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Klipsch Forte IV ... what amp ?

No , I am not asking for a particular amp style and brand here . Although I am not refusing any suggestions either !

What I would like to know first is what characteristics to look for in an amp to drive these speakers (Forte 4’s) to full performance .

Such characteristics as :

1.) What is needed to handle the low impedance of 4 ohms ?

2.) While the sensitivity is listed at 99 dbs. it is considered to be closer to @ 96 dbs,

3.) What about negative feedback ?

4.) Will the 12" woofer and 15 " rear radiator need special attention also ?

5.) Do the horns require special consideration ?

I feel that these considerations will go further to getting it right than , " hey , just get a tube amp and enjoy " .

Thank you & Be Safe .

saki70

Showing 3 responses by oddiofyl

oddiofyl's avatar
oddiofyl
4,066 posts
 

I'm using a pair of Quicksilver Mid Monos to drive my Forte IV and they sound fantastic.   40 watts PP ,  they are EL34 based but can use any EL34 / 6l6 variant 

They have a 4 ohm tap but I drive them off the 8 Ohm tap and they don't break a sweat.   I will soon be replacing the Quicksilvers with a 8 watt 300b amp,  the Forte are so to easy to drive 

oddiofyl's avatar
oddiofyl
4,066 posts
 

I've only had the Forte a little over a year.  The QS are really the only amps I've used except for a short period where I used an Acurus A150.   It sounded good with the Acurus but the QS were much better .   I had a bad tube,  thats really the only reason I hooked it up short term.

oddiofyl's avatar
oddiofyl
4,066 posts
 

Actually the Mid Monos don't even need a meter .  To bias you just turn each tubes bias pot fully counter clockwise . Old Mid Monos have one potentiometer per amp to bias and for those matched tube pairs for each amp are recommended.  The newest version has a bias pot for each tube which is better.   

So with all pots counter-clockwise, turn the amps on and let warm up for a few minutes

I recommend doing one amp at a time.   

After it has been on for a few minutes, press the bias test button, there are two for new units.   Press and hold the button as you slowly turn the pot clockwise.....slowly.  the LED will start to glow.  Just when it starts to glow, back off a little until it goes out.   Let the amp warm up for 15 , checking the single or both LEDs if so equipped to make sure it doesnt glow bright RED.  If it does back off counter clockwise a little.  

After the amp has been on for at least 15 or 20 min check bias and adj clockwise until the LED just starts to glow red.  REMEMBER TO PRESS THE LED CHECK BUTTON AND HOLD WHILE ADJUSTING.....

The goal is not to bias them hot for a long life.   If the LED barely glows the amp is in the correct range.  

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