Colorsound Power Boost debug (Aion Plasma)

[mth5044]

Hola - thanks for coming into the thread!

I'm attempting my second power boost, this time from Aion's Plasma project.

https://aionelectronics.com/wp-content/uploads/2015/05/aion-plasma-colorsound-overdriver-documentation.pdf

I attempted this pedal on perf in 2009 and it didn't work. Now, 9 years later, the second try still doesn't work 

I built it based on the Power Boost parts in the build doc. Things I changed:
- I'm using a MAX1044 based voltage doubler on perf, pins 1/8 connected, to get 18V.
- I left of D1 because it's present on the voltage doubler.
- I used a 10kA for the Gain pot rather than the 1kC (acceptable based on the build doc and the original pedal).
- I ran the the CLR directly from the power jack as to not draw the limited mA from the 1044 to power the LED. LED does work in this set up. So rather than the board LED switching, it goes power jack -> resistor -> LED on board -> Switch -> Ground
- Not really a mod, but C12 is an electro in the powerboost and the PCB doesn't have a polarity marked, so I put the negative side towards the volume control per some schematics of original units I've seen online.
- Also not a mod, but I'm using enclosed jacks, so the enclosure isn't grounded. I've grounded jacks, switch, PCB and power jack via wire. Don't think that's an issue, but thought I'd provide as much info as possible!

Voltages:
1Spot
9.45 V

Supply to board
18.04 V

Q1 2N5088
Q1
C 5.83
B 3.66
E 3.12

Q2 2N5088
C 9.99
B 5.83
E 5.18

Q3 2N5088
C 10.10
B 2.64
E 2.02

There is some issues with biasing the transistors. All three trimmers are basically turned all the way down. For Q1, I can't get it to go any lower than the 5.83V (build doc says 5V). Q1 and Q2 are almost all the way down, but have a little bit more travel on the trimmer before they bottom out.

It does pass sound, the EQ and the volume control work, but the gain control does nothing - no boost. With volume maxed, and the EQ set in the center, I get a slight volume drop. For testing, I've been plugging the pedal directly into my focusrite into my PC. I'd think if this thing was functioning, I'd be able to clip the input stage of the focusrite, but it isn't happening.

I have checked all resistor values using their color bands and all capacitor ratings. I have checked the pin out the transistors (they are also facing in the direction of the silkscreen). Working on getting a photo of the board up.

I have tried a batch of 2N5088's that I've had for a while and I'm having the same issue - if not worse. To get unity gain I have to have the volume full up. The Gain knob does very little right until it reaches fully on, then it gets a little sputtery, but there's no change in volume throughout the knob range. Still can't get Q1 collector below 5.8 and I can't really get Q2 or Q3 much above 10V.

Thanks for your help!

[mth5044]

I've done some more reading, and apparently a lot of people are unhappy with their gain knob use 

HOWEVER, I'm not having the issue of it all being bunched up on one small part of the knob, but the overall gain of the circuit is very low.

This demo, around 55 seconds, has a very apparent volume level difference between on and off that I am definitely not getting.

https://www.youtube.com/watch?v=37TWK0d0K5o

[mth5044]

I'm think I'm worrying TOO much about bias voltages. There are many threads with bias voltages all over the map, and they seem happy with them. I'm going to set the trimmers to get the resistances to be what they are in the schematic and see what happens. Damn the voltages!

[thehallofshields]

I built this one. Really looked forward to it and thought it would a cornerstone on my pedalboard.


Hated it. The crackly breakup was awful into a clean amp. Less noticeable into an already distorted amp but still...

[mth5044]

Alright, damning the voltages didn't do anything. But their does turning. The trim while playing, so I think next step is to reflow the joints in the area of Q1

[mth5044]

I've reflowed everything around Q1 without any effect on the problem.

The gain knob still does nothing across it's entire path.

[mth5044]

I had a second PCB, which I wired up. *Same results*

I took the charge pump out of the equation, removed it from the enclosure and used an 18V adapter. Did not have any effect.

Tried using a 9V adapter, same problem. Especially when trying to bias it, I again can't get Q1's collector down to an appropriate voltage.

So that leaves me with three things:

1) I've made the same mistake twice.
2) The parts I've used are somehow faulty.
3) The PCB has a fault.

To check #1, I think by checking the printed values of all components, searching for solder bridges and continuity has checked most of this one off.

