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DIY Stompboxes => Building your own stompbox => Topic started by: DrAlx on March 20, 2018, 03:26:18 PM

Title: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on March 20, 2018, 03:26:18 PM
A couple of years ago I built an 18V EM (Version 2) using the schematic from the Electric Mistress Mystery page.  Apart from the well known volume drop there was a surprising amount of clock noise.  I had experimented with various things to reduce the noise and managed to lower it a little but not to what I would consider an acceptable level.

I have also built the EM3207 clone of the 9V EM (which uses a LFO/VCO like the Deluxe EM).  That does not have the same noise issues.
I reckoned that the LFO/VCO of the original 18V EM was the problem, so I set myself the challenge of reworking the 18V EM with the following goals:

1) Get rid of heterodyne noise (due to RF picked up on the input line).
2) Replace the noisy LFO/VCO combination with something similar to the 9V EM.
3) Keep the simple SPDT switch to select filter matrix mode, instead of the more complicated DPDT of the 9V EM.
4) Have all the control pots work in the exact same way as the 18V EM. In particular ...
   The fastest sweep rate should match the original.
   The slowest sweep rate should match the original.
   The sweep (min delay to max delay) with the Range pot is at maximum should match the original.
   The sweep (min delay to max delay) with the Range pot is at minimum should match the original.
5) Fix the volume drop by adding a gain stage at the output.
6) Fit the whole thing in a 1590B on Veroboard. (I won't be running on batteries).

So I basically wanted the same sound and controls as the original 18V EM but without all the noise and the big box.  Point 4) was the trickiest to achieve but I got there within acceptable tolerances (a couple of percent).  Actually points 3) and 4) are related, and what allowed me to achieve both was a modification I made to the VCO that I'll explain below.

Here's a PCB layout with almost the same layout as the 25x21 hole Vero build shown in the photo:
(http://i64.tinypic.com/33l1rfm.jpg)
(http://i67.tinypic.com/2w555yt.jpg)
Here's the schematic:
(http://i64.tinypic.com/2maaf9.jpg)

The Audio Path:

The audio path is the same as the original 18V EM apart from the following.

1) Added C2.  This forms a LPF with R2||R3 giving a 3dB point of about 11 kHz.  I took the idea of having an RF filter at the input from the EM3207.
2) Added C4.  This is taken from the 9V EM.  This cuts more RF in the pre-emphasis section, starting at about 23 kHz.
3) The balance trimmer RT1 can be used to minimise clock glitches at the BBD output.  The change in BBD gain is insignificant.
4) The boost stage based on Q1 fixes the volume drop.
5) The Electric Mistress does not actually use parallel multiplexing (as I explained in another post) so I used just one of the delay lines on the chip.
This allowed me to utilise a half-working SAD1024 that I have.


The LFO:

IC3 is the basic triangle/square oscillator.  I chose component values that would give me the same set of rates as the original 18V EM.  Why the 10k||33k for R22,R33 ?  Because that's what's in series with the rate pot in the original, and I wanted to match the measured waveforms from my reference circuit.


The VCO:

Apart from component value changes, IC4 is like the VCO in the 9V EM, but there is one subtle but important difference.  The extra resistor R29 means the discharge diode D2 is no longer directly connected to the comparator output. (i.e. R29 would be 0 ohm in the 9V EM).  I'll explain the purpose of this resistor.

The basic principle in this VCO is the same as in all versions of the EM.
The clock capacitor C16 is charged by a constant current source (Q2), so the voltage on C16 increases linearly in time.  When this voltage reaches the level of the CV (applied at pin 2 of the LM311), the LM311 output is pulled low,
causing the capacitor to be quickly discharged through D2.  The capacitor then starts charging again.

The VCO characteristic (i.e. mapping of CV to BBD delay) for this sort of VCO is a straight line, with CV on the horizontal axis and delay on the vertical.  The gradient of the line is inversely proportional to the rate at which the voltage on C16 increases while it is being charged.  Any one of the following changes will cause the capacitor voltage to increase more slowly, and so make the gradient of the line steeper.

1) Increasing the clock trimmer (RT4) resistance (so charge current is lowered).
2) Using a Q2 with lower hFE (so charge current is lowered). 
3) Increasing the value of C16 (so the charge current produces a smaller voltage increase on the capacitor).

The above are all equivalent and they all increase the gradient of the line.

Note: Having said they are all equivalent, there ***is*** a practical problem with using too low a value for C16.  Using a value in the 10s of pF can give a non-linear charactersitic at low CV levels due to the effect of diode reverse-current when D2 switches off.  I mentioned that on the EM3207 thread.  So I used a value of 470pF in my VCO like the original 18V EM.  This is 10 times larger than the 47pF used in the 9V EM.

Now for a fixed CV range, increasing the gradient of the line using RT4 will give a wider sweep range but a lower sweep ratio.
Here is an example with some made up values to highlight the point:
  RT4 set to min:  BBD delay is 1ms to 5 ms ==> Sweep range is 4 ms.  Sweep ratio is 5:1.
  RT4 set to max:  BBD delay is 4ms to 12 ms ==> Sweep range is 8 ms.  Sweep ratio is 3:1.

