Marantz model 8b power capacitor replacement

C

cray

New Member
Hello everybody
Looking for help in replacing caps for the large can. For this task I was given three nichicons (65uf, 500v) by a friend who refurbishes these amps. I disconnected the leads to the can and soldered the new caps in place mounting them in under the chassis, The schematic for the can shows values of 40, 40, 20uf at 500v. First listen reveals thin bass and bright midrange. Finding this unpleasant, I reconnected everything to its original state and removed the nichicons.

My Question is this: What should the values for the replacement caps be? Also would like to hear opinions for type and brand. I'm not an electronics expert by any means but I'm thoroughly competent with this type of work as long as I'm getting advice.
The large can is C16 on the schematic.

model8.png
 
Register to hide this ad
The value of 65uf @500v for each section of C16 should not have any effect on the frequency response of the amplifier, considering the original values were 40, 40 and 20uf. Neither should their brand for that matter. Some questions for you:
1. Have C17, C19 and C20 been replaced?
2. Which input are you using, "Input" or "Test"?
3. Did you listen to the amplifier before swapping in the new caps?
 
Yes, 17, 19, and 20 have been replaced (months prior to changing C16). I'm using 'input' and I did not perform a pre-listen check. I'm pretty familiar with my setup but what I probably should have done was to pick a track for before and after the installation. Still, sounded off, and unfortunately I can't test it with electronics, just subjective listening. As for the brand question, what I should have added was types, like paper/oil and brands like Arizona cactus.
As you say, there shouldn't be any change to the frequency response, but is it appropriate to use a 65uf in place of the 20uf for other reasons. Im happy to reconnect the new caps and try it again provided they are the appropriate values.
Thanks
 
addendum: Was under the impression that replacing C16 would have given me better (increased and tighter) bass, should this be the case provided it's done correctly?
 
C16 is not in the signal path and is only part of the power supply. I think changing the coupling capacitors going to the output tubes would bring a different or better bass response.
 
cray said:
addendum: Was under the impression that replacing C16 would have given me better (increased and tighter) bass, should this be the case provided it's done correctly?
Click to expand...

First, the "Input" has a low pass filter, the "Test" does not. It is supposed to roll off at 20hz but as it is a simple filter it has to start above that. Second, good quality, telephone service rated (the best at the time) electrolytics were used by Marantz in C17,19 and 20 positions and good quality electrolytics should be used as replacements. Using a 65uf cap in place of a 20uf, after a solid state voltage doubler and a choke is not inappropriate. The ability to accept the voltage surge at turn on (hence the 500v rating) is more important than the 20 vs 65Uf. Third, simply replacing C16 is not going to change the low frequency response of this amplifier unless C16 is defective. The Marantz 8 (use mine every day) and 8B do not suffer from poor low or high frequency response nor is the original power supply design lacking in any way. Full disclosure, there are some who believe that additional capacitance and the use of the most expensive capacitors available will improve the sound of anything.
 
My experience is only replace cans or other power supply electrolytics if there is hum. (And, of course, to fix amps out of storage that blow fuses - different topic.)
 
@cray , do you have access to a scope? If so you could take a look at the B+ at the different positions on C16 and see what is riding on it.
 
You must log in or register to reply here.
Back
Top Bottom