Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Return to Tweakers' Asylum

Message Sort: Post Order or Asylum Reverse Threaded

SS amp bias question

70.190.67.72
Posted on August 4, 2024 at 07:04:36
airtime
Audiophile

Posts: 11322
Location: Arizona
Joined: February 4, 2003
 The sound of my NAD C275BEE was harsh and unpleasant. It had weak bass, no midrange and ear hurting treble. Instruments did not sound natural. I hated this amp and it was heading for the dumpster.

Skipping over all the cable, speaker and source swaps I'll skip ahead to the bias question.

The service manual has the bias at 6.6mv +/-1mv.

I turned the bias down to 3.5mv. When I gave it a listen the bass and midrange are now full and present and the treble is no longer ear splitting. There is also a nice/better tone and more natural sound to the instruments.

I don't have an oscilloscope so I'm asking if there are any "by ear" ways tweak the bias. It sounds 1000% better but I think there may be some distortion added. The bass can get a bit wooly at times.

Are there any danger points to avoid?

Why would the manual have the bias at a point where this amps sounds absolutely horrible?

Is too low a bias dangerous?

Also, this amp ran hot like a tube amp hot. Now it runs like a regular class A/B temperature.

 

Hide full thread outline!
    ...
RE: SS amp bias question, posted on August 5, 2024 at 08:06:47
Tre'
Industry Professional

Posts: 17587
Location: So. Cal.
Joined: February 9, 2002
 That seems backwards to me. Normally the higher the idle current is in the output devices the more linear they are. (up to the mid-point between cutoff and saturation)

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: SS amp bias question, posted on August 5, 2024 at 08:29:01
airtime
Audiophile

Posts: 11322
Location: Arizona
Joined: February 4, 2003
 The only thing I can think of is that either the engineers screwed up or a wrong valued component was accidentally put in both boards. But NO amp should sound like this thing did at correct bias.

I did try turning up the bias from 6.6 (+/-1mv) to 8.5mv. The darn thing ran hot as heck with no improvement. It still sounds MUCH better with the bias at 4-4.5mv.

Initially this amp ran as hot as a Class A or tube amp. I'm thinking the bias was set at saturation.

 

That could be. nt, posted on August 6, 2024 at 08:03:09
Tre'
Industry Professional

Posts: 17587
Location: So. Cal.
Joined: February 9, 2002
 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

Page processed in 0.030 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]