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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Mon 01, 2017 7:01 pm 
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Location: homestead, fl
Or the stock supply is just running out of gas. Seen that in cheap 70's audio gear. Lousy PSU = increased noise.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Mon 01, 2017 10:15 pm 
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True.

I've often found a large filter cap usually takes care of that for the most part for things that only need a little help, but if that don't work a more capable power supply is necessary.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Tue 02, 2017 1:56 pm 
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Mostly hum can be traced to the RF in AC power lines being picked up by receiver... This is usually why some radios may have issues and not others... Carefully orienting transmitting antenna away from power lines often reaps great rewards...

For P/S it's easy enough to look B+ with scope and see if it's dirty...


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Tue 02, 2017 5:09 pm 
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Location: homestead, fl
35Z5 wrote:
Mostly hum can be traced to the RF in AC power lines being picked up by receiver... This is usually why some radios may have issues and not others... Carefully orienting transmitting antenna away from power lines often reaps great rewards...

For P/S it's easy enough to look B+ with scope and see if it's dirty...


good point on scope, gonna try that. im gonna be a bit busy this week so wont have much time to experiment but this TH thing has been a longterm project with me. have 5 of them here so no fear if i trash one accidentally while hacking.

if we could only get a schematic to these darn things...


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Sun 01, 2017 2:52 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Tucson AZ
There is a fellow local to me that has 3 new 4.6 units for 50 each. I'm really tempted to get one.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Fri 20, 2017 3:17 am 
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Cleaned up A LOT of hum by disconnecting a ground wire that connects between the ground pin on the AC plug and the rectified output circuit board in the wall wart for the unit.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Fri 20, 2017 4:11 pm 
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Sometimes hum is less without a ground...

I wired the ground for one of my tube units thru a switch, can flip it back & forth to check what's best... It can vary day by day depending on how wet the roof is, what's in operation etc... Since I moved transmitter out to garage I rarely switch it, rainy day and a little hum, not worth getting wet to correct... Maybe one day I'll wire it to a relay controlled by a garage door remote receiver... Ummm, naah that ain't likely...


Tom


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Sat 21, 2017 1:36 pm 
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35Z5 wrote:
Sometimes hum is less without a ground...

I wired the ground for one of my tube units thru a switch, can flip it back & forth to check what's best... It can vary day by day depending on how wet the roof is, what's in operation etc... Since I moved transmitter out to garage I rarely switch it, rainy day and a little hum, not worth getting wet to correct... Maybe one day I'll wire it to a relay controlled by a garage door remote receiver... Ummm, naah that ain't likely...


Tom


Agreed.

Also depends on the radio.

My R-390 hums less with the ground lift switch one way and my RCA K-80 console in the same room hums less with the switch in the other position.

I also took mine and installed a transformer so I could have a balanced or unbalanced line connected and used one of those isolated 1/4" jacks so that the only ground is through the ground prong on the power plug.

That seemed to tame hum somewhat.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Mar Thu 01, 2018 1:10 pm 
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I just got a TH 4.6 and was disappointed with the audio and hum.
found this thread.
tried several caps on c301 and settled on tacking on a .015uf.
I noticed (accidentally) with the unit sitting on the metal drawer of my bench that when I moved it around sometimes the hum disappeared slightly. Did some experimenting and found that if I put a 3 prong to 2 prong adapter on the ac adapter (as some have tried), and then grounded the case of the TH to my bench frame (which is not grounded), then restarted the unit, the hum was gone. currently my antenna is parallel to the bench, and attached to a handle on a filing cabinet.

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Mar Thu 01, 2018 3:59 pm 
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My advice is this. Try using a 1:1 audio transformer between the source and transmitter and use as short of an audio cable as possible between the transformer and transmitter.

Sometimes the audio cable to the source plus whatever power cvable the source has can cause an increase in hum and the audio transformer eliminates the cable's ground connection to the transmitter. Plus it ensures that the only path to ground is the transmitter's ground itself.

I had a lot more hum issues until I installed the audio transformer in my two tube transmitter and used an isolated 1/4" jack since my case is metal and the transformer is mounted internally.

Some radios hum less with the transmitter ground connected to the power outlet ground and some hum more with the transmitter ground connected to the power outlet ground.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Thu 10, 2019 9:46 pm 
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Flinx wrote:
I just got a TH 4.6 and was disappointed with the audio and hum.
found this thread.
tried several caps on c301 and settled on tacking on a .015uf.


Hi Flinx - I know this is an older thread, but I just got around to working on my TH 4.6 I want to increase the bass response and I read changing the c301 capacitance helps. I removed the cover, but can't seem to locate capacitor "c301". Am I looking for an electrolytic cylinder shaped cap or a one of the round disc ones? Here's a picture of the board in my TH 4.6.


Attachments:
Talking House 4_6 board.jpg
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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Thu 10, 2019 9:57 pm 
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1988bluebird wrote:
Flinx wrote:
I just got a TH 4.6 and was disappointed with the audio and hum.
found this thread.
tried several caps on c301 and settled on tacking on a .015uf.


Hi Flinx - I know this is an older thread, but I just got around to working on my TH 4.6 I want to increase the bass response and I read changing the c301 capacitance helps. I removed the cover, but can't seem to locate capacitor "c301". Am I looking for an electrolytic cylinder shaped cap or a one of the round disc ones? Here's a picture of the board in my TH 4.6.


it's the green chicklette capacitor just below the white 3 pin connector:
https://youtu.be/l7ZHQvikSQM

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Thu 10, 2019 10:13 pm 
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Thanks Flinx! :D Here it is....not sure how I missed it :roll:


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Thu 10, 2019 10:16 pm 
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These;


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Tue 15, 2019 2:19 pm 
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I modded mine a few years ago and I don't remember the exact value I used other than it was less than 1uf. Something didn't sound right by going with a larger value cap but I don't remember what it was.You can see the original had a low frequency roll-off starting as high as 500 hz. There was almost nothing at 100 hz. After the cap change 500 hz was just shy of full and you can see the increase at 100 hz. Still not full range but then neither are the old radios I'm listening on.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Mon 28, 2019 8:06 pm 
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Just a followup, I made the c301 capacitor modification to my Talking House 4.6 this weekend, and it sounds radically better! The low and midrange is much more pronounced and music now has a "warm" sound. I might be using the Talking House a lot more now since it sounds so good :D

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Mon 28, 2019 11:29 pm 
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Awesome. Almost makes me want one, but I'm satisfied with my two tube transmitter.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Mon 28, 2019 11:46 pm 
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1988bluebird wrote:
Just a followup, I made the c301 capacitor modification to my Talking House 4.6 this weekend, and it sounds radically better! The low and midrange is much more pronounced and music now has a "warm" sound. I might be using the Talking House a lot more now since it sounds so good :D

Does yours have a background hum? That's the reason I got rid of mine, even after doing the cap change out.

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Mon 28, 2019 11:59 pm 
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Hum in these can be reduced or eliminated by using a 3 prong to 2 prong adapter on the power supply and more importantly giving the device a large ground plane and grounding the device to it, then turning the power on and letting it do it's tuning thing.

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Tue 29, 2019 12:17 am 
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Would it be even better if the talking house was grounded straight to a ground rod like some of us do with our communications gear?


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