corrections for LF and HF peaking
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 13th November 2010, 10:52 PM #1 pdcaceo   diyAudio Member   Join Date: Jun 2004 Location: HK corrections for LF and HF peaking HI, How to make correction on LF peak?? My 845PP has peak on low frequency. __________________ Wilson
 13th November 2010, 11:05 PM #2 DF96   diyAudio Member   Join Date: May 2007 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?
 13th November 2010, 11:19 PM #3 Wavebourn   Designer & Technologist diyAudio Member     Join Date: Sep 2006 Location: Pleasant Hill, CA Increase some interstage cap in feedback loop, and decrease another. See what happens. __________________ The Devil is not so terrible as his math model is!
 14th November 2010, 01:07 PM #4 pdcaceo   diyAudio Member   Join Date: Jun 2004 Location: HK 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 __________________ Wilson
 14th November 2010, 01:58 PM #5 DF96   diyAudio Member   Join Date: May 2007 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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