Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
tassosk wrote:I also have 4K between 5 and 7 as Lundhall suggest. Will this give the input impedance that the DAC needs? The imput impedance of the amplifier is 10K. Having that R there at the output is fine, but that really sets the load, not the input impedance (at least not at all frequencies). At low frequencies the input impedance of the transformer is extremely low (<50 ohms) so you will need series resistor(s) on the DAC output(transformer input). One easy way to do this (beside using one resistor on each DAC output) would be to use something like a single 1-1.5K resistor between 2 and 4. You may be able to decrease it slightly. Edited by user Thursday, May 21, 2009 12:33:41 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
When you are using a BAL/SE stage like this the caps will only degrade performance, so remove them. But you will need to use a piece of wire or a cut lead to short the two empty capacitor pads for all four output caps you removed. Alternately that might be a good spot to put some vertically mounted resistors in series with the output.
Cheers!
Russ
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 1/12/2009(UTC)
Posts: 20
Location: Greece
Thanks: 1 times
|
It sounds for more than 3 minutes with no aparent distortion. I'will try both configurations (series and between 2 and 4) and I will report the results.
Thank very much for your swift help and support (Can I say "crossfire support"? :))
My best regards,
Tassos
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Hi Tassos,
So are you happy with it? :)
Cheers!
Russ
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 1/12/2009(UTC)
Posts: 20
Location: Greece
Thanks: 1 times
|
More than happy. Excited! Since I have tried in the past various configurations between premium caps and output stages I can say that the OPUS with the transformers is by far the more detailed and dynamic source that I have ever tried in my set up (Magnum Dynalab MD208, Monitor Audio RS-6, MF X-CAN V8, Senh 595, PC-Foobar-FLAC-USB, CA DAC Magic, OPUS DAC with USB, S/PDIF Receiver and OTTO, WD media player with optical connection, Pioneer 575A, Marantz CD67SE). The bass is deep and very well defined; the highs are crystal clear with no sibilance and at the same time is tolerant to bad/old recordings. It is dead quiet too. I’ll wait for the transformers to break-in (~ 100 hours) and then I will experiment with the configurations that you proposed (in series resistors and also 1-1.5K resistor between 2 and 4 preferably using a quality pot for fine tuning) before I make the final decision. I’m seeking just a bit of more color and warmth although things are getting better with time. I hope to be able to measure it also with the equipment of the local Lundhal distributor in order to confirm what my ears are hearing and I’ll report the final configuration to the other members. I’m almost certain that I will rest in peace for a long time before I try something new. I did not hear yet the Buffalo, but I’m sure that OPUS with transformers deserves a place in the Pantheon of DACs.
Thank you very much for your personal time to make these kits available to us and your support to make them work.
You guys are the Saints of the DIY community!
Best Regards,
Tassos
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 1/12/2009(UTC)
Posts: 20
Location: Greece
Thanks: 1 times
|
Hi Russ/Brian,
I would like to try the transformer passive output with dual mono OPUS.
I will use 47R resistor to each output pin in order to sum the voltage output as you suggest in an other post but in this case what values should have the series load resistors before the transformer input (680R in stereo)?
Thanks in advance,
Tassos
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Hi Tassos, The summing resistor value can be a lot lower since the impedance is so low. I would try something like 4.7 to 10R. The WM8741 datasheet specifies an impedance of 2K, but I have had good success down to 1K. So just choose a resistor that gets you close to that value. Cheers! Russ Edited by user Tuesday, August 25, 2009 4:59:54 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Forum Jump
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.
