MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

Better circuit choices for Silent Way AC Encoder
MUFF WIGGLER Forum Index -> Expert Sleepers Goto page 1, 2, 3, 4, 5, 6, 7  Next [all]
Author Better circuit choices for Silent Way AC Encoder
os
Since I published the details of the circuit I'd been using with Silent Way AC Encoder (http://www.expert-sleepers.co.uk/siwaacencoder.html) various people have written in with suggestions for improvements, so I thought I'd sit down and properly try them out. (A big thanks to everyone who wrote in, by the way.)

All tests were done with my Metric Halo Mobile I/O 2882 interface and an Analogue Systems RS-95 VCO.

The original circuit
This one:
I measure 8V at the output when not plugged in to anything, and get about 7 octaves of calibration.

(You'll see therefore that I have a bit of a problem with the remaining tests - 7 octaves is about as much as I can hear, and 8V is not far off the supply rails of the modular, so I can't really expect much improvement in my own setup. However, the results should be useful for those with interfaces with less output.)

An even simpler version
It was pointed out to me that one of the diodes (pick one, doesn't matter) is redundant in the circuit above. To test that theory I removed the diode from the TRS ring and left it floating. Exactly the same results as above - so yes, you can do the same thing with just one diode.

Just as simple, double the voltage
It was also mentioned that connecting the TRS shield to the TS shield is a possible source of ground loops. Moreover, the above circuit isn't taking advantage of the balanced output's full voltage swing.
So, I tried a basic half-wave rectifier (see http://www.play-hookey.com/ac_theory/ps_rectifiers.html) using the TRS's T & R as inputs, leaving the shield unconnected. So like this image, but with the capacitor as above across the TS plug:


(Side note: from here on I did all my soldering at the TS plug end, leaving the TRS shield in place to actually be a shield down the length of the cable.)

Using this circuit I measured 16V on a disconnected lead, as expected. This is clearly a no-brainer improvement over the first circuit above.

Bridge rectifier
For completeness I also tried a bridge rectifier (same link, http://www.play-hookey.com/ac_theory/ps_rectifiers.html).

The results were the same as for the half-way rectifier - 16V.

Voltage doubler
Now this is a very interesting circuit: http://www.play-hookey.com/ac_theory/ps_v_multipliers.html

I made that, and true enough, I measure 32V on a floating cable! Now that's a potentially dangerous amount of voltage to be putting into a modular, so I adjusted the 'Max Out' setting on Silent Way AC before proceeding with calibration tests.

As noted above, 32 octaves or even 12 octaves just isn't a feasible thing to hear or measure. I will say though that with this setup I measured the actual voltage on the cable when under load i.e. plugged into the VCO, and I was able to get that comfortably up to +12V.

So, for those who've been reporting only one or two octaves of calibration, do try this circuit - it's only one more capacitor than the first one, and really does double the voltage.

Let us know how it goes!
os
In case anyone wanted to try the new options, but wasn't sure how to translate the circuits above into cable wiring, here are some diagrams:

Half-wave rectifier:



Voltage doubler:

jenamu6
This is great..........I still have to try mine out.
Arnoid
I checked the voltage doubler circuit now i'm getting 4,60 V at max smile
Almost 5 octaves smile

First I had 2,84 V at max...
Arnoid
I just made a voltage tripler circuit hihi


Now i'm getting 7V !!! at maximum...
Solid tuning over 7 octaves It's peanut butter jelly time!
os
applause
rv0
Arnoid wrote:
I just made a voltage tripler circuit hihi


Now i'm getting 7V !!! at maximum...
Solid tuning over 7 octaves It's peanut butter jelly time!

applause thumbs up

incredible
Klipspringer
I made both the voltage doubler circuit and re-did the original circuit with the new suggestions.

Maximum output with the new half-wave 5.6 Volts.

Voltage doubler is, well double, 11.2 volts or so.

