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Old 30th November 2003, 01:42 PM   #21
Henrik is offline Henrik  Denmark
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Default Uuppsss!

Quote:
Originally posted by Henrik
The output caps (C101 and C102) passes through the lower inverted frequencies, and then they will be fed back through the resistors (R122 and R123) and then attenuate the noninverted input as much as the shunt resistors (R120 and R121) allows. But at some point on the frequensy scale, the cap (depending at the value) will begin to act as a resistor, the higher the frequensy the higher the resistance becomes, and hereby lowering the feedback acordingly. But when the NFB is lowered the gain at the drain raises, but lowered again by the resistance of the outputcap, and thus the gaindvice keeps the gain close to constant within a wider band of frequencies. As long as the cap let some current flow through the feedbackresistors (R122 and R123) the gaindevice will compensate for the lack of gain, until the maximun gainlevel of the gaindevice is reached. From there the frequensy responce falls at the output.
This is not correct!
Thanks william for pointing that out!
I must have felt inverted some how.

It should have ben as the following:
The output caps (C101 and C102) passes through the higher inverted frequencies, and then they will be fed back through the resistors (R122 and R123) and then attenuate the noninverted input as much as the shunt resistors (R120 and R121) allows. But at some point on the frequensy scale, the cap (depending at the value) will begin to act as a resistor, the lower the frequensy the higher the resistance becomes, and hereby lowering the feedback acordingly. But when the NFB is lowered the gain at the drain rises, but again lowered some by the resistance of the outputcap, and thus the gaindevice keeps the gain close to constant within a wider band of frequencies. While the cap lowers the current flow through the feedbackresistors (R122 and R123) the gaindevice will compensate for the lack of gain because of the lower feedback, it will do so until the maximun gainlevel of the gaindevice is reached. From there the frequensy responce falls at the output.

Sorry for the confusion.
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Old 3rd December 2003, 07:26 AM   #22
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Default second test

Hi all,

yesterday I had another listen after modifiing the output caps / volume control.

Thereīs quite a change compared to the last time.

The soundstage has grown and is better defined now. The highs are not as grainy as before and bass level seems to be a bit louder.
The midrange sounds not quite as nice, tubelike (distortion?) as before but still very natural with good detail. The amp sounds very fast.

I only listened for a few hours and Iīm a bit handicapped cause Iīve lent my modified P3-A to my father and this way (standard P3-A) CD doesnīt sound as good it could.

Switching to the ONO+X-BOSOZ gave the biggest difference (ONO unchanged). Now the soundstage is huge, VTA seems to be allright again and bass is very good. The difference with CD is quite a lot bigger than it was before
The difference compared to my previous phono stage is more speed / attack and a bit more depth to the soundstage. Bass is still a bit down but I will wait a few more days (burn in has only been 30 hours or so because the casing is still not finished and I donīt want my daughter to play with 80V DC)

Most of the listening was in balanced mode (Kimber PBJ) but I will try it unbalanced too.

Will be continued........

William

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Old 3rd December 2003, 09:56 AM   #23
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William,

Glad to see (hear) all is well, enjoy.

Have you tried active current sources...it will sound different again

macka
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Old 3rd December 2003, 10:38 AM   #24
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Default Re: second test

William,

Great job as usual. You always have top notch information
Quote:
Originally posted by wuffwaff
...mode (Kimber PBJ) but I ...
BTW, what is PBJ???... Peanutbutter and Jelly???
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Old 3rd December 2003, 11:36 AM   #25
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Macka,

will try them (current sources) when everything else is ready and after Itried the cascoded version (without output caps). And maybe I will finish my Aleph-X first.........

Roddyama,

thanks for the compliment and yes, Peanut Butter and Jelly. In my opinion a cable with unbelievable value for money!
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Old 3rd December 2003, 08:40 PM   #26
Taco is offline Taco  Netherlands
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Good job Wuffwaff, I just finished my standard BOSOZ and now I am thinking of modifing it in a X-BOSOZ. But looking at the schematics of Henrik I must increase the output caps to very big ones. What for caps can I best use, MKP doesn't fit on the board and are to expensive.
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Old 3rd December 2003, 09:11 PM   #27
Mad_K is offline Mad_K  Norway
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Quote:
Originally posted by Taco
Good job Wuffwaff, I just finished my standard BOSOZ and now I am thinking of modifing it in a X-BOSOZ. But looking at the schematics of Henrik I must increase the output caps to very big ones. What for caps can I best use, MKP doesn't fit on the board and are to expensive.

-actually you can decrease them to 1uF if driving a 10K load because they are "multiplied" in the feedbackloop. The reason for the big caps in Henrik sch. is because it was designed to drive the xsoz with 120ohm input Z...
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Old 4th December 2003, 07:43 AM   #28
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Mad_K, Taco,


Iīm not shure about decreasing the output caps that much. There isnīt that much open loop gain to use as feedback. I wasnīt very happy with the sound of the 10muF I had (into 1k3).

Since the caps are in the feedback loop you could try normal 63V panasonic FC (50microF or so). They are biased with 32V so they will funktion well. All distortion will be cared for but you can always use a small (10-33nF) MKP in parallel.

william
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Old 4th December 2003, 08:15 AM   #29
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Default balanced v. unbalanced

yesterday I had the chance to do some further listening changing between balanced and pseudo balanced interconnects with just the flick of a switch.
Iīll try to explain:
To use my unbalanced outputs Iīve mounted a switch on the back of the preamp that connects -out to ground (after the series resistor of the balanced vol. pot). So it connects pin 1 and 3 on the XLR outputs and pin 1 and 3 on the Aleph XLR inputs. This is (very conveniently) just what you need to change the Aleph from balanced to unbalanced operation

A further bonus is that the 6dB extra gain of the balanced output are compensated for by the balanced volume control so you donīt have to change the volume when comparing (it took me a while to figure out why nothing went louder when changing from unbalanced to balanced........)

The pseudo balanced mode has the advantage that the common mode rejection is kept high. So the only thing that changes is the output from the preamp.

To make a long story short, no dramatical differences, no small differences and maybe some subtle differences but these will take a bit longer to find out.

I always thought that the X was only accomplished when using the X-BOSOZ balanced (out) or am I wrong?


William
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Old 4th December 2003, 12:00 PM   #30
Henrik is offline Henrik  Denmark
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Default Re: balanced v. unbalanced

Hi william!
Quote:
Originally posted by wuffwaff
To make a long story short, no dramatical differences, no small differences and maybe some subtle differences but these will take a bit longer to find out.

I always thought that the X was only accomplished when using the X-BOSOZ balanced (out) or am I wrong?

William
I had almost the same expirience with my analog output stage in my CDP, which I made like an XBSOZ but with current sinks. The sound from this circiut is just great, but the difference between bal and un bal is subtle.
The case is, that I have never realy heard my xbsoz in unbal mode, becauce my xsoz sounds not so good when driven unbalanced and also the gain became too low. So this told me nothing about the X and non X sound from my xbsoz, only that my xsoz canīt be driven unbalanced.

You must bee right, we canīt have any X in unbalenced mode.

I have tried to understand your way of connecting the attenuator and your bal/unbal swich.
Is this the way?


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