[lonewolfny42]

No hum here either....at any level....soft or loud (95db+).....

Good luck with your testing Jeff. Hope you can sort it out....

[Scott F.]

Preamp Volume knob at 0 to 2.30 o'clock: No his, no hum
But the hum starting at 2.30 and increases in volume as I increase the gain on the preamp
With preamp gain set at max, I can hear the hum clearly from 8 ft.

The hum go away if I turn Paradisea off or remove completely.

Dustin,

Turning your preamp all the way is definitely not the norm especially if it is a 'typical' preamp that has a gain of between 12 and 15. More likely your volume knob doesn't get much past 12:00 during a listening session. Both of my preamps have about 15db of gain. On one it seldom goes above 10:00. If I go past that, I send the system into clipping. My other is nearly the same except it can see about 11:30 (I think the gain rating on that pre is a little optimistic). That said, I have seen some transformer based pre's that you can crank all the way around without causing the system to clip. Is this the type pre you are using or do you have a 'normal' gain stage?

May be other Paradisea's owners should test their unit, and feed back.

I've had mind in about six or eight different systems and it doesn't have a hum or hiss. It now spends all its time in a system that uses 103db efficient speakers. If there was a hum or hiss, I'd hear it out of them.

[Captain Humble]

Scott,
I have a Dodd Battery Powered Preamp.
The volume on the preamp is at 0 in at about the 7 O'clock position.
With the volume at 0 the hum is audible through my midwoofers.
As I turn up the volume the volume of the hum increases, but not as much as it did prior to pushing down on the tube with an eraser.

I sent the following to the manufacturer this morning:
I am having a problem with my Paradisea.
Hum coming through my speakers and the hum increases in level as one increases the gain on the preamp. This does not appear to be a ground loop issue. Details contained on AudioCircle.
Here's a link.
http://www.audiocircle.com/index.php?topic=34151.0
Please review and advise the best path to take to resolve.
Thanks,
Jeff

[Captain Humble]

May be other Paradisea's owners should test their unit, and feed back.
Dustin

Dustin,
It looks like it's just you and me so far.
The good news is it would appear that there is something different about our units since others aren't having this issue.  Therefore I would think it can be fixed.

I'll keep you posted regarding the manufacture's response to my inquiry this morning.

Thanks for the feedback,
Jeff

[Scott F.]

Jeff,

Your issue is likely something internal to the unit (assuming you've tried another tube). I (sort of) doubt it's RF from the unit but who knows at this point.

When it comes to Dustin's unit, if he has a 'typical' preamp and is pushing his system to clip just to hear a hum and that same hum isn't audible at normal listening levels, I'm not sure how big of deal that is (not trying to minimize it but in the same vein if you don't hear it....  ) On the other hand, if his preamp isn't sent into clipping and he has that noise, then he should be in touch it MHDT for repairs or a new unit.

Be sure to keep us all posted on MHDT's customer service. I've got no doubt they will make things right though it may take a bit longer since you are dealing with a company overseas (shipping times and all).

[JoshK]

Yeah, it sounds like a bad tube.  Test it when you get the new tube and if it still has the problem, report back, or have Gary Dodd look at it.

[Captain Humble]

Jeff,

Your issue is likely something internal to the unit (assuming you've tried another tube). I (sort of) doubt it's RF from the unit but who knows at this point.

When it comes to Dustin's unit, if he has a 'typical' preamp and is pushing his system to clip just to hear a hum and that same hum isn't audible at normal listening levels, I'm not sure how big of deal that is (not trying to minimize it but in the same vein if you don't hear it....  ) On the other hand, if his preamp isn't sent into clipping and he has that noise, then he should be in touch it MHDT for repairs or a new unit.

Be sure to keep us all posted on MHDT's customer service. I've got no doubt they will make things right though it may take a bit longer since you are dealing with a company overseas (shipping times and all).

Mhdt Labs response was the quickest I've ever received from any manufacturer.
Here you go...

Hi Jeff,
Please read this article Finding and Fixing Hum http://www.psaudio.com/articles/hum.asp
Like the article says, very few audio or video systems are dead quiet. There are usually always a few hum related problems. Especially in tube gear. In tube gear, the designer usually use transformer couple or adding capacitors in + and - output jack (bad design) or use a heavy metal case to act as shield and ground.

Paradisea doesn't ground connected to 3rd plug of AC input. This is to avoid the dirty AC ground flow into Paradisea. However, this is also caused the Paradisea is floated in electronic ground.

