By the way, when I mentioned in post 1840 that the current should drop to zero, I meant in the output stages only - you will still pull current in the front end and TIS stage
Thanks Bonsai..
The Zobel is connected correctly, verified this. I will focus on fixing one board first.
The voltage at output w.r.t ground is -11mv.
Taken out R20 completely and when i measure current across POS fuse, its about 0.7A to start with and raising quickly all the way to 1.15A in about 2 mins. Its sort of hovering around 1.19A levels. Tested this for about 15 mins.
Across R24 and R25 its 350mv.
If its useful info, R30, R31 are 15 ohms as indicated on pcb.
One more observation: After taking R20 (its floating), adjusting R6 is increasing the current.. is this expected ... If i take out R20 does not it also take out R6 out of circuit??
Please advise..
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Hi, can anyone tell me where I can obtain KSC3503 and KSA1381 with the same suffix for HFE in the UK.
I can get KSC3503D and KSA1381E easily but cannot find pairs with the same Hfe band. Bonsai has mentioned that they should be the same,
Any ideas please.
Alan
I can get KSC3503D and KSA1381E easily but cannot find pairs with the same Hfe band. Bonsai has mentioned that they should be the same,
Any ideas please.
Alan
Pick you highest D grade and mix it with your lowest E grade.
When I bought my E grades I did not get much overlap in hFE and had to settle for quite a big differential in hFE across the pair.
When I bought my E grades I did not get much overlap in hFE and had to settle for quite a big differential in hFE across the pair.
Thanks Andrew T, if the matching of these drivers is not too good, what could be the resultant problems?
Alan
Alan
the biggest effect is that the current drawn from the VAS is not the same as the current injected into the VAS.
This can increase, or decrease, the VAS current from the design value. If the hFE error is very big, then the VAS current can end up being very low and you lose the output current capability.
Here are some good equivalents you can use:-
use KSA1142Y in place of KSA1381
use KSC2682 in place of KSC3503
use KSA1142Y in place of KSA1381
use KSC2682 in place of KSC3503
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A few weeks ago Mouser had them - I see they are marked as obsolete now.
A lot of leaded transistors are going 'end of life' - TO92, TO126 etc.
Looks like we are going to have to get used to using SOT223.
I will look around and see if there are some other devices that can be used.
A lot of leaded transistors are going 'end of life' - TO92, TO126 etc.
Looks like we are going to have to get used to using SOT223.
I will look around and see if there are some other devices that can be used.
Sot 223 is a big smd,easy mount with an adapter even to an existing board.
BTW now it's time for smd designing.
Thimios, I don't even think you need an adaptor for SOT223 - its very easy to place (maybe easier than TO126!)
hello, everyone!
i have built the nx-amp few days ago and today i got the chance to test it. i was very exited because i gave a lot of effort on buying the correct parts and not making any compromise... but unfortunately it didn't go well... :/
i bought the original pcbs, the parts were mainly from mouser, only transistors were from ebay, the output ones were matched, others no.
first power up went ok, adjusted the current to 300ma with no issue, emitter voltages were ok, ~40mv...
but when i tried to adjust the offset i encountered a big problem - minimum value is more than 2v and i cannot reduce it, no way.
the amp heats up i would say normally, there is no excessive temp from any of the components...
only difference to the original specifications is the trafo which is 35v so i get 50v on the rails, but that should make no difference for the offset, right?
is it possible that i got this problem because i didn't match any small transistor? but i at least followed closely the gain grades, they match the board markings...
any idea what could have gone wrong?
i have built the nx-amp few days ago and today i got the chance to test it. i was very exited because i gave a lot of effort on buying the correct parts and not making any compromise... but unfortunately it didn't go well... :/
i bought the original pcbs, the parts were mainly from mouser, only transistors were from ebay, the output ones were matched, others no.
first power up went ok, adjusted the current to 300ma with no issue, emitter voltages were ok, ~40mv...
but when i tried to adjust the offset i encountered a big problem - minimum value is more than 2v and i cannot reduce it, no way.
the amp heats up i would say normally, there is no excessive temp from any of the components...
only difference to the original specifications is the trafo which is 35v so i get 50v on the rails, but that should make no difference for the offset, right?
is it possible that i got this problem because i didn't match any small transistor? but i at least followed closely the gain grades, they match the board markings...
any idea what could have gone wrong?
With 2Vdc of output offset the DC detect should have triggered turning off the SS relay.
It is off? Both relays go to OFF when either channel has an excessive offset.
It is off? Both relays go to OFF when either channel has an excessive offset.
yeah yeah, it goes off, detection is ok, i forgot to mention that, but anyway i continued testing with only +0- connected... like mentioned in the manual...
EDIT: i'm sorry, i noticed a mistake now. it seems that i followed the photo from the manual instead of the board layout when installing C6, i made the same mistake as one user few pages ago, i was just browsing and noticed the same problem with my board... no time now to correct it, will try later and come back with the results!
EDIT: i'm sorry, i noticed a mistake now. it seems that i followed the photo from the manual instead of the board layout when installing C6, i made the same mistake as one user few pages ago, i was just browsing and noticed the same problem with my board... no time now to correct it, will try later and come back with the results!
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