corrections for LF and HF peaking - diyAudio
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Old 13th November 2010, 09:52 PM   #1
pdcaceo is offline pdcaceo  Hong Kong
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Default corrections for LF and HF peaking

HI,

How to make correction on LF peak??

My 845PP has peak on low frequency.
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Old 13th November 2010, 10:05 PM   #2
DF96 is offline DF96  England
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Does it have negative feedback? If so, the LF peak is probably a result of a bad combination of LF roll-offs in the open-loop gain. Can you post a circuit diagram?
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Old 13th November 2010, 10:19 PM   #3
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Increase some interstage cap in feedback loop, and decrease another. See what happens.
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Old 14th November 2010, 12:07 PM   #4
pdcaceo is offline pdcaceo  Hong Kong
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HI ,

The circuit like this


6SN7 direct couple to 6SN7 phase splitter ( 0.22uf + 1M)+ RC couple(0.33uf + 220K) to 300B( cathod is 220R + 100V 100uF) + RC couple ( 0.47 + 220K)to 845 + transformer
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Old 14th November 2010, 12:58 PM   #5
DF96 is offline DF96  England
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I calculate your LF corners at 0.72, 2.2 and 1.5 Hz respectively, plus whatever the OPT does. If the OPT is at 20Hz, then the 2.2 and 1.5 Hz may be a bit too close to it and each other. As a first approximation they will look like a single 3.7Hz roll-off in phase terms. Try increasing the 0.33uF capacitor. Alternatively, reduce it to 0.0047uF so it becomes the dominant LF pole instead of the OPT - although this will reduce your bass power handling.

How much feedback is used? An alternative is to reduce the feedback, probably by increasing the feedback resistor.
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