aphelion / DOD 250

[eh la bas ma]

Hello,

I am trying to finish this build and I have a few questions about it . https://aionfx.com/app/files/docs/aphelion_legacy_documentation.pdf

I notice that I have to turn the guitar volume all the way up to get a distortion with this pedal. If I let the guitar volume at 12' , the overdriven sound appears only when the gain knob is set almost at maximum . Does the DOD 250 normally behaves like that ?

Now, to the real issues :

Instructions lets us choose between several version. I did the '97 yellow 250, with 100k instead of 10k for R5 (near the clip switch) and 56n instead of 47n at c3.

Only the treble switch works.
The comp switch doesn't do anything (it should change a cap value, but aion seems to have supressed it in the newer version) and I get the same sound with or without diodes connected to the circuit. The clip switch and the trimmer doesn't do anything to the sound, not even a pop, like diode-lift mode in all 3 positions . I used the middle pads and maybe this is the mistake ? "Extra pads have been provided so you can stack two diodes in a row if desired. (The middle two pads are connected in each diode.) "
I  hesitate to change R5 for 10k and c3 to 47n because I could damage the pcb for nothing .
There is an empty IC socket but it is supposed to be like this. According to the instructions, the extra IC is for using a 4558. I use currently a LM741 despite the fact that i should use the other one for this version, I don't think that is the issue here, since I tried with both.
Here is some pics in case anyone spots something wrong :




Thank you very much for your help . Justin

[Vivek]

I would suggest first step would be to measure the voltages at each pin of the IC

[iainpunk]

I would suggest first step would be to measure the voltages at each pin of the IC

yes, but no
that would be the first step of debugging indeed if there is no sound, but he does have sound, just not clipped.

i believe that you should put the sockets/diodes in the outer holes for them to work!

its generally good practice to have the guitar volume on max and then set the volume on the amp and pedals accordingly. having the volume lower than full makes the impedance higher and the signal dull and noisy. having the volume on your guitar in the middle leaves only 1/4th of the voltage on the output because the pot is logarithmic, this is because we humans perceive volume on a logarithmic scale, this means that if we want to hear half the volume, only 1/4th the voltage is needed, if we want to hear double the volume, we need 4x as much voltage. to compensate for this, the pots are ''skewed'' in a way that 1/2 of the turn gives 1/2 volume and 1/4 voltage.

welcome to the forum!
Cheers, Iain

[eh la bas ma]

Yes, thank you, I was wrong on the diodes pads. Now it's working fine.

I broke (again...) one of the germanium diodes OA1182. I have one OA1182 left and one D9E. Do you think I can use those ?

I still have no change on the comp switch. I am guessing this is related to CX1, Cx2 and CX3. Any ideas in order to get this switch alive and interesting would really be welcome. I 'd like to get this distortion as good as I possibly can .

I give you my readings on the IC (RC4558 this time) just in case .

1= 4.50 v
2= 4.66 v
3= 4.41 v
4= 0.01mV
5= 8.65 v
6= 0.01mV
7= 8.65 v
8= 9.19 v

About guitar volume : I am using seymour ducan's Dave Mustaine pick ups. This is two active humbuckers and the signal is slightly distorded when I turn the volume all the way up. It acts almost like a boost. The guitar sounds more precise to me when it's set around noon on some other distortions or fuzzes .
Does your advice still apply with active pick ups ?

[iainpunk]

the comp switch's effect is super subtile, its affected by C2, CX1 and CX2. [CX3 is for tone control at the end].
the values in the file seem really large to me, i recommend the following values to make it way more pronounced, but sockets are quite usefull here:
C2    - 560pF
CX1  - 1nF
CX2  - 10nF
also, making C3 larger, like way larger, makes the comp switch more effective. i recommend 470n or bigger instead of 47n

About guitar volume : I am using seymour ducan's Dave Mustaine pick ups. This is two active humbuckers and the signal is slightly distorded when I turn the volume all the way up. It acts almost like a boost. The guitar sounds more precise to me when it's set around noon on some other distortions or fuzzes .
Does your advice still apply with active pick ups ?

ah, active pickups, that changes the game, your 12' setting is probably unity gain, or "normal" output volume, so its right to use!

cheers, Iain

[ElectricDruid]

Welcome!

It looks to me like R5 is 100K (brown, black black, orange) instead of 10K. That'd probably hit the volume going to the clipping diodes and prevent much crunch from happening.

