“Easy” 3-knob IC-based Overdrive suggestions

[DJPsychic]

Looking to build my first IC based pedal. I'm thinking of doing a simple build like Ross Distortion or a DOD 250, but would like some recommendations on 3-knob (gain, vol, tone) pedals that are at A similar build level.

I have some TL072 and RC4558 on order

Any suggestions would be much appreciated

[bluebunny]

Son of Screamer, or any of the other bufferless tube screamer variants.

[DJPsychic]

Son of Screamer, or any of the other bufferless tube screamer variants.

Cool thank you. Looks like a fun one!

[Fancy Lime]

The Fulltone OCD comes to mind. You can replace the MOSFETS with normal silicon diodes or generally experiment with different diode arrangements for different sounds.

The Timmy Overdrive is also very popular in this camp.

I would also recommend the DOD FX50B Overdrive Plus or the DOD FX55B Supra Distortion both with the buffer circuit removed and replaced with true bypass switching. Not because true bypass is better but because it is easier. These DOD circuits have a nice and somewhat undervalued (imho) tone control circuit.

Or you could try this (shameless plug):
https://www.diystompboxes.com/smfforum/index.php?topic=123516.0

Out of  all circuits mentioned, I like the DOD FX50B best, sound-wise. Give it a listen. It specifies an LF353 opamp but you can use the TL072. The only difference should be that the TL072 is less noisy. If you decide you want to try this we I'd be glad to help with how to remove the buffer. I am unaware of any schematics that have it removed already for true bypass operation although that seems to be a fairly popular mod on old DOD pedals.

Cheers,
Andy

[DJPsychic]

Very cool thanks for the recommendations, I really dig your pedal.

I definitely only want to build True Bypass pedals. I'm still somewhat of a beginner so I was browsing Layouts.

Do most layouts for the DOD and the ROSS floating have the buffers included? i.e :

[Marcos - Munky]

This one is bufferless.

[DJPsychic]

The Fulltone OCD comes to mind. You can replace the MOSFETS with normal silicon diodes or generally experiment with different diode arrangements for different sounds.

The Timmy Overdrive is also very popular in this camp.

I would also recommend the DOD FX50B Overdrive Plus or the DOD FX55B Supra Distortion both with the buffer circuit removed and replaced with true bypass switching. Not because true bypass is better but because it is easier. These DOD circuits have a nice and somewhat undervalued (imho) tone control circuit.

Or you could try this (shameless plug):
https://www.diystompboxes.com/smfforum/index.php?topic=123516.0

Out of  all circuits mentioned, I like the DOD FX50B best, sound-wise. Give it a listen. It specifies an LF353 opamp but you can use the TL072. The only difference should be that the TL072 is less noisy. If you decide you want to try this we I'd be glad to help with how to remove the buffer. I am unaware of any schematics that have it removed already for true bypass operation although that seems to be a fairly popular mod on old DOD pedals.

Cheers,
Andy

I do like your "greatest hits" pedal. Thanks for sharing

[Fancy Lime]

Well, if I am completely honest, the Chameleon has a few problems that need to be worked out. So I would not necessary recommend it to a beginner. (Sorry, I missed the "first IC based pedal" in the original post.) Actually in that light I would recommend you build a DOD 250 or MXR distortion+, which are essentially the same thing anyway, and add a tone control. There is a layout using a dual opamp here:
https://tagboardeffects.blogspot.com/2013/06/dod-overdrive-preamp-250-reissue.html
Add Mark Hammer's Patented Stupidly Wonderful Tone Control (not really patented) to this and you have an amazing Overdrive/Distortion that is really easy and quick to build. I would also change the horizontal 100k resistor to 10k in this case. The first example here is what I would use:
http://www.muzique.com/lab/swtc.htm
You don't need R1 in this case. Just run the wire labeled "Level 3" to the right lug (looking down the shaft) of a 50k linear pot. This will be your tone pot. Connect the left lug of that tone pot to the right lug of the volume pot and the center lug to a 3.3n cap, whose other end you connect to ground. The rest remains as the layout says.

I would recommend using sockets for the diodes and experimenting a bit here. This layout also makes it very easy to put in a switch to select different diodes. If you are interested in that, I can run you through that, it's very easy.

Oh, and do socket the opamp as well! The 4558 will probably sound best here but trying the TL072 wont hurt.

If you want something fancier, they have a layout for the FX50B as well:
https://tagboardeffects.blogspot.com/2013/01/dod-fx50-b.html
It has the buffers but not the soft switching, so it would still need a true bypass.

