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OpAmp update/mod in the Sony CDP-XA7 ES

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Crossy:
Well,
for starters, the Sony CDP-XA7 ES was one of the last Sony "high-end" CD players (available since 1995
up to 2005). It features a Bitstream DAC with internally balanced IO (although not taking fully advantage
of it in its original configuration). It also uses DC coupling in the output stage instead of a coupling capacitor.
(through an opamp based DC-Servo - OPA-27GP from Burr Brown, IC461/561)  8-)

To follow this thread, the reader needs a Service Manual that can be obtained from various sources,
for example from www.manuals-in-pdf.com via direct .pdf download.  :-D

Since the design is already high-quality (in typical Sony-ES series fashion), most of my
hints will involve merely chaning opamps to more current types, as there has been
TREMENDOUS progress in this field over the last decade with regard to noise immunity
(opamp voltage / current noise), output current capability, linearity and speed (slew rate, settling time).   8-)

http://www.thevintageknob.org/SONY/sonyes/CDPXA7ES/CDPXA7ES.html
http://cdp101.hp.infoseek.co.jp/cdpxa7es/cdpxa7es.html
http://translate.google.com/translate?u=http%3A%2F%2Fcdp101.hp.infoseek.co.jp%2Fcdpxa7es%2Fcdpxa7es.html&langpair=ja%7Cen&hl=fr&ie=UTF-8&oe=UTF-8&prev=%2Flanguage_tools

For most of the post-DAC filtering, the XA-7 ES originally relies on the AD-712. All these opamps are present  on the PCB as SMD types.
Note that the AD-712 is a FET opamp - in a dual opamp package. I found this puzzling as only the first stage after the DAC (labeled "de-emphasis" filter)
seems to require high-impedance (and hence a FET input opamp). Beyond that it appears to me that ordinary BJT opamps would do the job and provide
reduced noise and better sound also. Maybe back then only the AD-712 was available as an SMD chip.
Also present are NJM-2114D types in DIP package - I guess they are used where higher output current is required. Also, these are ordinary BJT opamps
(In the CDP-XA7 as Headphone driver and variable unbalanced output path amplifier). Essentially, they can be considerd "lower noise" NE-5532 replacement,
they calso can handle higher output current than the plain-vanilla NE-5532. The NJM-2114D are typically found in japanese Audio / Video gear and the
prefix "NJM" stands for "New Japan Radio Corp".
 
My plan is to get "optimal" state of the art opamp types in the audio signal path - for each of the functions the respective stage performs. So my gut feeling tells me
to minimize the parameters noise, "settling time", voltage and and maximize Slew Rate when possible. The problem is - what parameters take precedence in each function ?
 
IC-504, IC-404 ... OPA-27GP ... DC Servo - doesn't seem to require any change
 
IC-401,IC-501 (AD-712) post DAC Filter "De-Emphasis" handles balanced audio out from DAC.... appears to require High input Impedance
preference: replace with THS-4032  (dual type, BJT but 2MegOhm Rin, +/- 16V, 100Mhz, 1.6nV noise, 60ns settling time, 100V/µS slew, 2MegOhm Input Impedance, drives 90mA output, -90dB THD 1Mhz)
fallback: replace with AD8620 (dual type, slightly more noise, FET opamp, +/-13V max, 25Mhz, 6nV noise, 5fA noise, 600ns settling time, 50V/µS slew, THD 0,0006% 10kHz)
 
IC-402, IC-502 (AD-712) labeled "mix amp" (only 1 opamp of the dual AD-712 was used originally !) - makes single ended audio signal from balanced signal
replace with OPA211 (SiGe BJT opamp, +/- 18V, max. 80Mhz, 1.1nV noise, 1pA noise, 400ns settling time, 27V/µS slew rate, THD -136dB 1kHz)
     it appears to me that a BJT opamp can be used here to make the balanced signal single ended. Single type opamp possible since the original opamp used only one half od the dual AD712
     no need for a high-impedance opamp such a FET input opamp and the OPA211 should easily work here (not particulary demanding type wrt. oscilation)
 
IC-403,IC-503 (AD712) labeled "buffer" one for fixed out (appears to be I/V converter), another for Headphone stage
prefenence: replace with THS-4032  (dual type, BJT but 2MegOhm Rin, +/- 16V, 100Mhz, 1.6nV noise, 60ns settling time, 100V/µS slew, 2MegOhm Input Impedance, drives 90mA output, -90dB THD 1Mhz)
fallback: replace with AD8599 (dual type BJT, +/- 18V, 17Mhz, 1.1nV noise, 2000ns settling time, 17V/µS Slew, -120dB THD 1kHz) ... settling time a tad high, but a typical "audio friendly" opamp
 
