Focusrite 8i6 line inputs

FYI for others encountering this issue.

Picked up a Behringer 1002 @ $70, figuring it can be a backup mixer for my usual PA system, if my old Mackie loses the left channel output too (already) lost the right side!)

So, plugged the keyboard into the line inputs on the Behr. Nope. Channel volume up all the way, main slider up past unity, volume is still low unless I crank the keyboard volume way up (in which case its too loud out of the speakers, have to mute those with a plug in the headphone jack. So have plugged into the two 'line' inputs on channels 1 and 2 on the mixer, which really don't bypass the mic preamps as far as I can see. With the gain and volume controls on those channels at about 2 o'clock, there is now enough volume with the mixer's main slider at unity.
 
Right, keyboards aren't typically line level, they're instrument level, and the mic/line input has more gain. A TS-XLR cable into the mic inputs might be even better. That should bypass the 20? dB pad. Perhaps @ecc83 could chime in on that. I would probably try a pair of those cheap barrel type impedance matching transformers (of which I have half a dozen floating around), but an affordable stereo passive might be a more elegant solution.
 
bouldersoundguy said:
Right, keyboards aren't typically line level, they're instrument level, and the mic/line input has more gain. A TS-XLR cable into the mic inputs might be even better. That should bypass the 20? dB pad. Perhaps @ecc83 could chime in on that. I would probably try a pair of those cheap barrel type impedance matching transformers (of which I have half a dozen floating around), but an affordable stereo passive might be a more elegant solution.
Click to expand...
+1, I was surprised at how feeble keyboard signals are but then I suppose they are intended to be used with 'guitar' type amplifiers? Synths only need a 5 V supply to run the logic and so the available output is bound to be low (but a proper balanced output could still give you -10dBV levels with 20dB of headroom IF the kbd makers could be arsed!)

The "20dB pad" issue is red fish IMHO. The pad itself can do not harm. Just resistors. The idea that you need to bypass some g'dawful mic stage is really from the land of the beady hi-fi tweaks! Even the meanest budget AI or mixer will have mic pres these days that add almost undetectable distortion, especially at the low levels under discussion. AND! You are amplifying a SYNTH signal FCS! Not the pristine tones of a Strad from a $3000 ribbon!

That -10dBV to +4dBu box is one to be wary of IMHO. The 'gain' from a transformer is wholly dependent on the source and load impedances. If it is to present the minimum load we generally want for a line input of 10k then the secondary load must be no less than 160k! Not going to happen. Yes, the box will give SOME gain but I doubt 12dB (x4) and the load it will present will cause rather a lot of response wobbles and possibly some LF distortion. Give me a couple of op amps any day!

As it happens! I have just finished building a balanced drive device to take the signals from my home TV/VID/radio setup through a Mackie BK passive to my Tannoy 5As. As well as delivering a balanced signal at a very low source impedance I also get a near 6dB signal boost. Handy!

The device is built around two 'SparkFun THAT 1646 modules (little bigger than a TRS jack) They need a symmetrical power supply and so I have used a 1W DC-DC converter that is powered from a gash 12V wall rat I had in the junk box. I have also bought two more DC-DC converters that produce the 15-0-15V from a 5V supply and so I am going to knock that supply up next. That should work from any USB source.

I am in the process of writing up the build for the DIY section with piccies!

Dave.
 
As a point of reference. I never had to worry about it going into my old Tascam interface's line inputs. Always plenty of volume.
 
Just FYI. I fired up the Tannoys this morning and noticed a slight mains hum. Can't be 'avin that fekker! Turned that the unbalanced feeds from the gear were laying amonst the mains cable rat's nest left over from the construction work. Moved them a foot away and hum almost gone. BUT! I shall now need to build a low Z drive box and sit it close to the source so that the input lines pickup less noise. I shall go for a fully balanced setup after the holiday. So, next step. Get that 5 to 2x 15 volts supply built!

Dave.
 
