Re: Tape delay FDBK
« Reply #20 on: May 17, 2019, 10:57:39 AM »
oh, possibly...kind of tough to tell. I'll get the scope out and check. I guess I could use 2 different tones for input and return.

what could be done to prevent this?


Re: Tape delay FDBK
« Reply #21 on: May 17, 2019, 12:11:42 PM »
Post a new schematic. You never posted an updated schem. And check it to make sure it's correct and that you wired things correctly.

Thinking about it more, the dry cannot double back from the virtual earth of the feedback / dry summer. Something else must be wrong. My guess would be that your schem or wiring is actually just wrong. It happens. I don't think I ever created a board that was correct the first time.

Re: Tape delay FDBK
« Reply #22 on: May 17, 2019, 04:25:05 PM »
here's the last one I did. I left all of the 47pf caps on the schematic but did not install them. Also left the caps on the input but did not install them.


Re: Tape delay FDBK
« Reply #23 on: May 17, 2019, 05:45:35 PM »
You don't need to reverse the 1646 output. Only the "From Tape" needs to be reversed to account for it being inverted on the way out to tape.

Otherwise, I don't see where you could get dry / wet signal bleeding in. In the extreme positions, the wiper should completely shunt that signal.

It could be that the pot is crappy and the wiper doesn't really make full contact with the legs. If you measure the resistance with a meter between the wiper and each leg of the pot in the extreme positions, do you get zero (a few tenths of an ohm is not abnormal)?

Or maybe your ground isn't quite right. Did you use a proper bipolar supply or a virtual ground? If you measure the resistance between the wiper of the feedback pot and the ground on the summing op amp (IC1D) do you get zero? If you measure the resistance between the wiper and the ground at the power supply, do you get zero?

Or maybe the dry signal is coming from the tape machine. Meaning it's somehow mixing in some dry. Try listening to the output of the tape machine directly.

As for the "phasy" sound, it could be that the tape is just running too fast. At 15 IPS, it would sound doubled. It needs to be at more like 3.75 IPS to get more of a traditional delay / echo.

Re: Tape delay FDBK
« Reply #24 on: May 17, 2019, 06:43:40 PM »
Cool, thanks for taking a look. I haven't had a chance to look  scope but I'm sure it's something simple.

Re: Tape delay FDBK
« Reply #25 on: May 22, 2019, 01:11:42 PM »
Yea, everything is working fine. Wiper to gnd connection was uhhh...lazy...

Re: Tape delay FDBK
« Reply #26 on: June 06, 2019, 10:02:47 AM »
So after some experimentation, I've seen that I definitely don't need the R12. In fact, I'd like to add gain to return if practical. Would it be as simple as increasing the value of the feedback resistor around IC1C?
 Gain=RF/RIN ?
20/10=2 (3dB)

Missing something here?

Re: Tape delay FDBK
« Reply #27 on: December 30, 2020, 08:49:03 PM »
So I'm doing a new version with bax eq and an instrument input. I posted the 1st draft of the instrument input in another thread. If so inclined, tear it apart ha! I'm debating the That output IC since everything else is TL074 and 5532, But  I know it will work well on the output.

Re: Tape delay FDBK
« Reply #28 on: January 01, 2021, 12:07:20 PM »
How does the tone section look to you? Any obvious errors here. Eq points can be shifted and I plan experiment a little. Plan is to use a 5534 because well, i dunno.. maybe a doa in the future.


Related Topics

  Subject / Started by Replies Last post
3 Replies
Last post July 15, 2004, 10:40:40 AM
by Kid Squid
1 Replies
Last post April 15, 2007, 01:52:47 AM
by adamasd
19 Replies
Last post January 28, 2010, 04:05:47 PM
by gemini86
7 Replies
Last post October 18, 2010, 11:52:29 AM
by Marcocet