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Old 20th March 2013, 09:51 AM   #3201
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Quote:
Originally Posted by weslito View Post
I don't have a bookcase, but I do have a benchcase
Wow- what a setup! I'm too embarrassed to show my bench case. Maybe I will PM you my setup snaps
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Old 20th March 2013, 10:16 AM   #3202
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Quote:
Originally Posted by Namenlos View Post
This can't work, you just increase the load of the preamp. You have to create a voltage divider somehow.
Sorry for the unintended confusion.

With 4.7K (connected from centre to gnd of pot)
You get 3.2K pot

With 10K
You get 5K pot

With 40.2K
You get 8K pot

All combinations are above JRC 2068 lowest RL limit of 2K.I would highly recommend 10K as you may have extra pair in hands from BOM.No harm in trying. If this doesn't works for you can always clip the resistors.
BTW pot linearity will be thrown out of window.

Pls refer to attch. schematic.
Attached Images
File Type: jpg Vol. Pot mod.jpg (14.9 KB, 357 views)
File Type: jpg JRC2068.jpg (21.7 KB, 348 views)
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Old 20th March 2013, 11:21 AM   #3203
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Default O2 with stepped attenuator

Here are some photographs of my "Fossilised" O2 with stepped attenuator(11+1 steps)

PCB is mounted on brass studs separated by anti-static plastic sheet from the main body to prevent any accidental shorts. It has RCA i/p which are automatically disabled when 3.5mm i/p connector is inserted from front panel. The bare outer ring of RCA i/p connects i/p Gnd. to tin box reducing noise. Jumpers are used instead of gain switch giving me 3 gain options(1X,2X,8X).
Resistor values used in stepped attenuator 100,180,390,680,910,1K,1.2K,1.5K,1.8K,2.2K,2.7K (hand-matched).

It gets comfortably loud at 1X gain with RCA i/p from consumer DVD player , 2X from my laptop & 8X from ipod touch for my Superlux HD668B(56 Ohms, Sensitivity 98dB)
The vacant space(foam)will be used for installing DC protection relay circuit & 1/4" socket. Non-standard red LED used (fwd. drop of 1.78V) with R6 (33K) as suggested by agdr. PM circuit works like a charm.
Attached Images
File Type: jpg IMG_0119.jpg (815.9 KB, 368 views)
File Type: jpg IMG_0120.jpg (905.2 KB, 346 views)
File Type: jpg IMG_0121.jpg (606.4 KB, 319 views)
File Type: jpg IMG_0109.jpg (1,021.3 KB, 114 views)
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Last edited by availlyrics; 20th March 2013 at 11:40 AM.
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Old 20th March 2013, 05:43 PM   #3204
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Quote:
Originally Posted by availlyrics View Post
Sorry for the unintended confusion.

With 4.7K (connected from centre to gnd of pot)
You get 3.2K pot

With 10K
You get 5K pot

With 40.2K
You get 8K pot

All combinations are above JRC 2068 lowest RL limit of 2K.I would highly recommend 10K as you may have extra pair in hands from BOM.No harm in trying. If this doesn't works for you can always clip the resistors.
BTW pot linearity will be thrown out of window.

Pls refer to attch. schematic.

This does not work that way. You basically would get another taper characteristic and an uneven load with this. Mostly it would just attenuate the higher gain settings. With 4.7k parallel and the volume at 50% you would get about 16% less voltage which would just be 0.75dB at lower gain settings it is even less than that.
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Old 20th March 2013, 07:17 PM   #3205
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Finished my third O2+Odac combo today. Set a new personal speed record too, total build time was about three hours I think.
I have a step-by-step construction guide coming up on my blog within the coming days.
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Old 21st March 2013, 02:38 AM   #3206
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Hi! Im having tome trouble to find some parts here in Argentina.
What if on C13 and C14, instead of the Metal Film Polyester BOX capacitor i just use regular Metal Polyester ones like in the picture above?

http://theonlinetutorials.com/theonl...Capacitor1.gif

Will this change the operation of the amp? Change the sound of it?
Im the kind of person that chooses Rubycon caps over no brand caps , i think that matters.

And concerning the potentiometer , i cant get anything better than this.

http://www.onlinetps.com/shop/images...entiometer.jpg

How much matters if i use a cheap chinese pot instead Alps or Bourns ?

Cheers , Stefano
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Old 21st March 2013, 04:05 AM   #3207
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Quote:
Originally Posted by Namenlos View Post
This does not work that way. You basically would get another taper characteristic and an uneven load with this. Mostly it would just attenuate the higher gain settings. With 4.7k parallel and the volume at 50% you would get about 16% less voltage which would just be 0.75dB at lower gain settings it is even less than that.
Yes you are right on "uneven load" as seen by 2068 with added non linearity issues, but I've seen those type of implementation in electronic fan regulators
Chk this for more info
ESP - A Better Volume Control

BTW What is your music source? Can't you control vol. from there?
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Last edited by availlyrics; 21st March 2013 at 04:23 AM.
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Old 21st March 2013, 04:48 AM   #3208
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Quote:
Originally Posted by tecnogadget View Post
...Will this change the operation of the amp? Change the sound of it?
Im the kind of person that chooses Rubycon caps over no brand caps , i think that matters.
How much matters if i use a cheap chinese pot instead Alps or Bourns ?
I'm no expert on caps, but you will have hard time physically fitting non-standard BOM components. Believe me I've done that.

As for pot-don't even bother with cheap Chinese dump, you can short appropriate holes giving you full vol. from O2 & you can control your vol. from your source with its own digital vol. control(far better tracking than Alps or Chinese pot). Above all when those Chinese pot. wear out, you will have hard time de-soldering again.
See attch. for my implementation
Attached Images
File Type: jpg o2 with no vol. control.jpg (337.6 KB, 127 views)
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Last edited by availlyrics; 21st March 2013 at 05:03 AM.
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Old 21st March 2013, 05:31 AM   #3209
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Quote:
Originally Posted by Rullknufs View Post
Finished my third O2+Odac combo today. Set a new personal speed record too, total build time was about three hours I think.
I have a step-by-step construction guide coming up on my blog within the coming days.
Congrats-Keep up the good work. I read your blog, it reminded me of my school days when I had to borrow soldering iron from my friends to solder my broken h/p wires. Hope you build more such projects to finance your purchase of much needed measuring instruments.
Cheers!
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Last edited by availlyrics; 21st March 2013 at 05:40 AM.
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Old 21st March 2013, 03:04 PM   #3210
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Quote:
Originally Posted by availlyrics View Post
I'm no expert on caps, but you will have hard time physically fitting non-standard BOM components. Believe me I've done that.

As for pot-don't even bother with cheap Chinese dump, you can short appropriate holes giving you full vol. from O2 & you can control your vol. from your source with its own digital vol. control(far better tracking than Alps or Chinese pot). Above all when those Chinese pot. wear out, you will have hard time de-soldering again.
See attch. for my implementation
I know the non-standard BOM cap is larger , but i won't be using the official aluminium enclosure so that is not a problem. Your volume implementation is very clever , but does not suit for me , since i will connect the iPod Touch with a Line Out cable (3.5mm to 30pin Apple connector) , so the signal is sent at full vol. so i need to change it on the amp.
Thanks for your reply availlyrics

So besides the physical SIZE problem , can i use polyester caps without worrying about performance?
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