Best way to hook up a -10dBV console to a +4dBm tape recorder

timkroeger

timkroeger

Custom Title User
Hey there,

I have these nice pieces of gear:


The console's tape ins and d.outs are -10 dBV (TS). The tape recorders line input and output connections are 3-pin XLR +4 dBm. Some quotes from the manual first:

ATR-60/16 manual page 1-6 said:
Standard 3-pin XLR-type connectors as well as 25-pin D-sub connectors make it easy to connect cables from INPUT and OUTPUT to the sound system. These transformerless balanced XLR-type connectors are specified as follows: Input impedance: 10 k ohms, nominal input level:+4 dBm (1.23 V), output impedance: 20 ohms, nominal output level: +4 dBm (1.23 V).
Click to expand...

ATR-60/16 manual page 3-2 said:
XLR-type Input/Output Connectors (Balanced): Pin 1 is GND (Shield), Pin 2 is Cold (Low) and Pin 3 is Hot (High).

Note: Short circuiting between Pin 1 (GND) and Pin 2 (Cold) will change the ATR-60-16's Output to accomodate unbalanced cables.
Click to expand...

No mention of accomodating unbalanced inputs, yet.

ATR-60/16 manual page 4-6 said:
Input impedance is 10 k ohms (balanced), input level is +4 dBm (1.23 V), and maximum source impedance is 600 ohms.

Output level is +4 dBm (1.23 V). Minimum load impedance is 200 ohms (balanced)
Click to expand...

Does the maximum source impedance or minimum load impedance change, if I connect unbalanced sources/destinations?

ATR-60/16 manual page 7-23 said:
Nominal input/output level is +4 dBm (1.23 V) and nominal output load impedance is 600 ohms, regardless of the type of connectors (XLR or D-SUB).
Output level is always +4dBm even if the XLR type connector's Pin 1 (GND) and Pin 2 (Cold) are short-circuited to change the ATR-60-16's output to accomodate unbalanced cables.
Click to expand...

The following Figure 7-36 shows two XLR connectors for Input Connector Wiring. One for balanced, the other for unbalanced with Pin 1 (GND) and Pin 2 (Cold) short-circuited. So I think I can use an unbalanced input source, too.

Now, I calibrated the input amplifiers and meters using a +4dBu 1kHz testtone, configuring the amplifiers to read +4dBu at the output and the meters to show 0dB at that level. A few questions:

  • Do I need to fool around with a 600 ohms resistor on the input for a 1.23V +4dBm signal?
  • Was using another scale (+4dBu instead of +4dBm) wrong in this setup?



Look at the attached picture of block and amplifier diagrams below. It seems that internally everything is "amplified" to -10dBV just after the input and just before the output it's amplified back from -10dBV back to +4dBm (+2dBV). I am reluctant to use line level converters to mess with the signal since they are both expensive and introduce more gain stages. I'm also reluctant to tap into the circuits and fabricate some kind of break out cables... The questions are:

  • What else can I do?
  • What signals can I expect on an output that is short-circuited to unbalanced?
  • What unbalanced signal level do I need to provide to the tape's inputs in order to reach 0dB on the VU meters?

I could live with a "hotter" output from the tape machine but what can I do to reach the tape VU's 0dB? I think I could post additional pictures of the actual circuitry involved but I don't have a scanner right now so it would be pictures taken with my camera. Oh, thanks for reading ;)

Cheers
Tim
 

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The block diagram suggests that the output from the respective dbx units is operating at -10dB the same level as the console. I am not familiar with ATR series machine. The block diagram suggests you could bypass the line amp on the in put and out put at that point. What are the physical connections at the input and output of the dbx units? "Tapping" into the circuits may not be that difficult. The Tascam spec sheets says the dbx units are on cards, so maybe you would have to fashion a complicated "breakout" cable. If you don't want to use line amps as suggested above, you could use 4:1 and 1:4 transformers as well. The output impedance is probably low enough from the ATR that a 1:4 shouldn't present too much loading to the inputs of the 3500. However, the transformers may add color.

Viel spaß!
 