The original design gave me a max output of about 1.5 Volts. Seems to tracks OK now using the buffer of my MX61 into both the AsOL VCO-6 and ASol VCO-RM.

I've tried .22 uF and .1 uF caps. Seems to be good with both values.

This is with my FA-66. So it's tested and it works OK. Now I gotta buy Silent Way like I promised!

I think this needs a little box with maybe a variable cap or dip switches to select different capacitance (as that seems to be the variable for audio interface).

Sell it for maybe $39.95 applause
Johnisfaster
Klipspringer wrote:


Sell it for maybe $39.95 applause


I'd so buy that!
lombrose
How did you guys make the tests?


hmmm.....
oootini
hi guys. this all sounds totally amazing...
lombrose
Tested with m-audio lightbridge and presonus digimax fs, the original circuit, same as OS - 8v!!!


we're not worthy
SlayerBadger!
PolishMilk
I decided to have a go at this using a Focusrite Saffire audio interface. Put the voltage doubler circuit together on a breadboard using 0.1uf capacitors and 1N4148 diodes.

I'm pretty sure I put it all together right, but when it came to testing it on my modules it didn't work quite correctly. The voltage increases fine but when it comes to decreasing it gets stuck. So for example with an lfo on pitch cv it would reach the peak of the signal but never go down again.

However when I put my multimeter across the tip & sleeve of the output to measure voltage it does go down and the circuit behaves as normal, but only while the multimeter is touching. I decided to try putting a resistor [a large range of values work] between tip and sleeve of the output and hey presto it works fine. I get about 2.7v max output (even with the doubler circuit, so the interface presumably has a fairly rubbish output level) and good tracking for just over an octave.

So basically does anyone know what weirdness is going on here? Why do I need a resistor across the TS output to get the circuit to work properly? Anyone had any similar problems?

*Edit* It also does exactly the same thing using the original circuit and the half-wave rectifier
sgnelson
PolishMilk wrote:
I decided to have a go at this using a Focusrite Saffire audio interface. Put the voltage doubler circuit together on a breadboard using 0.1uf capacitors and 1N4148 diodes.

I'm pretty sure I put it all together right, but when it came to testing it on my modules it didn't work quite correctly. The voltage increases fine but when it comes to decreasing it gets stuck. So for example with an lfo on pitch cv it would reach the peak of the signal but never go down again.

However when I put my multimeter across the tip & sleeve of the output to measure voltage it does go down and the circuit behaves as normal, but only while the multimeter is touching. I decided to try putting a resistor [a large range of values work] between tip and sleeve of the output and hey presto it works fine. I get about 2.7v max output (even with the doubler circuit, so the interface presumably has a fairly rubbish output level) and good tracking for just over an octave.

So basically does anyone know what weirdness is going on here? Why do I need a resistor across the TS output to get the circuit to work properly? Anyone had any similar problems?

*Edit* It also does exactly the same thing using the original circuit and the half-wave rectifier


I have a Focusrite Saffire LE and I've had problems with mine as well. Mine would decrease, but it wouldn't track for damn, and it was always incredibly unstable (like someone using a modwheel as fast as they could), and horribly out of tune.

That was using the original designed cable with both a 1uf and .22 capacitor. I haven't messed with it much in a few weeks, but I may try your resistor trick and see how that works, along with using the doubling voltage trick as well.

What value resistor did you use?
os
PolishMilk wrote:
Why do I need a resistor across the TS output to get the circuit to work properly?

The capacitor does need a discharge path. Normally this is provided by whatever it's plugged into, but in your case you seem to be dealing with a module with a very high input impedance. What modules are you testing with?

2.7V is an astonishingly low output from the doubler circuit. Have you tried measuring the AC voltage output from the Saffire in normal use (e.g. when outputting audio)?
PolishMilk
sgnelson wrote:

That was using the original designed cable with both a 1uf and .22 capacitor. I haven't messed with it much in a few weeks, but I may try your resistor trick and see how that works, along with using the doubling voltage trick as well.
What value resistor did you use?


