I recently completed an upgrade of an Onkyo A7, which is the most comprehensive one for these amplifiers I have done. Since writing the original blog, I have made a number of further improvements, which are detailed below.
Starting with the power supply section, my customer asked that the 25,000uf 55v main capacitors be replaced, so after an analysis of the available options two Nippon Chemicon 27,000uf 100v units were installed, the original units were also Nippon Chemicon. These units are about 20mm taller, but the same diameter, and sit inside the case with no problems. As these had been done I decided to replace the main rectifier diodes, so UF5402 diodes were installed. The power supply capacitors were replaced with Nichicon PW series, except for C706 which is Bipolar, and here a Nichicon BP type was used. The relay was also replaced.
The main output transistors were fine, however I replaced all the driver and low level transistors on the main amp board. The differential amp was comprised of 2SC1775/2SA872 and these are now KSC1845/KSA992. The bias stabilization transistors were 2SC945 and these are now KSC2383. The driver amp pair was 2SA912/2SC1885 and these are now KSA1220AYS/KSC2690AYS. The complimentary pair were 2SD358/2SB528 and these are now KSC2690AYS/KSA1220AYS respectively, however although these work perfectly adequately, I have changed these to MJE15030/MJE15031, which are a closer match to the originals. That said there was no measurable improvement, nor sonic difference I could notice.
One thing that appears to regularly blow on these units are the 56 ohm resistors R653/R655 and R654/R656- so I always check them and generally replace them as well. All the electrolytic capacitors have been replaced, C605/C606 4.7uf 50v with WIMA film 4.7uf 50v, though again more recently I have been using 10uf UES Muse Bipolar caps, which is, to me, an improvement. Alternatively, there is sufficient room to put polypropylene caps here. Again after firther experimentation, I have opted for C619/C620 to be 1000uf UKA 25v caps. C633..C636 I now replace with 33uf UHE low impedance caps. The emitter resistors R659~R662 were replaced with Dale 1% 5W resistors.
The tone control board caps (C409/C410) were now replaced with Nichicon UES series bipolar MUSE caps.
On the pre-amp and equalizer board thedifferential amp (Q301~304) 2SC726 were replaced with KSA992 and the tone amp (Q305/Q306) were replaced with KSC1845. All the low value electrolytic capacitors were replaced. C201/C202 and C303/C304 were replaced with panasonic polypropylene caps of the same value. C319/C320 were replaced with 10uf MUSE UES bipolar caps. C225/C226/C317/C318 with replaced with 1uf 50v WIMA MKS film types. C211/C212 were replaced with Nichicon 470uf UKL low leakage types. C315/C316 were replaced with ELNA SIMLIC II 200uf. All the ceramic caps on both preamp and power amp boards were replaced with WIMA FKP of MLCC C0G ceramics depending on values.
All the switches and controls were deoxed , and the unit aligned as per the service manual.
The result is a very fine sounding amplifier!
May-2017– I have just completed another A-7 upgrade, and measure the distortion at around 0.02% THD+N- which considering the spec is 0.1% is quite an improvement. This unit has all new transistors, including the outputs, except for the phono stage, as well as the mods described above.
Jan 2021- With the new upgrades mentioned above, THD has come down to 0.003% and THD+N to about 0.09%. Sonically the amplifier is more transparent, detailed and dynamic.
Further updates: Since the original upgrades I have been refining the “recipe”, looking for further improvements in performance. This has involved further increasing some of the decoupling cap sizes, replacing some of the smaller ceramics and using more of the Panasonic polypropylene caps and WIMA FKP/MKP rather than the polyester MKS series where size permits. There are additional capacitors added to the phono section (the PCB has the markings for them) as well.