Deluxe Electric Mistress trimpots: help!!!!

[Plexi]

 Advertisement: I haven't oscilloscope!

So... Years ago I've bought this great flanger from an a**hole that screwed up all the trim pots, breaked the switch, cuted cables, etc...
I repaired it and tried to get back the trimpots to the best position.

I've readed a lot of threads about it, even this: http://www.metzgerralf.de/elekt/stomp/mistress/align.shtml#4
But, I'm far from somebody that have a oscilloscope

Anyone had the same experience?

Can anyone share the stock trimpot values?

I know that there are no set positions, each is adjusted to the correct values for each individual pedal.
But, I think some value can leave me closer.

[DrAlx]

You don't need a scope to set the clock trim. You can do that by ear.

http://www.diystompboxes.com/smfforum/index.php?topic=91981.msg1047491#msg1047491

You can do BBD bias by ear too. Bias pot too far left or right will stop the sound going through the BBD. So you just twiddle the pot to find those two extremes and set pot half way. Then play notes. If the are distorted, tweak a bit more left or right till distortion is gone.

Feedback pot is set to prevent the thing oscillating when color is high. You set of so there's is no oscillation at max color for all possible range values in filter matrix mode.

I would set BBD bias first.
Then clock trim.
Finally the regent/feedback pot.

[Scruffie]

As a very rough guide to do it by ear, set it to the filter matrix mode, feeback at half way, range all the way up, rate down.

Set all the trimmers to 50%, to start with and then feed an audio source (guitar, mp3 or whatever but it will need to be continuous) in to the pedal and adjust the bias trimmer until you hear the delay signal passing, it should have a small range where it works and then tweak it for the least distortion (if you have an audio probe, probing the output of the BBD will make this easier to hear) if you encounter oscillation, back off the feedback trim a little.

Then if you have a multimeter with a Hz setting, probe pin 1 of the 4013 and adjust the clock trimmer for 40kHz, if not, you'll have to adjust it to where you think it sounds best (delay sound not too sproingy or noisy) and tweak it as needed after you finish setting up.

Next adjust the mix trimmer, you'll want to turn the feedback control all the way down now and this is where an audio probe would be very useful (instructions to build one are in the debugging page tab above) and adjust for a 50/50 mix of dry and wet signal at the output.

Finally, turn the colour control all the way up and adjust the feedback trimmer until just before the point of oscillation.

Or do it how DrAlx posted while I was writing this

[Plexi]

Wow.... you guys are genious!
With all your advises, ASAP I get home, I'll try.

I'll use the note between C# and D, in A string.

Thanks a LOT!

[Plexi]

To update!
Ok ... I made the alignment with his advice.
The pedal works fine now!

Conclusions:
- BBD bias: it is where it stops sounding, and where to make the sound "distort" a bit. But I'm not sure; It did not distort in much rank. There is no fixed value / voltage for this?
- Setting the clock: put a bonnet on the 4th fret, and slightly adjust to the peg to get that C#/D in between note. Hit with a screwdriver the pickup and tune the trimpot with the string note.
- Mix: all the way up... what the hell... 
- Feedback: Colour at max, and set where the oscilation stoped.

I have my doubt's with the BBD bias....
It's like the college exams where all the exercises are related; and if you fail the first one, all the others are wrong. Even if you make that right. 

[DrAlx]

If the BBD bias is turned totally clockwise or totally anticlockwise you will get either nothing through the BBD or distortion. There is a small range of  trimpot settings somewhere between those two extremes that works best and let's the signal through with minimum distortion.
If you had an oscilloscope you would input an audio sound wave, either sine or triangle, and then turn the bias pot to the position that gives the least distorted output wave.  You don't have a scope so have to use a combination of your eyes (by looking at the angle of the trimpot setting) and you ears (to listen for distortion).
To give the signal the best chance of making it through the circuit undistorted, you need to set the color (feedback) to minimum, use filter matrix mode. Also put the range pot near the middle so it is not at an extreme setting. Play a clean guitar signal into the pedal. There will be a small range of bias settings where the signal out of the BBD will sound OK. E.g. if you from find that the bias sounds OK for bias pot angles between 4 o'clock and 6 o'clock then you would put the bias at 5 o'clock.

[Plexi]

Thanks again Alex.
This afternoon I'll put my amp as loud and clean as I can, and make it the most accurate as possible.

I'll keep you informed 

[StephenGiles]

If the BBD bias is turned totally clockwise or totally anticlockwise you will get either nothing through the BBD or distortion. There is a small range of  trimpot settings somewhere between those two extremes that works best and let's the signal through with minimum distortion.
If you had an oscilloscope you would input an audio sound wave, either sine or triangle, and then turn the bias pot to the position that gives the least distorted output wave.  You don't have a scope so have to use a combination of your eyes (by looking at the angle of the trimpot setting) and you ears (to listen for distortion).
To give the signal the best chance of making it through the circuit undistorted, you need to set the color (feedback) to minimum, use filter matrix mode. Also put the range pot near the middle so it is not at an extreme setting. Play a clean guitar signal into the pedal. There will be a small range of bias settings where the signal out of the BBD will sound OK. E.g. if you from find that the bias sounds OK for bias pot angles between 4 o'clock and 6 o'clock then you would put the bias at 5 o'clock.

That's the way I used to do it.

[Plexi]

So, I have good news.
I think I finally have it.

But there's something that I noticed: the sound start when I pass the half way on BBD bias trimpot.
Totally clockwise: distort a lil' bit.
Half way, to totally anticlockwise: clean sound.

