Author Topic: discrete dac mock up  (Read 24083 times)

0 Members and 1 Guest are viewing this topic.

Offline CKL

  • God Member
  • *****
  • Posts: 237
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #30 on: January 27, 2012, 12:14:43 AM »
Not much difference with a center tapped transformer.  ???

I will replace the diodes next week.

Offline yeo

  • YaBB Administrator
  • God Member
  • *****
  • Posts: 2043
  • diy rules!
    • View Profile
    • diyparadise
Re: discrete dac mock up
« Reply #31 on: January 27, 2012, 04:07:37 AM »
hi 86ivar

there is no opamp. just a buffer stage. so there's no gain stage at all.

hi ck

hmm... i'm puzzled. is your 20vdc regulated?

i have tried ei as well as toroidal transformer, no hum in either case.

yeo

Offline yeo

  • YaBB Administrator
  • God Member
  • *****
  • Posts: 2043
  • diy rules!
    • View Profile
    • diyparadise
Re: discrete dac mock up
« Reply #32 on: January 27, 2012, 04:08:50 AM »
hi ck

i don't think you need to replace the diodes. those are schottkies.

what do you use to supply the 20vdc?

yeo

Offline CKL

  • God Member
  • *****
  • Posts: 237
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #33 on: January 27, 2012, 04:17:19 AM »
Hi Yeo,

I do have those schottkies. I had replaced one as one was burnt. I am afraid other three are also damaged. How about the electrolytic caps? The regulated circuit should be simple enough to check.

I used a large bench power supply with adjustable 0-30V and adjustable current limit to power the 20V.

Offline yeo

  • YaBB Administrator
  • God Member
  • *****
  • Posts: 2043
  • diy rules!
    • View Profile
    • diyparadise
Re: discrete dac mock up
« Reply #34 on: January 27, 2012, 05:54:11 AM »
hi ck

i see. feel free to replace the schottkies.

the electrolytics should be okay.

yeo

Offline kp93300

  • God Member
  • *****
  • Posts: 214
  • Got to DIY!
    • View Profile
Re: discrete dac --prelim impressions
« Reply #35 on: January 27, 2012, 07:28:21 AM »
Hi

I follow the cue from CKL and feed the dac with another dc source at 24.8V.
This is a linear power supply with RCLCLC type of filtering. The total capacitance here is about  10 thousand UF . The transformer is about 250 W.
The hum is reduced but still audible with my ear about 3 inches from the driver. My loudspeaker is 93 db sensitivity. .Previously the hum is audible in my listening position that is about 6 to 8 feet  away.
The supporting equipments are qls 550 ,  10 W Class A JLH 69 amp and V2 from GR  Research .
Initial sound impressions:

The dac is smooth and very analogue type of sound . There is no glare and no lack of details.
I will post more in the days to come and compare it with Monica and TP  B2.
thanks


kp93300

PS The picture file is too big !


 

Offline kp93300

  • God Member
  • *****
  • Posts: 214
  • Got to DIY!
    • View Profile
Re: discrete dac - update
« Reply #36 on: January 29, 2012, 08:14:23 AM »
Hi

I notice that the output from the discrete dac is low and my single jfet 310 pre with a gain of 2x is not adequate.
The monica do not require any pre at all and sound more dynamic and  effortless !
The initial impressions of the dac is good but is below my expectations. The sound lack drive and energy. Details are there but i have to make an effort to listen. The sound is rather flat . I  switch  back to  monica fed by a USB to spdif converter.

After some thought, I dust off an unused  simple pre make from AD 815 op amp. I adjust the gain to 4  and   I have been listening for the past few hours . I  have to make an effort to stop and have dinner..

I  sample through my favourite tracks  and have thoroughly  enjoyed each one of them . Each track seems to show a new perspective.
I  became  involved with the musicians , sing along , tap my foot and nod my head.

I hope to try different types of power supply to solve the residual hum in the  next few days.

