Massdrop x Eddie Current ZDT Jr. (Official Thread)

Oh wow. That is shitty customer service!

 

Но это жужжит!

Пожалуйста, перестаньте гудеть!

(У меня не было никакого шума!) ...

 

I think @Torq might have a bee in his undies...

 

"But this is buzzing!
Please, stop humming!
(I didn't have any noise!)
"
) mine was a little bit less senile.

 

Well, it's been a while (about 22 years in practical terms), but my Russian isn't completely fucked it seems! (Though ... a bit fucked ...)

I have a pre-production/first-article build (don't think any components are different), and there's no buzzing nor any hum on either channel. That's with stock-tubes and high-sensitivity, low-impedance, cans. Both closed-back and open.

Can't speculate on what's going on with the delivered units (I missed out on the drop, and would happily buy a non-hum/buzz-afflicted production unit). But my loaner unit is a very enjoyable listen.

 

It is hummmm, not buzzzz
From the sound of it, my completely speculative uneducated guess would be that it is EMI from power transformer due to some part is not grounded properly or just too close.

 

Hey All,
We're in touch with everyone and working behind the scenes to check root cause and fix.
Hopefully more info next week...
If no answer from Russia, I can say that August is a vacation month for RU and Europe but we are in contact.
We are also in contact with a few community members behind the scenes to troubleshoot and understand scope.
Thank you to those who have been very helpful!

Best,
Christian

 

I just received mine after it spent a month with the customs who seem to have opened up the package and had a good look.

My chain is Mac mini + roon > Gungnir Multibit USB gen 5 > ghent audio rca cables > zdt jr > hd 800 sdr mod and hd 6xx.


I haven't noticed any channel humming so far.

Initial impressions while burning in are very positive. I find the amp very detailed with amazing mids. I've been listening to Buena Vista Social Club Live at Carnegie Hall and the whole presentation seems completely holographic - far beyond what I've experienced on my MCTH or Lyr 1.


I also tried it with the Audeze LCD 2 (pre fazor) but wasn't completely blown away.

Waiting for the amp to burn in before doing some critical listening. Exciting times!

 

Hello everyone, just thought I'd share my experiences so far.

Got my first unit and while it sounded great, I was aware of a low-level hum during silent or near-silent parts of tracks or in between tracks. I contacted massdrop support who were very helpful and sent me a replacement unit with no hassle. I got charged import a 2nd time as there wasn't any mention it was a replacement, but I am looking into claiming this back. Unfortunately, the new unit hums just as bad if not worse.

I still have both units. I have a label to return the 1st unit but I'll probably ask to send the new one back as it's worse than the 1st. Although the 1st has 50 - 60 hours on it at least, but the hum is unchanged from when I first noticed it early on. It's a shame as I really like this amp so far and is my first tube amp.

Some extra details: I'm in the UK. 220 Volt. Headphones tested HD800S (High Z) and TH-610 (low Z). When gently tapping on the metal sides of both units there is a metallic ringing like spring reverb in a guitar amp. This effect is far stronger tapping on the left side of each unit than the right. On my first unit the hum is predominantly on the left channel. On my 2nd unit the hum is predominantly on the right channel. I tried swapping both valves from the left side of one unit to the left side of the other and it made no difference. The hum is not affected by the volume dial. I have several other amps/dacs on the same power and none of them exhibit this hum.

 

My ZDT Jr. was working fine for a couple of weeks until tonight when it suddenly started to hum on the right channel, even after the amp is turned off for a few minutes. Is this what everyone which the humming issue is experiencing?

 

I think it is. I received my ZDT 8 days ago after a long and expensive (+$140) customs process. I tried the amp right after it arrived, and I didn't notice any hum with the HD-800 using the high gain connector. I thought that I'm lucky, or the problem doesn't exists on the 220V models. I started a burn in process (playing various music for 24 hours a day), and checked back 72 hours later. By that time, the humming was noticeable on the left channel. Very low frequency, quiet humming. I'd say barely noticeable, but it's there. I replaced the small tubes to the recommended type (GE JAN 5654W), but the humming remained. Another 72 hours later it's still there, without a change. It's volume is independent of the volume knob position.

I tried to find some information about the life expectancy of the bigger tubes (6N24P) without success. Could someone give an estimation for that? Based on my research I believe it's equal to ECC89 and 6FC7. Which brand of these are worth trying?

Update: By now, the hum can be heard on both side, and not as quiet as I remembered. The left is still louder than the right.

 

For those of you experiencing hum with ZDT Jr try this.

