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Thread: This guide is to help you build the DOUK KSL-M77 Preamp clone kit.

  1. #1
    Join Date: Jun 2016

    Location: Northampton

    Posts: 82
    I'm Karl.

    Default This guide is to help you build the DOUK KSL-M77 Preamp clone kit.

    The responsibility is with you to make sure you understand the safety implication of Valve amplifiers. They can kill you!

    The modification worked on my amp. If it does not work for you then I am not responsible for any damage you may incur.

    If you use this information its at your own risk. Itís a guide. I did a lot of research into building this amp I suggest if you donít like the suggestions then do your own research and your own modification.

    This is a very good sounding Preamp! Itís not by any means the Kondo M77 !! Just Google the real thing and be impressed by just the images! But for around 30k it should sing you to sleep and make your breakfast! Having said that you wont be disappointed with the clone its fun to build and lends itself to modifications and upgrades.

    There are some fundamental items you will need to complete this build.

    A soldering iron with a flat tip and a pointed tip
    Solder
    A test meter
    Screw drivers
    Wire stripper
    Heat shrink insulation
    Tweezers for SMD components.

    Best regards,
    Karl Anderson


    Building the KSL-M77 Clone from DOUK/NOBSOUND

    The build is relatively straight forward, even with very little Ďelectronicí knowledge. Having said that you will need a steady hand for soldering and if the amp does not work when finished you may need a friend who does know their way around a valve or two. The reason being is that at the time of writing this document the schematic that is supplied with the board is not accurate and there are a few values and items missing from it. One thing that you will notice is that there are 9 valves in total on the board but only 7 shown on the schematic. But if you look close you will see one section does show a 1/2 therefore implying the section is copied.

    The amp has a great sound! And for the cost itís hard to better! BUT out of the box build it ďHumísĒ like it donít know the words..!! The good news is that it can be fixed. This is where you need the soldering skills.

    The board can be bought in three states, just the board, built with no capacitors and finished. (There are no valves supplied with any build).

    Picture1.jpg

    I personally went for the finished board, mainly because its tested and one less issue for me to look into if it does not work. I then upgraded the parts I believe needed changing. The choice is yours..!

    You will need a box! And it needs to be big enough to fit the amp board, a good-sized transformer and an extra power rectifying/smoothing board. There are a number of boxes out there just be mind-full that many do not have holes drilled and text on them. Drilling holes not such a big issue but screen-printing text to get the ĎProí look isnít that easy. Again the choice is yours.

    I bought the ĎKondo KSL-M7 box off E bay purely because it has the right holes and the text is correct for the amp functions. The only issue I found is that the M7 board is smaller than the M77 board and fitting the Ďon offí and volume pot requires some thought and slight modifications. Also if you want to fit different caps later on as an upgrade the volume pot will limit the physical size of capacitors.

    The chassis comes with power inlet (cheap donít use) on/off switch (again not very nice) Two solid aluminium control knobs. All screws, An LED and a safety cap are supplied. The chassis was very well packaged and comes flat packed overall excellent quality. Very quick delivery too!

    Picture2.jpgPicture3.jpg

    The transformer, I purchased the DOUK 230V one meant for the board. Reasonable price plus itís got all you need for the amp on it. Again as long as you have the right outputs you can source a transformer of your choice. (Required Outputs are 100W, 250v-0v-250v 12.6v and 6.3v)

    Picture4.jpg
    Last edited by Kanders1; 17-04-2019 at 10:52.

  2. #2
    Join Date: Jun 2016

    Location: Northampton

    Posts: 82
    I'm Karl.

    Default This guide is to help you build the DOUK KSL-M77 Preamp clone kit.- pt2

    The mains filter, I bought a filter/fuse and mains socket combined to replace the cheap supplied one and to keep thing neat. It is very slightly larger so a small modification with a flat file is required.
    BULGIN IEC EMI FUSED INLET FILTER PS20/A0320 250V AC 3A RATING POWER ENTRY

    Picture5.jpgPicture6.jpg

    The additional rectifier/regulator Board. (To replace the original on board heater DC supply, this is the primary cause of the HUM)
    Supplied by - Jim’s audio (E-bay) LT1963A very low noise 1.2V-20V 1.5A - 6A power supply PCB w/soft starting! This comes as just a board; you will have to build it. Its not hard and you only need one side of the board to supply the clean DC for the valve heaters. The board uses SMD components so a pointed soldering iron, some tweezers and a steady hand is needed. (YouTube training if you have never done it plus you can practice on the spare side of the board. As some of the components come in qty of 10 only).

