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lykkedk 11th June 2003 03:52 PM

Balanced line stage gain problem !

I was just testing my balanced line stage, which i use unbalanced, where i put a short, where R14 used to be. I then use +IN and GND, for input of each channel. -OUT, i leave as it is. I then use +OUT and GND for each channel for output.

At the input i use a stereopot ( P1/P2 ) at 10Kohm
At the output i use stereopot ( P3/P4 ) at 4.7Kohm
No potmeter at P5
All pots logaritmic.
At first i used 430Ohm for R15, which i guess, couldent drive my Leach amp, very high (Half the strenght i guess).
Then i replaced the R15 with a 221ohm, now i could play nice and loud, at last i replaced R15 with a 183ohm, but that dident give me much i think.
Actually it plays very nice, but i would like it to give a little more power to my GAIN-hungry power-amp.

I have read in the pass DIY project, about this preamp, that lower values of P3/P4, would decrease the gain, is that correct, and would my amp, play louder if i replace P3/P4,with e.g. 6.8Kohm, would that be ok ?

How about P1/P2, i would like to leave that one out, how is the best way of doing this ?

Actually i got other quistion's comming up, one of theese day's, but this, i think, would be enoughf for now...

Hope to give you some pictures soon, just got my self a cheap kamera, just havent the time yet to use it :)...

Nelson Pass 11th June 2003 06:44 PM

The following procedure is one that I always recommend,
and since the question comes up all the time, it bears repeating.

The best way to do this is to use input divider pots P3 and P4
with values around 10K or so and output dividers around 5K
or so. The values are not critical, but I wouldn't use input pots
above 25K or output pots above 10K ordinarily.

To best set up the pot values, turn the output pots all the way
up and set the input pots for the loudest level you are likely to
want. Then use the output pots for day-to-day volume control.

Additonally you are free to adjust the value of R15 to further
expand the range. As R15 gets low, the gain goes up, as does
the distortion and noise, but at the same time the balanced input
common mode rejection also goes up, for what that's worth to
you. I have found that R15 values around the 124 ohm figure
in the article to give the best sonic results, but of course that
reflects my own taste and complementary equipment. Your
mileage may vary.


lykkedk 11th June 2003 06:55 PM

Hi Nelson Pass

OK, without using the P5 pot, I could reduce the R15 to 124ohm, from the 183 I have now ?

Where P5 is placed, I have made a short, as described earlier.

How much will this give me, at the output 2v perhaps ???

My CD gives 2v, at the variable line out, but, i
think it plays louder than with my Bal. line stage.

BTW. Thanx Nelson, i actually could hear better music quality, more clear i think ! when my signal streamed through this preamp, instead direct from cd variable out. GREEAT

Taco 12th June 2003 12:28 PM

If you use it unbalanced why don't you make a BOZ ?

Nelson Pass 12th June 2003 10:16 PM

BSOZ sounds a bit better by all accounts.

eLarson 13th June 2003 01:01 AM


Originally posted by Nelson Pass
BSOZ sounds a bit better by all accounts.
I thought it did, too, though I'm hard pressed to
put my finger on it. The "people behind the
speakers" just seem to be a bit more "there".
But only if I get the volume up to a certain

Know what I mean?


lykkedk 13th June 2003 05:49 PM

I was hoping, some could answer my quistion, if i could safely use 124ohm at r15 without the P5 pot...

Nelson Pass 13th June 2003 06:14 PM

Of course. That's the original value.

lykkedk 13th June 2003 06:16 PM


I Will let you know, if it work's better, than with my 183ohm...

lykkedk 19th June 2003 07:24 PM

Just wanna tell you, that the reason, why i coulden't play, as loud as i would like to, was that i mistakently have swapped the GND and +OUT at the input pot :goodbad:

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