[fjhuerta]

Had mine 8 months now, and though the stock tubes were good I replaced them quickly. Try some other inexpensive tubes before sending the amp back to replace or refund. When it works, it works very well and sounds great. Got my replacement tubes on eBay.

I hope it's the tubes, because this amp sounds as good as everyone else said it did. It's probably better than my old X-Can V2, much to my surprise. The noise is pretty noticeable. I'll have to hunt those tubes down, I haven't found them in the usual places.

 

[edulov]

Two most frequent reasons are:
1) Amp's PSU. Try to connect via good surge protector or UPS.
2) Audio cables, especially if amp is located near other electric devices with high energy consumption. I had this issue until I connected amp to DAC using HQ shielded audio cable. Prices for good cables actually start from 15 presidents, just look for oxygen free shielded male-to-male stereo 1/8" TRS (3.5 mm jack). Strangely, the best from cheap ones are labeled as Mic(rophone) cables while placing audio label triples the price. Huh-huh...
 
+3) Much rare. Try to hear music connecting DAC to laptop running on batteries.Not all desktop and AIO PSU's are good actually.
 
Keep us posted what you will discover.

 

[TheBIGKill1998]

  I hope it's the tubes, because this amp sounds as good as everyone else said it did. It's probably better than my old X-Can V2, much to my surprise. The noise is pretty noticeable. I'll have to hunt those tubes down, I haven't found them in the usual places.

My recommendation would be to upgrade the tubes first of all. You will find em relatively easy on ebay.
2nd you should take care of not using cheap cables. I also had noise problems with my amp in the beginning, but after i upgraded my cables to some higher quality ones from cordial, that problem was gone. 
 
And if you think the amp sounds good so far, then i really recommend to upgrade the opamp chips. 
After an upgrade this amp sounds even better IMHO. 
i know this has nothing to do with your noise problem, but its just some idea for you if you want to modify this amp a bit. 

 

[fjhuerta]

  My recommendation would be to upgrade the tubes first of all. You will find em relatively easy on ebay.
2nd you should take care of not using cheap cables. I also had noise problems with my amp in the beginning, but after i upgraded my cables to some higher quality ones from cordial, that problem was gone. 
 
And if you think the amp sounds good so far, then i really recommend to upgrade the opamp chips. 
After an upgrade this amp sounds even better IMHO. 
i know this has nothing to do with your noise problem, but its just some idea for you if you want to modify this amp a bit. 

 
Strangely enough, I ran an RMAA sweep yesterday, and got a very low noise floor of -96.9 dB, or so. I don't know what happened, but today the amp is as noiseless as a SS amp.
 
It still sings. I can't believe the price. I like it more than my X-Can V2.
 
RMAA shows it has somewhat of a roll-off in the upper and lower end. -2 dB or so at 30 KHz, IIRC. I wonder if that's the reason why it's so sweet.  I can post the graphs later, f anyone is interested.
 
I'll definitely upgrade the tubes and op-amps. Which would you recommend? Where could I get them?

 

[TheBIGKill1998]

   
Strangely enough, I ran an RMAA sweep yesterday, and got a very low noise floor of -96.9 dB, or so. I don't know what happened, but today the amp is as noiseless as a SS amp.
 
It still sings. I can't believe the price. I like it more than my X-Can V2.
 
RMAA shows it has somewhat of a roll-off in the upper and lower end. -2 dB or so at 30 KHz, IIRC. I wonder if that's the reason why it's so sweet.  I can post the graphs later, f anyone is interested.
 
I'll definitely upgrade the tubes and op-amps. Which would you recommend? Where could I get them?

oh, if the noise was only temporary it could have also been the burn in of the tubes! 
 
and yeah... it could be the roll-off. i may not be an audio tech expert, but this sounds plausible. 
which also might play a role it its sound could be the harmonic distortion. Do you have the chance to measure it? 
would be interesting to know that.
and yeah, i would be very interested in the graph! 
 
for the tube and op amp rolling:
i am currently using russian 6J9P tubes and LM4562NA opamps (since they are almost a perfect match electronically) and im quite happy with my setup.
 
Both components are available mostly on ebay. And there should be plenty of those russian tubes for a low price. I got 10 of them for 20 euros (shipping included). 
 
 
P.S.: if anyone has experience with other opamps, i would like to hear your opinions! 

 

[fjhuerta]

There's something really weird about the amp. Somedays it's noisy, and somedays it isn't. I'll post the graphs later today.

 

[edulov]

  There's something really weird about the amp. Somedays it's noisy, and somedays it isn't. I'll post the graphs later today.

I had such behavior several times, but in my case, it was unrelated to amp:
Amp <- Audio Cable <- DAC <-USB Cable <- Desktop PC <- Foobar2000 <- Windows 7
 
So, guess what? Connecting to other USB port is not helping, but restarting Windows always help. So it could be DAC driver, USB drivers, Direct X, windows audio service.
Next time it happens I'll try DirectX - ASIO since another DAC/AMP was playing OK.
 
I mean that without knowing how your amp is connected there exist too many possibilities

 

[fjhuerta]

The noise is mainly in the upper bass area. I'll post a noise spectrum analysis later. The amp seems pretty dead silent in the mids and treble. It doesn't have anything to do with my computer. The noise profile is still there, even when not connected to anything!

 

[fjhuerta]

These are the measurements. I'm really disappointed. This amp measures like a chinese made, $50  "tube" amp should, unfortunately. It sounds great to my ears, though. I guess it's the distortion. FR is very rolled off, the amp is quite noisy, it has tons of distortion and crosstalk. Measurements are overlaid with my sound card's reference measurements.
 

 

 

 

 

[MisterMudd]

If it sounds good to your ears, should that not be the top priority?

 

[edulov]

  The noise is mainly in the upper bass area. I'll post a noise spectrum analysis later. The amp seems pretty dead silent in the mids and treble. It doesn't have anything to do with my computer. The noise profile is still there, even when not connected to anything!

Mine problem always were mids both with stock and rolled op amps BTW. Permanent noise means 10% PSU and 90% cables and fitting

 

[diivve]

Can anyone make a comparison video stock tube and different tube? Highly appreciated.

 

[fjhuerta]

  Mine problem always were mids both with stock and rolled op amps BTW. Permanent noise means 10% PSU and 90% cables and fitting

In this case, I have to wonder if the problem is the circuit itself, and the SMD components. I mean, how nice can this sound with sub-standard components, even considering a nice topology?

Having said that, I was really curious and measured my X-Can V2 against this.

Guess what. Other than a flatter FR (which, I think, came to be because of the Rock Grotto upgrades), this unit is better performing everywhere else. Not kidding.

 

[dr3wd4wg]

I love this little amp, with LM4562s and Mullards it sounds great. Only issue is the volume pot, at lower volumes there is a channel imbalance.

 

[edulov]

Running through several tests just proved the well-known thing. A LOT depends on pre-amp or DAC. Made test with several tubes and different inputs. Mids, treble, high treble - no roll offs when no roll-off in input signal. Slight, but noticeable difference below 100Hz with different tubes. You need really good ears and headphones, but it is not an imagination. Above 100Hz no FR difference, just different noise specs and dynamic range.
BUT! My roll off "character" at lows look similar to yours, but not exactly the same in magnitudes. It goes slower than yours between 30 and 100Hz.
Since most people cannot hear the difference lesser that 0.5dB, there is no problem above 37Hz for me.