So it is not possible to set both a desired sweep range AND a desired sweep ratio with the single trimmer in the VCO.  The 9V EM circuit addresses this by shifting & scaling the output from the triangle wave generator so that is becomes a CV with a suitable range for the VCO.  That approach results in an extra op-amp, some scaling resistors, and the more complicated DPDT switch for filter matrix mode.

I took a much simpler approach.  I decided to shift the VCO characteristic instead of the CV, and that's what the extra resistor R29 is for.
As explained above, RT4 sets the gradient of the line in the VCO characteristic.  The extra resistor R29 allows you to set the vertical offset of the line.  Increasing R29 moves the whole line downwards, and providing R29 is kept small (under 500 ohms ) it has little effect on the gradient of the line.
This is how it works...

First consider the case when R29 is zero ohms.  Since C16 discharges through a diode, it never discharges all the way to 0V.  The lowest voltage it can discharge to is one diode drop.  Therefore the charging process actually begins with the capacitor voltage at about 0.6V.  So if the CV level is 2V, then the VCO period is roughly the time taken to increase the cap voltage by 1.4V.

Now consider the case where R29 is some non-zero value. R29 forms a voltage divider with R28.  When the comparator pulls its output low, the cathode of D2 no longer gets pulled to 0V but to some higher value instead (lets say 0.4V).  Accounting for the diode drop, C16 now discharges to a minimum voltage of 1V.  Therefore it starts its charge cycle with a voltage level of 1V instead of 0.6V.  Since the charge rate provided by Q2 is exactly the same as before, the CV level of 2V will now be reached in a shorter time.
 So the VCO period decreases.  Therefore increasing R29 has the effect of shifting the line in the VCO characteristic downwards.

The effects of these two controls on the VCO characteristic (clock trimmer to vary gradient, and R29 to vary vertical offset) are only weakly coupled.  This means you can set the clock trimmer to get the desired sweep range, and then increase R29 from zero to get the desired sweep ratio.  That's basically how I arrived at a value of 220 ohms for R29.  Using this value and adjusting RT4 gave me the required flexibility to match the sweep range and sweep ratio of the original 18V EM,  with the added benefit of being able to drop the extra op-amp and DPDT switch used in the 9V EM.

If R29 is made too large (say over 1k) then C16 will discharge more slowly.
 That's because D2 is effectively in series with R28||R29.  If the discharge period is significant, then the overall effect on the VCO period is less clear cut.
In theory it should still move the characteristic downwards because C16 discharges by less.  It's not a problem in this particular circuit though, and you can basically set R29 without worrying about it changing the gradient of the characteristic.

One other important component is R30. Together with C17, this prevents the VCO "thumping" when the range pot is at maximum and the sweep rate is high.  This "thumping" is not a clock tick but it can sound like one.
Note that if R30 was not there, then the series resistance going into C17 would be strongly dependent on the range pot setting.
In particular, with the range pot at maximum, the resistance would be zero and there would effectively be no filtering of the CV at all before hitting the VCO.  Unlike the 9V EM LFO, the filtering from R30 and C17 is light enough for the CV wave to still looks triangular.  In the 9V EM, the triangle wave is actually filtered twice before it reaches the VCO (once before the rate pot and once after).  So on that circuit the triangle wave looks almost sinusoidal at high sweep rates.  That is not the case with this circuit.

Given the high price and low availability of the SAD1024 I doubt anyone else will build this circuit, unless they have a vintage 18V EM and are keen to replace the guts of it with something without all the noise issues.  In any case, I was pleased with my VCO modification and thought it might be of interest.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: StephenGiles on March 20, 2018, 05:19:39 PM
Many thanks, very interesting indeed!
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: ElectricDruid on March 20, 2018, 08:11:00 PM
That's a great piece of work, thanks for sharing. It's nice to see the analysis of the problem and then the development of the solution instead of just "here's the schematic!". I've been thinking of building a chorus next, and I think it could benefit from some of the ideas you've presented there.

Tom

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Scruffie on March 20, 2018, 08:24:36 PM
Funny, i'd actually been working on a version with a 393 keeping the original LFO and using the 311 VCO today which being near rail to rail gave some rather large sweeps and a fair bit of dead sweep, i'll have to try your R30 approach.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: stringsthings on March 21, 2018, 08:21:56 AM
That's really cool!  Any sound samples by chance?  The old SAD1024 flangers were really great.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: JC103 on April 03, 2018, 06:38:29 PM
I've actually got an old flanger kicking around with a SAD1024... and it's in a socket to boot! Might have to give this a whirl. Out of curiosity, could a TDA1022 chip be retrofitted in your adaptation?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on April 03, 2018, 11:13:06 PM
TDA1022 is negative supply like the MN300x series. 
That isn't a problem, but if you want to make TDA1022 as close a fit to SAD1024 you would need to address the different BBD gain for the two chips.
Maybe with this sort of approach which I outlined for the MN3207:
            https://1drv.ms/i/s!AvrH61utWEtEiAbzPDPv5UK-geVK (https://1drv.ms/i/s!AvrH61utWEtEiAbzPDPv5UK-geVK)
You can control the BBD gain with R14, though not sure if its possible to get the same gain as the SAD1024. The TDA1022 appears to be lossy according to the datasheet.
The "Rds || 10k" comes to a value of about 1.1k to 1.2k based on my measurements on an actual SAD1024.
The point is that in in the original EM circuit, the impedance looking left from the 3n3 capacitor would be 10k in parallel with the drain-source resistance of the BBD output.  You need to have that same impedance for the frequency response to look the same.

