I have been sourcing a small power amp for my Open Baffle project but having some issues with noise.
Current setup is
Sources > DIY RCA Switch Box > MiniDSP 2x4HD > Decware Zen > Speakers
There is always a little hum but thats from the Decware, very low level and can only hear when you are right next to the speaker.
In the past few weeks, I have tried two power amps, a Parasound Zamp and Nuforce STA120.
The Parasound was damaged as there was a loud audible hum from the unit itself, as well as though the speakers so it was returned.
I then bought a Nuforce STA120 which is as new, and there is a constant hum that can be heard from the other side of the room, not as loud as the Parasound but still can be heard across the room.
When I have the MiniDSP connected to the PC, there is a loud digital noise signal, when its disconnected it goes away, and back to the background hum.
Now, the speakers are ~97dB/2.83v + which I guess does not help, but do you think this is an problem somewhere or just bad luck with the first amp and bad design with the Nuforce?
I’ve never had a problem with hum from other amps in this house (Denon PMA-2500NE, Rega Cursa/Maia) and all the stuff is connected through a Wychwood Prime 8.
I’ve taken out the sources and switch box, with the MiniDSP (nothing plugged in to it) into the Nuforce I still get the loud hum, turn the MiniDSP off and it gets a bit quieter but still there.
Doing the same into the Decware the quiet hum is constant with the MiniDSP on or off.
My system is quite similar to yours - I have just connected my Nobsound mini to my Supravoxes to see - No hum at all - even with the volume knob at max. There a just small amount of hiss at normal listening volumes - I would say that in my system the Mini DSP is about as hissy as the Decware but even together it’s barely audible even quite close to the speakers at normal volumes.
Thanks guys, I’m pretty certain its the MiniDSP and/or amp as I get the loud hum when its just the MiniDSP connected to the power amp, its just I can’t hear it on the Decware (over the very low level hum) but is a lot louder on the Nuforce.
Also, the ‘digital’ noise when the MiniDSP is connected to the laptop, through the Decware is barely audible even with you ear right up against the speaker, its at such a low level (with the Decware on full volume).
And to check as well, the Nuforce has an earth screw on the back, which I have connected to the star earth on the Wychwood power conditioner and no change.
I have also tried the MiniDSP with the 4v output rather than 2v (internal jumpers) and no change.
I think its certainly now something with the MiniDSP, it just shows up on the SS amps and not the Valve…
The Decware Zen is a low gain amplifier. The specs say you need to put 1.5V RMS in to get 2.3W out. 2.3W would be 4.3V RMS into an 8ohm speaker. So that’s a voltage gain of 4.3/1.5 i.e. just 2.9 times, or 9dB if you like.
The Nuforce STA120 claims to deliver 85W into 8ohms which would be 26.1V RMS output. You get this when you put just 1V RMS in. So that would be a voltage gain of (surprise, surprise) 26.1 times, or 28dB. It’s a much higher gain amp than the Zen.
If you feed the same noise signal into each amp then the STA120 will amplify it by 19dB more (which is rather a lot more) than the Zen before delivering it to your speakers.
Batteries are really, really quiet, but impractical in lots of ways. 850mA will discharge them quite quickly too (although the MiniDSP probably doesn’t draw that much current in reality). If you can cobble together 8 1.5V dry cells or a couple of those big 6V torch batteries in series then you might at least be able to check whether the psu is your problem (finding the right connector for the MiniDSP might be an issue though). And remember that polarity matters (it’ll be marked on the psu).
The other issue can be any signal path to the mains. These little psu’s come in at least two variants. The more expensive ones really are fully isolated from the mains. There are cheaper ones though which have a through connection to mains neutral. The connection is really high impedance, and guaranteed so, so the device is intrinsically safe. But there can still be low-level noise issues with it. Linear psu’s, with a transformer, shouldn’t present this problem.
Thanks VB, I’m pretty sure the MiniDSP PSU is the main culprit.
I tried another SS amp, a Cambridge Audio A5 I had lying around in the loft, when its turned on on its own, I get a lower level hum from it, like the Nuforce, audible but not from the other side of the room.
With the MiniDSP plugged in to the amp, its really loud again.
Some searching bought up some options, the Nobsound Linear PSU and the IfI and Russ Andrews ones
I don’t know what this one might be like https://cpc.farnell.com/duratool/d03232/power-supply-1ch-15v-2a-adjustable/dp/IN07999. It weighs 3kg so probably has a transformer inside it. They claim less than a millivolt of noise on the supply voltage. You get output cables for it but you’d need to join them to a suitable input cable for the MiniDSP (CPC might sell those too). This one is heatsink cooled, so there’s no fan noise, but they probably haven’t put much effort into making it free of acoustic/mechanical hum. Then again it’s low-powered so shouldn’t be really noisy. Just a thought.
The MiniDSP 2x4HD is 2V output I think too.
