few questions regarding this post. At your convenience. Thanks.

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