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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. SylvesterH

    Although everybody told me to stay away from OTL amps on low impedance headphones I can report the both k812 and Oppo PM-2 are behaving spectacularly on the DV 336SE.
    My set-up is OPPO HA-1 as Dac and DV 336SE - Amp.
    I want to note that if I set the OPPO to simply bypass the volume is too much for the amp. So there is plenty reserve even for a 32 Ohm can as the PM-2.
  2. Gallic Dweller
    Some things for D/V owners to think about - last night I set about removing the pot and then removed the pot PCB.

    Removing the pot - I had already desoldered the signal wiring but not the earth wire - I use the Stereo Coffee volume control/preamp. Please use SWIN's excellent photos on the preceding page/118 to better understand what follows. So, the only other desoldering is (1) the signal earth wire (2) the earth from the jack socket and (3) the hard wire after (R) 1K resistor.

    You would logically believe that all 3 of these soldered connections would be to earth - NONE ARE. Only the incoming power is earthed to chassis - see photo (2). The RCA input PCB has no earth, which means that the RCA chassis sockets are'nt earthed and that the signal wire earth wire is'nt connected to earth at either end. The jack chassis socket has an earth tang which is soldered to the pot PCB but not to earth - all this is very weird and I'm wondering if all these hum problems stem from this lack of earthing.

    I have created a chassis earth form the input PCB to the adjacent chassis, to which I shall run an earth wire from the jack socket and from the hard wire r/hand side after the r/h 1K resistor, effectively creating a star earth.

    SWIN - where are those voltage figures, others have measured the voltage at the output caps @ 70V - there can never be enough factual info. The supplied Chinese o/put caps are 250V? but only 10uF. Maybe the reason those using low Ohm h/phones have no problem is related to the fact that the D/V has AFAIK only one small 'sweet spot' below which no volume or way too loud. If these Chinese caps are foil then at higher values the cost of foil caps escalates hugely - this could explain this volume anomaly.
  3. SWIN
    Sorry about the delay, got the voltages, but got stuck trying to find a CAD program with tube symbols - found a few free CAD programs, but a bit steep learning curve.

    The output capacitors are the only thing that separates the B+ or drive voltage from your headphones, so a very important to select caps that can stand the whole B+, in case of a drive tube failure.

    That said, the orange blobs that are the output caps on this thing, are totally unmarked, and so nobody knows what they are, and what voltage they are rated at.
    One cheap and fast way to increase the value of the caps at the output, is of cause to add a electrolytic cap parallel with them.
    Just check how the acclaimed Bottlehead Crack does it, a very tiny high voltage electrolytic cap at the output.

    There are of cause som not too expensive high voltage foil capacitors suited as output caps in this application, but they are nearly as large as the 336, and would need an outboard case.

    The voltages so far - my unit is a 220 Volt 336, and I got B+ 134 Volt DC, 80 Volt DC across the 1 K 20 Watt "golden" large resistors, and that means 80 Volt DC across the output capacitors.
    One thing that stands out so far, is that the heater voltage is 6,9 Volt AC - a bit too high for prolonged valve life, standard is 6,3 Volt.

    All voltages measured with tubes in, and live working unit that was powered on 1 hour.

    As soon as I am back from work, I will try to find a easy to use CAD program, with tube symbols.
  4. Gallic Dweller
    SWIN - the o/put cap voltages are known, I put the voltage rating in my last post - 10uF/ 250V. You have confirmed what others found that the heater voltage is too high @ 6.9 V.

    Re. the earthing, I asked this question on another forum and the answer was - suck and see, I shall earth all 3 points I pointed out in my last post. If i find increased hum I shall simply disconnnect. Certainly earthing the RCA PCB correctly to the chassis leaves a very,very low hum that does'nt alter with increased volume. If the earthing programme works then the Fitz mod becomes redundant - vamos a ver/let's see.

