Total Recall Delay (EHX DMM)

[Timko]

This one was a real struggle for me.  I started this project in the winter because I've wanted an analog delay in my collection for the longest time.  But after finishing the build, nothing worked right.   The delay sound was incredibly distorted for the longest time.  The voltages were wrong on the Compander.  The oscilloscope wasn't showing useful waveforms.  The biasing directions weren't getting me anywhere.  So I put it in my box of half finished projects with the intention of getting back to it later.  Fast forward a few months.  I had to buy a relatively nice signal generator to aid in fixing a friend's Sunn Beta Lead amp (spoiler alert - those things are LOUD).  Armed with a new tool (toy?), I used it to do a lot of audio probing through the board, thinking some components were at fault.  And it turns out, some of the resistors around the recovery stage after the BBD chips (around Gain2) were either defective or incorrectly connected as I was getting no effect out of that 2nd Gain control.  So that got fixed, and man, does it sound great.  It's brighter than I thought it was going to be.  It also doesn't have the expanse of Feedback options I was expecting.  But I set it for 3-5 delays, set the delay time to what I need (somewhere between 11 and 1), and it's like going to a whole new world.  I played this things for the past few days for hours at a time - it's easy to get lost in it and very easy to be creative.

Artwork is from the Total Recall movie.  Yay finishing project that you have to set down!

[jimilee]

Nice job! That's really a neat delay.


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[blackhatboojum]

Nice!  Excellent work on not giving up and getting it working.  I just recently built one myself and was also pleasantly surprised. 

[Thewintersoldier]

 

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[jimilee]

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[thomasha]

Nicely done! The reversed etch looks good!

[diablochris6]

Good to see you stick with it and figure it out! The sounds coming out of this thing do not disappoint.  What a marvelous etch as well.

[cooder]

Fab job inside out cool graphics and most of all you got it over the line! Sweetness!

[danfrank]

I like Scruffie's gain setting instructions from Lectric FX...
Basically,  inject a 1kHz audio signal into the input of your total recall and measure it's amplitude before clipping (in millivolts). Now measure the amplitude of the signal at pin 7 of the compander and adjust "gain 1" to get it as close to the input amplitude. I was never able to get it equall to input amplitude but I can get it close...
Next, take amplitude measurement of pin 15 of the compander and use "gain 2" to adjust so it's equal to input amplitude. You should be able to get it exact.
Doing this, I find that the feedback control has a lot of useful range.
Hope this helps...

[jimilee]

I like Scruffie's gain setting instructions from Lectric FX...
Basically,  inject a 1kHz audio signal into the input of your total recall and measure it's amplitude before clipping (in millivolts). Now measure the amplitude of the signal at pin 7 of the compander and adjust "gain 1" to get it as close to the input amplitude. I was never able to get it equall to input amplitude but I can get it close...
Next, take amplitude measurement of pin 15 of the compander and use "gain 2" to adjust so it's equal to input amplitude. You should be able to get it exact.
Doing this, I find that the feedback control has a lot of useful range.
Hope this helps...

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[Timko]

I like Scruffie's gain setting instructions from Lectric FX...
Basically,  inject a 1kHz audio signal into the input of your total recall and measure it's amplitude before clipping (in millivolts). Now measure the amplitude of the signal at pin 7 of the compander and adjust "gain 1" to get it as close to the input amplitude. I was never able to get it equall to input amplitude but I can get it close...
Next, take amplitude measurement of pin 15 of the compander and use "gain 2" to adjust so it's equal to input amplitude. You should be able to get it exact.
Doing this, I find that the feedback control has a lot of useful range.
Hope this helps...

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If I opt to open it back up and adjust I'm definitely following this!!

[thomasha]

Posted by: danfrank
« on: June 25, 2022, 12:07:48 PM »Insert Quote
I like Scruffie's gain setting instructions from Lectric FX...
Basically,  inject a 1kHz audio signal into the input of your total recall and measure it's amplitude before clipping (in millivolts). Now measure the amplitude of the signal at pin 7 of the compander and adjust "gain 1" to get it as close to the input amplitude. I was never able to get it equall to input amplitude but I can get it close...
Next, take amplitude measurement of pin 15 of the compander and use "gain 2" to adjust so it's equal to input amplitude. You should be able to get it exact.
Doing this, I find that the feedback control has a lot of useful range.
Hope this helps...

Where exactly can I find this Info? Without knowing the setting of the potentiometers it's more difficult to compare to other procedures...
Gain 1 is between BBDs, after the compander. Do you mean Level?