THAT line & mic output stage

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: THAT line & mic output stage

Post by carlmart »

We are awaiting from some minor comments from THAT around the 4315 limiter we will be using, then design the pcb and build the first prototype with the THAT parts.

Of course I'm looking forward to that to make final judgements and eventual changes.
ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: THAT line & mic output stage

Post by ricardo »

carlmart wrote:This is the circuit with mods applied: diodes moved back before the caps and pot taken away.
Output side looks good. You may want to re-instate their Ferrite beads.

You need expert advice from THAT on the input side. Don't think 1606 allows even 47R, let alone 47R + 1n. BOTH inputs need LoZ to GND
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: THAT line & mic output stage

Post by carlmart »

Well, the ferrite beads are there. It's the semi-circles close to pins 2 and 3. :)

That filter was suggested, if I am not wrong on single supply implementation for the 1646, which was in fact using just one input.

Of course I'm asking THAT all these questions and many others I don't even mention here.
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carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: THAT line & mic output stage

Post by carlmart »

OK, this how the output now looks and the way we will use it.

A very nice trick THAT support suggested, and we adapted on our design was to use the resistor divider inside THAT 4315, which we are using on our limiter, and buffer it to feed all Vref on that channel.
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ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: THAT line & mic output stage

Post by ricardo »

What Recorders are your preamps most likely to feed? Brands & Model Numbers?
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: THAT line & mic output stage

Post by carlmart »

Probably any type, but mostly DSLR video cameras.

Why is that?
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: THAT line & mic output stage

Post by carlmart »

Just for a comparison with an existing product, now very popular, the Tascam DR-60D recorder, which also has unbalanced outputs.

Its maximum output line level is 10dBV, which is 3.16v RMS, which this preamp should exceed.

What do you think it might have problems with?
ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: THAT line & mic output stage

Post by ricardo »

carlmart wrote:What do you think it might have problems with?
To check this, we need to know the INPUT spec. for the DSLRs. Got any favourites?

I detail this process in my MicBuilders LNprimer document.

Why do you need a MIC setting for output? Are there DSLRs with XLR (or other 3p balanced) inputs which are ONLY Mic level?
carlmart
Posts: 169
Joined: Mon May 19, 2014 6:11 am

Re: THAT line & mic output stage

Post by carlmart »

This not the first time I build a preamp for video cameras, and I simply followed THAT's guidelines.

I'm not sure if I will not find a camera that will not have mic level output, so I have to be prepared. And I will use the unit for balanced and unbalanced situations.

The output cable will determine that, as there will be a multi-pin interface. The customer will get the cable he needs for his camera.

For instance, on my Blackmagic Pocket I can select which I want, and it's unbalanced. The Blackmagic BMCC has balanced inputs, both mic and line level.

I need this unit to be flexible.
ricardo
Posts: 262
Joined: Sun Apr 10, 2011 7:24 am

Re: THAT line & mic output stage

Post by ricardo »

carlmart wrote:For instance, on my Blackmagic Pocket I can select which I want, and it's unbalanced.
This http://www.blackmagicdesign.com/au/prod ... techspecs/ just says

Analog Audio Input
1 x 3.5mm stereo audio

Got a better spec? eg Input Sens.

Are you supplying the special cable to go from your device to the Blackmagic Pocket? How will it be wired?
The Blackmagic BMCC has balanced inputs, both mic and line level.
What's a BMCC? It's not on that website
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