Re: arsclist ELT TT

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 07-Jun-01, George Brock-Nannestad wrote:

> 
> No, but it is not the complete truth. The ordinary output is 
> unbalanced at a level compatible with a normal RIAA preamp. That 
> is, to all intents and purposes, the signal emulates a pickup signal 
> (velocity signal, not ceramic which was basically displacement). 
> That is why it is easy to do A/B testing with a suitable preamp. 
> And also, why a preamp for historical records will instantly work.

The tube-based pre-amps from Quad, made in the 1950s, had a system of
plugin modules covering a big range of equalisation curves for different
makes of 78 rpm disk. The plugins just contained different values of
resistor.

However, if you think about the tolerances that were usual for resistors
and capacitors before 1950, it's not very likely that recordings were
made with any precisely calibrated equalisation.  Early microphones and
monitoring speakers would also not be very precise.

A later Quad preamp, the model 44, made in the 1970s, included a "tilt"
control which is ideal for adjusting equalisation. This gives a level
response of, for example, -2dB in the low frequencies, then a gentle
slope up, levelling off again to +2dB through the high frequencies.
Adjusting the control knob changes these levels, always symmetricaly.
For example, +2dB in the low with -2dB in the high. 

As it is a smooth gentle curve, it avoids the problems found with
narrow-band controls as in graphic equalizers.

The circuit was in the manual and could easily be built by anyone with
electronics skills.  It is the kind of job that is suitable for an
analogue circuit.



Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx