INSIDE MARANTZ AV RECEIVER
Picked up a huge Marantz receiver (SR8200) at the local donation center for not very much money.
FAULTY VOLUME KNOB
Even though the donation center has a 7-day return policy for non-working electronics, the receiver was worth more than I paid (to me) in parts alone. I quickly discovered that the volume knob was “stuck”. It is a rotary encoder type (not a potentiometer type). The volume setting would barely move when turning the knob,
Thanks to my familiarity with rotary encoders, I quickly recognized this problem as “noisy transitions” within the rotary encoder. In other words, it needed (more) debouncing. What I did was to install some capacitors to the signal pins and viola! it works almost as new. There is still a bit of debouncing problem but does not affect the responsiveness of the rotary encoder. If I experiment with different value capacitors, I would likely solve the problem, but for now this is good enough.
Other than this, the unit seems to be working properly. The only disadvantage is that now I cannot justify gutting it for parts🙂
From the golden era of Made in Japan audio electronics. Things are put together with more screws than seemingly necessary. Plus, this is the first device where I find the use of copper (or some copper allow) screws. The chassis is made of traditional stamped steel.
Nice brushed aluminum front panel (but the knobs are “metal looking” plastic)
The most ELNA capacitors in one place!
One of the last through-hole, hand-crafted audio components…
This receiver, old enough to be powered by a liner supply, is rated at 6x130W (780W for the amplifier section).
It uses a large EI transformer with a copper flux band. These bands are used In order to reduce the radiated flux from the transformer core, acting as a shorted turn to the leakage flux (only), greatly reducing magnetic interference to adjacent equipment.
There are two 27,000 uF “Marantz” filter capacitors. Incredibly good looking! I believe they are made by ELNA (as every other capacitor is also ELNA). The heatsink behind the capactors is for the bridge rectifier. .
(Update: a reader alerted me that the caps are made by Nippon Chemicon. The logo is in plain sight)
There is space for two additional capacitors. A nice mod would be to add a couple of Panasonic 4-lead capacitors such as these: Panasonic T-HA 10,000-18,000 uF, 63V [link][link] (with care not to blow the fuse due to in-rush current during power-up)
The SR9200 uses 4 capacitors with higher voltage rating but lower capacity as shown in the photo below [link]
ANALOG VOLUME CONTROL
The volume control is provided by two 6-channel Toshiba TC9482N volume control [link]
These devices control up to 8 analog channels (7.1 multichannel) that area available as pre-out but only 6 of them connect to power amplifiers
The input and outputs are buffered by NJM 2068DD opamps [link]. The “DD” grade devices exhibit lower noise specification. Where have we heard about these NJM2068?… From the development of the famous O2 headphone amp [link]
BOTTOM LINE: For those wanting to skip the Tech Section, the conclusions can be summed up as follows:
At gains less than 4X nothing overall could beat the $0.39 NJM2068 in the O2’s gain stage. This is especially true if you’re concerned about power consumption for battery operation.
Current prices of the 2068DD are $0.60 in quantity 1 orders [link]
DIGITAL TO ANALOG BOARD
Stereo D/A board uses CS4396 D/A (3 of them).
A 6-channel module with forced cooling.
Local power supply bypass capacitors. Notice the space for larger size capacitors (the higher model SR9200 uses larger capacitors). Replacing these capacitors with larger ones (a 1000 uF nichicon KW [link] for example -maximum diameter is 16mm) would be an easy mod.
Local PS bypass capacitors in the SR9200
DIRECT AUDIO PATH
There is an 8-channel analog input option (7.1 input) that bypasses all the digital processing. They are controlled by the analog volume chips and the output is available through the 8-channel pre-out. Six of those 8 channels are connected to the 6-channel power amplification module. This receiver can be used as a stereo tri-amp setup.