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PostPosted: Apr Thu 21, 2011 11:08 pm 
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jamesdean wrote:
I found this on a site here in the UK talking about TH transmitters:

"Most of these basic designs use a 10.24MHz xtal which the PLL divides by 1024 to give 10KHz spacing. Change that to a 9.216MHz item and hey presto .. 9KHz channels for the UK and Europe."

Does this sound correct?
Not any use to you guys in the US but I will try anyway... when I get mine.

That sounds absolutely correct, and I have heard this suggested before. However I have never heard of any one doing it successfully (which does not mean it has not been done). I have a vague familiarity with the TH PLL circuit, and there is a lot to be desired. It could be reworked, dedicated power rail (not shared with RF as it is now). Also it uses ceramic capacitors, which is not ideal for a PLL design. It works but has a bit of FM'ing. None of it affects the sound negatively to any extent, therefore I elected to leave my TH alone. If I want another MW transmitter it will be scratched or kit built with a single freq programmable crystal (about $6 usd each). This will go in a WX box outside with the antenna.

As far as the crystal if you can find a 9.216 Khz crystal, with the right load and self capacitance (what ever that is) it might work? However I think there is more to it, but that is my ignorance, don't know. If that site said they did it, using Part #ABC crystal from XYZ supplies, and installation was straightforward, works, go for it. You might find quartz crystals going for $30 usd range. You can have custom ones made to your spec for about $40 each. So getting a crystal is only part of it. If there is an off the shelf one just right for cheap, you will be very lucky, I think. Again it has been suggested before, changing the XTAL, but talking to other people they have doubt.

This audio modification here, I stole from some one else who blazed the tail. He's in the Netherlands and suggested the crystal mod for 9 Khz spacing. As a favor, I called TH in NJ USA (now Radio Systems Inc, who bought the TH product line and remaining stock). They said they've had lots of requests for 9 Khz spacing; I gather there is no easy modification, OR they just are not interested. They did look into it. Radio Systems has a warehouse of TH units. They sell stock ones are $99; they charge $499 for the modified ones... which makes them sound better. I gather they do something like I did plus more things, just to make sure they are in good repair. A lot of these units have loose ferrite rods in the antenna tuner. There are two ferrite rods that are secured by glue. Very common for them to come lose. Fix is easy, just glue them back in the plastic holder.

So it would be fun to play with, but I don't have enough info to go on. It's pure experimentation. BTW there are no true schematics available, BUT there is a patent for the AM antenna auto tuning of the TH unites. This patent shows a schematic of the whole radio (mins lots of detail) and detailed text description of the antenna auto tune system. With backward engineering and schematic overview, it might help you figure it all out. It's a nice little unit and fun to play with, but it's not perfect.

For something better sounding (but lower power), SSTran kid. For something like C-QUAM there is a kit. C-QUAM is AM stereo. However CQUAM transmitters can be received on a regular AM mono radio just fine. The down side is there are not many dedicated CQUAM AM stereo receivers you can buy today. However the new crop of HD FM/AM radios that came out in the last 5 yrs has a C-QUAM decoder in it as a freebie. The C-QUAM kit I am thinking of is a programmable crystal controlled transmitter. You can buy crystals programed from the distributor to your desired Freq for about $6. Synthetic tuning and being able to change the freq with a push of the button is nice but adds some complexity. Because of FCC rules we can not have any FEED LINE. The antenna limit of 3 meter is total for antenna, feed-line and ground wire. So most guys have the transmitter outside near the ground (dirt) with the antenna and ground all there, no extended feed or ground wires. So you want a compact transmitter and don't need digital displays. Most of the time you settle on one Freq and that is it.

I see on eBay some AM transmitter circuit/display from Greece that looks nice; it's like $300 I recall, with variable RF power out from 100 mW on up. It does not come in a case, it's just the circuit board and display (that has data and menu to set up the transmitter). There is always better, but with the audio-mod the TH is pretty good for the price. In the USA I have bought them as cheap as $40 each. I bought a bunch and sold them for a small profit, so the one I kept is basically is free. Hard to beat free.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Apr Thu 21, 2011 11:32 pm, edited 1 time in total.

