Upgrading the Benchmark DAC 1?

[Salas]

Hello all and merry Christmas!

I had an interesting session the other day with a couple of friends (one is a piano player and excellent loudspeaker engineer, the other is the most famous Greek audio press scribe). We were evaluating CD playes and dacs using 2 very high resolution speakers and a wee full range bipole. One is a 2 box 3 way with PHLs and Fountek, other is a 2 way standmount with PHL and Audax, third is Salas TB3 revisited (you can search this forum about TB3 rev.). We had Unison Research moded Unico tubed CDP, Benchmark DAC 1, Deltec vintage hot rodded, Copland 288, Theta Gen V8, Creek Destiny.
Well, we came to the conclusion that CD replay is still a flawed case compared to a turntable (but we cant bear the fact that only 10% of an LP collection can prove this, until it will eventually worn out, so its practically an elite afair) and its replay (CD) did not come such a long way in 20 yrs. Tarted up yes but not fundamentally evolved.
Apart from the above blanket conclusion it was interesting to realise that each manufacturer was trying to present a credible rendering of music, doing his tone hocus pocus. The Benchmark had top resolution but was thin. Theta had the resolution and the guts (but at $$$$), Unison emphasised midrange musicality, Creek was treading a fine line between excess and restrain (overall the safest bet, also the best transport bar the expensive Theta). Copland was resolute enough but grandiose. Funny how the DPA little bit of 15 years old tech was still giving a valid point of view!
I ended up with the notion that I could buy the Benchmark if -and only if- I could flesh out its tone. To get a Theta is out of the question, I am not well off.
I thought of what is making it sound thin...this tone I have heard before...and then it dawned on me! Sounds like 5532! Ok I opened it up...11 NE5532's! silicon bridge rectifiers, smd coupling caps...
Gentlemen! your attention please! Suggestions are in order. Remember, there must be a double opamp thats unity stable and not a rare species with touchy behaviour for throwing out the 5532 among other hot rod suggestions.

P.S. The DPA little bit has 2604 smd, can a resistor from out to V+ or V- help it ? Had good results with 627 doing this once. If yes where is better with this chip? V+ or V-? ...Carlos FM?

See a picture of the benchmark with lid off :

[carlosfm]

Originally posted by salas
Gentlemen! your attention please! Suggestions are in order. Remember, there must be a double opamp thats unity stable and not a rare species with touchy behaviour for throwing out the 5532 among other hot rod suggestions.

AD827.

Originally posted by salas
P.S. The DPA little bit has 2604 smd, can a resistor from out to V+ or V- help it ? Had good results with 627 doing this once. If yes where is better with this chip? V+ or V-? ...Carlos FM?

You can bias the OPA(2)604, but you won't hear much of a difference, if any. The same for the OPA(2)132.
I have letf using the OPA2604 some years ago, because it sounds too distorted in the midband/treble for my ears, there are much better options.

Try the AD827.

Merry Christmas

[Salas]

Thanks Carlos! Much appreciated. Merry Christmass too and wish you many years of well functioning Epos tweeters!

In 2604 I hear the same nasties that is why I tageted it.

cheers.

[rdf]

Hi Salas. One approach:

http://www.6moons.com/audioreviews/b...rk/dac1_3.html

Can't vouch for it, know nothing more than what's described in the article. I also have a DAC-1, an early model, and have considered making a few mods (lowering the unbalanced Zout for one) but got put off by all the SMT. The bridge rectifiers will eventiually go.

[Salas]

Tell me how do you like the stock dac 1 and how is your system.

I am aware of the bybee voodoo. Too expensive, too fairy dust.
I would like to see changed opamps, PSU caps, regs. Real stuff.

[carlosfm]

Originally posted by salas
I would like to see changed opamps, PSU caps, regs. Real stuff.

What regs does it use?
I suppose it's those heatsinked to the chassis.
The pic is not clear enough...
Schematic?
Btw, all caps are SMD, including electrolythics.

[Salas]

78xx everywhere! What an inferno!

[carlosfm]

Originally posted by salas
78xx everywhere! What an inferno!

You can say that.
The board is not practical to work on, at all.
Standard rectifier bridges, SMD electrolythic caps, 78/9xx regs... :bs:

I can't see the bottom side of the board, but those regs should be bypassed (input and output to ground) with some small caps (100nF is fine) right on their legs.
No electrolythic psu caps on the analog stage... limits the opamp choice to... NE5532, and some others.
How practical is it to make a decent psu bypass on those op-amps?

Is this an expensive dac?

[Salas]

on the right hand side there is analogue PSU.
its $975.
Killer resolution but skinny tone. Flesh out tone for me Carlos! AD827 ok for that?

[carlosfm]

Originally posted by salas
Killer resolution but skinny tone. Flesh out tone for me Carlos! AD827 ok for that?

Yes, and a pair of 47~100uF caps per op-amp, directly from V+ and V- pins to ground.
100~330nF across the rails. On and SMD dual op-amp you can solder this cap directly on top of it, from pin 4 to pin 8.