IC-461, IC-561 ... (NJM-2114D) Preamp/Driver-Stage for Headphone Out and variable Out
preference: replace with THS-4031/32 (drives 90A, BJT but 2MegOhm Rin, +/- 16V, 100Mhz, 1.6nV noise, 60ns settling time, 100V/µS slew, 2MegOhm Input Impedance, drives 90mA output, -90dB THD 1Mhz)
fallback: replace with AD8599 (dual type BJT, +/- 18V, 17Mhz, 1.1nV noise, 2000ns settling time, 17V/µS Slew, 50mA output current, -120dB THD 1kHz)
           
IC-460, IC-560 (NJM-2114D) LowPass Filter for Balanced Out
preference : replace 2x AD8599 per channel with one OPA1632 and change the filter configuration accordingly (OPA-1632 is a fully balanced output opamp)
                  OPA1632 (full balanced audio output opamp, 1.3nV nosie, 50V/µS Slew, +/-16V, 150Mhz BW, 75ns settling time, THD 0,0000022%)
fallback: replace with AD8599 (dual type BJT, +/- 18V, 17Mhz, 1.1nV noise, 2000ns settling time, 17V/µS Slew, 50mA output current, -120dB THD 1kHz)
 
any input is much appreciated !
 
best rgrds from Vienna/Austria
Crossy

Crossy:
Okay,
yet another update and refinement
 
Cognizant of Per-Ander's assertion that replacement opamps should be audio-friendly and not prone to
oscillation, I figured it could be adviseable to use this "fully differential" new opamp OPA-1632 
also in place of the DE-Emphasis (IC501,IC401) and change the circuit design accordingly
(instead of having both hot and cold signals filtered by different chips, the OPA-1632 would handle
both simultaneously)
 
This is also a BJT opamp (like the THS-4031/4032) yet input impedance (Rin) is even higher,
this time - 34 MegOhm (instead of the 2 MegOhm of the THS-4031/4032). The filter circuit would have to be changed
somewhat since in place of two conventional single ended AD712 opamps, one fully differential OPA-1632 opamp would be present.
 
The OPA-1632 should be less prone to ringing and oscillation. According to specs
it should handle output currents of up to 150mA, even higher than the 90mA the THS-4031/32 can handle.
 
http://www.thevintageknob.org/SONY/sonyes/CDPXA7ES/CDPXA7ES.html
http://cdp101.hp.infoseek.co.jp/cdpxa7es/cdpxa7es.html
http://translate.google.com/translate?u=http%3A%2F%2Fcdp101.hp.infoseek.co.jp%2Fcdpxa7es%2Fcdpxa7es.html&langpair=ja%7Cen&hl=fr&ie=UTF-8&oe=UTF-8&prev=%2Flanguage_tools
 
IC-504, IC-404 ... OPA-27GP ... DC Servo - doesn't seem to require any change
 
IC-401,IC-501 (AD-712) post DAC Filter "De-Emphasis" handles balanced audio out from DAC.... appears to require High input Impedance
    preference 1: replace 2x single ended AD-712 with 1x OPA1632 (balanced IO) and change filter layout accordingly (OPA-1632 can handle hot and cold phase simultaneously)
         OPA1632 (full balanced audio output opamp, 1.3nV nosie, 50V/µS Slew, +/-16V, 150Mhz BW, 75ns settling time, THD 0,0000022%, 34MegOhm Input impedance, drives 150mA output)   
        this idea probably makes best useof the balanced output from the DAC and processes all post-DAC filtering with fully differential components as long as possible !
        it would also upgrade the balanced signal path as settling time of the OPA-1632 is ultra-low compared to AD-712 and NJM-2114D and slew-rate is way higher
   preference 2: replace with THS-4032  (dual type, BJT but 2MegOhm Rin, +/- 16V, 100Mhz, 1.6nV noise, 60ns settling time, 100V/µS slew, 2MegOhm Input Impedance, drives 90mA output, -90dB THD 1Mhz)
        fallback: replace with AD8620 (dual type, slightly more noise, FET opamp, +/-13V max, 25Mhz, 6nV noise, 5fA noise, 600ns settling time, 50V/µS slew, THD 0,0006% 10kHz)

