input sensitivity?

adrianc

Member
2008-01-13 11:51 am
i have been reading the specs on a preamp i have just bought, an adcom gfa750. it states that the output level is 1v. i am getting slightly confused here, my amp is an adcom gfa5802 which has an input sensitivity of 0.1v for 1 wattt and 1.7v per 300watts, does this mean that my amplifier will never reach its maximum performance with on 1v output? could someone please tell me ,if i am figuring this wrongly./

cheers adrian
 

adrianc

Member
2008-01-13 11:51 am
thank you for the advise,

i thought as much , that this would be the case.
i have looked at the schematics of the pre amp.(very new to electronics) but i am at a loss of how to increase the output voltage. would anyone know who on here that could point me in the right direction.

would i need to add another amplification stage externally, and just change a resister on the output path.
 
Hi,
the output level of 1Vac may be with a standard (but lower) input voltage stated in the specification. The input voltage could be specified as dbU or dbV or something referenced to another standard.

You may find that the maximum input voltage or the maximum output voltage is stated elsewhere and could be considerably higher than 1Vac.
 
Adcom is not going to design an amplifier that will not reach it output when driven with another Adcom product. This is totally wrong here. The specification you are looking at is probably referencing an output with a given input. This would be a common with any commercial preamp for sure and most home type equipment.

I had a preamp one time that specified a output of 1.5 volts at a given input at a given frequency. When actually tested the output was 16 volts P-P. This was more than usable with any amplifier.

I suggest that if this really bothers you then take it into a audio center that has trained people capable of measuring and understanding the specifications.
 
ally, fig.6 shows the GFP-750's percentage of distortion+noise in both balanced and unbalanced modes, plotted against output voltage into loads of 100k ohms and 600 ohms. At a 1% THD+N figure, the maximum output voltage in balanced mode was 26.5V (100k ohms) and 6.5V (600 ohms); in unbalanced mode, it was 13.3V (100k ohms) and 5.0V (600 ohms). All voltages are well above the level required to drive any known power amplifier well into clipping. Note that the shapes of these traces imply that the preamplifier offers its lowest level of distortion and noise at around 2V, the maximum voltage likely with a real-world power amplifier.

Note this in the above quote

All voltages are well above the level required to drive any known power amplifier well into clipping.

Nice reference awpagan
 
burnedfingers said:
ally, fig.6 shows the GFP-750's percentage of distortion+noise in both balanced and unbalanced modes, plotted against output voltage into loads of 100k ohms and 600 ohms. At a 1% THD+N figure, the maximum output voltage in balanced mode was 26.5V (100k ohms) and 6.5V (600 ohms); in unbalanced mode, it was 13.3V (100k ohms) and 5.0V (600 ohms). All voltages are well above the level required to drive any known power amplifier well into clipping. Note that the shapes of these traces imply that the preamplifier offers its lowest level of distortion and noise at around 2V, the maximum voltage likely with a real-world power amplifier.

Note this in the above quote

All voltages are well above the level required to drive any known power amplifier well into clipping.

Nice reference awpagan
is the GFA spec quoted similarly to the gfp spec?
 
is the GFA spec quoted similarly to the gfp spec?

If I could find something on the GFA I would gladly post it. It would stand to reason the specification would be very close to the GFP spec with respect to the unbalanced signal. I am assuming the GFA is a unbalanced out only piece. At any rate it should be understood the 1 volt output is a reference to a specific input signal and not the maximum available from the piece.
 
AndrewT said:
the output level of 1Vac may be with a standard (but lower) input voltage stated in the specification. The input voltage could be specified as dbU or dbV or something referenced to another standard.


burnedfingers said:
it should be understood the 1 volt output is a reference to a specific input signal and not the maximum available from the piece.
we think the same.
 
adrianc said:
sreten

would it be possible for me to email you a schematic ,
i am only a novice with electronics adrian


Hi,

Whilst I would like to help I am simply not convinced at all that there
is a problem that needs fixing, I know of no active preamplifier that
has a maximum output of 1V.

This is only possible with a passive preamplifier with a built in 6dB
attentuation driven by the 2V or so peak output of a CD player.

Doubling gain is one notch on the volume knob, and unless this
is used at its maximum position there is simply no problem to fix.

:)/sreten.