To check #2, I suppose I could start pulling components and checking their actual value vs. their printed. Any ideas on where to start? I suppose I'll start around the first gain stage, but I'm very poor at desoldering, so any tips on narrowing down component choice would be greatly appreciated. I'll likely start with the potentiometer. I'll get a 1kC from Small Bear and see if that makes a difference.

Could it be that 2N5088 don't ACTUALLY work in this?

To check #3.. I don't really know. I suppose that since it's sold on Musikding and there's one or two posts showing completed pedals with the PCB, this is the least likely (but the easiest to blame  )

EDIT:
I've confirmed that both the pot and trimmer read 0 to 10k across their sweeps when still soldered in.

[PRR]

The circuit is probably voltage-fussy.

What value for "RX2"?? Jumper, 470R? Math on your observed voltages hints at 150r.

Sure is a MIGHTY messy circuit, with too many bias-loops, bias trims, and NFB resistors.

[aion]

Do you have any other NPN transistors you could try? The 5088s are very high gain and it may affect the performance. 3904s tend to be a lot lower gain (120-180) and would be more like the original transistors.

The other thing I'd do is test it out in 9V mode (jumper the appropriate pads to bypass the charge pump) to see if it biases up that way. I don't think I've ever seen any actual Power Boost voltages, so I just conjectured that they should be doubled if the supply voltage is being doubled. It could be that the transistor performance is not linear. You did the right thing to set the trimmers based on the schematic resistor values - it should sound good at those settings (though it may still be able to be fine tuned from there) so if it doesn't then something is wrong.

Also, definitely do not use a 10k audio taper for the gain control. The original used 10kB, with 1kC being the recommended modern alternative, but 10kA is going in the inverse direction. If the stock value bunched all of the gain control up into the last 10%, by changing it to audio taper you are bunching it all up into the last 1%. So, you may still have some issues with the transistors (at full-clockwise the gain knob is electrically the same whether 10kA, 10kB or 1kC) - but that knob taper will be the next issue once the others are worked out.

[Electric Warrior]

The voltages are fine. Here are readings from my vintage unit for reference:

Battery: 18.84V
Q1 C 6.43V B 3.92V E 3.54V
Q2 C 11.53V B 6.44V E 5.82V
Q3 C 10.19V B 2.77V E 2.23V

Mine uses BC184L, so I can't say in which gain range they are without desoldering, but other units used BC169C. High-ish gains should be alright.

[intripped]

remove jumper in R6

i've checked Aion's pdf against EW schematics and i've found this error (even if i don't know if it's the cause of your issue).

so, for the Power Boost version, Aion's pdf should be: R6 (omit)

Also, for the Overdirver version, R6 should connect to the "-" side of C3

[Gus]

edit I am simming different adjustments. So far R11 looks like the best adjustment for the output section the input has a number of interactions

Electric Warrior posted voltages. I would try the stock collector resistor values and compare to the posted voltages from the vintage unit.

I would print the schematic and carefully check every connection against the schematic. Check that the parts are connected were they should be and also they are not connected anywhere they are not suppose to be. All the way from the input to output. This includes the jacks and switch. Mark the schematic as you go to keep track of what you checked.

[Electric Warrior]

The voltages seem to be in the right ballpark, which makes things a little confusing. Maybe the pot isn't wired correctly? Maybe an issue with its ground connection?

[Gus]

Looking at the linked PDF
If the Q1 bias control is set closer to 0 ohms the gain control will not have as much of an effect.

About the gain control action
Ignore the 22uf cap for now and do a test. Use ohms law and parallel the resistance of the gain control and Q1 bias total resistance (as you have it set with the 3.3k) as you move the gain control.

Older caps often measured higher than marked. 22uf often measured closer to 33uf. Newer caps often measure very close to the marked value.

[mth5044]

Wow thanks everybody! I really appreciate all the comments.

The circuit is probably voltage-fussy.

What value for "RX2"?? Jumper, 470R? Math on your observed voltages hints at 150r.

Sure is a MIGHTY messy circuit, with too many bias-loops, bias trims, and NFB resistors.

Thanks for working up that voltage diagram! I have looked at RX2 in circuit and have a yellow - violet - black - black - brown resistor in that place, which indicates 470. I have measured the resistor in place and am getting 467r, and I also measured the cut real that the resistor came from and got the 467r.

I checked R2 as well as it seems to be part of this bias network and read a 119.5k in circuit, so that one checks out.

Do you have any other NPN transistors you could try? The 5088s are very high gain and it may affect the performance. 3904s tend to be a lot lower gain (120-180) and would be more like the original transistors.

