Latest krell saga

[fas42]

Mark, just had a thought: it wouldn't be anything to do with the powered subwoofers, perhaps? Try pulling the plug on the mains to the speakers, see what that does ...

Frank

 

[microstrip]

Mine is a Fluke 77 also and is the same age. I have built lots of tube gear over the years with that meter. Mine still looks real good too. Are the diode bridges all on top of the main cap banks? Does anyone have a schematic for this amp?

(...)

Look for the flat terminals on top of the plate forming squares - the bridges are under the pcb and the terminals are on top - you can see it on the movie. The main caps are forcefully connected to the bridges + and - .
BTW, just read Frank suggestion - I assume you tried the amplifier with other speakers?

 

[RBFC]

You could try floating the ground to the subs....

Lee

 

[mep]

You could try floating the ground to the subs....

Lee

The subs have no ground on the AC plug.

 

[RBFC]

The subs have no ground on the AC plug.

Gotcha. Do they have size-keyed prongs, or could you reverse the plug in the socket? At this point, any small thing you could try may help. Is there still hum if you unplug the subs?

Lee

 

[treitz3]

You were thinking the same thing I was, Lee. One more thought......you don't have this system in any way hooked up to a cable box or satellite receiver, do you?

 

[mep]

Tom-My stereo is in a dedicated room and is only used for 2 channel stereo so no, there is no cable box or satellite receiver in my room let alone hooked up. Below are the results that Micro asked me for from measuring the 4 diode bridges for AC and DC.

These values will be given clockwise starting at 12:00, 3:00, 6:00, and 9:00 for each diode bridge looking at the board from the front of the amp where there are two on the left and two on the right and we will start with the bottom left bridge, then top left bridge, bottom right bridge, and top right bridge:

12:00 AC 32.2v, DC 0
3:00 AC 0, DC.35v
6:00 AC 30.7v, DC 40.5v
9:00 AC 0, DC 83v

12:00 AC 32.8v, DC -41.7v
3:00 AC 0, DC 0
6:00 AC 29.9v, DC -41.7v
9:00 AC .4v, DC -83.5v

12:00 AC 32.8v, DC 40.3v
3:00 AC 0, DC 0
6:00 AC 29.9V, DC 40.3v
9:00 AC 0, DC -.3v

12:00 AC 32.3v, DC -41.5v
3:00 AC 0, DC 0
6:00 AC 30.6v, DC -41.6v
9:00 AC 0, DC 0

All measurements were taken with both inputs shorted. Also, Micro wanted an AC measurement from the speaker terminals and they were both 0v.

 

[fas42]

Mark, a simple, definitive way of eliminating the subwoofers from the equation is to try another set of speakers, as micro suggested. Don't have to be good ones, a bit of rubbish will do, so long as they can do some sort of reasonable bass response.

Frank

 

[microstrip]

Tom-My stereo is in a dedicated room and is only used for 2 channel stereo so no, there is no cable box or satellite receiver in my room let alone hooked up. Below are the results that Micro asked me for from measuring the 4 diode bridges for AC and DC.

These values will be given clockwise starting at 12:00, 3:00, 6:00, and 9:00 for each diode bridge looking at the board from the front of the amp where there are two on the left and two on the right and we will start with the bottom left bridge, then top left bridge, bottom right bridge, and top right bridge:

12:00 AC 32.2v, DC 0
3:00 AC 0, DC.35v
6:00 AC 30.7v, DC 40.5v
9:00 AC 0, DC 83v

12:00 AC 32.8v, DC -41.7v
3:00 AC 0, DC 0
6:00 AC 29.9v, DC -41.7v
9:00 AC .4v, DC -83.5v

12:00 AC 32.8v, DC 40.3v
3:00 AC 0, DC 0
6:00 AC 29.9V, DC 40.3v
9:00 AC 0, DC -.3v

12:00 AC 32.3v, DC -41.5v
3:00 AC 0, DC 0
6:00 AC 30.6v, DC -41.6v
9:00 AC 0, DC 0

All measurements were taken with both inputs shorted. Also, Micro wanted an AC measurement from the speaker terminals and they were both 0v.

Mep,

There is something strange on this measurements - I find one AC voltage of .4V (the expected ripple of -83V at 4A ) but no AC ripple at +83V . Also too many zeros - and I assume it was not the wrong scale as the F77 is auto-ranging.

Could you check if there is no mistyping on the list?

