Complete newbie but I did it!

[Niiico]

Hi,

I ordered an AMP6 and I'm building it with the most carefull attention since I'm a complete newbie in electronics (but I don't like to be told I'm not able to do something )

This is even more difficult to me because I work only with 45 min sessions, 2 times a week.

The first thing I'll remember is : do not buy unleaded silver (4%) solder! It is even more difficult to solder because of the higher melting point! But that's all that I have, so...

First step, 2 weeks ago:

It was not yet finished, but it passed the onboard power supply test : I got 21.5 V between C99 leads and 14.61 V between C1819 leads. Hurra !

Since this is the first time I was doing this kind of stuff (I already made my speakers, you can see them here (http://blog.niiico.org/index.php?200...e-paire-de-217). The text is in french, photos are international ! ), I was very happy with this first result.

Here is the test board: http://blog.niiico.org/images/Hifi/P1020577.JPG

You can see the 39 KOhm resistor in place between C1819 leads for the power supply test: http://blog.niiico.org/images/Hifi/P1020579.JPG

Some details on the unfinished board:
http://blog.niiico.org/images/Hifi/P1020581.JPG
http://blog.niiico.org/images/Hifi/P1020589.JPG

I had next to solder the chip on the board...

Second step: yesterday!

my AMP6 is now functionnaly finished (I mean... it has no box today but it works ).

Let me tell you...

Last week, I have soldered the chipset and the caps within its legs without any problem. I had just some problems to identifiy the polarity of the diodes and ran out of time to finish it.

http://blog.niiico.org/images/Hifi/A...020592-web.jpg
http://blog.niiico.org/images/Hifi/A...020595-web.jpg

This was last week. As you can see, the FETs that drive the leds are in the orientation written on the PCB...

This week, Jan explained that the FETs had to be reversed... As a complete beginner, it took me 45 min at least and one of them is now, how to say... short!

But I did it. I connected also some temporary wires to test it for the first time...
http://blog.niiico.org/images/Hifi/A...030028-web.jpg
You can see the "shorter" FET...

So... Before to connect anything to the amp, i had to test it doesn't burn when plugged and turned on. [:P]

I put a 200mA fuse (as Jan advices it), put the amp in sleep mode and plugged it. No smoke, nothing weird. How is the fuse? Burned! $£*# !!

I checked everything twice, put a new 200mA fuse and tested again, watching the fuse while plugging the amp in. Instantaneously burned.

Re-check, re- new fuse, re- plug, re- $£*# !!

Everything looked fine, so I decided to put the final 2 mA fuse instead of the 200mA, ready to unplug the amp if it burned in smoke...

Looking at the fuse while I plugged, I noticed that the wire inside it "bent" a second but stayed in one piece. Nothing seems to be burning or becoming instantaneously hot, I woke up the amp and the green light went on. Ha haaaa, was I on the right way?

I think that the 200mA fuse burned because of the caps asking energy too fast... I hope it is that!

I measured 16mV and -54mv offsets (I don't understand why one is negative...). Looks correct.

Unplug, plug an Ipod, plug some small loudspeakers (my future surrounds), amp on...

Hurra! It plays music!

Here is a view of my "workshop", dedicated, as you can see, to my electronics experiences...
http://blog.niiico.org/images/Hifi/A...030031-web.jpg

It's time now to find a box, to wire it with the right cables and then to add a stiffener cap as suggested by panomaniac. But I think there is already some good power inside the caps: it takes about 5 seconds to the music to stop after unplugging the amp!

BTW, when I turn off the amp, at the end of the 5s music, the red led lights on about 1 second and then goes off. Why is the red led going on at the end?

You can't imagine how happy I was to make this work at the first attempt!

[Niiico]

I meant a 2A fuse, not 2mA

[Niiico]

Nobody to tell me if something wrong can lead to one positive and one negative offset? (if not, I must have make a mistake with my multimeter)

And why the 200mA fuse blows while testing?

The amp seems to be perfectly working but I'd like to understand those mysteries

[Niiico]

I meant a 2A fuse, not 2mA

[Niiico]

Nobody to tell me if something wrong can lead to one positive and one negative offset? (if not, I must have make a mistake with my multimeter)

And why the 200mA fuse blows while testing?

The amp seems to be perfectly working but I'd like to understand those mysteries

[ChrisM]

I can't explain + or - offset in this amp but in the gainclone setup its to do with manufacturing tolerences on the chip around the input offset which is them multiplied by the gain of the amp. Don't worry, mine is + and - also as are my gainclones!

Are u using slow or fast blow fuses? I found to my cost that fuses should be slow-blow to allow for the initial inrush of current at switch on - charges up the psup caps.

Chris

[Niiico]

Thanks for your explaination.

Jan also aswered in the support area, saying the offset can be both positive and negative, as you said.

My fuse is a slow blow and it seems that with medium and big transformer, 200mA isn't enough for the inrush of current. Jan told also that with my 80VA 15V transformer, I should use 5A better than 2A which my blow at higher levels.

Niiico

[Niiico]

Hi,

it has been a long time.

Since I still don't know if I'll use the AMP6 in an HC system or just in Hifi, I finally put the whole stuff in a paperboard box to test it in the Hifi part... Not very "safe" but sufficient to test it.

I still have my 2A fuse, but it seems to be ok (it becomes red in a flash when I turn on the amp, but it doesn't blow...).

I've added a stiffener cap (10000µF) and the speaker wires are made with 2 teflon 1mm diameter "silvered copper" wired together.
I use the same cable for the input, but I think I will use shielded cable in the final version.

Here is one picture : http://blog.niiico.org/images/Hifi/A...030865-web.JPG

So how does it sound ? Fan-tas-tic ! I re-discovered my speakers : the bass are dry as I like and it is well more precise and defined than my Atoll AV500 (I use the AMP6 with my Atoll PR 5.1 pre-amp).
I'm sure the stiffener cap help a lot for the basses...


I have only one concern : when I turn on the amp, I hear a little "cloc" in the medium...

Jan, is it possible to add some relays circuit somewhere to avoid this "cloc"?

Niiico

[Jan]

Hi,

There are basically two ways to avoid turn-on thumps.

- Delay the un-mutig until everything is stably up.
- Delay the speaker outputs by shutting them off with a relay similarly.

The very simplest way is to have the habit of always muting the amp with the murte switch before power-off and unmuting after power on.

A voltage sensing circuit with delay, could do something silmilar.
An MCP101 supervisor for 4.85V in TO-92 package would probably be the simplest. It has three leads; +5V, ground and output. The output is high until the +5V is above 4.75V and then after a time delay of 300 mS the output goes low. Bu wiring this to the MUTE, you get an un-mute when the +5V voltage has more or less stabilized.

The LEDs are driven by FETs (transistors) that are capable of 200 mA current. A 12V relay for speaker outputs would need about 30-40 mA so by changing the resistors that limits the current to the green LED and instead using that signal for a relay coil would be possible.

[Niiico]

Thanks, Jan, for the explaination.

I usually use the first method, but I alwas get a little "snap" or "cloc" (whatever...) even after waiting some time before to unmute.

But I'm still not sure to keep the AMP6 or to go an an AMP4.

For Hifi use, the AMP6 is perfect for me. But in HC, it lacks sometimes a little power and I wonder if the AMP4 with 20V or 24V rail (my speakers are 4 Ohms, see my thread in the AMP4 forum) couldn't be a better choice for me.