CM-7777 / 7778: "New & Improved"? - Page 3 - AVS Forum
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post #61 of 99 Old 03-08-2012, 08:45 AM - Thread Starter
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It sounds like the current CM-7777 may be a good choice for your location. To double check, see the following:

Per Tower Guy, the current CM-7777 is recommended if all of the follownig are true:

Quote:
Originally Posted by Tower Guy View Post

  1. There are no TV signals with a TV fool NM greater than 40 db.
  2. There are no FM signals with a signal strength 10 db higher than the strongest TV signal. (or you use a 7-69 antenna)
  3. The antenna is split to more than 2 TV sets.
  4. The cable length is longer than 50 feet.
  5. The weakest signal of interest has a NM plus antenna gain of less than 6 db.

Quote:
Originally Posted by Wendell R. Breland View Post

You may find this site useful, click CALCULATING SYSTEM NOISE TEMPERATURE

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post #62 of 99 Old 03-09-2012, 09:20 AM - Thread Starter
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After > 3,000 views in just 3 weeks, how many have decided to purchase or have ordered the current CM-7777 or 7778 instead of the "New & Improved" models? (See photos too.)

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post #63 of 99 Old 03-17-2012, 08:28 PM
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Somehow yesterday my attic installed Ability preamp stopped working. Don't know if it was due to a power surge during a thunderstorm, or due to overload from abnormally strong signals due to the weather conditions. The power supply still works, but I had to replace the preamp piece directly connected to the antenna balun. Fortunately, I had previously ordered a 2nd Ability preamp for future use, so I was able to determine and replace the part that was not working. The power supply is still good. Also, an original CM-7778 connected to another attic antenna and TV was not damaged. What do you think may have happened? I use the low noise Ability amp for weak distant signals, but perhaps it was overloaded and shorted out from strong local signals. Does that sound reasonable?
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post #64 of 99 Old 03-18-2012, 04:27 AM
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No. Strong local broadcast signals won't cause amplifier electronics to fail.

Surges from nearby lightning events, OTOH, is a common reason for amps to fail.
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post #65 of 99 Old 03-18-2012, 10:26 AM
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3 Types of Overload

 

Quote:



I use the low noise Ability amp for weak distant signals, but perhaps it was overloaded and shorted out from strong local signals. Does that sound reasonable?

The preamps that have the lowest noise figures use transistors in the front-end that are more sensitive to static and impulse (EMP) damage; that's the trade-off.

There are three types of preamp overload, in order of increasing signal strength:

1. The strong signals cause enough IM distortion to interfere with the reception of weak desired signals. This is the point that holl_ands uses in his preamp charts to obtain max SFDR (Spurious Free Dynamic Range). No damage will happen.

2. The strong signals cause overload to the preamp or tuner that makes it impossible to receive any signals. No damage will happen.

3. The signals are so strong that the input transistor is toast. You are not likely to encounter OTA signals that strong.


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post #66 of 99 Old 03-18-2012, 03:36 PM
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I think a power surge during a thunderstorm may have toasted the preamp. The signal was split to 2 TVs and one of them had no surge protector.
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post #67 of 99 Old 03-19-2012, 02:44 PM - Thread Starter
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Quote:
Originally Posted by rabbit73 View Post

The preamps that have the lowest noise figures use transistors in the front-end that are more sensitive to static and impulse (EMP) damage; that's the trade-off.

+1.

tylerSC,

You may wish to check out this thread if you haven't seen it already.

In my research to date, it appears that the very cost-effective orignal CM-7777 offers the lowest NF of all the preamps that have very effective static and EMP protection. Most preamps with a lower noise factor than the CM-7777, are either much more expensive and/or prone to lightning damage.

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post #68 of 99 Old 03-19-2012, 03:17 PM
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Overall, I have had best luck with the original CM-7777 and 7778. But somehow, only the Ability preamp would allow me to decode a weak, distant translator signal from about 65-70 miles. I suppose it is the low noise figure and phemt circuitry that makes the difference. But I removed the splitter, and have the new Ability amp only connected to one TV with a good surge protector. Hopefully this will lessen future power surges and reduce the impact of potential damage in the future.
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post #69 of 99 Old 03-19-2012, 03:32 PM - Thread Starter
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Quote:
Originally Posted by tylerSC View Post

Overall, I have had best luck with the original CM-7777 and 7778. But somehow, only the Ability preamp would allow me to decode a weak, distant translator signal from about 65-70 miles. I suppose it is the low noise figure and phemt circuitry that makes the difference.