 

[mep]

micro-I just checked my numbers against what I have written down and they are correct. Also, with the cover off, you can hear the transformer singing away and the mechanical hum you hear sounds a lot like what is coming from the speakers.

 

[fas42]

This is sending off alarm bells for me: 0V "ripple" for one voltage rail, 0.4V for the other; there is something going on here: I would suggest if you're game to measure the ripple directly across the smoothing caps. Utmost care here, otherwise fireworks galore ...

Frank

 

[mep]

I came home from work today and put a fresh battery in my trusty Fluke 77 and retook all the measurements today. Here they are again:

12:00 AC 32.9, DC -41.6
3:00 AC .007, DC .00
6:00 AC 30.02, DC -41.7
9:00 AC .38, DC -83.7

12:00 AC 32.9, DC -41.5
3:00 AC .20, DC -83.7
6:00 AC 30.11, DC -41.6
9:00 AC .007 DC .00

1200 AC 32.47, DC 40.8
3:00 AC .33, DC -.35
6:00 AC 30.85, DC 40.8
9:00 AC .085, DC 83.8

1200 AC 32.4, DC 40.8
3:00 AC .26, DC 84.1
6:00 AC 30.77, DC 40.8
9:00 AC .31, DC -.36

 

[LL21]

micro-I just checked my numbers against what I have written down and they are correct. Also, with the cover off, you can hear the transformer singing away and the mechanical hum you hear sounds a lot like what is coming from the speakers.

i am no engineer...is it possible the transformer needs to be epoxy'd down to the chassis? What happens with the cover off, if you dry to mechanically dampen the transformer...even if just for a second or 2?

 

[microstrip]

I came home from work today and put a fresh battery in my trusty Fluke 77 and retook all the measurements today. Here they are again:

12:00 AC 32.9, DC -41.6
3:00 AC .007, DC .00
6:00 AC 30.02, DC -41.7
9:00 AC .38, DC -83.7

12:00 AC 32.9, DC -41.5
3:00 AC .20, DC -83.7
6:00 AC 30.11, DC -41.6
9:00 AC .007 DC .00

1200 AC 32.47, DC 40.8
3:00 AC .33, DC -.35
6:00 AC 30.85, DC 40.8
9:00 AC .085, DC 83.8

1200 AC 32.4, DC 40.8
3:00 AC .26, DC 84.1
6:00 AC 30.77, DC 40.8
9:00 AC .31, DC -.36

Mep,
It looks much better - the voltages are symmetrical and very close. Ripple AC is within expected values - the mains capacitors seem in good condition.
What is the reading you get now at the output in AC?

 

[mep]

Mep,
It looks much better - the voltages are symmetrical and very close. Ripple AC is within expected values - the mains capacitors seem in good condition.
What is the reading you get now at the output in AC?

.007 in the left channel and .009 in the right channel.

 

[microstrip]

.007 in the left channel and .009 in the right channel.

It is really unacceptable - this means a signal to noise ratio of about 75 dB against the specification of 120dB! Even the tubed Audio Research REF150 I am using has less than .001V in any of the channels. Was this measured without speakers?

Considering the expense and trouble to ship it, I would try to carry it to another place with a good mains supply, and measure it there.

 

[RogerD]

It is really unacceptable - this means a signal to noise ratio of about 75 dB against the specification of 120dB! Even the tubed Audio Research REF150 I am using has less than .001V in any of the channels. Was this measured without speakers?

Considering the expense and trouble to ship it, I would try to carry it to another place with a good mains supply, and measure it there.

Egads!

 

[fas42]

It is really unacceptable - this means a signal to noise ratio of about 75 dB against the specification of 120dB! Even the tubed Audio Research REF150 I am using has less than .001V in any of the channels. Was this measured without speakers?

It is important to make sure we're measuring what we think we are: what is the null reading for the multimeter on AC? In other words, when you short the leads together for AC voltage do you get a 0.0V? Mine always give a non-zero reading doing this ...

Frank

 

[thedudeabides]

Oh my.

 

[microstrip]

It is important to make sure we're measuring what we think we are: what is the null reading for the multimeter on AC? In other words, when you short the leads together for AC voltage do you get a 0.0V? Mine always give a non-zero reading doing this ...

Frank

Frank,

Advertisement

You should get a Fluke - mine after 30 years of use shows it is still calibrated against our laboratory standards. And has no offset - it gives a 0V reading in AC and DC modes when I short the plugs.

End of Advertisement


Or you have such intensive AC electromagnetic fields in your house that the loop created by the probe leads generates a few mV EMF