Denon UDRA-M7 Receiver Upgrades

[linuxguru]

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 one out of pure curiosity, during one of my visits to Ritchie Street. Upon opening it, I found to my horror that Denon had cut corners - whereas earlier 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.

 

[Hiten]

Thanks Linuxguru
I have an old Pioneer SA-6750. Also have downloaded schematics. It sounds good. But I have always wondered do we need to change all capacitors ? what If I take one by one and check with capacitance meter and if OK keep the original caps.
Thanks in advance
Hiten

 

[linuxguru]

I have an old Pioneer SA-6750. Also have downloaded schematics. It sounds good. But I have always wondered do we need to change all capacitors ? what If I take one by one and check with capacitance meter and if OK keep the original caps.

If it sounds good, and there is no visible damage to the components due to heat or moisture, then it's probably not worth experimenting to try to improve the sound. Electrolytics can take a while to break-in, so some of those old electrolytics are actually desirable, as long as they're not leaking, bulging or dried out.

Therefore, on vintage working equipment, it's prudent to confine the upgrades to the main PSU filter electrolytics and socketed op-amps, if any. (I often violate this guideline, sometimes with disastrous results).

 

[vivek.saikia]

Hi LinuxGuru,
Is it worth trying to increase the PSU capacitor bank in an amp? Will it tighten the bass somehow?

 

[linuxguru]

Is it worth trying to increase the PSU capacitor bank in an amp? Will it tighten the bass somehow?

There's an optimal value of capacitance for best sonics in each amp circuit, and increasing it beyond this point may actually make the sonics worse. That said, most Japanese consumer-grade amps from the '80s-'90s have undersized PSU caps in the range of 3300uF-4700uF for both channels combined. A slight increase will not hurt.

Try not to increase it by more than 20-30% - the peak inrush current as well as 50 Hz ripple currents are a function of the PSU capacitance, and increasing the capacitance will increase the stress on the PSU rectifier as well as transformer.

Tighter bass is function of a lot of things, including circuit topology, layout and bypass. A small high-quality bypass cap near the output stage can work more wonders than a large PSU filter cap some distance away.

 

[linuxguru]

Documenting similar mods to the Denon UD-M3, which is a micro-component integrated CDP/Receiver/Amplifier in the same form-factor as the UDRA-M7 Receiver:

Tuner/Line Amplifier Board
--------------------------------------
1) IC702 JRC4558 line amplifier replaced with NatSemi LM6172 (SOIC8).
2) C715, C716 rail-to-ground bypass caps replaced with 22uF/16V Sanyo Oscon SC (Black Gate PKs are a good alternative here).
3) C708, C709 4.7uF/50V SSL Electrolytics (output DC blocking caps) replaced with 3.3uF/50V Wima MKS2 film caps, each bypassed on the underside of the board with Panasonic ECHU 100nF/16V PPS film caps.
4) 2x 4.7uF/50V SSL Electrolytics (input DC blocking caps) replaced with 3.3uF/50V Wima MKS2 film caps, bypassed by Panasonic ECHU 100nF/16V PPS film caps as above.
5) (Optional) One additional rail-to rail bypass capacitor added as shown in the picture below, on the underside - 22nF/50V Panasonic ECHU PPS film cap.

(The above mods are sufficient if the unit is only going to be used as a CD source connected to an external amplifier - the mods below can then be omitted.)

Input Selector Board
-----------------------------
1) Line opamp JRC4558 replaced with NatSemi LM6172.
2) 10uF/50V SSL electrolytic bypass for opamp replaced with 10uF/50V Elna Cerafine.

(Check the adjacent connector mounting board for cracks/fractures in the solder joints
for the input/output RCA connectors, Speaker connectors, etc. Reflow all such joints
with additional solder as needed.)

Power Amplifier Board
--------------------------------
(Lots of harnesses have to be disconnected and disentangled to be able to
unscrew 2 + 4 screws that are used to mount this board to the base-plate).

1) C521, C522 4.7uF/50V SSL electrolytics (Input DC blocking capacitors) replaced with 3.3uF/50V Wima MKS film capacitors, bypassed on the underside of the board with 100nF/16V Panasonic ECHU PPS film caps.

2) C501, C502 22uF/50V SSL electrolytics (Misc. bypass caps) replaced with 22uF/50V Rubycon YXG or equivalent.

3) C503, C504 100uF/50V SSL electrolytics (bypass caps) replaced with 100uF/50V Panasonic FM or equivalent 8mm electrolytics.

4) C508, C507 10uF/50V SSL electrolytics (Power rail bypass caps) replaced with 10uF/50V Elna Cerafine (other alternatives, including Black Gates, are possible - but anything bigger than ~6mm diameter will require some bending to provide clearance to the adjacent power connector).

5) (Optional) 2x 104K Nissei film/foil capacitors (Zobel/Boucherot Network caps) replaced with 100nF/100V ERO MKP1837 polypropylene film/foil capacitors.

