Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download nfb-cap-freq-respons..
Document related concepts
Transcript
Untitled Document START NEW THREAD Page 1 of 2 REPLY Top of Thread LIST PREVIOUS LIST Read 77 times From: Date: Subject: JR 8/28/2001 4:13 PM Feedback resistor size - bigger = less bass? I was looking at schems and the JCM800/JMP have a 100k feedback resistor where boogie has a 47K and the SLO has a 37K. What is the effect on low end? Also, I read somewhere that adding a .1uF in series with the resistor beefs up the low end? Cheers JR START NEW THREAD REPLY Read 76 times From: Date: Subject: Mark Lavelle ([email protected]) 8/28/2001 4:36 PM bigger = less NFB Higher value means less negative feedback. Less feedback means louder & 'looser' (more distorted, but not necessarily in a bad way). The problem with no or very little NFB is that the looseness can translate into unstable lows when you're pushing your amp. My homebrew has an on-off-on SPDT switch on the NFB so I can choose between none (no connection), 100K (light NFB) and 33K (tight). All three settings are useful. Can't help on the cap part... START NEW THREAD REPLY PREVIOUS LIST Read 49 times From: Date: Subject: eric ([email protected]) 8/28/2001 7:04 PM Re: Feedback resistor size - bigger = less bass? http://www.firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=135970-000000.msg 8/28/2001 Untitled Document Page 2 of 2 In regards to the .1uF cap, yes it can serve to add low end if placed in the feedback loop along with the feedback resistor. This is because a capacitor's impedance to a signal changes with changing frequency. If the circuit you are referring to is set up as some sort of an amplifier, the ratio of feedback to input impedance determines gain, so placing a cap in the feedback loop causes the gain to change with frequency. the relationship for capacitance, impedance and frequency is roughly z=1/(fc), so with this you can calculate at about what frequency the capacitor has a small effect on the gain, and then select the right value to get the desired cutoff point where the signal is no longer boosted above its "normal" level (the level without the cap). If you need any clarifications feel free to email me about. Eric alternate display for printing http://www.firebottle.com/ampage/bbs/fireBB.cgi?forum=ga&thread=135970-000000.msg 8/28/2001
