Is there a substitute for an LM1875 ?

[goldensteve]

Hi All,

I am trying to mend a Marshall MG15 combo, which is a little 20W job based on an LM1875T. I bought this for my own use, knowing it was bust, and thinking of it as a cheap enclosure and speaker etc for a desing of my own.

Anyway, I can't resist trying to mend it after all, and the real question is about a substitute part fot he LM1875. This is a 5 pin TO220 device, and seems to be obsolete, leastaways I can't seem to find a source of one. Hence: can anyone recommend a substitute part?

I may be jumping the gun of course, so here's the symptoms if anyone is curious. The amp just makes a loud hum in its speaker, and smokes the resistors in the zorbel network. I have checked the cap in series with the resistors, and it is fine, and showing the right val. when I measure it off board. The PSU is fine, and the only DC offset to the speaker is explained by a slight asymmetry in the split rail supply. There is however a significant AC ripple on the speaker output about 50kHz. This probably explains the smoking resistors, so next I'll check for the caps around the amp input and PSU decoupling.

Thanks for your interest if you've read this far ...

steve

[filholder]

Hi,

You can order then directly from farnell for about £2.16.

http://www.farnell.com/

order code

9488405

[diegot]

You can use the TDA2050.
But it have more THD.

[goldensteve]

Thanks Diegot - that's just what I needed to know. THD probably not too much of an issue on a guitar amplifier ;-)

As it happens, I was able to find the problem with the existing circuit: a capacitor on the input circuit of one of the op-amps had failed open circuit and was hooting. Replacing this and the system is hunky dory. I will still want to lay in some spares though as I plan to use this combo amp a lot.

Thanks for all the advice -

Steve