Re: HK 930 receiver blows right channel speaker fuse.

Peter Larsen wrote:
john jack wrote:

I small correction: the right channel was about 135 mv and the left
about 1oomv and the right channel is blowing the fuses.

with or without speaker load? ...

Without speaker load. I followed the diagnostic procedure spelled out by EchoWars on the AudioKarma forum:

As a semi-poll, I'd like to see those on this board whip out their multimeters and take a look at the DC that is being presented to the speakers. This means..

1. Speakers disconnected (or connect the meter to the 'B' speakers and set the front panel speaker control accordingly)
2. Input set to an unusued position (not Phono)
3. Volume control at minimum.
4. Balance in center
5. Tone controls either defeated or set to mid position
6. Set your meter to read DC, and set to a low scale (300mV scale is common) Connect directly to the Pos and Neg of the speaker terminals
7. Give the amp 10 minutes to settle. Report back...I'd like to see how healthy all these old amps are.

If you read:

0 - 15mV: Damn good!! If you read '0V', you may have a capacitor output, or your meter is set wrong

16mV - 50mV: An acceptable value, especially at the lower end of this range. 2nd harmonic distortion is probably twice to four times what manufacturer's spec calls for at higher frequencies. Probably not audible, as the distortion is mostly in the upper octaves. At the upper end of this range I begin to raise an eyebrow.

50 - 85mV: Something is certainly amiss, and while this is not enough to put your speakers or equipment in jeopardy, the amp is running nowhere near where it should. I'd venture to guess that most of the DC-coupled amps that are in use by forum members here fall into this range.

100mV to ?: A high enough voltage will cause the DC protection to kick in. This happens at a level determined by the designer, but is usually equivalent to about a diode drop (600mV)or so. Needless to say, if you are listening to an amp with 100mV or more of DC offset, you have no idea what the amp really is supposed to sound like. Indeed, some amps without a differential input are actually designed to have a bit of DC at the outputs, but this is triple-rare, and I don't think anyone here owns one. (in my book it's piss-poor design, but if you can sell it WTH..)

Soooooo...go grab a meter and tell me what you find...

http://www.audiokarma.org/forums/showthread.php?t=5634

that offset voltage can only cause blown
fuses in case of a shortcircuited load. Have you had a scope on the loudspeaker terminals?

I don't have a scope... yet.


Do NOT rush soldering until you know more about what takes place.

I'm still doing some diagnostic testing.

Here is what I have so far:

selector to aux 1
16 ohm speaker load
volume turned all the way down
tone controls and balance set to mid
unit has no speaker relay that delays speaker connection

Left channel when power switched *on* using analog meter across left channel speaker outputs:

1. DC volts goes to 16-17 volts
2. Goes down to 7-8 volts
3. Goes back up to 14-15 volts
4. Goes down to negative 9-10 volts
5. Voltage stabilizes at 125 mv (using digital meter)

Left channel when switched *off* using analog meter across left channel speaker outputs:

1. Voltage goes to 5 volts and back to zero

Right channel when switched *on* using analog meter across left channel speaker outputs:

1. DC volts goes to 16-17 volts
2. Goes down to 7-8 volts
3. Goes back up to 14-15 volts
Goes down to negative 9-10 volts
5. Voltage stabilizes at 100 mv (using digital meter)

Right channel when switched *off* using analog meter across left channel speaker outputs:

1. Voltage goes to 5 volts
2. Voltage goes to negative 6-7 volts and back to zero

With pre-amp to main amp jumpers removed

Left channel when switched *on* using analog meter across left channel speaker outputs:

1. Voltage goes to 3.5 volts
2. Volt stabilizes at ~116 mv

Left channel when switched *off* using analog meter across left channel speaker outputs:

1. Voltage goes to 3.5 volts and back to zero

Right channel when switched *on* using analog meter across left channel speaker outputs:

1. Voltage goes to 3.5 volts
2. Volt stabilizes at ~108 mv

Right channel when switched *off* using analog meter across left channel speaker outputs:

1. Voltage increases slowly and then suddenly to 3.5 volts and then back to zero

.

Relevant Pages

  • Re: HK 930 receiver blows right channel speaker fuse.
    ... A high enough voltage will cause the DC protection to kick in. ... Left channel when power switched *on* using analog meter across left channel speaker outputs: ... DC volts goes to 16-17 volts ...
    (rec.audio.tech)
  • Re: HK 930 receiver blows right channel speaker fuse.
    ... A high enough voltage will cause the DC protection to kick in. ... Left channel when power switched *on* using analog meter across left ... DC volts goes to 16-17 volts ... Left channel when switched *off* using analog meter across left channel ...
    (rec.audio.tech)
  • Re: HK 930 receiver blows right channel speaker fuse.
    ... A high enough voltage will cause the DC protection to kick in. ... Left channel when power switched *on* using analog meter across left ... DC volts goes to 16-17 volts ... Left channel when switched *off* using analog meter across left channel ...
    (rec.audio.tech)
  • Re: HK 930 receiver blows right channel speaker fuse.
    ... A high enough voltage will cause the DC protection to kick in. ... Left channel when power switched *on* using analog meter across left ... DC volts goes to 16-17 volts ... Left channel when switched *off* using analog meter across left channel ...
    (rec.audio.tech)
  • Re: HK 930 receiver blows right channel speaker fuse.
    ... A high enough voltage will cause the DC protection to kick in. ... Left channel when power switched *on* using analog meter across left ... DC volts goes to 16-17 volts ... Left channel when switched *off* using analog meter across left channel ...
    (rec.audio.tech)
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