ebay:Weiliang Dual X2 AK4399 DAC with LCD

[Valeri100]

I think that is not hard to find a musician in Vienna...

Yes, it is true. My ex-girlfriend is piano player. I am going to invite her.

My pre-amplifier case has a lot of space. I am going to put inside, transformers, HDAMs and the Bronskie cathode follower and make a switch for A-B-C test.

 

[dookie182]

sunsun22 what tube are you using in your UTO?

 

[tuxx]

so 5 days of burn in is done, HDAM modules compared against OP01 and everything I can say is simple.............I would be repeating myself how amazing those HDAM modules are so I'll be more than happy if someone else could buy it and test it otherwise I will look like an idiot who can hear weird stuff

p.s. I'm screwing in top cover means this does not need any additional touches and I won't do any other upgrade, it's finished and I'd like to thanks to all of you who helped

Hi all!

my dac is the following:

Finished AK4399 AK4113 DAC Decoder 192K Software Control in Case by Weiliang | eBay

I am using it with a gainclone lm3875 without dc protection circuit or input capacitors.

I decided to replace the ADA4627 (which had already replaced the stock opamps) with the hdam opamps bought from youbuy.


The first impression was very good but i realized that a weird hum appeared when I turned the amp volume up (without listening to music). Believing that it was a gainclone issue, I started searching what was wrong with my gainclone's grounding etc.

After many hours I realized that with the new hdam opamps my woofers were moving back and front when I changed the volume. My knowledge is not deep but I was told that this is a sign of dc offset.

I changed the opamps immediatelty, now back to ADA4627 and everything is fine. Zero hum and the woofers don't move when I change the volume.

Maybe I am the only unlucky here, but it was impossible to keep using the hdam opamps.

 

[Valeri100]

Hi Tuxx,
I think that the reason is DC offset. You should disconnect your amplifier, then adjust 0 DC on output of the HDAM modules using potentiometer on the HDAM modules.

I also have power amplifier without capacitors in signal path and everything is fine when I use the HDAM modules.

 

[tuxx]

Thank you very much Valeri100!

My knowledge is very limited. It seems that I will have to do my research on how to do the suggested procedure. I really hope I will be able to use them again because the sound result was better than the ADA4627.

 

[Valeri100]

That is very easy. Connect voltmeter to a output of one channel and start turning potentiometer clockwise or in opposite direction until voltmeter will show 0V. If nothing is changing then connect voltmeter to another channel output. Repeat the same for other channel.

 

[tuxx]

Thanks again Valeri100!

I did what you told me. Now the voltage on each channel output is zero. However i still get some noise and the woofers are still moving (not the same as previously).

It seems that i need a more accurate voltmeter.

 

[kukynas]

tuxx: can you let us know how is grounding of this DAC made? I had similar issue due to missing grounding from the main voltage socket, in my AKM DAC I had to even connect PCB separately as the chassis did not pass the grounding properly to the board, I wouldn't be curios if there isn't any grounding or it's not connected properly to the board which is common issue with these Chinese DACs...

 

[tuxx]

As far as I understand from it's internals, it doesn't seem to be grounded at all:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[kukynas]

can you post bigger pictures of the socket? can't see anything from pictures attached, use forum code or direct link...

 

[tuxx]

Sorry there was a problem with the embedding code:

View image: 2
View image: 20140825 175916

 

[kukynas]

here we go, so first of all make the grounding of the chassis, if it won't help connect pcb with additional wire like here (green cable around the top screw next to red WIMA caps) and post the result...

 

[tuxx]

Thanks Kukynas.

I am sorry for the stupid question (i am a totally diy newbie), but will it also help with the dc offset? My major problem is not the noise, but the result of the woofers moving, which is as far as I am concerned dc from the dac to the amp.

 

[kukynas]

I'm newbie too , don't know if it will help but due to fact that many of these transformers leak between the wirings it should help, if it won't help than as Valeri suggested you need to tweak with potentiometers on those HDAM modules

 

[Valeri100]

It is very strange that with ADA4627 it works fine. The HDAM modules are kind of OA. In any case you can add a capacitor between Dac and amplifier. Capacity depends on imput impedance of the amplifier which is usually high and 1 uF shold be enough

 

[tuxx]

With ADA4627 the noise is zero and there are no problems with dc offset.

After the issue I had I got very afraid and I decided to finally add two capacitors at the input of my gainclone. When I add them I will check again with the HDAM opamps.

 

[Sunsun22]

Altec 15335A is 15k:15k 1:1 transformer which has very high impedance in my opinion. Transformer users at V-out dac outputs generally recommending 600:600 1:1 type line output transformers.

Hi Terranigma, which transformer do you recommend?

 

[Sunsun22]

Hi Sunsun: did you changed only those 2 at top of the HDAM?

I also changed the input jfets to K170 (Idss 3.7 matched pair) and tied them with a nylon strip. As K170 has a reverse pinout than K30A, I soldered them on the other side of the PCB.
The K170/J74 pair have Idss of 6

 

[kukynas]

Hi Sunsun: I bought these but didn't tried them yet, 600ohm wirings 1:1 ratio...

 

[terranigma]

Hi Terranigma, which transformer do you recommend?

There are many options from many different manufacturers like Jensen, Cinemag, Haufe, Lundahl, Sowter etc. I'm not yet to able to install one of them but you can find many reviews from others in forum.

For example: http://www.diyaudio.com/forums/digi...ormer-dcx-2496-output-only-3.html#post2971866