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avr300  
#41 Posted : Sunday, October 10, 2010 2:32:27 AM(UTC)
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Next theory - it's heat related and the noise comes from the resistors R1-R4, R20-R21, R23-R24.

Streamerzone, you have changed all the active component and a bunch of capacitors, right ?

I'll let it burn now, cooled by a fan and I'll report back.

Just for the record, I have mounted the BII but its unpowered, just to rule out that factor.



(Come on - it's less than 20 components, how hard can it be d'oh!)



Steamerzone  
#42 Posted : Sunday, October 10, 2010 5:36:43 AM(UTC)
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I've replaced all but the power resistors, I didn't have those handy. (even replaced the trimmer)

All active parts excluding the opamp, all capasitors excluding C5-C8.


I get the most interesting sounds when it is warming up...

Edited by user Sunday, October 10, 2010 5:39:39 AM(UTC)  | Reason: Not specified

avr300  
#43 Posted : Sunday, October 10, 2010 8:12:57 AM(UTC)
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I can't judge whether it heat dependent or not. I might think it is, but it's too difficult to say.

Then I'll order power resistors in the morning. The only once which comes in handy is 180R and 390R, 1.6W metal film.

It better be those.... (or we have to change the coupling caps, that's the last chance, unless it is American noise trapped inside the PCB itself Whistle )

Edited by user Sunday, October 10, 2010 10:02:04 AM(UTC)  | Reason: Not specified

avr300  
#44 Posted : Tuesday, October 12, 2010 10:34:17 AM(UTC)
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Update time....

I think I found it. Change those power resistors and you're back in business.

My current draw has also settled again, to around 160mA in each rail making me able to burn just 260mA in the shunt. Much more comfortable with this.

The faulty resistors measures correctly when unplugged.

So - was it oscillation ? The increased current draw could indicate it.

Russ White  
#45 Posted : Tuesday, October 12, 2010 1:12:50 PM(UTC)
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Current is purely limited by the resistors for the I/V stage. The only thing that could possibly have been drawing more power would be the opamp.

Were you using stock resistors?
Russ White  
#46 Posted : Tuesday, October 12, 2010 1:16:27 PM(UTC)
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As for the placid HS, it is clearly spelled out in the manual that heatsinks will need to be chosen for the application. The ones that come in the kit are ok, but will run hot when used for legato, but still within specs for the transistors.
Russ White  
#47 Posted : Tuesday, October 12, 2010 1:22:14 PM(UTC)
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AVR300 based on the fact that only changing a resistor fixed your issue, that there may well have been a cold solder joint or something similar. Maybe even damage to the resistor itself. It impossible for me to say. The resistors are actually not terribly critical. You might try switching filter cap end from GND to VCC just to see if you get better results with one configuration over the other.

I have never seen this happen personally. I am trying to learn from what happened to you, but I am very short on clues at the moment. :)
avr300  
#48 Posted : Tuesday, October 12, 2010 11:09:00 PM(UTC)
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Russ White wrote:
Current is purely limited by the resistors for the I/V stage. The only thing that could possibly have been drawing more power would be the opamp.

Were you using stock resistors?


Yes. Absolutly stock.

Or a resistor that behaves wiered when warmed up.

Anyway, I'm very happy again.

Edited by user Tuesday, October 12, 2010 11:11:27 PM(UTC)  | Reason: Not specified

Russ White  
#49 Posted : Wednesday, October 13, 2010 5:22:01 AM(UTC)
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Excellent! :)
avr300  
#50 Posted : Friday, October 15, 2010 11:41:10 AM(UTC)
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It's still running - perfectly.

And it's now running with 2 parallel fet's. I think I like it.


Streamerzone, have you managed to cure your Legato problem ?
Steamerzone  
#51 Posted : Saturday, October 16, 2010 3:26:06 AM(UTC)
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I haven't cured the problem yet, I'll order some new power resistors on monday, I'll have them the next day.

