# organ donor volume drop



## Funnel (Feb 6, 2019)

Hi, I built the organ donor and the sound is perfect except for a slight volume drop.


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## stevtron (Feb 24, 2019)

got the same "problem" ... could be more volume . Only with all knobs full "open" it's just the same loudness as bypassed. Maybe that's correct, but if you wanna just add some octave down f.e. it's much to quiet.
Some mod ideas ?


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## Alchemy Audio (Feb 25, 2019)

This is an issue with the original EQD version too. Let me know if you have any mod ideas - since I'll be building one soon for a friend to (hopefully) replace hi EQD Organizer.


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## Robert (Feb 26, 2019)

I can bump up the effected volume in the algorithm if the dry signal is loud enough,  boosting the overall output would raise the noise level.


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## Alchemy Audio (Feb 26, 2019)

I'd be willing to try it. I just ordered the pcb yesterday - assuming you have time to make the change.


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## stevtron (Sep 10, 2019)

Is that problem solved ? Cool pedal, but that volume drop is not cool ...


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## Cybercow (Oct 6, 2020)

Robert said:


> I can bump up the effected volume in the algorithm if the dry signal is loud enough,  boosting the overall output would raise the noise level.


I just finished an Organ Donor build and am noticing the volume drop as well. Love the effect! I was thinking of adding a 10K trimpot between pins #1 & #2 of IC 4.1 (the final output stage of the second opamp) to find the sweet-spot and increase the output a bit. Thoughts?


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## smithcircuits (Oct 20, 2020)

Cybercow said:


> I just finished an Organ Donor build and am noticing the volume drop as well. Love the effect! I was thinking of adding a 10K trimpot between pins #1 & #2 of IC 4.1 (the final output stage of the second opamp) to find the sweet-spot and increase the output a bit. Thoughts?


Any luck w this? Just boxed mine up and have the same issue.


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## Cybercow (Oct 21, 2020)

smithcircuits said:


> Any luck w this? Just boxed mine up and have the same issue.


I've not gotten there yet. It's currently in my decals queue while I finish up a couple other projects. I intend to post back when I do get there.


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## smithcircuits (Oct 22, 2020)

@Cybercow Tried this, actually went up to 15k. Helps the volume drop a bit (not completely). Introduces a bit of noice into the wet signal. I’m keeping it there.


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## Cybercow (Oct 22, 2020)

smithcircuits said:


> Any luck w this? Just boxed mine up and have the same issue.





smithcircuits said:


> @Cybercow Tried this, actually went up to 15k. Helps the volume drop a bit (not completely). Introduces a bit of noice into the wet signal. I’m keeping it there.


I just tried the modification I mentioned. I lifted (cut) pin #2 and soldered a 20K trimmer across pins #1 & #2 of opamp #4. It made no audible difference to my ears. I futzed with the trimmer value all way off (counter-clockwise) to all the way up (clockwise) and could not hear a difference. I checked the trimmer variance with a DMM before I applied the modded opamp to the circuit and the trimmer does indeed vary from 0 Ω to 20k Ω.

After doing some remedial research on opamps, I'm thinking I may need to add a 1K Ω resistor from pin #2 to ground. Might even add a 100nF to 220nF cap in series with (after) the 1K resistor. (I'm thinking Tube Screamer gain section etymology without the clipping elements.) I'll report back after I try that.

Also, I'm guessing that the noise floor of the wet signal is an issue - based on other notes (further up in this thread) from PedalPCB on the matter.


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## zgrav (Oct 22, 2020)

it might be more productive to increase the amplification of the incoming signal when it goes to IC1.1 in the schematic.   same idea as what was done at IC4, just boost the signal at the start of the chain that feeds both the wet and dry signals.  

better still, if your mod above is only on the IC, try switching positions with IC1 and IC4 to see if it works better there.


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## Chas Grant (Oct 22, 2020)

You will need a resistor from Pin 2 to ground in order to get any gain out of IC4, or if you try, on IC1.  As far as the capacitor in series with the pin 2 to ground resistor, realize this will form a high pass filter which will attenuate frequencies below the cutoff freq. This may not work to well with the octave down of this pedal.


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## music6000 (Oct 22, 2020)

Chas Grant said:


> You will need a resistor from Pin 2 to ground in order to get any gain out of IC4, or if you try, on IC1.  As far as the capacitor in series with the pin 2 to ground resistor, realize this will form a high pass filter which will attenuate frequencies below the cutoff freq. This may not work to well with the octave down of this pedal.


Is this what you mean or lift Op Amp Pin 2 from PCB?


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## Chas Grant (Oct 22, 2020)

Like This 1K will give you a max gain of 20 which may be to high. Around 5K will give you a max gain of 5, you will need to turn the pot up some before you start to hear gain. I would go for the lowest value you can get on the pot. The idea is to recover the volume lost due to the circuit is all. Too much boost and you will start to pick up noise. this is the equation your looking at

Gain = 1+R pot/R 2ndresistor, so with 20K on pot and 5K resistor Gain will be 5, which means you will recover about 14db. You shouldn't be losing that much but if you are you can lower the value.


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## music6000 (Oct 22, 2020)

So Op Amp Pin 2 is still lifted as Pin 1 & 2 are linked on PCB?


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## Chas Grant (Oct 22, 2020)

music6000 said:


> So Op Amp Pin 2 is still lifted as Pin 1 & 2 are linked on PCB?


Yes, Pin 2 has to stay lifted.


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## Cybercow (Oct 22, 2020)

Chas Grant said:


> You will need a resistor from Pin 2 to ground in order to get any gain out of IC4, or if you try, on IC1.  As far as the capacitor in series with the pin 2 to ground resistor, realize this will form a high pass filter which will attenuate frequencies below the cutoff freq. This may not work to well with the octave down of this pedal.


Thanks! I get that - as I suggested in my last post where I mentioned that I did a little remedial education on opamps. I just hadn't gone there yet. Will post later with a photo of the additional resistor. I'll try a 5K Ω first. (It's been decades since I did the math.)


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## Cybercow (Oct 23, 2020)

I ran a 5K resistor from pin #2 of IC4 to ground and lost all signal at ANY setting of the 20K trimpot. (No sound output at all.) I also tried a 1K Ω resistor with the same result. When I opened the resistor's connection to ground, the signal reappeared. 





So, I think there is no "quick" modification that can fix the volume drop. I'm just going add a tiny "clean boost" daughterboard to the build, set the gain by ear to compensate for the Organ Donor's volume drop, and call the project done.


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## Chas Grant (Oct 23, 2020)

That sucks, it should work.


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## Funnel (Feb 6, 2019)

Hi, I built the organ donor and the sound is perfect except for a slight volume drop.


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## smithcircuits (Oct 23, 2020)

Same thing happened with mine. womp womp


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