Danny and Blue Jinn,

thanks for the input. I had looked up the Tascam LA-80 units (mkII and the previous model) before and I'm not too eager on spending EUR 800.00 on two units and introduce even more gain stages. I may be able to obtain one or two units used for a lower price and maybe they'll come in handy interfacing other +4dBu/m gear but I'd rather check other options first.

I had a look at the schematics and the amplifier PCBs operate on -10dBV unbalanced. The balancing input and output amplifiers are part of the dbx PCB. If the dbx is deactivated, the signals don't go to the dbx circuitry but still use the balancing amplifiers on the PCB. I need to check if there is an easy way to tap into the circuitry but I am a little afraid to fry the board. What I'd like most would be a nice add-on circuity that would check the Cold and GND pin for shorts (same potential) and then bypass the balance input amplifier (same with output) by connecting Hot with the former balance amplifier's output (-10dBV). Maybe a dual toggle switch would do, too, just to be able to switch it manually. Still, I'm feeling queasy hacking the dbx cards...

It's just that I see the machine working on -10dBV internally and that's what I could easily provide with my console, but the addon circuitry of the tape to provide balanced I/O is forcing me to jump through loops. Just a little frustrating.

Cheers anyway ;)
Tim
 
If you want nothing in between the desk and the recorder Tim and asides getting rid of the ATR for an MS-16 I think your options might be limited.

These may be just as expensive as the Tascam LA-80's but they go both ways and probably introduce little in regards to artifacts. I may be considering a pair myself to direct out and back my Studer 089 from the inserts. It's got the same problem - low gain.

ARX Balance 8

ARX De-Balance 8

A cheap option to try is this;

Behringer DI800

For $US150 it may or may not impact the signal quality but it's a cheap thing to try and you may find other uses for it if you don't like what it does in between the desk and the recorder.

:)
 
Tom, I know the LA-80/81's are expensive. My brother had to buy 6 units to run his JH24 with the M-3700.

I have a couple of these units (the 8 channel versions) here at my place that I use for various things and they work fine too.

http://www.ebtechaudio.com/llsdes.html
 
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:laughings::laughings::laughings:

My favorite part about that level diagram is the "putput" amplifier reference...:D Can't stop chuckling...

Tim, I don't know if there is any way to get me copies of the PCB layouts and schematics for the ATR60...

Even some pictures of the PCB to where the internal XLR wiring goes...you say that is straight to the dbx PCB's? That would be wierd...

My 58 (ATR60 grandfather in a sense) balanced I/O was on a separate board and the incoming/outgoing internal unbalanced -10dBv audio came to/went from the balance I/O PCB and split...one set of 8 channels to the balance/buffer amps and the other set straight back out to the unbalanced I/O jacks (the 58 has both balanced and unbalanced I/O).

The bottom line is that if you DO add a set of unbalanced I/O jacks to the ATR60-16 it is going to be a certain expense in time and materials. I'm pretty sure you would be able to do it without "hacking" the dbx PCB's because I'm pretty certain that the XLR jacks plug in to whatever board they go to, so you would conceivably be able to splice into those -10dBv in a non-destrictive/reversable way.

I'm pretty sure it CAN be done but you are talking about jacks, a rackmount panel or something to house them, cabling, internal connectors...

Put up some pics of the guts if you can.
 
I think its possible to put a resistor on the output side to passively scale it down to the -10dBv range...the input side is a different story.

Danny's right about those ebtech boxes...cheaper and still good quality. cjacek has had good things to say about them in the past.

I have an array of 3 LA-40mkII's that I use with my Tascam board...they are 4 channels bi-directional so I've got 12 channels unbalanced to balanced and balanced to unbalanced.

I got them for about $60USD each, but that was a pretty luck find.

Guts.

Pictures.
 
I'd suggest doing the following test:
1. Align 1 channel of the ATR in and out. (I'd suggest no higher than 250nwb)
2. Kludge one cable to interface the -10 output of the board to that machine channel's input.
3. Send a 1khz tone (sine wave) @ 0vu through the board to the machine. (make sure all nr is "out")
4. See if you can raise the machine input's level enough to achieve 0vu on the machine itself.
5. If the answer to # 4 is yes, then send some actual program to the machine to see how it sounds.

