?LOW FREQUENCY COMPENSATION? adjustment??
OK?so I recalibrated my Otari BIII yesterday using a fresh new MRL tape and the Visual Analyzer software (
http://www.sillanumsoft.org/) in place of a hardware scope (the VA software works great).
Now?everything went well, and I did a full alignment/calibration, covering everything accept the actual head height, zenith and head wrap. The deck is almost new, with literally no use, and based on the fact that all my other adjustments were relatively minute, I felt no need to mess with the physical positions of the heads at this time. I also didn?t touch the Erase head.
I?ll check and save those alignment procedures for the next time.
Now, the only one thing I wasn?t 100% clear about was the Low Frequency Compensation adjustment.
I think I know it?s basic purpose, but the full ?Alignment Procedures? manual I have talks about setting it for the ?flattest frequency response??though it requires the use of 20Hz to 200Hz tones from the oscillator?and there is no way to get all of those tones ?flat?.
Meanwhile, the ?Operations and Maintenance? for this deck says to run the oscillator at 0VU Source, and then adjust the LFC pot to match 0VU when at TAPE while running in Record mode. It never mentions which frequency(s) to use.
What I did was something a bit different.
I ran my Left channel in TAPE mode and my Right Channel in SOURCE mode while in Record.
Then, using the VA software, I was able to monitor the frequency response of both channels. That way, I adjusted the LFC so that my Left (TAPE) curve was matching my Right (Source) curve?however, there were level differences between 20Hz ? 40Hz ? 100Hz ? 200Hz.
IOW?if I match at 20Hz?then the TAPE curve was several dB higher at 40Hz...if I match at 40Hz?it was lower at 20Hz by same amount.
When I looked at 100Hz and up to 200Hz?the LFC adjustment had les effect, and the TAPE/SOURCE curves were matched throughout, so I concluded that the LFC was mainly for the sub-80Hz range.
So what I did was to find the mid-point between the lowest and highest points curve positions at the frequencies from 20Hz to 80Hz.
What I ended up with was -3dB at 20Hz as my lowest differential between TAPE and SOURCE curves?and +3db differential at 40Hz. The differentials at 30/50/60/80Hz were less than that.
To me?that was the only way to obtain the ?flattest frequency response? as mentioned in the manual.
Turning off the LFC?at 20Hz ? 40Hz there was greater +dB hump on the TAPE curve when comparing to the SOURCE curves?which means the deck was boosting those frequencies above their source levels without the LFC.
So?is that what the Low Frequency Compensation is meant for?to trim/flatten the low frequencies as close as possible to their source levels?
I?m assuming it isn?t meant to be used to lower them severely below their source levels????
Anyone have a better/clearer explanation of the LFC adjustment from what the manuals describes?
I just want to make sure I didn?t mess it up?.