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Ask help on PASS X150 dc output differential settings
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Old 8th October 2019, 02:06 PM   #21
gelly is offline gelly  Belgium
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hi guys, here some measurements:

figured out that pcb at the back is left channel, pcb at the front is right channel.

left dc offset was -27v this to minimum of -15v now (cant turn lower)
left diff voltage was -300mv, now 2 mv.

right dc offset was -15v, this is now -2v (cant turn lower)
right diff voltage was -60mv, now 3 mv.

is this okay ?

bias i cant figure out....
( to be clear, i did NOT change bias current pots)

left bottom is 60mv (underneat the left blue connector.)
left beside c1 is 12 mv.
left beside c2 is 7 mv.

right bottom is 70mv (underneat the right blue connector.)
right beside c4 is 15 mv.
right beside c3 is 6 mv.

here there is something wrong, no ?

greetings,
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Old 8th October 2019, 03:07 PM   #22
gelly is offline gelly  Belgium
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extra info...

disovered that the woofers 'popping' is only when preamp is connected.
tried to change outlet phase on preamp, didnt improve.

the max measured voltage peak when popping values are about 17 v or so!when preamp is disconnected, those valeus are max 'only' 1.2 v or so.

1 (maybe) important thing is that the amp is not earthed.
dont have an outlet there with earth/ground.
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Old 8th October 2019, 04:55 PM   #23
Nelson Pass is offline Nelson Pass  United States
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Ask help on PASS X150 dc output differential settings
It is not trivial to make these adjustments, and it takes patience.

It looks to me like the whole thing has managed to be un-adjusted at some point.

Are we talking about absolute offsets or differential or both?

The other thing is that the adjustments should be made with inputs shorted to
ground and compared with inputs open, and the difference should be minimal.

The standard for offset on amplifiers like this is around 50mV differential and less
than 1 volt absolute. Both have an influence on whether a preamp connection
creates a thump.
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Old 8th October 2019, 05:38 PM   #24
wayne is online now wayne  United States
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Ask help on PASS X150 dc output differential settings
Quote:
Originally Posted by gelly View Post
hi guys, here some measurements:

figured out that pcb at the back is left channel, pcb at the front is right channel.

left dc offset was -27v this to minimum of -15v now (cant turn lower)
left diff voltage was -300mv, now 2 mv.

right dc offset was -15v, this is now -2v (cant turn lower)
right diff voltage was -60mv, now 3 mv.

is this okay ?

No the DC is way to high on the left channel.

bias i cant figure out....
( to be clear, i did NOT change bias current pots)

left bottom is 60mv (underneat the left blue connector.)
left beside c1 is 12 mv.
left beside c2 is 7 mv.

right bottom is 70mv (underneat the right blue connector.)
right beside c4 is 15 mv.
right beside c3 is 6 mv.

here there is something wrong, no ?

Doesn't make sense to be the bias is only measured in four places across the 2 pin headers coming out from the board.

greetings,
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Old 8th October 2019, 06:05 PM   #25
gelly is offline gelly  Belgium
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Hi Nelson,
We are talking about both.
Differentiaal i managed to get at 2 and 3 mv.
The Absolute i managed to lowering but still to high. (-15V left channel).

About the bias...
Even if my measurements doesnt make sense,
The tempetature is stabilised at 48 and 50 degrees c. L/R.
That doesnt seam bad. (After 2 hours)

Still worried to damaging my woofers cause they go to max coarse.

It souds just great, but worried.
Like to solve this...

Thanx for input guys !

Ps: there are 6 points for headers.
Dunno shure what does what...
Ps2: that bopping is with and whithout preamp switched on.

Last edited by gelly; 8th October 2019 at 06:10 PM.
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Old 8th October 2019, 10:51 PM   #26
Nelson Pass is offline Nelson Pass  United States
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Ask help on PASS X150 dc output differential settings
-15 V is from the moon. Now wonder you have such problems. Looks to me
like it is either grossly imbalanced + to - on bias voltage for the Mosfets on the
modules (the pots) or you have no ground reference on the input or it's simply
broken.
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Old 9th October 2019, 07:17 AM   #27
jan.didden is online now jan.didden  Europe
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Seems to me if that offset really was 15V, how can it then 'sounds good, no problems' as the OP stated up front. Maybe it is a measurement error?

Jan
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Old 9th October 2019, 08:46 AM   #28
gelly is offline gelly  Belgium
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Hi Jan,

Therefore my question and remark about the 6 measuring points, for whitch measures what...

Measurements where made with 2 fluke dmm's.

Really, it sounds great and even better than my 2 other amps.
The one is the rega elicit_r and the marantz topline sr14mk2 in stereo mode.

If i new exactly what to measure at those 6 headers...
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Old 9th October 2019, 10:25 AM   #29
Zen Mod is offline Zen Mod  Serbia
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Ask help on PASS X150 dc output differential settings
you will know if you invest some efforts in reading post in my blog

physical differences are irrelevant , that's practically the same amp , setting wise
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Old 9th October 2019, 01:58 PM   #30
gelly is offline gelly  Belgium
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Zen,

i did read your blog.
i was stuck with the resemblance differenses between my 150 and your 150.5.

here a pic of the placings of the 6 headers. (with numbers)

left bottom is 60mv (underneat the left blue connector.) (number 5).
left beside c1 is 12 mv. (number 1).
left beside c2 is 7 mv. (number 2)

right bottom is 70mv (underneat the right blue connector.) (number 6)
right beside c4 is 15 mv. (number 4)
right beside c3 is 6 mv. (number 3)
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