Check that one, please.

HTH.

[eh la bas ma]

Thank you very much for your help.

About the comp switch, I will try these values as soon as I put my hands on the right caps. I am currently missing the 470n (C3).
I will report back once it's done.

I soldered a 10k in R5 today.

I can't really tell the difference from the 100k. The '97 yellow is the only version using a 100k on C5. I thought it could be somehow related to c3 which is the only other changing value compared to the other versions, but it doesn't sound noticeable .

Now that the signal is clipped, i am getting some distortion when i turn the gain pot from 12'.
Any position before gives a clean signal, but I am not sure this is anomalous .

[iainpunk]

have you checked the battery voltage of your guitar? or a higher setting?
or have you tried the pedal with another guitar?
checked all solder points?

i'm all out of new suggestions

cheers

[ElectricDruid]

I agree with Iain that the "Comp" switch is subtle - I would say "irrelevant" in this situation. If the pedal works, you'll hear it. If it doesn't work, you won't. Either way, it won't be the Comp switch that makes the difference. It simply doesn't change things enough.

If you're still not getting the gain you should expect from this circuit, you need to check the components that might cause a problem. With the power off, can you give us a multimeter reading of: R1, R2, R3, R4, and the gain pot. If we know these values we'll be able to see if the pedal is behaving as it should be.

Thanks, and good luck!

[eh la bas ma]

OK, here are the readings with the pedal turned off, and connected to the power supply.

R1 = 4.39 v
R2 = 4.36 v
R3 = 4.59 v
R4 = 0.00 mV

Gain pot : 0.000 mV on 1, 2 and 3

I just tried it with a passive guitar, volume set to max. On diode lift mode, the signal get distorted when the gain is set almost at max. With germanium clipping, it starts much sooner, there is some crunch (not a good type of crunch I think, but at 03:15 am, I am playing with headphones) around 9' and distortion around 11' .

I am looking at both Led in the diodes section. They light up when the signal get distorted. With active pickups on high volume, lights appear when the gain is set after 11'. With passive pickups at max , both led light up if the gain pot is almost fully CW .

The pots values are correct (C500K on gain and A100K on volume). I tested every resistor with a multimeter before I populated the pcb. There are 3 pads for C5, I used those with + and - markings, closest to the trimmer. I can't spot any suspicious solder joint, but i'll keep looking just in case.

[iainpunk]

OK, here are the readings with the pedal turned off, and connected to the power supply.

R1 = 4.39 v
R2 = 4.36 v
R3 = 4.59 v
R4 = 0.00 mV

Gain pot : 0.000 mV on 1, 2 and 3

we would like to see resistance readings, not voltage readings, with the power not connected of course.

it sounds like you have to little gain for some reason.
in generally, headphones make stuff sound worse

cheers

[eh la bas ma]

Resistance readings shows :

R1 = 9.89 k
R2 =0.466 M
R3 = 0.993 M
R4 = 4.66 k

There is a "1" marked on the pcb, near one of the pads, so I'll use it :

gain pot turned fully CW.

black on 1, red on 2 : 0
            1           3 : 2 ohms
            2           3 : 1.9 ohms

fully CCW :

            1 and 2 : 000.1 ohms
            1 and 3 : 0.549 M
            2 and 3 : 0.549 M

I am not sure if it means anything, but i couldn't have clear readings when i tried to probe on the solder joints. I had to turn the pcb around and put the probes on the little holes of the potentiometer.

[eh la bas ma]

[ElectricDruid]

I am not sure if it means anything, but i couldn't have clear readings when i tried to probe on the solder joints. I had to turn the pcb around and put the probes on the little holes of the potentiometer.

The resistances look ok, but the fact you can't get a connection on the solder joints could be a sign. You've tested that the pot works, so that's good, but it looks like the joints holding it into the board might be bad. If that's not connected properly, there won't be any gain at all!

Try reheating those joints on the pot and see if anything changes. If you've got a solder sucker, suck the old solder off and put some new on instead.

[eh la bas ma]

I reflowed the gain pot's joints, but it doesn't seems to change the gain level. I thank you all the same.

I think it is all about the diodes choice . Hypothetically, the gain problem is caused by a "bad" clipping.

