Circulator (rev.2) No Modulation

[djmiyta]

I'm getting basically a very slightly filtered signal when engaged. Turning any of the pots does nothing. Flicking the toggles does nothing> I'm getting voltage to all the IC's ( although I'm not sure what they should be) on all + supply pins I get 9v . I don't know how to check if the LFO part is working can anyone tell me how I can check if LFO section is working properly aside from using my ears?

 

[Mcknib]

All the VREF labels on the schematic should have the same or similar voltage to IC4.1 pin 1 which would be around half the power supply 4.5v ish all your VCCs 9v or whatever voltage you get at D100 cathode

The LFO output looks like IC3.1 pin 5 where you should get a varying voltage which you should also get on the rate pot check your LFO output with rate set around the middle of the pots rotation

When you flick the range toggle the range on the speed pot should alter going faster on the 1u side and slower on the 4u7 side

Post your voltages and some nice clear pictures so we can clearly see all component values and orientation and offboard wiring

 

[djmiyta]

All the VREF labels on the schematic should have the same or similar voltage to IC4.1 pin 1 which would be around half the power supply 4.5v ish all your VCCs 9v or whatever voltage you get at D100 cathode

The LFO output looks like IC3.1 pin 5 where you should get a varying voltage which you should also get on the rate pot check your LFO output with rate set around the middle of the pots rotation

When you flick the range toggle the range on the speed pot should alter going faster on the 1u side and slower on the 4u7 side

Post your voltages and some nice clear pictures so we can clearly see all component values and orientation and offboard wiring

Ahhh man thank you so much for replying . I have an up date - I found a mistake I made and fixed it (it happens when I rush it) pedals work better when then3pdt switch output lug is going to the tip of the jack not the sleeve. So now thats' handled I now get modulation happening but only when the sweep pot is being turned if Its not being turned its more filter/eq than anything. At least I'm getting signal in both directions of phase/vibrato toggle. I read the EQD manual for this and it mentioned the LED flashing out the tempo or rate. My build does no flashing. It lights up but the pots have no effect
I should mention though I don't think it matters but the 1 uf electrolytics I replaced with 1uf mlcc caps. I read the electrolytics can cause problems here’s pics and voltages coming up

 

[djmiyta]

Here’s my voltages and more pics I’m guessing IC3 voltages are different cause it’s doing something different than the other 13700’s Also the fact that the LED doesn’t flash I don’t know where to check for that

 

[djmiyta]

Odd. Re-reading what you said about Lfo IC3 pin 5 and varying voltage. ( I did not pay attention to pot and toggle positions) I now set the rate about midway and the only fluctuation is 3.9v to 4.0v at random times . By turning the sweep pot the voltage will go from 3.9v to 4.6-7v on pin 5 of IC3

 

[Coda]

This PCB only is one LED (pedal on/off). The current EQD version has a rate indicator LED, in addition to the on/off.

 

[Mcknib]

Can't see it clearly is C14 the wrong way round or is it bipolar + should go to the top

 

[djmiyta]

Can't see it clearly is C14 the wrong way round or is it bipolar + should go to the top

Sorry I should check my pics better before uploading and thank you for taking a look. I will double check C14 and report back. Should I upload more pics?

 

[djmiyta]

yes C14 is the right way. Do the voltages seem ok?

 

[Mcknib]

Most look pretty good to me ICs 4 and 5 look fine

I'm not an authority on OTAs or OTA based phasers so your phase stages ICs 1.1, 1.3, 2.1 and 2.3, I'm not 100% on, most again look good to me you can see the pins labelled VREF you're getting close to or exact VREF 4.54v

I'm unsure on what voltages you should get at the output pins perhaps someone with a working one can give you expected voltages but I'd assume they're ok if everything else is

Your PV switch position would affect your output obviously cutting the dry signal in one position

Is C8 100pF it looks the same as your 1u MLCC caps

I'd maybe change C4 that looks like it's took a major iron hit and although R8 looks the worst for wear IC1.1 pin 4 voltage indicates its ok but I'd double check voltage both sides of it anyway

 

[Stickman393]

Kinda sounds like the LFO isn't starting. From what I've read, if this is the case, it's a design issue with the original eqd circuit that relies on a leaky electrolytic to get it off the ground.

@Chuck D. Bones has a great mod thread in the boneyard, good read:

MODIFICATION - Teaser: I've got a Circulator mod in the works

I breadboarded the Circulator and it's a great sounding phase shifter, but there are a few opportunities for improvement. I've changed three of the pots, ditched the P/V switch, added a Throb LED and most importantly fixed the LFO so it will always start & never stall. Straightened out a...

forum.pedalpcb.com

 

[Chuck D. Bones]

Try connecting a 22K resistor from IC3-8 to GND and a 3.3M from IC3-1 to Vref (IC4-1). See if that gets the LFO working.

 

[Chuck D. Bones]

At the beginning of this thread, you said "Turning any of the pots does nothing." Let's revisit that. Put the P/V switch in the P position, turn DEPTH and RES to max. Rotate the SWEEP pot quickly back and forth. Do you hear any phasing?

C13 and C14 have to be low leakage for the LFO to work reliably. I prefer tantalum. The board needs to be cleaned; flux reside can create leakage paths which can mess up circuit operation.

Where did you get your LM13700s? If they are even a little bit out of spec, that could mess up the LFO.

 

[djmiyta]

Ahh just reading this and I think you already onto something I did replace several caps (the 1uf electrolytics which I thought I read caused problems with the circuit I’m not home at the moment so I’m not sure exactly which ones thank you very much for responding I’ve quite a few things you’ve written and really appreciate it Did you do some work with or on the Tight Metal and write some stuff up about it ? Well it was a pedal I was building at the time and your stuff helped me a lot it was on another forum a couple years back
As soon as I’m home I’ll get on it thank you again

 

[djmiyta]

That flux can mess up the circuit is something I would have never thought of .Funny and sad I just cleaned a board for the 1st time ever it definitely helps to see better that kind of info is priceless to me thanks

 

[djmiyta]

Where did you get your LM13700s? If they are even a little bit out of spec, that could mess up the LFO.?




Damn I really gotta slow down missed this so I got them
through
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M
A
Z
O
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And Tayda neither the most reputable when it comes to semi conductors not the worst either since I have used both successfully in other builds probably cause the circuit was more tolerant to out of spec stuff

also I have one of those cheap transistor , FET , JFET tester would that tell me cap leakage? is that known as SRS?

I came here real quick just to make sure I got all the suggestions right and here I am getting stuck on this forum but that's not a bad thing hey thanks for the people let's see how it goes

 

[Chuck D. Bones]

Amazon's a big marketplace. I've bought some working LM13700s there, but I don't know if it was the same supplier as you. Got some good ones from Tayda and Mouser too.

Not familiar with the term "SRS." My CCTT measure capacitance and ESR, but not leakage. You need to test them at something near their rated voltage to measure leakage correctly.

 

[djmiyta]

so cap leakage isn't an easy thing to figure out I get the feeling. Probably best I just get tantalum caps you think? and yes I meant ESR thinking it might be related to leakage.

 

[Chuck D. Bones]

You can review the datasheet to find out the leakage spec for the caps you have.
You can measure the leakage with a DMM and a power supply.
Or you can go the easy route: buy tantalums and don't worry about it.

Tantalum caps are polarized, so observe polarity when installing them.

 

[djmiyta]

I finally got tantalum’s and replaced c13 and c14 they are installed correctly and still no automatic phasing so my last guess would be my lm13700 are suspect seeing that I did the mods gonna be a PITA swapping them out .