R.G. Keen Neutron power issue

[Onion Ring Modulator]

Hello,

I have finished building my Keen Neutron and I am having a power issue that is confusing me.

Here's the voltages:

Supply  9.48v
+ on PCB 9.48v

Q1
E 9.48v
B 8.087v
C 0.06v

+ on 100u 0.24v

Charge pump (TC1044SCPA)
1 0v
2 0v
3 0v
4 0.04v
5 0v
6 0v
7 0v
8 0.03v

Not sure what's causing the power loss. I have swapped out the 1044, the 2N3906, and the 100u cap just to be sure. No change. Maybe there's a wiring thing I didn't understand? i am using a 9v DC jack, no batteries.

Thanks in advance for any advice.

[Fender3D]

I bet you didn't connected R20 to GND (via input jack)...
There's no wire in that pad

[Onion Ring Modulator]

I bet you didn't connected R20 to GND (via input jack)...
There's no wire in that pad

(SIGH).....it's always the little things. 

Thank you!

[Onion Ring Modulator]

Is there anyone reading who has built this pedal and can recommend a good value for the RX resistor, 150r TO 4k7?

[Kevin Mitchell]

Is there anyone reading who has built this pedal and can recommend a good value for the RX resistor, 150r TO 4k7?

Use a 10k pot or trimpot and dial it in to taste. You may replace the pot with a resistor once you can aproximate a value that works best for you by measuring the taper resistance in your favorable setting. Let us know if you need more info on how to do this.

Here's my build thread where I was working out some problems including the RX value.

[Onion Ring Modulator]

Is there anyone reading who has built this pedal and can recommend a good value for the RX resistor, 150r TO 4k7?

Use a 10k pot or trimpot and dial it in to taste. You may replace the pot with a resistor once you can aproximate a value that works best for you by measuring the taper resistance in your favorable setting. Let us know if you need more info on how to do this.

Here's my build thread where I was working out some problems including the RX value.

Good idea, will do. Currently checking over all my wiring again because i have the dreaded whine...but at least I have power now which is better than what i had before i started this thread. 

[Kevin Mitchell]

Good idea, will do. Currently checking over all my wiring again because i have the dreaded whine...but at least I have power now which is better than what i had before i started this thread. 

Sweet deal!
I absolutely dread the 7760 chips. I had used a LT1054 to avoid the whine - more on that in my build thread along with other notes you'd benefit from as well.
There's space for inductors on the board to help the whine when using the 7660 charge pump. That's covered in the build doc. Also a note about connecting pins 1 & 8 together which is usually done with the 7660 and LT1044 but not the LT1054.

[Onion Ring Modulator]

Good idea, will do. Currently checking over all my wiring again because i have the dreaded whine...but at least I have power now which is better than what i had before i started this thread. 

Sweet deal!
I absolutely dread the 7760 chips. I had used a LT1054 to avoid the whine - more on that in my build thread along with other notes you'd benefit from as well.
There's space for inductors on the board to help the whine when using the 7660 charge pump. That's covered in the build doc. Also a note about connecting pins 1 & 8 together which is usually done with the 7660 and LT1044 but not the LT1054.

I actually used a TC1044SCPA (would the 7760 be any better?), but I will be reading your thread and also giving that pin jumper a shot. I refuse to give up this easy, especially after how long it took me to source a 15u non-polar cap and a A150k pot. The best I could do there in these times of part shortages was to get an A250k and run a parallel resistor from pin 1 to 3 to bring it down close to 150.

[Kevin Mitchell]

I actually used a TC1044SCPA (would the 7760 be any better?), but I will be reading your thread and also giving that pin jumper a shot. I refuse to give up this easy, especially after how long it took me to source a 15u non-polar cap and a A150k pot. The best I could do there in these times of part shortages was to get an A250k and run a parallel resistor from pin 1 to 3 to bring it down close to 150.

The jumper may help! And I advised against the 7660. They seem to be more troublesome with whine from my experience. I haven't yet used the LT1044 myself but I know it's suggested to jump the boost pin (pin 1) to VCC (pin 8 ). Same when using the 7660 but not the LT1054.
I used a 1M linear pot with a 180K resistor between lugs 1 & 2 to get close to the same behavior as a 150K audio/log pot that is specified.

I hear ya on the 15uF NP cap. I now have a bag of extras that I don't know what to do with 
For the next Mu-tron I suppose!

[Onion Ring Modulator]

I hear ya on the 15uF NP cap. I now have a bag of extras that I don't know what to do with 

Same! Maybe we should list them on eBay individually with Mu-Tron Clone in the listing title. 

[Onion Ring Modulator]

Just to keep this updated for any future travelers -

I put a jumper in place on the underside of the board connecting pins 1 & 8 of the charge pump and that got rid of the whiny noise. Hooray!

I guess my last hurdle here is dialing in a value for the RX resistor. Messed around with it a bit this morning using a B10k pot but didn't get anywhere. I think my next move is to try a 5k pot instead and see how that goes.

I get a lot of distortion with the gain up all the way. Is that normal? Is it meant to overdrive?

[Mark Hammer]

Rx is actually one of those instances where homebrew LED/LDR "vactrols" can have an edge over commercial ones.  Ideally the value of RX would be one where, in the absence of audio input signal, the LED remains fairly, or even very, dim and strumming results in it lighting up.  Naturally if you can't physically see the LED, then it's hard to tell.

I just dug my 90%-done Neutron board out of the bin of unfinished things, and noticed that the Rx position lies empty.  My build uses homebrew vactrols with the little tip of one of the LEDs visible out the top of the heat shrink covering.  I'll try and get the unit working this weekend, and let you know what I used.

[Onion Ring Modulator]

Cool. Thanks!

[Kevin Mitchell]

I guess my last hurdle here is dialing in a value for the RX resistor. Messed around with it a bit this morning using a B10k pot but didn't get anywhere. I think my next move is to try a 5k pot instead and see how that goes.

This wouldn't do anything since the pot is being used as a variable resistor and 5k or less is included in the range of a 10k pot. Raising the value would give you more options but also raises concern about the functioning status of your choice of optos or the circuit itself. You can see in my thread where I was incorrectly adjusting RX just to get the response I was looking for before changing from hand-rolled optos to a pair of new-old-stock VTL5C3 and everything fell into place.

What I'm getting at is, there may be something else going wrong with your build.

I can open mine up tonight to relay what value of RX I had used - though we had used different opto devices. A record of RX choices would be ideal for future builders.

[Onion Ring Modulator]

Yes. Trying the pots did not help. I'm not sure what the problem is now. I am getting effect on all three modes, it just sounds really bad and is not adjustable into anything normal. I had to set it aside for now, which is a pity, because I made a really snazzy enclosure for it.



Maybe I should try one of the other opto options. I can't really think of anything else that would be causing this.

[Kevin Mitchell]

Oh man that's some nice box work!
I wonder if one or both of the optos are defective/damaged - though it looks like they can handle some abuse.

I've got an idea for you to try before you bench the pedal. Remove the optos and plug an LED in pin 1 (anode) and pins 6 or 7 (cathode) of your 14-pin DIP socket. See if you can dial RX to see if it can respond well visually. If you can't get that LED to light via the envelope then there's an error in the envelope section and we will find it!

Keep in mind the input's volume plays a huge part in the strength of the envelope. The mu-tron III is meant for a variety of instruments so it may be a simple matter of turning down your guitar's volume to get the envelope within an appropriate range. Messing with the position of the drive pot should also help.