    Picture7.jpgPicture8.jpg

    I used a Texas Instruments TPS7A4501KTTR IC, REG LDO ADJ 1.5A 5DDPAK regulator chip but the LT1963AEQPBF (PBF - lead free) is available at RS Components. The rest of the items I got from E-bay and Mouser (postage is expensive). Jim’s Audio supplies a parts list.
    Note: - The 100uf 50v 1812 SMD cap (C25 C26) is not easy to get. The voltage does not exceed 12v at this point so a 100uf 16v can be used (mouser have AVX 100uf 16v 1812 size) I didn’t use the 2 pin terminal blocks, easier to solder directly onto the board. Also you will need a heat sink for this. I modified a computer processor one to fit but they are easy to find on the web.


    Volume control, I used a China 24 step attenuator to start as I wanted the stepped volume control. As it happens it seems very good for the money! My intention was to upgrade it but can’t really fault it. The only issue is fitting it in! They are big fortunately the China copy does not have its resistors soldered the same way as the real thing so you can bend them out away from the valves located in that area. In hindsight the ‘ALPS RK27112 Audio Potentiometer 100k stereo’ would be best for packaging. (Beware of China copies! Info on the web how to tell the difference)

    Audio connections and wire, I used silver Phono sockets and RS wire to connect the inputs/outputs. I started with screened wire but found it not so easy to work with around the multiple signal in area of the board and also I think it may also have given me some grounding issues. So twisted single core wire for all the in’s and out’s.

    Picture9.jpg

    Building the amp.
    I put mine together as is from DOUK using the finished board. Most of the connections are oblivious. And labelled on the board. The AC connection to the board are 6.3v 250v-0-250v 12.6v I soldered them from below purely for neatness. They are labelled on the DOUK transformer but mine had yellow as 250v - 0v but actually was orange.

    The new mains filter socket has the safety capacitor already fitted, it is slightly larger than the supplied socked hole but a file is all that’s need to make it fit.

    I drilled an earth point for a nice solid ground point to the chassis next to this socket and connected the earth to it and then the earth wire from the transformer. And also an earth for a phono connection, I drilled mine in the middle but its better located near the divide as there is more room for the earth wire to the board and the banana plug socket. (The board earth is located in the centre)

    The Transformer is mounted on 10mm acrylic spacers to lift it from the chassis (this was a recommendation from DOUK when I queried the hum from the finished stock unit, not sure if it really made any difference TBH). The transformer is still connected to the chassis via nuts bolts and spring washers. I had to drill new holes for the Transformer fixings.

    The main board, its important to get this in the right place if you use the same box as I did as its a tight fit. There are pre drilled threaded holes but these are for the M7 board so no use. Also bear in mind where the chassis feet will go. There are pre drilled holes but even they interfere with some other threaded pre drilled holes.( I ended up moving the feet and using 3M double sided tape for a temporary fix whilst building).
    Fit the volume control into the front panel along with the selector switch. The on/off switch was not a nice one supplied so I went for a good old heavy-duty toggle switch; this is a problem though… as the heat sink for the power transistor gets in the way of the switch. I fixed this by removing the end two legs from the heat sink and then slightly bending the next two outwards.
    Last edited by Kanders1; 18-04-2019 at 07:08.

  3. #3
    Join Date: Jun 2016

    Location: Northampton

    Posts: 82
    I'm Karl.

    Default This guide is to help you build the DOUK KSL-M77 Preamp clone kit. - pt3

    Picture10.jpg

    You may also find the hole in the front panel to large for the switch. I turned a small aluminium bush to fix this.

    Fit your switch and locate the board into the best place and mark the holes for the fixings. Remember the valves!! They stick up!! So if you have them or just some that fit put them in to check clearances. Mark the hole positions and drill clearance holes for the supplied brass up-stand fixings.

    Put the center divide into place and position your transformer as close to the chassis side as possible (put the side on to check before you fix) it needs to go near the front so as to allow room for the LT1963A regulator board you will fit later. Remember the selector switch! it has a ribbon cable connected too so make sure you have it in. Position the transformer and mark the fixing hole positions.

    Once you have the locations and all seems to fit okay, you can solder the connections. If you use single core unshielded cable then make sure you twist each pair together. Make sure the phono sockets are tight before you solder. I only connected the Phono stage and CD to start with to test the board.
    The volume control is wired as a stereo duel pot. The pin out connections are not labelled on the board.

