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  #1  
Old 11-01-2013, 05:23 PM
vinyl_junkie vinyl_junkie is offline
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Bozak out of phase outputs

Hi,

I have a Bozak CMA 10-2DL which I think has a slight issue.

I have tested it with a signal generator a while back and a oscilloscope and whilst the main output and headphone outs tested ok the tape output was 180 degrees out of phase to the other outputs. Also it doesn't appear to be frequency dependant.

The wiring looks to be ok i.e. the polarity.

I was wondering if the summing amp flips the phase then it's flipped again after the eq? The tape out is pre eq, post summing board.

Those eq's have a lot of phase shift from memory some one told me. From memory they look like a buffered Bandaxall eq with the transistors for makeup gain.
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Old 11-02-2013, 12:44 AM
Pern Pern is offline
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Both the Summing Amp and the EQ Amp are inverting gain stages. The signal is inverted after the Summing Amp and inverted once again after the EQ, this gives the correct phase for the main outputs.

The design is called SRPP and mostly used in Tube Amps, this design can be implemented in a couple of different ways but here it's a fixed bias Transistor + FET design.
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Last edited by Pern : 11-02-2013 at 04:46 AM.
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  #3  
Old 11-02-2013, 04:55 AM
vinyl_junkie vinyl_junkie is offline
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Thanks for the clarification Pern, it's much appreciated.

One slight odd thing is the cue signal which is pre eq and summing the phase is ok
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  #4  
Old 11-02-2013, 05:03 AM
Pern Pern is offline
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The per channel CUE is taken just at the input and the PGM after the EQ, so the phase should be correct.
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  #5  
Old 11-02-2013, 05:12 AM
vinyl_junkie vinyl_junkie is offline
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Thanks again, all makes more sense now!
Going to reverse the polarity on the sockets for the tape out so they are in phase now I know there isn't anything wrong
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  #6  
Old 11-02-2013, 08:45 AM
Captainjr Captainjr is offline
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Also the tape outputs are pre tone control circuitry. This was designed for flat audio output in the beginning of the record chain signal.
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