I have been following this thread for a bit, and I would have to  
concur with Mike's assessment of the variable low-pass filter on the  
Packburn. Despite many attempts at trying to make this unit sound  
good, I have to admit I never liked it much.

Like most signal processors, if it was used sparingly, the artifacts  
weren't too noticeable, but high-amplitude pops or ticks could really  
put it over the edge.

Scott D. Smith
Chicago Audio Works, Inc.

Quoting Michael Biel <[log in to unmask]>:

> [log in to unmask] wrote:
>> IIRC the PB worked best with a stereo input to better define noise   
>> and make the choice of switching between groove sides. Better to   
>> sum the channels post-PB.
> The PackBurn works ONLY with a stereo input, at least for the switcher
> circuit.  There were three sections in it, and the first was the
> switcher.  It listened to the two groove walls and decided which one
> was the quietest at any point in the record.  If it did not have a
> stereo source, how could it tell????????????  And how could it give one
> or the other walls separately???  The original model gave an output of
> either the left or the right.  The "Centennial Model" numbered 1977 and
> issued in 1977 added a feature that would give the sum of the two
> channels when both walls were equally quiet.
> The second section was the blanker which was a mono impulse noise
> eliminator, and this is pretty much what most other noise-reduction
> systems in use are.  If all that was available was a mono source, this
> still would work.   The third section was the dynamic noise filter
> which we discussed yesterday.  This raised and lowered the top
> frequency of the low-pass filter to allow more highs when the louder
> musical content would mask the surface noise, but then reduced the top
> frequency when the program content was quiet and would otherwise allow
> the surface noise to be heard.  I HATED this filter, but as I mentioned
> yesterday, Dick Burns LOVED it. Of course any of these three sections
> could be switched in or out of the audio path. Mike Biel
> [log in to unmask]
>> John Eberle wrote:
>>> Playing 78s through an RIAA preamp basically  rolls off the highs   
>>> and boosts the lows dramatically altering the frequency  response   
>>> from what it should be . The RIAA pre-emphasis eq curve is applied  
>>>   during the disc cutting stage of 45 and LP record mastering . 78  
>>>  RPM records were not cut with RIAA pre-emphasis ; but rather were  
>>>  cut mostly  flat with perhaps some low end roll of to control the  
>>>  size of the bass  groove excursions .
>>> A simple and cheap way to playback 78 RPM records is  to connect   
>>> the turntable or tone arm audio out to the HI-Z microphone inputs   
>>>  available
>>> on many preamps . This will give the flat response desired for 78s  
>>>   and a little low boost will bring the lows back in to proper   
>>> perspective .  Also , most cartridges in current use for playing   
>>> 78s are actually stereo  and of course 78s are mono . It is   
>>> totally weird to hear a 78 RPM disc  being played with stereo   
>>> clicks and pops . The cartridge can be wired in the  headshell to   
>>> reproduce lateral mono modulation only . This makes the record    
>>> noise a lot less and less need for the Packburn or any other   
>>> analog or digital  transient noise reduction and better over all   
>>> quality . If anyone would like  an mp3 of one of my commercial 78s  
>>>  reproduced in this manner , just contact  me off list and I will   
>>> email it to you .
>>> John Eberle  : Over   27 years disc cutting experience and over 35  
>>>  years in Mastering  !
>>> 615-441-4660 **************Feeling the pinch at the grocery store?  
>>>   Make dinner for $10 or less.   
>>> (