2. amps-preamps
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Preamp for Mcintosh MC2500

Looking for feedback on what preamp would be a good match up for a MC2500 amp? Currently using a ARC LS3. I also see the MC2500 can be run without a preamp. Anyone with experience running this amp without a preamp?
2channeljunkie
georgehifi's avatar
georgehifi
10,312 posts
 
I wouldn't run the amp without a preamp. To easy to damage speakers that way.


Why would you say this, if the volume is up on a preamp it's just as deadly, if anything it's safer going direct as there would be less full gain than a preamp would give full, and therefore less chance of damage.

Cheers George  

zoya
120 posts
 
George, there is a big difference increasing the volume using preamp's volume control or doing the same using amp's gain control. When you adjust the volume using preamp you increase the signal level without changing the noise floor. So you are also increasing the signal to noise ration - which is good. When you increase the amp's gain you amplify everything - the signal and the noise. When you amplify the noise to high enough level  you can damage your speakers. Very loud undistorted signal will not damage your speakers but amplified noise will burn the tweeters.  

Y.
georgehifi's avatar
georgehifi
10,312 posts
 

You need to re-think Zoya.

EG: If an active preamp is accidently left up full connected to the direct input of the amp, and the source goes dc the amp will blow up and take out speakers.

If the source is only connected the passive variable input of the amp (no preamp) and the volume is accidently up full and the source also goes dc, it will probably still take amp and speakers out, but there is a chance of survival.

It has nothing to do with noise floor at all. It all about total gain and the amplification of a deadly problem.


Cheers George

normansizemore
601 posts
 
George,

My comment was based on using the MC-2500, which for all operating intents was exactly like my MC-2300.  The comment was not a 'unilateral' based expression. 

The MC-2500 has a left and right gain control. Looking the the schematics, they are exactly the same pots in my MC-2300.  They are not detented but are free wheeling. I tired running a CD player directly into my MC-2300, and while it can be done it was just 'way too easy' to increase the volume. Using a preamp gave much greater precision and control with regard to gain.  I also wasn't excited about the possibility of someone in my home using my system that way. 
Last of all, I don't like using left and right gain for volume. Much easier to use a single volume knob with separate balance. 
I know several people who choose not to use a preamp. I just don't recommend doing that with this amplifier. It it literally limitless in its power delivery.  The beast is rated to drive a half ohm load. 
N
georgehifi's avatar
georgehifi
10,312 posts
 

Yes I see that now you don’t like detented vc and dual mono they are a pain to some. But as far as being more dangerous because of power delivery, not so.

As your amp say for theoretical example has 10 x gain on it's intput driver stage, and when/if your source goes faulty dc to 2v or someone yanks an interconnect, that would be a total of 20vdc to the amps output stage and speakers, survivable.  

Slip an active preamp in with another 10 x gain, and you have 200v theoretical volts going to the amps output stage and speaker. Everything gets smoked.

What’s more likely to fry amp and speaker, 20vdc or 200vdc?

Cheers George

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