Analog Delay Report

[Christopher_List at Sonymusic.Com]

Howdy DIYers -

This weekend I finished the analog delay based on the MN3005 from the
Electronotes PCC. It worked perfectly on the first try. Considering the
fact that this IC goes for about $35, I was pretty happy about that.

It's really not a very complicated circuit - went together very easily. The
set up is:
Input summer -> 10kHz, 6pole LP filter  (one op-amp) -> MN3005 -> 10kHz,
6pole LP Filter (one op-amp)

The clock section that drives the MN3005 is voltage controlled and is made
from an op-amp, a LM566 vco, a 4013B, a 4049B, and the usual assortment of
transistors, resisitors and caps....

Very modular and easy to test piece by pice. I built the clock section and
the input filter the first night and tested them. Then finished the rest of
the circuit the second night, tested it again w/o the MN3005 in it's
socket, then socketed the chip and tested it again... The schem has a typo,
BTW, pin 7 of the 4013 must be connected to -V.

I'd give it a 3 out of 5 for complexity and a 5 out of 5 for cost.

Review -
Sure enough, it's a delay :). It's probably about the same as what you'd
get from one of those old Ibanez or Roland analog delay stomp boxes. The
nice thing is that it's voltage controlled. Delay time goes from about 20ms
to 204ms. Unfortunately, with long delays, you really hear the clock
feeding through the output filter. My clock goes down to about 5kHz - the
lower limit of the chip is 10kHz so this adds some funk to the sound - and
since the output filter is 10kHz, this clock feedthrough is not a surprise.
Best option is to run it through another lower filter if you're going to go
that low with the clock. Even better would be to build a second delay so
you don't have to go so low :). High feeback on the short delay gives that
nice metallic sound - and you can really overload the feedback. Clipping is
not too harsh - probably due to the output filter...

Anyway, this is a fun project, and I recommend it. Think about where you
would normally NOT put a delay, and you start to get the idea of what you
can do with this to get some new sounds - high feedback short delay between
a VCO and a filter for instance...

The stock circuit would definitely be more fun if beefed up - and I'll be
doing that this week. I'll be using 3/4 of a SSM2024 to give me VC feedback
as well as VC x-fade between the clean and the delayed signal. These could
obviously be made as separate modules (for added flexibility), but It's
nice to have it all in one place. It will also add several more op-amp
stages, but this circuit doesn't seem to introduce a whole lot of noise. I
can already hear that feedback rising and falling with the filter swell  :)

- Happy soldering,
CList