As far as the VCO/LFO goes, the mod I mention above would not need tweaking assuming everything is still running off a regulated 12V.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: KHStudio on September 10, 2019, 11:44:46 PM
Are the images still available somewhere?

Thx
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on September 11, 2019, 03:18:15 AM
Schematic:  https://1drv.ms/u/s!AvrH61utWEtEi1hXQjQDPCiV46Xc?e=8WBR4g
PCB layout: https://1drv.ms/u/s!AvrH61utWEtEi1oayThe2Upl7Z0X?e=4Wg774
Photo:         https://1drv.ms/u/s!AvrH61utWEtEi1mTTjjUznhTg6_7?e=uGbYjc

If you are on Windows or Linux Mint 18.3 you can download VeroRoute from
  https://sourceforge.net/projects/veroroute/.
The examples folder contains the PCB layout and a Vero layout.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: KHStudio on September 12, 2019, 09:21:00 PM
DrAlx, Thanks for the links!

Btw, the schematic is hard to read & only blurs when zoomed in but I can somewhat make it out if that's all that's available.
I've been working on several different builds of the EM & was just interested in your work for additional options & learning.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on September 13, 2019, 03:23:37 AM
Schematic in link looks ok on both my desktop and tablet. Maybe try download and view it in another app.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: bluebunny on September 13, 2019, 03:38:42 AM
Schematic in link looks ok on both my desktop and tablet. Maybe try download and view it in another app.

Yep, I concur.  Link looks legible (and appears to be a preview).  "View original" is even better: 2048x1452 and crystal-clear.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on January 25, 2020, 07:12:47 AM
Including C2 (2n7) was a mistake.  I didn't account for impedance of the input.
Having C2 is OK if the input comes from a low impedance source like another pedal (which is what I always have) but if you just have a guitar with passive pickup, then C2 sees (5k6 + pickup impedance) to its left and ends up killing high end.  Best to leave C2 out.




Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on April 20, 2020, 05:15:50 PM
Hi DrAlx and thank you for all this data. I was wondering if I could use the same values from the MN3207 schematic for an MN3007 ? Knowing that I would like to do a regulated 15V.

And what does the "Rds || 10k" actually stand for ? Just a resistor or something else  ?

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: bluebunny on April 21, 2020, 03:58:53 AM
Welcome to the forum!

And what does the "Rds || 10k" actually stand for ? Just a resistor or something else  ?

It's shorthand for a calculation: Rds "in parallel with" 10K.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on April 21, 2020, 01:26:26 PM
Thanks a lot and hope DrAlx can answer the other question :)
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on April 21, 2020, 03:03:05 PM
I will soon post a MN3207 based version of the above circuit.  I'm aiming to make it the best possible clone of the original V2 using a BBD that is still available. 
I'm waiting for the PCBs to arrive so I can do a final comparison against the SAD1024 circuit.

I tried to rework the LFO/VCO for 9V operation but couldn't manage to keep all the controls working the exact same way.
So in the end I decided not to rework any values and instead I just ran the LFO/VCO section off a 12V regulator, and ran the rest (audio chips, BBD and clock buffer chip) off a 9V regulator.
I have not tried a MN3007 but based on my measurements (posted recently on the EM3207 thread) and the datasheets, you will probably get a closer match to the SAD1024 using an MN3207 as opposed to the MN3007 (in the sense that BBD gain and hence wet/dry balance will be about 2dB closer match to the SAD1024 circuit).

Oh and ignore my previous posts mentioning circuit hacks to try and get an impedance of "Rds||10k".  It is not necessary if you just get rid of the emitter follower after the BBD.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 08, 2020, 06:06:29 AM
Thanks for these infos, I'm looking forward to the results for the 3207 !In any case for the 3007 I reach a result close to the original only by using it in 12v probably because of the LFO/VCO operation.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 19, 2020, 04:13:27 AM
How would you do both regulations here then? Powered in 18v DC then regulate in 12v and 9v with 78L12 and 78L09?

Do you already have a schematic?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Ben N on May 19, 2020, 04:29:57 AM
Following. With Madbean's Current Lover board unavailable, I have been looking for an EM project using obtainable parts. This looks exciting. Thank you DrAlx!
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 19, 2020, 04:35:57 AM
Boards arrived in the post. Just need to populate and test.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 19, 2020, 04:40:59 AM
How would you do both regulations here then? Powered in 18v DC then regulate in 12v and 9v with 78L12 and 78L09?

Do you already have a schematic?
Exactly that method.  The LFO/VCO/CD4013 run of a 78L12.   The audio op-amps/BBD/CD4050 run off a 78L09.

