2-channel gurus, I need help with matching my DAC/Pre with an amplifier. Curious about in/output impedance matching and in/output sensitivity matching. - AVS Forum
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post #1 of 4 Old 12-12-2012, 12:45 AM - Thread Starter
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Hello fellow enthusiasts,

I recently caught the 2-channel bug in a big way and I am in the process of putting together my first true "high-end" 2-channel system.

My DAC/Pre is the Berkeley Alpha DAC Series 2 and I had previously been using it with a Parasound Halo A23, driving the A23 directly via the Berkeley balanced outputs. Speakers are Focal Electra 1038BE. I have sold the A23 and am in the process of shopping around for a new amp to be used with the Berkeley driving it directly.

My question is how do I go about matching the balanced output level/output impedance of the Berkeley with the input sensitivity/input impedance of any particular amp? The Berkeley specs list it as having a balanced output level of +12dBu recommended and +18dBu maximum. There is no mention of an output impedance.

What specs should I be looking for in potential amps to ensure they will mate well with the Berkeley?

I have my eye on a McIntosh MC452 which is listed as having 4.2V balanced (for rated output) input sensitivity and a balanced input impedance of 22,000 ohms, but would this be a good match with the Berkeley?

Assuming that +12dBu is 3V and +18dBu is 6.1V -- and the McIntosh requires 4.2V to reach maximum output, but Berkeley recommends +12dBu or lower, is this a bad match or am I mis-understanding how this all works?

Why let facts or common sense get in the way of your opinions.

Quick shot of my gear/theater.
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post #2 of 4 Old 12-12-2012, 05:40 AM
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We don't impedance match any more.
If the DAC can output up to +18dBu, what's the problem?
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post #3 of 4 Old 12-12-2012, 08:40 AM - Thread Starter
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Quote:
Originally Posted by SAM64 View Post

If the DAC can output up to +18dBu, what's the problem?

That's what I was thinking, but I am not 100% sure.

What really got me thinking was the fact they "recommend" +12dBu or lower... as if going beyond that is operating outside of its optimal range or something and would be detrimental to sound quality. Maybe not a very linear volume range or introduce some clipping? I've read things like improperly matched in/output specs can lead to significant issues with regards to sound quality and really don't want to end up with a "bad match" and have to sell the amp.

Why let facts or common sense get in the way of your opinions.

Quick shot of my gear/theater.
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post #4 of 4 Old 12-13-2012, 12:07 PM
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The only real issue there is loading.

A 22,000 ohm input impedance should not be a problem with almost any preamp.

The only time you would need to be concerned is if the input impedance of the amplifier is less than two times the output impedance of the preamp.

Then the loading could be significant.

It is odd that there is no output impedance given for the preamp, but it is seldom more than 2000 ohms, so again a 22000 ohm load is not going to be a problem.

P.S.- I just talked to an engineer at Berkeley, and he says the output impedance is only 110 ohms per leg or 220 ohms total in balanced operation.

The 4.2 volts input spec for the McIntosh is probably the maximum input voltage allowable to avoid overloading the input circuit; that is also not going to be a problem. The output of your preamp will seldom exceed 1 volt, which will not overload the amplifier. There is no sound quality issue.
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