Hello all and good day! I finished my EH Pulsar build a few days ago with great success. No ticking at all and it sounds fantastic.
I wanted to share a couple of things (real quick) that helped make this a really great tremolo. First the tick that most people come across with this unit have built it from the Tonepad layout is that there is a trace error in the layout. You can see it if you look at Tonepad's schemo @ Q3's collector to R14. On the PCB Q3's collector connects to the wiper of R15. I have the schematic for the original version of the Pulsar and it's very similar to Tonepad's schemo so the fault lies in the PCB. Just cut the trace from Q3's C right before C8 and jumper that trace to R14.
There is also a treble (volume) drop due to the circuit being inherently muddy. This was easily solved by lowering the input cap from .1uf to .047 (you can lower it to taste). The only muddy problem I had after that was at it's highest speed the "OFF's" spacing seems a little wider than the "ON's". So at a high rate there (appears to be) are more OFF's than ON's so that it is hard to hear note/chord changes. You mostly hear the effect when the DEPTH control is set max.
So my questions are...
Can the OFF spacing be manipulated? (How?)
Can you get pulsating LED in sync with the LFO? (How?)
(http://i70.photobucket.com/albums/i83/van_girl_3000/eh_pulsar_orig.jpg)
The LFO looks like an Astable Multivibrator, so it outputs a square wave. This is shaped into something resembling a triangle by the 200k resistor (coming off drain of first LFO trannie) and the .22u cap when the tremolo setting is selected, and (I should imagine) something resembling a trapezoid when the smaller cap is selected. Either that or it'll be the same waveform as the other setting, only larger in amplitude.
If you look at curves for the charge/discharge of a cap through a resistor, you'll get an idea of the waveform that controls the base of the trannie used as a variable resistor. Not very symetrical and amplitude decreases with increasing frequency, hence the problem with on/off times being slightly out.
The treble loss you mentioned was probably the result of the low input impedance of the input stage. Buffer would be a good idea for this circuit and would be a better solution that cutting the low frequency content.
As for the flashing LED. If you just want on/off blink, buffer the output of the LFO and use it to drive your LED. A simple n-channel MOSFET with gate connected to the drain of the first transistor in the LFO should work. Source to ground and stop resistor and LED from drain to V+.
PS I've never built this circuit, the above is just my initial impression.
wow: all tantalums :icon_surprised:
can that be legal?
QuoteIf you look at curves for the charge/discharge of a cap through a resistor, you'll get an idea of the waveform that controls the base of the trannie used as a variable resistor. Not very symetrical and amplitude decreases with increasing frequency, hence the problem with on/off times being slightly out.
So do you think if I messed with the value of the 200k resistor right after Q1 I might be able to pull that in?
Quote from: vanessa on December 18, 2006, 03:27:11 PM
QuoteIf you look at curves for the charge/discharge of a cap through a resistor, you'll get an idea of the waveform that controls the base of the trannie used as a variable resistor. Not very symetrical and amplitude decreases with increasing frequency, hence the problem with on/off times being slightly out.
So do you think if I messed with the value of the 200k resistor right after Q1 I might be able to pull that in?
The problem is that amplitude of the waveform will always decrease with frequency. Maybe if you reduce the 200k it will help, but at the expense of depth/chop (effect will sound more prominent at slower speed settings). Plus, you may find 'on' time more prominent if you make it too small. Again, this is just speculation on my part, I'm not familiar with the circuit.
A true triangle LFO would be the solution - amplitude stable at all frequencies.
Quote from: TELEFUNKON on December 18, 2006, 03:09:08 PM
wow: all tantalums :icon_surprised:
can that be legal?
Only between consenting capacitors...
Quote from: gez on December 18, 2006, 02:41:40 PM
A simple n-channel MOSFET with gate connected to the drain of the first transistor in the LFO should work.
That should have read 'connected to the
collector of the first transistor...'
Quote from: vanessa on December 18, 2006, 02:12:38 PM
Just cut the trace from Q3's C right before C8 and jumper that trace to R14.
Which side of R14 do we jump to?
Thanks!
Gez, could you point me to a true triangle LFO? Maybe one that uses a single opamp?
Quote from: vanessa on December 18, 2006, 04:21:11 PM
Gez, could you point me to a true triangle LFO? Maybe one that uses a single opamp?
All the basic ones use a dual op-amp. Can't do a search now as I'm half watching a really interesting documentary about adoption and it's getting to a good bit. Will post later (or could someone else do the honors?). :icon_lol:
Just occurred to me, if you replace the existing LFO with a triangle LFO this assumes that the 200k and the caps would be dispensed with, so you're going to loose the 'pulse' setting, you'd only have the triangle. All swings and roundabouts I'm afraid. It would require a substantial redesign to get it to do what you're asking.
