amp1b psu

[billb]

I've just completed an amp1b and want to check a possible power supply issue before testing. I have some memory of reading that the chip can fail if the 5v supply fails while the rail voltages are present - anyone confirm this? If so, would it be a good idea to have the 5v supply switch the main rail voltages on via a relay i.e. so if you lose the 5v you also remove rail voltages and chip is safe. Comments please.

billb

[omishra]

billb,

I have AMP1 which same as AMP1B, TA2022 based amp. I don't think chip fails when 5v is absent while rail supply is present.

I encountered it two times.

First time my 7805 regulator went bad giving 0V output in place of 5V. Still chip survived. DC rail was constantly ON with +33 and -33V.

Second time just recently I made some modifications. I wound 50+50 turns of 28 SWG enamaled copper wire over main toroidal transformer (22-0-22,200VA)for getting 12+12 V AC which I used for driving control circuit and also to get 5V. This time some error caused input to 7805 to dip below 5V (7805 went off )still chip survived.

I think it is not necessary to add relay in DC rail.

BTW chip fails if >5V is provided in place of 5V,

Any better thoughts!

[billb]

Omishra, Thanks for that useful information. I'll just use a conventional 7805 then. I'm aware that chip fails if 5v goes high so maybe something like an LM2940 regulator might be "safer" than the 7805.

billb

[Sean]

I use a 7805 powered by the positive rail. I leave the rail power on at all times and switch the amp on/off with the 5v supply. Nothing to worry about.

http://i11.tinypic.com/2exshz8.jpg

[billb]

Thanks, that's reassuring. Nice picture BTW. I assume the amp to the left is for a subwoofer? What amp is it?

billb

[omishra]

I know 7805 is risky. But I added zener of 5.2V in output of 7805 to make sure it never reaches there. same time input has fuse of 100mA(fast blow). In case zener flows more current 100mA fuse blows. This is in theory so far.

[Sean]

[:0]... That's not an amp on the left hand side; it's the regulated supply for the AMP1-B.

omishra, no need to be so concerned about the 7805. I've used one on 3 different AMP1-B's with no zener and havn't had any problems.

I did however kill two chips from playing around with bypass caps on the 5v supply. I had accidently attached a cap backwards that still had residual charge on it while both of the amps were on. At least I think thats what did it.[xx(]

[billb]

"That's not an amp on the left hand side; it's the regulated supply for the AMP1-B"

Oops, I was looking at the power transistors on the heatsink and assumed it was another amp. I wasn't intending to regulate my supply but just use a conventional bridge rectifier and electrolytics. What rail voltage and speaker impedance do you have?

billb

[Sean]

I went with a regulated supply because 1) transformers voltage is too high 2) it was a good learning experience 3) I like regulated.

Right now the rail voltage is +-32v with 8 ohm speakers. If I use 4 ohm speakers I lower it to between 25-28v. Voltage before regulation is about 45vdc.

[xrcd]

Will there be big turn on and turn off thump when the rail power is on at all times and switch the amp on/off with the 5v supply ?