I think yeo have a winner here !

congrats to Yeo  and happy new Chinese new year to all  the chinese forumers!

kp93300






Offline yeo

  • YaBB Administrator
  • God Member
  • *****
  • Posts: 2043
  • diy rules!
    • View Profile
    • diyparadise
Re: discrete dac mock up
« Reply #37 on: January 29, 2012, 01:50:15 PM »
hi kp

thanks for taking the effort.

yes, the output is low because there is no gain stage. i intend to experiment further with regards to this.

for the power supply, currently there is just a clc filter. the pcb is large enough to house 4 large caps. feel free to break the link underneath to modify the supply to crclcrc or whatever as you see fit. a resistor of 47 or 100 ohm should work. as the current draw is low, this won't drop the voltage much.

it's strange as even with my 97+db speakers, it's quiet enough but it's good that i sent out units for you guys to try.

yeo

Offline kkerwin

  • God Member
  • *****
  • Posts: 168
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #38 on: January 29, 2012, 03:42:14 PM »
hi all,
i am noticing a bit less gain, but it is not bothersome. i am enjoying listening at about half volume, where before with monica mojo and 3k i/v resistors i was listening at about 1/4 volume. still breaking in.
k

Offline kkerwin

  • God Member
  • *****
  • Posts: 168
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #39 on: January 29, 2012, 03:44:15 PM »
btw,
my speakers re ~97db also.
k

Offline CKL

  • God Member
  • *****
  • Posts: 237
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #40 on: January 30, 2012, 12:28:20 AM »
Hi Yeo,

Could you advise a preamp stage for us? Should we use FET instead of opamp?

Thx

Offline yeo

  • YaBB Administrator
  • God Member
  • *****
  • Posts: 2043
  • diy rules!
    • View Profile
    • diyparadise
Re: discrete dac mock up
« Reply #41 on: January 30, 2012, 02:14:18 AM »
hi ck

a wise diyer once told me this, the hardest thing to build is a preamp.

likewise with gain stage, it could be a case of "pick your poison" or "pick your colouration".

i don't have a preference here, as long as it sounds "good" and this is so difficult!

if possible, i'll go without a gain stage.

in kevin's system, no gain stage is just nice and he gets the purest sound. of course his preamp/amp has enough gain to drive his speakers.

in kp's system, he needs a gain stage of 4x to bring out the music.

in my system, i don't need a gain stage as beyonce is more than capable of this gain.

i'll be experimenting with a few gain modules to see which i like. will share with you on this.

yeo

Offline CKL

  • God Member
  • *****
  • Posts: 237
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #42 on: January 30, 2012, 04:26:24 AM »
Hi Yeo,

My setup is like these: discrete DAC -> PassDIY B1 buffer -> Charlize2 -> DCA4.

The sound of the discrete DAC is not as good as the Monica3+LL1660. So I think I need a gain stage.


Offline kp93300

  • God Member
  • *****
  • Posts: 214
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #43 on: January 30, 2012, 05:11:50 AM »
Hi Yeo,

My setup is like these: discrete DAC -> PassDIY B1 buffer -> Charlize2 -> DCA4.

The sound of the discrete DAC is not as good as the Monica3+LL1660. So I think I need a gain stage.



Hi CKL,
I thought the 2 sets of 2sk170 are the B1 buffer on board. There is not much to gain by adding another B1 buffer.

I am going to increase the gain of my pre  to 5 to test soon. EVen with the gain of 4, it is slightly softer when compared to Monica 3 with 5.6 K IV resistor.
cheers
kp93300

Offline CKL

  • God Member
  • *****
  • Posts: 237
  • Got to DIY!
    • View Profile
Re: discrete dac mock up
« Reply #44 on: January 30, 2012, 05:45:37 AM »
Hi KP,

Yes, B1 buffer has no gain. Yeo is right. A bad preamp would destroy the discrete DAC but I think we still need a preamp. Could we use a passive output transformer such as LL1660 to have a gain of 5?

How about the other discrete DACs such as MSB, dCS or TotalDAC?