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Old 9th January 2009, 04:32 PM   #1
marko is offline marko  United Kingdom
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Default amps with bypassed preamp question

if an amp has a bypassed preamp section will the amp require more or less preamp voltage to have the same amplifer output?

just wondering as my hifonics viii amps have a bypass feature but i'm not sure which way the switch needs to be ie- in or out!

the manual is a bit vague and doesn't really go into much detail about this feature but i want the best sq possible out of these amps...
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Old 9th January 2009, 11:39 PM   #2
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The VIII's have built-in crossovers, right?

The series VII's have what is essentially a separate crossover built into the same chassis. You have to use short patch cords to jump from the crossover outputs into the amp inputs. That's a pain, but offered more system flexibility.

It's a nice feature and very convenient, and makes for a potentially messy install. It also required extra RCA jacks on the chassis, which aren't the cheapest components on the assembly line.

It sounds as if, in the Series VIII's, the crossover outputs were jumped internally to the amp inputs through a switch? Is that correct? A much neater way to do it.

If so, the switch is a crossover defeat.

As far as input voltage goes, those amps will make full power with as little as 100mV input. The amplifier input gain section should be designed in-circuit after the crossovers.

As well, I don't think the internal crossover has any significant voltage gain designed in. I used the VII's with and without the built-in crossovers and didn't notice any difference in gain.
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Old 10th January 2009, 06:42 AM   #3
marko is offline marko  United Kingdom
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no, the series viii are the same as the series vii, they have a seperate cross over section that need patch leads to work, these were only found in the 4 channels and monoblocks...

the switch on the front panel is to defeat the preamp section so one way it goes from .25-1.5v and the other way it's 1.5-9v.

my question is in which way are the preamps defeated? would i need more input voltage in the defeated mode or would it become very sensitive and require next to nothing?

mark.
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Old 10th January 2009, 02:42 PM   #4
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The preamp is a simple gain stage with voltage gain of 6x.

In the defeated mode, the input will be adjustable for 0.25V-1.5V.

If you have a head unit with significantly more than 1.5V output and operate it in the defeated mode, full power will be reached at a lower level on your volume control.
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