TDA2040 for TDA2050 in Fender Frontman

[LucifersTrip]

A friend brought over a dead Frontman practice amp. After a little reading, it seems the most common problem is a blown TDA2050.

Even though I rarely work with IC's (and know little of this type of stuff), I did actually have a bunch of TDA2040's laying around. After some more reading, it seems I can sub one for the other, but what differences should I expect?  Do I have to alter R40 or anything else? 


http://www.e-dan.co.uk/electronics/TDA2040.html
http://blueguitar.org/new/schem/fender/frontman15g.gif


thanx

[Seljer]

I believe the only difference is the power/voltage/current rating. If it falls within the scope of the amps power supply/speakers go ahead.

[teemuk]

TDA2050 is rated for 32W output while TDA2040 is rated only for 20W output, so most likely the 2050 can dissipate more waste power than the 2040.

I would not recommend TDA2040 for replacement of TDA2050. Assuming pinouts are compatible such swaps generally are "safe" when you replace a lower power chip with a higher power one, but not the other way around.

[PRR]

You can learn a lot by reading.

TDA2040 absolute maximum supply voltages: +/-20V.

Frontman 15 supply voltages: +/-23V nominal, un-regulated (will be higher in that bad-wired club with 130V coming out of the walls).

If a 20V chip fails at 23V, you can NOT complain to the maker. That's why they put ink on paper: to define what they will and will-not stand behind.

Yeah, I know: these chips are a glut on your bench and you won't be complaining to the maker. But if it fails, you sure will be complaining to yourself about extra work and wasted time.

I give 99% odds it will work, on the bench, for an hour.

I'll even bet a buck it works for months. (I've done worse things and didn't get bit for years).

I would not send a friend out into the world with a 20V chip in a 23V amp. It's gonna fail. (Especially if he already killed a 2050.) Murphy's Law says it will fail at a bad time (big audition, etc).

[LucifersTrip]

Thanx much for all the replies. It's just a cheap practice amp so not many worries about where it fails.

I did throw in the 2040 and the fuse blew instantly as it did with the 2050 I removed.

According to many, that amp has an issue when headphones or something else is plugged in. In this case it was a talk box.
http://music-electronics-forum.com/t10336/#post112072
http://forums.fender.com/viewtopic.php?t=24618

A few others mentioned that it also could be the J111 fet, but I actually pulled and tested that before replacing the 2050.

I'm going to order a few 2050's and try again. If the fuse blows again, I'm not sure where to go next, since the solution to this problem seems to be a blown 2050 90% of the time.

[Seljer]

Thanx much for all the replies. It's just a cheap practice amp so not many worries about where it fails.

I did throw in the 2040 and the fuse blew instantly as it did with the 2050 I removed.

According to many, that amp has an issue when headphones or something else is plugged in. In this case it was a talk box.
http://music-electronics-forum.com/t10336/#post112072
http://forums.fender.com/viewtopic.php?t=24618

A few others mentioned that it also could be the J111 fet, but I actually pulled and tested that before replacing the 2050.

I'm going to order a few 2050's and try again. If the fuse blows again, I'm not sure where to go next, since the solution to this problem seems to be a blown 2050 90% of the time.

If its blowing fuses, wire yourselft up a lamp current limiter ( http://www.geofex.com/article_folders/spo_test.htm ), so you can take measurements to diagnose where your problem is without blowing the fuse. And take caution working on live AC equipment obviously.

[PRR]

The JFET can't possibly be blowing a fuse.

> the fuse blew instantly

Take the chip out, then power-up. Does fuse blow?

If so, suspect/replace the main power rectifier and the two big electrolytic caps.

Yes, lamp-limiter is wise. Use 45W-60W *incandescent* lamp.