Has anyone determined how to bypass the internal AGC in the TH transmitter? The DBX compressor I use between my audio playback computer and the TH does all the limiting I need. Any "input" would be appreciated.
There does not appear to be any form of audio compression in the TH II. The "line in" goes straight to an audio op-amp which feeds the modulator.
The transmitter will not exceed 100% modulation by its design.
Actually there is an IC (BA3313L) that has an ALC circuit. I just don't know enough about what I'm doing to know whether I can jumper around it or part of it.
Here's the datasheet. Maybe one of you can offer some suggestions. I have couple of TH version 5's on the air and they are the ones I would like to modify. Boxed up in storage, I have a 5 or 6 versions III and IV that I'd be fine with blowing up one in the spirit of experimentation.
http://www.datasheetcatalog.org/datasheet/rohm/ba3313l.pdf
Thanks for your help.
See the audio selector switch for recorded and live?
Follow its 3 wire ribbon cable to the PC board. Unplug it. The MIDDLE pin on the plug is the direct trace to the modulation OP amp bypassing the AGC chip..as well as bypassing all the digital recording chip's audio and mic input.
RFB
Thanks RFB. I'll give that a try!
Thanks RFB. I'll give that a try!
See the audio selector switch for recorded and live?
Follow its 3 wire ribbon cable to the PC board. Unplug it. The MIDDLE pin on the plug is the direct trace to the modulation OP amp bypassing the AGC chip..as well as bypassing all the digital recording chip's audio and mic input.
Cool! Even a nonengineer, nontechnician such as myself could follow those directions. I don't actually have a TH, but have been eying them on ebay. I'll keep your information in mind for possible future use.
Very clear.
TH RM AMT
As for TH on ebay, I always wonder what audio quality to expect with the TH in comparison to RM and the AMT.
Just gave it a quick try sending audio in on the middle pin just using clip leads and it certainly works with the mp3 player but will take some more playing around with to use the output from my processing. I'll take one of the TH 4's and actually wire it in and properly ground it.
I have not used any of the other transmitters but I do like the Talking House units, especially Version 5, which I only have one of but the Version 4's are very close with just a little fine tuning of the EQ. I have one ATU and another on the way purchased off ebay. On a good day, range is a mile to mile and a half.
If you examine the PC board near the already present line input jack, there is an empty space next to it for another connector which is not installed from the factory. You can drill a hole on the back of the cabinet and mount a chassis RCA or 1/8 mini plug here. The foil trace for the center pin runs right to the middle pin of the connector I pointed out earlier for direct injection of audio to the modulation OP amp.
Neat thing about it is that the modulation OP amp, is that it's other half is what drives the internal speaker, so you can still hear incoming audio even when the other stuff is bypassed!
Cool eh!
RFB
The schematic I have is the original Patent info so perhaps the TH 5 had some major changes.
I'm curious as to why they would put a stereo ALC chip in there. Does the TH 5 have a stereo line input? The TH II just has a single RCA phono jack.
EDIT: Wow, a lot of posts happened before I posted. I'll have to crack open one of my TH II's to see if it's in there although I've never noticed any audio compression.
Follow up EDIT: I cracked it open and no chip like that in the TH II (PCB marked TH-III-M.) Also, no 3 conductor ribbon cable as described.
Post Follow up EDIT: There is a KA22134 which is a dual pre-amp and dual power amp (27 mw) with volume control. The data sheet stated typical application is for low power portable headset cassette recorders. No mention of ALC applications though. The TH II has no open space next to the rear panel jacks or open-pre drilled holes.
You must have a prior version before the V5...the "grey" cabinet perhaps or the very first run of the black cabinet V5?
Right near and behind the speaker and mic jack of the V5 is the AGC chip. All internal audio, and external line and mic input runs through this AGC chip. Two audio paths run to and from this chip. One is for the internal digital recorded audio, and the other is for the mic/line audio. Switching between the mic and line happens if you plug something into the line input jack.
These two paths are then fed to the plug I described earlier on the PC board. The 3 wire ribbon leads from that plug to the selector switch in the back. The two outer wires are what carries either the internal audio, or the external audio and depending upon the switch position, feeds one or the other to that middle pin which leads directly to the modulation OP amp.
Nifty little routing scheme for the audio paths.
RFB
The chip is in my IV & V models. I have not had a chance to check the earlier models yet.
"The schematic I have is the original Patent info so perhaps the TH 5 had some major changes."
I do not think the patent schematic is showing the entire unit's circuitry. I have studied it and compared it to the entire PC board circuits and quite a lot of the actual circuitry is missing from the patent schematic.
RFB
If you have access to a TH II take a look and see what you think. The patent schem seems to agree with that model.
I will look into that once I return home. I do know someone that has a TH II unit and can compare.
If I recall correctly, the TH V5 was the initial improvement model, but not to be confused with the current TH V5 that is sporting the new name "iAM". The iAM unit has further improvements over the TH V5 for audio quality, though the TH V5 stock has good audio on its own even with the 750hz roll off.
I ordered a complete iAM package including the ATU unit just prior to the holidays. It should arrive sometime next week according to the tracking info. Good thing too cuz I am not anywhere near home at the moment and don't want to miss the delivery!
RFB