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Old 22nd March 2011, 01:41 PM   #3741
piero7 is offline piero7  Italy
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Quote:
Originally Posted by kec View Post
Maybe prairiemystic can add the mods to his excellent schematic?
would be great
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Old 22nd March 2011, 02:23 PM   #3742
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Okay, I'll put the mods that worked for me on the schematic, just have to find a way to draw that as it's a pretty cluttered drawing. I want to fix up the O/P filter first and will simulate it. I drew the "stock" schematic, so all jumpers are what I found.
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Old 22nd March 2011, 02:57 PM   #3743
Jim W is offline Jim W  United States
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Quote:
Originally Posted by prairiemystic View Post
Has anyone questioned this DAC's output (reconstruction) filter?
It's quite different from Cirrus CS4398 datasheets and the values look weird for a 2-pole differential filter One leg is 45kHz and the other looks like 7.34kHz, which means a 1nF cap should be an 82pF cap...?
Yes, I'm pretty sure it's been questioned a few times. Don't know how it answered. Seriously, though, I think that has been addressed in this thread and possibly others and you are correct, the frequency response is less than optimal. Somebody posted a schematic which I might have saved had I not already decided to move to transformers. It might actually be faster just to redesign the think than to dig through bazillions of posts.
Jim

Last edited by Jim W; 22nd March 2011 at 03:00 PM.
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Old 22nd March 2011, 08:46 PM   #3744
piero7 is offline piero7  Italy
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Quote:
Originally Posted by prairiemystic View Post
Okay, I'll put the mods that worked for me on the schematic, just have to find a way to draw that as it's a pretty cluttered drawing. I want to fix up the O/P filter first and will simulate it. I drew the "stock" schematic, so all jumpers are what I found.
Thank you
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Old 22nd March 2011, 10:59 PM   #3745
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Quote:
Originally Posted by jerkbag View Post
Woot! Ran two wires from neg secondary of each OT to the ground hole from the original RCA output jacks and hum is instantly gone! Dead silent. Thanks everyone, and I hope this ends up being useful to someone else.

Oh one small thing: when I power down (it's in a switched preamp power input in a tube system) with the volume up I get some serious spacey / theramin sounds as the amp dies. Doesn't affect listening just wondering why that would be?

Thanks again!
Could you please explain in detail how you did it? Which one is "neg secondary"? One of the pins connected to output or?
I'm using this transformer:
http://www.google.hr/url?sa=t&source...TyDUZw&cad=rja
thx
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Old 25th March 2011, 11:09 AM   #3746
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Maybe I should clarify, this is schematic of the Monacor LTR-110 audio line transformer...output lines are conected to pins 8 and 6...I hear buzz when DAC is connected and turned on, it is posible to hear it when no musical signal is being played, with volume turned up halfway on (2x50W) amplifier. If music is playing, buzz cannot be detected since it's allways significantly quieter than the music signal.
Attached Images
File Type: jpg trafo.jpg (33.4 KB, 470 views)
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Old 25th March 2011, 11:26 AM   #3747
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This is what promo material has to say:
"Audio transformer 1:1/2:1 for line signals
Unshielded version with print connections
• Wideband version
• Change from unbalanced to balanced and vice versa
Galvanic isolation to avoid/eliminate hum loops
• Various level adjustment possibilities when windings are arranged accordingly
When installing unshielded transformers into units with interference fields (e.g. power transformers), attention
has to be paid to respective shielding measures
.
Technical data:
Frequency range : 15-30,000Hz
Transformation ratio : 1:1/2:1
Input impedance : 600 Ohm
Output impedance : 600 Ohm/300 Ohm
Optimum source imped. : 50-600 Ohm
Optimum load imped. : ≥ 5k Ohm
Max. input voltage (1%
THD/40Hz)
: 5V
Dimensions : 25x19x19.5mm
Weight : 28g"

Trafos are connected as per Legarem/Gerarda advice...

input side...please ignore the output side, it's wrong...
http://www.diyaudio.com/forums/attac...c-dsc00926.jpg

output side...
http://www.diyaudio.com/forums/attac...dac-filter.jpg
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Old 25th March 2011, 11:54 AM   #3748
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Have you tried moving them? There's nothing wrong with your wiring. You can also move your power trafo.
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Old 25th March 2011, 12:16 PM   #3749
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Quote:
Originally Posted by Bill Fuss View Post
Have you tried moving them? There's nothing wrong with your wiring. You can also move your power trafo.
I'll try,...thought of that, but unfortunatelly, I allready glued them to the board, so I'll have to be extra carefull, they are tiny...
They are allready as far from power trafo as board would allow (cca 15cm)...
BTW, how should one go about shielding them?
What I did not understand in few previous posts about grounding the output (audio) trafos is which leg I should ground? Edit: in post #3715...

And one more question: power trafo was taken from old CD player - I remember that at some point there was connection to the metal chassis, but I think it was from the internal PCB, not the trafo. Anyway, trafo has original two prong connector without grounding...and I don't know if maybe I should ground trafo chassis or something...I know, this is really not my forte, I should do some serious Electronics basics learning...

Last edited by gamgee123; 25th March 2011 at 12:19 PM.
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Old 25th March 2011, 01:58 PM   #3750
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If you're going to ground an output leg, ground the one that's connected to the RCA shell, naturally.

The chassis should ideally be connected directly to the house ground for safety, and a bit of shielding. You could use a steel partition to help shield the OP trafos from the power trafo if that is where the problem is.
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