- June 24, 2021 at 6:29 am #117864
I have been doing work on the TH 5 audio improvement phase.
Can anyone tell me just what the LM 358 does in the audio chain on the TH 5? I have been following some previous advice posted here on boosting the low end audio response of the TH 5. All good advice, however increasing C301 by 100 nano farads does greatly increase the low end audio response, it also seems to muddy up the audio and covers up the mid and high content. I know that it was recommended to reduce C337 to 30 pf to increase the highs; however I have not done that as of yet in conjunction with the changing of C301. Maybe I need to this to bring up the top end and notch out the midrange boost. Can anyone tell me why such a low value of microfarad is used in the first place for the coupling capacitor (C301)?
I see the modified iam schematic TH uses a 10 microfarad cap in the same location but there is an added series resistor after the capacitor, not sure what the purpose of that is, I haven’t tried that modification. The best results overall I have found is to leave the C301 capacitor at its original value, and use the windows media player equalizer set in a modified V configuration with no boost to the high frequency after 4, 8 and 16 Hz audio, this will boost the bass and knock out the midrange, this seems to put things in proper perspective on the transmitted signal as far as audio balance and frequency response. It would be nice to do this without using the equalizer on the computer when I use other audio sources. When using the built in windows media player equalizer, it makes for a very nice well pronounced audio signal. I know I can use an external equalizer, but would just like to modify the transmitter so a person doesn’t have to bend and twist the audio to compensate for the Talking house electronics. Just changing C 301 kicks up the bass but makes the audio signal more muffled than commercial stations. Thank you for any help anyone can give me on the above.
Radio JoeJune 24, 2021 at 9:14 am #117866MarkModerator
Total posts : 711
What’s happening is it’s boosting the bass to much and also affecting the mid to make it “muddy” as you are hearing. You can do two things, with your processing if you have EQ control lessen the bass a bit or with the windows EQ drop out 250Hz a bit by 5 or 6 dB.
Or try a 50nF cap instead of 100nF. As for boosting the bass with an equalizer or doing it with the windows EQ if the Talking house can’t hear it it won’t help. My suggestion is to try a 50nF instead of the 100nF and then do the rest with the computer EQ.
By the way what computer do you have that has the EQ in the windows sound settings?
The HP I use for the broadcast computer doesn’t have it and the Thinkpad T430 I use for my other computer doesn’t have that feature either!
I have the Schlockwood 200 for processing and with the 3 band compression in 3 frequency ranges it keeps every song balanced the same for EQ as if more energy is in the midrange as most songs are it has more reduction there and less in the bass and treble and if more energy in the bass it reduced it there but not everywhere and the balance stays even just like the commercial stations.
Maybe this is what you saw with the Talking house but here’s a video…
Another video…https://youtu.be/7mSZn5cPX5EJune 24, 2021 at 1:36 pm #117870
Thanks Mark, good advice, I am using the EQ on the windows media player I dont have any EQ on any window sound setting.
I will try 50 nano across the stock 47 nano farad cap, I was using 100 across it and also a 147 nano at one time. Each had its own pleasing sound but it got old after a while, I like bright well defined sound but the bass has to be better than stock to make me happy.
I also may try a DPDT switch with center off (stock) connected to a 50 and 100 cap mounted off chassis so I can pick and choose the best option for the day.
So what is the true function of that LM 358 IC? is it some kind of AGC or just an audio amp?June 24, 2021 at 2:04 pm #117871MarkModerator
Total posts : 711
I’m not familiar with what each IC function is, sorry. Probably controllers for certain functions like the display, PLL tuning, antenna tuner, etc as the majority is discrete components and the audio amp is most likely transistors.
That’s what I meant with the computer EQ. In the two computers I use for the broadcast one and other for all other stuff there’s no EQ adjustment in the sound card settings or Windows media or Groove music settings unless I missed something.
I have seen it but only in a store display on a more high end laptop.
Are you using just Windows Media for audio source?
Have you considered a free automated broadcast program like Play It Live where all tracks are automatically optimized to play back like a commercial station where one song or jingle will start as the other ends and no silence gaps?
The 3 or 4 second silence between tracks or more if silence at beginning and end of song doesn’t sound good on the air.June 24, 2021 at 5:26 pm #117877
I use a media player called foobar, free down load, it plays one song after then next no gap, with windows player ( Running XP for my radio compter) I set the crossover so the songs are pretyt much togehter or you can over lap too.I just use mine for around the house and that so not into a big production!
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