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    Another volume pedal question

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    Raf0419

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    Another volume pedal question

    Post by Raf0419 on Fri Dec 25, 2015 9:58 pm

    Good evening and Merry Christmas folks!
    I'm a noob. Still learning a ton. I purchased an optical volume pedal (Morley Little Alligator) and am trying to run it through channel 1 of my FSM-432. Ithe pedal works normally going through the front of the amp and I've not yet tried it theoigh the FX loop. At any rate, it's operating as an on/off style switch rather then providing the linear sweep these pedals are known for. I tried settings 56,57, and 75. Option 7 seems to to work the best. All operate similarly in that they do not sweep. Any ideas as to what I'm doing wrong or is it just the nature of this type pedal? Thanks in advance!
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    bordonbert

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    Re: Another volume pedal question

    Post by bordonbert on Sat Dec 26, 2015 11:08 am

    Hi Raf.  Merry Christmas to you and yours too.  I don't have your pedal so I can't be absolutely definitive but the idea is simple.  Here are a couple of points to think of.

    Your pedal has a mono in and mono out setup whereas the FSM requires a single stereo input for each of its channel controls.  How are you connecting the two?  You would need a splitter cable with the tip and ring each brought out to their own mono jacks.  The idea is to put a fixed DC voltage across the "pot" and to tap off a steady DC voltage from that to feed back to the FSM as a control signal.  The fixed DC voltage is supplied by the FSM across the sleeve and ring, while the signal voltage fed back is from the sleeve to the tip.  (The sleeve is the common reference, it may or may not be a true ground).

    The FSM says it needs to see a pot in the range of 25k-50k.  I've tried it with 100k and I found the results were very poor, similar results to your own.  I suspect your Morley may be a lot higher resistance than that as it is intended to be able to plug the guitar straight into it and you can't load that down with too small an impedance.  That means it should be above 500k at least, 1M would probably be better!  If that is correct then you will find that you have a bad mismatch and the results will be completely off the wall.  It may be that the Morley is simply not the unit for the job you need it to do.

    The optical approach that is used in the Morley basically has two light dependent resistors in series.  One is made to vary downwards as the other one varies upwards by lighting them up from LEDs while you vary the LED currents.  I'm not sure if there is a shutter arrangement inside as well to allow more or less light across.  Ideally the two LDRs should always add up to a constant resistance which stays fixed as they both vary together.  The changes in resistance will always be a little haphazard, it would be almost impossible to make them track each other as you would like.  This may make the overall resistance vary as the pedal is swept, perhaps not desperate but not what we would like.  I'm afraid there is no freely available info on the LDR that Morley say they use, M79-211564-000.  You can get replacements but not data!

    For reference, here is the schematic of the pedal just in case you don't have it already:

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    gravydb

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    Re: Another volume pedal question

    Post by gravydb on Sat Dec 26, 2015 11:52 am

    Yeah a few of us have been through this learning curve with the GM so I think we can help you out...

    You'll want an expression pedal (not a conventional volume pedal) if you're going to connect it to the FSM, and that's if you want to control any parameter including volume. However, don't expect it to behave like a conventional volume pedal, because it will control 0-100% of the volume knob (meaning, heel down = the volume knob being turned all the way down, and toe down = the volume knob being turned all the way up. It'd be nice if there was a way to set a max point but I wasn't able to figure it out. I tried a few different brands of exp pedals and eventually gave up.

    Alternatively, you can connect a conventional VP to the FSM using a Y-cable (one end being TRS and the two other ends being TS) but you'll still have to put up with the funny behavior as above.

    AFAIK, if you want a pedal that acts like a conventional volume pedal with the GM, you need to buy a conventional volume pedal, and put it either in front of the amp or in the fx loop. It's personal preference. In the fx loop, the pedal will act like a master volume, simply controlling the overall volume and not affecting gain. Before the amp, the pedal will control volume AND gain (no different than your guitar's vol knob).

    Personally, I want it to act as a master volume control. So, my VP in in the amp's fx loop. Be sure to use a LOW IMPEDANCE VP for this location (IE:25K) otherwise the swell taper will be funny.

    If you're going to put it before the amp, you should get the high impedance variety (IE: 250K) if it will be receiving a high impedance signal (such as the output from a guitar with passive pups).

    Hope this help!
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    Raf0419

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    Re: Another volume pedal question

    Post by Raf0419 on Sat Dec 26, 2015 12:01 pm

    Oddly my first reply seems fm have been lost....

    Bordonbert thank you for posting such an extensive and thorough reply. Currently I'm mono out from the pedal into channel 1 of the FSM. I will test the pedal in the fx loop to see how it behaves. I may also try splitting the signal into a stereo input just because I'm curious. I'll report back here.

    Gravy - thank you for the reply as well. Like you I'm looking for master volume control. I was really hoping this pedal could work, but if not, I'll go the low impedance route to satisfy my needs. Part of me wants to play with this stuff just to go through the learning process.

    Many thanks to you both!
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    bordonbert

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    Re: Another volume pedal question

    Post by bordonbert on Sat Dec 26, 2015 9:55 pm

    Gotcha Raf.  You can't get any sense out of it with just a mono connection!  The FSM MUST have a stereo connection as I described.  It has to be able to feed the maximum value voltage on the ring and take back the selection voltage (reduced) on the tip and these are both referenced (ground) on the sleeve.  You can do it with a jack splitter, 1xStereo->2xMono,  as I described.

