"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets - Page 197 - diyAudio
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Old 4th November 2012, 01:14 PM   #1961
qusp is offline qusp  Australia
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which points even more strongly towards a power supply issue.


buildmesomething: your hum/noise will be because being a battery powered device with virtual ground (the O2) when its off the inputs of 'the wire' are effectively floating because there is no stable 'ground' reference voltage, thus free to pick up any stray noise.

FR frugal horns with the wire and dps600? seems overkill no?

on the other hand I realize there is merit to the 'build once and build well' mantra. you are much more likely to build another set of speakers (or have more than one set) than build another 4 channels of poweramp (you have 4 channels dont you?)

my main concern with the frugalhorn and this amp is the gain structure, then again you are using the amp with some seriously efficient speakers arent you Owen?

Last edited by qusp; 4th November 2012 at 01:21 PM.
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Old 4th November 2012, 04:07 PM   #1962
AndrewT is offline AndrewT  Scotland
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Originally Posted by opc View Post
............... I know you were using a 10R resistor between GND planes..........
Yes I did try that and I did find an unbalanced Ground current between the planes. That current developed, as far as I can remember 8mV across the 10r resistor.
I also reported that I would and did put back in the 0r0 between the Ground Planes.
So that reverts my implementation back to one of the 4 given in the build sheets.
I think I also reported which of the 4 options I had built: AC coupled Single ended.

There is no other grounding that can be implemented on the as supplied PCB.

The screechy power down version is assembled using the official build instructions, except for adopting the NFB/gain components of the AC balanced in the AC single ended, i.e.30k/1k2 instead of 5k49/220r and reducing input cap from 330uF to 2u2F C78 and adding RF attenuation of 100pF across the 30k of R46. This is the version I have been listening to for the past few months.

Can anyone see any technical reason why any of those should leave a screechy output on power down?

However, I have modified the second and third PCBs to separate the Signal Ground from the Power Ground. This I have not reported since my experiments to remove the oscillation were abandoned some months ago, to devote time to some symasym style amplifiers.
I have also looked at, but not implemented a different version of the mute circuit, but due to a lack of suitable smd components that too is in limbo.
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Old 4th November 2012, 06:43 PM   #1963
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Thanks qusp, I can now remember that my O2 does generate some noise with the Pioneer cdp I'm using, but is quiet once both are on. Plus the O2 has it's own on/off transitions.

Just doing two channels, though did say I'd have liked to do more [5.1 amp - future project]. Just the idea of building the speakers is tempting, but I'll never be a chippy so cabinate work would be difficult in the extreme. The XTZ speakers appear to be good speakers and offer some tuning abilities as standard. Their UK distributer has closed so I'd have to go direct, & they have good representation on the UK based AVForum.


So with the dps-600's, the best way forward is to use the stanby circuit. This is something I was planing to do as part of the final build, a mains supply switch [rear mounted] & seperate standy switch [front mounted].

I too am using the AC Coupled SE build & everthing is as spec'd in the work sheet. With mine, I would expect all or most of the start-up noise to disappear once it's in a chassis & have moved away from using the O2.
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Old 4th November 2012, 08:49 PM   #1964
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I am using regulated linear supplies for testing till the parts I need to implement higher LME supply voltages arrive. With no input signal, the output has a soft low frequency approximately 1 volt thump at turn off. With an AC signal applied while the amplifier is shutting down, there is a bit of buzzing when the supplies reach around +/-10volts. This I believe is due to the sine waves distorting while the supply voltages decrease way below the permitted operating range +/- 20volts. I don't see any high frequency oscilations. Bias is around 200 ma
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Old 7th November 2012, 11:16 AM   #1965
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Default Zener orientation

Quote:
Originally Posted by BuildMeSomething View Post


Think I found the root problem, got the Zener Diode mounted the wrong way... Then probably shorted something trying to figure out why I wasn't getting any sound...

R39/46 are shot & will replace C71/81, one or both of these went poof... and reorientate the zener. Hopefully everything else is ok...
Hi BuildMeSomething,

I think that you are the second builder to get this wrong, Is it not obvious which way to mount the diode? ie line on device to line on PCB?
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Old 7th November 2012, 11:20 AM   #1966
AndrewT is offline AndrewT  Scotland
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I got my first build right, I got my second build wrong.
It took me a while to find the low voltage across the Zener. A very long while !

Now I state an observation.

The Zener is not needed.
We need a mute that has a delay on un-mute at start up and a near instant mute at power down. The Zener prevents near instant mute at power down.

I have words that describe this design decision, but I am not allowed to use them here.
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Last edited by AndrewT; 7th November 2012 at 11:23 AM.
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Old 7th November 2012, 12:29 PM   #1967
IanAS is offline IanAS  England
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With giving it more than a few seconds thought and going though a flow diagram or looking at the circuit, etc, I suggest this possibility is investigated:

You need to fit a micro relay such that a pair of normally closed contacts would short the Zener or cap or whatever. The relay coil is joined to a suitable power rail and earth. Instant enough power up, the de-thump works with the cap and diode as normal, then the relay goes off as the power rail drops, and mutes the chip. You'd have to do it such that the relay's coil is de-energised before the rail drops to the point where noise is output.
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Old 7th November 2012, 12:33 PM   #1968
IanAS is offline IanAS  England
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I've not started to build up a pair of these amplifiers yet. I probably would have if I had the parts and was gradually building up an order with Mouser but then instead I got on with other stuff for the last few months.
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Old 7th November 2012, 01:32 PM   #1969
AndrewT is offline AndrewT  Scotland
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simply use a resistor feed to the mute pin instead of a Zener stabilised feed. It's the Zener that holds up the mute pin voltage on power down.

I would have experimented with a resistor only feed on my second PCB if I had the more correct resistor values, but my stock of smd resistors is very small in comparison to my through hole stock.
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Old 7th November 2012, 01:41 PM   #1970
opc is offline opc  Canada
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Quote:
Originally Posted by AndrewT View Post
I got my first build right, I got my second build wrong.
It took me a while to find the low voltage across the Zener. A very long while !

Now I state an observation.

The Zener is not needed.
We need a mute that has a delay on un-mute at start up and a near instant mute at power down. The Zener prevents near instant mute at power down.

I have words that describe this design decision, but I am not allowed to use them here.
Andrew:

The zener is the only reasonable way to ensure the correct current into the mute pin given that people will be running supply voltages ranging from +/-20V up to +/-90V.

If just a resistor were being used, then I would have to supply several different values and people would have to populate the correct value based on what supply voltage they are using. There is a lot more room for error with that compared to getting a diode in the right way around.

Besides all that, if you don't want the Zener, then take it out! The resistor to Vcc is still present, you just need to change the value to suite your supply. You not having the correct SMD resistor values at hand is hardly a good reason to gripe about my design decisions.

Cheers,
Owen
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