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 Post subject: Talking House 5.0 audio overload and hum/buzz
PostPosted: Mar Mon 08, 2021 12:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 896
Location: Rockaway , nj 07866
i have one of these and my two problems are the audio overloads on the line input , i tried a attenuated plug in the mic input same thing , it only sounds ok when i feed the cassette deck in and use it as a level control , so the highest level on the cassette deck meters is half way , if you go 3/4 or to 0 on the level meters it distorts , so i can get around this by making a wire with a potentiometer ( volume control ) to prevent distorting unless theres something you guys know i should do.
The other issue is a hum/buzz thats audible between music tracks or if there is just talking , is this the power supply thats at fault ? if yes could i add a filter or do i need a different power supply ?

thanks


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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Mar Tue 09, 2021 4:21 pm 
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Posts: 745
Location: Equinunk PA 18417
Kramden, your idea to control level from you cassette deck to the transmitter is sensible. I don't have a Talking House transmitter and its user manual does not give audio input specifications. So, I don't have a clue how much level the input is able to handle before overloading. There is supposed to be an automatic level control to prevent overloading, but that is obviously not helping you. Wire in a separate potentiomenter! That's probably what I would do as a quick fix.

Regarding hum being received, that is a very different thing and probably why no one has answered your questions. There can be multiple explanations that are difficult to diagnose from a distance. Does the hum level change when you move your receiver around? A portable radio can be moved and oriented to "null out" the hum, or most of it. If that is the case for you, then it is a sure sign the hum is not from the transmitter itself, or its power supply, but is instead a result of the transmitter signal interacting with your home's AC power wiring. Any wiring and/or electrical conduits behave as efficient antennas that intercept some energy from your transmitter and re-radiate it, just like your transmitter's antenna. Some rf energy has a path to the AC wiring through your transmitter's power supply, and/or through the audio wirings back through your cassette deck into the mains wiring. No matter how it gets onto the AC wiring, the signal is there modulated by the mains power and re-radiated. Your radio receives signals directly from the transmitter and hum-filled versions from house wiring. By orienting the receiver, you can often find limited areas where the mains wiring version is much smaller, thus the hum is reduced. I often note that the hum is nearly gone when a portable receiver is within a foot or two of the transmitter. The direct signal dwarfs whatever re-radiation is happening.

Many of us have this problem and there are multiple things to try. Eliminating rf signal pickup through audio cables and power supply cables is a start. Inductors in series with audio lines, re-routing cables, grounded high quality EMI filters to plug the transmitter and audio sources into. It may help to connect the transmitter's metal chassis to a proper earth ground system, entirely separate from the AC safety ground. Of course, you have to install such a system. Personally, I chose to orient cables and receivers to reduce the effects. The other methods are time consuming and rendered ineffective as soon as anything is changed.

Good luck!

edit: I saw a TH document suggesting that 150mv peak audio signals are a recommended optimum audio signal strength. You don't say what type of cassette deck you have, but if it has RCA pin jack outputs they will be 5-10 times stronger than what is recommended and will require "padding" down. Directly plugging a personal device such as phone or even an old-school Walkman cassette player will come reasonably close to matching the recommended signal level.

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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Mar Tue 09, 2021 8:09 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: SoCal, 91387
I had given my solution to this in another thread recently, but will repeat.

I have a different AM transmitter which also experienced distortion from the input of my stereo receiver.

I built an LM386 based audio amp to use as an interface between the two, and with a radio receiving the transmission in the same room, then adjusted the volume level of the amp down to where the broadcast was received clearly.

AFA TH5 hum, I had one and got rid of it because of that, in favor of an SSTrans3000 when they were still available.

There have been posts here of members diminishing the hum by using a ground for the transmitter, adjusting it's antenna lead, using a ground on the audio input, using a transformer between the two, etc. It would be a matter of experimentation.

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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Mar Wed 10, 2021 11:35 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 896
Location: Rockaway , nj 07866
thanks guys for the input


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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Aug Sat 07, 2021 12:13 am 
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Joined: May Thu 29, 2014 5:15 am
Posts: 18
I just picked a Talking house 5.0 / TH5 on ebay. It's NIB, untampered.

Sure enough, the hum was there, and more than enough to make it unusable for music.

The hum was there on a close-by AA5 tube radio and also on a large console in the back room. This told me that it was not the close-by radio being overloaded and thereby made to hum.

Upon fiddling with the DC power plug, it changed. I think a poor connection between the DC input jack and the power supply's DC plug could be a cause of the hum. It is not a tight fit. Perhaps it is some light oxidation, unseen, since the new unit had been sitting so long.

