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Avalon VT-747SP TSP Sound Levels and Hiss Questions
Old 16th July 2014
Gear Head
Avalon VT-747SP TSP Sound Levels and Hiss Questions


I have just purchased an Avalon 747 second hand from a pro audio store and was supposedly tested and serviced. I have a couple of questions about the TSP Tube Signal Path.

When I engage the TSP the output level is about 4db quieter, is this normal? Also when the TSP is engaged the unit gives out A LOT more hiss when sound isn't playing, mostly in the right channel, even though the sound is quite a bit quieter when playing.

Had the unit running for a couple of hours.

Can someone advise me on this please

Old 16th July 2014
Lives for gear

it shouldn't be quieter when engaging the toobe, get the dealer to take a look.
Old 16th July 2014
Gear Head
Yes I am reading the manual here, which has a troubleshooting guide. This guide says low output volume or a cracking or sizzling sound are symptoms of a failing vacuum tube. Pretty angry now as I was told by a pretty big dealer in the UK it had been serviced and it even came with a sheet saying passed.

Thanks for the help
Old 17th July 2014
Lives for gear
TheBrightSide's Avatar
Just to second this, the signal shouldn't drop with TSP engaged, and more importantly, there should be ZERO hiss or noise.
Take it back.
Old 17th July 2014
Gear Addict

If it was shipped to you, don't assume it wasn't good when it left.

IF you PICKED it up? Then the dealer is lying.

Sadly with dealers its more cost efficient to fix things AFTER the fact than really make sure things are 100%- why check everything if only a few will come back.

Not all dealers are this way of course- but the potential is there. Perfect Circuit Audio (Ebay and Chatsworth, CA) is a perfect example. The ALWAYS claim everything is 100% and its absolutely not true... BUT they do honor their guarantee and try to make it right.

I just think its ridiculous to say "Tested 100% working" and have it turn out not to be true... EVEN ONCE out of 100.

Then the dealers chime in and say all the possible reasons things were missed, or just this once, or some other excuse... The problem with this is stating "100% working and tested" doesn't leave any room for error...

Marketing BS.
Old 18th July 2014
Lives for gear

I would not expect the signal level to change by more than a fraction of a dB, so something is 'amiss'.
ALL gear has noise, it is a fact of life, but in saying this the specifications for every piece of gear should say how much noise you should expect. In reality I would anticipate a couple of dB extra noise when the valve stage is introduced which if it is within the manufacturers specifications is fine.
It could simply be a valve is loose and making a bad connection (they are plug in devices) or there could be something else wrong with it.
Matt S
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