quick question about improper PS diode substitution

[gary h]

Hi everyone,

I'm building another gainclone using the basic PS for lm3886s on the chipamp website, I believe based on Carlosfm's design but without regulation.

I'm using this dual mono amp to power the tweeters in a small active eqed MTM pair and I'm waiting for the MUR860s to arrive. In the mean time I used MUR160s to test the PS on the breadboard and cooked them. (They are rated for 1A, 600V reverse voltage,) I'm using two dual secondary 21V transformers, 120VA each. Each is fused with a 1A slowblow fuse.

I'd like to have my understanding checked and corrected if possible, I'm assuming that the 1 Ohm resistor across the rail after the 4,700uF cap allows for nearly full current to pass and once I present the PS with the amp, the current will lower. Is this correct? I don't want to hook up the MUR860s and cook them too, (although this would sadly suit my idiom...) How much current will these chips typically pass during idle, regular use, and at peak moments?

Thanks for any quick comments

gary

[Osvaldo de Banfield]

Try less expensive devices, UF5408 by example.

[pacificblue]

With no load even 1 A diodes should be sufficient. You have either connected the diodes wrong or there is a short in your power supply.

The 1 Ohm resistor is in series with a 100 nF capacitor. Only very little current is needed to charge that cap. That is not the issue, except of course, if you forgot that capacitor.

That would be a nice amp that reduces the current in a power supply when you connect it. The current through the diodes will of course be higher, when the amp is connected, but the current through that 1 Ohm resistor will remain the same.

The idle current of the LM3886 is given with 50 mA typ, 85 mA max. The typical peak current is 11,5 A, although the Overture Design Guide peaks out at 8 A. Typical listening levels are below 1 W average, which means 500 mA or less. Even your 1 A diodes should cope with that as long as you don't crank the amp up.

Use ready-made rectifier bridges to avoid wiring mistakes. Use The Dim-bulb Radio Tester, when you test the power supply.

[gary h]

Thanks Pacificblue.