I guess I'll mess with the 200k resistor and see if that helps a bit. I'll post my findings soon.
Btw, how is this pedal? I can't decide between the Small Stone, Small Clone, and Pulsar for an Xmas gift.
Heh- then get all 3! Never heard a Pulsar, but you're gonna love the Stone and Clone!
I know, the Stone and Clone are kickass indeed!
I can't afford all 3. :(
The Pulsar (original) has a bad rap around here do to a lot of people having built the Tonepad version without having done the fix mentioned above. Without doing this fix the circuit has a crazy ticking noise when in the "chopper" mode. With this fix it is a very cool tremolo effect and the chopper switch is da bomb! Even at the fastest rates (I just turn the depth down a bit) it is very, very cool (think Pink Floyd "One of These Days" off Meddle). I will be messing with some values to see if I can get the fastest speed to be "all that and a bag of chips" (not that it is not that already).
BTW: It has a very low part count and can be made with spare parts lying around. I used 2 resistors in series for some of the values (30k = 2x15k, 200k=2x100k etc.).
Here is the corrected version of the PCB. I'll take it down in a bit as it is not my artwork. I just want to show the correction for reference.
(http://i70.photobucket.com/albums/i83/van_girl_3000/eh_pulsar_tp.jpg)
Do the reissues by EHX have the ticking problem?
Do you know?
I'd rather play it first, but I can't find a store around here that has any.
The "re-issue" is not a re-issue at all. It's a totally different circuit. Just the name is the same.
Really? You mean this one?
http://ehx.com/ehx2/Default.asp?q=f&f=%2FCatalog%2F14%5FModulation%2F02%5FThe%5FPulsar
From what I have read on this site it is not the same. (Puretube claims it is not...) I have not had the opportunity to peek inside. :icon_wink:
Quote from: vanessa on December 18, 2006, 06:55:40 PM
I guess I'll mess with the 200k resistor and see if that helps a bit. I'll post my findings soon.
It's the 200k connected to the collector of the first trannie in the LFO (bottom left) that you'd need to tweak, not the one connected to the base of the trannie used for the modulation (don't think I made this clear in initial post). Not sure how much difference it will make, but you never know...
Hmm, interesting. Hopefully Puretube will drop by.
until puretube drops by, i can tell you in the meantime that the newer pulsar must be a different animal, because i tested it already and could not find many similarities. actually it was hard for me to get a useable sound out of it.
i like the original much better.
cheers,
lowstar
I tried cutting and jumping and that didn't fix the tick, but it made the one of the pots reverse and the speed was so fast that it was unusable. I'll try your PCB later tonight.
Slightly off topic- my Rate is all bunched up at the end is this normal?
i tried the cutting & jumpering just now as well, the tick is still there (i´d call it a bop :)).
it is in the clean part of the signal, so the more the depth pot is set to fx, the less noticeable it is...the more the orig sig is mixed in, the more bop.
comparing the before & after, to my eye i see no difference cause the wiper and one lug of the pot are connected with a trace anyway, so jumpering or not, the end effect would be the same ?!?
cheers,
lowstar
I guess I should have mentioned this mod but I did not think it would have mattered...
When I first wired it up I had an initial tick problem. I did a search and found a mod by Mark Hammer where you change C2 from 47uf to 100uf and C5 from 22uf to 47uf. For better use with a dual opamp (the original used a single 741).
It did not solve my issue because I accidentally wired up a SPDT ON-OFF-ON instead of an ON-ON. :icon_rolleyes: After I put the ON-ON switch in my tick was gone completely (maybe also due in part to Mark's mod, and the trace fix). He speaks of a couple other mods that may help. One was raising the value of R5 a bit. I did that but it seemed to lower the depth of the effect. He also suggested running a .001uf cap parallel with R4. They may work for you. Like I said I had a ON-OFF-ON switch in and they did not do anything to cure the tick with the wrong switch in. After I put the right switch in I left the C2 and C5 caps in out of laziness... :icon_wink:
I'll try the cap changes tonight.
I just put a 500k and a 250k pot in place of R13 (200k). I liked the 500k the best. It seemed to give some changes in the spacing, but at around 390k and above it had a really bad ticking (oddly enough there was a faint ticking with the pot in the circuit where there was not before). The 250k had the same issue (ticking) but there was not much of a difference in spacing over the stock 200k resistor. I'm thinking that above 200k the spacing gets tighter (sounds like an increase in speed at higher speed rates). What I don't understand is why the ticking started at 390k on the 500k pot and why it started at about 225k on the 250k pot?