Onkyo A7 Upgrade

By October 7, 2016Audio, upgrades

 

 

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I recently completed an upgrade of an Onkyo A7, which is the most comprehensive one for these amplifiers I have done.

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 Fairchild 1N5402were 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.

 

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Those new power supply capacitors looking serious

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Completed unit

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.

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, CV605/C606 4.7uf 50v with WIMA film 4.7uf 50v and the others (C619/C620 and C633~C636) with Nichicon PW units. The emitter resistors R659~R662 were replaced with Dale 1% 5W resistors.

The tone control board caps (C409/C410) were replaced with Nichicon KL series low leakage units.

On the pre-amp and equalizer board theimg_0649differential amp (Q301~304) 2SC726 were replaced with KSA992 and the tone amp (Q305/Q306) were replaced with KSA1845. All the electrolytic capacitors were replaced, C201/C202/C303/C304 with WIMA 2.2uf 50v film as were C225/C226/C317/C318 with 1uf 50v WIMA film types. C211/C212 were replaced with Nichicon KL types as were C319/C320. C315/C316 were replaced with Nichicon PW types.

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.