I'll have a search through the bin and see what I can find.

The other thing I'd do is test it out in 9V mode (jumper the appropriate pads to bypass the charge pump) to see if it biases up that way. I don't think I've ever seen any actual Power Boost voltages, so I just conjectured that they should be doubled if the supply voltage is being doubled. It could be that the transistor performance is not linear. You did the right thing to set the trimmers based on the schematic resistor values - it should sound good at those settings (though it may still be able to be fine tuned from there) so if it doesn't then something is wrong.

I did try it at 9V and have the same issue where the bias values are either right on or slightly too high when using the 9V as I have at 18V.

Also, definitely do not use a 10k audio taper for the gain control. The original used 10kB, with 1kC being the recommended modern alternative, but 10kA is going in the inverse direction. If the stock value bunched all of the gain control up into the last 10%, by changing it to audio taper you are bunching it all up into the last 1%. So, you may still have some issues with the transistors (at full-clockwise the gain knob is electrically the same whether 10kA, 10kB or 1kC) - but that knob taper will be the next issue once the others are worked out.

My mistake on the first report, I have 10k linear pots in there per the original schematic, not log.

The voltages are fine. Here are readings from my vintage unit for reference:

Battery: 18.84V
Q1 C 6.43V B 3.92V E 3.54V
Q2 C 11.53V B 6.44V E 5.82V
Q3 C 10.19V B 2.77V E 2.23V

Mine uses BC184L, so I can't say in which gain range they are without desoldering, but other units used BC169C. High-ish gains should be alright.

Excellent! I can get ballpark those voltages, so things seem to be biasing (or whatever trim 1 actual does) correctly. Thank you for posting those.

remove jumper in R6

i've checked Aion's pdf against EW schematics and i've found this error (even if i don't know if it's the cause of your issue).

so, for the Power Boost version, Aion's pdf should be: R6 (omit)

Also, for the Overdirver version, R6 should connect to the "-" side of C3

GOOD EYE! Comparing it these schematics (which I think were originally drawn by Electric Warrior?), it does indeed look like that R6 should be omitted instead of jumpered. I will try this out when I test out a different jelly bean NPN.

edit I am simming different adjustments. So far R11 looks like the best adjustment for the output section the input has a number of interactions

Electric Warrior posted voltages. I would try the stock collector resistor values and compare to the posted voltages from the vintage unit.

I would print the schematic and carefully check every connection against the schematic. Check that the parts are connected were they should be and also they are not connected anywhere they are not suppose to be. All the way from the input to output. This includes the jacks and switch. Mark the schematic as you go to keep track of what you checked.

Good call Gus! Will be printing this out and tracing side by side with Aion's schematic and the three iterations posted above. Thanks!

The voltages seem to be in the right ballpark, which makes things a little confusing. Maybe the pot isn't wired correctly? Maybe an issue with its ground connection?

They are board mounted, so it's unlikely it's a wiring issue, but could come down to the traces. I'll determine the connections when going over the pcb and schematic as Gus suggested, but will pay extra close attention to the gain pot connections. Thanks!

Looking at the linked PDF
If the Q1 bias control is set closer to 0 ohms the gain control will not have as much of an effect.

About the gain control action
Ignore the 22uf cap for now and do a test. Use ohms law and parallel the resistance of the gain control and Q1 bias total resistance (as you have it set with the 3.3k) as you move the gain control.

Older caps often measured higher than marked. 22uf often measured closer to 33uf. Newer caps often measure very close to the marked value.

Does that jumper for R6 muck things up when doing this calculation? I thought it was weird that the gain pot had no effect on the bias - but I suppose the 22uF cap takes the gain pot out of the bias equation? As far as using ohm's law, I'm afraid you've lost me there. Am I solving for the current across the paralleled resistors?

[mth5044]

We have a boost! Thank you every one who took the time and helped out, I truly appreciate it - this was driving me nuts.

I at first put in BC109C's to rule out the 2N5088's. No effect, same bias issue, same sound. Clipped R6's jumper and viola! More boost than a monkey's uncle. Was R6 creating some sort of feedback that was taming Q1's gain?

In any case, thanks everyone, and thanks intripped for spotting that error in the build doc!!! Muchas gracias. Aion - seems like R6 aught to be an *omit* and not a jumper!

Thanks again everyone!

[aion]

Fixed it in the docs... the project has been released for 3 years and I guess no one ever built the Power Boost version! (or at least reported back on it)