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-   -   corrections for LF and HF peaking (http://www.diyaudio.com/forums/tubes-valves/177209-corrections-lf-hf-peaking.html)

pdcaceo 13th November 2010 09:52 PM

corrections for LF and HF peaking
 
HI,

How to make correction on LF peak??

My 845PP has peak on low frequency.

DF96 13th November 2010 10:05 PM

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?

Wavebourn 13th November 2010 10:19 PM

Increase some interstage cap in feedback loop, and decrease another. See what happens.

pdcaceo 14th November 2010 12:07 PM

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

DF96 14th November 2010 12:58 PM

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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