The hum was finally gone so far that it was barely audible in the silence in the audio input that it was satisfying.

I took the board out and looked at the solder side.

One thing I noticed is that the ground system is a star configuration. The power, audio, DC, and RF jacks are separated by some length of copper track, more or less, as they go to B-. I do not suggest changing the ground system and do not think it is a cause of the problem. It is a clue to the thoughts of the designer, and the technique is proper engineering. Anyway, one can look at the bottom of the board and trace the ground copper from the rear panel jacks to the power supply ground point. I didn't do this completely so don't take my words as gospel.

Another thing I noticed is that the main ground from the board to the enclosure/chassis is 'massively' made at the coaxial antenna jack, the female F connector. Also at the "message change prevention plug" jack, but that is little tracks.

The coaxial antenna jack is a low impedance (high current) connection, meant to go through coaxial cable many feet to a remote antenna tuner (they call it the booster) That would seem to make it very important to be common with the chassis.

Question for the group: Who has had hum issues with the remote antenna unit/booster?

The thing about the hum is that I would not think that these would have been passed QA and sold, if the hum was as bad as it was and is the fault of the unit. As a counterpoint to that, the freedom from hum may rest on some very small thing which is hard to find or prove.

I would like to have the schematic for this TH 5.0, but have not been successful.

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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Aug Sat 07, 2021 12:12 pm 
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Joined: Jun Sun 22, 2008 2:03 am
Posts: 1059
Location: Burke, VA 22015
There was a long thread about TH5 with discussions spanning over 10 years! It's worthwhile to go through that thread to find the answers to your questions.

Regarding resolving the hum issue, Richard's advice is a good one. TH5 or any other AM transmitter needs a proper ground. That ground must be separated from the AC wiring in your house. The AC/DC adapter supplied with TH5 incorporates circuitry to decouple the AC wiring from the TH5's chassis. Using the ground of the AC wiring will defeat that decoupling and result in more hum. Some people have good result in using a metal desk as ground. I have good result in using the metal air duct in my home. If you have easy access to a cold water pipe, use that as ground. The best ground to use is buried wire or metal pipe in a star configuration directly underneath the antenna.

For a schematic diagram of TH5, you'll find it in one of its patents like this one. I broke down that schematic diagram for simulation and modification purpose in the old long thread.

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Last edited by bb.odin on Aug Sat 07, 2021 5:55 pm, edited 1 time in total.

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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Aug Sat 07, 2021 1:54 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 733
What's the use of an expensive transmitter when audio quality is not that good? I have homebrewed several AM transmitters and none had this problem of hum. I use 7812 regulator to clean up the power supply. My TX consisted of CD4060, 2n7000, LM386, and a few other components. Cheap but FM like sound quality. I got 300 feet range with a 6ft horizontal wire antenna. Talking House is way too expensive. They are charging a premium.


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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Aug Sat 07, 2021 2:41 pm 
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Posts: 1059
Location: Burke, VA 22015
Dare4444 wrote:
What's the use of an expensive transmitter when audio quality is not that good?

TH5's audio quality is quite good actually. It was not designed for live broadcasting from an external CD player or a playback device. There is an internal electret microphone that allows a voice message to be recorded in an internal chip. The recorded message can be repeatly broadcasted on a selected frequency. The patented automatic antenna tuner is a plus. Just punch in a broadcast frequency and that is it. Considering its simplicity that enables a person with little technical background to operate, its price was pretty cheap during the time it was useful as a sales tool before the smartphone.

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 Post subject: Re: Talking House 5.0 audio overload and hum/buzz
PostPosted: Aug Sat 07, 2021 5:14 pm 
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Posts: 21406
Location: Warner Robins, GA
One thing that can cause hum is the audio cable that is connected to the transmitter as it then connects to the audio signal source and that cable ground and the ground side of the circuitry in whatever device is connected to it becomes part of the transmitter ground. If the audio device has a connection to ground somehow then that defeats the purpose of the TH5's design to isolate it from ground.

The cure is to take an Edcor XSM-15K/15K transformer if feeding a mono signal to the transmitter and connect it between the source and transmitter. That isolates the transmitter ground from the ground of the audio source

https://www.edcorusa.com/xsm15k15k

If feeding a stereo signal to the transmitter and its input is mono use this transformer
https://www.edcorusa.com/wsm6400

One benefit of those transformers is 1/2 of the secondary can be used to reduce the audio level.

I use the WSM-15K/15K transformer in my two tube transmitter and it helped greatly with the hum.


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