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PostPosted: Apr Thu 21, 2011 11:22 pm 
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I would guess TH are not interested in changing to 9 kHz steps as there is no need for the market they target so it stays at 10 kHz. According to the info the crystals on ebay.uk are available and cheap....IF they are correct? The full post was this:

Most of these basic designs use a 10.24MHz xtal which the PLL divides by 1024 to give 10KHz spacing. Change that to a 9.216MHz item and hey presto .. 9KHz channels for the UK and Europe.

A couple of suppliers on eBay at the moment ....


http://cgi.ebay.co.uk/HC49U-9-216-MHZ-X ... 562c8e89a9

or

http://cgi.ebay.co.uk/4-9-216-Mhz-HC49- ... 45f8d98861

So I will look into this, if it doesn't work surely it will be OK if I just replace the original crystal?


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PostPosted: Apr Thu 21, 2011 11:34 pm 
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jamesdean wrote:
I would guess TH are not interested in changing to 9 kHz steps as there is no need for the market they target so it stays at 10 kHz. According to the info the crystals on ebay.uk are available and cheap....IF they are correct? The full post was this:

Most of these basic designs use a 10.24MHz xtal which the PLL divides by 1024 to give 10KHz spacing. Change that to a 9.216MHz item and hey presto .. 9KHz channels for the UK and Europe.

A couple of suppliers on eBay at the moment ....


http://cgi.ebay.co.uk/HC49U-9-216-MHZ-X ... 562c8e89a9

or

http://cgi.ebay.co.uk/4-9-216-Mhz-HC49- ... 45f8d98861

So I will look into this, if it doesn't work surely it will be OK if I just replace the original crystal?


Go for it! Excellent. My guess is the displayed freq will not be correct, but again who knows? It sounds doable! Let us know how it works out and document it, with some pics and share it. I know there are many that want this over the pound.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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PostPosted: Apr Fri 22, 2011 6:03 am 
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I sure will go for it. Just got to wait for it to arrive. All these plans and it's not even here yet...lol.
Will be interesting anyway.


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PostPosted: Apr Thu 28, 2011 3:13 pm 
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Well it arrived today, actually quite quick I thought. It is new and a TH IV. I don't have a 240V to 110V step down converter yet (one on order) so I used my 13.8 volt power supply which seems fine anyway. I must admit the audio actually was not too bad, I was expecting it to be very flat but it was acceptable for AM. I am not too sure on the AGC though, I had to turn my mixer way down compared to on an FM transmitter. Can the AGC be bypassed easily? If not I will live with it. I will try the capacitor mods further back in this thread as I'm sure I can get the audio sounding a bit better by doing that. Regarding a crystal swap to change the step from 10kHz to 9kHz I don't know as the crystal in the TH says 4.000MHz and not 10.240 as I read it may do and changing it for a 9.125MHz one may totally mess it up? Again it's not a thing I need to do but I must admit I do like this TH, it's something different so I am glad I found one at a good price in the US and more glad I found this site and the thread. I heard the signal all around my house, down the garden and quite a bit down my street on a portable radio (during the day) on the 3 meter wire antenna included so that's a nice start. Going to enjoy playing with this, makes a nice change to the FM stuff. :wink:


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PostPosted: Apr Thu 28, 2011 7:02 pm 
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jamesdean wrote:
Well it arrived today, actually quite quick I thought. It is new and a TH IV. I don't have a 240V to 110V step down converter yet (one on order) so I used my 13.8 volt power supply which seems fine anyway.

I am sure that works; I have run it on 13.8 volts, but it's something like +18 volts DC in. A source of nose can come in through the power. If you don't have hum you are good to go. If you do have hum, some have found the solution in the power supply.

Quote:
I must admit the audio actually was not too bad, I was expecting it to be very flat but it was acceptable for AM. I am not too sure on the AGC though, I had to turn my mixer way down compared to on an FM transmitter.

It is a double edge sword. If you don't have enough volume you will handicap the audio and range. You do need the audio to drive the AM, amplitude modulation. Under modulated AM is almost as bad as over modulated. That is the game you have to play. As you indicated if you are driving it with the PC and stereo-tools, you can fine tune the audio and run up to the limit (loudness, Freq range, dynamics) and not get distortion. With the standard TH too much bass from the source can just muddle the sound. AM is harder than FM, at least when pushing AM to get the best possible audio. FM is pretty much set up with 15 Khz (stereo) out the box, and FM of course is less subject to RFI than AM. However if done right AM can sound quiet lovely, especially for voice and older music (pre-60's when audio was not recorded in "Hi-Fi").