The audible effect of all these changes is vastly improved transparency, imaging and sound-stage. The changes will need at least 20-50 hours of run-in before some edginess subsides. If edginess persists, further bypasses may be needed on the input-selector board only.

 

[Mano]

Hello linuxguru

Is there any reliable source for getting proper components in Chennai! Please help with the source info if possible.

Cheers

 

[linuxguru]

Swastik and Suraj at Ritchie Street have a reasonable selection of electrolytics, including a few NOS Japanese. However, you will not find any premiun audiophile capacitor like a Black Gate, Cerafine, Silmic, Muse, etc. locally - the only source is EBay or online retailers like Farnell, Mouser, RS, etc.. The same holds for most premium opamps and premium film capacitors - nearly unobtainium at Chennai. However, availability at S.P.Road in Bangalore is slightly better - I've bought Oscons and various Wima film caps there, a few years ago..

 

[Mano]

Swastik and Suraj at Ritchie Street have a reasonable selection of electrolytics, including a few NOS Japanese. However, you will not find any premiun audiophile capacitor like a Black Gate, Cerafine, Silmic, Muse, etc. locally - the only source is EBay or online retailers like Farnell, Mouser, RS, etc.. The same holds for most premium opamps and premium film capacitors - nearly unobtainium at Chennai. However, availability at S.P.Road in Bangalore is slightly better - I've bought Oscons and various Wima film caps there, a few years ago..

Thanks linuxguru. Yeah I have been many times to these two guys. Sometimes they are so busy especially Swastik nowadays who deals in bulk, they would not spend time to our queries.

I will look out at SP Road when I visit Bangalore. I was looking for some OP amps and other good quality capacitors like the ones you used for other purposes. I am a Ham Radio operator also and sometimes look for some components.

Cheers

 

[Shailesh Dhodia]

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 one out of pure curiosity, during one of my visits to Ritchie Street. Upon opening it, I found to my horror that Denon had cut corners - whereas earlier 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.

Hi,
During my last visit to Chennai, I had collected components from linuxguru (Siva) for level 1 and level 2 modifications for Denon UDRA M7. Recently I got done the modifications from a technician. The initial impression after the modifications was that the sound was warm but somewhat boxy. But after some run-in happened it started sounding amazing. The sound is very warm and non-fatiguing. I have B1-Amp Camp combination which sounds amazing and which is reference for me. Though UDRA M7 is a chip amp (STK 405); after modifications it is hard to believe that the sound is coming out of a chip amp. Further to the modifications listed by linux guru; some more level 1 modifications were done by him which haven not been documented in the thread. I plan to do those modifications as well once I get the components from Siva. I am really thankful to Siva for the thread as well as for the components.

 

[linuxguru]

Shailesh, thanks for the update and praise.

A few substitutions that work well at comparable or lower cost:

1) Instead of low-value Black Gate PKs, use Wima MKS2XL. For instance, substitute 4.7uF/50V BG PK with 3.3uF/50V MKS2XL, optionally bypassed on the underside with Panasonic ECHU 100nF or similar (BG PKs are unobtainium now, but MKS2XLs will be available for the foreseeable future).

2) Panasonic FM can be replaced interchangeably by Rubycon YXG, with improvement in sonics - better air and linearity in most bypass applications (both are available fairly easily, but Japanese-production YXG has better measured specifications for audio, at a comparable or lower price).

3) Large-value Elna RE2 can be replaced by equivalent Elna RW5 if available (largest values I've seen are in the region of 4700uF/25V in RW5; the voltage rating may be too low).

4) LT1361 is a very transparent-sounding opamp which can be used instead of LM6172. LT1213 and AD8022 are other alternatives.

5) Level 3 mods are optional - I haven't done most of them yet.

 

[alvin59]

Shailesh, thanks for the update and praise.

A few substitutions that work well at comparable or lower cost:

1) Instead of low-value Black Gate PKs, use Wima MKS2XL. For instance, substitute 4.7uF/50V BG PK with 3.3uF/50V MKS2XL, optionally bypassed on the underside with Panasonic ECHU 100nF or similar (BG PKs are unobtainium now, but MKS2XLs will be available for the foreseeable future).

2) Panasonic FM can be replaced interchangeably by Rubycon YXG, with improvement in sonics - better air and linearity in most bypass applications (both are available fairly easily, but Japanese-production YXG has better measured specifications for audio, at a comparable or lower price).

3) Large-value Elna RE2 can be replaced by equivalent Elna RW5 if available (largest values I've seen are in the region of 4700uF/25V in RW5; the voltage rating may be too low).

4) LT1361 is a very transparent-sounding opamp which can be used instead of LM6172. LT1213 and AD8022 are other alternatives.

5) Level 3 mods are optional - I haven't done most of them yet.

Hi linuxguru, would OPA1612 be good enough to replace the op amp at the tone board ?