A lot of noise in the Darkvoice 336SE (6SN7 culprit?--> NO!)

[Damian]

Hi,

So, this amp is so noisy past 11 (kind of RF noise) when connected to the PC that is driving me nuts.... I've changed the DAC, Cable, USB Port and nothing. I power it from the same extension cord or from the wall directly and still the same. My Burson connected in the same way is as quiet as it can get.

Then, I removed the 6SN7 tube, and it goes dead silent... changing the stock tube then gets rid of the noise? Or it might be the same?

 

[Blumlein 88]

https://www.audiosciencereview.com/...ements-of-darkvoice-336se-headphone-amp.6549/

It was reviewed and measured here by Amir. It looks like it has lots of hum and is very sensitive to the 6SN7 being used. Are you getting hum noise or some other kind of noise?

 

[Damian]

This kind of noise:

it gets louder the higher I turn the volume. I just also didn't use the ground plug and is the same.

 

[Blumlein 88]

Yes, the sound heard in the video is hum pickup. It might sound lower in tone with less buzz if it were just 60 hz or the first couple harmonics like 60, 120 and 180 hz. In the video the buzz comes from it being 60 hz and several harmonics. Looking at Amir's measurement it looks like it has considerable hum for 60 hz and at least the first 20 harmonics. Changing the tube can improve or worsen it. Probably will not ever make it fully quiet.

If you've just purchased it, I'd send it back. If you've had it awhile and that isn't an option you might make it better.

Amps like this probably have a very high input impedance which makes them more prone to picking up noise like this. Like in the video, reducing the input impedance by placing a lower value resistor across the inputs might reduce the noise considerably. Maybe putting a 20 kohm resistor across the input jack. But without knowing the circuit design I couldn't suggest too much more.

It also could be a shielding issue. Putting grounded foil or grounded metal shield around the tube or some other part of the circuit might very well help. I don't know how far you should go with this if you aren't experienced working on electronic gear.

Looking back after doing a quick search on other forums, a large number of these amps get complaints of hum and buzz. And being picky about tubes in regards to hum. This is going back more than 10 years.

Okay, it appears the heater circuit is where most of the hum is coming from on them. They use a solid core non-twisted pair of wires for the heater. They should have twisted them. Some people put large caps on the heater circuit. Not sure how much that would help. But I'd bet it helps.

So again if you've just purchased it thru massdrop or whatever I'd get a refund. If not, you can try some of the fixes people offer in other forums. I'd probably swap the heater wire for some stranded wire of the same gauge and twist it tightly. But if you don't work on such stuff, know the interior has some voltages of a few hundred volts floating around. So learn what you are doing and be careful.

 

[qwerty88]

Ah, the old buzzing 6SN7 tube issue. The Darkvoice is notorious for NOS and new 6SN7 tubes buzzing. I remember the stock 6SN7 tube buzzing in one of the earcups when turning on my Darkvoice for the first time. There are a few ways to overcome this issue:

1) Burn-in of the 6SN7 tube. Basically, while the amp is off, seat the stock 6SN7 tube and leave the rear power tube socket unseated. Turn on the amp and let it run for 24-48 hours. You'll find the amp to run cool while the stock 6SN7 tube is the only one seated there. Still, keep an eye on it for some time just in case. In my case 24 hours was enough for the buzzing to go away with respect to the stock 6SN7 tube; or

2) Perform the Fitz mod, which is just installing two 220uF in parallel as shown in the pic below (6SN7 socket). While this mod eliminates the hum associated with NOS and new 6SN7 tubes, the trade-off is increased volume gain. If you go down this route, you'll likely void any warranty. Also, make sure the caps are discharged; safety first!

 

[Blumlein 88]

Ah, the old buzzing 6SN7 tube. The Darkvoice is notorious for NOS and new 6SN7 tubes buzzing. I remember the stock 6SN7 tube buzzing in one of the earcups when turning on my Darkvoice for the first time. There are a few ways to overcome this issue:

1) Burn-in of the 6SN7 tube. Basically, while the amp is off, seat the stock 6SN7 tube and leave the rear power tube socket unseated. Turn on the amp and let it run for 24-48 hours. You'll find the amp to run cool while the stock 6SN7 tube is the only one seated there. Still, keep an eye on it for some time just in case. In my case 24 hours was enough for the buzzing to go away with respect to the stock 6SN7 tube; or

2) Perform the Fitz mod, which is just installing two 220uF in parallel as shown in the pic below (6SN7 socket). While this mod eliminates the hum associated with NOS and new 6SN7 tubes, the trade-off is increased volume gain. If you go down this route, you'll likely void any warranty. Also, make sure the caps are discharged; safety first!

Welcome to ASR.

Yep so caps on the heater pins. Looks like a good idea. Man why did they use those untwisted heater wires? Were it mine I'd add the caps and some twisted stranded heater wire.

Looks like a design from Aesthetics and not from sensible electronics principles. Should have seen some of my old VTL gear I modded. Super hand braided pure silver and teflon cable through out. Had a friend's wife do it as only she had the fine motor skills to make it happen. She shaped it and positioned it and I taught her to solder so she could put it in position. Not as strange as it sounds as she really dug cool music over cool gear like all tubed units.

 

[Wombat]

FWIW. I have found cheap modern valve sockets have poor contacts. Replace with NOS or better new ones.

 

[Damian]

Hello guys,

So, by chance when switching headphones I came to a moment of silence... when I push the jack the sound disappears... I then tried different headphones/adaptors and one gave no issues... but is obviously a problem with the headphone jack or the potentiometer touching something that it shouldn't?

Any ideas on how to fix it now that I know the problem is not the tubes?

 

[L0rdGwyn]

For future readers who find their way to this thread...

The 60Hz noise in the DarkVoice circuit is primarily due to the lack of a heater center tap. Instead, one leg of the heaters is connected to the amplifier ground bus, which was a very poor design choice. The noise can be completely eliminated by createing a virtual center tap with two 100ohm resistors and elevating the heater supply.

I completely overhauled the DarkVoice circuit and found the issue, quite unexpected as providing a center tap and ground reference is tube amplifier design 101...

Here is the circuit overhaul: https://www.audiosciencereview.com/...ice-336se-circuit-overhaul.20377/#post-672636

And guide to center tapping and elevating the heater supply in the stock circuit from Head-Fi: https://www.head-fi.org/threads/darkvoice-336i-336se-tuberolling-partii.348833/post-16182719

 

[Strangebru]

Ah, the old buzzing 6SN7 tube issue. The Darkvoice is notorious for NOS and new 6SN7 tubes buzzing. I remember the stock 6SN7 tube buzzing in one of the earcups when turning on my Darkvoice for the first time. There are a few ways to overcome this issue:

1) Burn-in of the 6SN7 tube. Basically, while the amp is off, seat the stock 6SN7 tube and leave the rear power tube socket unseated. Turn on the amp and let it run for 24-48 hours. You'll find the amp to run cool while the stock 6SN7 tube is the only one seated there. Still, keep an eye on it for some time just in case. In my case 24 hours was enough for the buzzing to go away with respect to the stock 6SN7 tube; or

2) Perform the Fitz mod, which is just installing two 220uF in parallel as shown in the pic below (6SN7 socket). While this mod eliminates the hum associated with NOS and new 6SN7 tubes, the trade-off is increased volume gain. If you go down this route, you'll likely void any warranty. Also, make sure the caps are discharged; safety first!

Thanks for the info. If the heater wires are the culprit, how does tube burn in help? Also, neither my stock tube nor a NOS RCA hum at all. Only my two brand new Psvane (high-end version) tubes hum.