Does this make sense ?

00940 · 27th March 2004, 10:54 AM

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 ?

analog_sa · 27th March 2004, 11:18 AM

Something doesn't seem right with the input diff pair. How do they get power?

00940 · 27th March 2004, 12:23 PM

hum, true. gonna check that.

btw :

Q1, Q2 : 2SC1030
Q9, Q10 : 2SA777
Q6, Q8 : 2SC1509
Q3, Q4, Q5 : 2SC1345
Q7 : 2SC458

00940 · 27th March 2004, 05:07 PM

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.

johnnyx · 27th March 2004, 06:11 PM

The circuit as shown is incomplete. Otherwise it looks like many other power amp circuits. Get it right before you try to copy it!

00940 · 27th March 2004, 07:19 PM

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

johnnyx · 27th March 2004, 08:14 PM

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.

00940 · 27th March 2004, 09:29 PM

I just found the service manual of this thing on audio asylum. Wasted time

I'm gonna check if my drawing is correct.

27th March 2004, 10:54 AM	#1
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	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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27th March 2004, 11:18 AM	#2
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Something doesn't seem right with the input diff pair. How do they get power?

27th March 2004, 12:23 PM	#3
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	hum, true. gonna check that. btw : Q1, Q2 : 2SC1030 Q9, Q10 : 2SA777 Q6, Q8 : 2SC1509 Q3, Q4, Q5 : 2SC1345 Q7 : 2SC458

27th March 2004, 06:11 PM	#5
johnnyx diyAudio Member Join Date: Jan 2004 Location: manchester	The circuit as shown is incomplete. Otherwise it looks like many other power amp circuits. Get it right before you try to copy it!

27th March 2004, 07:19 PM	#6
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	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

27th March 2004, 08:14 PM	#7
johnnyx diyAudio Member Join Date: Jan 2004 Location: manchester	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.

27th March 2004, 09:29 PM	#8
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	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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