Yes, the extra low noise figure will allow you to receive weaker stations.

Quote:
Originally Posted by tylerSC View Post

But I removed the splitter, and have the new Ability amp only connected to one TV with a good surge protector. Hopefully this will lessen future power surges and reduce the impact of potential damage in the future.

Yes, that should help with electrical power surges. However, what if there is lightining near your antenna? You may wish to check the preamp owner's manual to see what RF lightning protection if any has been included in their design. If they're proud to tell you about their low-noise phemt circuitry, they should also discuss thier static and EMP protection circuitry.

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post #70 of 99 Old 03-19-2012, 03:57 PM
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My antenna is in the attic, so my main concern is with electrical power surges that produce occaissonal pixelation and audio dropouts. Don't want the power surges to short out the preamp again. The power surges/electrical interference is noticeable on a weak UHF channel, and one VHF channel, usually between 5pm 6:30 pm most days and during thunderstorms. Trying to figure out if there is some type of whole house surge regulator that maintains stable power levels when the electrical currents enter the house. Going to Home Depot tomorrow.
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post #71 of 99 Old 03-20-2012, 01:13 AM - Thread Starter
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If you search the Home Depot website for "Whole-House Surge Protectors" it appears they currently sell one brand - Eaton (Cutler Hammer).

Quote:


The Eaton Cutler-Hammer Surge Protector is intended to help protect home electronics from voltage surges. This unit is ANSI certified and CSA- and UL listed. The protector is for use with AC power, has a 120,000 Amp maximum surge current and a total of 1,920 joules.

Use to help protect home electronics from voltage surges
1,920 joules total
120,000 Amp maximum surge current
Compatible with AC power
ANSI certified and CSA- and UL listed
MFG Brand Name : Eaton Cutler-Hammer
MFG Model # : CHSPMICRO
MFG Part # : CHSPMICRO

Note: the surge response time is not available. However, other brands list this important spec. Per James Dulley, "Any reaction time less than one nanosecond is adequate."

Per James Dulley, other brands of whole-house units (not: point-of-use or service entrance meter based) with < 1 sec. reaction time include: Intermatic, MVC. Inc., Siemans, and Square D.

Also, look for a higher surge current and a lower clamping voltage.

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post #72 of 99 Old 03-20-2012, 01:39 AM - Thread Starter
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Quote:
Originally Posted by tylerSC View Post

My antenna is in the attic, ... The power surges/electrical interference is noticeable on a weak UHF channel, and one VHF channel, usually between 5pm 6:30 pm most days and during thunderstorms.

From an antenna grounding thread:
Quote:
Originally Posted by kenglish View Post

A nearby lightning strike can still induce a surge in to the attic antenna. Your best bet is to ground the cable, along with a surge-limiting lightning-arrestor.

See the following very comprehensive post:
Quote:
Originally Posted by holl_ands View Post

There are three general types of coax surge protectors


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post #73 of 99 Old 03-20-2012, 04:58 AM
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Quote:
Originally Posted by tylerSC View Post

...The power surges/electrical interference is noticeable on a weak UHF channel, and one VHF channel, usually between 5pm 6:30 pm most days and during thunderstorms...

If you're experiencing dropouts, it's probably from impulse noise. If it occurs at a certain time of day, it may be from some electrical device a neighbor is using at that time, or you may have a power company problem with a nearby transformer, etc. Ferrite chokes that clamp on the coax where it connects to the TV tuner may offer some help. But you won't be able to eliminate VHF dropouts from lightning in the region; unless the station moves to a decent (UHF) channel and broadcasts at an acceptable power level. In lightning-prone areas, VHF is a very poor choice for a DTV channel to be on.
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post #74 of 99 Old 03-20-2012, 02:51 PM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

If you're experiencing dropouts, it's probably from impulse noise. If it occurs at a certain time of day, it may be from some electrical device a neighbor is using at that time, or you may have a power company problem with a nearby transformer, etc. Ferrite chokes that clamp on the coax where it connects to the TV tuner may offer some help.

Is there a recommended brand or model?

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post #75 of 99 Old 03-20-2012, 03:12 PM
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Any should work. Like these, for example:
http://www.avsforum.com/avs-vb/showt...9#post21795489
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post #76 of 99 Old 03-20-2012, 04:22 PM - Thread Starter
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And cost-effective too

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post #77 of 99 Old 03-20-2012, 05:09 PM
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Quote:
Originally Posted by ota.dt.man View Post

Is there a recommended brand or model?

