Quoted from Pinwiz1985:if you tap into the amplified signal going straight to the speaker in the cab...and run into the input of your powered or unpowered sub, kiss the input section of your sub good bye.
That's only true if you run to the low level (usually RCA plug) input on a sub. If the sub has a high (speaker level) input they'll be fine.
Quoted from copperpot:Note: This won't work on AC/DC and a handful of WPC-era pins, I forget which ones but you can search RGP and find out posts by TheKorn that talk about which and why.
It'll still work on ACDC, it just might not be optimal. On the pro's, no problem. On the LE's, Stern added a 6DB crossover, which will not exactly play nicely as it's engineered assuming the woofer is in circuit. To really do it RIGHT, you need to go before that crossover. (Should be a coil right near the cab speaker, but I haven't looked inside an LE for a while.) No idea what they did in the premium.
Early WPCs (BoP, FH) this method is more miss than hit due to the rudimentary crossover and the wiring. (Big technical reason omitted, for now.)
Quoted from Asael:But now I read Pinwiz1985 post, and he says that this way I would shorten the life of the input section, so did I wrong?
A friend of mine who is better with audiosystems told me, that I had connected the external sub parallel to my cabinet speaker and so I am going from 8 Ohm to 4 Ohm and that this coud be dangerous.
You'll be fine. If your sub has a high (speaker) level input, it's designed to present a VERY high impedance. The upshot is that it adds almost no load, so you wind up with whatever impedance you had there before.
If your sub does not have an amplifier in it (i.e. essentially a box and a speaker, with no power connection) then that doesn't apply.
Quoted from Pinwiz1985:Yes your friend is correct you are loading down the output section of your cabinet woofer down more than maybe it should be.
Theoretically yes, but functionally no. High level converters are designed to present an impedance anywhere from the high hundred-thousands to several meg ohms, depending on the manufacturer. Since the formula for impedance in parallel is 1 / ((1/R1) + (1/R2) + (1/R3) + ...), the numbers work out like this:
1/ (( 1 / 8 ) + (1 / 4M)) = 1 / (1/8.00000025) ~= 8
Quoted from Pinwiz1985:For your purposes, I dont think a small IC amp can handle anything more than what it was designed for at 8 ohms. If you do run it at a 4 ohm load, it will most certainly shorten its life.
For SAM, the output transistors are TDA2030As (same as WPC-95), which are specced to be just fine running into 4 ohms.
Pre-SAM they used other chips that aren't quite as beefy, such as MB3730As.
Quoted from Nevus:I am looking to run my ACDC sound through a small tube amp that happens to have a 1/8" input for iPods etc.
That's looking for a headphone level input, which is more-or-less compatible with line level. (They're not exactly the same, but usually close enough.) See earlier about hacking your board to get a line level output. Alternatively, you can use a high-to-low level converter (speaker to line level converter), available on amazon, and tap off the speaker like everyone else is doing. Not my favorite way of doing things, but it works.
Post edited by TheKorn : stupid auto smiley made "eight-parenthasees" into something.