Author Topic: Is Current Lover (2015) Calibration Possible with O-Scope or Frequency Counter?  (Read 1350 times)

Bio77

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Hi All,

I was hoping somebody with knowledge would be willing to lay out a method to calibrate the Current Lover (2015) with a frequency counter (if possible) or an o-scope.  I'm having some trouble with calibrating by ear.  I've gotten it to work, but I was looking for a more systematic way to get it really nice.   

I've looked at other MB posts and found the following reference: Mistress Mystery page http://www.metzgerralf.de/elekt/stomp/mistress/align.shtml.  I'd guess the Current Lover is a Delux Reissue V4 or V5, but I'm not exactly sure.   

I would really appreciate any help connecting this method to the Current Lover or developing a new method for calibration.

somnif

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The three Trimmers used for set up are Clock, Bias, and max Feedback, which would put it closest to the V6 on that page. (The volume trimmer is just a set-and-forget unity gain thing).


But I don't know how close the circuits are. Its a place to start though.

Scruffie

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It's the V6, SAD pin 6 & 12 are equivalent to MN3007 pin 7 & 8.
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Bio77

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Cool.  Thanks so much for the replies. 

For the Bias adjustment, the instructions say:
"Connect a 200 Hz sine wave to the input and adjust the BIAS trim for maximum input signal amplitude without clipping at SAD1024 pin 6 or 12 (TP2*). The input amplitude should now be greater than 1 V p-p."

What should be the amplitude of the 200 Hz input signal from the signal generator?

bsoncini

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Doesn't the last sentence say no bigger than 1v peak to peak?

So I imagine just slightly below or at 1v p-p.  Just make sure if you have to measure that it is peak to peak and not RMS. For instance your multimeter will most likely give you the RMS voltage.

Edit. I misread it. Thought it said should be no bigger than 1v p-p. It says should now be bigger than 1v p-p
« Last Edit: March 06, 2018, 12:58:51 AM by bsoncini »

Bio77

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I'm not sure that's what it means.  Pin 7 and 8 are outputs on the MN3007 (Thank you, Scruffie). Pin 3 is the input.

I'm reading this to mean: I place the 200 Hz input signal into the pedal input jack, measure the output at pin 7 or 8, adjust the bias trimmer until I see clipping, back off from that point until the clipping is gone.

So, I would assume the input amplitude should be in the range of a guitar pick up (maybe ~1V p-p).  Or maybe it doesn't matter.

Also, I just noticed on the Mistress Mystery page there is a link to the original EH calibration doc:
http://www.metzgerralf.de/elekt/stomp/mistress/images/nsc/dem_alignment_post_79.jpg

Bio77

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Hi All,

I put everyone's advice into practice this weekend.  The pedal sounds much better after this calibration compared to my initial "by ear" attempt.  I typed up a protocol below in case anyone would find it useful.  I used a cheap frequency counter I got on Amazon (Neoteck Multimeter, ~$22) and an old tektronix scope I bought on craigslist.   I used my smartphone as the signal generator.  There is an app called Function Generator Pro that I bought for a few dollars.  I soldered a few leads with clips on to an old headphone jack.

I did have a problem: there isn't enough range on the clock and bias trimmer to trim them properly.  I ended up setting the clock trimmer to ~42kHz (the lowest freq possible, trimmer at max position) and the bias trimmer still shows a small amount of clipping even at max position.  If any one knows a way to modify the pedal to get more range out of the clock and bias trimmers, please advise.

Procedure:
1.   Clock Trimmer (Freq Counter):  Set Feedback=0%, Range=100%, Rate=0%, Switch=Filter Matrix (left position).  Measure pin 1 of IC4 with frequency counter.  Turn clock trim pot until freq ~35 kHz.

2.   Bias Trimmer (O-scope): Set Feedback=0%, Range=100%, Rate=0%, Switch=Filter Matrix (left position).  Place 200 Hz 1V p-p (or ~p-p V of your guitar PU output) sine wave into the input jack of pedal.  Measure pin 7 or 8 of IC2 (MN3007).  Adjust bias trimmer until there is no clipping.  The output waveform will have an amplitude ~1.5 V p-p.

