Your speakers are fabulous ! Looks like you spent some time on these speakers. Front baffle is superb, real classic. I suspected you were building something else, not just pre-amp. Same with me - I have to build something all the time, there is never enough. I actually first built my speakers and then went to power amp / pre-amp combo. I absolutely accidentally came accross Denon power amp that I repaired and later modified. And only then came up with the idea of building KSL-M 77.
I hope to see more posts soon.
Last edited by Ned; 25-11-2019 at 20:51.
Reason: Adding pictures
Hi Ned,
Impressive build there Ned..! looks very well finished. Well done.
Thank you, they took a lot of hours work.. but the resulting sound is spectacular! unbiased as i am My main project is a turntable design Ive been working on, there are some prototype images on my profile.. Ive just moved house so my workshop is not up and running so a hold on all project work atm. looking forward to getting the finished model finalized with some modification like an interchangeable arm board and some isolation feet which im half way through making but on hold due to lack of machines etc... I hope to start making them to sell at some point.
First, thank you for taking the time to document and post all your hard work with this M77 Pre-amp clone. An impressive outcome.
I'm interested in similar and would also go down the seperate DC heater supply route. I see you plummed for the Jim's Audio low-noise regulated DC supply so I have a couple of queries if you could help me:
- were you able to measure the noise on the DC supply output? I can see no claim or spec. relating to what you might expect and I've found another supply using the same chip claiming <40uV RMS output noise.
- looking at heater spec. for 12AY7 @12.6v (AC or DC) heater draw is 0.15 amps. So, 8 valves = 1.2A. Did you measure/verify this at all? The unit I'm condering is rated up to 1.5A so has 25% headroom which is a good safety factor.
- the Jim's Audio unit has a time delay ramp up. Do you consider this to be a valuable enhancement or not particulalry of use since the B+ is not going to be delayed?
I appreciated I'm firing questions at you but it would be a plasure to share my results back to this thread when I go ahead.
Hi Ron,
Thanks for the kind words, the amp is well worth the time, it does have its issues but once sorted its a great sound.
So first of all let me say I'm no expert.. fortunately i work with one my "Valve guru" so when i get stuck he's the spurt !
You questions.. were you able to measure the noise on the DC supply output? - I did not as my man said that this board and the chip were well designed and would be perfect for the job.
heater draw is 0.15 amps. So, 8 valves = 1.2A. Did you measure/verify this at all? - Yes this is okay. and you are correct. The board is actually two independent supplies that you can use if you need more i only built one side and have had no issues. Also with that board you can tune the voltage nicely.
the Jim's Audio unit has a time delay ramp up - I only use the amp for the Phono input so its permanently switched to that, therefore as you say the B+ governs the supply so it has no real affect. (Ive not noticed any issues because of it).
Im in the process of making a little mod to the RIAA, it only uses a 47k resistor and relies on the circuit capacitance. For my current setup this is okay. I am running an SME IVarm with a Shure V15Vx cartridge and the VN5xMR stylus. These are very hard to come by now and very expensive. I bought the JICO versions but they are very "bright and quite harsh at the top end" there are a number of threads on this, so for future proofing I am making this little mod. once I've got it right ill post the mod. Its just a switchable set of combinations of resistors and caps.
Happy New Year to you all and I wish you some more new and exciting projects come your way !!!
Just a matter of interest - what's the progress of your turntable and the workshop ? As for myself, I was busy at work recently, but now starting to work on a custom audio rack - commercially available ones are too small for my gear...
Hi Ned, happy new year to you to..!
So, currently I’m working on my listing room. It’s gutted at the moment and I’m loving the echo !! Haha !! It won’t be there for long..!
I’m postponing my workshop build until the weather breaks and longer days. So that means the Turntables are also on hold..
Just added an SME IV to my working prototype and also managed to get the Mrs to let me have one in the lounge.. think she was drunk when she gave the go ahead and I had it in there before she sobered up 😈. So at least I have something to listen to until the room is complete.
I’m going to be building a rack as well for the new room so would be interested in what you are doing.
My deck will be mounted directly to an outside wall so as solid as I can get it.
I’m also into building a quadratic defuser which will be in the room. That’s a mammoth job as it measures 1200 x 2500 and weighs a ton !!
Attached pic is of one tile there will be 10 !! 🤪 9114ABA3-4354-4CE4-8C65-9721DA4FA8E3.jpg
It looks you're going full audiophile scale !!! Listening room, suspended shelf for turntable, difusers... Congrats ! When I own our own place I'll do the same. Just don't underestimate your Mrs ! She's a clever woman if she gave the go ahead. Lucky enough my Mrs likes what I do even though it takes me away for hours. It's a 'transition' period in our life, so I don't own a workshop any more and have to use an old wrecked garage at the house we're renting, but it can't stop me !
By the way, are you filling the inside of difusers with something ? I mean vibration absorbing. A while ago I was looking at different options. There's even decorative wall tiles made of straw... My rack is going to be simple, but solid and something cheap, nothing fancy. The only nice touch will be granite slab that friend made me. Just working on design now. It will take a while, but I'll update as soon as there's some progress.
Hello Karl,
Thanks for all the info relating to your M77 build it's given me the bug to try one myself! I've been in the process of building my own over the past couple of months and I've hit a stumbling block regarding the transformer wiring and was hoping you may be able to help! Like you I bought the Douk board and the Douk transformer. My problem is I cannot for the life of me work out what wires go where from the transformer to the IEC/PCB. I admit I'm a novice to this (although I did manage to build the EAR 834P from Lenco Heaven!!) I've been searching online the last couple of weeks trying to understand transformer windings but from what I can see the secondary windings won't produce the 240/0/240 required for the PCB. I have attached here a blank diagram showing the IEC/Transformer/PCB, would you have time to draw the wiring connections (Similar to your experience buying the DOUK transformer it doesn't help that the wire colour positioning doesn't quite match the diagram on the case!)? I'd really appreciate it if you could. I've not added the Jims Audio LT1963A as yet as I wanted to see how it sounded without initially. Anyway, thanks again and hope you can help!
It is difficult to read the lettering, but it looks like the green and yellow pairs together will provide the 240/0/240v you need. You will have to be careful with the phasing however.
Thanks ever so much for getting back to me especially as I noticed this thread is quite old now (a bit like myself!). And thanks too for your advice... could I ask another favour? As I said earlier I'm a beginner when it comes to electronics, if I have pic to follow I'm fine but when I try to understand the theory I fail. I have tried to get my head round reading about transformer windings/in series vs parallel/primary and secondary (and now phasing) etc but I still come away unconvinced I know what I'm doing. Would it be possible for you to have a look at the updated attached pic and judge if what I intend to do is correct? Sorry to ask and obviously I take full responsibility for any wiring I do!!
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My main project is a turntable design Ive been working on, there are some prototype images on my profile.. Ive just moved house so my workshop is not up and running so a hold on all project work atm. looking forward to getting the finished model finalized with some modification like an interchangeable arm board and some isolation feet which im half way through making but on hold due to lack of machines etc... I hope to start making them to sell at some point.
