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Old 24th April 2013, 02:47 PM   #431
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Quote:
Originally Posted by john curl View Post
It would be best to just use an open loop dual fet follower.
Thank you for your time!

I will try it.

Quote:
Originally Posted by AndrewT View Post
located at the tube output.
It would be the best of course to be placed in the player but in my case that is impossible (there are not enough space inside)

Regards
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Old 24th April 2013, 02:58 PM   #432
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Quote:
Originally Posted by gk7 View Post
Yes, I know. And what does this tell us about the content of the ULD-4 ? I donīt get your point.
I'm trying to say that ULD-4 = ML's "Class A Line Driver" module = John's line module, oder?

Last edited by elektroj; 24th April 2013 at 03:03 PM.
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Old 3rd August 2013, 09:13 PM   #433
pidigi is offline pidigi  Italy
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Default ferrite beads

Hi Georg,

since (I think) I have some oscillations in the preamplifier, I was wondering why did you put the ferrite beads on the resistors? Is it because you had oscillations too?

Ciao

Paolo


Quote:
Originally Posted by gk7 View Post
Here is a picture with the modules at work. I will do some measurements
in the next days and post them here if there is interest.
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Old 3rd August 2013, 10:46 PM   #434
gk7 is offline gk7
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Hi Paolo,

the ferrite beads were already originally there, a photo with the old resistors:
l1000109.jpg

I did not experience oscillations but only used the modules in the ML-1 with
a gain of about 10 (20 dB). They are not unity gain stable, how much feedback
you can apply (lower gain) without stability problems I donīt know, I would
estimate less than a gain of 5 is too low.
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Old 6th August 2013, 11:19 AM   #435
pidigi is offline pidigi  Italy
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Thank you Georg. Actually I didn't change the feedback from the original design values, I have used 22k from output to inverting input and 2k2 from inverting input to ground.
Anyhow, the presence of the ferrite beads in the original design makes me think they can be useful.

Basically the preamplifier sound very well but it is missing detail.

I have made some measurements using ARTA and a E-MU 0404 USB.
The first image is the loopback measurement that represents the noise/thd of the audio card, the second one is the spectrum of the output signal of the preamplifier, the last one is the frequency responce of the preamplifier.
As you can see there is a lot of garbage in the spectrum measurement of the preamplifier that makes me thinking that there could be a problem of oscillations. The frequency responce is enough extended but shows also some noise at upper frequencies.

Ciao
Paolo
Attached Images
File Type: jpg loopback.jpg (94.5 KB, 296 views)
File Type: jpg spectrum.jpg (98.6 KB, 286 views)
File Type: jpg frequency responce.jpg (89.6 KB, 277 views)
File Type: jpg CIMG0335r.JPG (166.5 KB, 293 views)
File Type: jpg CIMG0336r.JPG (146.9 KB, 295 views)
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Old 6th August 2013, 03:41 PM   #436
gk7 is offline gk7
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I will try to repeat the measurements with ARTA but this
has to wait until Iīm back from my holiday (beginning of September).
All I can contribute for the moment is an old measurement, it shows
about the same amount of 3rd you have, somewhat higher 2nd and not much else.
Attached Images
File Type: jpg line_right_1kHz.jpg (60.3 KB, 157 views)
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Old 6th August 2013, 04:51 PM   #437
FOXYE is offline FOXYE  Israel
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Someone tried the new version?
Click the image to open in full size.
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Old 6th August 2013, 05:13 PM   #438
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Borbely cascoded his line amp output stages when they were fets ( as did Pass), but both removed the output cascode becuase of a percieved loss of dynamics. However Erno indicated that his Japanese distributor and clients preferred the ouput cascode when jfets are used for the output stage. ( Borbely's Super buffer 2)
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Old 6th August 2013, 06:55 PM   #439
gk7 is offline gk7
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Quote:
Originally Posted by FOXYE View Post
Someone tried the new version?
Why would this be a "new" version ? Looks more like a (somewhat misguided) ebay copy.
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Old 6th August 2013, 08:12 PM   #440
FOXYE is offline FOXYE  Israel
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That's what the seller indicates: "Now this board has been improved.and the sound is better"

Assembled Preamp Board Base on JC 2 Circuit Class A Parallel Power Supply | eBay

Last edited by FOXYE; 6th August 2013 at 08:25 PM.
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