I will post a schematic as soon as I have tested the build.  There are a couple more component values that need a tweak and I don't want to post a schematic with incorrect values.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 19, 2020, 04:58:00 PM
Almost there.  I just need to find suitable values for the output gain stage to bring it to unity.  The new build will have an op-amp based gain stage (like the Madbean Current Lover) as tests showed it to be quieter than the single BJT stage used on the SAD1024 build.

I noticed something interesting while doing a sound comparison.  I compared the sound of my BL3207 based build to the SAD1024 based build I did a few years back.  As my BL3207 build isn't populated with an output gain stage yet, I took signals from before the output gain stages on both boards.  The BL3207 build appeared to sound warmer (bassier) than the SAD1024 build.  It was not a rigorous test because I was just plugging/unplugging jacks and trying my best to "remember the sound".  In fact if I remembered incorrectly it invalidates what you're about to read below!!!
Now I spent a lot of time carefully comparing the BL3207 against the SAD1024 (lots of measurement results posted on the EM3207 thread) and I know for a fact that in this particular circuit, the difference in BBD gain between these chips is a fraction of a dB, and often close to 0dB.  So the use of different BBDs could not explain the difference in sound. So I removed the BBDs from both boards to compare the sounds without any sort of delay in the circuit.  Guess what?  The MN3207 build still sounded warmer.  The audio paths are the same (i.e. same opamps and same R and C values) in the two circuits.  The opamp (TL072) is run at lower voltage in the 3207 circuit (9V instead of 12V) but I don't believe that is relevant.  I think the difference may be in the quality of film caps that I used.  I used Panasonic's in the MN3207 build (brown things in the picture below) and cheaper box caps in the SAD1024 build (yellow).  Normally I don't pay too much attention to what caps are made of, but there was another occasion about a year ago where I had two caps of the same nominal value giving a noticeable difference in the amount of bass (though in that case I was comparing an electrolytic to a film cap).

(https://i.ibb.co/5Lj5pjP/IMG-8286.jpg) (https://i.ibb.co/5Lj5pjP/IMG-8286.jpg)

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: StephenGiles on May 20, 2020, 02:18:51 AM
I built a TDA1022 version of the Electric Mistress a few years ago, which also included the Eventide Instant Phaser/Flanger bounce circuit for fun - must have been early 2000s. I'll try to locate the circuit which I drew out on that old large stripey computer printer paper, and also a few sound samples I did.

I found the samples:
https://www.dropbox.com/sh/4z6mog10ibaqh6o/AACReznX-f8p1hIVNkX7p4I9a?dl=0
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 20, 2020, 06:37:02 PM
OK I have finished with the MN3207 conversion.  I couldn't think what to call it so "EMV2 Flanger" will have to do.

(https://i.ibb.co/0qTnNcX/IMG-8287.jpg) (https://i.ibb.co/0qTnNcX/IMG-8287.jpg)
(https://i.ibb.co/dMkN9Qz/EMV2.png) (https://i.ibb.co/dMkN9Qz/EMV2.png)

So basically the LFO and VCO run from 12V supply.  The clock buffer, BBD and audio run from 9V supply.  You don't need to power the circuit with 18V of course (15V is enough).

Compared to the reworked SAD1024 circuit that started off this thread, I changed the output gain stage to an op-amp since its lower noise than the LPB style output boost I had before.

The only other LFO/VCO related changes are:

R27 in above schematic: Reduced from 220k to 180k as that was sufficient to stop the VCO "thumping".

R31 in above schematic: Reduced from 10k to 3k9.  This was key to getting the sweep range correct for the doubled clock.
If the ratio of R32/R31 is too low then it not possible to get a decent sweep range. Using a ratio of (220/3900) I can set the clock trimmer in Filter Matrix Mode and have the clock going from around 50kHz to around 400kHz (depending on Range pot setting).

Document with parts list here:   https://1drv.ms/b/s!AvrH61utWEtEjig_4U8k7-fGwkbv?e=69cQg1 (https://1drv.ms/b/s!AvrH61utWEtEjig_4U8k7-fGwkbv?e=69cQg1)

I have 4 boards but can't say how quickly I could get them delivered under current circumstances.  PM me if interested.  If there is sufficient interest I will order more.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 22, 2020, 09:47:05 PM
One other thing.  The circuit will run on a 12V supply (rather that 15V supply) without the need to reset the bias (because that runs off the 9V regulator) however the sweep range will be reduced.

I have not actually powered it with an 18V supply, only 15V.  I also have a cheap wall-wart that is labelled as 15V output but actually supplies over 20V.  When I used that the 12V regulator got really hot and died.  So I would recommend that the circuit supply is limited to 15V (despite what is says on the schematic).

I am not sure why the regulator died because when I calculate a worst case current draw from the 12V circuitry it comes to less than 10mA, which should be easily handled by the 78L12.  So I am not sure what is going on there.

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: rankot on May 23, 2020, 04:46:14 AM
One other thing.  The circuit will run on a 12V supply (rather that 15V supply) without the need to reset the bias (because that runs off the 9V regulator) however the sweep range will be reduced.

