Determining an older bridgable amp?

[jol50]

It would be nice if they had reverse switches on one, lol. That is ampguts picture but I can tear into mine later and tell you. They are kind of a pita to take apart as you can see. I should find some of those RCA terminals and drill the case, mount them in. Keep using a DIN to RCA dongle....in fact if I built a box for this I could power it off the DIN cables and not use RCA, unlikely I would use it on another set of amps anyway.

[tsmith1315]

Well, it *could* actually be as simple as swapping a couple of connections and rearranging resistor values...

[djQUAN]

here's what I did this afternoon....





I added a dual op amp on top of an existing dual op amp so that I could add an inverter and buffer before the input stage so the amp could be made tri-mode capable.

[jol50]

That is some handy work! I would try to convert these to modern bridgeable amps but I don't yet know if it is possible, or better to make a box/converter.

[tsmith1315]

jol:
When you have time, shine a flashlight through the vents on the side of the 3518 and see if you can read a part # on one of those IC's. They may allow changes similar to djQUAN's.

Tim

[Perry Babin]

If the circuit is like the one in the 3550, you should be able to make only a few changes to get the channel inverted.

[jol50]

It looks like upc1225H, not 100% on the 5 but 95% on it. Had to take it apart and still has stuff on it that will not come off.
http://www.datasheetcatalog.com/data...UPC1225H.shtml

[jol50]

Pin 4 and 5 are normal and inverted, but it can't be that easy....

[Perry Babin]

It wouldn't be quite as easy as simply moving the input signal to the other pin. If the circuit was similar to the 3550, you'd have to remove the signal from the + input and ground the +input. Then you'd have to change the value of at least one resistor and one capacitor before connecting the signal line to the - input.