[runeight]

This is the most likely problem, but if the LEDS still don't light under normal operation then crank up the current until they do.

 

[Scooba]

Alex, my leds light up only when I am increasing the current then they fade out, or if I am ventilating the heatsinks

.

T1-T2 = 360mV ; T1->342V ; V+ = 300V
T3-T4 = 420mV ; T3 -> -342V ; V- = -298V

Is this normal ?

 

[Beefy]

Quote:

Originally Posted by Scooba /img/forum/go_quote.gif Alex, my leds light up only when I am increasing the current then they fade out, or if I am ventilating the heatsinks . T1-T2 = 360mV ; T1->342V ; V+ = 300V T3-T4 = 420mV ; T3 -> -342V ; V- = -298V Is this normal ?

As the amp heats up, the current drops. Re-check it when hot, and you will find the current much lower than those initial readings you posted.

 

[runeight]

Quote:

Originally Posted by Scooba /img/forum/go_quote.gif Alex, my leds light up only when I am increasing the current then they fade out, or if I am ventilating the heatsinks . T1-T2 = 360mV ; T1->342V ; V+ = 300V T3-T4 = 420mV ; T3 -> -342V ; V- = -298V Is this normal ?

So if you increase the T1/T2 and T3/T4 voltages your LEDs will not stay lit no matter what?? If this is true then there is something wrong in the PS somewhere. If the shunt transistors are conducting the LEDs must also pass the shunt current and it hardly takes any current to light them.

If the LEDs will not light up at all (or light and then fade no matter what you d) then the primary shunt devices are not active and this means that something is not right.

Can you verify exactly the behavior. Thanks.

 

[Scooba]

Unfortunately my local time is PST + 10 hours (I wrote post #2791 at 2:11 local time , and went straight to bed after that) .

The LEDs faded out quite quickly after the increase of the current .
The values I posted were taken after ~10 minutes.

@Beefy: I'll let it run more time and see how it stabilizes. The PS load was the dummy one (10k on the + rail, 10k +51k on the - rail) .


Edit: I increased the current, and the LEDs stay lit now. I have +/- 303V on the load.
T1-T2 = 375 mV , T3-T4 = 445 mV .

 

[runeight]

Then you're probably ok. Your particular amp may draw slightly more current than the normal. You don't need to have the LEDS super bright but just to the point where they turn bright. Your current measurements, are really not bad.

 

[Scooba]

Thanks for the info. I was wondering how bright they should be ...
Incidentally, this is how I adjusted them: just below the point where they turn bright .

 

[Beefy]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Then you're probably ok. Your particular amp may draw slightly more current than the normal. You don't need to have the LEDS super bright but just to the point where they turn bright. Your current measurements, are really not bad.

That is a big difference to mine. As noted above, when fully warmed up my PSU is putting out 32/38mA, and the LEDs are still nice and bright. That is a whole 5-6mA less than scooba, or 20-25%!

Which part differences/tolerances could result in such a big discrepancy? I must admit, I still don't fully understand how the current mirror works......

 

[paxeaxe23]

OK. I'll check and see if the LED's are in the right orientation, then if they still don't light up we will crank up the current as suggested and see what happens then. Its such a nice day here in Germany (21°C and sunny!) so I may delay tests till later,but thanks for the advice everyone.

 

[paxeaxe23]

OK, as suspected I did have the LED's in the wrong way. The Boards are now wired up provisionally in my case and I'll get a photo up tomorrow if the weather is not as nice as today!

 

[Beefy]

Good to hear!

 

[Scooba]

Today I've just got the time to disconnect the dummy load and connect the amp boards. Everything went smooth . I managed to adjust the offsets - it is ok , too. Unfortunately I did not had the time to connect the headphones (I have to improvise a female STAX connector using socket pins, until the ones from Marc will arrive) . Quite frustrating being so close: everything is ready and running fine but missing a damn connector. Anyway, tomorrow I'll be listening to it for sure, no matter what

.

Edit:
I've managed to listen to it today.
With the amp heated, I have: T1-T2 = 368mV, T3-T4 = 432mV .

For the moment all I can say is that it is very promising. I've used an Edirol UA1-EX as source, and a pair of SR-303 for the preliminary test. I won't say anything about the sound yet, except that I think that it has great potential.
I'll post impressions after I'll take it home, and test it with EmmLabs DCC2 and SR-404 Limited.

 

[audionut]

Anyone know of another source for the P-Channel PS mosfets 512-FQP3P50? Mouser is out of them until sometime in June. Digikey no go, too. Thanks for any info.

Tommy

 

[pabbi1]

N/m - no stock at Arrow either

 

[ericj]

Looks like Farnell UK may be the only distributor with stock.

Newark will get you some from there, for just $20.