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Darkvoice 336i & 336SE Tuberolling PartII

Discussion in 'Headphone Amps (full-size)' started by heatfan12, Jul 31, 2008.
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  1. MelonHead
    This morning my right channel went completely out of service. I cant hear anything but some static noise. I've changed the tubes and the RCA cables which comes from the DAC, but none of these has solved the problem.
    The same situations occurs on the preamp output and on the headphone jack as well. If I connect the DAC directly into my amplifier, both channels are working.
    According tho my knowledge, I have ruled out every possible steps, but I'm wondering if somebody can suggest me some workaround to fix this annoying issue.
    My DV 336SE is pretty new. It arrived 3 months ago, and worked flawlessly until now.
    Thanks in advance for any help or suggestion!
  2. wwmhf
    Replace both tubes at the same time?
    Plug in another pair of phones?
  3. MelonHead
    Yes, I replaced both tubes, tried with different headphones and with my loudspeakers using the RCA output.
    Everything works fine when I remove the Darkvoice from the chain and use my DAC as preamp. :frowning2:
  4. volly
    Damn....doesn't sound good my friend. One thing to try is whilst everything plugged in and turned on. Play some music, while the music is playing then tap on the chassis and see if you hear any difference. Tap on the metal plate around the tube area, if for whatever reason the channel comes back (momentarily) then you might have something to investigate further.

    Good luck! :bow:

    P.s Dirty RCA ports? I've had RCA cables go bad too!
    Last edited: Oct 14, 2018
  5. Gallic Dweller
    His problem is simple since he has isolated the problem to the amp, one or more components have died in the right channel. Someone else has lost the right channel and I wonder if MelonHead has also removed the tubes/valves with the amp on for long periods of time, this is not clever, the valves are part of the circuit, removing them for a long period of time is effectively altering the operating points of the circuit.

    What needs to be done now is a simple continuity check on the right channel, this will determine what if any components are kaput.
  6. wwmhf
    Be very careful when tapping a troubled tube amp!!!

    First, to void a fatal electric shock caused by a random movement of a loose wire, do not use a bare hand to tap, use a plastic or wood stick. Second, use a pair of junk hones and do not ware them directly on your ears, a random movement of a loose wire might generate a huge pop/crackle that can damage you precious phones or ears.

    If you are not afraid to open the amp, I suggest you to unplug the amp, then open it. First, check whether there are anything burned out obviously. Then, use a screen driver to poke the solder joints, use a flash light can help in this task. This is in the line suggested by Gallic above.
    MelonHead likes this.
  7. MelonHead
    Since I found the Shuguang, and Sylvania I haven't been rolling tubes, and never left the tube sockets empty . I use the volume knob at 12 o'clock, as the volume is changed in Foobar 2000, or on my Electrocompaniet EC4.7, when I use my speakers.

    Thanks guys for the tips.
    Unfortunately these are above my skills. I guess, it's better to find somebody here who has some experience in tube amps and can find the source of the problem and hopefully fix it.
    volly likes this.
  8. Gallic Dweller
    that's sensible. There are lethal voltages in valve amps, this is not a problem when you take precautions. I got serious about my sound system when I decided to build from valve kits - World Audio Design in the UK. Once built you have to do various voltage checks with the amp powered up. A decent multi-meter is a good idea, that way you can test voltages. Long ago I bought an electrician's screwdriver ( I was a builder) with which to test if power was really off. I use this to do simple continuity checks. It is fitted with an LED, every home should have one.

    Had you bought the D/V through a hi-fi dealer you could take the amp back to be repaired. If you bought the D/V through Massdrop you have now encountered the downside - caveat emptor/buyer beware, they have no liability to fix anything they sell. The D/V can and does get very hot, the power resistors get extremely hot and they are directly soldered to the PSU caps, they re not good quality and should be changed for MIlls. Long ago when I got into hybrid head and power amps a Dutch friend suggested using a computer fan underneath with the amp base plate removed. I use my D/V on a slate box (open backed and site a PC fan directly underneath, so the amp which sensibly has perforated side plates can dissipate a lot of heat.

    Find someone experienced with valve amps, I'm sure they will find the problem. They may well agree about the power resistors and some other mods at the same time, so you may well end up with a much better amp.The volume control is really bad, a Valab att. with SMD resistors would be a distinct improvement or shunted Alps Blue. Chinese made amps are very cheap because they use some very cheap components, many need to be modded not only for better sound but sometimes for safety reasons.

    I made a review of the D/V for Massdrop with ideas that turn it from a good amp into a very good amp. Apparently the original makers have disbanded and some now make the Le Figaro. The actual workmanship of the D/V is extremely good if someone was to start from basics and design out the faults yes the amp would be more expensive but it would kill a lot of the competition. Not everyone wants to get involved in modding, they want to buy a piece of equipment that is plug and play. The D/V is my first experience of the OTL type of amp and I think the basic sound has so much going for it over other types, that's why so many rock on it.