Quote:
Can the AGC be bypassed easily? If not I will live with it.

Yes the audio section could be improved, and no the AGC can't be bypassed easily. If you open it up you will find a zip12 IC chip package. If you take the part # off it, BA3313L, it's a auto limiter for a stereo tape deck, for which they use half if the IC. Looking at the pdf for this IC:

    The BA3313L is a dual preamplifier IC with built-in ALC detector
    circuit, designed for use in stereo radio cassette recorders. It
    comes in a compact 12-pin ZIP package, and has two record /
    playback preamplifiers, and an ALC detector circuit.

    The preamplifiers can be directly coupled to the tape head without
    coupling capacitors to prevent tape head magnetization and “pop”
    noise generation. With the built-in ALC detector circuit, an ALC
    circuit with large dynamic range can be constructed with addition of
    just an external time constant circuit.
I assume ALC means Automatic Level Control. Also being about "recording levels" makes me wounder if this thing is just not ideal for the job (or not implemented properly). The pdf specs show the "standard application" circuit. I suspect some of the values in limiter circuit could be changed to make it more affective in the TH. Not being able to measure actual capacitance in circuit, I suspect some of the caps might be out of spec. This is one area I'd play with next, from the input (two 100K resistors) to this IC limiter. However you have to take the board out, and I am happy with the sound now. However that IC chip as a (dynamic/loudness) limiter really sucks at it's job, or the way it's integrated into the design is poor. I would most definitely play with the caps and resistors in that area, to in attempt to make it work better as a true limiter, thus making it more robust in accepting different audio sources of various levels, dynamics, loudness.. I had the wild idea of installing a compressor, limiter, EQ in the TH and just bypassing the whole mess in TH. May be some day, but as I say the capacitor change (which is after the ALC chip), plus Stereo Tools makes a big improvement, as good as I think this unit can do, which is darn good.

I still understand the SStran has just a tad advantage is audio fidelity over the TH (reading others opinions). The diminishing return of the SStran is despite flat audio near 15 Khz wide, there are no standard or even "wide-band" MW receivers that can receive base-band audio this wide; most radios are set up for about 4-8 Khz max, where 6 Khz is typical. This is more than enough to tune in the 5.1-7.5 Khz base band that AM radio stations transmit. In the USA the FCC limits the channel spacing, audio bandwidth a station can transmit, as I am sure UK has similar limits. We have so many stations, with out these limits it would be a mess. The TH is FCC approved and the SStran is not. The SStran as I said does have the 9 or 10 Khz spacing.

Quote:
I will try the capacitor mods further back in this thread as I'm sure I can get the audio sounding a bit better by doing that.

It's a dramatic improvement, a no brain-er, you should do it. If your TH is sounding good now, I respect you will need to only increase the 0.047 uF to 0.15-0.20 uF. Go buy a nice 0.15 uF non polarized, polypropylene, polystyrene or polyester (in that order I think). You don't need "audiophile" capacitors, just good quality and none metalized. You do NOT have to take the board out. Just clip the 0.047 uF off and so you can get as much stub exposed. On the new cap wind the leads around a tiny mini screwdriver making a little tight coil about 3-5 turns as needed. Slip over the stubs and solder.

Quote:
Regarding a crystal swap to change the step from 10kHz to 9kHz I don't know as the crystal in the TH says 4.000MHz and not 10.240 as I read it may do and changing it for a 9.125MHz one may totally mess it up?