I tried all the resistors I had (from a lucky dip multipack) and every one of them worked in terms of fixing the voltage decrease problem, but each one gave different tracking behaviour. Some would give me no tracking at all and some would give me an octave of tracking that started half way through the octave. I eventually settled on quite a small value (though I forget what that value was - I'll have to look when I get home) but this gave me totally different tracking behaviour when I changed the tune pot on my module. Was very confusing so I just settled on the small range I could get it to work in!



The module I was using to test on was an Analogue Solutions VCO-Sub. Makes sense about the high impedance, I can also try it on my Arp Axxe tonight to see if that helps - I didn't use it earlier because I didnt want to zap my baby if things went wrong!

Actually I've just thought - I had a bit of an odd setup with my TS wire because I didn't have a spare 1/4" to 3.5mm cable/adaptor. I had a TS 1/4" to RCA adaptor followed by an rca cable followed by an rca to 3.5mm jack! Could this be causing the high impedance?



I was surprised about the low maximum voltage of 2.7 too. I haven't tried measuring the normal output yet but I will when I get home tonight. According to the specs of the interface from the internet -
Nominal output level 0dBFS = 16dBu, electronically balanced
Which is fairly reasonable?
bsmith
Does capacitor choice not matter as much if using the half-wave rectifier or voltage doubler or will there still be an optimal choice depending on the interface?
os
Capacitor choice still matters.
PolishMilk
Finally got my problems solved. The low output was a stupid one - there was a toggle on the software mixer for the audio interface that was dipping the volume of the output for some reason (I bought the interface new for use with Silent Way so didnt know how to use it!) With that sorted I'm getting 6v with the half-wave rectifier, 12v on the doubler and 6 octaves of perfect tracking, so SW does work with the Focusrite Saffire.

The problem with the impedance does seem to be linked to the module I was using. The cables work fine on my Arp Axxe but when plugged into the Analogue Solutions VCO-Sub the pitch rises but never falls again.

Is there a better solution to this than just strapping a resistor across the tip & sleeve? Using the Axxe as a CV master for the VCO-sub has always worked fine so there must be a workaround?
os
PolishMilk wrote:
Is there a better solution to this than just strapping a resistor across the tip & sleeve? Using the Axxe as a CV master for the VCO-sub has always worked fine so there must be a workaround?

I think the resistor is the workaround. The Axxe might have a non-capacitative output (e.g. direct out from an op-amp) or might have a resistor across the output internally.

The better solution for all of this is to build an active AC Encoder interface circuit - that's still on my plan, but it will be a while before I have time to try it properly.
bsmith
I got one of the rean send/return boxes detailed in this thread:
https://www.muffwiggler.com/forum/viewtopic.php?t=11494
It works great for my lexicon mpx500's two outs, but I'd love to use it as well with with the ac encoder - it'd be nice having all the silent way stuff come out of it. Trying one of my soldered cables which works on its own I'm getting nothing when trying to run it through the box - have tried variations on different adapters, etc.. but am not getting signal through it using ac encoder/special cable. Any suggestion on how I could get this to work?
os
How exactly is your AC Encoder cable wired?
bsmith
Half wave rectifier
os
Is the box simply a passive set of sockets all wired up, or is there more to it?

Is it somehow shorting the cable ends together (because it's expecting a TRS input)?
bsmith
It's passive, I peeked inside it hoping I could just use it as a shell to ac encoderify it, but it has a little pcb for each channel with the send/return stuff on them. Yeah, I believe that it is expecting TRS. So to clarify, I'm wanting to find out what the cable would look like between the interface and this box - how would this be wired?
MUFF WIGGLER Forum Index -> Expert Sleepers Goto page 1, 2, 3, 4, 5, 6, 7  Next [all]
Page 1 of 7
Powered by phpBB © phpBB Group