But I think the 250 is probably more fun and less frustrating to build. Heck, I want to build me one of these now after listening to a few youtube demos while writing this...


Cheers,
Andy

[DJPsychic]

Well, if I am completely honest, the Chameleon has a few problems that need to be worked out. So I would not necessary recommend it to a beginner. (Sorry, I missed the "first IC based pedal" in the original post.) Actually in that light I would recommend you build a DOD 250 or MXR distortion+, which are essentially the same thing anyway, and add a tone control. There is a layout using a dual opamp here:
https://tagboardeffects.blogspot.com/2013/06/dod-overdrive-preamp-250-reissue.html
Add Mark Hammer's Patented Stupidly Wonderful Tone Control (not really patented) to this and you have an amazing Overdrive/Distortion that is really easy and quick to build. I would also change the horizontal 100k resistor to 10k in this case. The first example here is what I would use:
http://www.muzique.com/lab/swtc.htm
You don't need R1 in this case. Just run the wire labeled "Level 3" to the right lug (looking down the shaft) of a 50k linear pot. This will be your tone pot. Connect the left lug of that tone pot to the right lug of the volume pot and the center lug to a 3.3n cap, whose other end you connect to ground. The rest remains as the layout says.

I would recommend using sockets for the diodes and experimenting a bit here. This layout also makes it very easy to put in a switch to select different diodes. If you are interested in that, I can run you through that, it's very easy.

Oh, and do socket the opamp as well! The 4558 will probably sound best here but trying the TL072 wont hurt.

If you want something fancier, they have a layout for the FX50B as well:
https://tagboardeffects.blogspot.com/2013/01/dod-fx50-b.html
It has the buffers but not the soft switching, so it would still need a true bypass.

But I think the 250 is probably more fun and less frustrating to build. Heck, I want to build me one of these now after listening to a few youtube demos while writing this...


Cheers,
Andy

Thanks for the response. Yes the Chameleon looks really cool. I'll definitely try to take a stab one day.

And the DOD 250 looks like a fun one. I'd like to add a tone knob (a bit above my pay scale at the moment).



Is this layout without buffer?

Sorry for the total noob questions! I can't really tell, I would just wire up a 3PDT to it.

[Fancy Lime]

Hi,

the layout you linked is indeed without buffer but it is for an LM741 opamp. That is a single opamp. The opamps you have ordered, RC4558 and TL072 are dual opamps, which have a different pin layout so you cannot use them in a circuit layout designed for an LM741 (or any other single opamp). The layout you want to use is this one:
https://tagboardeffects.blogspot.com/2013/06/dod-overdrive-preamp-250-reissue.html
The KA4558 dual opamp specified here is pin compatible with the RC4558 and TL072.

For the tone control: I explained how to add that in my last post. Can you explain what is unclear to you? I don't know how to explain it any clearer with words only and don't have the time right now to draw it. I'll write a post to see if someone has a drawing and if not I'll try to do one myself later today.

Cheers,
Andy

[DJPsychic]

Hi,

the layout you linked is indeed without buffer but it is for an LM741 opamp. That is a single opamp. The opamps you have ordered, RC4558 and TL072 are dual opamps, which have a different pin layout so you cannot use them in a circuit layout designed for an LM741 (or any other single opamp). The layout you want to use is this one:
https://tagboardeffects.blogspot.com/2013/06/dod-overdrive-preamp-250-reissue.html
The KA4558 dual opamp specified here is pin compatible with the RC4558 and TL072.

For the tone control: I explained how to add that in my last post. Can you explain what is unclear to you? I don't know how to explain it any clearer with words only and don't have the time right now to draw it. I'll write a post to see if someone has a drawing and if not I'll try to do one myself later today.

Cheers,
Andy

Thanks for clarifying. To be honest I missed your tone knob instructions. Yep they're all there, I appreciate it! You've been super helpful

[Fancy Lime]

Hi,

I hacked together the relevant info in layout form. Due to copyright, I cannot put in the actual layout from tagboardeffects without asking them and I'm too lazy for that. I'm sure they would not mind but let's play it safe. So you have to combine this:



with the layout here:
https://tagboardeffects.blogspot.com/2013/06/dod-overdrive-preamp-250-reissue.html

in what I hope is the obvious manner. And you have to change the one horizontal 100k resistor above the IC to 10k. That's all.

