Replacing 4 x 1n4002 diodes with rectifier bridge

[Little Ricky]

I'm upgrading the ic on a Pathfinder from a 2030 to a 2040, at the same time replacing the main filter caps from 2200 to 4700. From research I believe this will allow me to safely run the amp with a 4 ohm load. The rectifier diodes are 1N4002s and first thought was increase them to 1N4006s but I believe a single rectifier bridge would be better, the KBU403.  One thing I haven't determined is the pin match up. Looks like the (+) at D7 anode and the (-) at D5 cathode, is that correct?  If so what about the other 2 legs? Thanks

[Enzo]

Crap, I had a nice response typed up, then hit the wrong key and lost it.

1N4002 is a 100v diode, 1N4006 is an 800v diode.  Both are 1 amp rated, so I am not sure how raising the voltage rating will do anything.  Your power transformner only puts out 12 volts.

To use the same voltages into 4 ohm instead of 8 ohms means you need twice the current in your power supply.  Without changing to a larger power transformer, changing the rectifiers will not increase anything.

A bridge won;t hurt it, so you can stick one in if you want.   On a diode, the cathode is the end with the line, th anode the other end.   A bridge is just four diodes in a single part.  The + pin goes to the +20 in your schematic, the - pin to the -20.  The two AC pins in the center of the bridge will connect to the two AC leads from the transformer.

[Roly]

Does this help?

[Little Ricky]

I hate when that happens I do it al the time, I do appreciate that you typed it again. Thanks


Thanks it does.  In my illustration purple and blue connections would be interchangeable correct?


Admittedly I'm learning but it appears that:

• a TDA2030 handles a max of +/- 18v. And at  +/- 14v makes 12w  at 4 ohm
• a TDA2040 handles a max of +/- 20v. And at  +/- 17v makes 25w  at 4 ohm

The schematic shows =/- 20v going to the IC. The way it was explained to me it's too much voltage for the 2030 in the stock configuration but correct voltage for the 2040. That is how I understood it any, I may have understood it incorrectly. Thanks.

[Enzo]

The schematic says 20v, but it also says 12vAC.  12vAC rectifies and filters only to 16v or so, so I don;t expect real 20v there unless the AC is a bit higher.

The 2040 will drop in place of the 2030.

The power amplifier stage of any amp is pretty much just a valve between power supply and speaker.  Any power to the speaker comes fromthe power supply.  A 2040 is able to control more power than a 2030, but won't create more power.   

[joecool85]

The power amplifier stage of any amp is pretty much just a valve between power supply and speaker.  Any power to the speaker comes fromthe power supply.  A 2040 is able to control more power than a 2030, but won't create more power.

That's a pretty good analogy.  To get more power out of your amp, you'll need to be upgrading your PSU as well.

[Little Ricky]

That analogy  would lead me to believe the 2040 would then be running well within limits and "safer"  Kind of like running higher pressure seals
on that valve.

Thanks. I do see that 12V as well. I'll get an actual reading tonight to see what's what. But with that being the case I should just use an 18-0-18 transformer and be able run a 2050 @ 4 ohm I'd imagine. At that time I can add use a bridge with a heatsink and add a heatsink to the IC and have everything relatively "safe"

In the time being to get the amp running again, would my logic be true regarding the the current transformer voltage being too much to run the 2030 @ 4ohm but the 2040 would be within spec to run @ 4ohm. And I would leave the 1N4002s in place

Thanks.

[Little Ricky]

As an update, I've measured the voltage coming out of the transformer  and it's 15.5v each side. Pin 5 of the IC to ground reads 20.7v.

[Roly]

In my illustration purple and blue connections would be interchangeable correct?

Yes.  In fact they are "interchanging" at the local line frequency, 50 or 60Hz.

When you reduce your load by half from 8 to 4 ohms, at a given voltage you are doubling the current throughout, from transformer via rectifier, filter, and output stage; so all of these items have to be able to handle the increased current or you will have problems (and any PCB traces in the path also need to be considered too).

Upgrade the tranny, same voltage double current rating - check.
Upgrade the rectifier ditto - check.
Upgrade the output stage - check.

Now what about the filter caps, C35 and C36, 2200uF/25V?  These also have a (lesser known) ripple current rating, so you would be wise to double up on those too, add another 2200uF/25V in parallel with each (noting the correct polarity).  If you can't find the ripple current rating of available caps, then look for ones of similar or larger physical size after matching the ratings.

HTH

[Little Ricky]

Thanks everyone. With your help I was able to replace the 4 diode rectifier with a 4 amp bridge successfully and learned something along the way. The substitution of the TDA2040 in place of the TDA2030 didn't go as well though, that's another story and another learning experience.