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Amplifier hum (Read 2706 times)
jslusarz
Ex Member



Amplifier hum
10/20/06 at 16:35:43
 
I am the happy new owner of the system below.  Does anyone have any insight into why I am experiencing a fair amount of hum from the Triode Amp?  I have only had the amp running for ~8 hrs so far, but the hum (with nothing save the speakers connected) has not reduced.  I am using the tubes and power cable suplied shipped from Decware.

Rega P2, rb250
Goldring G1006
NAD PP2
MB Quart QL-C104
Decware Select Zen Triode
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Rap
Ex Member



Re: Amplifier hum
Reply #1 - 10/20/06 at 16:50:22
 
I found the Ruby rectifier to have a higish amount of hum. I replaced mine with gz32īs that cut the hum in half. I also found that the Zen was sensitive to the mains power it self. It likes a clean power supply.
If you want I can give you the recipe for a cheap DIY power cord that takes care of a lot of the noise and spikes.
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« Last Edit: 10/20/06 at 18:22:22 by Rap »  
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jslusarz
Ex Member



Re: Amplifier hum
Reply #2 - 10/20/06 at 17:53:18
 
Thanks for the tip,  I'll look into my cabling/supply situation tonight.  My thought is that supply noise is a very likely culprit.  I'd love to see the plans for your DIY mains power cable!  Thanks for the help.
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Rap
Ex Member



Re: Amplifier hum
Reply #3 - 10/20/06 at 19:02:03
 
Well I (and others) have had some success with this simple design:


Basically itīs satalite cable that you braid.... Three strands one for neutral, one for live and one for ground.
The trick is that you connect the shield of the cable to the ground wire on neutral and live one the plug side of the cable(the side going onto the wall Smiley ) This works very well if you have problems with spikes in the power, the higher the spike the more capacitance the cable will produce. Iīve been running this to one of these:

And this seems to work very well if you have problems with fuses too. Both me and a few friends have had problems when you turn on a power hungry ss power amps (the fuse box gives out Sad) The previous solution was to turn every thing else, on that fuse, off and turn the amp on first but with this kind of cable that problem is no more. The cable causes a capacitance both ways, from the amp to power source and from power to amp. And the cap. law for coax states that the higher the spike(voltage) the higher the capacitance and hence less current flow.
I used coax cable with a solid inner diameter of 16 aug. This can handle about 4 amps ,which seems to be plenty.

Rap.
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jslusarz
Ex Member



Re: Amplifier hum
Reply #4 - 10/24/06 at 14:48:15
 
I am reaching the end of the break-in period of the amplifier and I am a little concerned that the top end has not filled in like I was hoping it would.  I am admitedly new to vinyl and tubes, but this is becoming a noticable deficincy in my system.  My listening tastes vary from classical to jazz to rock.  Are my speakers too low efficiency?  Do I have the wrong speaker cables ('standard' speaker cable)?  Or is it a matter of tuning my room?  Thanks!
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Rap
Ex Member



Re: Amplifier hum
Reply #5 - 10/24/06 at 15:01:07
 
Hmm, MB Quart QL-C104 are hardly state of the art, if you mind me saying so Tongue I think you should look into new speakers. 86db just isnīt going to make a zen happy. Take a look at the frugal project over on speaker build.
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« Last Edit: 10/24/06 at 15:02:39 by Rap »  
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jslusarz
Ex Member



Re: Amplifier hum
Reply #6 - 10/24/06 at 15:04:58
 
Fair enough.  The MB Quart are just to get me going until I have the money to invest in better speakers.  Maybe I can see about some more efficient speakers in the same price bracket.
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Rap
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Re: Amplifier hum
Reply #7 - 10/24/06 at 15:35:26
 
Canīt go wrong with a fostex fullrange and a little DIY Smiley
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chrisby
Ex Member



Re: Amplifier hum
Reply #8 - 10/24/06 at 16:51:30
 
[quote author=Rap  link=1161362143/0#5 date=1161698467]Hmm, MB Quart QL-C104 are hardly state of the art, if you mind me saying so Tongue I think you should look into new speakers. 86db just isnīt going to make a zen happy. Take a look at the frugal project over on speaker build. [/quote]

