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Digital Deaigns M4A
Digital Deaigns M4A
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Old 16th October 2020, 12:03 PM   #1
caraudioguy2100 is offline caraudioguy2100
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Default Digital Deaigns M4A

I do not get any rail to rail oscillation on the outputs .

I checked all of the regulators and all seem to work fine .

I checked all the 47mh inductors all are fine .

I get both positive and negative rail voltages .


Any ideas or common issues with this design of amp as to why it wonít oscillate
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Old 16th October 2020, 12:54 PM   #2
caraudioguy2100 is offline caraudioguy2100
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Iím gonna try replacing the smd transistors on the audio driver board since some appear a brownish color from heat
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Old 16th October 2020, 12:54 PM   #3
Perry Babin is offline Perry Babin  United States
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Black probe on the negative rail, what's the DC voltage on terminal 2 of the 21844s?

Do you have signal reaching the driver board?
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Old 17th October 2020, 10:23 PM   #4
caraudioguy2100 is offline caraudioguy2100
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The muting transistor is defective .

Itís marked K30A

So Iím assuming itís a KSC30A

Do you happen to know if any good replacements for that transistor ?
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Old 17th October 2020, 10:31 PM   #5
Perry Babin is offline Perry Babin  United States
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K30A is a jfet. It doesn't read like other transistors.

What do you read 1-2, on ohms?

Then read 2-3 on diode check. Reverse probes and read again.
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Old 17th October 2020, 11:03 PM   #6
caraudioguy2100 is offline caraudioguy2100
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Amp has no output I took it out of the amp and the amp plays audio so itís defective
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Old 18th October 2020, 06:03 AM   #7
caraudioguy2100 is offline caraudioguy2100
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Any ideas on what I might be able to use ?

Legs1-2:Ol
Legs2-3:1.455

Proves reversed

Legs1-2:OL
Legs2-3:1.455
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Old 18th October 2020, 12:24 PM   #8
Perry Babin is offline Perry Babin  United States
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Do you have any J111 jfets?
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Old 18th October 2020, 12:44 PM   #9
caraudioguy2100 is offline caraudioguy2100
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Yes
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Old 18th October 2020, 12:49 PM   #10
Perry Babin is offline Perry Babin  United States
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Check one like you checked the k30 and post.
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