Relay fluttering

[nightfire]

Hey everyone.

I successfully built my Amp5 and I've been using it for a day now. It sounds absolutely *excellent*. I'm very happy.

One thing though, every once in a while my relay starts fluttering when the amp is unmuted. Normally right after I apply power for the first time. It clicks on and off perhaps 10-20 times a second.. then stays on or off for a few seconds, and does it again.

After a few minutes of powerup, it's fine. Locks in and works beautifully.

The circuit is not currently grounded; it's just sitting on a plastic container while I wait for my chassis to arrive.

Is this likely to be the culprit? I grounded it with a clip cord, and it hasn't happened since... but it only happened 2 or 3 times.

Is there something else I should check?

- Gord

[nightfire]

Ok, it just came back, even when well grounded. It was running fine. Heatsink is maybe 30'C, while playing at about 10 watts. Then suddenly the relay started clicking randomly maybe once every couple seconds.. progressively worse.

Are there any voltages I could check? DC offset is fine. Input biases are fine. VN10 reads 11.1v. Both rails are at a steady 25VDC.

- Gord

[halvdan]

How many volts do you have over the relay coil? What resitor did you use in series?

It could also be the hmute signal that switch, which controls the relay. Is the hmute signal constantly low during the relay fluttering? If not, something in the chip mutes the amp, maybe the rail +/- voltage sensing? I'm not home at the moment so I can't look at my amp5.

[Fredrik]

Hi,
I have built two amp5.
They are working excellent. I have been using them for 1/2year.
I recommend you to drop the mute function.
I`m not using it, and the amp`s never complain.
Only a little speaker pop when turn on.
It`s easy to live with. Just remember to turn the preamp
down a little bit when turning on the amp.
The mute function can cause problems!!!!
Lovely lovely amps. I`m using 2 of them in parallel.

[nightfire]

The voltage over the relay is pretty much zero while the amp is in mute mode. HMUTE flutters between 0V and 5V and the LED flashes; it's definitely the chip muting for whatever reason.

I think it must be sensing an error condition, but I can't figure out what it is. Both rails are exactly +/- 25V and when it's unmuted the DC offsets are between 0 and 5mV. I measure 1.18V over REF (R42). 11.1V over VN10.

How would I go about dropping the mute function?

- Gord

[nightfire]

Ok, it's the chip. Actually it was two problems.

First, one of the 0.1uF caps had some flux gunking it up that I didn't notice. That solved the internal amp muting problem. However, the HMUTE is now hanging around 0.4V when muted (though the output section shuts off) and 0V when not muted.

Guess I'll have to order another TA2022. Grr.

- Gord

[nightfire]

Nevermind... solved it for real this time. Lol.

Suspecting that maybe U4 was somehow pulling HMUTE low, I reflowed the joints and that seemed to do it. Must have been more flux that I couldn't see.

God I'm such a noob.

- Gord