A Question of Balance (and Impedance)

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cloakhead

New member
Sorry if this is in the wrong subforum, please move it if it is.

Following an impulsive last-minute ebay bid, I am soon to be the owner of a Tascam DP-004 digital recorder. It was only after I had won the auction that I noticed something in the specs I hadn't before - the inputs on this thing are unbalanced. My microphone preamps, on the other hand, only have balanced outs. Maybe that'll teach me to research thoroughly before buying, but unfortunately it probably won't.

Anyway, I've never tried connecting a balanced out to an unbalanced in, so I've been looking online to try and figure out the best way to do it. Apparently I'm not very smart, because reading about the technical details of connections and impedance matching issues and such is making my brain hurt. So I thought, why not get some other people to do the thinking for me? ;)

Here are the relevant specs:

DP-004 Inputs:
Standard Phone Jack, Unbalanced
Input Impedance: 10k ohms min.
Standard Input Level: -10 dBV
Maximum Input Level: +6 dBV

VTB-1 Studio Preamp Outputs:
Male-XLR Balanced Output: 100 ohms (50 ohms each leg)
TRS Line Out: 300 ohms (Impedance balanced)

The VTB-1 also has an Insert Jack. I'm not sure if it will help, but I've heard that they can be used to send a signal without the return if an adapter is used:

Insert Jack (TRS): Nominal level approx 0dBu
TIP=Send: 50 ohms output impedance
RING=Return: 7500 ohms input impedance

Any suggestions on the best way to (preferably inexpensively) connect these two devices, or links to sites that can explain this stuff to a moron like me, would be greatly appreciated. Thanks!
 
just use a trs-trs cable... in most cases a ts-ts will work fine.. a small % wont like the - grounded to it's system ground.. that's why i use the trs's for this... when you start to bring it up have any pads turned to max and bring up slowly the pre-amps out so ya dont overload the tascam...
 
Thanks, dementedchord. I guess I've been trying to fix a problem before I'm even sure that a problem exists...

The DP-004 is supposed to arrive today, and while I don't have any TRS cables handy I have some TS's, so I'll give 'em a try.
 
I've had some time to play around with the DP-004. The good news is that I'm not getting any hum or interference while using a short TS cable. The bad news is that I'm having a hard time getting a usable signal that doesn't clip. I have to keep the Vtb-1 very low and crank up the Tascam's input level, which adds hiss to the signal. Even then I'm constantly flirting with the recorder's overload light. It's not too bad, but it seems like there must be a better way. Would a line level converter solve this problem? Some sort of impedance adapter? I'm feeling pretty clueless about all of this, but I was able to get some overtime this weekend so I don't mind throwing some money at the problem if it makes it go away. Any suggestions?
 
cloakhead said:
I've had some time to play around with the DP-004. The good news is that I'm not getting any hum or interference while using a short TS cable. The bad news is that I'm having a hard time getting a usable signal that doesn't clip. I have to keep the Vtb-1 very low and crank up the Tascam's input level, which adds hiss to the signal. Even then I'm constantly flirting with the recorder's overload light. It's not too bad, but it seems like there must be a better way. Would a line level converter solve this problem? Some sort of impedance adapter? I'm feeling pretty clueless about all of this, but I was able to get some overtime this weekend so I don't mind throwing some money at the problem if it makes it go away. Any suggestions?
Click to expand...
Turn the gain all the way down on the input to the Tascam and then turn the output of the preamp up until you start clipping on the Tascam and then back off a bit... that should work...
 
MOFO Pro said:
Turn the gain all the way down on the input to the Tascam and then turn the output of the preamp up until you start clipping on the Tascam and then back off a bit... that should work...
Click to expand...

mofo said it better than i did... ya want theoutput of the pre low and the pad on full at the recorder...

sounds strange cause you appear to be turning down to get the full pad...
 
Well, I've been trying to get a usable signal with the Tascam per your suggestions, but I just haven't been happy with the signal to noise. Before giving up on the unit entirely, I decided to order an Ebtech line level shifter to see if it helped: http://www.sweetwater.com/store/detail/LLS2XLR

I received it earlier today, and I have thirty days to decide whether or not I want to return it for a refund. As far as I can tell so far, it works just fine at allowing me to run my preamps at normal levels, while keeping the inputs of the Tascam down where they aren't so noisy. However, for some reason running the signal through the shifter causes it to pick up a noticeable buzzing noise, as well as some faint voices which I think are from a radio transmission (although I haven't ruled out the possibility that it could be haunted). Oh, and the noise disappears completely whenever I touch the preamp. Moving the shifter further away from the preamp changes nothing. Different TS cables don't seem to change anything, and I've never had a problem with interference with these cables before.

