From: Edward Ianni 
To: psnlist 
Sent: Mon, 17 Sep 2012 23:56
Subject: Re: Old hobby resurgence


             =20
I have found my old "Robert's"      equalization circuit (physical circuit)=
..  I can't remember how      succesful it was (but it would probably be in =
operation, if I had      it working). It has 6 Lm741's on it. I will check =
it out lead by      lead against the old schematic. Question: Do I have the=
 option of      just hanging it on the back of the Sprengnether or MUST I p=
lace it      further back (behind the Amp)? At this point I just want to se=
e if      I can extend the period significantly. Thanks Gang.  Sincerely,  =
     Ed.
     =20
      Hi Ed,=20

    741s are quite noisy, but try out the circuit 'as is'. Do check on the =
turnover boost frequency / period.   =20

    One weakness of the Roberts circuit is that it can provide very high ga=
in at long periods - far longer than your sensor registers and what you MAY=
 see is greatly amplified 1/f noise. You really want to follow the Roberts =
circuit with a two pole high pass filter. This is not quite so important wh=
en using 4.5 Hz geophones, since the periods are shorter, but we still used=
 two stages of HP filter.=20

    Putting the filter at the output of the amplifier will enable it to 'se=
e' higher levels of long period noise.
Putting it on the amplifier input will add quite a lot of noise to the whol=
e system chain. The optimal place is after the first amplifier. =20


           =20


       =20
  Amaseis also              has the inverse filter which can only be used o=
n SAC              files, so you can still try out inverse filtering on eve=
nt              files.
       =20
           =20
Do try out the long period filter in AmaSeis, but remember the mathematical=
 limitations. If you want a x10 increase in period, your input signal will =
have fallen in amplitude to 1/100 at this longer period. So you need signal=
 amplitudes of several hundred counts at the resonant period for the compen=
sation to work correctly.=20
    This is why I prefer to use hardware - this works regardless of the uni=
t  digitisation step height, but noise limitation is still critical.
=20






                                 =20
                                   =20
 Could you possibly "                                      point" me to the=
 schematic of the                                      serial AS-1 period "=
extender". I searched for the                                      AS1 sche=
matic/detail but only                                      found very gener=
al info on it. I                                      haven't "played" with=
 this "stuff"                                      for years but I feel a v=
ery strong                                      resurgence of interest in  =
                                    Seismology since I started this        =
                              project again. .












     =20
I modified my AS-1 to extend it to about 18 seconds period. This made it FA=
R, FAR easier to use. I can scan that circuit and send it to you.=20

    Regsrds,=20

    Chris Chapman
 =20
=20
=20







From: Edward Ianni <edwianni1@...........>


To: psnlist <psnlist@..............>


Sent: Mon, 17 Sep 2012 23:56


Subject: Re: Old hobby resurgence

















 =20
   =20
 =20
 =20
   =20


I have found my old "Robert's"
      equalization circuit (physical circuit).  I can't remember how
      succesful it was (but it would probably be in operation, if I had
      it working). It has 6 Lm741's on it. I will check it out lead by
      lead against the old schematic. Question: Do I have the option of
      just hanging it on the back of the Sprengnether or MUST I place it
      further back (behind the Amp)? At this point I just want to see if
      I can extend the period significantly. Thanks Gang.  Sincerely,&=
nbsp;
      Ed.



      



      Hi Ed, 





    741s are quite noisy, but=
 try out the circuit 'as is'. Do check on the turnover boost frequency / pe=
riod.    





    One weakness of the Rober=
ts circuit is that it can provide very high gain at long periods - far long=
er than your sensor registers and what you MAY see is greatly amplified 1/f=
 noise. You really want to follow the Roberts circuit with a two pole high =
pass filter. This is not quite so important when using 4.5 Hz geophones, si=
nce the periods are shorter, but we still used two stages of HP filter. 





    Putting the filter at the=
 output of the amplifier will enable it to 'see' higher levels of long peri=
od noise.



Putting it on the amplifier input will add quite a lot of noise to the whol=
e system chain. The optimal place is after the first amplifier.  =







       =20

  Amaseis also
              has the inverse filter which can only be used on SAC
              files, so you can still try out inverse filtering on event
              files.


       =20


            




Do try out the long period filter in AmaSeis, but remember the mathema=
tical limitations. If you want a x10 increase in period, your input signal =
will have fallen in amplitude to 1/100 at this longer period. So you n=
eed signal amplitudes of several hundred counts at the resonant period for =
the compensation to work correctly. 



    This is why I prefer to use hardware - this works r=
egardless of the unit  digitisation step height, but noise limitation =
is still critical.



 






















                                 =20


                                   =20


 Could you possibly "
                                      point" me to the schematic of the
                                      serial AS-1 period "extender". I=
 searched for the
                                      AS1 schematic/detail but only
                                      found very general info on it. I
                                      haven't "played" with this "stuff"
                                      for years but I feel a very strong
                                      resurgence of interest in
                                      Seismology since I started this
                                      project again. .









































      

I modified my AS-1 to extend it to about 18 seconds period. This made it FA=
R, FAR easier to use. I can scan that circuit and send it to you. 





    Regsrds, 

 

    Chris Chapman



 =20