For those with larger rooms (or needs) - there's also Scottmoose's expanding family of  BVR/"horns"  

http://www.diyaudio.com/forums/showthread.php?s=&threadid=85156&perpage=10&pagen...


and you might also want to seriously consider upgrading your phono pre- there are several reasonablye cost options in kits or proven DIY circuits that would be as much of an improvement over the NAD as your Decware amp was over previous SS gear.
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« Last Edit: 10/24/06 at 16:57:01 by chrisby »  
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jslusarz
Ex Member



Re: Amplifier hum
Reply #9 - 10/26/06 at 13:26:58
 
Well as a work around until I can get to the hardware store for cabling and connectors, I moved some components around to put as much space between the amplifier and everything else as I could.  Now I am not sure if the hum is reduced after break-in or if it is reduced because I moved some EM noise away from it.  Either way the noise issue is reduced to a manageble level for the time being.

Last night another issue diveloped:  I started to hear popping from one of the speakers on particularly loud sections of music.  My first instinct was to try a different record, but to no avail.  I then reseated all the tubes to see if it was a faulty connection...no luck. Cry

So I am a bit worried that in my first week of ownership I managed to break something.....any ideas where popping at higher levels on one channel, then spreading to two could be coming from?! Sad
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Sam in USA
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Re: Amplifier hum
Reply #10 - 10/26/06 at 17:14:40
 
[quote author=jslusarz  link=1161362143/0#9 date=1161865618]Last night another issue diveloped:  I started to hear popping from one of the speakers on particularly loud sections of music.   [/quote]

My guess is you are clipping the amp.
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jslusarz
Ex Member



Re: Amplifier hum
Reply #11 - 10/26/06 at 18:06:49
 
The clippping begins at a volume(control) level near half of full scale.  The signal is generated from the Rega P2, through NAD PP-2 phono preamp and then into the variable inputs on the Zen Select.  How is it possible that I am clippping at an output level around what I would consider normal listening volume.  I will try a digital source tonight to localize the problem to either the amplifier or the phono section.
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chrisby
Ex Member



Re: Amplifier hum
Reply #12 - 10/26/06 at 19:22:38
 
[quote author=jslusarz  link=1161362143/0#11 date=1161882409]The clippping begins at a volume(control) level near half of full scale.  The signal is generated from the Rega P2, through NAD PP-2 phono preamp and then into the variable inputs on the Zen Select.  How is it possible that I am clippping at an output level around what I would consider normal listening volume.  I will try a digital source tonight to localize the problem to either the amplifier or the phono section. [/quote]

First thing to check out is the cartridge alignment.  As I recall, Rega's past philosphy as regards to VTA was "don't worry, just buy one of our cartridges, and you'll be fine" .  Unfortunately if you're using something else, adjustment can be a bit tricky,  If any of the 3 dimensions are out of alignment, or if the cartridge body is loose, tracking distortions will occur than can be localized to one channel.

As to clipping the amp, it's quite simple - the Goldring is a reasonably high output cartridge (6.5mv), and the NAD's input sensitivity is 3.5mv .  

While you're not likely overloading the phono pre-amp (NAD's specs say that would take 10mv at 20Hz) , it's certainly possible that it's putting out more than enough voltage to drive the Zen to clipping, even with the input level control at  "half".

Couple  that with the MB Quart's moderate sensitivity of  88dB, and depending on the size of room and your definition of "normal" listening levels, clipping of any 2 watt amp is quite possible.    


BTW, we got a bit derailed regarding your original query - have you solved the hum issue yet?  
Have you tested the amp with a shorted input?  Create a shorting plug by soldering a piece of wire from center to ground on a cheap RCA plug. If the noise disappears, it's either the source or the interconnect.  

While you're checking out the cartridge alignment, you might also want to look at the grounding of  cartridge/tonearm wiring.  
If the above test isolates the problem to the table, does the hum get progressively louder as the arm moves towards the center of the disc?  The motor is not particularly well shielded in the Rega table, and a loose connection or poor solder joint anywhere in the arm wiring is another potential problem.    

The Rega arms are huge bang for the buck value, but the quality of wiring and workmanship on early production models was particularly suspect.  A guaranteed huge improvement is something like the Incognito arm wiring upgrade.
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« Last Edit: 10/26/06 at 20:45:17 by chrisby »  
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