EQD The Depths

[Plexi]

Hi forum!

Anyone?

Schematic:
http://i.imgur.com/8R4keTO.png

http://1.bp.blogspot.com/-Zog3lZeCRD4/WHf_9OLLaCI/AAAAAAAAEgQ/zuHk_dgB_MYwJJsgP02cUjo6ZlhxkSejgCK4B/s1600/EQD%2BDepths.png

I finished it yesterday.

I do not know why, but it didn't work fine.
Sometimes led don't blink, and when it blinks, the effect is weak.

Due that I didn't find any MPS18, used sockets and tried every kind of NPN there.: MPSA13, 2N4401, BC548, 2N3904 ... but not MPSA18.

That's the problem?

[GibsonGM]

Dude - is there an actual schematic available?  Layouts don't tell a whole lot.   

Not seeing any reason why your other tranny's wouldn't work the same as the MPSA18...

[Plexi]

My bad!
I thought I had put it on the first post.

Here it is!
http://i.imgur.com/8R4keTO.png

[GibsonGM]

Ok, well - look in the LFO section around the transistors - the LED should blink reliably!  Something loose, etc....

As for weak - was there a specific LDR to be used? That can make a difference, if so.   How the "vactrols" were made (shrink tube?)...also, the depth ("intensity" here?) control might not be biasing the LED enough (?)

I'd 'fix' the LFO first, see if that helps!

[Plexi]

Thanks GibsonGM

I used 5mm ldr's, and red LED.
Didn't used shrink tube, just the four ldrs facing to the LED, and then black tape to avoid any light when I check for problems.

I noticed something, when plug in the sockets any transistor, at Q1, the LED start to blink very strong a few secs... then it stop, and start to blink weak.

[ElectricDruid]

Starts off blinking then stops blinking sounds like something charging up to me. I'd check all those electrolytic caps in the LFO section and make sure they're the right values and the right way around.

HTH,
Tom

[Kipper4]

Without breadboarding the PSO it's hard to say for me if it would stall or not.
The PSO looks a bit weird to me. I feel sure though that EQD would have done their homework so as the others say check your connections. Non polar 1uf caps might help?

[GibsonGM]

Thanks GibsonGM

I used 5mm ldr's, and red LED.
Didn't used shrink tube, just the four ldrs facing to the LED, and then black tape to avoid any light when I check for problems.

I noticed something, when plug in the sockets any transistor, at Q1, the LED start to blink very strong a few secs... then it stop, and start to blink weak.

What the others said, re. performance of the LFO.

The depth issue may be how the LEDs are just 'facing' the LDR...might need to put them in a film can or find out if this is how the designer intended it.  Best results I've had have been 1 LED per LDR, inside shrink tubing, touching each other....but this depends on the design...

[Kipper4]

^yep that.
Before now I've used an 8pin dip socket to mount the ldrs. (IIRC it was a 4 stage phaser)

So the led goes down the centre cavity of the dip socket.
the 4x ldr's each have a leg in the sockets. (soldered in)
Then I've heat shunk wrapped the whole thing with some wide shrink.

It depends on the application and layout.

I've also done dual LDR ,single led vactrols    just on the pcb No heatshrink.
It's confined in the box after all. you might have to consider the effects of a bypass indicator led shining back in the box though.
Maybe use black epoxy or silicone sealant or a sharpie to dull the underside inside the box.

Needs must.

[ElectricDruid]

The on/off resistance of your LDR is going to have an effect here too, and that's by no means the same between LDRs. In this circuit it'll shift the frequency of the phaser notch, and it could easily shift it to somewhere you won't hear it much (sub-bass, or high treble) if the resistance isn't right. You might need to adjust the related capacitor value to compensate.

