Tape noise reduction

[StephenGiles]

I still say that you could do a lot worse than building a Drawmer DF320. Actually, Craig Anderton designed a very cheap to build noise reduction system published possibly in Guitar Player back in the 1980s, which I might have somewhere at home.

 

[lucidtone]

All circuits welcome! 

 

[StephenGiles]

All circuits welcome!   

Can't locate it yet, it's one I never scanned so it could be in any number of piles of papers!

 

[JohnRoberts]

All circuits welcome!   

Well if you're even interested in Craig Anderton's NE570 based NR here's my last kit NR effort. I did a NE570 based kit in 1977 but IMO that is not worth pursuing for open reel tape.

As I mentioned earlier, this is based around NE572 which is not as good of a gain element as THAT VCAs. Also this circuit will not translate directly to VCA's log domain control voltages, but the concept of using multiple time constants for quick and slow response is the same.

Too much going on for me to write a quick synopsis, but I'll be glad to answer specific questions about what does some specific part do? There is really quite a lot going on, so don't assume any parts in there are not doing something useful.

JR

PS: Sorry about the size

 

[StephenGiles]

Many thanks, that looks very interesting. Craig's NR was fairly simple built around a hi freq boost pre tape and a hi freq cut post tape and was reasonably effective.

 

[JohnRoberts]

Yup, 12dB of pre/de-emphasis in primary audio path, and side chains.

One major improvement over old NE570 is the use of better external opamp.. the 570 was lucky to do .5V/uSec with a tail wind.

JR

 

[lucidtone]

Sadly I got sidetracked by some synth DIY, didn't build any NR stuff this weekend, but it's on the cards for next.

OnSemi still makes this chip, but the specs are better these days:
http://www.onsemi.com/PowerSolutions/product.do?id=SA572

Thanks for digging up that circuit JR!