Quote:
Originally Posted by albee1952
1) Use Mic Pre (my friend uses Universal Audio 4-710d for his vintage synths) Yes, do this as it solves all your problems.
2) Use a DI unit to convert/boost the unbalanced signal to balanced
A DI does not exactly do this. It converts a high-impedance unbalanced instrument source(which you have) to a balanced mic-level source(which you still need a preamp for)
3) Input everything directly to the -10dB inputs in HD I/O and adjust the gain input on each channel. I haven't tried this yet but I'm guess the HD I/O has enough headroom to boost the signal
Read the manual that came with your HD IO as it says very clearly that unbalanced connections MUST NOT ground the cold side(which is exactly what happens when you plug a standard TS cable(as you would use with most drum machines and keyboards) into a balanced TRS patchbay. I would use a preamp, but the 4-710D might be pricey for this purpose.
Having said all that, you could save lots of cash and use something like SMPro's EP84. http://www.smproaudio.com/index.php/...s/preamps/ep84
One last option; if you are good at soldering, you could make "quasi-balanced cables to connect your unbalanced keyboards to balanced inputs(the -10 inputs on the HD IO), but these need to be wired correctly. Using balanced cable(assuming white and black wires, plus shield), connect the unbalanced end as tip=white, sleeve=black(do not connect the shield at this end). At the balanced end, the TRS plug would be tip=white, ring=black, sleeve=shield. |
If you want to skip the need to use a mic preamp/DI combination to interface the unbalanced line outs of the gear, the use of a unbalanced to balanced converter will keep everything at line level, this way the TRS patch can be used at ease. Thereīs various models on the market for stereo or multichannel, hereīs an example of a device I did use a lot in the past for the same purpose as the OP:
http://www.canford.co.uk/SONIFEX-RED...TERFACES-Input
Itīs also worth noting that the use of a TRS patchbay for mic signals is not advisable as each time you insert the jack you momentarily short circuit the sleeve and cold. Preamps donīt like that, in particular when phantom power is on.
Regarding the use of the-10 dbv inputs on the HD I/O, yes, you need at least 6 db of gain to compensate. I used this inputs several times for connecting semi pro gear and used a plugin like EQ1(with no eq applied) that has gain adjustment, on the channels fed by those inputs. It can be any plugin that has gain, but the idea is to spare the cpu load, so I opted for this.
One of the disavantages of using the -10dbv inputs on the HD I/O at the same time of the normal +4dbu inputs is that you need to make sure the correct channels are selected on the I/O hardware menu for each of the 8 channels available as either +4dbu or -10dbv. In a fixed instalation is OK, other than that you need to keep changing it.