advertisement


Feedback capacitors for Naim power amplifier.

G

guy

pfm Member
As far I read in the forum big improvements can be achieved using:

Evox Rifa MMK
AVX FFB

Other experiences?

G.
 
I currently have cheap/small (well, relatively) 47uF polypropylene, paralleled with 1uf mil-spec russian polystyrene, paralleled with 0.1uF russian mil-spec teflon. Looks a complete pigs-ear, but I am very happy with the sound I am getting.
 
For the feedback capacitor that goes to ground after the resistor from the base of TR2, I used 2 Black gate BG-NX (non polarised) 220uf 6.3V back to back to give 440uf. Not many of these left now unfortunately. I did this on a NAP140 and a NAP250. The voltage may seem low but if you calculate the maximum signal accross this part it is pretty small. Changing to almost any non polarised cap of similar or greater size should give an improvement.

I went for the larger capacitance not to increase bass ouput as such because it already went below what my speakers could produce, but it does have the effect of reducing phase shift, which means the lower frequencies your speakers can reproduce are more focused, and less muddled, with better timing. The NAP250 I did was for the person I sold my old NAP140 to, and he liked it too.

Ian
 
I'm resurrecting an old thread here-just wanted to enquire from 337 exactly what type of mil spec axial tants you have used here, as your description of the sound is exactly what I'm seeking
 
Not in a Naim (so YMMV) but I swapped the electrolytic feedback caps in my power amps for polypropylene, and got worthwhile increase in bass clarity and tunefulness in the context of my system.

On one specific track ("She's Lost Control", Joy Division) I was suddenly able to resolve the low bass synth part that had previously just been blurred into the texture.

But others have had very different experiences, and don't like the sound of a film cap in this position.
 
If you have an active system, you can use caps appropriate to the frequency range. I like AVX up top & wet tants down low.
If one Naim amp is driving full range, then it's more a matter of system and taste. At the moment, I'd use the wet tants as a best all-around solution. It's what Avondale use.
 
Fatmarley says : "I've noticed Les W uses a Vishay 150D solid tant in the feedback position of the latest NCC200 power amp. The 150D series are very low leakage compared to most other solid tants. I've ordered a pair from Mouser to compare to Maplin bead tants."

HTH
 
Yes but it should be at least 100uF, I use the ones Les supplied as above they are 150uF.
 
Thanks GWM, to clarify- Is it a 250 you re using the 150uF in? Everything I've read on here seems to say use 47uF as per the original spec?
 
Hi Pete, Is the hackernap essentially the same circuit as the 250? Should I go the same route? CAn you pl explain the effect of increasing the capacitance on output- ie increased/decreased bass/treble? I'm looking to reduce the -for a better word- top end 'glare' from the 250
thanks
bryan
 
Its an much updated version with a regulated front end local decoupling for the driver and output transistors etc.

The type of cap has a big effect I first started with some 68Uf film caps but they sounded thin with no bass so I whacked the 47uFs in and it sounded much better.
You should try a few different combinations and see what you like.

Pete
 
337alant said:
Mil spec wet axial tant, fast transparent but sweet treble not hard like solid tants ;)

Alan
Click to expand...

You don't maybe mean solid tant axials as opposed to sintered bead tants?

Wet tants are silly money! Like £100+ each for 100uF and above! A 12,000uf 75V wet tant is around.... £750 each!
 
Here's a 100uF wet tant for about £35.
I would buy a couple if I had confidence they would address the top end long term listening fatigue I find with the 250.
Does anybody have any advice or alternatives?
 
diybry said:
Here's a 100uF wet tant for about £35.
I would buy a couple if I had confidence they would address the top end long term listening fatigue I find with the 250.
Does anybody have any advice or alternatives?
Click to expand...

Avondale audio might be worth talking to, they do a drop in replacement amp board.


Have you tried changing the caps on the regulator boards? they can cause it to oscillate and sound harsh.

Pete
 
You must log in or register to reply here.


advertisement


Back
Top