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Reviews Categories | Filters, Audio: (DSP and others) | MFJ-722B Help

Reviews Summary for MFJ-722B
MFJ-722B Reviews: 2 Average rating: 4.5/5 MSRP: $99.95
Description: Op amp-based audio filter (FILTER, CW/SSB AUDIO FILTER, NOTCH, AMP)
Product is in production.
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KF7AC Rating: 5/5 Aug 9, 2014 20:29 Send this review to a friend
A quality product, but needs modification.  Time owned: 0 to 3 months
Just received my new MFJ-722b from Universal Radio. My first impression was it was not working correctly because the audio out was very weak while driven with my Kenwood TS-590. (I purchased this unit to filter out noise for my MFJ CW reader. There was not enough audio to drive the CW reader.) I reviewed the schematic and realized the input audio was fed into hi Z op amps and there was no impedance matching. I purchased a 8 ohm to 1000 ohm audio transformer from Radio shack and installed it along with a 5K pot into the 722b such that the Kenwood was driving the 8 ohm side of the transformer. This mod gave me too much audio drive and had to be adusted with the 5K pot I had place across the 1K side of the transformer. I found plenty of room for this installation. With this change, the 722b works great. The notch function is impressive and the CW filtering is just the thing to clean up the hi freq audio spikes for the CW reader. I was impressed with the assembly of the 722b, the surface mount technology looked clean and well done. This is one of MFJ's better products.
WB1AAL Rating: 4/5 Feb 7, 2013 17:29 Send this review to a friend
Lastest Addition to MFJ Audio Processor Line  Time owned: 0 to 3 months
More MFJ gear seems to be finding its way into my shack. I know that there are quality control concerns with MFJ, but their gear has managed to fill some of the gaps left by the departure of Heathkit and others from the ham radio market. That alone makes MFJ gear an attractive addition to my shack.

The most recent shack addition is the MFJ-722B "Optimizer"--and name clearly borrowed from the Heathkit folks (e.g. the Heathkit "Microlizer.") Basically, the MFJ-722B is the most recent rendition of the MFJ op amp-based audio filter. It is useful with vintage rigs from the pre-DSP era--although the MFJ-722B can also be used injunction with a DSP rig.

In my shack this is the latest in a line of aftermarket audio filters looking to assist my Kenwood TS-430S in ferreting the signals out of the noise and QRM. Preceding it was a Heathkit HD-1418 Active Audio Filter and the Autek QF-1A audio filter.

On the pro side:

* It works well especially in reducing QRM and atmospheric noise

* It has an all metal case (the earlier MFJ-722 units [pre B] had plastic in their cases)

* I find it more intuitive to use than either the HD-1418 or Autek QF-1A

* It supports a notch filter, a notch filter with HP filtering, a notch filter followed by HP and variable LP filtering for SSB and CW. Very logical.

* It is smaller in size than either the HD-1418 or Autek QF-1A

On the con side:

* It came out of the box with a noisy pot (contact cleaner session coming up!)

* It doesn't have enough power to adequately drive my RCA PRO-X33AV speaker--something that the Heathkit HD-1418, Autek QF-1A or even the Kenwood TS-430S can do with ease. (This con was overcome by the addition of a spare Heathkit AA-18 mono amplifier placed after the MFJ-722B. But that's yet another piece of gear taking up space on my ham shack desk and sucking power from my AC line.)

BTW, although the instructions are decent, don't even try to read the schematic diagram in the manual. It is reduced to a tiny size and nearly impossible to read. I've mentioned this before in other vendor equipment reviews and it will be repeated here. Hams are generally technically oriented folks. Vendors should include schematics with their devices--but PLEASE MAKE THEM READABLE!

If you think I was shouting that last part out, you are entirely correct!

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