If everything checks out ok, do the procedure in reverse by reducing the machine's repro/sync gain so that 0vu from it gives you the same reading at the board input when everything is set @ unity.
 
One thing not mentioned is that tapping ahead of the balancing/unbalancing amps eliminates a gain/attenuation stage.
 
I would just go with the LA 40s or the like. I have the older, non MKII type. They cost me about $30 and $50, used and they work great. I actually just got the manual for it today along with one rack ear from Tascam. They also have balanced in/out +4 1/4" in the front. The 1/4 and xlr are transformerless. The transformer is at the -10 rca jacks.
 
Hey,

thanks for all the suggestions, I'll definitely check all this out. I'm still keeping my eyes peeled for line amplifiers from Tascam, Fostex, Ebtech, ARX, etc. and I think it can never hurt to have some of those tools around. I checked out the Behringers' spec sheets and it seems they're trying to offer a generic conversion interface. I like things more, that serve just on purpose. I always become suspicious if a unit offers too muchg quite a small price. And I don't like front access units. I have a large patchbay, and I need them to be accessed from the backside.

I'm not at home at the moment but will be in a few days. Work has begun for me again, so I won't be around that frequently from now on but I have some notifications set up and there's always the weekends.

What I'll be doing when I'm home again:
  • Try to raise / lower the built in I/O amps to accomodate -10dBV as RRuskin suggested
  • Have a look at the schematics / PCBs of the dbx and amp cards again. See where the wiring goes to/from.

The whole thing why I don't simply go with a line level converter/amplifier is what BlueJinn pointed out again. The tape recorder works at -10dBV level internally and the balancing is done via two additional gain stages. Knowing that I'd add a total of 4 gain stages per channel by putting line amplifiers in front of the machine (-10dBV to +4dBu to -10dBV again on input and again at the output), is enough for me to think about alternatives. It would be ok if I had about 30 feet to cover from my console to the ATR but I don't see that at the moment.

Cory, the 58 design sparks a small hope ;) I am pretty sure that there are no seperate balancing boards for the ATR-60/16 but I'll have a closer look at the PCBs once I'm home again. I'll put up schematics and photos, too. Do you have the 58 schematics for the PCBs in question available? I'd like to compare them to the ATR-60-16's design and see if Tascam did something different to present additional -10dBV I/O (e.g. additional decoupling or something).

Cheers
Tim
 
Well then...if you don't need a level bump up/down and you only need to go bal<---->unbal...then just wire up your cables for that. It's not a bid deal, IMO unless you plan on doing very long cable runs in a very bad EMI/RFI area.

I interface bal/unbal all the time with NO special conversion boxes.
It's all about how you wire the cables at each end. I made sure I did that wiring the right way at my patchbays for both bal/unbal, and paid attention to the grounding and now I just connect a patch cable between them...no problems that I've ever noticed.
I even have my longest unbalanced runs going out to about 25 feet (7.6 meters)...and NO problems.

Check out this RANE Note...it gives you several variations for doing that, and just find the one that works best in your environment and setup.

http://www.rane.com/note151.html
 
Yo Tim! I appreciate not wanting to add a second gain stage. Maybe I'm missing something, but it seems this would be your ticket, assuming you need 8 channels converted:

http://www.8thstreet.com/product.asp?ProductCode=2206&Category=Recording_Accessories

This is an 8 channel, no power, no gain stage, transformer based line level shifter. Its 1/4" "smart jacks" can accept a 1/4" unbalanced TS input, and will put out your choice of a 1/4" TS unbalanced or 1/4" TRS balanced output. I've used the 2 channel version for years for a variety of purposes without a problem. It can convert from +4 to -10 or the other way around, and can change balanced to unbalanced or unbalanced to balanced connections in either direction. What's not to love? It looks like what you are trying to build. Best of luck.-Richie
 
My $0.02

For me I'd see about tapping into the internal -10 dBV in a way that does not subtract from the value and is easy to remove should you want to sell it some day. The balanced amp adds a slight amount of noise. A good starting point is the DBX bypass switches.

