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 )

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 )

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

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?

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. :)

Excellent! :)

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

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)

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

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.

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