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Old 27th May 2010, 03:11 AM   #2631
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Default New Version

I just got my copy of this DAC in the mail today. Gigawork apparently has a new version of this unit. The power supply caps seem to be larger, the diodes appear to be different, and most importantly the op-amps are now pairs of OPA627's on adapter boards. A lot of the analog stage seems to have been streamlined as well. Here's a couple pictures:


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Sheldon
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Old 27th May 2010, 08:31 AM   #2632
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Originally Posted by Ryssen View Post
Ok,now i connected MJE350 the right way..that you described it.
And it works,gives 3,3v..Thanks for telling me about it!
You're welcome Glad that it worked for you. I just measured voltage between collector and emitter, and it is 3.3v, which means that transistor is working (i think ). As for why it was working the first time - if you'll look at the schematics, it's actually first MOSFET doing all the dirty work, second MOSFET is just to soften what's left from first. So, even without second transistor, board will still give out 3.3v (or whatever is set via trim pot). Again, that's just my thougths, we better ask Salas how exactly it works But that's outside of current topic, of course.
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Old 27th May 2010, 06:24 PM   #2633
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Hi Bill, just bought the 20k resistors and replaced the 13k on the secondary leaving the 620pf cap intact. Powered up and tested... still no change. Next thing i did was to remove the links on the caps then remove the 12 volt supply, did another test... still the same. Last thing I did was to isolate the can and internal shield but got no improvement whatsoever. I'm beginning to think that this is the normal response of the trafo with this dac. One thing I haven't tried is the 2.2nf capacitor across the primaries coupled with 220r resistors in series. I'm listening to the dac right now and there's adequate bass from 20hz onwards. The midrange and treble response are great. Thank you for your patience.. Sonny
Hi Bill, sorry for I misunderstood your instructions. Now I have tried connecting the 20k resistors across the secondaries. Also tried different values. Finally got a flat response from 10hz, dropping only by 1db from 10khz, by placing a 15k resistor on the positive of the secondaries. Is this response ok? Could we further improve on the treble response? Right now im happy of the results... Thank you so much to all who helped specially to you Bill..

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Old 27th May 2010, 07:22 PM   #2634
Ryssen is offline Ryssen  Sweden
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Quote:
the op-amps are now pairs of OPA627's on adapter boards. A lot of the analog stage seems to have been streamlined as well. Here's a couple pictures:
Hmm.the OPA627 is a single opamp,have they made a channge in the schema?

Quote:
As for why it was working the first time - if you'll look at the schematics, it's actually first MOSFET doing all the dirty work, second MOSFET is just to soften what's left from first.
The first transistor is the current source,that sets the current,the second is the shunt element,that shunts to earth,and should set the voltage,why it worked with the transistor backwards i don´t know...
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Old 27th May 2010, 08:04 PM   #2635
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Originally Posted by Ryssen View Post
Hmm.the OPA627 is a single opamp,have they made a channge in the schema?
Nope, you misread my description (Or I didn't make it obvious). There is a PAIR of OPA627's on each adapter board. You only see one, the other is tucked underneath.

Sheldon
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Old 27th May 2010, 08:13 PM   #2636
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I think its just a mistake from Gigawork since they haven't changed their description and pricing.
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Old 27th May 2010, 08:49 PM   #2637
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so at the end what is better OPA627 or transfo?

CS4398 or PCM1793 ?

CS8416 or DIR2009?

to much option to take a décision..
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Last edited by juanitox; 27th May 2010 at 08:53 PM.
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Old 27th May 2010, 11:32 PM   #2638
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Originally Posted by sdcz View Post
Hi Bill, sorry for I misunderstood your instructions. Now I have tried connecting the 20k resistors across the secondaries. Also tried different values. Finally got a flat response from 10hz, dropping only by 1db from 10khz, by placing a 15k resistor on the positive of the secondaries. Is this response ok? Could we further improve on the treble response? Right now im happy of the results... Thank you so much to all who helped specially to you Bill..

Click the image to open in full size.

Click the image to open in full size.
A 1db hiccup could be from anything, I would listen and not worry about it. Enjoy.
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Old 28th May 2010, 12:39 AM   #2639
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Finally got my DAC all wired up on a board with temporary connections. Everything powers up fine and I am getting voltage at the output pins on the 4398 and at the primary connections on the transfo. However, I am not getting anything at the secondaries. I have Edcor XSM 10Ks and am using the filters as shown in the schematic in the post below, except I have 13k resistors and 680uf caps on the secondaries.

http://www.audiocircle.com/index.php...2243#msg752243

Any ideas of what might be wrong?

The coils on the transfo seem to be fine - they all read between .52 and .55 when I test them on the 20k setting on my multimeter.

This is my first DIY project so any help is greatly appreciated.
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Old 28th May 2010, 05:51 AM   #2640
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Originally Posted by sdcz View Post
Finally got a flat response from 10hz, dropping only by 1db from 10khz, by placing a 15k resistor on the positive of the secondaries.
Hi, can you detail this a little bit? the 15k resistor is put in paralel with the signal coming out on the secondaries separatelly on each channel?
also what do you mean by the positive of the secondaries? thanks
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