DOUK EAR834 by Marek GRANDE FINALE

[Marek]

LIST OF MODIFICATIONS

1. Set based on DOUK elements from ebay as full package - from China via Luxembourg - in two weeks delivered
2. Transformer from local TOROIDY - https://sklep.toroidy.pl/pl/p/TSTA-0060002-Transformator-sieciowy-do-urzadzen-lampowych/639  AUDIO#7 version 230 V - 6,3V-250V
3. Housing/Case/Box - however you call - https://www.modushop.pl/obudowa-galaxy-2u-1gx388-panel-3mm-srebrny.html - customised by Modushop - perfect cooperation holes paintings etc all possible with some parts like RCA, fused power connector, etc, etc, and so on
4. PSU Resisitor replaced by Hammond choke accordingly
5. RIAA caps will be replaced by 1% CD silver mika caps - ordered in transit - DONE

6. PSU transformer will be screened/separated from preamp by 0,8 mm copper plates - already in hands - maybe better all PSU part - will consider this option
7. Signal caps upgrade - moved for future to have comparison between standard parts and SUPER parts
8. TUBES applied V1 - MESA SPAX7, V2,3 - JJ 12AX7 E83CC - all ECC83 - all brand new
9. Cables between RCA and preamp - had some leftovers from pure silver 999 single wire ,5 mm dia in 2/3 or 2/4 teflon tubing
10. Soldering - old fashioned 60/40 tin - tried once with other project to use Pb free with Ag/Au - never again
11. Power cable - just 3x0,8mm2 copper standard cable from street shops (IEC plug on housing)
12. 0,8 mm copper plate screen between amp and PSU


A voila. Feel free to comment criticise suggest. I am patient and flexible person (with some borders).

Ciao MArek. And will continue in Lenco folder doing my L75 reconstruction - you are invited here https://www.lencoheaven.net/forum/index.php?topic=36239.0 - as you see I have bodyguard or Lencoguard.

[Marek]

Brilliant Marek. Well done!

Thx. Tomorrow will use it more intensively.

[Marek]

Additional modification. Copper screen between low signal and PSU part made by 0,8 mm copper plate. Maybe not in full execution but better than nothing. Just had two plates soldered them together to one part folded 1 cm 90 deg to connect to chassis and DONE.

[Marek]

Nearly done. Two components still missing - global supply chain problems - but majority already soldered.

Douk PSU replaced by Jessica's PSU. Fits perfectly in my enclosure. Small tunning with preamp position and cabling and should be perfect.

If all will go as expected Douk PSU will be for sale with choke. All was in working condition last off.

and this one intended for sale soon

[Marek]

ANd now upgrade/changes again but I am looking for your input here. Focus on red marked specially

Is it still valid according to the latest developments ? PLEASE CONFIRM if possible DO NOT WANT TO DO IT TWICE.

Copied from main thread. - Red ones are subject to discussion.

1. Bridged the 0.1uf cap location with wire. To reduce likelihood of oscillation use a 100ohm 1/4W carbon composition resistor in this position. - OK this is simple and low investment - are carbon as must or can be metallized like Vishay/Dale RN55D (CMF55D) - just have them _ I red a comment from Troels Gravesen Denmark - speaker designer - that resistors do not play so better to focus on caps. This is also my feeling.

Summary of changes:
2. The 680k and 110k resistors are in a series in the 750k resistor position.  - so the value here should be 790 k instead of 750 k - 5% difference so in the range of cheap resistors tolerance already - OK going to 1% makes sense maybe
3. The 270 and 33pf silver micas are wedged in the 330pf position in parallel. - so the value here should be 303 instead of 330 - to be honest I invested already in Cornell Dubille 330 so does it make sense to go down 27pF ??? to 303 - new investment
4. The 110pf silver mica has been replaced with a 100pf silver mica. - so the same 100p instead of 110 - this is easy as I have 100+10 so desoldering 10 pF is a closing issue - worth doing it  ??? Probably it will work all together only in the RIAA line so complete 2+3+4 makes sense only. Right ?
5. The 2M and 3M3 resistors are removed entirely. They do not require bridging. - OK - no investment
6. The 0.1uf capacitor is replaced by a 100 ohm 1/4W carbon comp. resistor. - what about metalized resistors like Vishay/Dale RN55D (CMF55D) - just have them above the same - LOW INVESTMENT EASY - comment as above

7. Douk delivered electrolytes 6 x 22uF. I see on the list 47uF or even more are recommended so better to go higher eg 47 uF plus bypass caps at 0,47 uF ?