I really want the days of Zoom open mics and streaming to end so I can take my Mackie Big Knob out of the chain and get back to balanced cables and more volume (or at least not having my Scarlett's volume control at 4 o'clock on the dial!)
 
bouldersoundguy said:
They might have been -10 dBV sensitivity rather than +4 dBu sensitivity.
Click to expand...
The specc for the fixed gain inputs on the 8i6 have always confused me a bit? They quote "maximum input +18dBu" one assumes for 0dBFS? If so then for the average input of -18dBFS the voltage is 0dBu/0.775V rms not +4 dBu BUT alongside that spec is "at minimum gain" But they are FIXED gain inputs! Is there something in ControlMix that can adjust the gian?

Gain speccs and output levels for interfaces are total mess and minefield to the tyro. About time reviewers took them to task over it.
No technical reason why every AI could not have the same input voltage for -18dBFS and same for output voltage. The "professional" world is pretty well setup for the 'operating level' no reason $150 interfaces can't be the same.

Dave.
 
ecc83 said:
Is there something in ControlMix that can adjust the gain?
Click to expand...
Unfortunately, no. Seems like an oversight, but I think its true for most commercial gear theses days: no gain control on line inputs (like this new Behr 1002 I just got).
 
mjbphotos said:
Unfortunately, no. Seems like an oversight, but I think its true for most commercial gear theses days: no gain control on line inputs (like this new Behr 1002 I just got).
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You say Mike?
10 XENYX 1202/1002/802/502 User Manual
4. Specifications
Mono Inputs
Microphone Inputs (XENYX Mic preamp)
Type XLR connector, electronically balanced,
discrete input circuit
Mic E.I.N.1 (20 Hz - 20 kHz)
@ 0 Ω source resistance -134 dB / 135.7 dB A-weighted
@ 50 Ω source resistance -131 dB / 133.3 dB A-weighted
@ 150 Ω source resistance -129 dB / 130.5 dB A-weighted
Frequency Response
<10 Hz - 150 kHz -1 dB
<10 Hz - 200 kHz -3 dB
Gain range +10 dB to +60 dB
Max. input level +12 dBu @ +10 dB GAIN
Impedance approx. 2.6 kΩ balanced
Signal-to-noise ratio 110 dB / 112 dB A-weighted
(0 dBu In @ +22 dB GAIN)
Distortion (THD+N) 0.005% / 0.004% A-weighted
Line Input
Type ¼" TRS jack, electronically balanced
Impedance approx. 20 kΩ balanced,
approx. 10 kΩ unbalanced
Gain range -10 dB to +40 dB
Max. input level +22 dBu @

Gain range -10dB to +40dB.
I also have a brand new Xenyx 1202 and the line inputs have a range of inf' attenuation to +15dB. That mixer has been re packed after testing and will probably get shipped to son in France but I could hoik it out and run a sensitivity check on it if you wanted?

Line inputs on mixers often have a less than 0dB capability because they sometimes need to handle pretty hot signals. Those two Behringers have a maximum output of +22dBu (abt 10 volts rms) and so are intended to 'fit in' with professional operating levels.

Dave.
 
ecc83 said:
You say Mike?
10 XENYX 1202/1002/802/502 User Manual
4. Specifications
Mono Inputs
Microphone Inputs (XENYX Mic preamp)
Type XLR connector, electronically balanced,
discrete input circuit
Mic E.I.N.1 (20 Hz - 20 kHz)
@ 0 Ω source resistance -134 dB / 135.7 dB A-weighted
@ 50 Ω source resistance -131 dB / 133.3 dB A-weighted
@ 150 Ω source resistance -129 dB / 130.5 dB A-weighted
Frequency Response
<10 Hz - 150 kHz -1 dB
<10 Hz - 200 kHz -3 dB
Gain range +10 dB to +60 dB
Max. input level +12 dBu @ +10 dB GAIN
Impedance approx. 2.6 kΩ balanced
Signal-to-noise ratio 110 dB / 112 dB A-weighted
(0 dBu In @ +22 dB GAIN)
Distortion (THD+N) 0.005% / 0.004% A-weighted
Line Input
Type ¼" TRS jack, electronically balanced
Impedance approx. 20 kΩ balanced,
approx. 10 kΩ unbalanced
Gain range -10 dB to +40 dB
Max. input level +22 dBu @

