[tketcham]

What is the cause of a "rushing" sound when you turn the volume up? (Not playing the lp but the turntable is turned on.) The solid state phono preamp without the Piccolo is nearly dead silent until the volume is turned almost to max. When I plug the Piccolo into the signal path there is a "rushing" sound that starts being heard (from the listening chair) at just under half volume and gets progressively more noisy as you increase volume. And there is more noise using batteries than with the wall wart.

The noise is tolerable since you don't really start to notice it until the volume is turned up past normal listening levels but I'm wondering what causes it and is there something I can do to reduce it.

I have the Piccolo sitting behind the phono preamp on the same shelf with 1.0m cables from the turntable to the Piccolo and 0.5m cables from the Piccolo to the preamp. The turntable motor is at least 60cm away on a higher shelf and the amp is about 30cm below.

Any thoughts?

Tom

Deleted: "The noise increases as you increase the gain settings" I realize now that my test for this was wrong. TK

[hagtech]

Maybe it's all that extra gain.  You could put the PICCOLO after your phonostage (just to listen to noise) and the hiss will also increase.  Most of the hiss is from the input resistance, usually defined by the cart.  With no cart plugged in, the 47k loading has much more hiss than the other settings.  Internally, the relatively high value of the 4.75k drain resistors presents some noise (about 1.3uV). 

Hmmm, I didn't notice it was worse with batteries.  I will have to run some tests.

jh

[tketcham]

Thanks for the quick reply, Jim,
I forgot to provide some info that may or may not help in diagnosis:

I originally set the gain on the phono preamp at 46 dB and used 20 dB of gain with the Piccolo but found that the noise was reduced if I used the 50 dB of gain on the preamp and used 12 dB of gain with the Piccolo. This combination has the volume at about 10:00 to 11:00 for normal listening levels, which is just before the point where I can discern noise.

In hindsight I could have ordered the Piccolo with a 0 (zero) gain setting and eliminated the "off" position of the switch since I have plenty of gain available (up to 65 dB) with the preamp I'm using.

One other thing, I do not have the Piccolo hooked to ground. I didn't think I'd need to (there's no hum present) but perhaps I should check to see if that makes a difference.

Tom

PS: Other than the noise at high volume settings the Piccolo is working out great. The 20 to 75 ohm range of resistance settings is just right for the LOMC I'm using. I ended up at the 44 ohm setting. Sounds very good!

[hagtech]

PICCOLO ground is only for hum.  It will not affect hiss.  And usually hum is the big problem.  How would you rate the hiss level between needle up and needle down?

44, eh?  Guess you nailed that range pretty good.

jh

[tketcham]

No problem with hum at all.

There wasn't much difference in hiss between needle up or down if the record was stopped. When playing a 'dead' spot in the groove there was a slight increase in hiss. But that may be a psychological effect from the ambient groove noise at high volume levels. As I noted previously, the noise isn't really noticeable until just past the upper end of normal listening levels.

You mentioned the input resistance of the cartridge as a primary source of the noise. Unfortunately I don't have another LOMC cartridge to compare.

What would be interesting is to rewire the headamp so that there was a zero gain position (instead of "Off") to see if the noise was further reduced.

[hagtech]

One simple test is to unplug the cart.  Then the 47k position will have much more hiss than the other settings.  Plugging the cart back in will reduce this level.  Of course, to do these tests, you have to crank volume way up.  I use headphones for noise testing.  Easier than dealing with a speaker.

jh

[tketcham]

Thanks, Jim,
I'll do some homework.