They also sell them at Radioshack, but not sure about price. And they are normally an included accessory when you purchase a plasma TV.
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post #78 of 99 Old 03-20-2012, 09:12 PM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

If you're experiencing dropouts, it's probably from impulse noise. If it occurs at a certain time of day, it may be from some electrical device a neighbor is using at that time, or you may have a power company problem with a nearby transformer, etc. Ferrite chokes that clamp on the coax where it connects to the TV tuner may offer some help.

arxaw,

1. Would there also be a benefit to adding a Ferrite choke to a CM-7777 power supply at the antenna input?

Parts Express customer reviews:
Quote:
I bought this size for my mircowave's cord and it fit snug the way u want any size ferrite suppressor to fit snug ... Your household eqipment like your microwave your fridges anything with a motor in it will send out bad noise into the current and you can hear it on headphones or tv as a buzzing and that what it does to your tv screen when the device is in use. It did the job perfectly suppressing the noise ...

Quote:
... noise polluting devices like refrigerators, (it works wonders on my 2 fridges though double coiled works even better), clothes washer, computers, Flatscreen TV's DVD players, ( it works wonders on all my DVD players including my super $700 Samsung BluRay).

Use in all digital and motor/compressor devices that produce EMI RFI into the electric mains grid of your house, that will help all your audio and video gear sound and look better, also using it on TV's and DVD's helps them look sharper, better colors, more defined imaging etc.

2. Are all the customer suggested uses also necessary / recommended or is TV tuner coax input sufficient?

Thanks

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post #79 of 99 Old 03-21-2012, 04:50 AM
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Quote:
Originally Posted by ota.dt.man View Post

1. Would there also be a benefit to adding a Ferrite choke to a CM-7777 power supply at the antenna input?

If it reduced interference; yes.


Quote:
2. Are all the customer suggested uses also necessary / recommended or is TV tuner coax input sufficient?

It would depend on the type of noise, how bad it is and whether or not the ferrite choke at the tuner input eliminated it or not.


Quote:
"using it on TV's and DVD's helps them look sharper, better colors, more defined imaging etc."

It's certainly not going to do this. That claim is total BS.
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post #80 of 99 Old 03-21-2012, 06:27 AM - Thread Starter
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Quote:
Originally Posted by tylerSC View Post

... The power surges/electrical interference is noticeable on a weak UHF channel, and one VHF channel, usually between 5pm 6:30 pm most days and during thunderstorms.

Quote:
Originally Posted by arxaw View Post

If you're experiencing dropouts, it's probably from impulse noise. If it occurs at a certain time of day, it may be from some electrical device a neighbor is using at that time, ... Ferrite chokes that clamp on the coax where it connects to the TV tuner may offer some help.

Sounds like an appliance that's used at dinner time - perhaps a microwave? Our Panasonic microwave interferes with our TV and VHF channel 7 is most affected by it.

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post #81 of 99 Old 03-21-2012, 09:00 AM
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Quote:
Quote:
"using it on TV's and DVD's helps them look sharper, better colors, more defined imaging etc."
It's certainly not going to do this. That claim is total BS.

Reminds me of Black Friday 2003 when the guy at Best Buy said i needed that $200 Monster power strip with my new 52" RP RCA set, otherwise, it would get all kinds of bad images from dirty power.

Tech support for Antennas Direct
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post #82 of 99 Old 03-26-2012, 10:02 AM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

If you're experiencing dropouts, it's probably from impulse noise. If it occurs at a certain time of day, it may be from some electrical device a neighbor is using at that time, or you may have a power company problem with a nearby transformer, etc. Ferrite chokes that clamp on the coax where it connects to the TV tuner may offer some help.

Quote:
Originally Posted by ota.dt.man View Post

Our Panasonic microwave interferes with our TV and VHF channel 7 is most affected by it.

arxaw,

Have you had any experience with solving microwave interference with Ferrite chokes either on the TV tuner or microwave or both?

Thanks

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post #83 of 99 Old 03-26-2012, 10:06 AM
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Quote:
Originally Posted by ota.dt.man View Post

...Have you had any experience with solving microwave interference with Ferrite chokes either on the TV tuner or microwave or both?

No, but they are cheap and worth a try. Also, check your breakers to make sure the micro and TV tuner, preamp, etc. are not on the same circuit. Unlikely, though.
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post #84 of 99 Old 03-26-2012, 10:27 AM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

No, but they are cheap and worth a try. Also, check your breakers to make sure the micro and TV tuner, preamp, etc. are not on the same circuit. Unlikely, though.

