US-1800 balanced output suitable for unbalanced input?

L

LeadPaint

New member
I need to know whether the Tascam US-1800 balanced outputs are suitable for connecting to a consumer grade amplifier's unbalanced inputs.

The US-1800's manual on it's outputs: "Output impedance: 100Ω, Nominal output level: +4 dBu (1.228 Vrms), Maximum output level: +24 dBu (12.277 Vrms)"

The amp's (Sansui A-1000) manual on it's inputs: "Sensitivity 150mV/47kΩ"

I'm considering buying the Tascam US-1800 audio interface. I like having more inputs than I need at the moment, so I'm not limited when I want to record more tracks in the future. Also, my old Terratec DMX 6Fire doesn't work with 64-bit Windows 7 so I temporarily have to use my PC's onboard soundcard's line output. I hope the US-1800 outputs provide higher sound quality and won't overload my amp's unbalanced inputs so I can kill two birds with one stone with the US-1800, by using it both for recording and casual music listening.

Thanks for any help. :)
 
If you turn down the volume control on outputs of the US-1800, you are effectively reducing the +4dB output to a -10dB output, it just means that you need to run the output of the tascam at a lower setting and if you get tempted to turn it up you may distort the input of the amp.

The balanced to unbalanced does not matter, in fact when you convert a balanced +4 output to an unbalanced input the +4 is reduced already which is what you want.

Finally, if you find that you have too much output from the tascam and you are not getting volume control as it get too loud too quick, you can make a pad to reduce the +4 balanced to -10 unbalanced with just a few resistors, check here.

Alan.
 
I suppose the Tascam uses electronically balancing so the cold wire should be unconnected to get the 6dB attenuation you meant? I've read the page on the pads. I find the formulas very difficult. Can you help me get the values for 8dB attenuation?

I've found a schematic for a conversion circuit. (attachment) Would this have any advantage?
 

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  • Balanced-Unbalanced.jpg
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If this pad is for connecting a +4 output to a -10 input you need a 14 dB pad, the pad site has the calculation for balanced to unbalanced pads, basically you half the resistance of the 2 in line resisters.

So you need a pad like the "U" diagram. The resistor values to use are R1 = 5K and R2 = 3.6K to the + connector goes to one incoming leg (diagram top), the - connector goes to the other incoming leg (diagram bottom), the common goes through (it's not shown on the diagram). You get the output side + (diagram top) then the - by connecting the common and the diagram bottom output.

This will give you the attenuation you need to not overdrive the power amp and to give you a workable volume control.

The diagram you attached looks very complicated you don't need that.

Alan
 
I thought I needed a 8dB pad because the balanced to unbalanced connection already reduces 6dB.

This page says you shouldn't connect the cold and common leads with active balanced units. You're sure it's safe with the US-1800?

Thanks for helping me out Alan.
 
LeadPaint said:
I thought I needed a 8dB pad because the balanced to unbalanced connection already reduces 6dB.

This page says you shouldn't connect the cold and common leads with active balanced units. You're sure it's safe with the US-1800?

Thanks for helping me out Alan.
Click to expand...

Where does it say in the manual that it's an active balanced unit? It just says balanced.

Line output (Balanced) terminals (LINE OUT 1-4)
Connector: 6.3 mm (1/4”) TRS Standard phone jack (Tip: HOT, Ring: COLD, Sleeve: GND)
Output impedance: 100Ω Nominal output level: +4 dBu (1.228 Vrms) Maximum output level: +24 dBu (12.277 Vrms)
Monitor output (Balanced) terminals (MONITOR L/R)
Connector: 6.3 mm (1/4”) TRS Standard phone jack (Tip: HOT, Ring: COLD, Sleeve: GND)
Output impedance: 100Ω Nominal output level: +4 dBu (1.228 Vrms) Maximum output level: +24 dBu (12.277 Vrms)


This gear is usually made so that if you wanted an unbalanced connection you would just plug in a TS connector instead of a TRS connector. Using a TS connector short the - and ground within the plug. As you want a +4 to -10 conversion you can do this link after the pad or you can make an unbalanced pad after using a TS plug using the unbalanced schematic.

To be honest as I said earlier I would just plug in an unbalanced jack and connect it to the amp. If you get the -6 db reduction all that will happen is that you won't have to turn up the volume control as loud to get full volume on the amp. For example if you get to 3/4 on the control it's likely thats about when the amp will be overdriven. You will hear distortion if this happens. If it's not workable and you cannot get enough control over the volume then you will need a pad.

I am running balanced +4 into unbalanced -10 amp input in my studio for years with no problems. I have + to + and - and shield to ground as described and it works fine. If you get a ground loop lift the shield.

Alan.
 
Please don't be offended by my n00bness. I have ordered the US-1800 yesterday. For my income it's a pretty expensive device. So it worries me when I read that connecting balanced devices in a particular way can damage them (or my amp). Didn't mean to question your expertise as you're probably much more experienced with audio stuff than I am.

I'll make the TRS to RCA cable as you suggested when the package arrives and I'll try it out. I can still make a pad afterwards if I feel it's really necessary.
 
No problem with being careful, I would think that with the number of Tascam units being sold and the number of users that would have plugged in an unbalanced jack intentionally or unintentionally, if there was a serious problem Tascam would have released a warning about this. I don't believe there will be any problems, I have tons of balanced gear that gets connected to unbalanced gear and I have never had anything fail through this.

Is there any US-1800 users out there that have had problems?

Alan.
 
Got the Tascam yesterday. I made TRS to RCA cables with cold floating. I could change it if it wouldn't work, but since it works properly I leave it this way. I also think, as you said, a pad is not really necessary. I heard no distortion from my amp with the output knob on maximum and very loud music (constantly clipping junk). Having the the output up so high makes no sense in my set up, because I have to turn the master on the amp so low left/right channel relation gets out of balance. I keep the knob between 12 and 2 o'clock.

Thanks again for your responses Alan!
 
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