A little noisy

[corndog71]

So I've been enjoying my Smash a lot.  It really brings more dynamics and detail and oomph than my Quickie did.  I did notice a bit more hiss from my speakers vs. the Quickie (which also had a slight amount of hiss)   I recently swapped the .1uf VR cap as well as the 2.2uF output caps to Clarity ESA and MR respectively.  I'm not sure the former did anything to the sound but the MR caps brought their usual excellent sonic qualities. 

Still, when nothing is playing I can hear the hiss from my sitting position roughly 6-7' away.  I'm fairly certain it's not my VTA ST120 amp as that has been checked before and is virtually dead quiet with its inputs shorted.  I have noticed that my Musical Fidelity V-DAC II seems to add some noise to the signal but even when I unplug it I'm still getting a fair amount of noise which leaves the Smash as the culprit.  Could it be a noisy OD3?  Everything else but the 3 caps I swapped are still stock.  I did leave the leads of the caps intact which makes me wonder if they're acting like antenna for noise.  I should probably add that my interconnects are all braided and unshielded but I do try to keep them away from power cords as much as possible.

I haven't tried shorting the inputs of the Smash yet.  I can do that tonight.  Over all I'm still really happy with the Smash but this noise issue is confounding.

Any thoughts? 

[Doc B.]

I don't see a gain spec for the VTA amp, but as long as you are not pegging the Smash volume control to get to the listening level you want the easiest thing to do is to pad the input of the amp.

[corndog71]

All I could find on my amp is that it takes 1 to 1.1 volt to get the rated 60 watts.  My speakers are 90db.

So I did a little measuring and here's what I found:

Ambient room noise: 44db

Sitting position is 7' from speakers.  At this distance my spl meter reads the same ambient noise level but I can hear a barely audible low hiss from the speakers.  The hiss does not change when adjusting the volume control.

Bringing my spl meter right up to the drivers of my 3-way speakers brings interesting readings.

I unplugged the Smash and shorted the inputs of the ST120 and measured 43db in front of the tweeters, 45db in front of the mids, and 49db from the woofers.

Adding the Smash and shorting the inputs I get 53db in front of the tweeter, 57db in front of the mids, 64db in front of the woofers.

That seems like a fairly significant addition of noise to my system!  Overall It's a minor annoyance as the musical performance of the Smash is very good.  Still, I don't think my Quickie had noise levels like this. 

Hmm, maybe I need to try a different power cord.  I'm currently using a Kimber power cord which is unshielded.

[Doc B.]

You could try a different 0D3. Bear in mind that the Smash has more gain than the Quickie, so the noise floor from the Smash could sound a bit louder because of that. And of course the Quickie uses a battery supply so it is particularly quiet. If the 0D3 doesn't change the hiss level, try padding the amp input.

[corndog71]

Just wanted to follow up on this.  I did change the OD3 and that solved the problem.  The VA in my amp's driver circuit was getting a bit noisy too.  Replacing that cut the noise down further.

In other news I should be receiving my Smash-up tonight!  So excited!