EE Minimax DAC repair

Have you tried placing the stock opamps back into the EE DAC?

Did you insure that you oriented the Opamps in the correct direction? Do the stock Opamps work when placed back in their original location? Did you turn the tube button off if you aren't using a tube?

NJS and Morganc - thanks for the input...

Both original OpAmps and proposed, regardless of position / orientation, do not change the outcome - unit no longer powers up.

I'm assuming this is a power thing, but can't rule out the board - anyone have wiring diagrams, specs, or similar for these?

Thanks

Daveaudiony, I have been thinking this over, frustrated that you are having a bad experience. It troubles me that someone tried a method I suggested and is having a problem.

Imo, little or distorted output means the unit will need repair. It sounds like one of the Opamps was inserted in 180 degree reversed position from proper alignment. I know, because it happened to me one time.

I have two of the EE Minimax DACs, an original in my office and the Plus unit in my listening room, and have been Opamp rolling both of them over time. I have rolled so many opamps, literally dozens and dozens of times, in both units that eventually I mistakenly placed one in backwards and that was it, the unit died. I simply had the Opamp not oriented correctly with the very small indicator of directionality in the right place - so the Opamp was inserted wrong, and the unit went PPHHHHTT... a small sound of something frying was emitted, and the unit died.

As frustrating as it is to believe that such a seemingly small action as putting in the Opamp reversed could kill the unit, this is consistent with what you are describing. So, I believe that you inadvertently placed one of the Opamps wrong. The indicators of directionality on the IC Opamps are maddeningly small, and easily missed, which is why one must exercise extreme care when aligning them. I do not intend to insult your experience or intelligence, but I know of no other reason why the unit would fail as it did. Similarly to your experience, there were no obvious signs of damage to the board when my unit died.

In the article I mention that I had switched positions - that is, tried a single in the place of a dual, or vice-versa - occasionally of a few Opamps without harm to the unit. I now strongly suggest NOT to do that, as I was informed that there are some modded units which may be adversely affected by it. I know of no instances in which a unit was damaged from it; the objection was theoretical, and I followed up with a warning addendum to my article.
However, from discussion with designers regarding the distinct purposes of the pins of the Opamps I believe reversed placement would cause major damage to the circuit, rendering the unit inoperable.

Check to see if the yellow light at the center of the circuit board is illuminated. When the Opamp incident happened, the yellow light died, showing the integrity of the circuit was compromised. If that yellow light is not lit I think you definitely have a repair happening.

Other good suggestions have been mentioned including deselecting the tube button, as when you remove the tube the entire unit falls silent if it is not turned off. I don't even know how to approach the possibility of there being a "bad" Opamp inserted; I think the likelihood of it is slim. Some people have bought Opamps from alternative sources and some have bought ones with longer legs and trimmed them down. I have no comment on that except I would think it more safe to do the swap precisely as I indicated.

Now, here is some encouragement; get it repaired and then as crazy as it may sound, do not sell it, but rather consider moving on to the Burson or DEXA discrete Opamps, as they are worlds better! They are absolutely worth the extra money. I have been using the DEXA Opamps with scintillating results. They are larger and easier to handle when rolling as well. Both the Burson and DEXA brands are far simpler/easier to work with both in terms of placement and identifying the orientation of the Opamp in relation to the circuit board. You absolutely must observe meticulously placing them with the half circle to the right as you face the unit. Otherwise, there may be another repair coming. :(

I urge you not to give up on it because there is a lot of change/improvement available via the discrete Opamps. I would not even consider going back to the IC Opamps, but move directly to the discrete Opamps.

Feel free to conatact me via the Audiogon message system if you wish. :)

I have no particular familiarity with the Minimax, but as an electrical design engineer, and after looking at the pin configurations of these devices (shown on page 3 here and page 5 here) I believe Doug is absolutely correct. Inserting either of these op amps oriented the wrong way is a disaster, which will almost certainly destroy the op amp, and probably damage other devices on the circuit board that connect to it, and possibly also those that supply power to it.

10-15-12: Daveaudiony
Both original OpAmps and proposed, regardless of position / orientation, do not change the outcome - unit no longer powers up.

This seems to say that you have tried both the original and the new op amps with both orientations. If so, all of them are almost certainly destroyed. If you are not certain that you used the correct orientation when you first re-tried the original op amps after noting the problem with the new ones, it might pay to obtain replacements (for either or both sets) and try again, in the off chance that other devices on the board were not damaged.

Also, be sure to follow good anti-static practices when handling these devices. As a minimum, that means touching a grounded metallic structure immediately before handling them, avoiding contact between your fingers and device pins (perhaps using a DIP puller to handle the devices), and not working where carpets or other static-prone surfaces are present.

Regards,
-- Al