[sdiy] SIP filter modules coming

[Tom Wiltshire]

> On 12 May 2018, at 00:40, KD KD <pic24hj at gmail.com> wrote:
> 
>> Yeah, ok. Maybe “stupid” is a bit strong. But I’d much rather have had an
>> op-amp there instead, even if it was only a 741-type thing. Then you could
>> have done a unity-gain follower for your OTA Cap-to-ground style filters, or
>> an inverting integrator, and you’d also be able to implement a proper I-to-V
>> stage for VCA applications, which gives a much better result than a resistor
>> to ground followed by the buffer.
> 
>> Anyway, I can see why Alfa left them off. Many, or even “most”, designs with
>> the 13600/13700 seem to leave them out. I only really see them used in
>> stompbox circuits where minimal parts seems to be a more important design
>> objective then overall quality.Tom!
> 
> A FET tranny will do wonders, anyhow of-course i concur it would be nice to have
> proper buffer but if you look into the SDIY archive you will find when
> Harry Bizzell
> sorted out the difference between 13600 and 13700 buffers and why.
> 
> What we wanted is the 13600 buffers high beta auto bias but without CV
> shift poping but instead we got low beta 13700 buffers.
> 
> You have to go way back in time to see lots of buffer usages but thats
> with 13600.

Totally agree about the FET buffer. There are several classic Roland filter designs done this way; 13700 Ota with FET buffer. In some ways this combination is what “the Roland sound” means to me.

Tom