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Hiss from Project Sunrise II?

post #1 of 7
Thread Starter 

Recently acquired a pre-built Project Sunrise II from a fellow Head-Fi'er.  Love the sound, but there is a noticeable hiss, even with absolutely no source or input cables of any kind connected.  The hiss is present with both Grado MS2s and JVC DX-1000s.  I've rolled 3 tubes through it, no change.  I know that using low-impedance cans can bring out tube hiss, but this is loud enough to be audible with the headphones pulled a couple inches away from my ears.  I did some digging in previous threads, seems like the wall wart or caps are to blame.  Was just wondering if anyone else had any experience with this amp and had the same issue?

post #2 of 7

What signal are you amplifying?  Make sure that the amp is the only ground in the loop and that the other sources are ungrounded.  For example if you are using a turntable make sure the amp is the only thing rounding ( i.e. 3-prongs into the wall output ).  This will prevent any ground looping.

 

A hiss is typically a sign of capacitance as it is pretty hard to have a resistance make noise other than a pop.  Because you hear the hiss all of the time it appears that it is on the output stage of the amp.  You may want to look into replacing or verifying what caps were used where when the amp was constructed.  Perhaps the builder installed a cap in the incorrect location or made substitution.

 

I find this review:

 

http://www.head-fi.org/t/601207/project-sunrise-ii-kit-review

 

It mentions:

 

"Be sure to ground the volume pot (per the manual). It's critical for quiet operation. While it's not discussed in the manual, I highly recommend another 90% Isopropyl Alcohol bath on the bottom of the PCB to remove the rosin. You may need a couple of passes to get all the rosin off, but it will extend the life of your circuitry."

 

This leads me to think perhaps your volume pot is not grounded.

 

Give it a check and report back.


Edited by NA Blur - 10/30/12 at 2:29pm
post #3 of 7
Thread Starter 

Thanks for the tips Blur...didn't receive a manual along with the amp (as stated, I purchased it pre-built) but I have contacted the seller and will receive a manual soon hopefully.  I dug around in search engines for a PDF but no luck.

 

I'm amplifying the signal from my Meier Corda Opera pre-out (using the Opera as a DAC).  The amp uses a wall wart with only 2 prongs.  The Opera, however, has the standard 3-prong cord.  I should note, however, that the hiss is present regardless of whether or not the Opera is plugged in, regardless of the specific outlet used, and regardless of whether or not the stereo audio cables from the Opera to the Project Sunrise are connected.  Capacitors are still on the table, as is the volume pot ground.  Will check it out as soon as I receive manual.

post #4 of 7
Thread Starter 

So just tried bypassing the input caps.  Hiss completely disappears.....but so does all sound.  Any thoughts on that?

post #5 of 7
Thread Starter 

Received PDF manual last night...the volume pot is grounded as specified therein.

post #6 of 7
Thread Starter 

Was playing around with input cap bypass again.  Inexplicably, I now get sound with caps bypassed.  No hiss either.  No idea what the problem was before with no sound coming out with the caps bypassed, but that and the hiss problem appears solved for the time being!

post #7 of 7

I found a few ideas here:

 

http://www.diyaudio.com/forums/solid-state/157572-amplifier-hiss-what-causes-its-bothering-me.html

 

You can try grounding the inputs and see if the hiss goes away, but in the end it is most likely low quality caps that are causing the issue.  Using inefficient headphones could also help.

 

If the amp has more than one tube you may want to check the order of the tubes as well.

 

Probable Causes:

 

1.)  Poor grounding somewhere

 

2.)  Tube order

 

3.)  Low quality caps.

 

I also found this advice:

 

"I have a victorilux with 4 el-84 tubes and 2 twelves. Same problem. I pulled out 2 of the power tubes and unplugged one speaker to match up the impedance, and now it is perfect.

It is an old trick that used to be done for marshall 100 watters. In many amps that use 4 power tubes, they are running in 2 pairs, so you pull out one pair (not one out of each pair) and then reset the impedance selector to half of the impedance.

Im most amps, it will be the 2 outside tubes or the 2 inside tubes. Unplugging one speaker of a pair will cut the impedance in half."

 

--http://forum.gibson.com/index.php?/topic/66981-fighting-tube-amp-hiss/


Edited by NA Blur - 10/31/12 at 8:29am
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