ttworld wrote:
Recently only one channel my preamp started having random crackle and
pop noises. The music on this channel also sounds distorted when the
crackle and pop noises are present. The noise is only intermittent.

The noise is not affected by the signel source, dub and mono
switches,
the balance and volume knobs nor the tone switch/settings.

The functional block diagram on page 21 of the Hafler manual shows
only
the high level gain stage and the dc feedback sections as unaffected
by
all of these controls.

Can anyone suggest where to look / test for the source of these
noises?

The manual is available on line at

http://www.hafler.com/techsupport/index.asp?ID=3

Thanks for any help.


--
ttworld

Loooking at the actual schematic on pages 12 & 13, it looks to me like
the DC feedback path is through the Bass control. Does turning that
control do anything with the crackles? You mentioned all the controls
except the Bass and Treble controls. I haven't probed it but I would
expect the Bass control to read 0 volts DC (give or take a few mV) on
all 3 lugs with no signal. Electrolytic capacitors are the most
frequent failures in old electronics. An ESR meter would detect them
easily.

I bought my DH-101 back in '79 in kit form. I haven't had any issues
with it yet -- after only 26 years. I did modify it to convert the
phono 1 position to a high level input for the CD player and hardwired
the phono cartridge input directly to the phono preamp which still
comes up as phono 2. Also altered the grounding by using a 5-way
binding post for the ground wire from the turntable directly to the PCB
rather than the chassis. Its a good unit if you like the minimalist
approach to audio.

Let us know what you find.
GG