"midrange dip" - Lew - OTL Asylum

OTL Asylum

OTL, Output Transformerless Amplifier User Group.

"midrange dip"

In Reply to: Re: my two cents posted by Roy on July 15, 2002 at 13:25:18:

Here is my "experience" with the midrange dip: Kevin Covi did a computer-generated analysis of the expected impedance curve using the new hi-pass filter (C=24uF/R=12 ohms/L=15mH) compared to the old one (C=48uF/R=6 ohms). In BOTH cases, the predicted impedance starts off very high at low frequencies and falls to about 4 ohms at 500 Hz. (Z is a little higher at 500 Hz for the new filter compared to the old one, but not much, and probably not noticeably so.) Above 500 Hz, the new filter offers a considerable increase in impedance vs the old one, until up above 6 kHz, when Z falls below 4 ohms again. (I don't think the low Z at high frequencies is a real problem for our amplifiers, however.) So, I cannot say that I really experienced the midrange dip; I just examined Kevin's graph. Previously, when I owned the U2s, with the old standard hi-pass filter, I definitely DID notice a lower midrange "suck-out" in the frequency response, which was completely ameliorated by using the Zeros. I had hoped that with the new network, the Zeros would be dispensible, but we shall see. I need to understand one very important implication of your post: Did Dr. West actually suggest doubling the value of R again, to make it 24 ohms total instead of 12 ohms? If so, I am very surprised, since he previously feared that increasing R much above 6 to 7 ohms (or 12 ohms with the new network, since it affords a 12db/octave roll-off) would risk saturating the toroid. IF it's OK to go to R=24 ohms without harming the performance of the toroid, that might be a great help.

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Follow Ups Full Thread

Topic - Pure Magic - Roy 15:21:40 07/05/02 (14)

Re: Pure Magic - David M. 08:07:04 07/07/02 (13)

Re: Pure Magic - Roy 10:15:17 07/07/02 (12)

Re: Pure Magic - David M. 20:11:33 07/07/02 (11)

Re: Pure Magic - Roy 05:00:04 07/08/02 (10)

Re: Pure Magic - David M. 21:38:05 07/12/02 (9)

Re: Pure Magic - Al Sekela 13:07:36 07/13/02 (8)

Re: Pure Magic - David M. 19:01:39 07/13/02 (7)

Re: Pure Magic - Al Sekela 21:09:05 07/13/02 (6)

Re: Pure Magic - Roy 03:11:31 07/14/02 (5)

my two cents - Lew 10:49:44 07/15/02 (4)

Re: my two cents - Roy 13:25:18 07/15/02 (3)

"midrange dip" - Lew 14:25:02 07/15/02 (2)

Re: "midrange dip" - Roy 15:49:36 07/15/02 (1)

Re: "midrange dip" - Al Sekela 20:06:52 07/15/02 (0)

Follow Ups

"midrange dip" - Lew 14:25:02 07/15/02 (2)

Re: "midrange dip" - Roy 15:49:36 07/15/02 (1)

Re: "midrange dip" - Al Sekela 20:06:52 07/15/02 (0)

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