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Preamp Comparison - RCA vs. CM-7777

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  • Preamp Comparison - RCA vs. CM-7777

    I got my hands on a new-in-box vintage Channel Master 7777 preamp from Chad Bryan...
    IMG_9700.JPG

    Up until I received it, I was using the commonly available RCA TVPRAMP1R with separate VHF and UHF inputs. I'm only 1 to 2 miles from several FM and DTV broadcast stations that overload the preamp unless I filter them out before the preamp. I use a couple Tin Lee filters to filter out the strong DTV blowtorches...
    IMG_9157.jpg

    I was doing a side-by-side comparison of these two preamps, and I definitely noticed improvement using the CM-7777 over the RCA. The CM-7777 will not overload nearly as easily. With the RCA, I had to use a full-band FM trap before the preamp or else VHF TV would be severely overloaded. With the CM-7777, I can use a selective FM notch filter before the preamp, and it won't overload like the RCA did. Here is the custom FM filter I use...
    Multi-Notch FM Filter.jpg

    This helps because I can now DX both FM and VHF TV at the same time using this preamp.

    Another observation is that the noise is much less using the CM-7777. By comparing signal strengths on the HD Homerun tuner, the vacant channels look much cleaner. The CM-7777 provides way more amplification than what I needed, so I applied some attenuation after the preamp to help reduce possible distortion and lower noise. I determined that I needed to add about 11.5 dB of attenuation (in addition to the long coaxial cable) before I began to see decreases in the SNRs.

    I'm much happier using the CM-7777. It's too bad it was discontinued.

  • #2
    Channel Master has a new CM-7777 pre-amp, called the "Amplify", model CM-7777HD. Using "7777" again is going to cause confusion. I'm thinking of trying one out here next Spring. It is UHF/VHF, and it has choice of 30db or 17 db gain, and has FM trap and LGE filter.
    Chris - Poughkeepsie, NY
    DTV DXer since April 2009
    See last 24hr DTV DX on Autologger Map here: https://rabbitears.info/tvdx/one_tun...01803EF/tuner1
    DTV DX screenshots at: http://www.flickr.com/photos/dtvdxer/sets
    DTV DX Videos at: http://www.youtube.com/user/dtvdxer

    Comment


    • #3
      Anybody try the 7777HD yet? I'd like to replace my aging Radio Shack amp and built-in cell tower filtering sounds pretty appealing.

      Comment


      • #4
        Ryan, I have not tried the Channel Master 7777HD yet, but I just ordered one through www.channelmaster.com I tried to order one from this site a few weeks ago but was told it was out of stock and not available. Today I found it available. It's $89.00 but they do provide free shipping on orders over $49. I have found it elsewhere but at higher prices. I did find a few open box units at Ebay for slightly less dollars.

        I will try to perform some testing with it once it arrives but because it is Winter in the Midwest, I'm not sure how productive the tests will be right away. I have a great DTV DX test location in mind where a nearby cell tower seems to pose a few audio issues on a couple UHF channels, so it will be interesting to see how well the built-in LTE filter works.

        BTW, thanks Andrew for your fine review above between the RCA TVPRAMP1R and the vintage Channel Master 7777. I own both of those units and hope to compare them with the 7777HD unit sometime next year.

        Comment


        • #5
          With 65 deg. weather yesterday, I lowered the tower and replaced the Winegard HDP-269 preamp (12 dB gain) with the new Channel Master 7777HD preamp (17dB gain or 30dB gain) and the Channel Master 4251 UHF parabolic. Since I live 5 miles from the Indy antenna farm, I'm using the low (17dB) setting. A button on the unit allows you to select between low and high gain. So far, absolutely no good tropo DX to check on distant reception. As for local reception, with the 4251's high gain, even the low setting is overloading when the antenna is aimed at the local towers, as a couple stations actually drop below the decode threshold. This didn't happen with the HDP-269. Once some decent tropo shows up I'll know more about how it works with weak, distant reception. It may not stay on the tower very long, as I would like to perform some comparison testing along with some other models in an area away from the city with less high RF issues. http://www.channelmaster.com/Amplify.../cm-7777hd.htm

          WP_20170222_001.jpgWP_20170222_003.jpg

          Comment


          • #6
            I have tried all of the preamps and my favorite is the Channel Master "vintage" 7777 with dual inputs, and then the Winegard AP-2870.

            The best all in one, is still the Winegard AP-8275. A solid performer.

            The "currently" made preamps, are not as robust as the "vintage" models.

            There are some listed in the "For Sale" section as well.

            Comment


            • #7
              I'll add a preamp observation from some A/B testing this August. While doing maintenance on my other tower, I have, for the last 10 days, had two 4-bay antennas on the same mast on my other 66' tower- a Solid Signal HDB4X and Antennacraft 10-7-13 yagi with a Radio Shack TVPRAMP1R preamp at 79' and a CM4221HD with a Winegard HDP-269 at 74', both above tree level in many directions. The RCA preamp overloads from very local LTE transmissions and perhaps FM, too, even with the FM trap on. The overloading is on UHF only, and the 10 7-13 yagi works very well with the RCA preamp to my HD HomeRun tuners.
              I see on my AirSpy that the low end of the FM band is not attenuated very much by the RCA FM trap, and a couple of very strong signals may interfere with low band VHF, but don't seem a problem with Hi-band.

