Allison Labs Analyzer 605 - Schematics?

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jimfowler

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Anybody have any documentation on this thing? I'm considering trying to restore the gain functionality.
 

mjrippe

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Allison Labs (passive filters, EQs for lab work) or Allison Research (Gain Brain, Kepex, etc.) ? Never seen this model by either of them so just asking (y)
 

jimfowler

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Labs. It’s cool and works as a filter but I have a nagging compulsion to attempt to restore the missing functionality.
 

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Bo Deadly

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It looks like it has the passive LC filters which are very similar to the Pultec HLF3C but 5 poles instead of 3. So they're 30 db/oct which is pretty steep. If the LC filters are critically damped, they are excellent for aggressive low-cut / high-cut effects and isolating tracks in a mix for understanding how some old recording was done. Does this have active circuitry in it? If there is actually gain, it must. Open it up and post pics of the inside.

I have a 2AB and a 2ABR. These are somewhat undervalued IMO. Or at least the prices are not absurd like they are for pultec stuff.
 

Bo Deadly

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I believe they are rated at 24dB/oct, not 30. Could be wrong.
They're 30 db/oct. They're CLCLC. So 5 poles * 6 = 30. A 600 ohm in / out LC filter has to start with the same component type and orientation to have the same characteristic impedance in and out. So it has to be odd numbers of elements. The Pultec HLF3C is 3, the Allison Labs 2BR / 2ABR are 5. The low cut is capacitors in series and inductors as shunts. The high cut is capacitors as shunts and inductors in series.

1637633272881.png
 

mjrippe

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I stand corrected, thank you. Also, the inductors are huge continuously variable jobs which are amazing and would cost a fortune to replicate!
 

jimfowler

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Guts attached. Curiously there’s no input voltage data stamped into the serial number badge on the rear
 

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Bo Deadly

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Yup. Definitely the 5 pole filters. But I have no clue what those cans are. Maybe transformers. Looks like some cut wires under one of them. Shouldn't be hard to trace the bits other than the filter ins and outs which should be just 4 wires each. But not from pictures.
 
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