PCBs for Thomas Henry's X-4046 VCO

pre55ure · Joined: Aug 17, 2012 Posts: 1 Location: Orange

Sorry if this was asked before- but I couldn't find the information. Is it possible to run this VCO from +/-12v? If so, are there any components who's values need to be changed?
Thanks!

Really looking forward to building a couple of these!

fonik · Posted: Sat Aug 18, 2012 7:06 am Post subject:

no need to change anything...

elanhickler · Posted: Sun Sep 02, 2012 11:36 pm Post subject:

Fonik, my build is a total failure Sad

Symptoms:

1.Turning coarse or fine pots causes pitch to change... except that it is slewed.

2. PWM Init pot is extremely sensitive, you can only hear a pulse output if the PWM init is exactly center.

3. Multimeter shows Pin 1 and Pin 2 of PWM Attn (PCB) connected to ground. The actual pot seems fine.

4. I get no sine output.

5. Triangle out is intermittent

5. Sync seems to work.

Crying or Very sad

fonik · Posted: Mon Sep 03, 2012 6:34 am Post subject:

no so good, however, there is good news for you:
the project and the PCBs are well tested and build many times, so they are fine. something you can rely on.
so there must be at least one error on your side which you can troubleshoot and solve...

so i recommend troubleshooting as usual.

anyways, from what i understand reading your post, you have some issues with the waveshaper, and some with the core PCB.

i would recommend to completely remove the waveshaper board at first, and get the core board running. if the core board is fine, then add the waveshaper again to see what's the matter with it.

fonik · Posted: Mon Sep 03, 2012 6:43 am Post subject:

so let us address it more specific:

elanhickler · Posted: Mon Sep 03, 2012 10:15 am Post subject:

I removed the waveshaper. I have a patch cable going into my computer so I can hear what's coming out.

-Ground hum is coming from +/-15v power pins and ground pins.
-Ground hum is coming from ground pads (pad1) and signal pads (pad2) of the pcb (saw and tri pads)
-No waveshape or ground hum is present when cable is inserted into jack.

-I have all jack/signal wires going to pad2 of the PCB

-Check my LM394 connection.

Edit: NOTE I do have a second fully populated X-4046 that I could attempt to wire... or test?? Not sure what tests I'd do.

elanhickler · Posted: Mon Sep 03, 2012 11:21 am Post subject:

here is my lm394 pic

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fonik · Posted: Mon Sep 03, 2012 2:10 pm Post subject:

re ground hum:
1. re-check all your grounding/wiring.
2. connection to computer correct?
3. is your PSU clean?
4. what resistance do you measure across +V and GND, resp. GND and -V?

re LM394:
what transistors are you using? is the pin out correct? same as LM394?

fonik · Posted: Mon Sep 03, 2012 2:14 pm Post subject:

i see you did not socket the 4046.
hopfully it is still alive with no GND connected. i am not sure what this part can bear...

anybody?

elanhickler · Posted: Mon Sep 03, 2012 3:20 pm Post subject:

Resistance across gnd/v+ and gnd/v-

Power on: Seems to be infinite resistance???
Power off: Resistance slowly falls to 0 and then goes back up to 2.2K for v+ and 1.45K for v-

Power on: No audible waveform
Power off: A high pitched waveform appears and quickly falls to 0hz at which point a waveform is no longer heard. Both saw and tri outputs exhibit this behavior and the waveshape seems to be correct for the brief moment I get the waveform during power down.