              On UHF the HDP-269 overloads much less and receives many more channels, channels which have a stronger Signal Strength using the RCA, but 0% Signal Quality (no decode at all). Previously, on the other tower, the CM4221HD at 74' with 90' of RG6 provided excellent reception with no preamp, almost as good as my 2 x 91XGs at 72' with a Winegard LNA-200 using a CM LTE filter. The M 4-bay is autually better for automated scanning because of its greater beamwidth.

              I can't reach the RCA preamp without a lot of work removing the rotator and letting down the mast, but I wonder how the RCA preamp would do with a CM LTE low pass filter. Maybe I'll get to test that this autumn. At present, the HDB4X and RCA preamp are practically worthless on UHF.

              Doug Allen
              Inman, SC EM85wb

              BTW, I infrequently post because I usually loose what I've tried to carefully write. Even though I'm logged in, I get the following error-
              "The following errors occurred with your submission-
              You do not have permission to perform this action. Please refresh the page and login before trying again."
              Many attempted posts never make it because I forget to save my message. Why can't the WTFDA log-in last long enough for one to compose a post?

              Comment


              • #8
                Hi Doug...

                I use 4G-LTE (low pass) filters (MFC or Rad-Shack) on all pre-amp inputs... I've got a local cell site (and another one on the way, UGH!) so filters are just standard procedure, anymore.

                I too, have seen the, 'You've taken too long to type up your post so now you've gotta refresh the page and start all over again' message... So, now, I type up everything in my e-mail program, first, then do a 'cut & paste' to the forum.

                73, Ed NN2E
                Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds
                "You Might Be a Redneck If...
                Your TV is on 24/7.
                Your TV has been permanently on for over a decade.
                The only time your TV is off is during a power outage.
                Your TV gets 512 channels, but you go outside to use the bathroom.
                Your new TV is sitting on top of your old TV.
                Your TV costs more than all of your other furniture.
                Your deer-stand has a TV antenna on it.
                Your cable provider has no idea that you exist."
                Jeff Foxworthy

                Comment


                • #9
                  Originally posted by NN2E View Post
                  Hi Doug...

                  I use 4G-LTE (low pass) filters (MFC or Rad-Shack) on all pre-amp inputs... I've got a local cell site (and another one on the way, UGH!) so filters are just standard procedure, anymore.

                  I too, have seen the, 'You've taken too long to type up your post so now you've gotta refresh the page and start all over again' message... So, now, I type up everything in my e-mail program, first, then do a 'cut & paste' to the forum.

                  73, Ed NN2E
                  Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds
                  Thanks Ed,
                  It seems I never learn! I know I should compose my post elsewhere and then paste it. Still, I wonder why we're logged out so quickly that composing a post online is sometimes impossible. As to LTE filters, glad to know your response. I have two cellphone towers within 150 yards of me! I hate to add the 2, 3, or 4 dB to the NF of my system by adding the extra attenuation of LTE filters, but 20, 30, or 40 db attenuation of the 700 mHz cellphone frequencies is needed to keep the preamps from overloading. Preamps overload more easily than DTV tuners, and I'm finding sometimes the cable attenuation and extra NF of the tuner (compared to the preamp) results in a better solution than adding an LTE filter and preamp. Everyone's situation is different.
                  Doug

                  Comment


                  • #10
                    I install the low pass filter between the antenna and the pre-amp input. This limits the ammount of RF crud getting to the pre-amp. It seems to work OK for me. The orginal cell site is about 3/4 mile from here. The new site will be about 1/2 mile away. I imagine more filtering will be needed once it goes into operation. Someday, I'll do more experimentation, with & without the pre-amp, to see what works best.

                    73, Ed NN2E
                    Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds
                    "You Might Be a Redneck If...
                    Your TV is on 24/7.
                    Your TV has been permanently on for over a decade.
                    The only time your TV is off is during a power outage.
                    Your TV gets 512 channels, but you go outside to use the bathroom.
                    Your new TV is sitting on top of your old TV.
                    Your TV costs more than all of your other furniture.
                    Your deer-stand has a TV antenna on it.
                    Your cable provider has no idea that you exist."
                    Jeff Foxworthy

                    Comment


                    • #11
                      I did some testing with their new product, CM-7778HD dual input model and did some comparing to the vintage models. I used the HD Homerun Tuner and positioned the tuner on 4 channels - ranging from my locals to the Detroit market.

                      With recording the stations signal levels and then replacing the preamplifiers - I feel this new product is a marketing play on words. It is great for a box with dual inputs and a built in LTE filter, but no improvement over the vintage model.

                      When I tested I did not see any improvement in signal quality over the vintage model I simply returned it.

                      As others tested this model, we are all in alignment that this model is not reflecting the so-called lower noise margin.

                      Comment


                      • #12
                        I've been forced into testing sooner than planned...

                        The CM-7777 (2nd generation - single input) quit working. It was in use with the P-7 UHF parabolic.

                        I climbed the tower and replaced the pre-amp with a 'barrel' connector. Now I can do some, on-the-ground, filter testing. So far the Zenith DTT-901 box is working, just fine, without any filters.

                        73, Ed NN2E
                        Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds
                        "You Might Be a Redneck If...
                        Your TV is on 24/7.
                        Your TV has been permanently on for over a decade.
                        The only time your TV is off is during a power outage.
                        Your TV gets 512 channels, but you go outside to use the bathroom.
                        Your new TV is sitting on top of your old TV.
                        Your TV costs more than all of your other furniture.
                        Your deer-stand has a TV antenna on it.
                        Your cable provider has no idea that you exist."
                        Jeff Foxworthy

                        Comment

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