You are on your own. I would research it more and put it up on the Internet boards/forums on your side of the Atlantic, since that is where the 9 Khz spacing is. As I said I have heard this idea but never seen/heard it done. I came to the conclusion that there are other AM transmitters with 9 Khz spacing to buy, making this mod to the TH questionable. I have no reason but opinion and ignorance that makes me think that it's more than a crystal change. That whole tuning and PLL section is a bit confusing to me. I have a rule, if I don't understand it, I don't screw with it (usually). :roll:

Quote:
Again it's not a thing I need to do but I must admit I do like this TH, it's something different so I am glad I found one at a good price in the US and more glad I found this site and the thread. I heard the signal all around my house, down the garden and quite a bit down my street on a portable radio (during the day) on the 3 meter wire antenna included so that's a nice start. Going to enjoy playing with this, makes a nice change to the FM stuff. :wink:

For me I have 10 antique tube radios. Being into FM most of them are AM/FM tube radios from 1947-1960. However AM is fun and I like to play podcast (talk shows) in AM, where FM and stereo is not critical. For music, FM stereo is still going to have the edge over AM always (as much as that PO's AM radio fanatics).

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Apr Thu 28, 2011 7:34 pm, edited 2 times in total.

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PostPosted: Apr Thu 28, 2011 7:25 pm 
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Thanks for the reply/tips. I will leave the frequency spacing well alone for now and just concentrate on the audio, I think just that one capacitor mod (0.15uF) will do it also and out of all the many caps I have in stock... I don't have that so some ordered now. I did have a little hum on the carrier but only slightly noticeable with no audio. I will see what it is like when I can use the 18volt DC supplied power supply but if I plug that in now it will go bang with our voltage.
I can use quite a lot of frequencies as I found being just 1kHz out even sound fine so my digital radio on 1431kHz sounds fine if the TH is on 1430kHz and so on but I did my main tests on 1440 anyway.
I may do the RCA socket mod which I saw further back as this improves the audio it said? Got to be better than the standard stereo input jack I would have thought?
I was never much of an electronics fan but I can solder, replace components etc.. but this makes me want to play and try things, probably because it is rather unique over here. Start of a new hobby. :)


Last edited by jamesdean on May Sun 08, 2011 5:59 pm, edited 1 time in total.

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PostPosted: Apr Thu 28, 2011 7:43 pm 
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jamesdean wrote:
I can use quite a lot of frequencies as I found being just 1kHz out even sound fine so my digital radio on 1431kHz sounds fine if the TH is on 1430kHz and so on but I did my main tests on 1440 anyway.

Actually that is a known trick to do intentionally to improve the audio, off tuning slightly. By shifting the tuner up from the station you can increase the highs! There is a slight loss theoretically in lows but with old analog radios you could TUNE the radio for best sound. With digital it's all very much on and you have less control of off tuning, unless you have a very good digital radio with 1 Khz or 0.10 Khz or less tuning steps (as you might have with a "communication" or Ham or Shortwave radio). Most digital tuned consumer radios go in full station steps (9 or 10 khz).

Quote:
I was never much of an electronics fan but I can solder, replace components etc.. but this makes me want to play and try things, probably because it is rather unique over here. Start of a new hobby. :)

I would not mess with the Freq spacing unless you really understand PLL. The audio mod is simple and you should have no problem doing that. For grins and giggles just hold a capacitor onto the existing capacitor. Jump the stock capacitor in place with a 0.15 uF capacitor (any kind non polarized). You will hear the difference. Go up to larger capacitors, try other capacitors, experiment. You will quickly reach a limit and the sound will get muddled. Capacitors in parallel add their capacitance. In theory you could just tack the new capacitor onto the old one, leaving it in place. I did that for a while, but it's best to just replace the old one with a new one, of one kind of capacitor, than two in parallel.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Apr Thu 28, 2011 11:26 pm, edited 1 time in total.

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PostPosted: Apr Thu 28, 2011 8:05 pm 
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Yep I'm going to leave the channel spacing well alone unless I find some real good information but I think the info I found regarding xtal swap is not relevant at all to the TH.
All the capacitors I have are 1uF and above with different voltages (16V, 25V etc...) so I think way to high to even tinker around with on the audio. I have some small ceramics also but most say 101 on them and from what I have read are not much use either. I need to get some pF ones in stock. Any recommendations or commonly used ones to get?


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PostPosted: Apr Thu 28, 2011 11:31 pm 
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jamesdean wrote:
Yep I'm going to leave the channel spacing well alone unless I find some real good information but I think the info I found regarding xtal swap is not relevant at all to the TH.
All the capacitors I have are 1uF and above with different voltages (16V, 25V etc...) so I think way to high to even tinker around with on the audio. I have some small ceramics also but most say 101 on them and from what I have read are not much use either. I need to get some pF ones in stock. Any recommendations or commonly used ones to get?


