power supply problem (beginners question)

[yumiyoshi]

hi,

i'm just getting my power supply ready for my amp-6. following problem: the transformer delivers 2x15VDC/4A. as recommended by the manufacturer of the transformer i mounted slow fuses, 4A, between transformer and power connector for the amp. now: when i switch on power, all fuses "go" (as we say in german). tried twice, same result, also if nothing is connected to the transformer. i mounted four fuses, one for each wire coming from the transformer, after the fuses i lead the two currencies together to get 1x15VDC/8A for amp-6 and preamp. no, i didn't short circuit anything. the currency before the fuses is always fine. i use slow fuses, not quick ones.

where's the bug? thanx @ all!



<i>don't shoot me - i'm just the piano player...</i>

[Scratchy]

First question - do you have AMP6 or AMP6-Basic.
Second point - transformers are AC, not DC.

If you have the AMP6-Basic, then you need a rectifier and capacitors.
The voltage cannot exceed 14.6 VDC for the Basic model.
15VAC when rectified will give 21.2VDC much too high for this amp.

You should be able to connect the 2x15VAC output directly to this the AMP6.
The AMP6 has a built-in rectifier, smoothing cap and voltage regulator.


***For first time power up:
Always clean PCB with ISO before applying power & use of a current limiting resistor highly recommended***

quote:Its easy to ask questions but please try to be constructive

[yumiyoshi]

my amp is an amp-6. yes, you're right, transformers deliver ac (of course), this was a very embarrassing translation mistake and not a lack of basic knowledge. sorry for that.

to specify the problem:

my transformer has two secondary windings (sec A and sec B) which deliver 15VAC/4A each. the wires of sec A are red and black, those of sec B yellow and orange. so i connected red and orange, and black and yellow, to get a single 15VAC/8A currency. double-checked the connection, nothing wrong (means: no, i didn't short circuit the secondary windings...).

the transformer powers both the amp-6 and a preamp. for the preamp i built a stabilization, which i tested with the transformer (both secondary windings connected as described above), everything fine.

now i built everything together into the case, and when i switch on power, it blows all my fuses. tried it first with the stabilization connected to the transformer, and then a second time with nothing connected to the transformer. same result. double-checked all conections, no short circuit anywhere. double-checked the fuses, yes, 4A, yes, slow ones. so what the heck is wrong?? i really would not like to operate the amplifier without or with too high rated fuses...


don't shoot me - i'm just the piano player...

[krilli]

That's kinda odd. Just out of curiosity, I don't know if this will net you much, have you measured the impedance at the power input of the amp? Just to see if there's a short.

Do you have a small 12V supply anywhere? To use for testing? 500mA should be enough.

[yumiyoshi]

i haven't donnected the amp to the power supply yet. wanted to know if there's everything ok with the power supply first since i experienced murphy's law often enough. and - the fuses blew also when nothing was conected to the transformer...

maybe i'll have a closer look at the transformer if it delivers more currency than rated...!!??





don't shoot me - i'm just the piano player...

[krilli]

Ah! If it hasn't been connected at all, no current should flow and nothing should blow. If I understand everything correctly here, there's definitely a short somewhere. Do you have it mounted to anything?

Are the fuses blowing on the primary side or secondary?

[yumiyoshi]

quote:Originally posted by krilli

If I understand everything correctly here, there's definitely a short somewhere. Do you have it mounted to anything?

yes, there SHOULD be a short somewhere. but where? the shematic looks like the following:



there's no short between sec1 and sec2 before the fuses, and no short between the wires after the fuses. the fuse holders are mounted on a piece of plywood with about 4mm airspace between connectors and case. everything on the safe side.

quote:Are the fuses blowing on the primary side or secondary?

secondary.



don't shoot me - i'm just the piano player...

[krilli]

Well, I'm pretty sure you've double-checked all the connections you did. ... I'd start being suspicious of the transformer.

[yumiyoshi]

quote:Originally posted by krilli

Well, I'm pretty sure you've double-checked all the connections you did. ... I'd start being suspicious of the transformer.

you pointed into the right direction. but it was no fault of the tranformer. got a hint in another forum. the problem was: i led the two AC currencies togehter with the wrong polarity. changed the polarity of one secondary winding, now everything's fine. always the same: strange faults are always caused by very simple mistakes. often too simple to think of them...

thanks@all for your quick responses and your wilingness to help!



don't shoot me - i'm just the piano player...

[krilli]

Good luck in completing and enjoy the amp!