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Old 29th March 2009, 02:39 PM   #211
udovdh is offline udovdh  Netherlands
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Default Re: LPF components

Quote:
Originally posted by Segran
I haven't removed the second OP yet since I'm contemplating the best way to do it. I want the mute relay still to work.
Can't we just make wire/bridge from the caps between opamp #1 and #2 to the output pins of removed opamp #2?
Please elaborate if this is not the right approach.
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Old 29th March 2009, 03:03 PM   #212
anbello is offline anbello  Italy
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Hello,
i bought another similar DAC from ebay seller snow48_6, it's very similar to Franz's one but without the ASRC and with the USB interface unpopulated

Click the image to open in full size.

some things i noted: there are no coulping 'lytics from cs4398 to first opamp and the arrangement of resistors and capacitors for the LPF are different from what i see on post #138 from Kevin.

The frequency response from RMAA:

Click the image to open in full size.

I have to correct the component for the LPF.

Ciao
Andrea
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Old 29th March 2009, 03:08 PM   #213
Segran is offline Segran  Sweden
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Quote:
Can't we just make wire/bridge from the caps between opamp #1 and #2 to the output pins of removed opamp #2?
I would take the signals from between R23/C26 and R38/C29 and connect it to pin 1/7 of the 2nd opamp. You also need to remove R4, C44, R37 and C55.

I haven't got round to do this myself yet so it would be interesting if you could tell us if this mod will make much of a difference.
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Old 29th March 2009, 03:28 PM   #214
Segran is offline Segran  Sweden
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Default The new version

Quote:
The frequency response from RMAA:
Hmm, seems they have made "some" improvements compared to the first version luxury54 tested, but still haven't got it right!

It's a new PCB layout, so the components are moved around.

Hope you can post the mod instructions for the revised version!
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Old 29th March 2009, 03:55 PM   #215
anbello is offline anbello  Italy
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Quote:
Originally posted by hafp
Have a schematic of a similar DAC I got a few months ago on eBay.
It may not be exactly the same as the model you guys recently purchased, but is does use the CS4397/8416 chips and 2 opamps.
Would be interested in any successful mods you come up with on bypassing the second opamp and coupling caps.
PM me with your email if any of you want a PDF of the schematic.
I can't post is as the file is too large.
Cheers.

Hi hapf,
can you send me the pdf
anbello_at_gmail_dot_com
_at_ <-> @
_dot_ <-> .

Thanks
Andrea
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Old 29th March 2009, 04:02 PM   #216
Thomo is offline Thomo  United Kingdom
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Hi guys. Could anyone tell me where to get some of those output transformers Franz Gysi has used on his output stage please? or any similar will be appreciated.

I have a dac kit on the way at the moment and it'd be nice to get everything ready for when it arrives.

Thanks and kind regards,

Lee.
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Old 29th March 2009, 04:24 PM   #217
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Quote:
Hi guys. Could anyone tell me where to get some of those output transformers Franz Gysi has used on his output stage please? or any similar will be appreciated.
This trannies, you will hardly find some. Look for used Studer equipment...

I work with Studer and I found them in the garbage box, really!

But you will find suitable transformers from Lundahl or Sowther or other manufacturer. Look for 1:1 versions.

And be aware: this is not a good solution to drive long cables to the preamp!

Franz

Click the image to open in full size.
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Old 29th March 2009, 04:51 PM   #218
Thomo is offline Thomo  United Kingdom
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Many thanks Franz. Sorry to be a pain, but are there any other specs I should look for? Are these line input tx's?

Sowter have lots and I'm a little lost as to what I need to look for.

Regards, Lee.
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Old 29th March 2009, 04:56 PM   #219
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Lee

I am not an expert in trannies, I just had good luck :-)

The trannie should not have to low impedance. 1k or greater is O.K. for the CS4398.

And it should be 1:1

Everything usable as line driver or input-trannie with above specs is suitable.

Maybe there are also more cheap solutions? I remember, some people bought Behringer DI boxes just to remove the trannies.

Here a foto from my desk (sorry, explicitly content):

Click the image to open in full size.

In the back, the disks where the uncompressed sound is coming from. In front the DAC and blue the FE83E double bass reflex box with fronthorns, driven by a small TA2024 amp.

This setup reveals everything, a perfect nearfield setup. Quasi a extended headphone.

And it sounds absolutely great with this DAC. I will build it in the Studer 52 amp directly as it is now.

Franz

/Edit
The trannie solution allows further buffer, line driver or filter circuits! One of the best DAC's I ever heard, was a Zhaolu D2 CS4398 with coupling trannies to balanced Aikido amps, at the European Triode Festival.

/second edit
Be carefully, when buying DI boxes: today, most of them don't include trannies anymore.
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Old 29th March 2009, 05:00 PM   #220
johnm is offline johnm  United Kingdom
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Would any of the these be of use?

http://www.sowter.co.uk/pro-audio-transformers.php

Cost doesn't look too bad on the 600-ohm side of things...
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