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What caps for NAHA

T

Trigeek

New Member
Hello,
I am thinking of replacing the output caps of my NAHA Naim headphone amp with Elna Silmic or Cerafine caps. The current caps (blue Rubycon) are 1000uF, 35V and are roughly 25mm x 12mm, and I have a total of 32mm from the PCB to the top of the chassis. To get a 1000uF in the Silmic, the 16V version is 31.5mm and the 25V is 35mm. Do you think I could get away with a 1000uF, 16V cap? I believe the internal voltage is lower, but would appreciate your opinion. Also, any opinions on using a Silmic II vs Cerafine caps? Any other caps in the Headline that I should consider changing while I am in there?
Thanks in advance.
Jim
 
Do you think I could get away with a 100uF, 16V cap?
Click to expand...
Two things come to mind:
1) The Headline runs on 24v (I think), so - although the output is at about half this voltage, 16V really isn't enough. On three counts, actually: the cap may have to withstand full rail voltage under transient conditions (hard running, and esp. switch on/switch off) higher voltage-rating for electrolytic caps brings with it lower ESR for the same capacity; and caps suffer from increased leakage currents as you approach the voltage rating. The existing parts are 35v for good reason.
2) Depending on which phones you use, 100uF could lead to audible roll-off in the bass. If the amp is paired with 300ohm phones(Sennheiser 600/650 etc) then 100uF is -3dB at 5Hz, which is fine. But if you use it with 32ohm phones (e.g. many Grados) that becomes -3dB at 50hz, enough to rob the sound of ambience, bass weight and impact.

It could simply be worth trying some small bypass caps across the existing 1000uF parts if you want to play. I'm not usually a fan of this, but some small 47-100nF film caps (eg polypropylene, polyester) could be worth trying given the limited space available.

While in there - the other caps to try replacing are the two 47uF caps in the feedback loop in each channel. Replacements here follow exactly the same rationale as in the Naim linestages/preamps - lots of opinions on what's best here in past threads ! Silmics work very well, very smooth though perhaps a touch soft-centred ultimately. If there's space in the case then try big film caps like the Evox MMKs...
 
Apologies... All the caps I was speaking of are 1000uF, not 100uF. I corrected my post. And I am using Sennheiser 600's, so 300 ohm.
Have not heard of the Evox, I'll look them up. Is the output caps or the caps in the feedback loop the bigger influence on overall sound?
 
When used with a NAPSC PSU the Headline is fed with 16.5V and regulates the input rails to down to 12.8V(output stage) and 12.2V (input and VAS stages) internally. When used with a HiCap the internal regulators run warmer as they drop the voltage from 25V to 12.8V and 12.2V respectively. I have to agree with Martin on all the points he makes though.

When I built my DIY Headline I made it dual mono by giving each channel it's own internal regulator system. (The external PSU also has dedicated left & right outputs.) I included 100uF 10V Tants in the feedback loop instead of the 47uF 6V and 2200uF 35V output caps instead of the 1000uF 35V that are standard. It sounds superb as is, although I am sure there are better options for the various tants in the circuit. May develop a split rail version which will negate the need for the output cap completely.

Peter
 
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