Author Topic: Neutron question about "optional CHOKES"  (Read 725 times)

half_smith

Neutron question about "optional CHOKES"
« on: August 02, 2022, 03:29:06 AM »
Hey gang, I've got my Neutron "working" - I used a Hamamatsu P873-13 (EBAY seller, United States)
had to use a 50k pot on Rx (set around 20k maybe?)

It sounds pretty decent in LB, LOW, DOWN - a little "flutey" lots of harmonics, maybe too much...

all the other settings "function" but at any other setting there's a bad whine.

I was looking through the forums and documents for any way to remedy this (I jumpered pins 1,8 on the Max1044, improved the noise but still very whiney)

I read somewhere about cable management and keeping things sheilded... well, there's a rat's nest in there, hard to imagine keeping it less of a mess?

The RG Document mentions two "CHOKES" to "clear up even hard cases"

Can anyone point out where on the circuit these "chokes would go"?
Is a choke another way of saying a power filtering Cap across the rails?

thanks!






bluebunny

Re: Neutron question about "optional CHOKES"
« Reply #1 on: August 02, 2022, 04:15:55 AM »
A choke is an inductor.  It blocks high frequencies.

R.G. says to replace the bottom two links with chokes.  I guess he means the ones below RX and U3.
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Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #2 on: August 02, 2022, 04:21:35 AM »
The RG Document mentions two "CHOKES" to "clear up even hard cases"

Can anyone point out where on the circuit these "chokes would go"?
Is a choke another way of saying a power filtering Cap across the rails?


From RG's docs
http://www.geofex.com/PCB_layouts/Layouts/neutronpub.pdf

"If you have wired the battery
power correctly and still have a whine, you can insert chokes instead of the two jumpers at the
bottom of the board in the power lines. This should clear up even hard cases."

What he's saying is:
- In difficult case place chokes in place of the links at the bottom of the board.
  The first link is the link under "Rx"
  The second is the link under "U3"
- U4 and the chokes only applies in the case where you are powering from a single 9V rail.
  The single 9V rail connects to the bottom left corner.
   The +9V 0V and -9V at the top of the board are not used.

Chokes are coils or inductors.  They are connected in series with the power lines.
Capacitors are connected across, or in parallel with, the power lines.

Chokes have a value in micro Henries (uH) or milli Henries (mH).
They also have a maximum current rating.
Typically the higher the value or current rating the larger the part and more expensive the part.
If you look at inductors in the same manufacturers range or series you will see parts with
the same size buy the current rating decreases as the value increases.

For that circuit I suspect you will need at least 100uH.

Best to try it out first to see if you need chokes at all.

Pay attention to RG notes about grounding.   There's no point doing that wrong and expecting the added chokes to fix things up.
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half_smith

Re: Neutron question about "optional CHOKES"
« Reply #3 on: August 02, 2022, 04:47:30 AM »
Thanks Rob, I did some reading after my post and got caught up on what an inductor choke is, I've never used one before...

I am using a single 9v power supply (not a battery, DC jack), and I am getting whine all over the place. seems like the chokes are what I need to try next.
Makes sense

Small Bear specifically stocks a 680uh "for neutron" I will order them and try.

Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #4 on: August 02, 2022, 04:48:41 AM »
Quote
Small Bear specifically stocks a 680uh "for neutron" I will order them and try.
That value looks fine.  Sounds like someone has already been there and solve the problem!
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half_smith

Re: Neutron question about "optional CHOKES"
« Reply #5 on: August 02, 2022, 04:53:11 AM »
practical question: when I add the chokes, do I have to physically cut the jumpers (they are built into the pcb)?

Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #6 on: August 02, 2022, 07:25:15 AM »
Quote
practical question: when I add the chokes, do I have to physically cut the jumpers (they are built into the pcb)?
No need to cut.   The jumpers or links are just solid wires you solder in like resistors.  In fact often you can form them from off-cuts from resistor leads.  In your case you would not load them in at all and put the chokes in their place.   When you cut the copper on the board people usually say "cut tracks" or "cut traces" or something similar.
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half_smith

Re: Neutron question about "optional CHOKES"
« Reply #7 on: August 02, 2022, 03:12:54 PM »
Rob, the PCB came with the jumpers laid in. I think I do need to cut them?

Kevin Mitchell

Re: Neutron question about "optional CHOKES"
« Reply #8 on: August 02, 2022, 03:30:15 PM »
Get rid of the jumper you've added for the MAX1044 and use an LT1054.
No more tricks needed to mitigate the whine!

I will forever suggest this for all Neutron builds.
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Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #9 on: August 02, 2022, 08:44:35 PM »
Quote
Rob, the PCB came with the jumpers laid in. I think I do need to cut them?
I'm assuming you mean there are track hard-wired on the PCB where the jumpers would go?
If yes cut them.  If you means some one has soldered jumper links into the PCB already then
you need to de-solder them so the chokes can be added.   You can cut the wire links
then desolder them one at a time.

Kevin's suggestion of changing the chip is also good.    The different chip pushes the switching frequency up beyond the audio range and the whine is no longer audible.

As far as I know, the jumpers Kevin mentions aren't actually on RG's PCB.   What he is referring are jumpers that appear on *other* PCBs which allow you to use different charge pump ICs.  This gives an option to jumper pin 1 to pin 8.  You can only do this on some ICs.  You might need to check if the PCB layout is different to the PCB layout in RG's document.

