Simple monitor knob with INA137 and DRV134..?

[JW]

In another thread, Jeff at CAPI suggested a INA137 as a -6dB receiver, 10K level control to DRV134s. Balanced in, balanced out +28dBu of headroom. I'd like to use this circuit, attached to an ACA mixer output. (API 2503 transformers secondaries). I'd also like to be able to patch a low impedance D to A converter output to it's input if I like to monitor directly off the DA. Is this possible?

Does someone have a schematic for this?

 

[gyraf]

INA137 is discontinued recently IIRC

 

[abbey road d enfer]

It seems that TI's audio IC's are not easily available.
A similar circuit can be built with THAT 1206 and 1646. Level control implies teh addition of a buffer (single opamp per channel).
See attachment using THAT1243 and 1606. You need to provide + and - rails

 

[Khron]

... Or a pair of OPA1632’s for the in/outs?

 

[dmp]

Why not INA134PA? In stock
Difference is 0dB vs -6dB, shouldn't be a problem.

 

[dmp]

INA137 is discontinued recently IIRC

TI page says it is an active product. Lot's of items are out of stock everywhere currently but not discontinued.
If it is going to be discontinued I'd be curious to see the source.

https://www.ti.com/product/INA137

 

[dmp]

Level control implies teh addition of a buffer (single opamp per channel).

I'm curious why a INA134 -> 10k pot -> DRV134 wouldn't be sufficient?
The C2 could be eliminated since the INA134 has low offset voltage. (If needed could be trimmed as in figure 2 in the datasheet.)
The input impedance of the DRV134 is 10k. Is a buffer needed?
I am also curious about this as I'm working on a monitor controller design at the moment.

 

[ccaudle]

It seems that TI's audio IC's are not easily available.
A similar circuit can be built with THAT 1206 and 1646. Level control implies teh addition of a buffer (single opamp per channel).
See attachment using THAT1243 and 1606. You need to provide + and - rails
View attachment 103465

Wouldn't the gain of the buffer in the middle depend on the position of the pot? Any particular reason to use an inverting configuration and not just a non-inverting unity buffer?

 

[ccaudle]

I'm curious why a INA134 -> 10k pot -> DRV134 wouldn't be sufficient?

Look at the block diagram for the DRV134, the output buffers have one input driven by the input buffer, and one input driven directly from the input pin. That means the source impedance directly affects the balance of the output, and the source impedance is changing over a pretty wide range when connected to a pot.

The very first note under Section 11.1, "Layout Guidelines" is:
"The DRV134 input should be driven by a low impedance source such as an op amp or buffer."

 

[abbey road d enfer]

I'm curious why a INA134 -> 10k pot -> DRV134 wouldn't be sufficient?
The C2 could be eliminated since the INA134 has low offset voltage. (If needed could be trimmed as in figure 2 in the datasheet.)
The input impedance of the DRV134 is 10k. Is a buffer needed?

Proper operation of cross-coupled balanced drivers relies on being driven by a very low impedance. If not, CMRR can be degraded.

 

[abbey road d enfer]

Wouldn't the gain of the buffer in the middle depend on the position of the pot?

Of course it would. benign in the context of a level control.

Any particular reason to use an inverting configuration and not just a non-inverting unity buffer?

Yes. The only reason was that I started with an existing schemo that I modified with Paint. Of course the buffer stage could be inverting or not.
And actually I should have reversed polarity somewhere.

 

[abbey road d enfer]

... Or a pair of OPA1632’s for the in/outs?

Once you dialled in the cost of 0.01% resistors, the monolithic solutions are about the same price and less hassle.

 

[Khron]

Once you dialled in the cost of 0.01% resistors, the monolithic solutions are about the same price and less hassle.

... Or 100pcs of cheap bog-standard 1% and 5-10mins to match a few pairs...

 

[abbey road d enfer]

... Or 100pcs of cheap bog-standard 1% and 5-10mins to match a few pairs...

Getting 3 sets of 4 resistors (one set for the diff input, another for the input resistors of the EBOS and yet another for the FB resistors in the EBOS) matched within 0.01% takes more than that.
And it doesn't even start to address the tempco subject.
I understand that it's a proposition that's acceptable for a DIYer that has plenty of time and not a lot of money, though.
I know that many commercial products have relied upon unselected 1% resistors, often associated with inadequate trimmers. That's because the actual requirements in terms of CMRR were not terribly high, because the level of interference that the systems were facing was not as high as today in most practical cases. A practical CMRR of about 40dB was usually adequate. But today, the level of interference has considerably increased, particularly with WiFi, GSM and VFD motors, so better implementations are required.
I switched to monolithics about 20 years ago, and never looked back.

 

[gyraf]

TI page says it is an active product. Lot's of items are out of stock everywhere currently but not discontinued.
If it is going to be discontinued I'd be curious to see the source.

https://www.ti.com/product/INA137

Recently got a "Lifecycle Change Notification" from Mouser:

https://www.mouser.dk/ProductDetail/595-INA137PA
Lifecycle: Obsolete

(and it's compatible cousin, the SSM2143, is gone as well)

/Jakob E.

 

[abbey road d enfer]

Now is it a sign that they're gonna replace it with a new model, or they are losing interest in the ex-SSM products?

 

[dmp]

Yes, I see now the INA137 in DIP is obsolete (but only the DIP). I doubt it will be replaced since the SOIC is not discontinued. Maybe not a big seller?
The INA134 is available in DIP though. In this application a 0dB version would be fine

 

[JW]

So, on the THAT1606, we could invert it too. So, flipping pins 4 and 3, and then 8 and 1? Thanks for that schemo Abbey.

 

[abbey road d enfer]

So, on the THAT1606, we could invert it too. So, flipping pins 4 and 3, and then 8 and 1? Thanks for that schemo Abbey.

Yes, or change the opamp arrangement from inverting to non-inverting.