Earlier in this thread Legarman posted about changing the Paridisea opamp to the LM4562. Apparently MHDT paid attention:
I bought this DAC six months ago when someone came at home with his homebrew non oversampling Dac and when I read Scott Faller report.
I really like this dac but in stock form, it lacks a little definition and soundstaging. I replaced the tube with a 396A. I began to draw the circuit and took some measuremnents. V+ and V- for the OPA2604 is +17V and -17V. This means that the op amp is feed with more voltage that specified by the company. First, I don't like the OPA2606 very much. It is a dark sounding chip and lacks definition. Finally, I decided to place a 8 pin socket at the place of the SOIC chip installed in the Paradisea. I used a socket because I wanted to try many op amps. First with +17 and -17V, these supply voltages are too high. The V+ and V- come from two TL431 shunt regulators that feed the tube cathode follower. Yes, you read correctly, the cathode follower has a 100 ohm for RP and another 100 ohms for RK. only +19V feeds the 100 ohm RP and only -19V feeds 100 ohms RK. This means that the tube operates with only 38V (I made a drawing but can't insert it with my message). From the +19V and -19V, there's 100 ohm resistors for decoupling and lower the voltage to the OPA 2604. The op amp is not decoupled with any capacitors at all. I replaced the two 100 ohms feeding the op amp with 330 ohms resistors and got _+14.5V and -14.5V. Near the op amp, I placed from V+ and gnd and V- and gnd 10mfd tantalum caps paralled with .01 mfd ceramic caps. These caps are placed aside the op amps. (I took some picts). Here are the op amps tried: AD826 = too much high mid, too hard. Two OPA627 placed on a Browndog adaptor = Mellow sound, very good soundstage, too much laidback sounding for my taste but WAY better than OPA2604. The surprise came from the newcomer National LM4562 specially designed for audio. When I got samples from National this new chip was on market since only two days. Soundstage and image are very good. Definition is excellent. At first there was not too much bass but things were correct after about 100 hours of playing time.
Placing this op amp in the paradisea with good decoupling caps across it means a new dac. BIG LEAGUE name dacs simply can't stand with the Paradisea about sound quality when modified. More on that later
Legarem
And a reply:
Legarman,
Many thanks for your generous contribution to AC. An auspicious start!
For those seeking a simpler, inexpensive alternative to 'brown dogged' OPA627s, I'd suggest an OPA2107 (surprise, surprise!) which is a dual, available in both SOIC8 and DIP8. For those who like the Burr Brown warm sound, this chip is about as close to the OPA627 in a drop in dual as one can find. It might be a good alternative to the AD826 that comes in the Constantine. While I subjectively like the BB sound, I've always found the OPA2604 gritty, unresolving, unextended and closed in and never found a situation where the OPA2107 wasn't a substantial upgrade. (given the relative prices I'd expect nothing less)
Like the LM4562, the OPA2107 are relatively low speed, low bandwidth (in comparison to many AD chips), but nevertheless wonderful opamps, and unlikely to oscillate or be otherwise problematic when swapped with most other opamps. The LM4562 is an appealing alternative to AD chips for those seeking less warmth than typical in BB opamps. ( I've presently one cooking in the center position of my Zhaolu 2.0)
I believe the easiest way to desolder a SOIC8 chip, lacking access to appropriate desoldering equipment, is to use a safety pin and slide the point between the body and the legs as you desolder. Slide the pin point further in as you desolder each pin. When you've lifted the pins on one side, repeat on the other side.
Regards,
Paul
The opamp seems to make a difference in what caps, if any, sound better, Robert Brown installed the OIMP's in the original Paradisea and loves them.
