Even though it's not indicated in the service manual, both Cerafine 27000uf 50v power supply caps are bypassed with a 100uf 50v Cerafine cap. It looks original. 😕
Why are these there and does it really make a difference in sound? Should I replace these when recapping or leave them out?
Why are these there and does it really make a difference in sound? Should I replace these when recapping or leave them out?
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In some cases a smaller bypass capacitor can improve the performance and sound.
Marantz seemed to think so, although this can depend on the exact parts used.
By now, these 40 year old parts should certainly be replaced.
Marantz seemed to think so, although this can depend on the exact parts used.
By now, these 40 year old parts should certainly be replaced.
I measured the ESR of the 27000 uf caps and they measures fine (I should still do other tests to establish the overall condition). The bypass caps will definitely be replaced. I have already started recapping the rest of the boards with 105 degree caps as this amp gets seriously hot!
The self resonance frequency of large caps is very low, perhaps less than a few kHz. Smaller caps have SRF higher up, over 100kHz even for electrolytics. So most likely the small cap is there to shunt away some HF hash present on the power rails.
Ditto for the ability to stiffen up the rail and provide current at high di/dt (fast transients).
Ditto for the ability to stiffen up the rail and provide current at high di/dt (fast transients).
Large electrolytics can be a little inductive so a smaller less inductive cap helps get rid of HF noise.
Semperfi...
Seriously? Kilohertz???
If you said multiple tens to hundreds I would not have stopped and sought a fact check.
Seriously? Kilohertz???
If you said multiple tens to hundreds I would not have stopped and sought a fact check.
Well I do exacerbate now and then and certainly my memory is like a goldfishs. But yes when large the SRF is shockingly low. I will try to find some measurements later today...
Maybe I should replace the 2x 18000uf 80V and 2x 27000uf caps (50mm x 100mm) in the future. I looked on the Mouser website and the ones that physically fit are different values. Could I use the following without problems or will I have problems with the inrush current? There is a soft start build in, but perhaps it needs to be adapted accordingly?
Mfr. No: LNR2A223MSE
Mfr.: Nichicon
Aluminium Electrolytic Capacitors - Screw Terminal 100volts 22000uF 0.2 51x100 85c
Mfr. No: LNR1H683MSE
Mfr.: Nichicon
Aluminium Electrolytic Capacitors - Screw Terminal 50volts 68000uF 85c 51x100
Mfr. No: LNR2A223MSE
Mfr.: Nichicon
Aluminium Electrolytic Capacitors - Screw Terminal 100volts 22000uF 0.2 51x100 85c
Mfr. No: LNR1H683MSE
Mfr.: Nichicon
Aluminium Electrolytic Capacitors - Screw Terminal 50volts 68000uF 85c 51x100
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