OK, I'll give it a try.

Breakers: The microwave, TV tuner, & preamp are all on different breakers. The microwave is on a dedicated 20 amp breaker.

The TV & tuner are also connected to an APC SurgeArrest. The preamp PS is connected to a Belkin SurgeMaster that's connected to a GFI outlet.

Any other suggestions would be welcome.

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post #85 of 99 Old 03-30-2012, 04:28 PM - Thread Starter
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The Parts Express ferrite core order arrived today. I attached one to the most proximal end of the microwave power cord, turned it on and checked channel RF 7. I saw an immediate reduction in the degree of intereference. Given this improvement, I added a 2nd ferrite core in series with the first one and repeated the test. With 2 ferrite cores in a row, the microwave no longer interferes with the TV. Thanks for the recommendation arxaw.

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post #86 of 99 Old 03-31-2012, 03:57 AM
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Glad it solved your pesky VHF reception/interference problem.
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post #87 of 99 Old 04-02-2012, 08:22 AM - Thread Starter
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Quote:
Originally Posted by tylerSC View Post

Somehow yesterday my attic installed Ability preamp stopped working. Don't know if it was due to a power surge during a thunderstorm, or due to overload from abnormally strong signals due to the weather conditions. The power supply still works, but I had to replace the preamp piece directly connected to the antenna balun. Fortunately, I had previously ordered a 2nd Ability preamp for future use, so I was able to determine and replace the part that was not working. The power supply is still good. Also, an original CM-7778 connected to another attic antenna and TV was not damaged. What do you think may have happened? I use the low noise Ability amp for weak distant signals, but perhaps it was overloaded and shorted out from strong local signals. Does that sound reasonable?

Quote:
Originally Posted by tylerSC View Post

I think a power surge during a thunderstorm may have toasted the preamp. The signal was split to 2 TVs and one of them had no surge protector.

Quote:
Originally Posted by tylerSC View Post

Overall, I have had best luck with the original CM-7777 and 7778. But somehow, only the Ability preamp would allow me to decode a weak, distant translator signal from about 65-70 miles. I suppose it is the low noise figure and phemt circuitry that makes the difference. But I removed the splitter, and have the new Ability amp only connected to one TV with a good surge protector. Hopefully this will lessen future power surges and reduce the impact of potential damage in the future.

Tyler,

Was your CM-7778 connected to a TV with or without a surge protector?

Quote:
Originally Posted by tylerSC View Post

My antenna is in the attic, so my main concern is with electrical power surges that produce occaissonal pixelation and audio dropouts. Don't want the power surges to short out the preamp again. The power surges/electrical interference is noticeable on a weak UHF channel, and one VHF channel, usually between 5pm 6:30 pm most days and during thunderstorms. Trying to figure out if there is some type of whole house surge regulator that maintains stable power levels when the electrical currents enter the house. Going to Home Depot tomorrow.

What did you decide to do to protect your back-up Ability preamp?

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post #88 of 99 Old 04-02-2012, 10:20 AM
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I replaced the fried Ability preamp with the other one I had ordered for future use. It is now connected to one TV again with a good surge protector, no splits. All is working well there. And the orig 7778 was also connected to a separate TV and antenna, also with a surge protector, so it was not damaged. I just wonder if splitting the first Ability amp caused some sort of uneven power flow, and that is what caused the damage.
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post #89 of 99 Old 04-02-2012, 12:40 PM - Thread Starter
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What did you decide about protection for a lightning-induced surge through your attic antenna?

Quote:
Originally Posted by kenglish View Post

A nearby lightning strike can still induce a surge in to the attic antenna. Your best bet is to ground the cable, along with a surge-limiting lightning-arrestor.

Quote:
Originally Posted by holl_ands View Post

There are three general types of coax surge protectors ...

Your ultra-low noise Ability preamp may need more lightning protection than your CM-7778. The devices recommended by kenglish & holl_ands are much less expensive than a new Ability preamp.

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post #90 of 99 Old 04-02-2012, 02:24 PM
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Originally Posted by ota.dt.man View Post

What did you decide about protection for a lightning-induced surge through your attic antenna?




Your ultra-low noise Ability preamp may need more lightning protection than your CM-7778. The devices recommended by kenglish & holl_ands are much less expensive than a new Ability preamp.

Is there a link to a post where they recommend these devices? I am not an electrician nor engineer, so hopefully there is a somewhat simple, nontechnical solution. What is the best way to ground an attic antenna and protect the preamp?
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