Metal case can perform a shielding of audio unit to acts as a stand alone unit; however, this shielding and grounded shield kills some skill of natural and musical sound characteristics of audio system. To get the maximum natural and musical performance, Paradisea use acrylic case instead of metal case. This leads Paradisea to has its ground limited to its own PCB copper layout. Paradisea need to balance its ground by itself and this is very hard in design as well as in pcb layout.

The design of Paradisea is to be no hum in audible/hearing range; however, there could be some trivial and tiny hum problem in some cases:
1. If you turn your volume knob all way down trying to bomb your ears.
2. The input impedance of pre is high (>100K) will usually easy to get this problem, however, this is only in the case that volume at > 12 o'clock.
3. The ground of Paradisea and the ground of pre amplifier becomes a new ground trough the connection of IC and this new ground will interacting each other to find their balance.

If the case 3, the hum will eliminate in about one month (burn in or keep operation) when the new balance established in new ground system.

The sound of Paradisea is unique and its sound is out of whole design, if you don't like the sound or you are in trouble of or hating this hum, I will refund to you.

Best Regards,
Mhdt Labs

My plan at this point is to:
1.  Wait for my Tung-Sol tube and try that although I now suspect the tube isn't the issue.
2.  I need to get over to Gary Dodd's this week anyway, so I'll take the Paradisea with me and see what happens there.
3.  Assuming that we still haven't figured it out, I'll write back to Mhdt and ask if I can continue the burn in for a month per his note number 3 above and see if it corrects itself.  Based on my dealings with Mhdt Labs to date I think they will be fine with this.
4.  Assuming that doesn't work, I might like to send it to Chris (lonewolf) to see how it acts in his system.  Since he has one that doesn't hum, if mine hums in his system then I can assume I have a defective unit and will ask to exchange it for another unit.

So...we have a plan.
Again I want to be clear that the hum is not audible from my listening position.
I just want to make sure it is functioning properly.

There is a definite improvement in the sound with my Paradisea in the loop so if it doesn't hum in Chris's system, we'll know it's fine and I'll probalby keep the one I have.

If anyone sees something I'm missing here please advise.

Thanks,
Jeff

[shooter]

I have a Paradisea in Dallas, with 98db high efficiency speakers no noise no hum, you can check against mine locally instead of sending it out of town.

[Captain Humble]

I have a Paradisea in Dallas, with 98db high efficiency speakers no noise no hum, you can check against mine locally instead of sending it out of town.

Thanks Shooter!
That would be a lot easier and less chance of it getting damaged in shipment.
I'll pm you when the new tube comes in.

[Asic81]

First, thanks Mhdt Labs for super quick response, I got the same answer from Mhdt Labs.

Hi D,
Please read this article Finding and Fixing Hum http://www.psaudio.com/articles/hum.asp
Like the article says, very few audio or video systems are dead quiet. There are usually always a few hum related problems. Especially in tube gear. In tube gear, the designer usually use transformer couple or adding capacitors in + and – output jack (bad design) or use a heavy metal case to act as shield and ground.

Paradisea doesn’t ground connected to 3rd plug of AC input. This is to avoid the dirty AC ground flow into Paradisea. However, this is also caused the Paradisea is floated in electronic ground.

Metal case can perform a shielding of audio unit to acts as a stand alone unit; however, this shielding and grounded shield kills some skill of natural and musical sound characteristics of audio system. To get the maximum natural and musical performance, Paradisea use acrylic case instead of metal case. This leads Paradisea to has its ground limited to its own PCB copper layout. Paradisea need to balance its ground by itself and this is very hard in design as well as in pcb layout.

The design of Paradisea is to be no hum in audible/hearing range; however, there could be some trivial and tiny hum problem in some cases:
1. If you turn your volume knob all way down trying to bomb your ears.
2. The input impedance of pre is high (>100K) will usually easy to get this problem, however, this is only in the case that volume at > 12 o’clock.
3. The ground of Paradisea and the ground of pre amplifier becomes a new ground trough the connection of IC and this new ground will interacting each other to find their balance.

If the case 3, the hum will eliminate in about one month (burn in or keep operation) when the new balance established in new ground system.

The sound of Paradisea is unique and its sound is out of whole design, if you don’t like the sound or you are in trouble of or hating this hum, I will refund to you.

