I have the Theta TLC for years that I recall & its quite a wonderful little piece of device. Oflate, it is giving trouble. While the CD Transport is locked to the dac via this Theta TLC, it loses the lock status and upon toggling the push-button switch on the back of the Theta that toggles the input between Toslink or coax, the "lock" resumes.
Further, even in locked status, the LED lock on the dac flickers and I can faintly hear high freq distortions in the background of the music playing.
I'm unable to figure out what may have gone wrong in the Theta TLC. I did remove the Theta from the setup to see if my DAC was creating the problem but its fine. The symtoms resumes back upon bringing the Theta back to the setup. Hence, its the Theta.
I'm quite a newbie in this. Can fellow members kindly guide me as to how to go about solving the high freq distortions that I hear bleeding into my music and also the sudden unlocking of the DAC.
I desperately need your help. I dont have schematics or any circuit diag for the Theta Digital TLC.
Will appreciate if someone can come forward.
Thanks in advance!!
Further, even in locked status, the LED lock on the dac flickers and I can faintly hear high freq distortions in the background of the music playing.
I'm unable to figure out what may have gone wrong in the Theta TLC. I did remove the Theta from the setup to see if my DAC was creating the problem but its fine. The symtoms resumes back upon bringing the Theta back to the setup. Hence, its the Theta.
I'm quite a newbie in this. Can fellow members kindly guide me as to how to go about solving the high freq distortions that I hear bleeding into my music and also the sudden unlocking of the DAC.
I desperately need your help. I dont have schematics or any circuit diag for the Theta Digital TLC.
Will appreciate if someone can come forward.
Thanks in advance!!
Theta Digital apparently has no information available for the TLC, I looked on their site. This has been a problem with a lot of products that were made by the previous incarnation of this company both under the Theta label and as an OEM for others. Hopefully someone out there might be able to help you.
http://www.thetadigital.com/faq.shtml#time_linque
I was faced with similar issues with my PSA Lambda Drive about 4 yrs ago (this was made by Theta) and ended up selling that and the matching Ultralink II. I was pretty unhappy at the time, but there is much better sounding gear out there today.
http://www.thetadigital.com/faq.shtml#time_linque
I was faced with similar issues with my PSA Lambda Drive about 4 yrs ago (this was made by Theta) and ended up selling that and the matching Ultralink II. I was pretty unhappy at the time, but there is much better sounding gear out there today.
@kevinkr Thanks for your post. I really need to get hold of the schematic. Is there anyone who could help??
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The TLC uses a free running PLL within the CS8412 interface for clock recovery and jitter suppression without a second crystal-based lock (as used by Audio Alchemy, for example). The digital output is re-clocked via a Dual D-type flip-flop MC74ACT74N with extra signal conditioning provided by a high-speed hex unbuffered inverter MC74HCU04N—hence the TLC's high output level, clean waveshape and fast risetime. There's also a Quad-2 ch multiplexer 74HC157AP.
This output is transformer coupled via a Pulse Transformer but, because Theta uses a 'stereo' dual-RCA phono socket (a cost-saving, presumably), the grounds of both coaxial input and outputs remain connected!
I am experiencing "tiny high freq chirpings" in my music when playing (just like small scraches in an analog LP) and suspect its a semiconductor device slowly malfunctioning. I have now removed the PCB from its chassis to track which of the ICs it could be.
With multitude experience of fellow members, I would appreciate if you would help me/ guide me as to how I may be able to rectify the snag I am experiencing.
Many Thanks in advance !!
The only component I see on there that I know to be unreliable is the CS8412. I've seen a number of these fail over the past few years. The symptom each time was failure to lock onto the signal, but I could see it causing your symptom in early stages of dying.
@ stephensank
Many thanks for pointing me to the right direction as its getting increasingly difficult to get hold of CS8412 ICs these days. Ebay has some leads so I reckon I better hurry...
Many thanks for pointing me to the right direction as its getting increasingly difficult to get hold of CS8412 ICs these days. Ebay has some leads so I reckon I better hurry...
They also say that this Theta TLC uses a stereo RCA female set for the coax IN and OUT - having a common Gnd pin. And a chance for interference - hence higher jitter.
