Mic preamp with THAT1510

[nonoxxx]

Hello,

I started to make a mic preamp with the that1510 chip and when looking at the documentation of the chipset.

I wander what is the purpose of C4/C5 and R3/R4 onthe figure 5 , I know that the caps are here to block the 48 v phantom power and also blocking the 15V but the resistors aresupposed to make an high pass at 720 (approximatly) wich is pretty high.

http://www.thatcorp.com/datashts/THAT_1510-1512_Datasheet.pdf

Thanks

 

[JonSnell Electronic]

C4/5 block the DC on Phantom power as you correctly surmise.
R3/4 are there to limit any excess current. If there is a fault and an unknown but potentially mains leaked input is applied to the input resistors R3/4, they will be safety components, (rated at 1/10W) so the diodes D1/2/3/4 will block the high voltage and the resistors will limit any damage. It is nothing to do with frequency response as they have little or no effect.

It is not uncommon for microphone leads to be damaged and touching other dangerous cables or faulty gear is being employed as there were no safety checks done before use.

 

[nonoxxx]

thanks,

So if I understand correctly , the resistor need to be 10 ohms or less, and the caps something like 22u/47u.



Thanks a lot

 

[JonSnell Electronic]

10R up to 47oR is fine. Any less resistance and you will need to reduce the wattage to compensate for the safety section. If you don't have a resistor and you know it will never be used in a situation that is not controlled, it should be fine but may introduce HF noise.

 

[PRR]

... what is the purpose of C4/C5 and R3/R4 onthe figure 5 , ...the resistors aresupposed to make an high pass at 720 (approximatly) wich is pretty high. ....

No. The high-pass is C4/C5 against R1/R2, 6Hz.

(Ah. The second paragraph on page 6 is mis-leading, perhaps tangled-up in final editing.)

R3/R4 causes a loss like 1200/1210 or less than 1/10th dB. They also "add hiss" but less than 1/2 dB added to the microphone self-hiss.

R3/R4 allow D1..D4 to protect against over-voltages. If R3/R4 were zero, "infinite" current could flow. This would not happen often, but it would kill the chip, so they want some series resistance.

If R3/R4 were as high as 50 Ohms, the hiss level would be slightly higher. For 99% of recording situations, 47 Ohms would be fine.

 

[nonoxxx]

Thanks a lot for your replies I am actually waiting for the components
But as soon as I receive the chipsets will try .

Another question when I looked at the schematic of the SK1DIA preamp from Five fish they put an output transormer (in option) after the 1646 , I don't understand because for what I know the 1646 is made to work like a transformer , and does this design is good ?

http://www.fivefishstudios.com/pdf/SK1DIAssemblyGuide.pdf