I have not actually powered it with an 18V supply, only 15V.  I also have a cheap wall-wart that is labelled as 15V output but actually supplies over 20V.  When I used that the 12V regulator got really hot and died.  So I would recommend that the circuit supply is limited to 15V (despite what is says on the schematic).

I am not sure why the regulator died because when I calculate a worst case current draw from the 12V circuitry it comes to less than 10mA, which should be easily handled by the 78L12.  So I am not sure what is going on there.

Couldn't you run it on 9V with, for example, 15V generated with LT1054 or something similar? It could use normal PS then.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 05:03:56 AM
Couldn't you run it on 9V with, for example, 15V generated with LT1054 or something similar? It could use normal PS then.
Not sure it's a good idea. You could get heterodyne noise due to the clock from the charge pump beating with the clock used for the BBD. That's the case for all BBD based effects. Low pass filtering on the audio is very light on the EM and that is part of the sound, so it is more likely to be a problem on this circuit than on other BBD circuits.

I have not actually used a charge pump with a BBD, so maybe that could work. Layout would be important.
You could always try to use a small daughter board (or is it motherboard?) to do the 9v to 15v conversion.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: diffeq on May 23, 2020, 05:46:27 AM
One other thing.  The circuit will run on a 12V supply (rather that 15V supply) without the need to reset the bias (because that runs off the 9V regulator) however the sweep range will be reduced.

I have not actually powered it with an 18V supply, only 15V.  I also have a cheap wall-wart that is labelled as 15V output but actually supplies over 20V.  When I used that the 12V regulator got really hot and died.  So I would recommend that the circuit supply is limited to 15V (despite what is says on the schematic).

I am not sure why the regulator died because when I calculate a worst case current draw from the 12V circuitry it comes to less than 10mA, which should be easily handled by the 78L12.  So I am not sure what is going on there.

Couldn't you run it on 9V with, for example, 15V generated with LT1054 or something similar? It could use normal PS then.
Not sure its a good idea. You could get heterodyne noise due to the clock from the charge pump beating with the clock used for the BBD. That's the case for all BBD based effects. Low pass filtering on the audio is very light on the EM and that is part of the sound, so it is more likely to be a problem on this circuit than on other BBD circuits.

I have not actually used a charge pump with a BBD, so maybe that could work. Layout would be important.
You could always try to use a small daughter board (or is it motherboard?) to do the 9v to 15v conversion.
You can use capacitance multiplier at the charge pump output - 1 transistor, 1 resistor and 2 electro caps will shave of all of high frequency noise (at the expense of 1V drop).
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 06:07:58 AM
Found this that has 9V -> 18V followed by a regulator to 15V that powers the circuit.

http://moosapotamus.net/images/FlangerClone_SCH_rev5_MN3007_jan2010.gif

So daughter board might do it.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: StephenGiles on May 23, 2020, 06:38:58 AM
Me being me would use 2 x rechargeable 9v PP3 batteries for testing during building, then a battery pack of rechargeable AAs - only because I don't mess with mains on effects!
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 06:59:41 AM
Me being me would use 2 x rechargeable 9v PP3 batteries for testing during building, then a battery pack of rechargeable AAs - only because I don't mess with mains on effects!
I'll give that a try (test with 2PP3s).  So just figured out why my regulator died. It is rated as being able to supply 100mA at 12V but this circuit draws less than 10mA at 12V, so the excess voltage fed into the reg gets converted into heat.  Damn wall-wart cost me a load of hassle trying to unsolder/resolder parts on my PCB which was very fiddly to handle with the cramped space and plated through holes.

Question:  Does anyone have a technique for easily replacing parts on a PCB with plated through-holes?  I found it hard to get the parts out and they always left a hole filled with solder.  I ended up trying to push a needle into the hole and wiggle it while heating the pad, so the needle point would push the solder out.  I am wondering if there is some tool for the job (an awl of some sort)?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: diffeq on May 23, 2020, 07:45:02 AM
You can use capacitance multiplier at the charge pump output - 1 transistor, 1 resistor and 2 electro caps will shave of all of high frequency noise (at the expense of 1V drop).
Better still, is to use to use BBD clock itself to run a voltage multiplier (doubler@9V, x3/x4 @5V ), followed by regulator/cap multiplier  filtering. Solves the noise issue.

Question:  Does anyone have a technique for easily replacing parts on a PCB with plated through-holes?  I found it hard to get the parts out and they always left a hole filled with solder.  I ended up trying to push a needle into the hole and wiggle it while heating the pad, so the needle point would push the solder out.  I am wondering if there is some tool for the job (an awl of some sort)?
I did the same but using toothpick. Ends being conical work better than a needle. Ideally one would use hot air gun and a copper wick, but I imagine fixing through-holes would still require lots of practice.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: bluebunny on May 23, 2020, 08:34:35 AM
Yep, toothpick every time.  :icon_cool:
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 23, 2020, 09:13:58 AM
Quote
Question:  Does anyone have a technique for easily replacing parts on a PCB with plated through-holes?  I found it hard to get the parts out and they always left a hole filled with solder.  I ended up trying to push a needle into the hole and wiggle it while heating the pad, so the needle point would push the solder out.  I am wondering if there is some tool for the job (an awl of some sort)?