    Glad you came in on this Gravy.  There IS an easy way to set up a maximum point as long as you start off with the right pedal in the first place.

    You just need to have a pedal with a 25k lin pot installed, the minimum resistance the FSM will cope with on its own.  You may get away with a little below that but it is a good starting point.  You can now add to it up to 25k additional series resistance taking it to the 50k maximum.  Let's say this is 2 x 15k pots, a little over but not much.  It doesn't matter if this is added at the top or the bottom of the pedal pot.  Any resistance added below the pedal will act to restrict how low the pedal can go, likewise any added above it will just prevent it from going all the way up.  You have a restricted range at both ends.

    So you could add a pot below the pedal to set the minimum (as is sometimes already done) and a pot above it to set the maximum.  When both trimming pots are set to 0 you have a full range 0-100% on the pedal at a resistance of 25k.  If each trimming pot is used exclusive of the other one they should have the ability to reduce the max or increase the min by about 37% at a resistance of 40k.  If they are both used together to their max values then the overall resistance is 55k, not too far over the recommended.  With the additional pots set for the most restrictive minimum and maximum levels at the same time you have a control range of about 27%->73%.

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    If you were prepared to go to a powered active pedal we could do much better than that as the various voltage levels could be buffered using simple transistors and you could then achieve much greater amounts of lift and reduction at either end as you are not constrained by the 25k-50k range of pots.  It's not complicated or expensive and would be much more flexible.  And no bleating from the "tone suck" crowd.  The buffers are on the DC control voltages only, the signal does not get touched by anything at all.
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    Raf0419

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    Re: Another volume pedal question

    Post by Raf0419 on Sat Jan 02, 2016 8:32 am

    Happy New Year!
    Just a quick update for those who may be considering this pedal. I tried the pedal in the fx loop with no success. The pedal did not work at all within the fx loop. Amp master volume worked just fine. It was so puzzling I triple checked connections. Given the excellent explanation by bordonbert I wasn't surprised, but I thought some odd clipping or an on/off type operation might be heard. Oh well. Que será será.

    Looks like I will review the expression pedal posts and go this route.
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    gravydb

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    Re: Another volume pedal question

    Post by gravydb on Sat Jan 02, 2016 4:24 pm

    This might be a dumb question so please do be offended - but did you make sure the fx loop is on? I can't think of another reason why a volume pedal wouldn't work in the amp's fx loop... assuming we're still talking about an actual volume pedal and not an expression pedal...
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    Raf0419

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    Re: Another volume pedal question

    Post by Raf0419 on Sat Jan 02, 2016 4:53 pm

    Hi Gravy- not a dumb question at all! I thought it was on, but I certainly didn't verify. Lol. I'll double check and report back. Thank you for pointing out what may have been a major oversight on my part!
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    Raf0419

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    Re: Another volume pedal question

    Post by Raf0419 on Sat Jan 02, 2016 8:05 pm

    Gravy you are the man! So here's what happened. I know because I did it twice. This evenings test began much like my first test. (What is it they say about doing the same thing repeatedly and getting the same result?)

    I turned on the GM36 and engaged the effects loop. I then dialed up different preset and completely ignored the fact that the preset didn't have the FX loop engaged. A quick engagement of the fx loop and I was back in business. Gravy thanks for pointing out that the fx loop was probably off and forcing me to pay attention. I can now report the pedal works rather well in the FX loop.

    Oh and by all means feel free to have a good laugh. I certainly did! Embarassed
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    gravydb

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    Re: Another volume pedal question

    Post by gravydb on Sun Jan 03, 2016 9:15 am

    Oh I'm laughing alright but only because I had made the same goofy mistake a while back. And probably more than once! I'm glad you have it sorted out. Yeah the fx loop on/off status is saved as part of the preset.

    I made a similar silly goof a couple nights ago at a live show. My band had soundchecked, and then we took our peripherals off stage so that the opening band could do a quick soundcheck. When they were done their show, in the rush to get all our gear ready, we overlooked the fact that my send/receive cables got disconnected from the volume pedal, and of course I wasn't getting any signal thru. Semi-panicked troubleshooting began and of course I'm checking everything: wireless, master volume, gtr volume, re-seating cables - and then I looked down at my board and saw the 2 stupid cables laying there Embarassed duh... If the fx loop is on and there's no device there - it no worky.... Wink
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    Raf0419

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    Re: Another volume pedal question

    Post by Raf0419 on Tue Jan 12, 2016 3:36 pm

    Side note - I decided to return the pedal. The sweep as it needed some adjustment, which wasn't a big deal. However after laying out my few pedals for a pedal board, I decided I would prefer something smaller. Also a quick thanks to Gravy for his volume pedal thread!
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    gravydb

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    Re: Another volume pedal question

    Post by gravydb on Tue Jan 12, 2016 6:15 pm

    Raf I can't remember if I had mentioned this but I'm using a Boss FV-30L and it's working well for me. It's very compact compared to a typical volume pedal, so much in fact it might take some adjusting too. I like it a lot.
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    Raf0419

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    Re: Another volume pedal question

    Post by Raf0419 on Tue Jan 12, 2016 7:32 pm

    Gravy- I read somewhere you were using that particular pedal and I was hoping to replicate. Thanks for saving me a hunt for the thread!

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