Based on the RG documents the circuit is layed out for an ICL7660.   This has pin 1 left open.   The oscillation frequency is 10kHz which is why you hear the whine.  When you add the chokes it reduces that whine.

What Kevin is suggesting is to use an LT1054.   That will plug straight into RG's PCB.   It oscillates at about 25kHz so you wont' hear the whine and you don't need any chokes (so leave the jumpers in.)

There are many different charge pump ICs.  Each have slight differences relating to voltage ratings, switching frequencies and some require pin 1 to be connected to pin 8.    Some (other) PCBs have options to use all the different charge pumps.    If you stick to above options you don't need to think about it.


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half_smith

Re: Neutron question about "optional CHOKES"
« Reply #10 on: August 02, 2022, 09:55:05 PM »
I wish I knew about Lt1054's, I just placed an order for the Chokes from Smallbear and would have gotten some.
I've had whine problems with all the charge pump circuits I've built.

I got my PCB from GGG and it has those jumpers traced into the board.

Fingers crossed the chokes alleviate the whine.

Any other solutions? Can I use foil tape and cardboard to further shield the board from wiring RF?

Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #11 on: August 02, 2022, 10:22:06 PM »
I wish I knew about Lt1054's, I just placed an order for the Chokes from Smallbear and would have gotten some.
I've had whine problems with all the charge pump circuits I've built.
It happens more often than not with the ILC7660.

Quote
I got my PCB from GGG and it has those jumpers traced into the board.
OK, So it's not quite what they have on their site since all those DOCs look like RG's docs.

http://www.generalguitargadgets.com/effects-projects/filters-envelope/neutron/

Quote
Fingers crossed the chokes alleviate the whine.

Any other solutions? Can I use foil tape and cardboard to further shield the board from wiring RF?
Shields etc won't help, not significantly anyway.   The problem is the ripple on the power lines.

Without the chokes you might be able to increase C15, C17, C18.   C18 is already quite large
so that leaves increasing C15 and C17 to say 100uF.  I've got my doubts how well it will work.

The chokes help reduce ripple but they also work in combination with C10 and C11.
You really need chokes to make C10 and C11 work, otherwise it's not much different to
playing with C17 and C18.

If you still have problems after adding the chokes you could use larger caps for C10 and C11.
At the moment they are only 4.7uF but you could go up to 100uF.

In some circuits you can use low valued resistors instead of the chokes and use the larger C10, C11 values.   If you already have the chokes there[s no point going back to resistors.
« Last Edit: August 02, 2022, 11:00:37 PM by Rob Strand »
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half_smith

Re: Neutron question about "optional CHOKES"
« Reply #12 on: August 02, 2022, 11:04:02 PM »
Thanks for all your feedback Rob

I don't mean to be argumentative, just want to get it correct, but from my reading of the RG Keen doc (found on GGG where I got the PCB, I'm assuming they have a relationship), it says that using a battery (I'm using a 9V DC jack, but I think that's the same - as opposed to a bi-polar power source)
you omit C10, C11, C12, C13 and then use the chokes.
« Last Edit: August 02, 2022, 11:13:10 PM by half_smith »

Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #13 on: August 02, 2022, 11:19:50 PM »
Quote
I don't mean to be argumentative, just want to get it correct, but from my reading of the RG Keen doc (found on GGG where I got the PCB, I'm assuming they have a relationship), it says that using a battery (I'm using a 9V DC jack, but I think that's the same - as opposed to a bi-polar power source)
you omit C10, C11, C12, C13 and then use the chokes.
No problem at all.

Can you cut and paste the text where it says that?  I can't find it in the PDF.

To me, it actually doesn't make sense to leave those caps off.

When I read the parts list I see leave out C15, C16, C17, C17 when you run form 2x9V batteries.  ie. omitting parts for the case you aren't using.
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Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #14 on: August 02, 2022, 11:52:10 PM »
OK, I think I found where it is.

http://www.generalguitargadgets.com/pdf/ggg_neutron_sc.pdf

I'm pretty sure that's an error because RG documents don't imply the same thing.
If you don't have any chokes it might be OK to leave off C10, C11 but with the chokes
it doesn't make sense.
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half_smith

Re: Neutron question about "optional CHOKES"
« Reply #15 on: August 03, 2022, 01:58:26 AM »



I may have been mistaking the part where it says to leave out the 7660 and associated parts when using a bipolar power source.

Since I'm using a DC Jack, I was leaving out the bi-polar circuit, C10, C11, C12, C13
I suppose these caps could be doing some filtering I'm missing *doh!
I am putting them back in.

Rob Strand

Re: Neutron question about "optional CHOKES"
« Reply #16 on: August 03, 2022, 02:06:47 AM »
Quote
Since I'm using a DC Jack, I was leaving out the bi-polar circuit, C10, C11, C12, C13
I suppose these caps could be doing some filtering I'm missing *doh!
I am putting them back in.
OK got it.   Without the chokes they might help a bit but I have doubts it will fix the problem.
More the issue is if you add the chokes and C10, C11, C12, C13 aren't present the effectiveness
of the chokes is much reduced.  (If you still have problems after that try increasing C10 and C11,
as mentioned a few posts back.)
« Last Edit: August 03, 2022, 03:09:54 AM by Rob Strand »
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