[ValentinHogea]

Hi.
 
Long story short. I want to power my LCD-3's with my Audio Research SP16L pre-amp into my Gainclone PA-150 power-amp.
 
The pre-amp doesn't really matter but the power amp puts out:
50W into 8 Ohms and 150W into 2.7 Ohms.
A quick calculations gets about 80W into 5.1 Ohms.
The impedance of the LCD-3's is 50 Ohms. So a damping factors of about 10 is achieved at 5.1 Ohms output impedance.
 
The circuit I want to adapt looks like this:
 

 
It's based on: http://sound.westhost.com/project100.htm Which however has the output impedance set to the industry standard of 120 Ohms, which is in my book too high? Right?
 
I want to set the R3 to 5.1 Ohms.
1) What should the R1 and R2 be in order not too lose too much dynamics, but without blowing my LCD-3's up? My Pre-amp has a 70-stepped digital attentuator. So there's some "room".
2) What power (W) should the resistors tolerate?
 
Am I thinking right? It was over 8 years ago since I calculated this kind of stuff. Honestly I've forgotten almost everything.
 
Kind regards,
V

 

[DingoSmuggler]

50W into 8ohm translates to 8W into 50 ohms at the same output voltage. I'm pretty sure audeze rate the lcd3 with some crazy high power rating, so from a protection side of things output resistors might not be necessary. You'd probably not want to run them anywhere near that power though as that would be deafening, but that's what a volume control is for.
 
I'd only look at using output resistors if your usable volume is too low, or if your worried about something/someone turning the volume up.
Apart from adding output resistors, you might also be able to reduce the gain of your amp, should just involve changing a resistor or 2 per chip amp (nat semi chip amps can be operated with a minimum gain of 10).

 

[ValentinHogea]

Quote:

50W into 8ohm translates to 8W into 50 ohms at the same output voltage. I'm pretty sure audeze rate the lcd3 with some crazy high power rating, so from a protection side of things output resistors might not be necessary. You'd probably not want to run them anywhere near that power though as that would be deafening, but that's what a volume control is for.
 
I'd only look at using output resistors if your usable volume is too low, or if your worried about something/someone turning the volume up.
Apart from adding output resistors, you might also be able to reduce the gain of your amp, should just involve changing a resistor or 2 per chip amp (nat semi chip amps can be operated with a minimum gain of 10).

Hi!
 
Thanks a million for your answer!
 
The LCD-3 are rated at 15W (133 dBSPL or something like that). Okay! Since it's a chip amp and not a tube amp, it's linear and I don't have to worry about "correct" loads etc...
This is starting to turn out to something very easy. Especially considering I have a 70-stepped digital attenuator in the pre-amp.
 
Can I wire 4 speaker wires directly into a 4-pin XLR?

 

[DingoSmuggler]

Quote:

The LCD-3 are rated at 15W (133 dBSPL or something like that). Okay! Since it's a chip amp and not a tube amp, it's linear and I don't have to worry about "correct" loads etc...
This is starting to turn out to something very easy. Especially considering I have a 70-stepped digital attenuator in the pre-amp.

Yeah, a 50 ohm load won't be a problem at all.
 
 
 

Can I wire 4 speaker wires directly into a 4-pin XLR?

 
yes, no problem. If I'm not mistaken, AKG used to supply the K1000 with a speaker wire to 4-pin xlr socket adaptor for exactly this purpose.

 

[ValentinHogea]

Thanks a million mate!
Consider the problem "solved".
 
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For discussion though, if someone searches and finds this thread.
 
If one would like to use a tube amp...
It would be "best" to do the following:
 
R1 = close to 7 Ohms
R2 = 1 Ohms
No R3....
 
Then the amplifier sees R1 + R2 in series = 8 Ohms (which it's probably rated for)
And the Headphone sees an Ouput impedance of 1 Ohms, good damping factor.
 
I'm pretty sure that that is correct after reading around on some threads and reviving all the resting neurons in my head that once knew all that basic stuff from high school.