2. amps-preamps
  3. 1214697858

Help preamp problem: overload?

OK, so I bring home my brand spanking new Bryston BCD-1 and hook it up (Audioquest Emerald balanced) to my Sonic Frontiers Line Stage 3.

I cue up the last movement of Sibelius's 5th, and sit back to bask in the glow.

So far so good, until the last minute or so of the piece, where it reaches its glorious, rousing climax. At this stage, I've got the preamp up pretty loud (72 on its numeric scale), but still within limits. Suddenly, the preamp starts going into standby and muting for 2-3 seconds on the loudest chords, then turning back on automatically and continuing until the next very loud chord. Did it three times in the last minute of music.

(You can tell when it goes into Standby, because the volume numbers disappear and are replaced by six dashes, and you hear a relay clicking.)

I repeated the experience exactly, to make sure it wasn't random dips in the power supply, but no, it went into standby at exactly the same points in the music again.

Then I backed the volume on the preamp down to 67 (a good average everyday listening volume for this recording), and it played through to the end without a hiccup.

So my question is: what was going on?

Was I driving the preamp into overload, and if so, should it be overloading at that kind of volume?

Was that a protection circuit cutting in and putting it into standby/mute? (I trawled through the owner's manual and it makes no mention of such a circuit or safety feature.)

Is there some sort of less-than-ideal synergy between the Bryston and the Sonic Frontiers (you'd have thought not, both being Canadian and all...)?

Does this mean that the tubes (all? some?) are aging (remember: there are lots of them, in the head unit and in the separate power supply). I put my ear to both channels of the loudspeakers with no music playing, and couldn't hear anything anomalous--no crackling, hissing, etc.

Suggestions, expert advice, consolation please. This has certainly taken away from some of that high associated with installing a new component...
128x128twoleftears
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uru975
684 posts
 
My first thought would be to call Bryston first thing Monday morning. It's their equipment, so they should be familiar with it.
Both being Canadian doesn't necessarily mean anything. It all gets back to synergy.
Have you a tube tester?
Just some quick thoughts, probably no different from yours.
carey1110's avatar
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carey1110
566 posts
 
There are several possibilites.
--You may be overdriving the preamp with your CD player. If you have a variable output try turning down the CD player output.
--There could be a short in one of you output cable of the preamp.
-- While calling bryston might help I would try to contact a Sonic Frontier expert to find out what causes the preamp to mute on its own.
rodman99999
6,132 posts
 
If that Sibelius CD is not overly compressed, and actually exhibiting the dynamic range that the medium is capable of: When your pre's volume knob is turned to the level you mentioned(to sound good at the lower end of the dynamic range)- at the orchestra's FFF or FFFF levels you're asking for more output from the pre than it can deliver, and it's "muting". Does the new amp have less sensitivity or lower power than your old one, or were you (perhaps) trying to listen at a louder level than normal? The fact that you're experiencing no problem with the gain reduced points to the pre protecting your downstream components. Instead of using(as most tube designers do) a capacitor to block DC at the output of the line stage, Sonic Frontiers uses a DC servo mechanism to minimize DC offset.
blindjim
3,092 posts
 

I'm with the asking SF support waht's up? poster.

I also am wondering about the tubes in the preamp... and if this event occurs with any other music, media, etc., given the same conditions.

I'd try to recreate the same event using other music or media. I'd also recommend checking the connections yet a second time or more to ensure in the haste of anxious setting up, some loose fit along the way was not present, thereby causing a resistive connection and increasing the power draw inadvertently, further taxing the system.

Brand spankity new amp or not, I'm still thinking the issue lays within the SF III line stages tube compliment, or it's output circuitry... provided all is connected well... ICs, PCs, etc.

Sonic/Anthem support is very good indeedd and they respond quickly via email too... and Bryston is not far from them either... give 'em a shout ASAP.
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