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Listing of Opamps for EE Minimax DAC Plus

Phil from Cimmaron Technology sent me a list of approved Opamps for
respective positions on the board of the EE Minimax DAC Plus; prices
include the Brown Dog Adapters provided by Cimmaron. I have been using
in the U1/U2 position the OPA2604 and in the U6/U7 position the OPA827.
I have not Opamp rolled this unit much, as I have been busied with other
components for review. I attest that the DAC Plus in SS output with the
tube removed and these opamps is sensational.

(NOTE CAREFULLY the warning at the bottom NOT to use the AD 8620 in the U1/U2 positions!) Also note that the positioning of the opamps/adapter is always with the small square solder point on the topside of the Opamp at the upper right hand when the unit is facing the installer. Finally, it is recommended that an opamp extraction tool and an anti-static device be used when removing/installing Opamps.

Is it "worth it"? YES! YES! YES! :)

RECOMMENDATIONS OF OPAMPS FROM CIMMARON TECHNOLOGY:
For U1/U2
Single-channel op-amps mounted on the 020302 SO8-to-DIP8 single-to-dual
channel adapter:
qty 2 each required

020302-OPA627 $48.00 x 2 = $96.00
020302-OPA827 $38.00 x 2 = $76.00
020302-AD797B $48.00 x 2 = $96.00

. . . also for U1/U2
Dual-channel op-amps mounted on the 970601A SO8-to-DIP8 adapter
qty 2 each required

970601A-AD8620 $23.00 x 2 = $46.00
970601A-OPA2604 $13.00 x 2 = $26.00
970601A-OPA2134 $10.00 x 2 = $20.00

For U6/U7
Single-channel op-amps mounted on the 970601A SO8-to-DIP8 adapter
qty 2 each required

970601A-OPA627 $28.00 x 2 = $56.00
970601A-OPA827 $23.00 x 2 = $46.00
970601A-AD797B $23.00 x 2 = $46.00

The AD 8620 should not be used in the DAC PLUS.
"On some forum there was a suggestion to use the AD8620. for positions U1
and U2. While this is a dual op-amp, it is only rated to use up to
plus/minus 13 volts. The circuit in the EE Mini Max DAC and DAC Plus is
plus/minus 15 volts."
douglas_schroeder
sibelius
256 posts
 
I've been experimenting some more with opamps and have to say that the only combination I like a tad bit better than what Doug recommended (2604 in U1/U2 and 827 in U6/U7 with tube removed in SS mode)is to replace the 827's with Dexa discrete opamps. I'm finding the discrete opamp seems to add a bit more air around the instruments while making things a tiny bit warmer. However, the cost of the discrete opamps is rather high and the difference is not night and day. I think the 2604/827 combo is probably the best mod for the $.

I'm going to try two more experiments. The first is to go back to tube mode with a NOS mullard 12AU7. The second is to add Dexa discrete opamps in U1/U2 and see how an all Dexa system works.

More to come ...
skomak
4 posts
 
Thank you Bill

Very proffesional from your side
Rgds
sibelius
256 posts
 
Here's an update on some of my tinkering.

As I mentioned before, the setup I've settled in to this point is 2604 opamps in U1/U2, Dexa Discret opamps in U6/U7 (just a smidge better than the 827s) in SS mode with tube removed.

I'm on record as stating I did not like the Dac+ in tube mode with the stock EH tube. I felt the sound was veiled and muddied. However, I have read where several people liked tube mode with a better tube. So in the spirit of giving tube mode one more shot, I ordered a mullard NOS 12au7. Well, after some more extended listening I need to ammend my original statement. While the SS mode still has more detail, the mullard tube is much less veiled than the EH tube and scored points by smoothing out rough patches in bright recordings.

At this point, which mode is better really becomes a function of the recording in my system. If a recording is bright or hard, I prefer the mullard tube mode. In exceptionally well recorded music, I find I enjoy the additional detail of SS mode. I guess the take away is don't ignore tube mode until you first try it with a better tube.

My next experiment will be to replace 2604's in U1/U2 with Dexa Discrete opamps. Will see how an all Dexa opamp unit sounds.

The good news is that regardless of your personal views, the Dac + allows for tremendous flexibility and experimentation. I'm sure almost everyone can find a setting which will be optimal in your system.
mrtennis
3,295 posts
 
hi sibelius:

what do you gain by replacing the stock op amps ?

my take on the stock 12au7 is the opposite of yours, namely, bright, thin and lean.

which mullard did you use, the long or short plate ?

thanks
sibelius
256 posts
 
Hi Mr. Tennis:

Moving from the stock opamps to 2604's and 827's gave me a sharper and larger soundstage. It was very noticeable. Not a subtle change. Since then I have swapped out the 827's with Dexa Discrete opamps. This move was more subtle. A little bit more air around the instruments but not as dramatic a move as changing out the stock parts.

My tube is a standard plate mullard rebranded as Daystrom from the early 1960's I believe. Now that I know that NOS tubes makes a difference, I will probably try some additional NOS tubes. Pricing is pretty good when you only need a single.

Changing out opamps is not that expensive. With Brown Dog adapters (which makes installation a snap) I believe I spent about $85 or so including shipping. Well worth the effort IMO.
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