Help! No Sound being Output

pjnad · « **on:** 14 Apr 2012, 05:44 pm »

Hi all,
Turned on my system and nothing...everything is powered up, no cables disconnected, no knobs turned...
If I put my ear up to the speaker I can hear the music very faintly, so I guess that a signal is going through but not being amplified?
I have a Krell KSA150 amp and the MW SWL 9.0 Signature pre. A transport is feeding the signal to an Eastern Electric Dac...which I tried bypassing and running the output from the cd player into the pre...still nothing.
Any ideas?
Paul

*Scotty* · « **Reply #1 on:** 15 Apr 2012, 01:25 am »

pjnad ,This is a guess, and only a guess, it is possible that you have blown the speaker fuses in the right and left channels. The reason you may still hear some very low level sound from the speakers is due to the speaker fuses being bypassed by small value capacitors. When the fuse blows the only thing left that will still pass a signal is the small capacitor which will only pass very high frequencies and these are usually much lower in level than the rest of the frequency range. This could happen if there is a turn on pop or surge from the output of the preamp during power up or when it is turned off.
This can happen if the preamp does not have a relay which keeps the preamp's output muted to ground until the output coupling cap is charged and the circuitry is stable. If it does not have relay to protect down stream components from its turn on transient thump or pop a power up sequence has to be absolutely
adhered to which requires that the preamp is always turned on first before the power amp and the power amp is always turned off before the preamp. This works fine until you suffer a sudden power outage, in which case all bets are off and you will probably have a big problem.
If your speaker fuses are not blown then obviously something else is amiss and in that case you can ignore everything I just posted.
Scotty

pjnad · « **Reply #2 on:** 15 Apr 2012, 01:37 am »

Scotty,
thanks. my preamp does have that relay, and takes about 45 seconds to engage. I also do follow the turn on/off sequence...although now you have me wondering if I turned off the pre first late last night...don't think so, because turning the amp off first is habit and pretty ingrained.
Now, if I wanted to check the fuses in the speakers, I have a problem...they are Von Schweikert Vr-4s and I wouldn't even know where to look or how to get to them...and I guess there would probably be 4 fuses as there are 4 modules, 2 bass, 2 mid/treble

*Scotty* · « **Reply #3 on:** 15 Apr 2012, 02:35 am »

The Krell has pretty sophisticated protection circuitry that supposedly protects against fault conditions at both the input and the outputs. If it says it's okay then I am kind of at a loss to explain how you can be hearing almost no output from the speakers. Do the VR-4s have any fuses mentioned in the owners manuals.
Also If you have a Digital Multimeter and a test CD you could set the CD player to play a track with 120hz sine wave tone and then see if you can measure any voltage at the outputs of preamp. You should be able easily measure 1 volt a the outputs depending on position of the volume knob.
Scotty

pjnad · « **Reply #4 on:** 15 Apr 2012, 12:40 pm »

Scotty,
I just brought one of my outdoor speakers in and hooked it up...no sound from that either. So, I'm thinking that it's got to be the amp or the pre. Since the Krell is behaving as it should, I'm thinking it's the Modwright pre. I have no ability to test it , but I do have a buddy with a whole bench set up...unfortunately he's away until tomorrow.

borism · « **Reply #5 on:** 15 Apr 2012, 01:15 pm »

Hi Paul,
If your friend has a working preamp that he could bring that would seem the easier way to find out what component (preamp vs. amp) is causing your problem. Good luck!
Boris

pjnad · « **Reply #6 on:** 15 Apr 2012, 01:22 pm »

Quote from: borism on 15 Apr 2012, 01:15 pm

Hi Paul,
If your friend has a working preamp that he could bring that would seem the easier way to find out what component (preamp vs. amp) is causing your problem. Good luck!
Boris

True. He might have one sitting around...he certainly won't be dismantling anything from his system, it's an outrageous 150k + set up in a dedicated space that he has along with his workshop. But sometimes he has some odd units that he is either working on or buying/selling. We'll see.
Thanks!

pjnad · « **Reply #7 on:** 15 Apr 2012, 08:43 pm »

Problem solved!!!

I had written to Dan at Modwright last night and received this reply today:
Hi Paul, check the connection of the two purple wires that terminate in a white connector, that plug into the power supply board in the 9.0. These supply power to the rectifier tube filament. If loose or not making a good connection, it will cause exactly what you are describing. Please let me know.

So, I checked, nothing obvious but I removed the connector and replaced it and voila...
thanks to all for your input...
Paul