I used matched transistors 2N3904 from MusicFromOuterSpace.com
link: http://www.musicfromouterspace.com/analogsynth_new/ELECTRONIC_PARTS/Matched2N3904_MFTempco.php

fonik · Posted: Tue Sep 04, 2012 5:48 am Post subject:

if you used 2N3904 transistors, then it looks like you have an error in the current mirror (Q1/Q2), according to your picture.

take a look at the 2N3904 pinout here:
Posted Image

and then take a look at the LM394 datasheet (edited by me):
Posted Image

if you wanted to use 2N3904 the 2nd transistor (pins 5, 6, 7 of the LM394 footprint) would have to be flipped. according to your picture the 2nd transistor is rotated...

elanhickler · Posted: Tue Sep 04, 2012 8:31 am Post subject:

elmegil · Posted: Tue Sep 04, 2012 10:11 am Post subject:

Yah, I'd say likely a typo. The bottom line is if you're using 2 NPNs of any sort, they both have to face the same way, they can't face one one way and one the other. Collector will always be the same pin on both, and if you reverse one to make them face each other, you're connecting collector to emitter and emitter to collector.

Skrog Productions · Posted: Tue Sep 04, 2012 10:27 am Post subject:

Hi all ,
Is your faults occuring when the pcbs are stacked on the pillars ??.
It may be several shorts to ground, if it is causing shorts , just use thin nylon washers to isolate.

Dave.

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elanhickler · Posted: Tue Sep 04, 2012 10:05 pm Post subject:

I think I got it working. I switched the transistors legs for "6,7,8" And the saw is supposed to be twice the frequency, right?

The waveshapes seem a little unclean to my ears. That's fine, but just want to make sure my build is as correct as possible. Can someone verify my waveshapes are as they should be? See attached wav file.

Edit: BTW, people describe the hardsync on this as VERY HARD and AWESOME... but I would describe it as very clean, that *is* awesome.

x4046-waveshapes.wav

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fonik · Posted: Wed Sep 05, 2012 1:36 am Post subject:

elanhickler · Posted: Wed Sep 05, 2012 2:04 pm Post subject:

yeah, could you check that my core waveshapes are correctly trimmed before I add the waveshaper to the circuit? (see above wav). thank you!

elanhickler · Posted: Wed Sep 05, 2012 10:52 pm Post subject:

OK! Now I'm adding the waveshaper to the circuit and getting strange behaviors.

1. Sine output is 100% saw-shaped
2. Skew output is SAW ONLY and the skew pot simply turns the volume of the saw up or down. No triangle is heard
3. PWM init is extremely sensitive with the square output being inaudible most of the pot turn.

I checked pot values, I checked wiring... im using a header/pins for the saw/tri in/out. Maybe I have a bad connection there. Multimeter ran out of batteries so I need to recharge it before i can test for connection...

Read carefully: To test to see if the connection was bad I used an alligator clip that went from "TRIANGLE pin2" of the core to "SAW/TRI IN pin1 (triangle)" of the waveshaper. Basically, the waveshaper would in theory be receiving two triangle outputs into its one triangle input... both the "TRIANGLE" and "SAW/TRI OUT" from the core....

-Doing this made the sine output a weird shape in which the sine trimmers could affect, but it could not be trimmed to a sine. Before making this connection, the sine trimmers did nothing.

Any ideas? Thank you!

fonik · Posted: Thu Sep 06, 2012 3:52 am Post subject:

fonik · Posted: Thu Sep 06, 2012 4:02 am Post subject:

fonik · Posted: Thu Sep 06, 2012 4:34 am Post subject:

elanhickler · Posted: Thu Sep 06, 2012 12:41 pm Post subject:

fonik · Posted: Thu Sep 06, 2012 1:34 pm Post subject:

ha! this is great news! Very Happy

before talking about the pulse, how does the sine wave look? maybe you could send me a wavefile from the sine output (m at fonitronik dot com)?

fonik · Posted: Thu Sep 06, 2012 1:39 pm Post subject:

fonik · Posted: Sun Sep 09, 2012 8:44 am Post subject:

i took a look at the wave file you sent me via emal, and indeed the sine wave seems to be a little bit weak compared to the other outputs. the shape looks quite fine though. no idea how to solve that by now. so for now re-check all components values again...

if you could live with that, and just want to get a better pulse width control, then let me ask the following: is it just the manual control that is unsatisfying, or do you find the CV control (PWM) too sensitive, too?