DAT-Heads Digest #729, Volume #3 Tue, 23 Sep 97 15:15:01 EDT ---------------------------------------------------------------------------- From: Len Moskowitz Subject: TCD-D100 Digital Interface Information Date: Tue, 23 Sep 1997 14:16:38 -0400 (EDT) Back in late August, Doug Oade wrote: > CAUTION !!! do not feed anything with the output , but another > D100. This will work okay, but to feed anything else from the output > can cause damage to your D100 !!! ( I have tested the d100 to > d3/7/8 passive connection and some work, some do not. The > data stream gets very distorted , when viewed with an o'scope, > for the d7/8's that will not work when driven by a d100). >From the mail we receive, it seems that Doug scared a lot of folks. We (Core Sound) finally received the TCD-D100 Service Manual and had a chance to compare its 7-pin digital I/O circuitry to the older TCD-D7. I already knew that our 7-Pin-to-Coax cable works fine between the TCD-D100 and the Tascam DA-20 and that a TCD-D3/-D7/-D8 can feed the D100 via our TCD-Cable (7-Pin-to-7-Pin cable). Still, I was wondering if there were any surprises in the D100's circuitry. Here's a short post that should calm the fears. (If you don't like technical stuff, skip to the "Conclusions.") TRANSMIT The older TCD-D7 used an SC7S04F inverter chip to drive a 100 Ohm current limiting resistor. The chip is powered from a 4.1 Volt DC supply. The resistor limited the drive current to 41 milliAmps maximum, even if the output was shorted to ground. The output was clamped with diodes to output a signal between roughly 0 and 4.1 Volts. The output is not shaped or bypassed with capacitors. The TCD-D100 uses a TC7SU04F inverter chip to drive a 100 Ohm current limiting resistor. The chip is powered by a 3.5 Volt DC supply. The resistor limits the drive current to 35 milliamps maximum, even if the signal is shorted to ground. The output signal is not clamped by diodes but is filtered by two 100 pF caps, before and after the 100 Ohm resistor. RECEIVE The TCD-D7 receive circuit sends the received signal through a 100 Ohm current limiting resistor to a pulse filtering RC network, and then to the input of a SC7S04F inverter (the same type of chip used in the transmit circuit). In the absence of a signal, the input is held to a voltage slightly less than half the supply voltage by a resistive divider network. The TCD-D100 Receive circuit schematic has some labelling errors. The receiver inverter is mistakenly labelled as a VCO and the IC designation next to the symbol is for the op-amp below it. Once these errors are cleared up, the circuit ends up being similar to the one in the -D7. Like the D7, the signal first passes through a voltage limiting 100 Ohm resistor. A zener diode protects against signals greater than 3.9 volts. A pulse shaping network filters the received pulse; it's then fed to the TC7SU04F inverter's input (again the same chip used in the Transmit circuit). In the absence of an input signal, the input is held to half the power supply voltage (~1.75 Volts) through a resistive divider. (Note that there may be more errors on the schematic's voltage readings: for example, look at the inverter's input and output.) CONCLUSIONS Could you damage your D100 by feeding (or being fed by) another machine? Sony seems to have adequately protected both the transmit and receive circuits. This is true even if the D100's Transmit output were shorted directly to ground. 3.5 Volts across 100 Ohms gives a bit less than 125 milliWatts of power dissipation. That just isn't enough power to damage the transmitter. If the Transmitter is asked to drive too small a load, you may not get a usable signal (the signal may get distorted), but the transmitter will not be damaged. Even so, to prove it once and for all, we've ordered one of the chips from Sony; we'll test it to destruction and I'll report on it here. On the receive side, the limiting resistor and zener clamp makes the receive circuit pretty immune from being destroyed by any signal we expect will be presented to the D100, including accidental application of a 5 Volt AES/EBU signal. If you want to connect your D100 directly to an older TCD-D3/-D7/-D8 with something like our TCD-Cable (7-Pin-to-7-Pin), have the older machine feed the D100; the D100 may not drive the older machines adequately. If you have a device that's S/PDIF compliant and that accepts a signal from the TCD-D7 (e.g., DA-20, DA-P1) via something like our 7-Pin-to-Coax cable, it will most likely accept a signal from the -D100 too. If you have a device that's S/PDIF compliant but drives the D7 directly (e.g., DA-20, DA-P1) via something like our Coax-to-7-Pin Cable, it will likely be able to drive the D100. If you want to feed an AES/EBU device (e.g., Fostex D5) from the D100, the lower voltage may cause problems -- it may or may not work. I'll post the news as we get a chance to try out the different machines. I welcome comment and correction. Len Moskowitz Core Sound WWW site: http://www.panix.com/~moskowit moskowit@panix.com ---------------------------------------------------------------------------- From: "Doug Oade" Subject: d100 info Date: Thu, 21 Aug 97 16:55:32 PDT Hello ! Here is a little test bench info on the D100. The mic inputs overload at -20db with no attenuation and at -40 db with the -20db switch on. Unlike the D3/7/8's the D100 WILL switch record inputs after being set to record. The D3/7/8's would stay in analoque in or digital in, after record was engaged, no mater what you did to the 7 pin a/d switch. The D100 , however, will respond to the switch , even after record is engaged. This makes plugging a 7 pin adapter into a D100, running analoque in, risky. The unit may switch out of the analoque mode and give a "no input" message !! BEWARE !! Here is a list of the compatible digital cables for the D100. They are the POC-DA12P, POC-DA12MP, POC-DA12SP and the RK-DA10P. You cannot use the following: POC-DA12, POC-DA12M, POC-DA12S or RK-DA10. These require 5 volts to operate properly and the D100 only supplies 3.5 volts. There is also a question of damage to the driver IC's and the 3.5 volt regulator that supplies the power for adapters. We have seen many D3/7/8's 5 volt regulators shorted by the use of homemade, unsheilded 7 pin cables, when the pins get bent. The same may happen to the D100 , due to excessive current draw. Here is what Sony ( and all DAT machine manufacturers) say about tapes longer than 120 minutes (124 minutes are okay). " Do not use cassette tapes with playing time of over 120 minutes to record important material since such tapes are subject to the following problems: * Sound distortion * Unstable tape speed after repeated AMS, rewinding, fast- forwarding, cueing or reviewing operations. * Incorrect writing and eraseing of start ID's " We feel this is VERY GOOD advise , as do all DAT machine manufacturers. Peace.... Doug Oade Oade Brother Audio www.oade.com 912-228-4480