There are many ways to do it outboard. Active level shifters etc. Here is a pointer to the Jensen transformer app note on level shifting that gives a lot of info and theory.

http://www.jensen-transformers.com/an/an003.pdf

Regards, Ethan
 
Do you have the 58 schematics for the PCBs in question available? I'd like to compare them to the ATR-60-16's design and see if Tascam did something different to present additional -10dBV I/O (e.g. additional decoupling or something).
Click to expand...

Tim, you bet. You want docs that cover from the jacks to the PCB they hook up to?

All good info in the posts above. The test to see if the gain trimmers on the ATR60 will sweep to accommodate -10dBv coming into and going out of the deck will be an important one. This may actually work out. They may not have wanted to make a big deal out of pointing out that the ATR60 could do this (if it can) because the ATR60 was marketing straight to the pro outfit...-10dBv would make it seem semi-pro. :rolleyes::drunk:

But the Otari MX5050 and many others could handle +4dBu to -10dBv on the same set of jacks with level adjustments. I even worked through helping a fella with his Studer 24-track to see if he could interface with -10dBv gear and indeed the trimmers could easily sweep to cover that range.

If your deck will do it, then it is a matter of deciding if the unnecessary gain stages bother you that much. If it were me, and the deck could accommodate the levels, I'd leave it alone until it became a real problem, if ever it did. My guess is you'll have more noise through the mixer gain stages than in those two stages on the deck. My 2p.
 
sweetbeats said:
Tim, you bet. You want docs that cover from the jacks to the PCB they hook up to?
Click to expand...

Yes, and the schematics of the corresponding PCBs so I can see what hooks up where. That would be terrific. I will be home again tomorrow around 2 pm GMT+1 and hopefully have some time to look into the schematics. I've been told that the mouser order has arrived and I'm quite eager to fabricate the micro lynx transport cable :)

sweetbeats said:
If your deck will do it, then it is a matter of deciding if the unnecessary gain stages bother you that much. If it were me, and the deck could accommodate the levels, I'd leave it alone until it became a real problem, if ever it did. My guess is you'll have more noise through the mixer gain stages than in those two stages on the deck. My 2p.
Click to expand...

Exactly what I am thinking. If it can accomodate and sounds good, than I'll leave it the way it is. Right now the ATR is standing next to the console so the cabling is short enough and unbalanced will do. If I need to move it away in the future I'll definitely think about the line level amplifiers to get balanced connections. I think the added gain stages are a lesser evil compared to the hum/noise that may be introduced by long distance unbalanced cabling. It might take some time to get lucky on ebay and score a few amplifiers/converters but we'll see.

Cheers
Tim
 
Tim,

Here is a select schematic pack for the 58 with regard to the inputs and outputs. It includes the overall wiring diagram as well as the "IN/OUT PCB" (i.e. balance amp PCB) and I threw the amp PCB schematic in there too...let me know what else would help.

The 58 in its basic for is unbalanced. The 58-OB achieves its balanced I/O feature by the addition of the IN/OUT PCB that is powered by a separate secondary power supply.

I looked at the 48-OB again too...the balancing amps are actually on the amp cards in that deck, but that (like the 58-OB) has unbalanced input and putput :laughings:...sorry...output jacks as well as balanced jacks on XLR's.

Keep in mind that the 48 and 58 feature no integrated noise reduction. They were designed to interface with the DX-4D units whereas (obviously) your ATR60-16 has noise reduction "inside" the inputs and outputs.

I am genuinely curious to see how Tascam handled the signal balancing on the ATR60-series.

I think the added gain stages are a lesser evil compared to the hum/noise that may be introduced by long distance unbalanced cabling.
Click to expand...

I agree 100%.

The 58-OB on paper performs better using the unbalanced I/O. There's no shame and obviously a potential advantage to utilizing an unbalanced path as long as noise rejection is not a concern. And a balanced path is not always an answer to a noise problem too. Complex matter in an industry with years and years of loose standards between manufacturers, and hungry marketing departments.
 
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