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Old 27th March 2004, 11:54 AM   #1
00940 is offline 00940  Belgium
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Default Does this make sense ?

I tried to get the schematic of my old HK A401 by following the layout.

Does this look like a possible amp and if it does, is there a way to improve it ?

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Old 27th March 2004, 12:18 PM   #2
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Something doesn't seem right with the input diff pair. How do they get power?
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Old 27th March 2004, 01:23 PM   #3
00940 is offline 00940  Belgium
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hum, true. gonna check that.

btw :

Q1, Q2 : 2SC1030
Q9, Q10 : 2SA777
Q6, Q8 : 2SC1509
Q3, Q4, Q5 : 2SC1345
Q7 : 2SC458
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Old 27th March 2004, 06:07 PM   #4
00940 is offline 00940  Belgium
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Quote:
Originally posted by 00940
hum, true. gonna check that.
Q3, Q4, Q9, Q8, Q2 get power from V+

Q5, Q6, Q10, Q1 get power from V-

Q7 gets about no power. Checking with a dmm while having the amp playing, the transistor has about 1V at each pin. I ran a basic electric simulation in LTspice, using generic transistor and it's in line with what I get.

furthermore, voltage with load are in fact +/- 37V.

I'm trying to get this schematic straight because this amp sounds (very) good and I could perhaps try build a few, to use them in a small home theater project for my father.
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Old 27th March 2004, 07:11 PM   #5
johnnyx is offline johnnyx  United Kingdom
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The circuit as shown is incomplete. Otherwise it looks like many other power amp circuits. Get it right before you try to copy it!
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Old 27th March 2004, 08:19 PM   #6
00940 is offline 00940  Belgium
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i updated the schematic. I forgot to add a small pcb hanging right under the main pcb for the amplification section.

As is, all the parts on the pcb are on the schematic, as well as all the wires coming in and out. If it's incomplete, it'd mean that they put a section of the amplification on the preamp pcb, which doesn't really make sense since they have put this input cap
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Old 27th March 2004, 09:14 PM   #7
johnnyx is offline johnnyx  United Kingdom
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I think it's just the way you've drawn it. I can see bias paths now. Maybe you could build it up on a breadboard to try it out.
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Old 27th March 2004, 10:29 PM   #8
00940 is offline 00940  Belgium
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I just found the service manual of this thing on audio asylum. Wasted time

I'm gonna check if my drawing is correct.
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