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Class A Preamp into....

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Class A Preamp into....

Postby Steve Watts » Tue Feb 23, 2021 9:50 am

Hi. I have been a professional music producer for years and as such I have been quite happy with the setup up I have - the latest incarnation of which uses the Focusrite Saffire Pro40. As 90% of the stuff I produce has been in-the-box, the Focusrite has performed extremely well for me.
However, I am moving into a new area for me (high quality spoken voice) and looking to buy a dedicated Class-A preamp, but I have a question about it and hoping for some help. To get the output of the Preamp into my DAW I would have to go via a line input of my Focusrite. I'm not too worried noise-wise as the Pro40 is pretty quiet at unity, but surely it's going to introduce THD which is one of the great bonuses of using a Class-A in the first place. So would I be shooting myself in the foot or am I missing something? I realise that THD is a function of level and therefore it's going to be better at line level than at mic level but is it still going to negate the benefit of using the dedicated preamp? Looking forward to your views. Thanks :)
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Re: Class A Preamp into....

Postby Tim Gillett » Tue Feb 23, 2021 10:47 am

Others with more knowledge will follow but I'm not sure where you are coming from. Firstly what is the weakness in the Focusrite pre's that wasnt an issue with music recording but will be with spoken voice?
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Re: Class A Preamp into....

Postby Hugh Robjohns » Tue Feb 23, 2021 11:12 am

Steve, I fear you have been sucked into a world of jargon and hype...

THD -- total harmonic distortion -- is so low in most modern preamps that it's bordering on unmeasurable and it's certainly inaudible.

Class-A defines the way in which the electronics are biased and nothing else. It has a certain marketing cache because it offers much lower distortion (THD) than class-B biasing... However, there is no class-B in decent audio equipment, and actually most gear operates in class-A or something very close to it ... As evidenced by my statement above that THD is incredibly low in all decent gear.

The weird thing is that people who rate 'class-A' as a good thing are usually thinking about vintage designs like the revered Neve 1073, which actually has quite high THD (especially if intentionally 'pushed), partly because of its use of input and output transformers.

You are right in that, in theory, passing a signal through any electronic stage will add some noise and THD... but in practice, the contribution of these things by modern, well-designed electronics, really is negligible. So if you want to buy an external preamp, you need have no quality concerns whatsoever about connecting it via the line inputs of your interface.

But if this idea is still troubling you, the obvious solution is to buy an external preamp with an integral A-D converter, and connect it to the interface via a digital port, thus bypassing the interface's analogue stages completely.

If you want a recommendation for a superb and highly cost-effective external preamp, I'd suggest the Cranborne Audio EC1 or EC2 (depending how many channels you need!) It offers a generous level of ultra-clean gain, but has the ability to add 'classic class-A' colouration too, if you want that! ;-) And you get an excellent headphone amp thrown in too. I am using an EC2 for almost all my studio work now, it's that good!
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Re: Class A Preamp into....

Postby Steve Watts » Tue Feb 23, 2021 12:14 pm

Tim Gillett wrote:Others with more knowledge will follow but I'm not sure where you are coming from. Firstly what is the weakness in the Focusrite pre's that wasnt an issue with music recording but will be with spoken voice?

My concern is that I'm recording much lower level source (ie spoken not sung) and capturing a much wider dynamic range and the result is largely untreated and completely exposed - no mix to hide behind.

I'm not criticising the Focusrite - I've been very happy with it and would buy it again. I'm just very budget conscious and I don't have the wiggle room to experiment with different bits of gear so I was just trying to get to the nub of something I basically understand but have no experience of. I think Hugh has nailed it for me.

Thanks for responding :thumbup:
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Re: Class A Preamp into....

Postby Steve Watts » Tue Feb 23, 2021 12:19 pm

Hugh Robjohns wrote:Steve, I fear you have been sucked into a world of jargon and hype...
Hi Hugh. That's a brilliant reply thank you. I understand how Class A works (having been a bench engineer many moons ago) but I have no experience of the reality in modern gear, and as you say there is much hype and it's difficult to interpret specs as they are presented in so many ways. I will take a look at the Cranbourne as you suggest. May I say how amazing it is to find that 20 years after I opened my first studio with SOS's help (I was a "Sounding Off" contributor in 2000) that 21 years later here you all are still on the case. :thumbup: :clap:
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Re: Class A Preamp into....

Postby Hugh Robjohns » Tue Feb 23, 2021 12:25 pm

Here are the EC2 and EC1 SOS reviews.
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Re: Class A Preamp into....

Postby Tim Gillett » Tue Feb 23, 2021 1:46 pm

Steve Watts wrote:
Tim Gillett wrote:Others with more knowledge will follow but I'm not sure where you are coming from. Firstly what is the weakness in the Focusrite pre's that wasnt an issue with music recording but will be with spoken voice?

My concern is that I'm recording much lower level source (ie spoken not sung) and capturing a much wider dynamic range and the result is largely untreated and completely exposed - no mix to hide behind...

...Thanks for responding :thumbup:

You're welcome. I agree spoken voice can have a large dynamic range but so can the sung voice depending on the genre. OTOH some voices have very modest dynamics.

We live at a great time for recording in general and capturing large dynamics in particular. For many years I worked in audio book recording, much of it recording to analog tape. Some of our narrators came from a theatrical background and man could they do dynamics, especially with dramatic material. I had to work out how to squeeze those dynamics onto the tape without the tape overloading but without it sounding too strange to the listener. These days capturing is a lot easier, almost luxuriously so. As you say with unaccompanied speech, the voice is very exposed, but so are other sounds such as room reverb, extraneous noises including bodily ones, chair squeaks etc. It can take a while to iron out the bumps.

All the best with it.

Tim.
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Re: Class A Preamp into....

Postby ef37a » Tue Feb 23, 2021 4:03 pm

Steve, as Hugh says, you are worrying about something that is so covered in snake oil it is no wonder the buying public slip up.

Your (very excellent I am sure) Pro 40 contains op amps, if there is an op amp with a class A output stage it is unknown to me! "Class A, B or A/B" makes no difference if the design is good enough. Yes, it is I think possible to buy a pre amp made with only discrete 'class A' transistor stages but in fact the THD would likely be higher than one with the same gain but made with those dreadful 'class B' op amps!

In my world of guitar amplifiers the adpuff copywriters even confuse "class A" with "Cathode Bias"! Even fixed biased amps are AB because biased back to pure B (no Iq) would sound 'orrible!

"Dynamic range" what microphone will you be using? If a low output dynamic such as the 7b you would have to "speak" very loudly indeed to overload almost any decent AI front end or pre amp!
I will give you that the Focusrite pre amps might just be borderline for noise or/and gain for such a low sensitivity mic?

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