IC-402, IC-502 (AD-712) labeled "mix amp" (only 1 opamp of the dual AD-712 was used originally !) - makes single ended audio signal from balanced
       replace with OPA211 (SiGe BJT opamp, +/- 18V, max. 80Mhz, 1.1nV noise, 1pA noise, 400ns settling time, 27V/µS slew rate, THD -136dB 1kHz)
       it appears to me that a BJT opamp can be used here to make the balanced signal single ended. Single type opamp possible since the original used only one half od the dual AD712
       no need for a high-impedance opamp such a FET input opamp and the OPA211 should easily work here (not particulary demanding type wrt. oscilation)
 
IC-403,IC-503 (AD712) labeled "buffer" one for fixed out (appears to be I/V converter), another for Headphone stage
       prefenence: replace with THS-4032  (dual type, BJT but 2MegOhm Rin, +/- 16V, 100Mhz, 1.6nV noise, 60ns settling time, 100V/µS slew, 2MegOhm Input Impedance, drives 90mA output, -90dB THD 1Mhz)
       fallback: replace with AD8599 (dual type BJT, +/- 18V, 17Mhz, 1.1nV noise, 2000ns settling time, 17V/µS Slew, -120dB THD 1kHz)
 
IC-461, IC-561 (NJM-2114D) Preamp/Driver-Stage for Headphone Out and variable Out
       preference: replace with THS-4031/32 (drives 90A, BJT but 2MegOhm Rin, +/- 16V, 100Mhz, 1.6nV noise, 60ns settling time, 100V/µS slew, 2MegOhm Input Impedance, drives 90mA output, -90dB THD 1Mhz)
       (am besten wohl mit 2x 4031 mittels SMD/DIP Adapter um Übersprechen nochgeringer zu halten)
       fallback: replace with AD8599 (dual type BJT, +/- 18V, 17Mhz, 1.1nV noise, 2000ns settling time, 17V/µS Slew, 50mA output current, -120dB THD 1kHz)
           
IC-460, IC-560 (NJM-2114D) LowPass Filter for Balanced Out
     preference : replace 2x AD-712 per channel with one OPA1632 and change the filter configuration accordingly (OPA-1632 is a fully balanced output opamp)
                     OPA1632 (full balanced audio output opamp, 1.3nV nosie, 50V/µS Slew, +/-16V, 150Mhz BW, 75ns settling time, THD 0,0000022%)
    fallback: replace with AD8599 (dual type BJT, +/- 18V, 17Mhz, 1.1nV noise, 2000ns settling time, 17V/µS Slew, 50mA output current, -120dB THD 1kHz
 
The essence of these mods would be to upgrade all audio signal paths materially. (Voltage) Noise is reduced to 1/10 to 1/20 of the original configuration,
THD drops from -110dB to less than -125dB
Slew rate is increased  from 13 to at least 27 (50 in the balanced audio path)
settling time from 3000ns (original total signal path) to 800ns or less (400 in the balanced audio path)

best rgrds,
Crossy

peranders:
You can edit your post, no time limit. Just a hint.....

Crossy:
P-A,
thanx for the reminder ! Already altered and slightly corrected both posts !

Another goodie I found today browsing on recent opamp developments.

Bruno Putzeys is one of the key guys behind this odd recent TI/Burr-Brown full-differential audio amp, the OPA1632 - he wrote a lot of TI's application notes on fully differential opamps...
http://recforums.prosoundweb.com/index.php/mv/msg/24704/0/0/0/

He recently linked to this extensive bench-measurement comparison (>370pages !). Most common opamps are being compared for audio purposes there !

http://www.sg-acoustics.ch/analogue_audio/ic_opamps/pdf/opamp_distortion.pdf

best to you and all
CROSSY

Crossy:
Yet another potentially interesting opamp using
the SiGe process... OPA-827 from TI/BB ... to me
looks like an improved OPA-627 replacement. In
Europe, AVNET appears to be stocked with the type..


OPA-827 : http://focus.ti.com/lit/ds/symlink/opa827.pdf

to be compared with the well-known highend OPA-627:
 
OPA-627 : http://focus.ti.com/lit/ds/symlink/opa627.pdf
 
the new OPA-827 seems to offer even lower voltage noise (4nV * sqrt(Hz)) compared
to the 4.5nV of the OPA-627. Settling time is unchanged, however slew rate is reduced
to 28V/µS from 55

CROSSY

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