PSN-L Email List Message

Subject: Re: Old hobby resurgence
From: Edward Ianni edwianni1@...........
Date: Mon, 17 Sep 2012 21:14:27 -0400


Thanks a lot Chris. ALL this info is great, and yes please send me the 
scanned circuit.  I really appreciate it.  edwianni1@...........


On 9/17/2012 9:07 PM, chrisatupw@....... wrote:
> From: Edward Ianni 
> To: psnlist 
> Sent: Mon, 17 Sep 2012 23:56
> Subject: Re: Old hobby resurgence
> 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,  Ed.
>
> Hi Ed,
>     741s are quite noisy, but try out the circuit 'as is'. Do check on 
> the turnover boost frequency / period.
>     One weakness of the Roberts circuit is that it can provide very 
> high gain 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 when using 4.5 Hz geophones, since 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 period noise.
> Putting it on the amplifier input will add quite a lot of noise to the 
> whole system chain. The optimal place is after the first amplifier.
>
>>> 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.
>>> 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 compensation to work correctly.
>>>     This is why I prefer to use hardware - this works regardless of 
>>> the unit  digitisation step height, but noise limitation is still 
>>> critical.
>>>
>>>>          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 FAR, FAR easier to use. I can scan that circuit and send it to you.
>     Regsrds,
>     Chris Chapman


  
    
  
  
    
Thanks a lot Chris. ALL this info is great, and yes please send me the scanned circuit.  I really appreciate it.  edwianni1@...........


On 9/17/2012 9:07 PM, chrisatupw@....... wrote:
From: Edward Ianni <edwianni1@...........>
To: psnlist <psnlist@..............>
Sent: Mon, 17 Sep 2012 23:56
Subject: Re: Old hobby resurgence
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,  Ed.

Hi Ed,
    741s are quite noisy, but try out the circuit 'as is'. Do check on the turnover boost frequency / period.   
    One weakness of the Roberts circuit is that it can provide very high gain 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 when using 4.5 Hz geophones, since 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 period noise.
Putting it on the amplifier input will add quite a lot of noise to the whole system chain. The optimal place is after the first amplifier.  

  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.
            
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 compensation to work correctly.
    This is why I prefer to use hardware - this works regardless of the unit  digitisation step height, but noise limitation is still critical.
 
 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 FAR, FAR easier to use. I can scan that circuit and send it to you.
    Regsrds,
 
    Chris Chapman


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