The best solution for me is the desoldering pump with the addition of tin, until the hole is free. (sometimes I need three additions to make it right but it works all the time).

Have you tested antoher reg 12v ? Maybe the first was not so good
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 11:09:06 AM
I got the same overheating with the new regulator if I powered it with too much voltage.
With 20V input, regulator stops regulating and I measure 20V on all the circuitry that should be running at 12V.  C20 which was rated for 16V could have got damaged in the process, so when I changed the regulator I replaced it with a 47uF cap rated at 35V.

Assuming circuit takes 10mA, power disipated in reg = (20-12)*0.01 = 0.08W.   Multiply by 200 degrees C per W = 16 degrees C increase.  That's not big but the reg was way too hot to touch, so I can only guess that the circuit is actually using a lot more than 10mA.  I'll have to measure current consumption.

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: rankot on May 23, 2020, 12:35:37 PM
I got the same overheating with the new regulator if I powered it with too much voltage.
With 20V input, regulator stops regulating and I measure 20V on all the circuitry that should be running at 12V.  C20 which was rated for 16V could have got damaged in the process, so when I changed the regulator I replaced it with a 47uF cap rated at 35V.

Assuming circuit takes 10mA, power disipated in reg = (20-12)*0.01 = 0.08W.   Multiply by 200 degrees C per W = 16 degrees C increase.  That's not big but the reg was way too hot to touch, so I can only guess that the circuit is actually using a lot more than 10mA.  I'll have to measure current consumption.

Maybe you have a short somewhere?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: rankot on May 23, 2020, 12:37:35 PM
Better still, is to use to use BBD clock itself to run a voltage multiplier (doubler@9V, x3/x4 @5V ), followed by regulator/cap multiplier  filtering. Solves the noise issue.
Sounds good, could you draw a schematic for that?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 02:42:05 PM
Measured current consumption. Whole circuit takes 30mA when clock is at maximum rate.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 02:51:05 PM
Better still, is to use to use BBD clock itself to run a voltage multiplier (doubler@9V, x3/x4 @5V ), followed by regulator/cap multiplier  filtering. Solves the noise issue.
Sounds good, could you draw a schematic for that?

+1. Interested to see how such a circuit would fire itself up.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: rankot on May 23, 2020, 06:22:59 PM
Why do you have to run the clock at 12V at all?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 23, 2020, 08:01:33 PM
Why do you have to run the clock at 12V at all?
The LFO/VCO gives a different sweep range/ratio at 9V.  It was easier to take what I had done at 12V (a time-consuming piece of work BTW) and tweak one resistor value rather than rework everything I did two years ago.

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 24, 2020, 05:07:12 AM
So is it not better to run just on 12v DC and use a 9v regulator ?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 24, 2020, 06:22:12 AM
If you have a regulated 12V supply then of course you don't need to use the on-board regulator, so you could leave that part out of the board and use a jumper wire. I don't have a regulated 12v supply.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 24, 2020, 07:41:34 AM
I'll do the first test with the 12v supply and compare with my original mistress. I juste need a 9v reg wich is coming tomorrow. But it's really strange that the 12v reg blows up...
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: diffeq on May 24, 2020, 12:05:56 PM
Better still, is to use to use BBD clock itself to run a voltage multiplier (doubler@9V, x3/x4 @5V ), followed by regulator/cap multiplier  filtering. Solves the noise issue.
Sounds good, could you draw a schematic for that?
Here's a schematic.
(https://i.postimg.cc/hz94zF2Z/bootstrap-regulator.png) (https://postimg.cc/hz94zF2Z)
Done like that, it'd bootstrap its own rail, which is both silly and clever.
Couple of thoughts. D1-R1-D2-R2 do the ORing 9V and the doubled voltage. 12V regulator starts to regulate when Vin is above 14V or so, and before that, it passes 9V through with some voltage drop out. The question is, will LFO-VCO even start oscillating at all at 7.2V, to start doubling? I do not know. Q1-Q2 supply higher current to doubler because clock buffers can supply only 10mA or so. C3-C5 should ideally be non-polarised (maybe several large, like 10uF, MLCCs in parallel), and that might need to be adjusted to clock frequency. It could probably be made to work, but the time you're done it makes you wonder why not try simpler ways. That doubler can develop stability issues too, mind you.

Why do you have to run the clock at 12V at all?
VCO frequency depends on power supply voltage. With the regulator you can be sure the sweep range stays the same with varying PSU voltages. One way to solve it is to change the current source in VCO, make it constant and run off 9V. Second is to use charge pump and excessive rail filtering. All of it requires time to test and make it work (it may not even after that), which is DrAlx tries to prevent by building on what time was invested in already.


Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 24, 2020, 01:05:20 PM
I removed all the ICs in the 12v circuitry. With a measured power supply of 13.8V the regulator was warm even though there was no LFO/VCO. So then I measured voltages across all resistors in the 12v circuitry, calculated current in each one. Even if I sum all the currents (i.e. pretend all resistors are in parallell) I get a total current of about 2mA in the 12V circuitry without ICs. Such low current draw does not explain the warmth I am seeing on the 12V regulator. If I have a short then it is a strange one because the circuit still works and voltages all look ok.
Could the problem be related to the fact I have 2 regulators? I assumed that putting them in parallel was better than having the 9V reg be supplied by the output of the 12v reg.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: diffeq on May 24, 2020, 01:17:57 PM
I removed all the ICs in the 12v circuitry. With a measured power supply of 13.8V the regulator was warm even though there was no LFO/VCO. So then I measured voltages across all resistors in the 12v circuitry, calculated current in each one. Even if I sum all the currents (i.e. pretend all resistors are in parallell) I get a total current of about 2mA in the 12V circuitry without ICs. Such low current draw does not explain the warmth I am seeing on the 12V regulator. If I have a short then it is a strange one because the circuit still works and voltages all look ok.
Could the problem be related to the fact I have 2 regulators? I assumed that putting them in parallel was better than having the 9V reg be supplied by the output of the 12v reg.
Could be that. Even opamps shall never get outputs connected together directly, only through some resistance. Otherwise output will 'fight' and it will seem like a short circuit to each of them. So they'll heat up a lot. Inside of 78L12 is something like an opamp so it won't be different. It can supply up to 100mA, so one is enough for this circuit.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: rankot on May 24, 2020, 05:19:38 PM
Maybe you shall limit the current at LM311 output or you shall limit CD4050UB outputs? Did you check for pin shorts?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 25, 2020, 11:35:09 AM
I don't think it is a short.  No short is visible on the board and all the voltages measure as expected.  The circuit works remember.  It's just that the regulator is warmer than I expected.

I removed all chips from the board and also removed the 9V regulator.  I took voltage measurements (in red below) on the resulting simplified circuit, and used those to calculate currents (in blue below).  The 12V regulator was still warming up as before with this set up.

(https://i.ibb.co/9tB8CrD/18-V3207-debug.png) (https://i.ibb.co/9tB8CrD/18-V3207-debug.png)

Voltages are reasonable and total current draw is 0.47mA + 0.49mA = 0.96mA.
The measured current into the regulator (using a multimeter) is about 10.5mA.  It actually starts out at around 9.5mA and then slowly increases which I think is the result of the regulator heating up towards its final temperature.

The regulator datasheet says the regulator quiescent current is about 6mA but I don't know if the test circuit they used to measure that for the datasheet means I should expect the same sort of quiescent current in my example or larger.
Assuming quiescent current is 6mA, then I am still short of couple of mA.  My scope and multimeter are not great quality so I don't know what the measurement errors are like.

The strange thing is that the regulator on my SAD1024 build doesn't get warm (even when I increase the clock rate to match the 3207 circuit).  It's the same LFO/VCO remember.  So maybe I have a bad regulator on my 3207 build. Unfortunately my soldering iron broke in the process of desoldering (handle actually snapped off and I was lucky not to burn my other hand) so my work on this is done.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: duck_arse on May 25, 2020, 11:43:16 AM
Quote
The regulator datasheet says the regulator quiescent current is about 6mA but I don't know if the test circuit they used to measure that for the datasheet means I should expect the same sort of quiescent current in my example or larger.

look on that same datasheet for the standard connection circuit, whatever they call it. it will show an input capacitor and an output capacitor. your output cap is 100uF, C19. what value does the datasheet recommend?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 25, 2020, 01:56:30 PM
Sheet recommends minimum of 0.01 uF.  I had already replaced C19 with a 0.1uF ceramic since I was wondering if I had damaged the electrolytic that was in there before.  The circuit works OK with 0.1 uF ceramic for C19 ... and regulator still gets warm.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 27, 2020, 05:49:10 PM
Hi Alex! Do you by any chance have the layout for veroboard? Thank you.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 28, 2020, 03:25:40 PM
Hi Alex! Do you by any chance have the layout for veroboard? Thank you.
No.  I went straight to PCB on this one.  It was the only way to make it fit a 1590B.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 28, 2020, 05:22:23 PM
Fixed the problem. I removed the regulator and 2 caps from the PCB and put them on a breadboard for testing with a dummy load. The regulator worked fine at 20V with no overheating.
So I ran jumpers from the breadboard to the PCB and that was fine too. Resoldered the parts to the PCB and it was then working fine.
So I reckon I had a short of some sort that was fixed by desoldering/resoldering.  Given that the voltages I measured before all looked correct, I am guessing the short must have been between the regulator output and ground. The circuit now draws 20mA (measured at supply into the board).

I think the circuit was probably fine when I first built it, but then I accidentally shorted the regulator to a pot casing when the pedal was boxed.  Replacing that blown regulator is what gave me the subsequent problem that took so long to resolve.

A few other things I noticed/learnt in the process...

1) C18 can be lower.  33uF is fine.  Datasheet minimium is 0.33uF.

2) C19 and C21 can (and probably should) be replaced with a MUCH lower value. It worked fine with a 100nF ceramic.