Please see pict marked in :
GREEN +ve OUT
PINK +ve IN
RED Common GND
I want to install separate high Quality Female RCAs. Could I use the GNDs marked with X ??
Please see pict marked in :
GREEN +ve OUT
PINK +ve IN
RED Common GND
I want to install separate high Quality Female RCAs. Could I use the GNDs marked with X ??
An externally hosted image should be here but it was not working when we last tested it.
Don't know the TLC circuit, but if it is feasible, I would definitely suggest isolating the output ground, which would require jack replacements. Always a good idea to replace those crappy jacks, anyway, of course. I do think it is marginally possible that you simply have a ground loop problem caused by the grounded transormer output.
What is that switch used for? Given the age of this unit, if it has anything to do with bypassing the circuitry in the TLC you might want to clean it. (Contact oxidization)
Edit: I see now that it appears that switch selects toslink device or RCA, presumably an input. Cleaning would be a good idea - eliminating that switch altogether if you only use the RCA would be better.
Another area of concern is all of those tantalums, long term they aren't that reliable and replacing them with Sanyo Oscons could be a good move.
If the PLL in the CS8412 is loosing lock due to deteriorating caps in its loop filter the symptom you describe would be exactly the result. I would check or change those caps first thing. Finally I would consider replacing the CS8412, OTOH you could eliminate the need for it by reclocking the spdif input internal to the DAC.
I'm gonna be mean, but I'm pretty sure a WM8804 spdif I/O module from Twisted Pear Audio will blow the TLC right out of the water if you use it for reclocking, and not cost you a lot in the bargain. Link here: http://www.twistedpearaudio.com/digital/wm8804.aspx - it's temporarily out of stock as these guys products are quite popular. (I use this as a receiver in my home brew dac, but it receives and transmits spdif and can do so simultaneously.)
IMO RCA jacks are NEVER the right choice for 75 ohm spdif audio, I recommend you find the right BNC and cables - really helps with reflections at the connection interface point. (My homebrew dac and transport use "true" 75 ohm cable and connectors.)
Edit: I see now that it appears that switch selects toslink device or RCA, presumably an input. Cleaning would be a good idea - eliminating that switch altogether if you only use the RCA would be better.
Another area of concern is all of those tantalums, long term they aren't that reliable and replacing them with Sanyo Oscons could be a good move.
If the PLL in the CS8412 is loosing lock due to deteriorating caps in its loop filter the symptom you describe would be exactly the result. I would check or change those caps first thing. Finally I would consider replacing the CS8412, OTOH you could eliminate the need for it by reclocking the spdif input internal to the DAC.
I'm gonna be mean, but I'm pretty sure a WM8804 spdif I/O module from Twisted Pear Audio will blow the TLC right out of the water if you use it for reclocking, and not cost you a lot in the bargain. Link here: http://www.twistedpearaudio.com/digital/wm8804.aspx - it's temporarily out of stock as these guys products are quite popular. (I use this as a receiver in my home brew dac, but it receives and transmits spdif and can do so simultaneously.)
IMO RCA jacks are NEVER the right choice for 75 ohm spdif audio, I recommend you find the right BNC and cables - really helps with reflections at the connection interface point. (My homebrew dac and transport use "true" 75 ohm cable and connectors.)
@ stephensank
You may be just spot-on with the Gnd loop thing that you point out. In fact over last 24 hrs, the circuit PCB is totally out of its chassis, sitting on a wooden platform all hooked up and very happily singing to glory. Haven't had those high freq "chirpings in my music" and apart from once or twice not locking straight-away, its been pretty good in locking transport to DAC otherwise.
Meanwhile, I heatsinked the CS-8412-CP hoping if it had some minor problems it would be better.
I am working at removal of those crappy RCA female sockets with better chassis mount ones but Theta isn't kind in giving sufficient space for those - hence will have to mod the chassis back plate.
I'll be "watching" the PCB behavior over time now and will keep you posted. Thanks once again for the great help. Much appreciated!!
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@kevinkr
The switch is there to select Toslink as 1 or Coax RCA as 2. Anyway, I use only only coax so plan to pluck out that Toslink connector & the switch.
Also, am building a 2amp powersupply with good regulation to power up the Theta TLC. Hope all this would solve my hassles with this otherwise quite a wonderful device.
Also, many thanks for your help.
