INA217 preamp buliding question.

[nguitar12]

Hello everyone I am building a INA217 preamp based on the above schematic.
However the power pin of opa137 is not indicated.
According to the data sheet pin7 is V+ while pin4 is V-

Is it pin7 should be connected to +15V while pin4 is connected to the GND (or -15V)?

Thanks in advanced

[bool]

-15V

[therecordingart]

I'm in the process of finishing up a layout for the INA217. It's double sided so not really home-etch friendly, but I can provide you the gerber files if you want to have them fabbed. Group buys aren't allowed otherwise I'd just order a batch of boards and sell them here.

[nguitar12]

I'm in the process of finishing up a layout for the INA217. It's double sided so not really home-etch friendly, but I can provide you the gerber files if you want to have them fabbed. Group buys aren't allowed otherwise I'd just order a batch of boards and sell them here.

Hi therecordingart yes I am total interested in that. I just finished breadboarding the circuit yesterday. However the circuit will distorted easily not sure it is normal or not but half of the pot is totally useless. I am testing with a dynamic microphone and using a 1K pot for the gain control. When I shouted to the microphone  (semi hard) it will have a weird distortion. What was the problem??

[therecordingart]

I'm in the process of finishing up a layout for the INA217. It's double sided so not really home-etch friendly, but I can provide you the gerber files if you want to have them fabbed. Group buys aren't allowed otherwise I'd just order a batch of boards and sell them here.

Hi therecordingart yes I am total interested in that. I just finished breadboarding the circuit yesterday. However the circuit will distorted easily not sure it is normal or not but half of the pot is totally useless. I am testing with a dynamic microphone and using a 1K pot for the gain control. When I shouted to the microphone  (semi hard) it will have a weird distortion. What was the problem??

Were you using a bipolar supply?

[nguitar12]

I'm in the process of finishing up a layout for the INA217. It's double sided so not really home-etch friendly, but I can provide you the gerber files if you want to have them fabbed. Group buys aren't allowed otherwise I'd just order a batch of boards and sell them here.

Hi therecordingart yes I am total interested in that. I just finished breadboarding the circuit yesterday. However the circuit will distorted easily not sure it is normal or not but half of the pot is totally useless. I am testing with a dynamic microphone and using a 1K pot for the gain control. When I shouted to the microphone  (semi hard) it will have a weird distortion. What was the problem??

Were you using a bipolar supply?

Yes I stepped up 9v from dc supply into 30v with XL6009 module and split it into dual 15v.

[therecordingart]

Are you using the OPA137 on the output? The only thoughts I have are that either the power supply isn't right which means the chip isn't biased right or there is an issue with the OPA137 and you have DC on the output.

[nguitar12]

Are you using the OPA137 on the output? The only thoughts I have are that either the power supply isn't right which means the chip isn't biased right or there is an issue with the OPA137 and you have DC on the output.

No I  just build a simple version like this.



I grounded pin 5 and using 1k pot instead of 4.7 and 100. A 470uf cap instead of 47uf.

[therecordingart]

You're certain that pin 5 is connected to ground and not -15v?

[nguitar12]

You're certain that pin 5 is connected to ground and not -15v?

This is a quite simple circuit and I am sure that pin 5 is connected to the GND ( btw It make no different even i leave it unconnected)
Chip are sample from TI official site. Branded "BB". I order 5 and try 3 different chip with no luck.

[nguitar12]

Are you using the OPA137 on the output? The only thoughts I have are that either the power supply isn't right which means the chip isn't biased right or there is an issue with the OPA137 and you have DC on the output.

I fingered out one reason that may cause the issue. I am testing the preamp using my usb sound card that have mic input only. IIRC a mic preamp signal should be a line level. Will it be the reason why the signal distorted so badly (However I have turned down the gain on my sound card as a compensation )

[tubegeek]

How do you have the 1K pot set? If the Rg is too small, you would have quite a lot of gain for a dynamic mic and you'd possibly be overloading the input of the soundcard as you suspect. Turning down the soundcard gain may not prevent this, either.

[PRR]

> sound card that have mic input only. .... However I have turned down the gain on my sound card

The card's MIC input is a high-gain amp *followed* by a turn-down control.

So it distorts first. Turning-down doesn't change that.

If all you have is a mike input, why do you need a mike-preamp?

[nguitar12]

I test my circuit with my hand held record via the line input. Seem the situation is much better.
My sound card preamp is crap so I build another one.

At what level should INA217 distort? How can I ensure my build is correct?
I always feel there a little distortion before recorder peak is reached.

[PRR]

> At what level should INA217 distort?

Output clipping level (about 5Vrms or +16dBu) divided-by gain.

Gain "can" be adjusted from over 1,000 to nearly unity.

The plan you post with 1K pot can turn-down to gain of 10. This should be OK with dynamic and reasonably loud studio levels.

However it is super-likely that your handheld recorder can not take 5V inputs cleanly. Maybe 2V, maybe less. Then for gain of 10, a LOUD shout into a SM58 "may" clip the recorder input.

Run your recorder gain-control fairly high, like "7". Use the gain control on the preamp to get into a happy ballpark.

[nguitar12]

> At what level should INA217 distort?

Output clipping level (about 5Vrms or +16dBu) divided-by gain.

Gain "can" be adjusted from over 1,000 to nearly unity.

The plan you post with 1K pot can turn-down to gain of 10. This should be OK with dynamic and reasonably loud studio levels.

However it is super-likely that your handheld recorder can not take 5V inputs cleanly. Maybe 2V, maybe less. Then for gain of 10, a LOUD shout into a SM58 "may" clip the recorder input.

Run your recorder gain-control fairly high, like "7". Use the gain control on the preamp to get into a happy ballpark.

Here is the rating of my TASCAM DR-40

Nominal input level    -19dBV(MIC) / +4dBu (LINE)
Maximum input level    -3dBV (MIC) / +20dBu (LINE)

I don't really clear about the rating unit of dBu/Vrms. But I have a recorded file that clip a -2dB while the peak indicator on recorder never light up. And I am using the line input. Why is that?