Pulsar HELP!!!

[oldrocker]

I'm trying to get the Tonepad Pulsar pulsing.  I was trying to use my audio probe to debug it but I don't know if it will work or not.  Q1 has the input signal going into the collector.  Is the signal supposed to come out the base?  How does the oscillator circuit manipulate the audio signal?  It's below the output section.  Is the effect from the oscillator circuit supposed to came back through the base of Q1 out the collector.  This circuit has me baffled.
All I get is an unchanged audio going in and coming out.  Even with no battery power.  It's just passing the signal through  with a little less gain.  I know this circuit has been an issue with alot of builders.  They either love it or hate it.  I can't tell yet.

[tiges_ tendres]

One of the issues I had with this pedal was Q1.  It worked fine at first, and then an hour later it packed in.

I think what happened with mine was I may have accidentally switched the battery the wrong way, and there is no reverse polarity protection.  I socketed my transistors so it was a pretty easy to fix by just dropping another one in.

If you haven't already, you should read the thread: "what to do when it doesn't work" 
The info there is great.

[oldrocker]

I have read "When it doesn't work the first time." a long time ago.   Been there done that.   I've been over this circuit upside down and backwards literally.  Normally I follow the input signal path to the output using the audio probe and testing continuity and voltages.  But this schem is different.  The input signal always make it to the output even without battery power.  Then the oscillator circuit below I assume feeds back up up through Q1 to effect the output.  This seems strange to me.  At what point can this osc circuit have any effect on the pass though signal.  How does the input ever activate this oscillator circuit or vice versa?

[geertjacobs]

When looking at the circuit I come to the same question as you on how this thing can work.
Nevertheless my Pulsar is working fine. I did have troubles with the orientation of my transistors.
What I'd do in your case:
- check the orientation of all your transistors
- check the wiring of your pots and test the circuit with your pots at different settings.
- replace the transistors one by one

Hope this helps...

Oh, and check the fix that is mentioned in the build reports at tonepad

[oldrocker]

Thanks geertjacobs,  I will try your suggestions.  I'll need to buy more trannys.  I'm not having any luck with any tremolo builds.  I just built the Kay trem on my breadboard and I can't get that working either.  It must have something to do with the trannys.  Maybe I'm burning them up as I install them when I put them in the wrong way.  I wish I had a transistor tester like when I was in electronics school.  I'm afraid to stick more in.  The only trannys I haven't tried are the ones in my other DIY's.  I'm pretty sure I have them in right but I thought that once before and found out that I didn't.
Thanks  tiges_ tendres your right I might have fried those transistors a while back and not realizing it.  All the tracing and testing won't work without good transistors.

[R.G.]

The Pulsar uses the variable resistance region of an NPN bipolar transistor as part of the gain controlling elements for an opamp.

The transistor is either turned more or less on by the trickle of current through that high resistance attached to its base.

The LFO is a discrete transistor astable oscillator, making a square wave at its output. The square wave is either fed semi-directly to the base resistor, or filtered to a more-or-less triangle or trapezoid by the selection of a capacitor on the base circuit.

Switching in a shunt capacitor to shunt across the transistor ups the opamp's gain to "bypass".

If your transistor is fried, it ain't gonna work.

[oldrocker]

Thanks for the tech. info.   I'm trying to understand the builds I do not just use them.  I can't believe how much better I'm getting at building more complicated circuits in such a short time.  I still have a LONG WAY TO GO.   These trem builds really had me confused.  It seems like I'll never get this one going.  But I won't give up until it works.  I'm going out soon to get more trannys.  I had a lot but I've used them up already with all the builds I've done recently.   My wife thinks I went nuts since I got addicted to DIY builds.  Everyday I'm searching for new projects and either modifying them or breadboarding some new effect. Thanks again.  R.G.

[oldrocker]

Here's a thought.  On these trem builds I used the large 2A I believe metel film caps.  Normally I use ceramic caps because they're easier to get and always work for me.  But on my Pulsar build I paralled a bunch of these large caps together to make a .47uF.  Could this cause a problem?  These huge caps take up all the room in the oscillator section of the perf board.  They don't seem to discharge the voltage.  I notice after I remove the battery I still have the full 9 volts on the pos / neg input.  Should I try a smaller amp and voltage size caps?

[R.G.]

The issue of film caps versus ceramic producing better sound is fairly tricky. The difference is subtle. It's only detectable for caps that the sound actually passes through.

In the case of the Pulsar, make sure that the caps you have subbed in film for are actually in the audio path, not in the LFO or the control line for the transistor. They do you no good at all there, and the smallest cap is probably the best.

[oldrocker]

OK I replaced the large film caps with the smaller voltage ceramic caps and found a major cold solder joint.  So it's working now.  The wire I had bringing 9 volts to the oscillator circuit was not makeing contact to battery power.  I don't know if the caps made much difference but I like the way the perf board looks now.  Not so cluttered.  Thanks to all who tried helping me out on this especially R.G. with the technical info it's much appreciated.

[R.G.]

Hey, you're welcome. I've made a number of cold solder joints myself.

Congrats on the new build.

[oldrocker]

Thanks R.G.  Yeah this Pulsar combined with the Dr. Quack I just built sounds really funky and seventiesish.  As my nick name implies I'm an old rocker so seventies rock and funk is my thing.  That's not including all the distortion fuzz effects I built also.  Man I'm gonna haveta stop doing DIY's for a while or risk devorce.  LOL    My wife is getting irritated at me for spending all my time building effects.  She's right though I must've built an effect every two or three days.  I'm on my 9th DIY in less than a month.