SONY DAS-703ES Op Amp Bypassing

For my ear, this Sony’s old school TOTL DAC sounds strange, despite its non-compromise construction or parts selection.

It sounds, for me, not being alive, masked, veiled. Older CDP-101 sounds much better for me.

I experienced similar sound with later CDP-777ESA, and tried to do something on the 777. What I found was that NE/JRC5532s used in LPF stage of 777ESA were the main cause, while 101 uses JRC4560 for LPF.

5532 is a good audio op amp, but only when there is just one 5532 in the circuit, IMHO.

Now inside of DAS-703ES, we can find total six 5532s, work as generalized impedance converter to configure 6th order LPF.

In my previous Japanese post, I tried to reveil its sound by op amp rolling, and my choice was;

IV ... AD797

LPF ... AD827

Output ... AD797

To put single channel op amp to output stage, I needed to make adapter. Different connection for L and R.

For me, AD8065 was the best for output stage here, sound-wise. But after tried 8065, I noticed this chip has clear compatibility issue with 28.4V supply rail of 703ES.

So, I viewed schematics to find out what I can do.

LPF output goes into common drain FET, M5240 op amp drives push pull FET buffer. All these 3 components are in same feedback loop.

What came to my mind was ‘can I simply remove op amp?’

It has a common drain FET input stage, and should be no problem in receiving LPF’s higher impedance signal and in driving push pull FET. Since the load of common drain FET is a constant current, T.H.D. is much less than simple register load. But still we may have 0.2% or something, much worse than Sony’s number in brochure, 0.004%. But, who cares? IMHO, T.H.D. has almost no relation to sound quality, unless it is not much higher than 2~3%.

Ok, let’s try.

Remove M5240.

L-ch: short #1 and #7.

R-ch: short #16 and #10.

Works pretty fine.

Better transparent sound, lower power consumption and being free from headache of op amp selection, at the cost of worse T.H.D.

Beautiful modd ;-)

This success encouraged me to work on other op amps, especially 2ch x 3 in LPF for each L and R.

AD827s already achieved good airy sound, but very hot - power consuming, and make power regulator TR really hot.

By simply removing all of LPF op amps, we still can hear sound. But highs are reduced just as my Spice simulation above.

On Spice, I found my solution.

Bypassing all 5532s and C and R connected to op amps, and connecting 2.2k just before LPF and 2.2k just after LPF by 10mH inductor.

Above fig shows my two mods, bypassing output and LPF op amps.

Points of registers leads we need to pull out from PCB.

Done. Using TDK 10mH coil.

Result? Perfect.

Sounds are now totally unveiled, and good for healthy power supply operation also.

You can also try simply short two 2.2k registers, without using 10mH inductor. In such case, frequency response will be as below.

For my ear, this setup sounds bit strange, and I recommend to use 10mH.

Finally, I have only one op amp left in the circuit, IV conversion.

After all above mods, I found OPA627 clearly outperforms other amps for IV stage.

AD797 ... Good detailed and dynamic sound with unique sense of quietness. But sometimes, I can notice not natural expression.

(Later, I found AD797 was slightly oscillating...)

MUSES03 ... Detailed and airy, but no emotion.

AD844 or AD846 ... Start oscillating.

Bottom line.

To unveil the sound of 503ES, most important modd is bypassing tons of 5532 LPF by 10mH. Or, you can replace all of 5532s by AD827s.

Stock LF356 at IV and M5240 at output stage are not really bad. Works on these are optional, still recommended though.

My next try can be replacing final op amp by discrere components. Before that, I need to study more about base-common BJT, current mirror and so on.