I'll report back, keeping my fingers crossed, at the moment when warming up, I get sounds from the right speaker like there are some mice living in there...and running around. :-/

Emile
avr300  
#52 Posted : Saturday, October 23, 2010 5:38:56 AM(UTC)
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What's up Streamerzone. Are you back in business ?
Steamerzone  
#53 Posted : Monday, October 25, 2010 11:23:48 AM(UTC)
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Sadly I haven't recieved the correct resistors yet. Have to order them overseas with mouser.

To keep the s&h costs down I'll tag along with a company order, but that takes a little bit more time.

You're strange sound havent returned? (modified my legato with 3 paralelled fets)
avr300  
#54 Posted : Monday, October 25, 2010 11:52:24 AM(UTC)
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Mine is still running.

Keep a track on this: http://www.diyaudio.com/...o-tweakers-thread-7.html
Steamerzone  
#55 Posted : Tuesday, October 26, 2010 12:22:00 PM(UTC)
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Hello Avr300,

Wasn't aware of the thread on diy, thanks for that.

As I said i'm currently running 3 fets, and apart from the mice that are running around in one speaker it sounds pretty good to me.

Settings:
Powersupply +14,5 and -14,5 volts
Placid 'extra' current 100ma
Voltage at output around 7,3 volts

Changing back and forth between 3 and 1 fet isn't exactly easy, so I havent made my mind up about what I like better. But I do think the legato design responds greatly to (little) modifications....but not to sure if they all are in the right direction. :-)

Emile
avr300  
#56 Posted : Friday, November 18, 2011 4:56:41 PM(UTC)
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Waking up this old treat again.

The same issue has happened to my Legato 3.1.

After has been running perfectly since the 3.1 became available, the other day it began to crack/phiffss/pop. Tonight I replaced R9-R16 with 4 x 330ohm (yes, only 4 pieces, placed at R10-R11-R14-R15) and it's now running again.

I might say, I'm running it in a well vented box. There's no heat build up inside the enclosure.

Russ, you should consider the lack of thermal stability on those Dale resistors.
Russ White  
#57 Posted : Saturday, November 19, 2011 7:52:49 PM(UTC)
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I am not sure what you mean because I have never seen anything like this occur. The resistors are well within their rating with a rather large margin. I would be careful about cause and effect.

I don't know what may be causing your issues, but I don't believe it is the resistors. I can't say I have ever seen anything like it in legatos that have been running more than a year.
avr300  
#58 Posted : Sunday, November 20, 2011 2:17:59 AM(UTC)
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I can only conclude based on my findings. Now I have changed the resistors and the problem is gone, I must conclude that they were the origin of error.

I know they are within rating, so whether it is due to heat I'll let it up to the reader to decide. They were far from touchable when running (and still is).

My conclusion, last time and now: I don't believe it the resistors, I'm convinced it is ;-)

Have a nice Sunday.

Edited by user Sunday, November 20, 2011 2:49:40 AM(UTC)  | Reason: Not specified

Russ White  
#59 Posted : Sunday, November 20, 2011 6:49:55 PM(UTC)
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If you are convinced you should take your reliability argument up with Vishay/Dale. The resistors should in no way come anything close to exceeding their rating regarding either heat or power. Too hot to touch is not too hot. 65C is hot to the touch, but definitely not worrisome. But honestly, I just checked a stock L3.1 running 15V rails and the Rs while quite warm measure only about 58C. I would not be surprised if they run a bit hotter, but not much. :) At that temp they have another 100C or so to the absolute max temp of 175C. So we could easily double my measured 58C temperature before they are in any danger at all. And these are very good resistors designed to take the power - so unless Dale is misrepresenting what they can handle one should feel quite confident when running them in the Legato. :)

If you have some reason to believe (data) that they are out of spec I am would be glad to learn of it.

As I said, having run a half dozen legatos for many many *many* hours I have never had a resistor "fail". And if anybody can break something I can. I drive these things very hard. :D

All of this is not to argue, but to explain that they are extremely far from the edges of safe use.

I am simply glad your situation has improved for whatever reason. That is the most important thing.

Cheers!
Russ

Edited by user Sunday, November 20, 2011 6:56:39 PM(UTC)  | Reason: Not specified

avr300  
#60 Posted : Monday, November 21, 2011 11:38:09 AM(UTC)
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I just a customer with a former problem. I have fixed it.
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