Thank you
Mhdt Labs

Scott
My tube preamp is 12 db of gain, and my volume knob never gets past 12:00 during any listening session.
I test the hum without music playing of course, and the hum only starting if I crank the volume knob past a 2:30 o’clock
Base on Mhdt Labs explanations, possible some ground sensitive between Paradisea and my tube preamp, no problem there, never crank the volume knob to 2:30 any way.

Thanks again to Mhdt Labs for quick response and 100% stand behind your product. For the sound you bet I am a very happy camper.

Dustin

[tvad4]

I went back today and listened for hum at higher volume levels (12:00+ on the volume pot). There is some audible hum starting at about 12:00 and increasing as the volume is turned up. Swapping in different 5670 tubes did not ameliorate the hum, so in this case the tube does not seem to be the cause (although tubes can and do cause hum if they're bad).

The hum is not present when the Paradisea is taken out of the system chain.

However, the hum is not audible at normal listening levels. Chalk it up to part of the Paradisea's charm. 

[toobluvr]

With mine I get a very slight hum starting at 2 o'clock.
All gear is turned on, no music is playing, and selector switch is set to Pardisea.
It increases slightly as volume is turned up....but only slightly.

But who cares?!   
I never even approach 12 o'clock when I listen.
And the hum is sooooo minor, even with volume pot fully open, it's not even worth discussing.
If music was playing that loud, there's no way it could even be noticed.

I've owned the Paradisea for about a month now and would not have even noticed it had I not went looking for it.

I don't think this is a problem that one needs to worry about or seek to remedy.

[tvad4]

(I) would not have even noticed (the hum) had I not went looking for it.

I don't think this is a problem that one needs to worry about or seek to remedy.

Agreed. However, I can understand how the hum might be more noticeable at lower volumes to someone using high efficiency (100+dB) loudspeakers.

[Scott F.]

Agreed. However, I can understand how the hum might be more noticeable at lower volumes to someone using high efficiency (100+dB) loudspeakers.

Its not noticeable on my 103db efficient horns and I tend to play them louder than most people. Now on the other hand the dimmers in my kitchen drive me absolutely nuts. If only I could talk Occam into designing and marketing an audiophile dimmer (that fits in a standard 2x4 handy box) I'd be one happy camper and he'd make zillions by selling them to us at $100 a switch 

[legarem]

My speakers are biamp Onkens (97 db/1w/1m) and my Paradisea has some hum when the volume control of my tube preamp is cranked over 12 O clock.

I don't think that this hum is normal but it doesn't bother me because I can't listen music in my system with the volume control settled for hearing it.  At this level my ears would bleed.

As i made some modifications to the Paradisea, I will investigate this problem later when i'll do more mods.  I'll probe at the TL41 regs to see if there's ripple there.

If your problem seems worse than mine, try to reverse the plug in the outlet to see if it is better.

My 120 VAC supply is balanced so in my case it changed nothing.

For those who don't know this product, never have any doubt about the parts quality they use in this dac.  This is really a high end gear.

Marc Legare

[NewBuyer]

...I don't think that this hum is normal... As i made some modifications to the Paradisea, I will investigate this problem later when i'll do more mods.  I'll probe at the TL41 regs to see if there's ripple there...

Very interested in your findings. Thanks for being willing to check this out legarem!

[Captain Humble]

The Paradisea induced hum is not the fault of the tube.
I received my new Tung-Sol Tube yesterday and the hum remains the same.
Next step is to take it to Shooter’s to see if the hum is specific to my system.

Shooter Said:
I have a Paradisea in Dallas, with 98db high efficiency speakers no noise no hum, you can check against mine locally instead of sending it out of town.

If mine hums at Shooter’s house we will know that the unit needs work and I’ll request a new unit from the manufacturer.  I suspect that this is what we will find.

If it doesn’t hum in Shooter’s system I’ll assume my unit is functioning properly and that the hum is specific to my system.  Should this be the case I’ll probably just live with the hum.

Toobluvr Said:With mine I get a very slight hum starting at 2 o'clock.
All gear is turned on, no music is playing, and selector switch is set to Pardisea.
It increases slightly as volume is turned up....but only slightly.

But who cares?!    
I never even approach 12 o'clock when I listen.
And the hum is sooooo minor, even with volume pot fully open, it's not even worth discussing.
If music was playing that loud, there's no way it could even be noticed.

I've owned the Paradisea for about a month now and would not have even noticed it had I not went looking for it.

I don't think this is a problem that one needs to worry about or seek to remedy.