The second 2M resistor that was located above the 2.2K resistor has been replaced with a 680k resistor. - all logically explained below so easy. Will stay with 680 as I have modern tubes

Note on the 2M replacement resistor: This area may effect bass response under 100hz with certain tubes. We are working on a solution to this, looking at more tube data and may have a recommendation of either an optimized value for the tube you are using, or a variable resistor which you can adjust if you do a lot of tube rolling.

Signal caps I red a lot about it - important change from DOUK - list your recommendations please position 1 and 3 only

The general consensus is:
680k for NOS tube examples
2M for new production chinese examples  - I have Slovak E83CC JJ and MESA SPAX-7A
3M3 for 6N2P-EV

Last view with Jessica's PSU. AC Cables twisted now

[Marek]

cleaned

[Marek]

Having no feedback decided to go forward  

So all 6x22 uF from Douk replaced by 47uF bypassed with 0,47 film
RIAA line - changes in progress only 303 still on the road
100uF with 1uF bypass cap - replaced by ELNA SILMIC /installed

heaters bypassed by 100nF accordingly

0,15 + 1uF upgraded to Mundorf Oil/Alu

Busy time

 

[Marek]

LT 1764 finally arrived  (6 weeks delay) so time to do something. Tomorrow first startup. Stressed a little.

[sigma6]

Hi Marek.
Do you hear any noticeable changes in the sound with your upgrades?

[Marek]

Hi Marek.
Do you hear any noticeable changes in the sound with your upgrades?

Currently I hear nothing as some issues arrived at start up at 280 V section. 6,3 V is stable @6,27. I do not expect massive change rather long term stability of working parameters for tubes. And my experience with original DOUK version is also poor as my Lenco is still on construction stage. You have to ask friends with better experience.

[Marek]

LT 1764 finally arrived  (6 weeks delay) so time to do something. Tomorrow first startup. Stressed a little.

So startup done with 50/50 success help needed

6,3 part is working I got 6,27V stable voltage on outlet

280 V failed
- first problem is I cannot set more than 3V TP1/2 voltage (by last 1,4 to 2,5 via full range of potentiometer)
- on outlet by last measurement I have 240 V (should be 280 V) On the beginning I had 272 V but dropped down to 240 by latest measurement.

- Overnight I decided to de-solder LT3092 and put new one as I had spare. I made contacts on PCB a bit bigger by scrapping some paint. Solder back carefully new one and small success I can regulate TP1/2 voltage up to 12V so massive improvement but this is a limit so maybe still something is wrong. Game not finished yet. 280 DC is now back to 275V - 5 still missing.


Thanks to Jessica support PSU is working now as expected - short experience so far -  with possible regulation as in manual. Jessica Thanks a lot. SO tomorrow will start to connect preamp to PSU
 Marek

[Albertfifties]

275 is OK. Do not bother about it.
[In my case the transistor broke down; I now have a Mosfet there with a special grid drive. Is now great & . . . 275V]

[Marek]

275 is OK. Do not bother about it.
[In my case the transistor broke down; I now have a Mosfet there with a special grid drive. Is now great & . . . 275V]

Thx. The biggest problem was missing regulation on potentiometer. But Jessica proposed to remove R8  resistor from circuit replacing with wire giving extra 40 V somewhere and now all is perfect. (But still 275V) on out DC what is fine as I learned.

[Marek]

So my friends. Yesterday I finally decided to connect EAR DOUK preamp to my ProJect with 2M Blue (as Lenco still under neverending story).

Wow. full success. No hum no brum no fire no explosion. It works as expected. Initially I was a bit stressed as sound was over amplified not really clear but fast action showed that cartridge was set 2,6 g instead of 1,8g (effect of moving up and down- house refurbishment). Now I am quite happy - have to listen more vinyls. So first step is closed - next is to close  Lenco with my SME III (waiting for arm rewiring - hopefully nothing more will appear) This will work with ATVM95SH - shibata high compliance ca 20 so should work well with low mass arm like SME III+2,2 g plate. As interconnects I used Project cable phono-preamp (just have it from set) and XLO-HT to AMP.. NO big issues so for now this will stay as it is - I am not a big fun of investing to cabling (did some job in the past and impact is/was very subtle) - room acoustic is changing much more than cables. So I moved all stuff from big open living room to 20 m2 upstairs room. Much better lower frequencies and in general better.

Pro-Ject 2Xpression with modified plinth - simply 36 mm mdf plate added to original one with some 4 mm bitumen between. Just to make it heavier more stable as original one is quite light. Does it work ? Difficult to say in terms of sound for sure is heavier - more stable.

[RobTX]

Looks great! Extremely well done.