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Gain staging GAP Pre-73 into Babyface / hiss

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Gain staging GAP Pre-73 into Babyface / hiss

Postby Guitarking » Fri May 07, 2021 8:43 pm

Hi everyone,
Trying out my Neumann TLM102 into a GAP Pre73 (neve preamp-style) into my RME Babyface.
I like the sound but there's also hiss apparent (apperent enough that it annoys me, I can here it in the mix).
I'm running the input of the pre73 at the second 'click' and the output full open.
Is this not wise, would thise cause the hiss? I like the second 'click' because it gives subtle coloration.
Thanks!
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Re: Gain staging GAP Pre-73 into Babyface / hiss

Postby Hugh Robjohns » Fri May 07, 2021 9:19 pm

Which input on the babyface are you using, and what input gain?

If you're running 70dB of gain with a TLM102 it's really not surprising you have some coloration... And it's also not surprising you have some hiss either.

In an original 1073, running with that much gain invokes an additional gain stage, but many 73-alikes don't do that and just run the other two stages with extra gain, which does compromise the headroom and noise performance slightly. I can't remember off-hand how the GAP73 is structured, and it might vary with the different marks anyway.
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Re: Gain staging GAP Pre-73 into Babyface / hiss

Postby Guitarking » Sat May 08, 2021 5:53 am

The input gain of my babyface is set to the lowest and I am using analog input 1 but I think analog 2 would sound the same. These are mic inputs (im not using the di function)??? I think theres no line inputs on the babayface, only mic. Is that a problem?
Anyway, thats why I thought I should get all of the gain from the pre73.l and have the babyface work the least.

On the pre73 there's 2 levels of click on the input (by heart: from 0 to -50??) then a click which is silent and then a second level of clicks of even more input gain. I had mine set to the first click, so not much input gain. In order to compensate (and to have more output transformer than input transformer.sound I thought) I turned the output knob of the pre73 fully up.
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Re: Gain staging GAP Pre-73 into Babyface / hiss

Postby Hugh Robjohns » Sat May 08, 2021 11:04 am

Guitarking wrote:The input gain of my babyface is set to the lowest and I am using analog input 1 but I think analog 2 would sound the same. These are mic inputs (im not using the di function)??? I think theres no line inputs on the babayface, only mic. Is that a problem?

It's not an ideal situation. The babyface has mic inputs which can be padded slightly for line inputs when you select the 0dB gain mode. But it is compromised with a very low input impedance and reduced headroom margin, both of which compromise the Gap73's operation too.

On the pre73 there's 2 levels of click on the input (by heart: from 0 to -50??) then a click which is silent and then a second level of clicks of even more input gain. I had mine set to the first click, so not much input gain. In order to compensate (and to have more output transformer than input transformer.sound I thought) I turned the output knob of the pre73 fully up.

Ah. Perhaps we're clicking around the gain knob in different directions!

Given the minute headroom of the babyface when in its 0dB 'line' mode! I would try turning the Gap73's output control down to around the 12 o'clock position, and wind up the gap73's gain a little to compensate. It's worth a try, anyway.
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Re: Gain staging GAP Pre-73 into Babyface / hiss

Postby Guitarking » Sat May 08, 2021 11:24 am

Mmm ah I see. Thank you Hugh!
Is it worth acquiring a (supplemental) interface which has line inputs? And which has the same quality as the Babyface?
Also, is it useful to use my ADA8200 adat interface? Dont know whether that has line inputs (and the quality kight not be up to par with the babyface?)?
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Re: Gain staging GAP Pre-73 into Babyface / hiss

Postby Terrible.dee » Sun May 30, 2021 1:37 pm

If you want to use external pres....yes. You need straight line inputs. Also check I/O impedance on both devices.
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Re: Gain staging GAP Pre-73 into Babyface / hiss

Postby James Perrett » Sun May 30, 2021 1:50 pm

Guitarking wrote:Mmm ah I see. Thank you Hugh!
Is it worth acquiring a (supplemental) interface which has line inputs? And which has the same quality as the Babyface?
Also, is it useful to use my ADA8200 adat interface? Dont know whether that has line inputs (and the quality kight not be up to par with the babyface?)?

It isn't worth acquiring another interface as you'll either need to switch interfaces each time you want to use it (on Windows) or create an aggregate device and then have to worry about synchronising the clocks on both interfaces (Mac). You could certainly use the ADA8200 which has a bit more headroom on its line inputs but there may be a very small loss in quality - although the loss in quality isn't going to be huge and it would be worth trying. Another alternative would be to find a 2 channel line level A/D convertor that you could plug-in to the Babyface instead of the ADA8200.
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