I'm thinking about contacting someone at Ebtech about this, but I thought I would ask here in case someone is familiar with this type of problem. I like the DP-004 overall and would like to get it to work, but all of this is getting frustrating and I'm pretty close to just returning/selling everything and buying something else.
 
cloakhead said:
I have to keep the Vtb-1 very low and crank up the Tascam's input level, which adds hiss to the signal.
Click to expand...
That is the perfect recipe for horrible S/N

cloakhead said:
Even then I'm constantly flirting with the recorder's overload light.
Click to expand...
Something just sounds wrong here... where are you clipping, on the preamp or the recorder, is the overload light on the input or output, are you hitting the recorder too hard or are you cranking it to much on the output. You really shouldn't have to be turning the gain on the recorder way up to compensate for a turned down output of the preamp... somethings amiss here...

Oh, and the voices... they're in your head (don't fret, you get used to them)

No, actually the line level shifter probably drops your ground through a transformer (current's induced there's no direct connection), and also picks up the radio signal off-air at the same point
 
sorry for the confusion... that's the opposite of what we were trying to tell you...

1. turn the pre output down...

2 turn the tascam input to minimum... the confusion comes form the way a pad works... at it's maximum it's the minimum signal...

3 mic the instrument... bringing up the input of the pre slowly watch for oberload lights on the pre if it doesn't have ab actual meter... if it's got 2 led's then the first should come on regularly but when the second starts to flash then back off a smidgeon... the pre is now "correct"...

4. bring the tascam up slowly... using the same criteria on it's own led's/meters...


makes sense??? ya want the pre signal to be strong and clear... and you dont want to overload the next stage.... this is what is meant as gain staging... and ultimately applies at each inter connection within your rig...
 
Sorry to take so long to get back to the thread, I've been pretty busy.

MOFO Pro said:
Something just sounds wrong here... where are you clipping, on the preamp or the recorder, is the overload light on the input or output, are you hitting the recorder too hard or are you cranking it to much on the output. You really shouldn't have to be turning the gain on the recorder way up to compensate for a turned down output of the preamp... somethings amiss here...
Click to expand...

Hopefully I'm just doing something stupid, although I don't see where what I've been doing is different than dementedchord's suggestion above. But as I believe I said in the OP, I'm not very smart, so maybe it would help if I go into some more detail about how I'm attempting this.

I'm using a miced acoustic guitar to set the levels, starting with the input and output on the vtb-1 and the input on the Tascam all the way down.

First, I bring up the input on the vtb-1, strumming the guitar as loud as I would when playing until it clips the vtb-1's input meter, then backing off a little.

Second, I do the same for the vtb-1's output, bringing it up until the Tascam's overload light starts to flash, then backing off.

Finally, I start to bring up the input on the Tascam. At this point, I'm barely registering a signal on the Tascam's input meter (which is seperate from the overload light). Even when I've got the input at about 1 o'clock, which is about as high as it will go before starting to add noise to the signal, the meter only reads at about a quarter high while I'm playing the guitar. Even with the Tascam's inputs all the way up, which is very noisy, the meters only get up to around half way. Basically, I can't even get the meters on the Tascam anywhere near full, which is where they should normally be clipping.

And that's where I'm stuck. I can't bring up the vtb-1's output any more, because the Tascam's overload light will flash and the signal will clip (this happens regardless of where the Tascam's input is set). I can't bring up the Tascam's input, because it starts to get noisy as hell.

Oh, and I've tried exporting tracks to my PC to see if the quieter tracks sound okay once I've brought up the volume digitally, but the signal to noise is not good (although it's better than when I crank up the Tascam all the way).

Oh, and the voices... they're in your head (don't fret, you get used to them)
Click to expand...

Heh, they're so hard to hear that I was beginning to wonder. The buzz, on the other hand, is pretty loud.

No, actually the line level shifter probably drops your ground through a transformer (current's induced there's no direct connection), and also picks up the radio signal off-air at the same point
Click to expand...

Would that cause the buzz as well? And is there anything that can be done about it? If not, it's a shame because the shifter resolves the problem I'm having with the recorder, if it weren't for the buzz. Oh well, at least I can return it.
 
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