Turn ZDT Jr power off. Disconnect power cord. Disconnect RCA cables.
Is hum still audible?
If so, while wearing headphones move JDT Jr around several cm / inches. Does the hum increase or decrease as moved around?
If true, there is a source of magnetic field nearby. ZDT Jr output transformers are sensitive to magnetic fields. Using ZDT Jr as a detector the source of magnetic field may be identified.
Now move ZDT Jr away from magnetic field source until hum is no longer heard. Or alternatively move the magnetic field source away from the ZDT Jr. until hum is no longer heard.

A common magnetic field source that many on this forum have is any Schiit DAC or Amp with wall wart transformers or the Cthulu. If ZDT Jr and transformer are located within approximately 17 cm hum will be heard. This distance varies with size / power of transformer involved.

Modi MB transformer wall wart at 7 cm


Modi MB transformer wall wart at 17 cm


Hum measured -64 dBu with Modi MB wall wart transformer at 7 cm


Hum measured -75 dBu with Modi MB wall wart transformer at 17 cm


Using Sennheiser HD800 with sensitivity of 98 dBSPL / mW and 300R impedance (ignoring frequency response for this calculation) the following SPL will be achieved:
-64 dBu produces 37 dB SPL
-75 dBu produces 26 dB SPL

37 dB SPL is audible in quieter ambient settings.
26 dB SPL is on the threshold of audiblity in my acoustic lab.

 

• Turning off: The hum is not audible, even if the power cord is connected.
• Disconnect RCA cables: Doesn't matter. The hum is always present when the unit is turned on.
• Moving around the unit a few inches, or even meters: No change in the volume of humming.
• Nearby magnetic field sources: It would be a reasonable explanation, but it's not the case. Here is my testbed, still humming:

If it's the result of a magnetic field, then that is generated by the unit itself.
Other observations:
- The humming can be heard with the HD-650 too.
- It appears immediately after turning on the amp. The volume level of it changes during the first approx. 10 seconds. After that it's fix.
- I estimate the humming volume to be about 30 dB.
- Humming is independent of the volume knob's position.
- It's volume is NOT the same in the two channels (this might be an important clue)
- Switching left/right tubes doesn't change the humming. On my unit it's allways louder on the left channel (this clue might be important too)
- It strongly reminds me to a sound of a ground loop. But AFAIK you need at least two units to create a ground loop.
- Tapping, touching, pressing, putting weight on top of the unit doesn't change the humming at all.
- The humming is present on the high impedance and the low impedance outputs too.
- Seems like no "upload image" option in my SBAF editor, so I had to use external link.

 

Hi AtomicBob,

To add to AudioFriend's observations, I too still had hum when unplugging RCAs and moving unit to the centre of the room (HD800S). The room is nowhere near as empty as AudioFriend's but the unit was at least 1 metre away from any other device. I happen to have a Magni 3 and moving the unit close to the wall wart did increase humming. The humming remains at the regular level though with the wall wart unplugged.

 

Perhaps the power transformer for the unit itself is generating the magnetic field that is causing output transformers to hum?

 

I know its a big ask, but is anyone willing to send their "hummy" unit to @Hands to compare to his pre-production unit? I'm assuming Hands is up for it, and it might get to the bottom of the whole "did something happen in production" question.

 

I remember at my buddy's place as a kid, he would know if he was getting a text or phone call before a notification showed up because his crappy Logitech desktop speakers would make this weird buzz sounds temporarily, I assume because of some signal sent or received.

Maybe a phone test? Having my router too close to my tube power amp causes it to make funny noises that change as I move it further and closer.

 

The loaner prototype residual hum + noise measurements may be seen in the last graph found here. Hum was approximately -80 dBu for both channels.

Here are quick internal hum measurements for my production unit (I was in the drop too.) These are with 300R load on the high impedance output.

ZDT Jr internal hum measurement setup


ZDT Jr internal hum 300R load high impedance output Left channel -63.1 dBu


ZDT Jr internal hum 300R load high impedance output Right channel -79.1 dBu


ZDT Jr with rudimentary additional steel shield placed between power transformer and left channel output transformer


ZDT Jr internal hum 300R load high impedance output Left channel with additional steel shield -66.4 dBu


Rudimentary additional steel shield drops 60 Hz hum by 3.3 dB suggesting a magnetic coupling between power transformer and left channel output transformer. Orientation of the power transformer field may be such that it has a much lower coupling to the right channel.

This would explain audibility of left channel hum in very quiet ambient environments.