With led clipping the signal get distorted, but the overall texture of the sound is close to the diode lift mode ( rough and granular ).
Since I broke one OA1182, I use one D9E instead, with the remaining OA1182. So the clipping may be affected by this .

I just swapped both led with two 1N4148. The distortion is much "cleaner", the pedal sounds closer to the dod 250's demos I have been listening, and finally the gain pot's action is more suitable.

I suppose D9E is a poor equivalent to replace OA1182. Or it is good, but I need to replace both and not use one of each together ?

I found this usefull topic here : https://www.diystompboxes.com/smfforum/index.php?topic=109233.msg998309#msg998309

"The original used a pair of silicon diodes, like 1N914/1N4148" : Does he mean only one of each ?
Would two 1n914 sounds different than two 1N4148 ?
I am not sure they fully exhausted this topic of conversation in 2014 . I might resurrect this thread in a near futur...

Would you have some suggestion about what sort of diode I can try, that fits well in this circuit ? This pcb allows me to use up to 4 diodes, twice.

[willienillie]

Since I broke one OA1182, I use one D9E instead, with the remaining OA1182. So the clipping may be affected by this

Any difference between the two clipping diodes, even if they are the same type, will result in asymmetrical clipping.  This isn't necessarily a bad thing, if you like the sound go for it.

"The original used a pair of silicon diodes, like 1N914/1N4148" : Does he mean only one of each ?
Would two 1n914 sounds different than two 1N4148 ?

No, he means two of either.  1N914 and 1N4148 are essentially the same diode, and can be subbed for each other in nearly all applications.

----------

I admit I haven't completely read the thread or linked documentaion.  But starting with this:

I notice that I have to turn the guitar volume all the way up to get a distortion with this pedal.

Do you not normally play with your guitar volume all the way up?  Except with a Fuzz Face (or similar), most would play full on for distortion.  The Dist+/DOD250 isn't a very high gain pedal, more like an overdrive.  Germainium clippers (Dist+) will give more dirt at the cost of overall volume.

[iainpunk]

have you looked at the values of the leg to ground in the feedback loop? having too small of a cap or a too large resistor or just a bad solder joint will take out a bunch of the gain,
maybe you want to check that out
 
cheers,
Iain

[duck_arse]

Since I broke one OA1182, I use one D9E instead, with the remaining OA1182. So the clipping may be affected by this

Any difference between the two clipping diodes, even if they are the same type, will result in asymmetrical clipping.  This isn't necessarily a bad thing, if you like the sound go for it.

this. one big difference, in your stated case, is the diode body markings. if you put an OA-type and a D9-type with the body bands pointing opposite directions, the kathodes will both be at the same end, as the russian diodes, famously, mark the anode with a band, whereas the OA and AA types mark the kathode instead.

peer into the glass body, look for the little disk - it will be the kathode-end in both types. both diodes same way will mean no clipping one half cycle.

[edit:] gah! spellings are like I'm typing on another of jim's keyboards.

[ElectricDruid]

The Dist+/DOD250 isn't a very high gain pedal, more like an overdrive.

The OP has 1M and 4K7 as the values in the feedback loop, so that's x213 gain, or +46dB. That's quite a lot of gain, I'd say. Or it should be.

It's enough gain to slam a 45mVpp signal into the 9V rail. Given that even quiet guitars put out a 100mVpp and that we're clipping the signal using diodes (so a lot earlier than 9V) I'd expect there to be quite a lot of crunch possible. I'm still not convinced the pedal is working correctly.

have you looked at the values of the leg to ground in the feedback loop? having too small of a cap or a too large resistor or just a bad solder joint will take out a bunch of the gain,
maybe you want to check that out

We've checked the resistor values, and they're ok. And we've resoldered the pot, so that's ok. Could still be a bad joint on the cap C3 or R4, I suppose.

[eh la bas ma]

I wanted to give you the readings on LM741 on IC1 (earlier I gave RC4558 in IC2) but the 8th leg was unclear, so I followed your advices and reflowed R4, C3 and IC1. Unfortunatly it didn't give a clearer reading.

1 = 2.5 mV
2 = 4.68 V
3 = 4.42 V
4 = 0.000 mV
5 = 2.5mV
6 = 4.71 V
7 = 9.40 V
8 = 006.5 to 002.5 mV with the (-) symbol appearing and disappearing quickly

I took pictures in case it's obviously wrong somewhere.
C3 and R4 are between the switches, and the first pic shows IC1 :