Advice on testing?

[matthewpunger]

Hi there,
i have just finished my build of the amp10B and the soldering process went quite well I think, I replaced the R5 with 360ohm instead of the 120 ohm, the input gain is 22K and the modulator resistors are 8.2k. I have a 12v walwart that i tested the 5v section and it powered up adequately. I hooked up both rails to the 12v supply (I think in series-the power goes to the positive rail and i have connect cable running from that to the negative rail - just to test (i hope that wasn't crazy)) and tested them and they both read a voltage. I haven't heard the relay click though, but thought it might be that the voltage is too low for it to function (?).

I am wondering - do people think I am ready to hook up the tranny to the amp now? I have a 20v x 300va (ATN3220) toroid, with a 5A slow blow fuse.

one other question - I was thinking of acquiring an IR relay attenuator and selector that requires a 5v power source. Can I tap the 5v section on the amp for that?

thanks for any help.

[Scratchy]

Hi Matthew.

I'm not sure the test you did with the Walwart was really a test, as the AMP requires a split AC supply.
Please check the other post in this forum - Amp10 in flames for more tips on powering up for the first time - http://www.41hz.com/Forums/topic.asp?TOPIC_ID=2166

quote:When powering up the amp for the first time, it is good practice to use a 60W light bulb in series with the primary of the transformer to prevent this kind of damage.
The fuse should be sized according to the VA rating of the transformer.
EG. 300VA/120V = 2.5A
A short circuit or overload on the secondary will cause this fuse on the primary to blow.

You don't want to use the 5V section to power anything else.
It is sized to provide only 100mA of current.
The 5V rail also needs to be kept noise free, or it will affect the sound of your amp.

-=Cheers=-

***If it was easy, everyone would be doing it***

[matthewpunger]

Thanks Scratchy, I'll work towards a proper testing situation and report back.

Another really basic question regarding grounding. I've read through the manual, but have also read that it might amp5 specific in terms of input grounds and whatnot. Can I test initially by setting the amp and transformer up on a wooden board? If so - What grounding considerations should I take: Input signal, mains ground, speaker?

I really appreciate the help,
Matt

[Scratchy]

You can bench test the amp with no problem.
Nothing on the amp is connected to ground or "earth" directly, so there are no special precautions to take, other than what I have already mentioned.
In the finished amp, the only thing connected directly to earth is the chassis.
So all you are doing is testing on an insulated surface, without the chassis.

***If it was easy, everyone would be doing it***

[matthewpunger]

Thanks Scratchy. So I've bench tested with the light bulb and fuse, everything checked out fine. I got the relay to switch on and off, the Mute LED works great; all very exciting. I hooked up a CD player and a speaker and got sound. The only problem is that I haven't been able to test the outputs properly in terms of DC draw, and can only get a reading on AC when when I test the outputs. Also, when i hook up sound and unmute the relay begins to click on and off slowly.

At the rails, the tests read around 29 volts. I have 360ohm on the R5, 8.2K on the modulator, and 22 on the input gain.

Would you have any idea of what could be triggering the relay to repeatedly switch on and off?

thanks a lot for the help,
Matt

[matthewpunger]

OK...some more tests - over J10 on the 5 volt I'm reading 5.8v, on the on the AC inputs I'm reading 24 volts (my trafo is a 3220 - so should be 20 volts). So rectified I'm reading 32 volts DC. over C150 i'm reading 30.3 volts. The rectifiers are placed correctly, and I've wired the secondaries on the trafo in mirror image to each other so that both greens go on the inside and both blues go on the outside. I've ben checking all the soldering and have been re-soldering anything that looks suspicious, but overall the soldering is fairly clean and precise.

so I'm still getting the repeated on and off on the relay switch.

would anyone have an idea as to what's going on?
thanks again,
Matt

[matthewpunger]

umm...OK sorry for all the crazy questions. I'm just a bit confused presently! So now - I've just been testing the AC inputs over a couple of minutes. It seems that the voltage slowly rises from what it should be - 20volts, to over 24 volts in about 10 minutes. at the beginning of hooking it up, everything is fine, there isn't the repetitive switching off and on, but seems to occur when the voltage rises. And when it gets up to this level the 5v regulator gets really hot! When i unplug it at this point then try again, it's up to 24.5v.It seems bizarre and dangerous to me, its like something is acting like a capacitor or a short on the trafo...

Would this have anything to do with the light bulb still being hooked up in series on the trafo?

thanks [:I],
Matt

[Scratchy]

I have only built AMP1-B, but 5.8V is too high on the 5V line.
You run the risk of frying your chip at this voltage.
It should be between 4.9 & 5.1 volts.

I believe the problem is related to the AC inputs from the Toroid.
According to this page (your model did not have a PDF)
http://www.toroid-transformer.com/AN-3222.pdf
you should wire it up as per the diagram and not mirror the wiring as you have done.
In other words, on one input blue is on the outside and the other green is on the outside.
You should have one blue and one green on each of the inside connectors.
This assumes the 2 inside connections on J4 & J5 are connected to PGND.
I have a beef with the AMP10 AI, as this is not shown anywhere.


If I had the PCB in front of me I could trace the connections and verify this myself.
Another user on this forum had the exact same issue and it would have been much easier if there was a schematic showing how J4 and J5 are connected on the board, as well as to the transformer.
The other possibility is the PGND is derived after the full-wave rectifiers, in which case this polarity would not matter?!?

Think of the output as 2 batteries in series. What you have done is reverse one battery.
If during a positive AC pulse blue is + and green is -, then you must connect the 2 center wires together so you have the positive of one coil connected to the negative of the other coil.

BTW, your voltage readings also sound odd.
A 20VAC transformer should not be at 24VAC with no load - that is very poor voltage regulation.
Check your input voltage, as this is rated 20VAC with and input of 115VAC.
If your input is 120VAC, then the rated output voltage at full load should be 20.9Vac
I would expect the no-load voltage to be no higher than 22VAC.

***If it was easy, everyone would be doing it***

[matthewpunger]

Thanks so much for the information and help. I've disconnected the 5v presently. When i had just a small 12v dc power on it, the voltage was correct, so I don't think there's a problem there. In terms of the wiring of the secondaries, I believe I read that posting and the way I interpreted was that as long as the secondaries were placed the same way for both the positive and the negative rail. So...i tried switching one rail of the AC so it was as you had said, but i still get an increasing current, but it seems to rise a bit faster like that. Just to make sure - could one wire the secondaries so that both the green would be on the + rail and both blue connected to the - rail?

[Scratchy]

quote:Just to make sure - could one wire the secondaries so that both the green would be on the + rail and both blue connected to the - rail?

Definitely not. You may short the transformer doing that.
First thing to do before anything else, PLEASE, PLEASE wire a 60w light bulb into the primary path of the transformer so you can't hurt anything in the power circuit.
Also if the light bulb stays on, you know you have a short somewhere (or are drawing way too much power). The bulb should flash very briefly and then go out.

Please see this diagram of a split power supply:


I suspect the AMP10 uses the second arrangement in this diagram, in which case the secondary coil polarity shouldn't matter.
Can anyone speak to the design of the AMP 10 rectifiers and Power Supply?
It would help so much if there was a basic schematic of the AMP10 PCB.


***If it was easy, everyone would be doing it***