Toolbuvr,
If my experience with the Paradisea mirrored yours I would agree with you. 
Unfortunately it doesn’t.

If I touch pause while listening at normal levels I can hear the hum from my listening position which is 12 feet from my speakers.  Trust me; I didn’t have to go looking for a hum and it is a problem since 4 people out of the 8 that responded to this thread experience NO hum.

If Scott and I were selling our Paradiseas and Scott had reported no hum after trying his in several different systems and I reported that you can hear mine humming, when the system is paused at normal listening levels, 12 feet away which one would you buy?

Though I can’t hear the hum over the music this thread has clearly established that our collective experience with Paradisea induced hum varies significantly.

NO AUDIBLE HUM:
Woodsyi - No hum up to 110 dB and that’s as far as he went - albeit far enough
Lonewolfny42 - No hum here either....at any level....soft or loud (95db+)
Scott F. - He’s had his in about 6 or 8 different systems and there is no hum or hiss
Shooter - No noise or hum

MILD HUM
Asic81 - Hum starts at 2:30
Tvad4 - Audible hum starts at 12:00
Toobluvr - Hum starts at 2:00

STRONG HUM
Captain Humble - Hum starts as soon as powered up with volume set at 0.
At this position no music can be heard but there is a slight hum.
The Dodd Battery Powered Preamp is at 0 volume a couple of minutes past the 6:00 position.  Most CDs are at normal listening levels at 9:00 plus or minus a couple of minutes.

If I pause my CD player at normal listening levels the hum from the Paradisea can easily be heard from my listening position which is 12 feet away from the drivers.

DODD BATTERY POWERED PREAMP SPECS:
•   Continuous battery operation
•   Input Impedance 100K ohms (Quieter and more universal)
•   Output Impedance: Less than 200 ohms
•   Gain 16 dB

Speaker Sensitivity 87 dB @ 1 watt / 1m

I'm sending shooter a PM to see when we can plug my Paradisea into his system.
I'll post our findings asap.

Thanks to all that have responded.
Jeff

[toobluvr]

Just a guess here, but my intuition tells me the following:

The slight hum is there on all units, but goes unnoticed because when testing for the hum, I see that some people here are turning gain pots way up while the music is playing....rendering the hum basically inaudible.  I would have been in the "no hum" camp myself had this thread not inspired me to  go looking for it.  I had never heard it while music was playing....even at loud levels.  The only way I can hear a slight hum is with high volume levels, and no music playing.  And the hum is very slight, so it is never an issue for me.  Dead quiet at my normal listening levels, and even at loud levels since it is drowned out by the music.

I do not believe it is the tube.  I have tried several different tubes, and it is always there.  I believe it is instrinsic to the unit.  I suppose how loud it is can vary across units, but I suspect the level of intrusiveness is a function of speaker sensitivity and overall system gain.

[Scott F.]

Hiya Jeff,

The Paradisea induced hum is not the fault of the tube.
I received my new Tung-Sol Tube yesterday and the hum remains the same.
Next step is to take it to Shooter’s to see if the hum is specific to my system.........


.......If I pause my CD player at normal listening levels the hum from the Paradisea can easily be heard from my listening position which is 12 feet away from the drivers.

I'm sending shooter a PM to see when we can plug my Paradisea into his system.
I'll post our findings asap.

Thanks to all that have responded.

Thats interesting. When you take it to Shooters be sure to try different digital and analog cables and power cords (even some really cheap ones) and be sure to play with the units placement relative to everything else. You may even want to try a cheap $6 Toslink form Wally World or Rat Shack.

I'm assuming the hum is a 60Hz hum with likely a fundamental at 120Hz (that is significantly less pronounced) also. If after trying all the different combinations I would point towards the power supply. Either a cap that is out of spec or maybe even a diode or regulator. It's not inconceivable that MHDT got some parts that were out of tolerance and didn't notice the hum when he tested the unit before shipping. Not sure if you are communicating directly with him but you may want to point him to this thread. He could register and and (maybe) pick up something obvious that all of us have missed.

[nakolawala]

All

I just received my Paradisea a couple of days back and it also has this HUM problem. When connected to my preamp, after 12 oclock position I can hear a slight hum and becomes louder if you increase the vol. I have tried all possible things but the hum remains. I believe it is in the design . Other than the hum, the Paradisea sounds absolutely fantastic. I am using the WE 396A tube and sounds better than stock tube.