corrections for LF and HF peaking

pdcaceo · 13th November 2010, 09:52 PM

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.

13th November 2010, 09:52 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, 10:19 PM	#3
Wavebourn 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 mathematical model! Wavebourn: We Create Creativity!

14th November 2010, 12:07 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

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13th November 2010, 10:05 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?

14th November 2010, 12:58 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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