by Scruffie » 06 Aug 2015, 02:12
Minor update!
The 3007 Echoflanger i'm doing with Lectric FX is still in progress, a rather large break was taken after the first go due to both parties having other shit to do.
Anyway, back on it and here's what's what.
The circuit works great but, charge pump on board or not (fixed 18V supply tried stand alone didn't change much) and layout fixes, among other minor issues there was still some heterodyning on board from the dual clock/buffer set up.
While using 2 x 4049 was in current limits of the charge pump (the max clock reading is only about 550kHz) the excess drain made issues worse so a single chip will now be used like the original, experimenting if it should be split between the 2 chips or just buffer the what i'll call 'high chip' is in progress, on the protos. It worked fine with it only buffering (in the popular 1 in to 2 set up) the high clock chip, but to test that adds no ill effects to the second chip we're doing further testing.
We added some extra filtering too, nothing massive, some simple 15kHz-ish filters at the input of each BBD as is fairly standard practice (and the original lacked) which seems to have taken care of most of the issues and cut noise down considerably without affecting tone.
Speaking of noise, to the person who mentioned MN3001s as a suitable substitute to the original SAD's as "they were dual 512 stage chips" on a whim I did try them after some hacking and as I suspected, the added gain needed to recover the massive losses (remembering that SAD's actually add gain) made an already high noise circuit unbearable... there's a fairly good reason they were lost to obscurity (even the MN3004 can be a bit of a noisy chip!).
Some added minor filtering updates other than that, mainly in the LFO/VCO (a bit of filtering in the feedback loop in the gain stage pre/including the VCO considering where you want to say it starts reduced some annoying thump at high depths and on the LFO its self) and it should be a go this year.
- For this message the author Scruffie has received thanks: 2
- Nocentelli (06 Aug 2015, 08:21), theehman (06 Aug 2015, 10:24)