You may be just spot-on with the Gnd loop thing that you point out. In fact over last 24 hrs, the circuit PCB is totally out of its chassis, sitting on a wooden platform all hooked up and very happily singing to glory. Haven't had those high freq "chirpings in my music" and apart from once or twice not locking straight-away, its been pretty good in locking transport to DAC otherwise.
Meanwhile, I heatsinked the CS-8412-CP hoping if it had some minor problems it would be better.
I am working at removal of those crappy RCA female sockets with better chassis mount ones but Theta isn't kind in giving sufficient space for those - hence will have to mod the chassis back plate.
I'll be "watching" the PCB behavior over time now and will keep you posted. Thanks once again for the great help. Much appreciated!!
------------------------------------------------------
@kevinkr
The switch is there to select Toslink as 1 or Coax RCA as 2. Anyway, I use only only coax so plan to pluck out that Toslink connector & the switch.
Also, am building a 2amp powersupply with good regulation to power up the Theta TLC. Hope all this would solve my hassles with this otherwise quite a wonderful device.
Also, many thanks for your help.
Hi Arupg,
I own the same Theta TLC.
Did you isolate the output earth at the pulse transformer. May I know how you do it and its effect on the sound?
Thanks
Tong
I own the same Theta TLC.
Did you isolate the output earth at the pulse transformer. May I know how you do it and its effect on the sound?
Thanks
Tong
Hi Tong
Well - I just gotta round the Isolating the RCA digital OUT GND. You had asked how to do it? Please follow this:
1. Unsolder the Pulse Transformer having 4 pins.
2. Carefully - bend out Pin-4 of the Pulse Transformer so that it does not go thru the PCB.
3. Insert the Pulse Transformer & resolder pins 1, 2 and 3.
4. Take the RCA OUT GND DIRECTLY from "Pin-4 lifted" on the component side of the PCB.
5. The GND of the digital out is now totally isolated.
6. Be very careful : make sure the RCA female sockets of digital coax IN and OUT are NOT touching each other either on the chassis or by themselves - thus re-creating back that "common GND" which you broke by making this Pin-4 direct connection.
E N J O Y !! a totally new level of performance from the Theta TLC now... 🙂
regards
Arup
The above mentioned procedure is all due to the very kind gesture of Roy Brown - who had been very nice to help me out with the Theta. Thank you very much Roy!
Further to the post # 12, latest inputs from Roy suggest
-- Connecting Pin-4 for Signal OUT
-- Connecting output from resistor next to Pin-4 of Pulse transformer for OUT GND.
Am yet to try but will very shortly....
Thanks Roy!!
-- Connecting Pin-4 for Signal OUT
-- Connecting output from resistor next to Pin-4 of Pulse transformer for OUT GND.
Am yet to try but will very shortly....
Thanks Roy!!
ok - the swapping turned out to be better than the previous. Hence would recommend mods as per post # 14.
Also, the TLC require a stiff PSU & with that, the performance boost is phenomenal. Suggest to go with Toroidal of 30VA, some schottky for rectification, good Nichicon Gold Tunes of 4700uF for filter with 1uF MKP bypass & 9V reg into the TLC.
You will be smiling then.....
Also, the TLC require a stiff PSU & with that, the performance boost is phenomenal. Suggest to go with Toroidal of 30VA, some schottky for rectification, good Nichicon Gold Tunes of 4700uF for filter with 1uF MKP bypass & 9V reg into the TLC.
You will be smiling then.....
For those who are interested if you ruin the pulse transformer the Pulse PE-65612NL is a direct replacement. Avilable on *bay in batches of 4 for circa £8.
I resurrected my TLC from the back of the closet & popped it open to reveal an engineering change that was done on U5. There is a piggy back MC74AC74N tied to U5 MC74ACT74N. The top chip is connected to the bottom one thusly, pins 1, 7, 8, 10, 13 & 14 are in parallel & the other pins are lifted up. Then on the top chip pin 1 is tied to pin 4, 2 to 6, 9 to 5 & 7. Then pin 3 on the upper chip is connected to pin 19 of U4. Looks pretty sloppy for a production unit, but it works OK. May look at doing the mods listed here, thanks. BTW the piggy back chip is an AC not an ACT. Serial number is, 20561.
Cheers,
kev
Cheers,
kev
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