"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets - Page 226 - diyAudio
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Old 5th February 2014, 03:01 PM   #2251
opc is offline opc  Canada
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Yikes! Not good...

Did everything else survive?

I suppose it certainly is best to swap the pots for actual resistors once you've found the level, but I've never personally experienced this issue.

Alternatively, the resistors around the pot could possibly be adjusted to provide a "fail safe" level, but this will vary depending on the implementation.

Let me know how the fix goes... hopefully everything else is alright.

Are you using the pots from the BOM? If not, what make/type/value are they?

Cheers,
Owen
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Old 5th February 2014, 07:36 PM   #2252
Mark Kravchenko --- www.kravchenko-audio.com
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A good thing you caught it when you did!

A better thing you knew exactly what the problem was.
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Old 6th February 2014, 08:36 AM   #2253
AndrewT is offline AndrewT  Scotland
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Temperature switch on the heatsink to switch off on overtemp.

DC detection and some form of isolation to protect the speaker?
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Old 6th February 2014, 10:12 AM   #2254
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I have a schematic drawn that should:

Allow input from SMPS to switch from low bias current during SMPS start up then some delay with 555 timer before switching to 'full bias' current that is based on current heat sink temperature.

Have two operating bias settings based on temperature (summer/winter or similar) using a daughter PCB that mounts in the position of the pot that has 3 resistors and 2 smd relays.

Overtemp shutdown

Momentary switch to control SMPS on/off or SSR power control.

Momentary switch for mute

A few other things I've forgotten.

When I looked at it last (12months ago or something probably) I had trouble working out a PCB layout it was the first layout I'd ever looked at seriously and there was a lot of interconnected devices trying to work on a 2 layer PCB and it was too much for me at the time. I could revive it if it would be useful for a few 'The Wire' builders? I'd want to do some thorough testing of it before sending out PCBs though. At the moment it's just TTL logic and comparators. I could convert it to be a mix of logic ICs and an arduino that would make the PCB design simpler.



Thoughts?

Cheers,
Chris
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Old 6th February 2014, 10:42 AM   #2255
opc is offline opc  Canada
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Quote:
Originally Posted by AndrewT View Post
Temperature switch on the heatsink to switch off on overtemp.
Very good idea. Easy to implement and a decent safeguard.

Quote:
Originally Posted by AndrewT View Post
DC detection and some form of isolation to protect the speaker?
Any suggestions that don't involve a relay?
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Old 6th February 2014, 11:39 AM   #2256
AndrewT is offline AndrewT  Scotland
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A few Recent Threads on using fast acting solid state relays assembled from appropriate devices that do not interfere with sound quality.

Some locations offer different types of protection.
In the SPKR output
In the SPKR Return
In the Supply rails
Across the speaker to audio ground.

All of these can be "add ons" not on the amp PCB.
But many would suit smd on the PCB and still retain the compactness you have achieved.

A suggestion if you do design an "all protected PCB" :
add space for more air circulation around the driver heatsink, including getting the capacitors away from the hot surfaces.
Or even better: a bigger heatsink for the higher supply voltage Builders.
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Last edited by AndrewT; 6th February 2014 at 11:43 AM.
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Old 6th February 2014, 12:33 PM   #2257
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Quote:
Originally Posted by hochopeper View Post
Have two operating bias settings based on temperature (summer/winter or similar) using a daughter PCB that mounts in the position of the pot that has 3 resistors and 2 smd relays.


Thoughts?

Cheers,
Chris
Why not control the bias with an optocoupler?
Short one resistor from the bias circuit with that to allow a lower bias setting?
Makes the bias circuit nice and compact compared to relays and stuff?
Could also make the bias adjustable by varying the opto led brightness???
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Old 6th February 2014, 03:19 PM   #2258
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Nothing else appeares to be damaged. Once the bias current was set to 145ma, I left it powered on for > 24hours and checked every few hours and it was steady. The amplifier is back in the living room and lets say I shook some of the dust off the speakers with Led Zepplin, Hendrix and Emmerson Lake and Palmer. Everything appears to be fine.

Yes the pot was from the BOM.

There is speaker relay DC protection.

There are fuses for the amplifier boards and a line fuse if things go real south.

I must have adjusted thousands of multi turn trim pots over the years and I don't recall ever having to do a board replacement because of a multi turn trim pot going bad. Single turn pots, yes
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Old 7th February 2014, 02:46 AM   #2259
Mark Kravchenko --- www.kravchenko-audio.com
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Takes a likin and keeps on tickin.

Sweet!
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Old 9th February 2014, 09:12 AM   #2260
manudrz is offline manudrz  France
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Hi all, I'm reading this interesting thread.
I already have a large number of pieces, 2 transfos (200VA/35V), 2 unreg power supplies (≈+/-50V), source selection board, soft-start, heat-sinks ...
I wanted to build 2 SKA amps in dual mono, but finally I think I'll go with The Wire.

1) I add myself to the GB list and OPC contact me for the payment?

I'd like to see more wiring diagrams, rookie inside, 1st amp build

I also have a question, my relay based source selection board is designed in dual mono, no problem, but I would add a volume control Dantimax RelVol1C RelVol1 & 3

2) Can I keep my separate signal masses (dual mono) with this volume board control?

3) For the attenuator resistors, 20K value is ok?

Thanks a lot guys
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