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Old 31st December 2012, 11:59 AM   #11
Zen Mod is offline Zen Mod  Serbia
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please think

you said - you have protection circuit implemented on board

so , if I look at Aleph 30 schematic , I can't see schematic of missing part - protection

i have this schematic , collected from somewhere

is it similar - regarding protection ?
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File Type: jpg Aleph-5-China.jpg (88.7 KB, 114 views)
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Old 31st December 2012, 12:19 PM   #12
vivanco is offline vivanco  Italy
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Quote:
Originally Posted by Zen Mod View Post
please think

you said - you have protection circuit implemented on board

so , if I look at Aleph 30 schematic , I can't see schematic of missing part - protection

i have this schematic , collected from somewhere

is it similar - regarding protection ?
the protection circuit I bought from Jims_audio (indicated below the photo), I try to ask him if he can provide me the circuit.(but I think it will be very difficult)

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Old 31st December 2012, 12:22 PM   #13
Zen Mod is offline Zen Mod  Serbia
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ok - for now just exclude speaker protection ( but do not connect speaker to amp output)

post schematic here , which you're using and familiar with , and I'll mark what to measure
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Old 31st December 2012, 12:31 PM   #14
vivanco is offline vivanco  Italy
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Quote:
Originally Posted by Zen Mod View Post
ok - for now just exclude speaker protection ( but do not connect speaker to amp output)

post schematic here , which you're using and familiar with , and I'll mark what to measure
you mean the diagram of the amplifier? If so, the circuit is this:

Pass Aleph 30 Sch original.pdf
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Old 31st December 2012, 01:47 PM   #15
Zen Mod is offline Zen Mod  Serbia
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so - download this file , open it in MS Paint or some other graphic editor program , measure all red circle marked voltages in your actual circuit and write them on schmtc

then post it here

do not forget - both inputs grounded while testing

nothing connected to output

disconnect
speaker protection circuit from amplifier for now
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Old 31st December 2012, 02:37 PM   #16
vivanco is offline vivanco  Italy
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my power supply provides 23 volts, so you wonder if the values you have indicated no change;

however, if it can help you, I did a test and that is the extent of the offset : without signal, the measurement is 54mV, while inserting the plug XLR (even with the preamp off) the value increases to 0.54 V

NB: the protection circuit has been removed
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Old 31st December 2012, 02:45 PM   #17
Zen Mod is offline Zen Mod  Serbia
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do what I wrote - measure everything with red circle

there must be something - either broken part or wrong wiring
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Old 31st December 2012, 03:26 PM   #18
vivanco is offline vivanco  Italy
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Quote:
Originally Posted by Zen Mod View Post
do what I wrote - measure everything with red circle

there must be something - either broken part or wrong wiring
These are the measurements:

on resistor 221ohm 4,88 V (you post 5 V)
on zener 8,64 V (you post 9 V)
on drain IRF9610 (current generator for differential) 3,53 V (you post 4 V)
collector-emettitor ZTX450 UP 3,93 V (you post 4,5 V)
collector-emettitor ZTX450 DOWN 4,27 V (you post 4,5 V)
on first triplet resistor 0,47ohm : 0,40 V - 0,39 V - 0,38 V
on second triplet resistor 0,47ohm : 0,41 V - 0,38 V - 0,38 V
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Old 31st December 2012, 03:49 PM   #19
vivanco is offline vivanco  Italy
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however, the thing that continues to leave me perplexed the fact remains that if not connect the signal, the output voltage is around 40mV, while connecting the signal rises to 0.54 V, hence the reason for which the speaker protection (which currently is disconnected) goes in protection.
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Old 31st December 2012, 04:48 PM   #20
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so , after several posts - I'm realizing that your problem is combined from two things :
1-unmatched input mosfets
2-missing procedure/possibility for setting output offset

cure :

replace R11 with 500R multiturn trimpot (connected as variable resistor - middle leg connected with one (any) outer leg)

set it , prior to soldering , to half value

short both inputs to ground


power up

set offset with that trimpot , after temperature equilibrium

do the same for other channel

shorting inputs to gnd during setting offset and Iq procedure is a must
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