Questions regarding the AMP6-BASIC

[Petter]

Hello

I'm helping a friend of mine putting together the AMP6-BASIC, and I've come across a few issues and have questions.

1. In bag no. 2 the resistors R5 and R6 are suppose to be 56 Kohm, but looking at the color code, the ones provided seem to be 82 Kohm (grey-red-black-red-brown). I don't have any equipment for measuring resistance available so I cant say for sure, but this can't be good right? Bag no. 1 includes two extra 22.1 Kohm resistors which can be used for setting the gain to -1 V/V, but I think the amp will be used with an IPod so the -2.5 V/V gain would be desirable.

2. How do I tell the polarity of the diode D1 (the one that provides polarity protection for the power supply connection)? In other words, which end of the diode is plus and which is minus?

3. Looking at the PCB, the end of D1 which is connected to the fuse holder should be plus. Is that correct?

4. According to the instructions the sleep/mute jumper or whatever it is, has two pins. But it actually has four. I've searched the forums and it appears that this is a question of different revisions of the board. But I'm confused. Can someone explain exactly what these jumpers do and if they should be in place or not when the amp is in use?

5. The two jumper connection pins closest to the edge of the board seem to be connected to ground so I'm guessing the jumpers, if in place, should be placed perpendicular to the closest edge of the board. Is that correct?


Best Regards
Petter

[krilli]

Wish I could help with all of it, but:

Re. 2) - you should be able to see some kind of marking on the diode ... it's hard to see on some diodes, but there should be some kind of sloped edge or a slight linelike mark on one end - and IIRC in the Amp6-B the board position should be marked on one side too

This also kind of answers 3) --- that is to say, I've always just oriented my diodes according to the markings, never really being sure about + / -

[hybridfiat]

4. As I understand it the first 2 pins are Awake when bridged and Sleep when when unbridged.
The 2nd 2 are mute when unbridged and unmuted when bridged.
So to sum up the amp will work when both sets of pins are bridged.

5. Yes the little black bridge caps are fitted perpendicular to the edge.

Entia non sunt multiplicanda praeter nessitatum

[Saturnus]

1. 82K Ohm feedback resistors are optimal for iPod use. I think Jan changed it to be standard because so many uses iPods. The old 56K Ohm was optimal for higher output mp3 players and older versions of iPods, prior to the EU restrictions on maximum output.

2. A diode only show the negative side, in this case with a dip in one end.

3. Follow the markings on the PCB but yes, the negative side should be away from the fuseholder.

4. If there's 4 pins, it's rev 1.10. And there's actually only one jumper, and that's the mute jumper ... there's no sleep jumper on any version of the amp6basic. The other pin set is for the fault LED.

5. Yes, but note that only one set of these pins are jumpers. If the fault LED is not used, it should be left open.

[Scratchy]

My suggestion is you get yourself a basic Digital Multimeter (DMM) to assist in building and testing this amp.
It can be done without one, but only if you are experienced in working with electronics.
There are several sections in the Assembly instructions which require some type of electrical measuring device such as a DMM.
Please see the Tek Doc Wiki for basic tools required to build one of these amps:
http://wiki.41hz.com/Tools.ashx

***It's so easy, everyone should be doing it***

[Petter]

Thanks guys! That helps a lot. I've a few follow-up questions.

1. So J2 has four pins. Two of them are the mute jumper. They should be bridged when the amp is in use. Is that correct? Two of them can be connected to a fault indicating LED and should be left open if a LED is not installed. How do I tell which of the pins that are the mute jumper and which of them that can be connected to the LED?

2. There're no possible polarity issues regarding the capacitors C12, C13, C22, C25, C27 and C28 (because theyre not electrolytic capacitors) or regarding the inductors L1 and L2 right?

3. Are there any other crucial differences between the revisions of the amp?

[Saturnus]

1. the two pins closest to the chip is the mute pins (note: I'm not 100% sure about that but I am 100% sure that the amp will not take damage if you jumper the wrong ones so it's trial-n-error without risk).

2. Correct

3. Not that I know of

[Petter]

Ah, okay.

Cheers!

[Petter]

Hello again.

I've put the AMP together now using the 82 kohm feedback resistors, but it doesn't work properly. I connected it to two 4 ohm, 35 W (max 150 W) speakers, the sound source was an Ipod Touch and the power source a 12 V sealed lead-acid battery.

I got sound from the speakers but after a little while they (the speakers) started to smell of burnt electronics and there was a faint trail of smoke coming from them. After that I tried the speakers one at the time, and also switching their polarity. It seem like it works when the polarity of the speakers is switched, but it doesn't sound too good and occasionally there're horrible whining and clicking noises coming from the speakers. When the speakers are connected with proper polarity these noises gets worse.

Another peculiarity is that the jumper(s) does absolutely nothing. Connected or not, it still plays.

So what's going on here? The speakers survived the treatment (tested with another AMP) so it's nothing wrong with them. I have at least double checked that everything is properly soldered. Could this be related to the feedback resistors in any way?

[V-bro]

What DC voltage do you measure across the speaker outputs?

------X-max. can be several meters on any driver, too bad it can be done only once...------