You contradict yourself, Rob - the diagram of the 25 year old M50
(1983) shows the mic trim AFTER the first amplification, not before.
It is an obsolete model and I don't think it is applicable to modern
recorders of any kind. That generation of Tascam mixer was never the
quietest or best except for the low cost. No ICs either.
Do you have access to the circuit diagram of the Fostex? I am
disinterested personally as I use a SD recorder, but the
contradictions in this thread are annoying me.
Sometimes "trim" controls are mislabeled "gain" and sometimes vice
versa! Some control the gain of a preamp stage and others attenuate
the in- or output of a preamp. The effect is not interchangeable.
I have never even seen an FR 2E, but common audio practice would be
to have the single large knob in a middle range posiyion, and set the
input trims so it is an effective level control. With loud sounds,
turn down the trims, with softer sounds, turn them up for extra
gain... But I had a Technics cassette recorder (also in the 80s)
where the big knob wanted to be all the way up, with the trims mid-
range, so you could do nice fade ins and outs. But again that is not
the current technology.
Mainly though, the statement and the diagram you cite are in
conflict. And I'm afraid newbies to recording will be mislead. I am
not the expert but the contradictions are painful to witness.
Lou
On Apr 27, 2008, at 9:30 PM, Rob Danielson wrote:
> Hi Mike--
> I suppose there are exceptions to everything, but in all of the mic
> preamp circuits I know of, "trim" is attenuation only. Fully
> clock-wise or "off" can't add noise because its not adding
> amplification. It could sound as if it is, I suppose,.. such as when
> the headphone level is high or when a mic has exceptionally high
> output. Given the very low-noise performance of this recorder's mic
> pre, with the trim "off," it could be that you are hearing more of
> the mics' self-noise.
>
> Some mic sensitivity/sound level combinations create circumstances
> when one would want to routinely run with trim, but doing so to
> improve noise performance isn't the way I understand mic pre circuits
> to be designed.
>
> Here's a block diagram showing trim adjustment before amplification:
> http://music.concordia.ca/Programs/Electroacoustics/M50_mixer/
> Mixer_Input_Schematic.html
>
> Rob D.
>
>
> At 10:54 PM +0100 4/27/08, Michael Oates wrote:
>> The problem with turning those trim knobs fully clockwise is that
>> the preamps get very
>> noisy, you really need to reduce them a bit.
>>
>> Mike
|