    Picture11.pngPicture12.jpg

    The connection nearest the edge of the board is pin 1

    There is a balance control but I did not use this.

    Connect the transformer to the mains filter and earth tag on the chassis, (the filter does not come with a fuse) the chassis supplied one does..! Make sure you twist the transformer leads together for each set of voltages (reasonably tight twist is best) then solder to the main board. As its AC it does not matter which way round the12.6v and 6.3v supply wires go, but make sure the 250v-0v-250v are correct!

    The mains switch, depending on what type you want connect it as required, switch the mains 230v live.
    **MAKE SURE YOU HEAT SRINK WRAP THE CONNECTIONS OF THE SWITCH!!**

    If you don’t things could get a little hot and sparky!! Including you! If you can see any metal or wire on the switch connections you are asking for trouble. Be warned!!

    There is an LED for on off supplied but I used one of the on board ones this is located by the 7805 chip. Either remove and put a 12v LED of your choice or just move it to the front panel. (I would leave this until you have had the board working).

    So now you should have all the parts secured and connected. Check over for anything obvious like ins and outs connected the wrong way round and look for anything that may short out like bits of wire or loose solder that’s dropped into the board or even the chassis. Put the 12ay7 valves in. Leave the rectifier valve out that way you don’t get B+ high voltage through the board yet. Switch the selector to CD. If all is good you should see the pre amp valve heaters glow, then turn the selector switch to phono to get the phono stage valves to light up. Check the voltage ‘CAREFULLY’ at the 12.6v test point. Mine read low set to phono and correct set to CD. Don’t worry too much about this at the moment because there is a good chance the amp will hum anyway and you will be replacing the 12.6v supply with a much cleaner and adjustable one.

    If all the heaters work switch off and put the rectifier 6X4 valve in. Connect a CD player and try the amp. Mine worked fine first time, as it was a complete tested board. If you have built yours and its not working then good luck with fixing it! ;-)

    So if you have a preamp that works and does not HUM Then congratulations!

    But if like a few others and myself you do have a hummer then you can fix it. The Hum in mine was two fold. One was with the Preamp volume down power amp volume up which I think was due to an earth loop. I rewired later without screened cable, which I believe was the cause, but can’t verify. And the other HUM was from the heater supply being on the main board, and to close to the audio signal paths. There is a ton of info about this on the web if you are interested.

    Teaching the amp to sing and not hum !

    The schematic is not so helpful, but its not a million miles away. I printed it out on A3. There is a version that is on a white background most are on a black background that makes it hard to read. I got this from DOUK. I also printed the images of the circuit board, both sides on A3 this is a double sided board so having both sides is important. (Google images)

    You need to construct the LT1963A board including a heat sink! And test its supplying 12.6v (its adjustable with the small variable pot that’s on the board) use the 12.6 AC supply from the transformer and measure the output. It should be set to 12.6V DC. Once you are happy its working mount the board behind the transformer. I used the brass up stands again stacked two high to let air get around but you can mount side on its up to you. You will be connecting the output directly to the main board so some long wires required.

    Because you now have a new 12.6V smooth ripple free DC supply you don’t need the rectifier or smoothing capacitor on the main board. These components need to be removed. So remove the four diodes and the first 4700uf 25V capacitor after them. The cap is stuck to the board with mastic.

    Capture.JPG

    Connect the new supply to the middle 1000uf 25v capacitor that is located just below the two 5 ohm 5W resistors. MAKE SURE YOU GET THE + and - the correct way round !!! solder to the underside. (See images)

    Re assemble the amp and test again without the 6X4 check and adjust the 12.6 voltage when the phono is selected. Replace the 6x4 and play the CD. Hopefully you have a great sound with no hum..!! Well done. If all works well connect the other inputs and tidy up.

    If you have Hum still.. Check your “earth’s” you may have an earth loop somewhere.


    I have changed the supplied caps with better quality parts, but even so the original amp configuration sounded very good indeed. You may need to stack the caps due to the volume control position.

    Capture1.jpg
    Last edited by Kanders1; 18-04-2019 at 08:38.

  4. #4
    Join Date: Jun 2016

    Location: Northampton

    Posts: 82
    I'm Karl.

    Default This guide is to help you build the DOUK KSL-M77 Preamp clone kit.-pt4

    Here are a couple of images of inside the chassis, any question I will try to help as much as i can.