    I'm going to use 1 x Audyn ERA rough foil 100uF/100V + K73-16 2.2uF/250V as o/put caps. As i may not like the Audyn caps I shall use silver 1mm wire pins so I can change the caps without having to remove the PCB again.
  5. wwmhf
    Thank you very much for sharing these finding with us!
  6. wwmhf
    Your experiments with the earthing and the Fitz mod will be valuable to us whose has a 336 amp.

    The earthing issue of the 336 found by you is really unusual for a HIFI equipment.
    Last edited: Nov 9, 2018
  7. Gallic Dweller
    SWIN/others - can you measure the resistors on the output PCB - the legend reads 10K but mine read violet/black/red = 7K / gold = 5%. These caps and resistors are important to the sound o/put, so, if your changing either or both, matching values is a good idea. if your removing the o/put PCB it's a good idea to use some 1% resistors of your choice.

    It's best to measure resistors but to get an accurate reading in situ that means lifting one leg and with these particular Rs that will be difficult, so, can others at least accurately read the colours of these 4 band resistors. There are lots of resistor colour code charts on the net.
  8. Gallic Dweller
    Re. the resistors - a big boo-boo, especially as I had my eyes checked the next day and got a thumbs up - so I have to blame the lighting, I mistook brown for violet. When I actually measured them they were 9.90 & 10.05 , which is very good for 5% resistors. one of them has a damaged casing so I shall replace them with 1W PRPs.
  9. Gallic Dweller
    It's a real shame that the D/V is like a lot of other amps built into a very small chassis. However there is plenty of room for the makers to have moved the PSU caps back further and to have made a deeper PCB for the output caps. If they had, I could have used K73-16 10uF/100V caps to replace the Chinese ones, that I know would have given me an outstanding sound.

    This could be done by deconstructing the circuit to remove the steel plate on which it sits, cut off the vertical piece and replace with a new extended section enabling much longer caps to be used but this is a lot of hassle.
  10. wwmhf
    I am considering increase the volume inside the amp by putting it one another box, even a wood one.
  11. ThermalAlchemy
    Orange blob caps if somebody had a old-style capacitor checker from the 50s or 60s like to Heathkit or any other you can test those capacitors simply running up the voltage in till shows failure, that would give you the rough voltage capacity. If somebody else had a good ESR meter in capacity tester we would get a ballpark figure on the capacitance value.
    Instead of a cad program how about train a PCB layout programs to manufacture PCBs . I believe you’ll find it much easier learning curve and they already have a lot of electrical symbols people have put in and they have it easy to training with videos how to make up and use the program . And in the end you’ll have a working layout for PCB that you could release on a file on this form for everybody to make as a kit they simply just go to easy EDA’s website to the Gerber file that you produced on the layout and request a circuit board to be sent to them for about 20 bucks . https://easyeda.com/ Not only do they have mini video tutorials but you go onto YouTube and other people show you how to use this program they made it very easy so even a first time user can get it done right and order a PCB from them .
    Last edited: Nov 12, 2018
  12. Gallic Dweller
    You should read previous posts - for the third time the Chinese o/put caps are rated @ 10uf/250v, I measured 4 - 3 x @ 10.2 and 1 x @ 10.3.
  13. Gallic Dweller
    The problem is your still left a restricted space re. the o/put caps. You can easily change the pot and jack socket for better. Here's an idea - you would have to desolder an awful lot but if you do this you could then remove the plate on which the circuit sits. There are 2 screws underneath the output circuit board - by cutting off the vertical piece of the steel circuit plate and making a new L shaped piece of steel or aluminium, you could greatly extend the plate here to allow for much longer o/put caps. The new L shaped extension piece could then be secured with the existing 2 screws and bonding adhesive. Also if you use a wooden box be careful with earthing the whole thing.
  14. xmdkq
    336 Se在336 C现在停止生产后不再生产,目前只生产339台。
  15. Gallic Dweller
    This is an English language forum, I'm not familiar with any Asian scripts, could you please translate.
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