Here is a fully passive device for inserting Harrison filters into balanced lines with complete circuit isolation. It consists of a pair (L and R) filters between two "converter/adaptor gadgets". ART features this gadget (see artproaudio.com), called DTI, as a noise reduction device. It is a balun (for BALanced-UNbalanced) which will convert either way. Input and output impedances are suitable for typical interstage application in either +4 dBu or -10 dBV system level domains. Being a passive unity-gain device, it will not convert between system level domains, and there is some small insertion loss. I expect that it will generally be used to isolate two circuits having independent gain-staging, so that would not be a practical concern. ART does have the CleanBox Pro which is an active balun that will do level conversion with adjustable gain, unnecessary in this application.
The input DTI will accept either TRS plug or XLR-3F and convert to RCA SE. The output DTI will convert RCA SE to balanced line with both TRS jack and XLR-3M available. So with the DTI you get a balanced line wye in the bargain, as the XLRs and TRS jacks are parallel connected. TRS and XLR connections can be used in any combination. Of course, there are two channels. The SE connections pictured are cable adaptor combinations, but RCA cables could be used. The purpose of this particular assembly is to obtain a 70 Hz low-cut with isolation between connected circuits.
The input DTI will accept either TRS plug or XLR-3F and convert to RCA SE. The output DTI will convert RCA SE to balanced line with both TRS jack and XLR-3M available. So with the DTI you get a balanced line wye in the bargain, as the XLRs and TRS jacks are parallel connected. TRS and XLR connections can be used in any combination. Of course, there are two channels. The SE connections pictured are cable adaptor combinations, but RCA cables could be used. The purpose of this particular assembly is to obtain a 70 Hz low-cut with isolation between connected circuits.