Ceramic is a poor choice for audio unless it is a bypass. Yep 1uF is too much, and it sounds like those are electrolytic. Those you don't want either, for the low values. HOWEVER try it 1 uF. Just jump it and hear the affect. Note the polarity in the previous post if using an electrolytic. Some people found they could go up to 10 uF. It seems to vary from unit to unit? However if you go that big it will have to electrolytic.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Apr Fri 29, 2011 10:12 am, edited 1 time in total.

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PostPosted: Apr Fri 29, 2011 8:41 am 
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Yes they are electrolytic.
Do you or does anyone know what the spurious output is like on these? Any bad harmonics? I may think of using a pallet amplifier in the future for a bit of a boost but I don't want to amplify any bad signals further up the band.


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PostPosted: Apr Fri 29, 2011 10:11 am 
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jamesdean wrote:
Yes they are electrolytic. Do you or does anyone know what the spurious output is like on these? Any bad harmonics? I may think of using a pallet amplifier in the future for a bit of a boost but I don't want to amplify any bad signals further up the band.

It depends. I don't know how much antenna you put on it, but near field there is splatter on multiples of the Freq you are transmitting on. But with low power and smaller antenna it should not bother anyone beyound your property. However longer antenna and more power you can bleed into the shortwave band.

If you decide you are going to use this as an exciter to drive another RF linear amp of higher power, which I assume is what you mean by "pallet amplifier... boost", then you may consider audio limiters and brick wall RF bandpass or lowpass filters. A RF filter on the antenna feed coxial is what you would need to assure you do not splatter. A custom DIY filter could be a masters class on RF filter design. It is something you could do, and would be a learning experience. By limiting the source audio bandwidth you limit the total RF bandwidth, so you don't bleed into adjacent Freq. All these limits and RF filters will keep your signal in check.

I can tell you that when I transmit with my TH on 1380 Khz, I can hear that signal (near field, with in 10 feet of the antenna) up to 11040 Khz or 12420 Khz (9th harmonic) on a sensitive SW receiver. If I go 30 or 40 feet then I might splatter only one or two harmonics, say 2760 khz faintly. This is just overloading the radio.

All bets are off if you start running watts and longer antennas. Not sure why you would do that if you are happy with coverage now. For you with no antenna restriction in UK I would just make the antenna longer. That will improve efficiency. I can tell you that efficiency for a 3 meter long antenna, even with the automatic tuner is very low. You are lucky to be radiating a one or two milliwatts of that 100 milliwatts. (Note the TH from my measurements seems to make more than 100 milliwatts, may be 40% or more depending on Freq.)

With 10 watts and longer antenna you are talking about a range of only 5-6 statute mile. I don't get the attraction of transmitting for strangers as a pseudo radio station. I don't recommend pirate radio stations. I am sure even in UK there are laws about that.

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PostPosted: Apr Fri 29, 2011 12:19 pm 
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Yes there are strict laws on pirate radios here, I am trying to gain knowledge and see what the scenarios would be, it is all hypothetical, at least at this stage. My main interest is to get a really efficient (as possible) antenna on the standard power. That is the main aim.


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PostPosted: May Sun 08, 2011 6:07 pm 
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Just an update, I did the audio mod to the TH 4, C301 I changed to a .15uf and I clipped one leg of C337 as I agree that it sounded just that little bit better with it disconnected. The next day I found a new TH5 on ebay in the US for $59 so I sold the TH4 on and I got enough to more than cover the cost of the TH5 with shipping to UK also so that worked out well. I'm expecting that to arrive within the next few days so then I can continue playing. I guess I may not have to do the audio mod on that one if it's a good one, that remains to be seen.... or rather heard!


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PostPosted: May Thu 12, 2011 10:14 am 
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jamesdean wrote:
Just an update, I did the audio mod to the TH 4, C301 I changed to a .15uf and I clipped one leg of C337 as I agree that it sounded just that little bit better with it disconnected. The next day I found a new TH5 on ebay in the US for $59 so I sold the TH4 on and I got enough to more than cover the cost of the TH5 with shipping to UK also so that worked out well. I'm expecting that to arrive within the next few days so then I can continue playing. I guess I may not have to do the audio mod on that one if it's a good one, that remains to be seen.... or rather heard!


