I am thinking of building up an Opus based DAC, and am planning on using the IVY III in order to avoid coupling caps and achieve very low output impedance. I have a couple of questions though:

1. It looks like the filter circuit in the IVY III consists of 15 nF and 195R(?), giving a corner of 54 kHz-do I understand the schematic correctly, and does the Opus really need this filtering?

2. What about avoiding the second stage including the filter circuit, and just using the first opamp's output, jumping it over to the output point of the second opamp (which would be powered down), would this approach achieve the DC nulling and low output impedance I am looking for (governed essentially by the 21R output resistors) and result in a simpler signal path?

I know, I know-it would be even simpler to take the Opus' output directly, but then I would need caps, and would not have the buffer, which I really want to drive the amplifier's input stage well.

Thanks for any help...

Thanks Russ. It sounds like I am better off using the circuit as designed then as I want to have low Z output.

To be clear, this is my understanding:

1. If I keep the filter stage (390R-15 nF-390R), and skip the second OPA1632, then output Z will be high, so if I want the filter I should use the second OPA1632 to keep the output Z low.

2. Or, I can skip the filter stage altogether, and take the direct output from the first OPA1632, jump it over to the output pads for the second OPA1632, and then the output Z would be governed by the output Rs (21R) but I will have no output filter.

I can experiment and try both and listen, and I even might try driving a 1:1 transformer using approach 2, at least the transfomrer will do a bit of filtering due to limited bandwidth, and driving the transformer from a low Z will keep any added distortion to a minimum.

Russ, if you have a chance, a simple "yes" answer if my understanding as expressed is totally adequate, and thanks again!

Thanks for your help and patience Russ, I will be sure to report on my results for the benefits of other users.

I have two further questions:

1. What values would be required for R1-4 to achieve 2V-2.2V output (with Opus) from the 1st stage of the IVYIII alone, would one still use 2.2K?

2. If I want to add analog filtering, it occurs to me that I could so at the input of the first stage, in conjunction with the 2.2K input resistors by adding 100pF to ground directly after them. Is there any reason this would be bad idea?