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Hi there,

Got time to make a few tests with my brand new ISA Two.
I adjusted my Delta 44 à +4db and tried to calibrate the output of the ISA to match the signal input in my computer without any luck. It seems the signal of the ISA is too for +4db to be equal unless I adjust the audio interface further. At +4db, for a signal of -9db on my DAW, the ISA shows -18db or less... (with the led calibration at maximum on the ISA)

Questions :
- if I run a hotter signal through the ISA and lower the converter input will the sound quality change ?
- I know that a tube preamp needs to be driven enough so the tube will make it's magic, is it the same with transformer preamps as the ISA ? or what ever the output level, the sound will be the same. (at the exception of overdriven signal that will distort I guess)
- if I ajust the audio interface input lower, and the ISA output Higher, will I damage the interface or the sound quality ?

Or should I forget about all this and just look the input in my DAW ;)


KurtFoster Wed, 06/05/2013 - 11:53

your post is a bit confusing so i will run through it for you from the top just to be clear.

+4 Vu is a reference level used with professional analog gear. 0VU is equal to +4 [dBm], or 1.228 volts RMS across a 600 ohm load. this is old school telephone company talk.

forget the number. with the Delta 44 set at +4 input level you want to run a test signal up to 0 Vu on the ISA. that signal should reference to somewhere between -22 digital to -16 digital, depending on your interface. different digital interfaces use different reference levels but it usually works out to somewhere between -22 and -16 digital level.

you should be able to push the ISA to 0 or +4 on the meters and still be able to keep peaks well below -10 digital on your DAW with the inputs set to +4.

and while we are at it, the ISA is not a tube pre. it is a solid state with transformers. it's the transformers that you want to saturate to get that "goodness" you are referencing.

btw, ISA, mmmmmm - lucky you!

rock on!

pcrecord Wed, 06/05/2013 - 14:20

Thanks for the reply Kurt. Reading it just made me realise where I was confuse. The ISA TWO has a DBFS led display. I was originally going for the ISA ONE and in the manual they say you can ajust the leds to so the peak of it match the maximum input you want in your DAW (let's say -12db) The ISA TWO DBFS is not ment to be use that way.

The drivers of the Delta cards has a meter that shows the VU value of the input signal. When I match the output of the ISA to 0VU of the delta (ajusted on +4db), my DAW register -11 -12 on the track input meter And Actually it's also -12DBFS on the ISA TWO !!

But If I run the ISA approaching the peak of the onboard led meters, I need to lower my DAW input because it peaks badly and once I lower the input in the delta, the signal sounds distorted...

I figure I just need to ajust the preamp to the level I want in the DAW cause I figured the numbers match..

I'm I lost or what ? ;)

pcrecord Thu, 06/06/2013 - 04:53

That's what you don't get, even if I lower the delta input, the signal is distorted.
First wave you see is (-6dbfs on the ISA +4db/0VU on the delta) .. second is (-6dbfs on the ISA and -10VU on the delta) :
  Both signal are distorted

with any ajustments to the delta, I must lower the output of the ISA to -12DBFS to get a clean signal...
I think it's a physical limit on the delta...

Attached files

Davedog Thu, 06/06/2013 - 10:10

pcrecord, post: 405435 wrote: That's what you don't get, even if I lower the delta input, the signal is distorted.
First wave you see is (-6dbfs on the ISA +4db/0VU on the delta) .. second is (-6dbfs on the ISA and -10VU on the delta) :
  Both signal are distorted

with any ajustments to the delta, I must lower the output of the ISA to -12DBFS to get a clean signal...
I think it's a physical limit on the delta...

You may have hit the nail on the head. Also be sure you don't have the 30-60 db button pushed on your ISA. Thats a ton of gain and usually will only be needed with older ribbon mics and low output sources.

pcrecord Fri, 06/07/2013 - 03:44

It did not work kmetal...

This whole thread is about how better the sound will be if I push the ISA output nearer to it's peak level. But the Delta 44 failed to accept a signal this hot.
So either the delta card can't take this much electricity or the ISA LED metering is faulty.

I just made the test of pluging the ISA to my soundcraft consol and there's no distortion unless the ISA clips...

As I said, it must be a limitation of the delta card. I'll try another I/O soon...

pcrecord Fri, 06/07/2013 - 15:31

Blaumph: Although, better converters is one thing I have on my purchasing list, the ISA was a big step for me (and my budget). I have 4 delta card 2x66 and 2x44, I've been using them for the past 10years and they served me well.. They never distort and the noise floor is not so bad. So I'll wait before I throw them away.
If I don't push the ISA to loud the sound is very clear and warm enough depending on the impedance and mic choice.

The first thing I noticed about the ISA is that I don't need to hard EQ my tracks anymore. While I was sometime doing up to -12db cuts on some tracks, I now hardly need to touch it or go -3db at worst... Good difference!!

All in All I'm pretty happy. I'll let you decide if quality converters or quality preamps comes first ! (y)

kmetal Sun, 06/09/2013 - 22:12

It did not work kmetal...

man that's a bummer. what's up w/ the delta i mean, if a pre-amp overloads it at -10, that's just weird. i mean why haven't they distorted before w/ other pre's like from your soundcraft. the isa can't be that hot. and still the discrepancy between the isa meters and the DAW is concerning. there's gotta be a good reason for this. (brainstorming). ugh. bewildered here, have you tried to use the same amount of gain on the isa, and the soundcraft w/ the same source, to witness the the differences?

this whole thing is one reason why i like to have input and output knobs on pre's. digital is so 'scientific w. the levels. the input knob allows the tone to be controlled, while feeding the machine what it wants.

it's cool that your impedence knob does something audible! same kinda idea of pushing into resistence. still, driving a transformer into saturation is cool. i'm stymied that the delta is restricting this. it makes no sense on a technical level.

i use an m-audio fw 1814 at home, and haven't had any issue w/ the converters overloading prematurely, i would bet there are very similar converters/clocking in the devices we use cuz they're from around the same time of production. they're not the best, but functional.

anyway glad you like you pre, i've been eyeballing the 8ch version since it came out, for a drum strip. still, i'm not letting this issue rest (lol), the delta's should not distort, and since they haven't since the new pre was introduced, that's the red flag. can you borrow a buddies interface and see? maybe there is an issue (defect) w/ your pre.?

pcrecord Wed, 06/12/2013 - 03:14

Just to do a follow up, the focusrite scarlett 8i6 wasn't better than the delta 44 card. I tested it and found out there's no real signal level compensation like the Delta (-10, consumer, +4) You must know that choosing +4 actually lower the input volume in order to match units that has +4 outputs. The scarlett has 2 ajustments line and instruments. So with a signal that is not registering on the ISA TWO leds, it was already peaking in Sonar and in the Mixwizard software.

Conclusion ; I seem to be in good shape for the next customer.. I'll plan and querry for better converters when the budget allows it.

Thanks to all for your answers !