I mean: 50% no effect, 30% the same good effect, and the last 20% a bit distorted.
So, as you recomended, I leave it at the halfway of the good effect sound, it is at 2 hours, like in this pic:



As I can figure out, the most critical one, is the fine tuning clock.
Now, I feel the flange is like "armonic".

I'll keep playin it this days and see if they're fine 

Thanks a lot!!!

[PRR]

> 50% no effect, 30% the same good effect, and the last 20% a bit distorted.

Play louder (more signal IN to the Mistress). The "30% the same" will now show some distortion. Trim for largest signal with least distortion. It isn't critical, but there will be about a 10% span that is "best". It will very-likely be just about the center of your "30% good" range, so you could just center there and get on with the music.

[Plexi]

> 50% no effect, 30% the same good effect, and the last 20% a bit distorted.

Play louder (more signal IN to the Mistress). The "30% the same" will now show some distortion. Trim for largest signal with least distortion. It isn't critical, but there will be about a 10% span that is "best". It will very-likely be just about the center of your "30% good" range, so you could just center there and get on with the music.

I'll try again as louder as I can 

[Fenderstratocaster0]

Hi Everyone.

Brand new to the forum and I didn't want to start a new post as I feel like the knowledge from the members posting to this topic can help!

I have a 1978 DEM Version 1 with an issue I believe is trimpot related (but could be wrong).

Here is the issue:

When the effect is engaged and the Flanged Output is being used there is an audible loud hum sound. However every 10 seconds or so, it goes away and the beautiful flanger sound comes through for a split second before the hum returns. The best way I can describe it is that the effect is not audible and the dry signal is heard for 10 seconds of playing and then for an instant the wet signal kicks is and the loud hum stops before reverting back.

I am by no means knowledgeable about these but I have checked all the connections for soldering breaks or bad connections etc. Everything internally appears to be in place.

Would anyone know specifically if a trim pot adjustment to a certain pot would be the correction?

When I adjust the bottom knob I am able to adjust the duration of time between the non Flanged sounds with the hum and the effect kicking in super briefly.

It's almost like the effect is being blocked from coming through and then the connection aligns for a split second and repeats on a cycle.

Please help!!!

[Rob Strand]

When the effect is engaged and the Flanged Output is being used there is an audible loud hum sound. However every 10 seconds or so, it goes away and the beautiful flanger sound comes through for a split second before the hum returns. The best way I can describe it is that the effect is not audible and the dry signal is heard for 10 seconds of playing and then for an instant the wet signal kicks is and the loud hum stops before reverting back.

Given the clean signal is coming through and it goes noisy when there is no wet signal I'd be looking at things that go open and float in the wet signal path.    The biggest suspect would be the 1k bias trimpot.    Usually you don't get enormous amounts of hum when something on board goes open.

[Scruffie]

I don't think it's a trim pot issue, with a trim pot i'd expect hiss, whine or distortion.

Hum to me suggests you have a/some bad caps, they're 40 years old now after all and have a limited life span, i'd start with the two large caps in the power section before moving on to the audio path.

[Fenderstratocaster0]

Thanks to you both for the quick replies!

I guess before I start to take stabs at anything would the caps be able to temporarily work for a split second and then revert back??

I'm probably explaining it poorly but when the pedal effect  is engaged an audible hum is present which I know these older pedals were louder then modern but the part I am puzzled with is that after 5-10 seconds the hum stops and the flanger sound kicks in for a super short instant and then reverts back to the non Flanged signal and the hum.

My understanding is the Caps would be continual hum regardless and the effect would be audible the entire time?

I was guessing trimpots since the effect is present albeit briefly for that split second on a regular interval. I read somewhere that the position of certain trimpots can block the signal entirely from coming through.

I unfortunately do not have an oscilloscope but i also don't want to send it for service of $100 upwards if it's a simple fix by tweaking a trim.

[Scruffie]

Does the problem change with the rate setting? And have you measured the voltage from the regulator to make sure it's correct & steady.

[Fenderstratocaster0]

Yes. When the rate setting is changed the intervals of time between the hum and non Flanged sound and the instant of no hum and Flanged effect either shortens or lengthens depending on which way I turn it.

So might be 10 seconds of non Flanged signal and hum and 1 second of Flanged no hum at the longest range. And when I turn the knob the other way it's probably 3-5 seconds of non Flanged signal and hum and 1 second of Flanged no hum.

So the period of time the effect is working is unchanged (milliseconds) but the duration of time between when it kicks in and out is shortened or lengthened.

I have a multimeter but was having trouble locating the voltages for the ICs to validate each Pin correctly.

[Scruffie]

Ah, that sounds like it might be the 1uF tantalum cap off pin 2 of the 311 in this schematic then http://www.metzgerralf.de/elekt/stomp/mistress/images/deluxe-electric-mistress-v1-schematic.gif

As long as the 78L15 regulator has a steady 15V on its output pin, it's fine.

[Fenderstratocaster0]

These are the readings on the output pin. There were 2 and I'm not sure which one it would be. The reading on the first was steady at 16v. The second was all over the map between 1-3 and changed constantly.

I also pulled the 2 chips and reset them in the plugs as some suggest it can be loose but that didn't help.

The 3 potentiometers are all functioning as i can hear the changes to color and range and rate.

[thermionix]

If it still has the original 1978 electrolytic caps, I'd say it's overdue for a new set.

Edit:  Sorry, already suggested, I should read instead of skim.