Nighthawks are here...inspiring a rewire for 4ohms.

D

dmhenley

New member
Started the build with 8ohms because the SEX was powering my AKG Q701(62ohm), and the speakers as well - 8ohm Tekton Lore (98db).

1. A bit of hum is now audible via the AQ Nighthawks (25 ohms), so I'd like to experiment with the 4ohm setting.
2. I plan to build a Stereomour2 for the 2 channel later.

Anything I should be concerned about, rewiring for 4 ohms? I'm reviewing both the forums and manual, but thought I'd also check with you.

Also need to add that my initial listening with the NH is very encouraging!  Need time to let them settle.



 
Holy crap. Thank you again, Mcandmar!

Based on the Ramblings thread...

I went ahead and added the 100ohm resistors at C1&C2 ->C3, and the hum that became more prominent with the headphone switch, is reduced to a very subtle noise. And, this is with my Nighthawks (25ohm impedence).

I love this amp in my system, and with these 'phones more so, but the hum was ever present. This has lowered the noise floor enough for me to forget about it. My most quiet record - Mark Hollis' solo record (1998) - is beautifully recorded, and it's my go to for this kind of listening test. Even in it's quietest moments, I'm not distracted by the hum.

Just waiting on the Jupiter caps...
 
Excellent :)

....if you still find the background noise intrusive you can look at adding the two filter chokes to the power supply, its a pain in the butt to do as you need to fabricate some method of securely mounting them, but it will remove that last bit of noise.

Enjoy!
 
@Mc
Where would these filter chokes go in the circuit, and what model/spec choke? I'll breadboard it up, just to test it, I'm getting desperate here
 
I would hold off until you come to a conclusion on the hum debugging thread before you start modding the circuit away from the stock design, there is no way the BH guys can support/troubleshoot an amp that isn't in a stock configuration.

Having said that, what you want to do is replace the two 680ohm 3watt resistors in the power supply marked RPSU in the schematic.  They are the big fat ones across terminals 6-10 and 16-20. Chokes to use are the Triad C-3X, 10H 50ma 500ohms.
 
Thanks Mcandmar,
I think it's just about wrapped up. Paul J just chimed in so I'm going to see what he has in mind. I'm not going to mod anything yet, I'll send it to BH for a check before I put anything in permanently. I am going to breadboard some things up just to see where it goes. If BH says this is as good as it's going to get, then I'll start thinking about changing things up.
 
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