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.

Mike Phillips


  1. Hi there.

    I have a DAP 310 that I am trying to repair. I received it and it had some mods on the input transformer. Seems that they bypassed it although I’m not certain.

    I have good schematics but unfortunately i can not figure out where to connect the input leads to the sensitivity switch. None of the schematics shows how its connected. I used the small bits that were left from when they cut them off to try to re connect them but i have no clue.

    Also, the sensitivity switch is supposed to have four detents but when i removed the knob the detent lock washer came off and I’m not sure where the detents are supposed to start or stop. With out the washer lock my sensitivity switch has 11 position although it should only have four.

    I really appreciate any help you can give me. Im not sure why it seems people are bypassing the input transformer.


    Will Edwards

    • There was a period of time when many people thought that removing transformers improved fidelity. Later, we learned that some of us prefer the sound of the transformer. It’s personal preference. With few exceptions, I prefer the DAP as it was shipped. (One exception includes the power supply regulator modification, which is mandatory.)

      • A 7812 or replace the no longer available voltage regulator in the power supply, or you can bypass most of the power supply circuit and use a 8712 / 7912 or 7815/ 7912 TO03 case mounted to the back

      • my 310 went suddenly dead and there was a burnt smell in PS section. Happened suddenly. You think the PS regulator mod would return to normal or could it have damaged something further? I can’t seem to find a match on the update sheet publication for part number LM342-10

        • Richard, there’s no way to tell without looking at it. Can you take some high resolution pictures? When were the power supply capacitors replaced last? Is any of them bulging on the ends? It would be unusual for the LM342-10 to fail since it has almost no load on it. Any shorted component in the unit could put a heavy enough load on the power supply to cause heating of the current limiting resistors. The good news is that it is all repairable.

          • No visible cap bulges and the PS is all original as far as I can tell. The LM342-10 was the upgrade I read about, but has not been done on this unit. I was therefore looking to do it now hoping to revive it but not sure on that part number with the dash-10 being available. Will try for a photo when in position.

          • Now I can’t recreate the problem! The 310 decided to repair itself and wont quit, no heat, no smell and its alive and well. Most unusual. Perhaps a screw that was too long on top cover hit something it didnt agree with. Once apart and checked out and powered back up there was no longer an issue. hmmm.. Haunted. I’ll take it.

          • Stranger things have happened, I guess. Glad you got it sorted out.

  2. You wouldn’t happen to have an equalizer PCB would you? I could trace it and make a replacement, but if there’s one out there….

    • There’s not much to making one if you still have it the card just buy a piece of circuit board a little time with a Dremel tool and a permanent marking pen you can make your own, probably one of the simplest cards in the whole box.
      I’ve done one mod, 3-way active crossover board off of eBay for $10
      Cool part is that lets you change the crossover frequencies. But it’s not OEM

  3. If you contact meter man down in Los Angeles, he can get you the bezels you’re looking for comma be warned they are about $15 each for the plastic ones and 35 for the bare aluminum ones, I replaced all the ones in mine with aluminum painted bright Fire Red and they look damn slick!!!!

    ps, I have a whole bunch of the FET’s used by the 310, email me we’ll set up a deal!

    • I’m looking for old siliconix fets with very specific serial numbers. Do you have
      any marked 7522?

      • By the way, those are date codes, not serial numbers. You are correct to look for the right ones since some FETs even with the correct part number will not work correctly.

  4. The NTE312 (actually an ECG 312) is a direct replacement for the original FET’s, the NTE468 will not work at all it sounds horrible

  5. To the gentleman with the burnt smell coming from the power supply. there are four silicon diodes that were used in the rectifier circuit. They were a weak point in the design, as those types of diodes were relatively new at that time. Next thing to look at is the circuit board anywhere that it looks like it’s been overheated. You will normally see that where the two voltage regulator transistors and pass transistors are mounted, those can short to ground and smoke. Also, there is a single op amp that is used to drive the voltage control. That is sent to the two pass transistors that can also short and burn. On the power supply card in the rear where the transformer is mounted to the card, is the output buffer amp drive stage. The two transistors mounted to the board in that stage, should one of them go bad and short out, it will create a cascading failure that will destroy the second transistor and the op amp driving them. The power supply in these units is a very straightforward dual rail plus and minus 15 volt. If all else fails, just disconnect the transformer and purchase a small plus and minus 15 or plus and minus 12 volt power supply on eBay, and mount it to the inside of the chassis making sure that is well-grounded and kept away from any audio lines. I have done this on a couple units where the power supply was a complete basket case, and the traces had come off the board.

  6. Regarding the FET transistors used in the Durrough 310, the original factory ones are completely unavailable. Even if you do find them New Old Stock, there is a good chance that just this year age of them they have been damaged as they were extremely sensitive parts. The closest equivalent is an NTE312. Do not use the direct NTE cross reference as they will not work at all. I would also suggest you do the FET alignment after you have set up the initial adjustment. I would connect a distortion analyzer to the output of the unit to give you a good widerange vu. Then increase the bias slightly per FET so that it becomes linear. The stock factory instructions do not create a completely linear bias of the FET and you will not have full ratio as you should on the compression when it starts. With a minor increase in the bias, you will notice that the FET will linearize and you can have 30 DB of straight compression. If you do not do this, the knee of the compression will vary slightly from card to card, which will cause the audio to someone wander.

  7. Is it OK to install 220uf/63v in place of the 250uf/50v caps that are on the CARDS?
    I ask because I have enough new 220’s to do it. The old 250’s some are blown completely at the ends so the 63v is a comfort anyway. I’m wondering if going a bit lower in uf’s would introduce any hum or not. Don’t like hum!

  8. The 220uf caps on each card. We’re redundant Overkill should be regulator filter cap fail, and provide inrush current for the older op-amps. And total without the light bulbs that box uses about 250madc per side

  9. Hello! Anyone know of a DAP 310 for sale in any condition? I prefer one that at least powers up and the meter lights work. Please advise and thank you! Stay safe! Jim in ohio.

    • They’re getting harder to find, and the demand is increasing. As a side note, the meter lights are only an indicator that the power transformer is good. The bulbs are almost always burned out and have to be replaced. If you find a DAP, be sure to get pictures of the insides before you decide. A lot of these have been butchered. I can almost always put them in good shape, but there are a few things that get prohibitively expensive to replace because of time and materials.

  10. So have you heard about any of these units in any condition for our new broadcasting museum? I saw one for sale on ebay but the listing was ended early because of an error in the listing. Please advise and thanks again!

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