[sdiy] website update - VC-Delay

[Scott Stites]

Scott Gravenhorst wrote

> If this IC is using the resistor to ground as a "current sink", then
> it seems that an opamp with BE junction of a darlington pair inside
> the feedback loop with collector to the pin instead of the resistor
> might work.  + input to ground.  You have to make sure you have the
> correct transistor type (NPN vs PNP) so that conduction is in the
> correct direction.  Then feeding the summing node with a current will
> cause the collector emitter circuit to have an inverse copy of that
> current.  Essentially, the collector emitter circuit becomes the
> resistor which goes to the opamp's summing node virual ground.  This
> will give nice linear control over the current.  Something to try if
> you have not.

I haven't, but I will now!  Thanks, Scott

Cheers,
Scott


> >
> >
> >-----Original Message-----
> >From: Theo <t.hogers at home.nl>
> >Sent: Jul 15, 2004 3:45 PM
> >To: destrukto at cox.net, synth-diy at dropmix.xs4all.nl
> >Subject: Re: [sdiy] website update - VC-Delay
> >
> >The RAM addressing is probably straight forward.
> >If I had to do it I would first read the delay-ed data and than write the
> >new "sample" to the same address.
> >However the CAS/RAS multiplexing is why lifting address lines don't work,
> >even in the simple scenario above.
> >They may write both CAS and RAS for every access or use burst mode and
only
> >write CAS on a new cycle of the RAS counter.
> >Monitoring the CAS line with a scope would tell you.
> >
> >Anyways, to drop address lines you (probably) need to do so for CAS only.
> >Some gates that block part of the CAS data might work.
> >That would need 2 or 3 standard TTL ICs.
> >
> >Also completely other variation comes to mind.
> >Use two delay ICs, one with a fixed delay the other with VC.
> >That would result in a direct signal with a delayed chorus, could be a
nice
> >effect in it self.
> >Using some smart audio routing the same unit also may do more complicated
> >delay work.
> >
> >When doing the above, the shortest delay of the chorus would be around
33ms.
> >Don't know if 33ms or so "latency" of the chorus would be a problem.
> >Walking on thin ice here, but cause the "latency" is under the 50ms,
> >chorus and direct signal may be perceived as one.
> >
> >Just me 2 cnt.
> >
> >Theo
> >
> >
> >
> >
> >----- Original Message -----
> >From: Ryan Williams <destrukto at cox.net>
> >To: <synth-diy at dropmix.xs4all.nl>
> >Sent: Thursday, July 15, 2004 7:00 PM
> >Subject: Re: [sdiy] website update - VC-Delay
> >
> >
> >>
> >>
> >> I originally planned on doing another chorus type circuit using a few
of
> >> these but couldn't figure out how to shorten the RAM size. It was
> >> suggested that it could be done by simply disconnecting address lines.
I
> >> tried that and couldn't get it to work and left it at that because I
> >> wanted to finish my module and move on to something different. If
anyone
> >> figures that out, I would like to hear about it.
> >>
> >> but, I had another idea that might work out. that is to put a similar
> >> circuit in a FGPA. it's more expensive and alot more work but I plan on
> >> trying this after I finish my digital IC design course and also finish
> >> some other projects and save enough money for a development board (that
> >> might be a while). I suppose it would be easier to find out what the
RAM
> >> access pattern of that PT2395 is.
> >>
> >> -ryan
> >>
> >> Nils Pipenbrinck wrote:
> >>
> >> > Ryan's circuit made me think.... I doubt that the delay chip does any
> >> > complicated acesses to the ram: Most probably it just alternates
between
> >> > write a byte and read a byte.. maybe even with a fixed address offset
or
> >> > no offset at all.
> >> >
> >> > If we would ignore the internal address-logic of the chip and roll
our
> >> > own we could make the delay time as small as we would like to, right?
> >> > Can't be that complicated. I doubt we'll need much more than some
> >> > counters and a binary adder.
> >> >
> >> > So, does anyone knows the ram access pattern of the PT2395?
> >> >  Nils
> >>
> >>
> >>
> >
> >
> >
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