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mpopovics 23rd January 2003 12:39 PM

2 Attachment(s)
whole unit, with replaced power cord...

Nicke 23rd January 2003 09:19 PM


Originally posted by mpopovics
I have made already some modification, temporary on my DX7711.
But, I still have left some things to do (I do not have too much time).

What I did is many of Nicke's changes, mentioned in Onkyo DX7711 thread.
1. Changed resistors (Holco)
2. Changed capacitors (Elna Cerafine)
3. Eliminated mute transistors
Some differences:
1. The opamps, what I use is OPA627 (all together 8 pcs, not cheap...)

BR, Milan

I did make some similar boards for the opamps myself.
But I used AD797.

Looks nice.


Henrik 24th January 2003 07:01 AM

Indeed, it looks great.

Thanks a lot for the scans, I am doing some serious studying, hope it will get me somewhere.
I will be back!

apassgear 24th January 2003 03:05 PM

Scanned files
Tanks Nicke for the scanned schematics I have already made some study there.

What I will try first of all is to take the output directly from Q405/406 and get rid of the deemphasis removing R439/443 and signal resistors R437, R441, R451 plus Q407 and think I already eliminated R457. Also since i'm driving a 50K pot at the preamp will lower also C463/470 from 10u to 2/5u.

if I'm not satisfied with the results will try driving directly from Q403 which will eliminate all opamps except the mentioned one.

Did you ever test this Nicke?

Henrik 24th January 2003 05:12 PM

Hi apassgear and all!

Since I want balanced output to my XBOSOZ I will try to take the output direct from Q403 and Q404. I have simulated this and it should give about 3.5 V output singleended. If this could be done, I will change to better opamps an bias them to class A by the currentdiodes sugested by Nicke.
And I will go for outputcaps at 33uF wich gives -3dB at 0.5Hz into a load of 10K.
Unfortunately I am too buisy the next week, so it will take a little while before I can try it out.

apassgear 24th January 2003 07:31 PM

Good Henrik, try that and let me know of the results.

i also thought what you proposed, but since for the moment I don't have a balaced pre I'l have to wait for that one.

Have been to lazy to build the BOSOZ for which I have most all the parts but continue to play whith vacuum preamps which are way more interesting than SS.

Nicke 25th January 2003 01:12 PM

Re: Scanned files

Originally posted by apassgear

Did you ever test this Nicke?

No I didnīt but let us know the results.


Henrik 26th January 2003 07:39 PM

2 Attachment(s)
I now have some idea of what to do.
I hope that someone will make some comments if I am wrong in my proposal.

To day I tried to connect the balanced nodes marked 2 in the original scematic to my headphone amp. unfortunately this one is not balanced, so I was only able to hear one channel at the time. First I tried singleended by connecting + and GND and then - and GND. At last I connected + and - to the RCA input at my headphone amp and this time it played louder as a sign on the balanced output.
The sound was very good indeed, all though it wasnīt stereo.
My next step is to drill some new balanced outputterminals at the back of the CD, and the just connect them to the balanced nodes at mark 2, and the listen to it more proberly.
If this test comes out well, I will replace Q403 and Q 404 with four handmade and descrete opamps like in the second atached scematic. This is just a first draw of the idea, I have to consider supplyvoltage, wich transistors to use, the current flow, ccs design and many other elements, but all based on this topology.

Henrik 26th January 2003 07:41 PM

2 Attachment(s)
and then the handmade opamp scemaric

Henrik 26th January 2003 07:42 PM

And by the way, I did it all DC coupled.

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