The Denon UDRA-M7 is a late-'90s 2-channel integrated amplifier and AM/FM receiver in a convenient micro-component form-factor. I picked up a pre-owned one out of pure curiosity. Upon opening it, I found to my horror that Denon had cut corners - whereas other Denon equipment that I have seen generally had high-end Japanese electrolytics (e.g. Elna Cerafines), this one had generic Samsung (SSL) electrolytics for almost everything except the main PSU filter caps! The power amp was an STK405 stereo module, and the visible opamps were RC4558 (another disappointment).
It worked ok, with a typical Japanese consumer electronics solid-state sound - lots of bass, etched metallic highs, etc. I decided it was time to bring out the soldering iron and try to mod/upgrade it with minimal expense. I did two levels of mods, but most people can safely stop with the Level I mods.
Level I mods (electrolytics only)
------------------------------
Main Board:
1) Change C002, C009 from SSL 100uF/50V to Rubycon YXG 120uF/63V.
2) Change C507, C508 from SSL 100uF/50V to Rubycon YXG 120uF/63V.
3) Change C322, C323 from SSL 10uF/25V to Elna Cerafine 10uF/16V.
4) Change C325, C326 from SSL 10uF/50V to Black Gate PK 4.7uF/50V.
5) Change C511, C512 from SSL 10uF/50V to Black Gate PK 4.7uF/50V.
Tone-Control Board:
1) Change C413, C414 from SSL 10uF/50V to Nichicon Muse SW 10uF/25V.
Level 2 mods (Op-amps)
-----------------------
(Warning: this requires removal and installation of small SMD components.)
Volume-Control Board:
1) Change IC402 from RC4558 to Natsemi LM6172.
Main Board:
1) Change line-amp located on underside of board near AM/FM tuner from RC4558 to NatSemi LM6172.
Tone-Control Board:
The RC4558 op-amp on this board needs to be upgraded, but I skipped this upgrade since the layout of the tone-control board does not have adequate supply bypass capacitors to support stable operation of the LM6172 or similar.
Level 3 mods (possible future capacitor mods)
------------------------------------
1) Replace all SSL 1 uF/50V electrolytic coupling capacitors on all boards with film/foil caps (e.g. 1uF/63V Wima MKS2XL). There are over a dozen of these caps, mostly on the tuner board. The 5mm pitch MKS2XL is a tight fit at some locations, but barely feasible.
2) Replace main PSU filter caps (4700uF/35V 16mm Elna RE3) with Nichicon Muse KG or similar high-quality electrolytics.
3) Replace the 4x Polyester film 0.22uF/100V caps in the Zobel/Boucherot network with Polypropylene caps (e.g. Wima MKP2 or similar).
4) Replace the 5x Polyester film caps in the tone-control network with Polypropylene or Polystyrene film caps.
Preliminary audible impressions of Level 1 & 2 upgrades:
----------------------------------------------------
It has definitely opened up, with improved highs and clearer detail across the spectrum. Soundstage needs to widen further as the Black Gates break-in gradually over the next 100-300 hours. Imaging is adequate, but not pin-point precise - a possible artifact of the remaining electrolytic coupling caps and the RC4558 op-amp on the tone-control board. The metallic, etched treble has smoothened out considerably- the overall audible sonics are now consistent with a $1000 amplifier, not a $50 'Made in China' bargain special at Wal-Mart.
It worked ok, with a typical Japanese consumer electronics solid-state sound - lots of bass, etched metallic highs, etc. I decided it was time to bring out the soldering iron and try to mod/upgrade it with minimal expense. I did two levels of mods, but most people can safely stop with the Level I mods.
Level I mods (electrolytics only)
------------------------------
Main Board:
1) Change C002, C009 from SSL 100uF/50V to Rubycon YXG 120uF/63V.
2) Change C507, C508 from SSL 100uF/50V to Rubycon YXG 120uF/63V.
3) Change C322, C323 from SSL 10uF/25V to Elna Cerafine 10uF/16V.
4) Change C325, C326 from SSL 10uF/50V to Black Gate PK 4.7uF/50V.
5) Change C511, C512 from SSL 10uF/50V to Black Gate PK 4.7uF/50V.
Tone-Control Board:
1) Change C413, C414 from SSL 10uF/50V to Nichicon Muse SW 10uF/25V.
Level 2 mods (Op-amps)
-----------------------
(Warning: this requires removal and installation of small SMD components.)
Volume-Control Board:
1) Change IC402 from RC4558 to Natsemi LM6172.
Main Board:
1) Change line-amp located on underside of board near AM/FM tuner from RC4558 to NatSemi LM6172.
Tone-Control Board:
The RC4558 op-amp on this board needs to be upgraded, but I skipped this upgrade since the layout of the tone-control board does not have adequate supply bypass capacitors to support stable operation of the LM6172 or similar.
Level 3 mods (possible future capacitor mods)
------------------------------------
1) Replace all SSL 1 uF/50V electrolytic coupling capacitors on all boards with film/foil caps (e.g. 1uF/63V Wima MKS2XL). There are over a dozen of these caps, mostly on the tuner board. The 5mm pitch MKS2XL is a tight fit at some locations, but barely feasible.
2) Replace main PSU filter caps (4700uF/35V 16mm Elna RE3) with Nichicon Muse KG or similar high-quality electrolytics.
3) Replace the 4x Polyester film 0.22uF/100V caps in the Zobel/Boucherot network with Polypropylene caps (e.g. Wima MKP2 or similar).
4) Replace the 5x Polyester film caps in the tone-control network with Polypropylene or Polystyrene film caps.
Preliminary audible impressions of Level 1 & 2 upgrades:
----------------------------------------------------
It has definitely opened up, with improved highs and clearer detail across the spectrum. Soundstage needs to widen further as the Black Gates break-in gradually over the next 100-300 hours. Imaging is adequate, but not pin-point precise - a possible artifact of the remaining electrolytic coupling caps and the RC4558 op-amp on the tone-control board. The metallic, etched treble has smoothened out considerably- the overall audible sonics are now consistent with a $1000 amplifier, not a $50 'Made in China' bargain special at Wal-Mart.