    This thread is about tube rolling but that really should come second to fixing some basic problems first.
    MelonHead and volly like this.
  9. MelonHead
    Yesterday I unplugged the DV336SE, and removed it from the chain.
    I arrived home an hour ago, and after reading the new posts, I put the system together again with the DV, and what a miracle... it works again without any problem.... :)
    I don't know if it's temporary or permanent betterment, or it was a cable which caused the problem or something else, as I've changed the cables at least four times.
    But right now I'm happy and very thankful for your cooperative and valuable attitude.
    Meanwhile I found a very good mechanician who is specialized on Valve/tube amps and retro audio. He can execute the changes to make the amp even better, so I will look for your advice @Gallic Dweller.

    Edit: That lasted for ten minutes. The right channel went away again... :frowning2:
    Changed both tubes, but it didn't help.
    Last edited: Oct 15, 2018
  10. wwmhf
    Sorry for the trouble again. Here is my speculations:

    1. Loose solder joints
    2. Capacitor failure
    3. Semiconductor parts
    MelonHead likes this.
  11. Gallic Dweller
    So, the problem is intermittent, looks like a dodgy solder joint rather than a failed component. Get in touch with that man - he can fix the minor problem and at the same time mod the amp.
    MelonHead likes this.
  12. MelonHead
    My DV336SE will go to the service tomorrow and I would like to ask them for the additional upgrades as well.
    Before that, I want to collect all the affordable and useful modifications to help them.

    Maybe I was not meticulous enough, but I haven't found a detailed, all-in -one compilation regarding the advised upgrades.
    I've seen your posts @Gallic Dweller but I'm not professional enough, to gather the useful pieces of information.
    Will you or somebody else be so kind to help me regarding this?

    All what I know that I don't want to cut out the preamp output as I use my DV336SA as a valve preamp in my loudspeaker chain as well.

    Sorry if I was offtopic and thanks in advance for any help.
  13. Gallic Dweller
    Hi Melonhead,
    as there is to my knowledge only one volume sweetspot how do you use the pre-amp by that I mean - there is either no volume or it goes too loud. Choices (1) fit a 100K or other value Alps Blue (discuss this with the technician/s) shunted with z foils - total transparency, other resistors will colour the sound. Shunt resistors should be 90% of the pot value, so this will mean a drop of around 6% in sound. (2) a Valab att. built with SMD resistors/23 positions, I personally have no experience of them but have only ever heard good reports from those who have and they are not expensive.

    Consider changing the signal wiring to the pot, stay with solid core. I don't use sheilding and have never had a problem with any kind of interference. Discuss this with the technicians. As with any mods you have done you need to find out if they are open minded or hidebound. Many EEs (electrical engineers) have stepped outside the box their training put them into and think freely.

    You say you have never had the problem of hum, there are at least 2 forums where mods were done that eliminated this problem - if the EES don't know tell them to check out pinterest - there are visuals and info of those who overcame this problem. Rock Grotto has a thread and solution - worth a look.

    The output caps - I am dealing with these at the moment. At the moment they consist of 3 x 10uF unknown Chinese polyester caps per side. 100V caps have been used successfully. I would love to have been able to use K73-16 here but the highest value is 22uF and these are only 63V. 30uF polyprops will be expensive

    100uF will enable lower Ohm h/phones to be used and should give a bigger sound. Bipolar - Parts Express/ F&T/ Nichicon/Audyn rough foil - I intend to try these and the Parts Express or polarised electrolytic. I will almost certainly use bypass caps with whatever I choose - high voltage K73-16 - 1600V or 1000V 1.5/3.3/ Very good caps don't need bypassing but here it should be a good move. A suggestion if the EEs can use PCB pins or similar, then you could easily experiment with these output caps - the sound is all about personal taste - there is no right or wrong. I have learnt from experience that mucking about with PCBs can easily mean track lifting - not funny. The Chinese do seem to like using PCBs everywhere eg. RCA inputs, the pot PCB and the output caps PCB - again discuss with the EEs.

    Point-to-point wiring has to be good for sound and what there is in the D/V is very good indeed. I'm surprised that no enterprising Chinese hav'nt remedied and improved what is the basis for a superb headamp. Hope this helps
    MelonHead likes this.
  14. Gallic Dweller
    After a few mistakes on my part I finally got my Stereo Coffee preamp to work. I have disconnected the D/V pot, made a new earth and used my own multi conductor signal wiring fed by the S/C. Absolutely no hum and the bass is outstanding, awsome,really deep and layered. Top end is congested, the amp had only been on for a few minutes.

    I have yet to change the output caps - vamos a ver. Maybe the hum problem is tied up with the standard pot configuration.
  15. wwmhf
    "Top end is congested"? This is a shortcoming, isn't it?
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