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Hi support community, I built one of the first batch of Buffalo II with IVY III back in 2010. It has been working well ever since. Anyway, got the itch to update as there had been much water under the bridge at TPA. First added the latest AVCC, then a bit later the latest Tridents and then the latest Placid BP HD supply. Each step gave a very positive uplift in sound quality. I was going to stop there but thought I would try the Legato to compare with IVY. Build went OK just had one transistor QN4 (right channel) the wrong may round but noticed before applying power, so de-soldered and turned round (I was pretty careful with the heat - should have just clipped the legs though). I am applying 360ma on each channel (14/14v), when I power on the the right channel shunt measured on Placid R2 = 0ma and the left channel R2= 360ma. When I measure the op amp pin out get: 1 150mv 2 2.7v 3 2.7v 4 14v 5 2.6v 6 2.6v 7 0.6v 8 14v When remove op amp and measure socket pins get: 1 7v 2 7.2v 3 2.7v 4 14v 5 2.6v 6 7.5v 7 7.5v 8 14v All measurements without Buffalo connected. Any advice on how to debug much appreciated? Bishopoz bishopoz attached the following image(s):  IMG_0311.JPG (135kb) downloaded 17 time(s). IMG_0312.JPG (119kb) downloaded 13 time(s).You cannot view/download attachments. Try to login or register.
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Rank: Member
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Location: Sydney
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Rank: Member
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Joined: 6/17/2008(UTC) Posts: 921  Thanks: 1 times
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Hi. Start by looking for tiny solder bridged. I have marked a few spots - (it could be due to picture quality) . Edited by user Saturday, August 8, 2015 6:31:20 AM(UTC)
| Reason: Not specified avr300 attached the following image(s): cut.jpg (106kb) downloaded 25 time(s).You cannot view/download attachments. Try to login or register.
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Rank: Member
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Thanks avr300,
cleaned up the solder and reflowed most components - the solder circled on far left is where I stuffed up the transistor and had to remove it.
Placid set to deliver 14/-14v & 230ma
The right channel now shows -14v at power input and left 1.64v
right channel is shunting 40ma and left shunting 0ma
Pin 4 has -14v and Pin 8 1.635v without opamp.
To me this seems to indicate the right channel is looking OK?
Can I compare voltages left v right to isolate the problem location?
Bishopoz
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230mA isn't enough.
Aim for ~300mA for a start - then measure the actual shunt current once operational.
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I have measured with opamp (OPA2134) installed but not connected to Buff Current 310ma both sides right shunting 160ma left shunting 0ma Voltage 1.37/-14 Edited by user Monday, August 10, 2015 9:17:13 AM(UTC)
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You're saying that you power first left side and then the right side.
How exactly are you doing this.
By picture you have J1-J2-J3-J4 jumpers installed. That means that you're powering both left and right through the middle connector block.
(I just have to make sure that I understand what you're doing. If done without the J1-J4 installed I'm following you.)
To me it looks like that you have a (semi)short from + to GND on the left side. That why the placid is shunting 0mA. The Legato consumes it all.
Once again, look (really carefully) for excessive solder.
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Rank: Member
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Joined: 1/28/2010(UTC)
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I am powering both channels simultaneously via placid, jumpers are installed.
Will recheck my soldering.
Thanks
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