Well the TH5 arrived yesterday and after a quick test I really don't know if the audio is any better than the unmodified TH4 or not really. If it is, it is a slight difference. I think I may well try changing C301 on this to see if it changes the sound. The original capacitor at C301 looks the same as what was in the TH4 so maybe it is the same original value? I need to do a longer test but time is against me at the moment. That's the latest update! 8)


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Jul Mon 11, 2011 5:59 am 
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I had been wanting to experiment with improving the audio in my TH5, and finally got around to it this evening. I tried the recommended .1, .15, and .2 for C301, each with and W/O D/C C337, but no combination seemed to defeat the distortion.

I finally settled on what gave me clear audio, along with more bass;
C301 = .068
C337 = .0047

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Jul Mon 11, 2011 7:18 am 
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fifties wrote:
I had been wanting to experiment with improving the audio in my TH5, and finally got around to it this evening. I tried the recommended .1, .15, and .2 for C301, each with and W/O D/C C337, but no combination seemed to defeat the distortion.

I finally settled on what gave me clear audio, along with more bass;
C301 = .068
C337 = .0047


The capacitors don't fix distortion, they increase the audio response and give lower lows and higher highs.

Two things:
what kind of capacitor?
what audio are you feeding it? *

Don't use electrolytic, get some good Polypropylene or at least a ploy cap of high quality.

*The TH is sensitive to the audio input. The input amplitude and audio Freq range you feed it can distort audio (through the audio input section before the caps). No capacitor will help. ** I highly recommend using a computer with at least EQ control, and better would be something like stereo tools, that has electronic compression, limiting and dynamic loudness control (for different Freqs if you like).... Once you tailor the input audio the capacitors make the deeper bass and higher treble obvious.

** The TH should do well to have the whole input stage bypassed and a basic limiter/compressor (hardware) to feed the talking house, so it would not be so picky about the what you feed it. The current limiter circuit chip they use is pretty limited and takes very little to overload it.

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Jul Mon 11, 2011 7:45 am 
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gmcjetpilot wrote:

The capacitors don't fix distortion, they increase the audio response and give lower lows and higher highs.

Two things:
what kind of capacitor?
what audio are you feeding it? *

OK, practically speaking the mod seemed to eliminate distortion. I don't notice higher highs, but the lows are definitely lower.

For C301, Polystyrene Film, & for C337, Polyester film. No rhyme or reason, they were just what I happened to have on hand.

I am feeding the TH5 directly from my stereo receiver, which receives SiriusXM, OTA FM, and from the PC, internet stations and music on my drive.

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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Aug Wed 03, 2011 3:23 pm 
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Given the ALC chip is designed for a low level tape head input that might be where the distortion comes in as the audio signal has to be fed through a resistor before the chip. I suspect it would be possible to disconnect the chip and connect the audio to the output of the chip where it connects to the rest of the circuitry.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Aug Wed 03, 2011 4:39 pm 
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Tube Radio wrote:
Given the ALC chip is designed for a low level tape head input that might be where the distortion comes in as the audio signal has to be fed through a resistor before the chip. I suspect it would be possible to disconnect the chip and connect the audio to the output of the chip where it connects to the rest of the circuitry.


Yep that ALC chip was made for a tape recorder. Those are good points. The input uses resistors, the standard two 100 ohm resistors, to tie Left and Right together. That's pretty simple and personally don't care for that. I would re do all that.... like the mod I posted earlier in this thread, making it a MONO input with a small Pot/Tone control.

Also on the ALC chip I think some of the surrounding components for it's installation are still suspect. If I take the board out I will definitely change some of the capacitors there. I think some one screwed up and put the wrong sizes in or the parts them self were out of spec. One thing seems to be for sure, it is TOO complicated. Simplicity is golden. May be it works well for voice which is in a very restricted Freq range.

I agree with you, bypass the chip altogether, but not having schematics it would take some more hunting and there is always chance of making it worse.

I invite folks to research that. I got such good results with the capacitor change I gave up with further mods. Also using the computer to feed the TH helps.... using a good EQ and ever better, advanced software that does limiting & compression... (aka Win-amp with Stereo Tools add on). This software is free or shareware.

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Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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