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Old 4th August 2012, 09:24 AM   #151
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there is hum and hiss when setting like this: (dc out 80-300mV)
Click the image to open in full size.

but will be silent with this setting: (dc out 0-25mV)
Click the image to open in full size.

Last edited by wengtech; 4th August 2012 at 09:27 AM.
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Old 4th August 2012, 09:36 AM   #152
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1. setting DC offset and bias - all inputs grounded , amp hot , lid on (take it off just for quick re-set)

2. first pic is correct for unbalanced input

3.second pic is example of nada,zilch,hogwash ; neg leg input is floating , and you're not having full gain ; it is not balanced config

so - for proper operation - either connect it as per pic 1 , for unbalanced (RCA ) input , or bring proper balanced signal (as XLR wiring - remember that ? )

give us more pictures , so we can comment your grounding scheme and find culprit why you are having hiss & hum
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Old 4th August 2012, 10:21 AM   #153
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yes Zen Mod, i know how to wire XRL or RCA'
the pic above only to shown the changes dc output voltage with -IN shorted and unshorted.

this is basically i do with the amp:

Click the image to open in full size.
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Old 4th August 2012, 11:36 AM   #154
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you must ground both inputs (+ and - ) when setting offset

have you any pic of your PSU pcb layout ?

I mean , traces - that will help to see is there any room for improvement
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Old 4th August 2012, 12:21 PM   #155
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okay i see both + and - are grounded.

this is my PSU wiring:
Click the image to open in full size.

bleeder R and bypass Caps i mean:

Click the image to open in full size.

according to mr pass files,
there are no setting for this amp.

so, which component should be setting?
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Old 4th August 2012, 02:08 PM   #156
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i am using un matched IRFP244.
so voltage across each 0.47ohm are:
Right Ch: Left Ch:
R34 = 397mV 434mV
R35 = 517mV 486mV
R36 = 434mV 412mV
R37 = 508mV 496mV
R38 = 481mV 414mV
R39 = 363mV 438mV

original pass file, it should be 250mV across that resistors.

i am using this schematic:
Click the image to open in full size.
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Old 4th August 2012, 06:24 PM   #157
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pcb seems adequate

so - for that pcb,best takeout point for gnd routing to output pcbs is point where you connected two wires from bridges , establishing gnd .

regarding Iq - do you hear benefit of increasing it , ref. original ?
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Last edited by Zen Mod; 4th August 2012 at 06:28 PM.
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Old 6th August 2012, 09:39 AM   #158
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this is my first time to build aleph30 amp.
so i dont know what is the difference.

i am planning to re-wiring my PSU like this one:

Click the image to open in full size.

what do you think? will this solved the hum and hiss problems?

thanks.
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Old 6th August 2012, 09:42 AM   #159
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it'll be probably just fine

do not forget to put 10R/5A NTC between audio GND and chassis
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Old 6th August 2012, 10:12 AM   #160
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yes of course,
each channel will be equipped with :
- 2x2k2/2w as bleeder,
- 2x1ohm/5w in parallel on each rail to perform CRC,
- and 2xwima4.7uF/400v as bypass caps.

i hope this is enough for my aleph30.
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