THAT1510 Based Preamp for Mic with Unbalanced Output

[Matt Syson]

Hi
If you are wanting it unbalanced input and single supply rail I would suggest an 'ordinary' op amp rather than the THAT part. A NE5534A is good enough for many of the oldish Neve designs and there are stacks of other types you could fit and most would be a lot cheaper. Since it is battery powered look for low current consumption as well as low noise.
Matt S

[Pramod Kumar]

Originally Posted by Matt Syson

Hi
If you are wanting it unbalanced input and single supply rail I would suggest an 'ordinary' op amp rather than the THAT part. A NE5534A is good enough ..........

Hi Matt,

Thanks for your response. I have made a couple of mic preamps using NE5532 and a slightly modified version of the circuit at Simple Stereo Electret Mic Preamp. Later, I replaced the NE5532 with LM4562 and this resulted in a much improved performance. I was hoping that THAT1510 would give a still better performance.

[Matt Syson]

Hi
The THAT part is optimised for balanced input among other things so by the time you have added all the extra bits to render it unbalanced I doubt it would be any better than some of the other widely available parts and I suspect worse than many.
If you are driving any significant length of cable you should use a buffer amp to follow the 'gain' stage otherwise the cables will affect the performance. The 'skeleton' circuit shown should have other parts added to reduce possible RF pickup and take it away from a 'suggested starting point' to being a proper design.
Matt S

[JohnRoberts]

The 1510 is designed for <200 ohm floating or balanced sources, the capsule you are interfacing with will likely have a higher source impedance and higher output, besides being single ended.

If you don't have data on the capsule you may want to experiment with different opamp or discrete gain stages (Bipolar vs. FET, etc).

JR

[Minion]

Originally Posted by Pramod Kumar

I would like to make a portable (battery powered) mic preamp based on the IC THAT1510. I am attaching the basic preamp circuit given in the THAT1510 data sheet. This circuit is for a mic with a balanced output. Can someone please suggest what modifications are required in the circuit to make it work with unbalanced output from an electret mic capsule. Also, is it possible to further modify the circuit to make it work on a single 9 volt battery? Thanks in advance.


Pramod Kumar

The That 1510 Has an UN-Ballanced output but a Diferential Ballanced input....The Chip should work fine with a Unballanced mic but I do not think you are going to get very good performance if you try running it off of a single 9v Battery ,I would use at least two 9v Batteries or maybe some sort of DC -Dc Converter to get a +/- supply......

If you want to make a Basic portable Mic preamp then I suggest useing a Low Power Fet input opamp like a TL082 but make sure that the Output is Cap coupled to block the DC Offset.....

Good luck

[TAVD]

New Page 1 has a schematic for +/- 9v from a 9vdc source. I haven't tried it and it might need additional filtering for a mic pre. It's no cheaper than a 2nd 9v battery and probably takes up nearly as much space.

[Tim Farrant]

Originally Posted by Minion

If you want to make a Basic portable Mic preamp then I suggest useing a Low Power Fet input opamp like a TL082 but make sure that the Output is Cap coupled to block the DC Offset.....

TL082 will be too noisy for this job. I would suggest looking at some of the Texas opamps that are designed for single rail operation down to 5V. Most are designed to swing rail to rail for max headroom and there are some low noise types. I have not got enough spare time to dig one out for you.

A typical circuit would be as follows. The divider at the input sets the opamp at mid rail and also powers the electret capsule (assuming it's one with FET buffer inside). Set the AOT cap around the feedback so that it does not oscillate, 22pF might be a good starting value.

Cheers
Tim.

[tINY]

Op amps and "pre-amp on a chip" may be a bit of overkill in this case.

A JFET or a MosFET might be a better approach. If low ouput impedance is needed, a BJT for an output driver might be good (though it will use more power).



-tINY

[Tim Farrant]

If you want gain, a single FET device won't do it. If you just want a buffer between capsule and the outside world, then that's a possibility.

[tINY]

True enough. But a FET and a couple of BJT's could get you where you needed to be.




-tINY

[Pramod Kumar]

Originally Posted by Tim Farrant

TL082 will be too noisy for this job. I would suggest looking at some of the Texas opamps that are designed for single rail operation down to 5V. ....... A typical circuit would be as follows.

Hi Tim,

Thanks for the circuit. As I mentioned earlier, I have already constructed some preamps using the circuit at Simple Stereo Electret Mic Preamp which is very similar to your circuit. I have used National Semiconductor's LM4562 which has very low noise.

BTW, what is an "AOT" capacitor? I have not provided this cap in my preamp without any apparent adverse effect.

Cheers!

[Matt Syson]

Hi
Adjust On Test.
Using a square wave and 'scope' or a signal generator and suitable meter check that the frquency response is 'flat' up to say 20 or 25K then rolls off gently above that without any tendancy to 'ring' when loaded with typical cables and cable lengths.
Also that it cannot be 'provoked or even naturally oscillate at any time.
This is the minimum testing you should be doing.
Matt S

[Tim Farrant]

Originally Posted by Pramod Kumar

Hi Tim,

Thanks for the circuit. As I mentioned earlier, I have already constructed some preamps using the circuit at Simple Stereo Electret Mic Preamp which is very similar to your circuit. I have used National Semiconductor's LM4562 which has very low noise.

BTW, what is an "AOT" capacitor? I have not provided this cap in my preamp without any apparent adverse effect.

Cheers!

The LM4562 is a decent device, but I mentioned the low voltage single rail devices because they are designed for single rail, and also designed to work good at low voltage (), which means maximizing headroom. They should perfrom much better than the THAT chip in this app.

There is an amazing selection at the Texas website, and you can order free samples.