[sdiy] AC coupling on inputs/outputs.

[Dave Kendall]

Thanks Tom.

A nice concise answer. There are single turn DC offset trimmers 
available on the VCA circuits, but I might go with a switched input 
jack solution. The input paths on the VCA5B and VCA6B are quite 
comprehensive, allowing DC in, AC in and inverted versions of both. An 
ON-ON-ON DP toggle wired as a 3-way selector would allow perhaps DC, 
inverted DC and AC as possibly the most useful range of inputs for a 
single input socket.

cheers,
Dave



On Aug 27, 2010, at 15:11, Tom Wiltshire wrote:

> This topic came up recently with Dave Dixon's filter. The problem with 
> DC inputs on filters and VCAs is offsets. If there is one, the output 
> will thump with a fast envelope, even if no signal is applied. AC 
> coupling should eliminate the DC offset and minimise the thump. If 
> you've carefully trimmed all the DC offsets out of your circuits, then 
> I suppose you can go ahead and use DC inputs on everything.
>
> T.
>
>
> On 27 Aug 2010, at 14:32, Dave Kendall wrote:
>
>> Hi all.
>>
>> I think I understand why this is often done, but wonder how useful it 
>> really is in a modular. I have some EFM VCA PC boards that offer 
>> independent DC and an AC signal paths on inputs and outputs. Is there 
>> any particular reason why a VCA might benefit from AC coupling, 
>> rather than simple DC-capable Inputs/outputs?
>>
>> I'm re-panelling several modules, and wonder whether the extra 
>> sockets/switches are worth including....
>>
>> cheers,
>> Dave
>>
>>
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