Gain range -10dB to +40dB.
I also have a brand new Xenyx 1202 and the line inputs have a range of inf' attenuation to +15dB. That mixer has been re packed after testing and will probably get shipped to son in France but I could hoik it out and run a sensitivity check on it if you wanted?

Line inputs on mixers often have a less than 0dB capability because they sometimes need to handle pretty hot signals. Those two Behringers have a maximum output of +22dBu (abt 10 volts rms) and so are intended to 'fit in' with professional operating levels.

Dave.
Click to expand...
They have gain, but no 'gain control' on the line inputs, only 'level' knobs.

New problem has now cropped up on my 8i6 - one of the headphone outputs is dead. Not scratchy/bad connection - it was live one day, then dead a few days later, headphones were plugged in the entire time. There is no separate control in the software for headphones vs monitor outputs, so its not that.
 
"They have gain, but no 'gain control' on the line inputs, only 'level' knobs." Sorry Mike I am not looking to start a cow here but can you explain that a bit further please?

Bummer about the 8i6. I have one I rarely use but you are a bit of a schlep away!

Dave.
 
ecc83 said:
"They have gain, but no 'gain control' on the line inputs, only 'level' knobs." Sorry Mike I am not looking to start a cow here but can you explain that a bit further please?

Bummer about the 8i6. I have one I rarely use but you are a bit of a schlep away!

Dave.
Click to expand...
Dave - the first 2 channels have 'gain knobs' to adjust the level of the preamps for those inputs. The line-ins do not have preamps, no gain control.
 

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mjbphotos said:
Dave - the first 2 channels have 'gain knobs' to adjust the level of the preamps for those inputs. The line-ins do not have preamps, no gain control.
Click to expand...
O....Kay? I would say therefore that those line inputs have an amplifier with 15dB of gain as marked probably preceded by a pot that can insert 'infinite' attenuation. Not likely to be a 15dB amp followed by a pot as that would severely limit headroom.

So, you need MORE than 15dB of gain?

Dave.
 
Found a schematic! Behringer have used a rather complex circuit (or more likely just lifted it from someone else 15 or so years ago!) The balanced input amplifier has a gain much less than one and that is followed by another stage with a gain of about 19dB. The arrangement gives good headroom but probably not optimum noise performance? There is a simpler and far more elegant solution by Duggy Self.
 

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All I know is that if I plug my keyboard outputs into the line inputs of the Behr, and then the main outs from that to my 8i6, there is virtually no volume increase unless I crank the channel levels and main volume sliders all the way up (and yes, they get noisy). If I plug the keyboard into the 1/4" jacks on channels 1 and 2, and put the gain at around 1 o'clock and the channel levels at noon, main volume slider at unity, I've got plenty of usable volume.

Oh, on a good note, I got the 2nd headphone output working on the 8i6! Kept futzing with the Focusrite software until I noticed that the 2nd headphone is ganged up with line outputs 3 &4 and it had got switched over to different line outs from Reaper, I guess so you can do a different headphone mix.
 
It looks therefore that I am on the right track then Rob? The kbd signal is silly feeble and that line input is not a low noise design* The line ins on the mic channels are simple attenuators feeding a very low noise mic amplifier and I have always found Behringer mic pres to BE very low noise.

*To be a bit fair to Behrrys? The line inputs are almost certainly good enough for +4dBu levels and even neg ten. The shame of it is there is a perfectly good way to make a balanced input with a gain range of -10-+40 db and a noise output close to -100dBu.

Dave.
 
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