3) The circuit works fine with C20 removed and R33 shorted.
C20 and R33 are there because I had them in the SAD1024 circuit that started this thread.  I included those parts in that circuit to stop LFO ticks making it onto the audio supply.
It was an overly-cautious measure in the SAD1024 circuit (i.e. probably not needed) but in this MN3207 conversion there really is no point in having them at all, since the LFO is fed by a different regulator to the audio.

Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 28, 2020, 05:55:16 PM
Ah too bad... I only have pcb adapted to 9v so it's very complicated to put two separate power supply circuits.

Can you send me one of your PCB in France ?

Oh and why else do you use the TL062 instead of the LM339 as in the original ?
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 28, 2020, 06:20:31 PM
Yes I can post to France. PM me.

The original 339 based LFO/VCO is unforgiving on layout and noisy.  The whole point of this thread was to show how you could make an LFO/VCO that has the same behaviour as the original but without all the problems.
Also the 339 is too slow to give the doubled clock rates required to drive the MN3207.  I tried that as an experiment many years ago and couldn't get an acceptable sweep.  Either the top end of the sweep would disappear or the bottom end would.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 28, 2020, 06:28:15 PM
3) The circuit works fine with C20 removed and R33 shorted.
C20 and R33 are there because I had them in the SAD1024 circuit that started this thread.  I included those parts in that circuit to stop LFO ticks making it onto the audio supply.
It was an overly-cautious measure in the SAD1024 circuit (i.e. probably not needed) but in this MN3207 conversion there really is no point in having them at all, since the LFO is fed by a different regulator to the audio.

In fact, R33 should ***definitely*** be shorted.  That is because Vlfo (the supply voltage to the LFO circuitry) also feeds R26 for filter matrix mode.  R33 stops the regulator from keeping Vlfo at a steady value.   In other words, the LFO sweep will cause Vlfo to vary, that means that even in filter-matrix mode there will be a variation in the CV applied to the VCO. 
So unless R33 is shorted, filter matrix mode will have a small sweep.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 28, 2020, 06:59:56 PM
I corrected the schematic to show changes to the regulator section, and replaced "Vlfo" with "Vdd".

(https://i.ibb.co/myJqgBB/18-V3207-topublish-simplifiedreg.png) (https://i.ibb.co/myJqgBB/18-V3207-topublish-simplifiedreg.png)

EDIT: I have updated the build document too.
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: Aurae on May 29, 2020, 04:19:33 AM
Ok I MP you :)
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 29, 2020, 04:43:54 PM
I have updated the build document information on setting the clock trimmer.
Aurae kindly provided measurements of the sweep behaviour of his V2 EM (1ms to 12ms when Range Pot is at maximum) and I was
pleased to find I had the same sweep on my MN3207 build :)
To set clock trimmer, FM mode with Range pot at maximum should give clock (measured at pin 2 of BBD) of 42.55 kHz (about 23.5 uS period).
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on May 30, 2020, 12:03:06 AM
I found an error in the schematic at the very start of this thread (a wrong component value).
I didn't correctly document what I had actually built with the SAD1024 circuit, and that schematic error then made it into the MN3207 design and build.

In the MN3207 schematic, R21 should be 5k1 instead of 5k6.   This change affects required component values in other places, namely the ratio of R32:R31.   So the MN3207 circuit needs the following two resistor value changes:

R21:  5k6 --> 5k1
R32:  220R --> 180R

If anyone has already done a build, then those changes can be made by adding resistors in parallel to the old values.
    5k1 ~  ( 5k6 || 56k ).
   180R ~ ( 220R || 1k ).

With these 2 resistor value changes (and a clock trimmer readjustment), the sweep range on my build with Range pot at maximum goes from 1ms to 12 ms as before.  So why make the change?
The difference is that with the Range pot at minimum, it will now sweep slightly higher (i.e. under 1ms) which is what happens with the original V2 EM.  Using a value of 5k6 would not let that happen.

I won't keep posting schematics. I will just update the schematic and parts list in the build document:

https://1drv.ms/b/s!AvrH61utWEtEjig_4U8k7-fGwkbv?e=69cQg1 (https://1drv.ms/b/s!AvrH61utWEtEjig_4U8k7-fGwkbv?e=69cQg1)
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on January 17, 2021, 03:09:15 PM
Here's a vero layout of the latest version (Revision 7) in the build document (https://1drv.ms/b/s!AvrH61utWEtEjjKUFA56edLu66rO?e=KWptlq (https://1drv.ms/b/s!AvrH61utWEtEjjKUFA56edLu66rO?e=KWptlq)).
Note some tracks near ICs are broken between holes rather than on holes.
The easiest way to make those breaks is to use a sharp knife to make two close parallel cuts and then lift out the bit of copper in between.
It's also a good idea to keep the two tracks to the Rate pot really short rather than have them as long strips.

(https://i.ibb.co/cgp8W0D/EMV2-Vero-C.png) (https://ibb.co/M2j1zrM)
Title: Re: 18V Electric Mistress with reworked LFO & VCO
Post by: DrAlx on January 19, 2021, 03:26:48 PM
Oops repost