Cool audio's V3207 App circuit, no echo

[acidblue]

Only getting clean single from my V3207/V3102.


I'm using the application circuit from the datasheet to test some 3207's I got from AliExpress, but first I bread boarded the App circuit with Cool Audio's V3207 and V3102 I got from Cabin Tech to make sure I got the circuit right.
The only changes I made were 47pf instead of the 68pf and I tried 120K and 200k for the 180k across pins 7 and 6 of the 3102, made no difference.
Granted the App circuit is just to get you started ,but I should be hearing some echo, shouldn't I?
Any help would be appreciated.

[Mark Hammer]

I would suggest looking at the datasheet and appnote for other BBDs.  In principle, that Coolaudio circuit ought not to work.  Normally, the audio/AC input to pin 3 needs to ride in on a DC bias voltage.  I have never seen that DC bias be anywhere near Vref, like the diagram you present shows.  Conceivably Coolaudio was presuming a great deal more background knowledge of the end-user.  Try looking at some of the more familiar chorus or flanger pedal circuits.  For instance, while the MN3102 subcircuit is necessarily more complex, you can see the bias trimmer tied to the MN3207 input in the Boss BF-2 here.
Try tacking that bias circuit on to the V3207 input, and offsetting the Vref that the audio input is feeding pin 3.

[anotherjim]

+1 what Mark said.
Also, are you certain the clock is clocking? If you can't scope it, the clock pins 2 or 6 ought to read 1/2 supply volts DC on a DMM since they are 50% duty square waves. If you have 0v or Vcc, it probably isn't clocking.

[Slowpoke101]

You're getting clean audio out of it. OK
Usually when the delay chip doesn't have any clocking pulses going into it you get nothing out of it. You are getting an audio signal out of it so the clock is OK and the delay is OK. But clock is running very fast so any delay effect would be less than 6mS - which is very difficult to hear.
So the circuit is working - very surprising that it does so without "correct" biasing but there you go.
If you could mix the incoming clean signal with the output of the delay (blend) you may hear a slight chorus effect.

[acidblue]

Voltage @ Pins 2 & 6 are 4.35V, my bench PS is set @ 8.5V.
Frequencies are 42.6khz for pin 2 and 85.7khz for pin 6.

I tried the bias circuit on pin 3 and the volume/gain? goes up and down.
Between 2.95V and about 2.4V sounds best, but still no echo.

[anotherjim]

Hmm, well, clean signal it ideally would be albeit delayed. There is no wet/dry mix in the app circuit so no other effect but delay. For obvious delay try a bigger cap on the clock chip. I'd want to hear delay and some clock breakthrough (need lower clock frequency to hear that).
If it's a very clean signal and twiddling the bbd pin3 bias doesn't make signal come and go, I'd start to suspect something and before I blamed the chip, I'd wonder if there isn't something wrong in the breadboard.
Pins 2 and 6 of the bbd should have same frequency only opposite phase?

[acidblue]

After double checking both pin 2 and 6 are 42.67khz.
Do you mean the 68p on pins 5 & 7?

EDIT:
I added a 560p across pins 5 & 7 + the 47P that I originally put for a total of 606pf.
That gives about 3.7khz at pins 2 & 6 of the 3207.
I did add a mix pot for the input and output.
The output does sound different to the input, but I still cant hear an audible echo.

[Mark Hammer]

There are both upper and lower limits to how fast BBDs can be clocked.
Read this.  I'm trying to watch a football game.  https://www.premierguitar.com/articles/25035-behind-the-bucket-brigade

[acidblue]

Now using a 100p and getting 18.7khz at pins 2 and 6.
Still no echo

[Fender3D]

...
I did add a mix pot for the input and output.
The output does sound different to the input, but I still cant hear an audible echo.

I think you don't clearly get what a delay line can do.
Mark explained it well, you can't "hear an audible echo" without a proper mix-and-recover stage:
signal from BBD's output will be significantly dimmed respect dry signal, especially with this diagram, since you can't set a proper bias voltage (this can prevent BBD from functioning) and because that 220nF cap on output.

You can't also hear a clear repeat because of the short delay time involved. Remember the 3207 is mainly used in flangers and chorus effect in which you're supposed not to hear repeat or "echo"...

You might sub the 180K with a 220K pot + 22K resistor in series: moving the pot while playing you should hear some kind of "detuning" which will show your BBD is working.

Definitely, if you see on your o-scope, the waveform applied at input move and streching when you move the above pot, then your BBD is working...

[Mark Hammer]

1024-sage BBDs can yield an audible echo.  In fact, it was what Radio Shack used for their "electronic reverb" units.  BUT...you have to have very modest expectations for what sort of delay can be achieved (100msec is really pushing it), and you have to use a lot of lowpass filtering to keep the aliasing and clock-noise to a minimum.

[Fender3D]

1024-sage BBDs can yield an audible echo....

Yes, but you'll hear it only if you mix it with dry signal, then you hear 2 signals: dry and, suddenly after, wet.
If you don't mix the 2 sounds you won't hear an echo, 'cause you won't distinct dry from wet hearing wet only...

... and if you wanna hear it, wet signal should have an audible level (then bias properly adjusted and a small boost, at least)

1... and you have to use a lot of lowpass filtering to keep the aliasing and clock-noise to a minimum.

of course.. but 220nF is quite a high value....

BTW 3207 with ~ 20KHz clock yields ~25ms not quite "an audible echo"

[acidblue]

...
I did add a mix pot for the input and output.
The output does sound different to the input, but I still cant hear an audible echo.

I think you don't clearly get what a delay line can do.
Mark explained it well, you can't "hear an audible echo" without a proper mix-and-recover stage:
signal from BBD's output will be significantly dimmed respect dry signal, especially with this diagram, since you can't set a proper bias voltage (this can prevent BBD from functioning) and because that 220nF cap on output.

You can't also hear a clear repeat because of the short delay time involved. Remember the 3207 is mainly used in flangers and chorus effect in which you're supposed not to hear repeat or "echo"...

You might sub the 180K with a 220K pot + 22K resistor in series: moving the pot while playing you should hear some kind of "detuning" which will show your BBD is working.

Definitely, if you see on your o-scope, the waveform applied at input move and streching when you move the above pot, then your BBD is working...

Dont have a 220k pot so I used a 500k with 22k in series.
Do hear a slight de-tune, kinda fades in and out, on the scope the wave form wobbles a bit when i adjust the pot.
BTW I'm inputting a square wave from a 40106 schmitt trigger.
Think Im gonna try a different circuit, this one just isn't worth it IMO.