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<blockquote data-quote="John Roberts" data-source="post: 24099" data-attributes="member: 126">Re: Active vs Passive Direct Boxes&nbsp;I have designed a few different DIs (two active while only one was a serious commercial product), though not lately. I repeat IMO there could be 2 or 3 categories for what we now call DIs, based on their different applications. The traditional design brief and primary rationale for an &quot;active&quot; DI, is high input impedance and low noise to buffer a passive guitar pickup, or passive keyboard pickup (like Rhodes, anybody remember them?). One metric that is valued for such DI applications is high input impedance to not load down the relatively high source impedance pickups (some active DI claim tens of MegOhm). Active DI can draw power from 48V phantom so intelligent use of that available voltage can provide more than enough signal headroom to accommodate passive pickups. FWIW If the passive pad is completely switched out of the input when not used, it is possible for an active DI to deliver adequately high input impedance when desired &quot;and&quot; have an input pad if needed.&nbsp; &nbsp; &nbsp; If the guitar or keyboard has active electronics it will have a relatively low source impedance so can tolerate a low impedance pad, but likewise it can also drive a passive transformer DI directly.&nbsp; Passing signals through an extra active stage, when not needed is generally undesirable.&nbsp; (Note: for recording I lean toward using active instead of transformer stages for slightly better signal integrity. For live use transformers are desirable for ease of managing ground potentials and generally less parts to fail than with active circuitry.)&nbsp;&nbsp; Using DIs to interface with speaker level signals, or hot line level outputs from active electronics is perhaps popular today, but an evolution away from the original intent of DIs. It sure seems to me that any sources that are too hot for a 48V supplied active DI, may not really need a DI.&nbsp; But the customer is always right, and manufacturers will make and sell them pretty much anything they ask for. Modern DIs have evolved into a hybrid cross between preamp, ground isolation, un-bal to balanced, swiss army knife, doing whatever it takes.&nbsp; JR</blockquote>

[QUOTE="John Roberts, post: 24099, member: 126"] Re: Active vs Passive Direct Boxes I have designed a few different DIs (two active while only one was a serious commercial product), though not lately. I repeat IMO there could be 2 or 3 categories for what we now call DIs, based on their different applications. The traditional design brief and primary rationale for an "active" DI, is high input impedance and low noise to buffer a passive guitar pickup, or passive keyboard pickup (like Rhodes, anybody remember them?). One metric that is valued for such DI applications is high input impedance to not load down the relatively high source impedance pickups (some active DI claim tens of MegOhm). Active DI can draw power from 48V phantom so intelligent use of that available voltage can provide more than enough signal headroom to accommodate passive pickups. FWIW If the passive pad is completely switched out of the input when not used, it is possible for an active DI to deliver adequately high input impedance when desired "and" have an input pad if needed. If the guitar or keyboard has active electronics it will have a relatively low source impedance so can tolerate a low impedance pad, but likewise it can also drive a passive transformer DI directly. Passing signals through an extra active stage, when not needed is generally undesirable. (Note: for recording I lean toward using active instead of transformer stages for slightly better signal integrity. For live use transformers are desirable for ease of managing ground potentials and generally less parts to fail than with active circuitry.) Using DIs to interface with speaker level signals, or hot line level outputs from active electronics is perhaps popular today, but an evolution away from the original intent of DIs. It sure seems to me that any sources that are too hot for a 48V supplied active DI, may not really need a DI. But the customer is always right, and manufacturers will make and sell them pretty much anything they ask for. Modern DIs have evolved into a hybrid cross between preamp, ground isolation, un-bal to balanced, swiss army knife, doing whatever it takes. JR [/QUOTE]

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