[flavo]

I've got an STA-200 in my system
https://www.optoma.com/ap-nuforce/product/sta200/#
and I absolutely love the sound it produces. It replaced my Decware Torii and is powering my Dali Helicon 800s with a sensitivity of 89.5
 800s https://www.dali-speakers.com/discontinued/helicon-mk1/dali-helicon-800/
I can hear an audible buzz pretty easily from my seated position when no music is playing.
I've read that this amp was built with a pretty high gain and that could be causing my hum. I knew this going in and bought a Rogue Audio Magnum 99 preamp because it's got the tube compliment I was looking for and has adjustable gain.
http://www.rogueaudio.com/Products_99.htm
I don't know if it matters but adjusting the gain knob on the pre does nothing to affect the hum.
Also I shut off every breaker in the house except the one powering the stereo stuff with no positive results from that either.

What do you think?
Should I try to de-oxit the amp? Does that even work with an amp with no moving parts?
Should I try another STA-200 and see if it does the same thing?

My other cheapish DIY power amp also makes an audible hum but I have to be close to the speaker to hear it.

Thoughts?

[marvda1]

try different cables.

[FullRangeMan]

You have got a hum in your STA-200 just recently?
Or he always had the hum ?
Its hum in one channel only or in both channels?

[Urassner]

PS-audio ( no affiliation) has a detailed approach on how to diagnose issues with hum. Maybe that can help. https://www.psaudio.com/ps_how/how-to-find-and-fix-hum-extended/

[JLM]

Of course try "DeoxIT".  Many recommend using it on all electrical connections every 6 months as good audio hygiene.  But doubt it will help. 

What frequency is the 'buzz'?  Does it get louder as the volume is turned up?  Is it a 60 Hz (grounding) hum?  If so try a cheap "cheater" plug (three lug on the input end, two lug plus grounding wire on the output end).  Leave the grounding wire unattached.  (Wonder if the Torii had a 3 lug plug.)

[flavo]

You have got a hum in your STA-200 just recently?
Or he always had the hum ?
Its hum in one channel only or in both channels?

I bought it used and it came that way.
Both channels.

try different cables.

Did that, speaker wires too.

[flavo]

PS-audio ( no affiliation) has a detailed approach on how to diagnose issues with hum. Maybe that can help. https://www.psaudio.com/ps_how/how-to-find-and-fix-hum-extended/

I will look at that tonight, Thank you.

What frequency is the 'buzz'?  Does it get louder as the volume is turned up?  Is it a 60 Hz (grounding) hum?  If so try a cheap "cheater" plug (three lug on the input end, two lug plus grounding wire on the output end).  Leave the grounding wire unattached.  (Wonder if the Torii had a 3 lug plug.)

I have no idea what the frequency is at. But it does not change with volume control. It does go away when I hit the mute button on the pre-amp.
One of these? That's an easy try. Thanks


https://www.homedepot.com/p/GE-Polarized-Grounding-Adapter-2-Pack-14404/203684998?mtc=Shopping-B-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE&cm_mmc=Shopping-B-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE-71700000034239050-58700003946878360-92700050456676628&gclid=Cj0KCQiAwP3yBRCkARIsAABGiPo3H9x9FuTL1mxNWb2JdsFq3BYGxhIVae55ljNPT6vN8SaOrYTe9hcaAnvREALw_wcB&gclsrc=aw.ds

[JLM]

I will look at that tonight, Thank you.


I have no idea what the frequency is at. But it does not change with volume control. It does go away when I hit the mute button on the pre-amp.
One of these? That's an easy try. Thanks


https://www.homedepot.com/p/GE-Polarized-Grounding-Adapter-2-Pack-14404/203684998?mtc=Shopping-B-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE&cm_mmc=Shopping-B-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE-71700000034239050-58700003946878360-92700050456676628&gclid=Cj0KCQiAwP3yBRCkARIsAABGiPo3H9x9FuTL1mxNWb2JdsFq3BYGxhIVae55ljNPT6vN8SaOrYTe9hcaAnvREALw_wcB&gclsrc=aw.ds

That'll work, but have seen cheaper versions.  Read the PS Audio link, should be well worth your time too.

[charmerci]

If you hear the buzz physically coming out from the amp (most likely the transformer), this got rid of my buzz.

[BillG]

It does go away when I hit the mute button on the pre-amp.
One of these? That's an easy try. Thanks

Maybe power supply noise ( bad filter caps ) in per-amp?..Is buzz on all pre-amp inputs?

[FullRangeMan]

I bought it used and it came that way.
Both channels.

Since your speaker are low efficiency at 89dB I would emailed Nuforce and ask if its normal or a fault.

[flavo]

So today I decided to take the Pre amp out of the equation. I hooked my phone up to the inputs of the power amp and it was dead quite. 

So I'm assuming it's an issue with the Rogue. I tossed the ground plug cheater on there to see what would happen and it had no affect.

Time to contact Rogue I guess.

[bacobits1]

Does your system pieces have anything to do with a Cable box home theater or equipment?
Check the outside ground to the cable equipment. Or of course unplug that stuff see if it helps

[flavo]

Good idea on unplugging everything else. T

There is cable hooked up to my modem and my PC is my music server. But it's 20 feet away from the pre and amp.
I'm assuming that wouldn't affect anything?

OHH!! I just realized I can feed my pre with my phone too. Then I can unplug everything but the amp and pre and shut all the breakers off in the house.
I'll report back tomorrow:-)

[roscoe65]

You already have your answer:  the Rogue preamp is not quiet enough for your amp.  The Nuforce is a very high gain amp which does not need - or really want - an active preamp.  I own a STA-200 and use a passive transformer preamp or run it directly off a Chord Mojo.

I own a Dennis Had Inspire LP-27a tube preamp that is unusable with this amp.

[chrshanl]

I agree with roscoe65 I had the same issue with mine when using an active preamp and solved it by using a nobsound passive in between my preamp and the Nuforce. In fact I will let you use it to see if it works out for you. PM me and I will send it to you.

[flavo]

I agree with roscoe65 I had the same issue with mine when using an active preamp and solved it by using a nobsound passive in between my preamp and the Nuforce. In fact I will let you use it to see if it works out for you. PM me and I will send it to you.

Awesome, thank you!
Do you run it in between pre and power amp?
Someone on an older post from audiogon mentioned running the schiit sys to achieve the same thing I think.
Am I understanding that right? I could still use my rogue?

https://www.schiit.com/products/sys?gclid=CjwKCAiAzJLzBRAZEiwAmZb0auQ712EeK_6cwEy5By9LSuQD5pL1i-EdKxN7XQMgpPs4n5dU9lKkJxoC8qIQAvD_BwE

[chrshanl]

Yes thats exactly what I did.

[FullRangeMan]

I could still use my rogue?
Two pre-amps are too much for me YMMV.
More cables, more connectors, more transfer losses.

[mocenigo]

Awesome, thank you!
Do you run it in between pre and power amp?
Someone on an older post from audiogon mentioned running the schiit sys to achieve the same thing I think.
Am I understanding that right? I could still use my rogue?

https://www.schiit.com/products/sys?gclid=CjwKCAiAzJLzBRAZEiwAmZb0auQ712EeK_6cwEy5By9LSuQD5pL1i-EdKxN7XQMgpPs4n5dU9lKkJxoC8qIQAvD_BwE

It is a nice little thing but the potentiometer is really poor. I would rather go for something like this which costs a bit more but is based only on resistors, no moving parts, and has a remote (my wife complains that changing the volume is a bit to clickety-clackety)