Toshiba RX179 output a TTL level signal? - diyAudio
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Old 28th June 2004, 05:54 PM   #1
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Default Toshiba RX179 output a TTL level signal?

Hello,

I assembled a circuit to convert from TTL level S/PDIF to coax. When I connect a TTL level signal from a DIT4096 to it I get audio out. When I connect a powered Toshiba RX179 toslink receiver to it, I get silence. I connected a good known working toslink cable to a known working toslink transmitter and to the receiver but I get nothing. The transmitter is connected to the same TTL level signal output from the DIT4096.I used an SN74HC04 which is CMOS inverter and two resistors and a cap on the output for dc blocking and impedance matching. It works well when I connect a TTL level signal to it, but not that receiver. Am I missing some circuitry or shuld I use another receiver?

Thanks
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Old 30th June 2004, 08:58 PM   #2
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No one has played around with toslink receivers? The reason why I ask is for my devices (like my directivo, XM radio S/PDIF circuit, etc) only have a toslink transmitter. The XM radio circuit uses the DIT4096 and outputs a TTL level signal which I convert to coax easily and connect to a toslink transmitter, but I am in need of a working receiver, especially for my directivo! No one has anything for me to try?

Thanks.
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Old 1st July 2004, 03:43 PM   #3
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I connect the TORX179 directly to a DIR1701 and it works without problems. I would not block DC on a TTL signal. Try connecting it directly.
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Old 1st July 2004, 07:26 PM   #4
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You do not need "impedance matching" there. Or a DC bloacking cap.

It puts out a signal that any CMOS logic gate can handle.

It helps to have a 'scope...........

Jocko
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Old 6th July 2004, 06:27 AM   #5
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dip16dac,

I had to do it this way to connect the TTL output to the TTL input of this circuit.

Jocko Homo,

This is the circuit I am using.

I went to give my Pace soldering equipment a test so I desoldered a TORX194 receiver from a Sega Naomi system. It also used a TOTX195 transmitter as well. I desoldered both. These are used for two player game link ups between two Naomi systems. Anyway, I figured I'd give this receiver a try. The one thing I did different was that I used a coil and a cap on the power supply and ground like the datassheet said. The other receiver I used had no cap or coil in the Vcc and ground. So, once everything was soldered, I powered it up and gave it a try with the schematic above. It worked perfectly. Now I'm able to convert the optical output on my DirecTiVo and xm radio to coax and use it with jwb's DAC. What is good software to draw up a schematic for this so if other people need a schematic that works they can use this one?

Thanks.
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Old 6th July 2004, 06:57 AM   #6
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I wouldn't put inverters in parallel like that. Increase jitter. Which there already is a bunch....but no sense on adding any.

So......your diagram is a SPDIF output, right? (0.5 V_pp)

You could try a ferrite bead designed for decoupling in place of the coil, as the data sheet suggests.

Jocko
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Old 7th July 2004, 03:47 PM   #7
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Jocko Homo,

It's a TTL input to coax output. Jitter is increased, but does it benefit in anyway to connect gates in parallel like that? I've seen a circuit that has 3 gates connected in parallel and that connected to another gate for inverting. I've tried both and have gotten good results. Using an Onkyo AVS250 receiver, using this circuit connected to a coax input of the receiver and the same TTL signal driving an optical transmitter, I plugged that into the optical S/PDIF input. Both sound exactly the same, with either two gates or 3 gates and inverted on the TTL to coax circuit. As long as it can work with jwb's DAC, I'm happy. The TTL to coax circuit also works well with ac3 streams too.


Next I'm going to try transmitting S/PDIF via RS422/485. The RS485 driver I'm going to use is a DS3695. It operates at up to 100Mb it seems, so I'll give it a try with long cable runs.
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Old 9th July 2004, 12:28 AM   #8
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Well guys, I have an update:

First of all, I ordered parts for another TTL to coax circuit. The circuit is:

S/PDIF output
(RCA or BNC)
|\
TTL level signal -----+-----| O-----680R--+---------+ +------- center pin
| |/ | | |
| | )||(
| |\ | )||(
+-----| O-----680R--+ )||(
|/ | )||(
100R | |
74HC04 | | +------- ground
+----+----+ T1
|
---


This was taken from here and it works very well. I put it on the same PCB as the previous circuit. It's powered from the same power supply. The transformer works well. The TTL signal feeding it was a sharp toslink receiver. I put an inductor and a capacitor on it and it's working quite well. I also used the TORX179 again with a cap and inductor and I get absolutely nothing. Both the outputs of both receivers were on a switch so I can switch between which TTL signal goes into the circuit. I like this circuit better because it's transformer isolated. I think my TORX179 receiver might be damaged, I don't know and am tired of farting around with it. So, what I'm going to do is take out the TORX179 and replace it with a 10 or 20Mbps RS422/485 tranceiver. This way I can connect a device with S/PDIF output that is quite a large distance from this circuit. I plan on using standard cat5 cable or telephone cable for the RS422/485 transmission, it should work well. Instead of that very slow DS tranceiver, I'm going to use a faster 10 to 20Mbps one from either Sipex or Maxim. This will allow me to transmit thousands of feet if I wanted to. The RS422/485 transmitter will be on a seperate PCB with switchable TTL, optical (with the second sharp receiver I have), and coax inputs. This is a very flexable project I'm doing. Multiple switchable converters are much cheaper and more fun to design and assemble on your own. I like the conversion circuit with the transformer the best.
This is just an update so far, I'll keep you posted with what comes next.
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Old 9th July 2004, 12:32 AM   #9
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The ASCII schematic does not look to well. The circuit is the first one on the conversion section of the page. Has the 74LS04 inverter (I used an SN74HC04N CMOS inverter), the two 680 ohm resistors, a 100 ohm resistor and a 1:1 pulse transformer.
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