Pulsar from tonepad fix layout search

[percyhornickel]

Hi, could please sobody explain what is the fix made in the pulsar pcb/layout from tonepad? or maybe post the fixed layout.

There are some posts saying there is an error in the pcb showed there and all post I found are too old and the images links doesn´t work anymore.

I have all components arriving soon and really would try to make it right. I hope you guys can help me.

Thank you

[GGBB]

From reading the build reports, I think it's not a fix to the layout but a fix to the wiring of the rate pot. I think the PDF shows that fix. The parts list calls for a 100k log pot, but rate pots for oscillators are often anti-log so that the effect of adjustment is evenly spaced out over the whole range of the rotation. If you use a log pot, the rate only changes during the last 5-10 percent of rotation due to the opposite taper. You can fix that by either using the proper anti-log pot, or by wiring the log pot backwards - swap the connections to pins 1 and 3. Note that this fix will make the pot adjustment work "backwards" as well.

So you just need to make sure you connect the rate pot properly - the layout is fine.

[percyhornickel]

Thank you for the answer and yes are right, I could see the rate pot is backwards. The tonepad´s schematic shows C8 (0.47u) right to the wiper, but the pcb shows C8 is connected to Lug2/Lug1/R14 and R20/Q3 collect below.   

Even, I have build the circuit it LT Spice and conecting the just C8 right to the wiper (like the schematic) and doesn´t work that way, but the simulation runs perfect conecting C8 to R14/Lug1/Lug2 and I can hear the effect.

I have found the original EH Pulsar schematic and the conection is like the second one (C8/Lug2/Lug1/R14 and R20/Q3 collect), that´s why I still think something is wrong with tonepad diagram, pcb is not equal to the schematic.

Please let me know if you could see this, if you use Lt Spice I can send you the simulation to check what I said.

[GGBB]

Even, I have build the circuit it LT Spice and conecting the just C8 right to the wiper (like the schematic) and doesn´t work that way, but the simulation runs perfect conecting C8 to R14/Lug1/Lug2 and I can hear the effect.

Yes. The schematic is wrong, the layout is fine. The schematic should be:

[percyhornickel]

Thank you, I was going nuts because of that. I have read in some posts about the thick/LFO problem of this circuit and  that´s why I made a pcb design adding some changes.

The + input of the opamp must be isolate from the other parts of the circuit, so the opamp is feeded directly from vcc and then I add a 470 ohm resistor in series plus a 47u to ground to feed the rest.

According LT Spice, after 470 ohm the circuit is feeded with 8.8 volts which is enough to make the LFO to work properly.

I´m planning to isolate de output jack and the rate pot solder points with aluminium tape (with no contact between) like I read here:

https://www.ehx.com/forums/viewthread/9710/

If you have another advice to avoid LFO/bleed/Thick please let me know.

Thanks again...  ...and yes, my english is not perfect!

Saludos desde Venezuela

Percy

[GGBB]

If the ticking is due to the output jack being too close to the circuit, you can make sure your build does not have this problem by placing the jacks appropriately and keeping the wires away from each other.

Another possibility is to modify the layout so the output connection is in a different place:



It could also help to use a bypass wiring that grounds the PCB output when bypassed:

[percyhornickel]

That is exactly what I´m planning to do. I made the pcb design with V+, GND and Output points below then I will shield this once the pcb is in the enclosure. There is a space for the 470 ohm and 47u to isolate power section and I have separated a little more the potentiometer solder places.

I put a aditional point in the chop caps section to solder a wire and test different caps values and a pull down resistor point to the output.

Well, I will let you know the result later. 

Thank you

Percy

[percyhornickel]

Hey I made it, works great. No thick!!!--    ---just a small one in chop mode so I changed the cap for 4,7n and sounds great both modes.

I have tested with my DIY´s RAT and 808 in front and after, works great. It change the tone a little bit but I think is because the TL072 (sounds with more treble) so I will put a 4558 instead. I tried once the TL072 with the TS808 but I had the same issue.

I´d like to solve the 5 degress problem and I have read an old post (tonepad) with a solution from a guy (Pekka) but the link is broken.

Tested the pot backwards but didn´t work out that well. I will try some other solutions with LT Spice and see.

(BTW I changed output resistor R7/47k for 1Mohm to avoid LFO bleeding to ground / The green points in the image is for the led circuit part). 

[percyhornickel]

Hey I made it, works great. No thick!!!--   

I have tested with my DIY´s RAT and 808 in front and after, works great. It change the tone a little bit but I think is because the TL072 (sounds with more treble) so I will put a 4558 instead. I tried once the TL072 with the TS808 but I had the same issue.

I´d like to solve the 5 degress problem and I have read an old post (tonepad) with a solution from a guy (Pekka) but the link is broken.

Tested the pot backwards but didn´t work out that well. I will try some other solutions with LT Spice and see.

(BTW I changed output resistor R7/47k for 1Mohm to avoid LFO bleeding to ground / The green points in the image is for the led circuit part).

[GGBB]

I´d like to solve the 5 degress problem and I have read an old post (tonepad) with a solution from a guy (Pekka) but the link is broken.

Tested the pot backwards but didn´t work out that well. I will try some other solutions with LT Spice and see.

The best solution is a reverse-audio taper pot. A linear taper pot would also feel different than the audio taper pot. You can also try changing the values of the pot and the parallel resistor R14. A 50k pot with 220k parallel will provide the same overall resistance ~40k but the overall control taper will be a bit different. Not sure if this would be better or worse -you can also try a larger pot and smaller resistor to adjust the taper in the other direction - try a 250k or 500k pot with 47k parallel.

Note that the original EHX Pulsar schematic (below) specifies a regular log (audio taper) pot the same as the tonepad schematic.

[percyhornickel]

Ok, I tried with the 50k pot and 220k but it was a weird response. I have not chance to find a reverse-log pot where I live so testing with what I have at home and simulating is the only way for me right now (I live in Venezuela). 

I decided to cut the trace between 1 and 2 of the rate and bingo, it works better that way in my circuit, increases the speed at the end and decrease at the beginning, not that lineal as I would like but works ok, can ble handled.

I made another pcb design with gnd traces for AUDIO and LFO, and or course Isolating the opamp from the LFO too. There will be no ticking this way and letting spaces in case RATE would need to be put togheter. There are points for "extra caps" needed to separate LFO and AUDIO, they are joined just in the maint GND point.

I could send it to you if you wish.

Percy

[GGBB]

If you can post it here, others will be able to use it. Thanks.

[percyhornickel]

Ok you are right, that´s fair...      ..this is the guide:

[percyhornickel]

Ok you are right, that´s fair...      ..this is the guide:

[duck_arse]

percy - I'm not sure your Q1 is drawn right in those images. you may have your base and collector connections swapped.

[percyhornickel]

percy - I'm not sure your Q1 is drawn right in those images. you may have your base and collector connections swapped.

Yep, you were right, I didn´t put a led in the mine, the circuit works fine.

Here you´ve got the correction:




...and thank u....    ...btw..   ...works amazing with a RAT distortion.