jd3rdcoast
Super Member
I took in a 2015 to calibrate for a friend. Really nice looking Baby Marantz. Tested it on a set of Large Advents and sounded good. But with quite a difference between L & R output levels.
Checked the Bias settings and both sides were way down around 1.0 mV on both sides so adjusted with VR's R627/R628 to 7.5 mV spec. Set equal clipping which was a bit off. The bias was not staying stable so gave each VR a shot of DeOxit and worked them. Much more stable now.
Inputting a 1kHz sine wave and watching the outputs was seeing much higher output on R channel and it would go noisy and clip much sooner than L channel. I checked the inputs from Preamp section and they were equal and quiet. Using my scope I checked after the Pre-drivers H601/H602 going into base of H603/H604 and noticed large noisy signals on R side so I replaced H601 (2SC1327 S/R Hfe_518 => KSC1845FTA Hfe_364) & C611 (10uf/25/v => Elna 10uf/50V)
Also some suspect solder joints were re-flowed.
That cleared up some of the noise and the output signals are closer with the R side still a tad higher but very close. The right side still clips a bit earlier as would be expected.
Here is image of the signals at clipping with R on top. 5v/div. calculate to apx 17W R & 9W L. L will clip at 30p-p or 14W but R is already severely clipping by that time.
At 10v/div
Tired outputs?
I am still seeing a significant ripple (0.4 V-L and 0.35 V-R) on this board and a noticeable hum (not Vol dependent) when speakers are engaged and volume down. (This is with the input side of board lifted and jumpers for inputs and grounding. I also get a pop in speakers when touching the front panel after a few minutes of warm up.
I'll be replacing main power supply cap (3300uf C004) and filter caps on Amp 2200uf C601/C602.
50V rail output is reading 47.6 V.
Image at 50V input to boards.
0.2v/div
Image on 2200 uf Filter Caps C623/C624.
0.1v/div.
Checked the Bias settings and both sides were way down around 1.0 mV on both sides so adjusted with VR's R627/R628 to 7.5 mV spec. Set equal clipping which was a bit off. The bias was not staying stable so gave each VR a shot of DeOxit and worked them. Much more stable now.
Inputting a 1kHz sine wave and watching the outputs was seeing much higher output on R channel and it would go noisy and clip much sooner than L channel. I checked the inputs from Preamp section and they were equal and quiet. Using my scope I checked after the Pre-drivers H601/H602 going into base of H603/H604 and noticed large noisy signals on R side so I replaced H601 (2SC1327 S/R Hfe_518 => KSC1845FTA Hfe_364) & C611 (10uf/25/v => Elna 10uf/50V)
Also some suspect solder joints were re-flowed.
That cleared up some of the noise and the output signals are closer with the R side still a tad higher but very close. The right side still clips a bit earlier as would be expected.
Here is image of the signals at clipping with R on top. 5v/div. calculate to apx 17W R & 9W L. L will clip at 30p-p or 14W but R is already severely clipping by that time.
At 10v/div
Tired outputs?
I am still seeing a significant ripple (0.4 V-L and 0.35 V-R) on this board and a noticeable hum (not Vol dependent) when speakers are engaged and volume down. (This is with the input side of board lifted and jumpers for inputs and grounding. I also get a pop in speakers when touching the front panel after a few minutes of warm up.
I'll be replacing main power supply cap (3300uf C004) and filter caps on Amp 2200uf C601/C602.
50V rail output is reading 47.6 V.
Image at 50V input to boards.
0.2v/div
Image on 2200 uf Filter Caps C623/C624.
0.1v/div.