3.   Set T1 (O-scope): Set Feedback=100%, Range=100%, Rate=50%, Switch=Flange (right position).  Turn off signal generator.  Set T1 at full counter clockwise.  Measure signal at output of pedal (tip wire of output jack).  Signal should grow in and out with the clock (will be ~2V p-p at max). Adjust T1 trimmer until signal significantly diminished (barely visible).  There is a sweet spot where the signal will go from ~1V p-p to almost nothing.

4.   Set T1 (Amp): Set Feedback=100%, Range=100%, Rate=50%, Switch=Flange (right position).  Turn off signal generator. With no input, plug out put of pedal into amp.  Turn feedback trimmer clockwise until a horrible high-pitched tone breaks all the windows in your house.  Reduce (turn CCW) until horrible noise subsides.  Donít go to far, you want to be slightly below the horrible noise to have good flanging.

5.   Set Vol (O-scope): Set Feedback=50%, Range=50%, Rate=50%, Switch= Filter Matrix (left position).  Apply 1V p-p sine wave to input jack.  Measure output jack.  Set vol trimmer until output = 1V p-p.


Scruffie

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You need to set the clock to 70kHz, not 35, just had this in another thread, the original used a 512 stage chip but as we're using double the stages, gotta double that clock frequency to get the same delay time range.

As for the bias trim, yes, the 82k resistor in series with it is suitable for the SAD which has a lower bias point but not the 3007 so just reduce it or jumper it if you fancy.
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Bio77

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Cool.  Thank you. 

Bio77

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I followed all your advice. I jumpered a 43k resistor across the 82k to lower the resistance at R10.  This fixed the bias issue.  I set the clock to 70 kHz.

Wow, the pedal sounds really good!  Thank you so much.

I wanted to edit the protocol from above:

2(edit). For the bias trimmer I used a 2V p-p input wave, this let me dial in the bias more accurately.  Anything above 2V and there was no position on the trimmer that didn't have clipping.  After setting the bias at 2V, it was fine at any lower voltage.

5(edit).  Looking again at the original documentation, I realized I made a mistake.  For the volume trimmer a 3k Hz 0.5 p-p input signal is used.  The output signal pulses up and down, I set the volume trimmer so the minimum was ~0.5 V p-p.   

Masochist

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Just wanted to thank you for taking the effort to work this out and share your results!! I actually had my first attempt at doing the calibration by ear today. Although it went fine I do suspect it's capable of sounding much better, so when I came across your post I thought I might give this a try. I haven't had any experience with oscilloscopes etc but I'm feeling brave!! :)

You mention connecting a 47k resistor in series with the existing 82k.. would it be easier/neater if I just removed the 82k and replaced with a 150k or similar value?

Thanks again and wish me luck ;)

Bio77

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Just wanted to thank you for taking the effort to work this out and share your results!! I actually had my first attempt at doing the calibration by ear today. Although it went fine I do suspect it's capable of sounding much better, so when I came across your post I thought I might give this a try. I haven't had any experience with oscilloscopes etc but I'm feeling brave!! :)

You mention connecting a 47k resistor in series with the existing 82k.. would it be easier/neater if I just removed the 82k and replaced with a 150k or similar value?

Thanks again and wish me luck ;)

This is a modification you would only need if you find there isn't enough range on the trimmer.  It was easier to jumper in because I had already boxed the circuit. 

Good luck!

Masochist

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Hi guys, I'm looking to perform the calibration described here but I'm a total noob when it comes to oscilloscopes and I'm looking to pick one up. I've been looking at those hand held, DSO211/212 or similar ones and was just wondering if these will do the job? Are there things I should look out for in the specs/features that tell me if they are up to the task? Here's a link to one I'm looking at.. https://ebay.us/lxii5V

That last one is the cheapest, nastiest one I've seen. Here's another one I'm considering.. still cheap but not quite as nasty? https://ebay.us/KFFPyW

Any help much appreciated! :)