HTH,
Tom

[duck_arse]

I noticed something, when plug in the sockets any transistor, at Q1, the LED start to blink very strong a few secs... then it stop, and start to blink weak.

this suggests to me that one leg of the pso is not grounded right, or has too high a resistance to ground. check very carefully the resistances to ground from C8//C9 and C8//C12. try turning the rate pot to one extreme or the other before powering on. once the osc "dies", turn the pot all the way opposite, see if it starts up again (gradually).

make sure your dual-pot connections are sane, they should both sweep higher/lower resistance together, not opposite. changing the 1uF caps for polys might also help.

I also think that circuit is drawn wrong, because the rate pots will go to 0R across the phase-shift network, stopping the osc EVERY TIME. that's if I'm reading the dia right. the pots should have a stop resistor between them and ground (the 3k3 would suffice), and that string should be parallel across the 220k's slung between the caps and ground. see R.G.'s univibe oscillator diagrams.

[Plexi]

Thanks guys for all your help...!
That's why I love this forum

As soon I get back home, I'll check all your suggestions.

Thanks again

[Plexi]

Ok, here's some update.
First of all, I would like to say that I'm checking carefully every advise you guys suggest (thanks a lot).

I swapped the transistors for the most closest hfe to MPSA18 that I have: BC109 and 2N2907, and it works better in many ways.
Still haven't the regular working, and rarelly stopped.

I'll keep working on.
Thanks again!

[sominka]

Please note. The 150n cap on the layout should actually be 15n which is what is shown on the schematic. I finished building this a couple of days ago using the layout from the perf and pcb layouts  site and it works really good.
I used a 10mm red led and bent the LDR's to face it after soldering them in position. LDR's were just some random ones I had in stock but measured roughly 1K in the room light I was working in.

MPSA18 for the transistors and check you have all the jumper leads in place on the board if using the pcb layout.

Hope this might help.

[thehallofshields]

Is this thing any different from a standard Phase Shifter?

[ElectricDruid]

Is this thing any different from a standard Phase Shifter?

No, not really. It's the standard phase stage circuit, done with LDRs as the variable element, as many others have been. Some use FETs in this same position. It's about as standard as it gets, TBH.

Edit: I don't mean that to sound like a criticism. Just to be clear, some of the reasons that circuit is widespread is because it's simple, reliable, and does the job well. But it's not winning awards for originality any more!

[pinkjimiphoton]

i love this circuit, i swapped out my dunlop univibe for it. aisha built mine for me as a gift a couple years ago, used a 3mm green led and bog standard ldr's. works great. led in the middle, and ldrs around it like a univibe.
i am pretty sure you don't want the ldrs against the leds like a vactrol. it needs a little room for the led to fade.
now... from your problem and description, one of the pots should make the led brighter as ya turn it up... any chance a pot is wired backwards, plexi?

[thehallofshields]

No, not really. It's the standard phase stage circuit, done with LDRs as the variable element, as many others have been. Some use FETs in this same position. It's about as standard as it gets, TBH.

What's the advantage of LDR in this case? More linear response than FET?

[Mark Hammer]

FETs can distort.  Some phasers use a network around the FET to raise the clipping threshold, though they do not render the FET immune from clipping.  LDRs, on the other hand HAVE no clipping threshold.  They are, after all, simply resistors.  One of the things that allows is goosing the input level of the circuit such that a better S/N ratio can be obtained.

Additionally, many LDRs have a little bit of lag in them (or at least can selected for that property), as they adjust to the onset and offset of illumination.  That lag introduces a certain distinctive shape to the modulation sweep, that can sound more "musical" to many ears.  When it comes to modulation pedals, I find a lot is riding on "the turnaround", when the sweep gets out to the end-point and begins in the other direction again.  Another part of that is also the lag introduced by the warm-up and cool-down time of incandescent bulb filaments, that also changes the shape of the modulation sweep.

Sometimes, a little bit of sluggishness is a good thing.

[PRR]

> LDRs, on the other hand HAVE no clipping threshold.  They are, after all, simply resistors.

They are terrible resistors. Run fine music at 3V across one, you will hear it. (I used some as last-gasp protection for Crown D-150s.)

Yes, at the sub-Volt levels in guitar chain they are inoffensive.