    Picture13.jpg

    Picture14.jpg

    Hope this helps someone.. and saves some time in research Good luck if you have a go at this project.

    Cheers K

  5. #5
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 8,743
    I'm Oliver.

    Default

    Great post.
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK6 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken Valves)
    Digital: Raspberry Pi 3+/Allo Boss 1.2/Isolator 1.3 & 2x LPSU's with Volumio & JRiver
    Amplification: Nelson Pass DCB1 with Khozmo 48 Step Series Attenuator & Krell KSA100 MK2 Amplifier
    Cables: SPOTFIRE Speaker Cable & SPOTFIRE IC Cables & SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A
    Price List For SPOTFIRE Cables here:https://bit.ly/2Uxiv3j

  6. #6
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 39,985
    I'm Geoff.

    Default

    Good stuff!
    "when common sense, logic and plausibility are excluded. All that remain are foolishness and lies"

  7. #7
    Join Date: Nov 2010

    Location: Yorkshire

    Posts: 7,725
    I'm AnDreW.

    Default

    Surely best post of the year! Well done!!
    SS CD Teac VRDS25X(Audiotuned) DAC Caiman SEG+15V PSU DECK 1210 Mat SPH SSS Mods MN Base/Bearing/Platter+Ebony armboard Feet Isonoe/Ebony PSU Paul Hynes SR7EHD-27XL/DCSXL Ag DC lead/3 Stage Regs/Recap PCB+No Pitch/Strobe/Light ARM SME V(Kondo Ag Rewire&Tags) MC Cadenza Black CABLES Arm Yannis SPD-4 IC Yannis 222 Litz+Ag bullets Power WAR PRE ATC SCA2 SPEAKERS ATC 50ASL STANDS Atacama PHONO Sugden Masterclass PA4 SUT Ortofon ST80SE POWER PSAudio P10

    Valve PRECroft Epoch(Mega Modded) AMP Sondex S100 (modded) SPEAKERS Tannoy 15"MG+RFC Warwick cabs+ Reference XO DECK Garrard301 Mat Teunto Bearing 401 Plinth Moldovan Arms 3009/3012(Ikeda Ag wired) PSU Eagle+Tachometer MCAg Meister v2 / Rpyall N SPU's CABLES Arm Yannis 420.5 Litz+ Speaker VdH 6mm Blue IC Oyaide FTVS-510 AgWBT 0110Ag Phonostage Paradise(4 Box) / EAR 834 Clone (modded)


  8. #8
    Join Date: Jun 2016

    Location: Northampton

    Posts: 82
    I'm Karl.

    Default

    Thanks gents...! 😊

    Very kind words..

  9. #9
    Join Date: Jun 2016

    Location: Northampton

    Posts: 82
    I'm Karl.

    Default Update on the Chassis..

    I have just found that you can buy the actual chassis for the M77.. Ive ordered one Its from China of course and Ive not used this web site before.. so my house could now belong to the peoples republic of China... Ill update post if and when I receive it.

    M77 case.JPG

    K

  10. #10
    Join Date: Feb 2010

    Location: Berkshire, UK

    Posts: 3,791
    I'm Tom.

    Default

    Anyone else feel a bit uneasy about branded knock-offs like this?
    Main: Speakers 'RFC' Tannoy Canterburys / custom crossovers with Tannoy ST50 supertweeters; Amp - Silvercore 833C monoblocks; Pre EAR 912; Vinyl: Thorens TD124 MkII + Ikeda IT345-CR1 9 inch and Ikeda IT-407 12 inch tonearms; Cartridges Stereo - Miyajima Madake, Miyajima Takumi, Ikeda 9TT, vintage Ortofon SPU GE; Mono - Miyajimas - Zero 0.7, Premium 1.0, Miyajima/Edison '78' 4.0 conical, and Shure M44 strapped for mono with several Expert Stylus conicals for different eras of 78s; Phono stage and SUT from EAR 912 + Miyajima ETR-Mono SUT; Esoteric Sound Re-Equalizer for equalisation of early mono and 78, switchable in from tape loop; Digital: Audio Note CDT2/II transport, heavily modded AN Kit DAC + Mutec MC3+USB.

    Study: Speakers - Tannoy DC6; Amp: Sony TA-F3000ES; Digital: CDP Sony CDP-X3000ES & Arcam rBlink; Vinyl: Technics SL10 with Pickering TL-3.

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