BTW, thanks for turning me on to this. I had never considered a 250 but after listening to lots of youtube video demos I decided to build one with the SWTC as well, as soon as I'm back to my workbench (currently expatriated to the in-laws because of closed day cares). Sounds really great with bass, too:
https://www.youtube.com/watch?v=yjQdVeEGxIA


Or you can expand the whole thing with a SPST (center off) switch like this:

If you do that, the tree diodes at the switch should have lower clipping thresholds than the two on the board. I'd recommend red LEDs for D1 and D2 on the board and 1N4148 for D1-D3 on the switch. This will give you two different symmetrical options plus one asymmetrical. It is a popular mod for a reason.


Cheers and have fun with that,
Andy

p.s. drop us a line when you run into problems or when you get it working.

[DJPsychic]

Hi,

I hacked together the relevant info in layout form. Due to copyright, I cannot put in the actual layout from tagboardeffects without asking them and I'm too lazy for that. I'm sure they would not mind but let's play it safe. So you have to combine this:



with the layout here:
https://tagboardeffects.blogspot.com/2013/06/dod-overdrive-preamp-250-reissue.html

in what I hope is the obvious manner. And you have to change the one horizontal 100k resistor above the IC to 10k. That's all.

BTW, thanks for turning me on to this. I had never considered a 250 but after listening to lots of youtube video demos I decided to build one with the SWTC as well, as soon as I'm back to my workbench (currently expatriated to the in-laws because of closed day cares). Sounds really great with bass, too:
https://www.youtube.com/watch?v=yjQdVeEGxIA


Or you can expand the whole thing with a SPST (center off) switch like this:

If you do that, the tree diodes at the switch should have lower clipping thresholds than the two on the board. I'd recommend red LEDs for D1 and D2 on the board and 1N4148 for D1-D3 on the switch. This will give you two different symmetrical options plus one asymmetrical. It is a popular mod for a reason.


Cheers and have fun with that,
Andy

p.s. drop us a line when you run into problems or when you get it working.

Hey man thanks! You didn't have to do all that, but it's much appreciated!

I actually went ahead and ordered some LM741's and TL701's that I should be getting tomorrow (hopefully). Our postal service has been backed up where I'm from. I have many tiny packages with Germanium transistors floating around somewhere 

I'll let you know how it goes. I found a pretty cool "how to breadboard" DOD 250 I'll start of with.

Thanks again man, cant wait to get into this pedal 

[DJPsychic]

p.s. drop us a line when you run into problems or when you get it working.

Well, i finally got the chance to breadboard a 250, using this fantastic diagram



Credit: https://www.diystompboxes.com/projects/intro.html

And I managed to fit your recommended "super simple dumb" tone knob too! Again thank you so much for going through that with me.

Here are some issues I'm encountering:

1) There's only really any gain at the last turn of the pot. I'm using a B500k

2) Tone knob works, but anything past 9 o'oclock when turning CCW it's too muffled and not very usuable. Is there a way to widen the tone sweep?

3) How can I achieve more headroom from the Volume pot? I'm using A100k. I know when using clipping diodes loss in volume is inevitable. Is there a resistor I can increase value of? On my FF, I can increase the 470R before output cap to 3.3k and get a substantial amount of volume increase. is there an easy fix like this?

[antonis]

There's only really any gain at the last turn of the pot. I'm using a B500k

Absolutely natural..
500k pot at 90% of its turn acts as a 50k pot at no turn at all..
(well, almost..)
50k original value pot gives a Gain of  41 at 12 o'clock where 500k gives a gain of only 5 at same position..
(ignoring 4k7 resistor for easy calulations..)

How can I achieve more headroom from the Volume pot? I'm using A100k. I know when using clipping diodes loss in volume is inevitable. Is there a resistor I can increase value of?

No..
You can't raise voltage by passive items at the specific configuration..
(you could add diodes series resistor to offset clipping threashold but it would "soften" clipping effect..)
More Volume means more Voltage so, for a resistive divider its value doesn't count (i.e. same result for 10k pot as for 100k pot..) 

[Fancy Lime]

Hi,

good to hear you're making progress!

1) In a gain pot configuration like the DOD250, you want to use a reverse logarithmic taper gain pot for an appropriate sweep. These are usually labelled "C" taper, so C500k is what you want. You can try C250k or C1M as well if you happen to have one of those but not the C500k. The B500k you have is linear taper, which does not work very well in this configuration. If you have a normal logarithmic taper A500k (or A250k or A1M) you can try those as well but you have to wire them "backwards" (pin 1 and 3 switched) and they will work backwards (CW for less gain, CCW for more gain). The "feel" will be the same as with C taper only backwards. Since it is often more difficult to get C pots, using As backwards can be useful for testing while waiting for delivery of the "right" pot.

2 and 3) What value are you using for the tone pot? C50k? In that case you will get quite some volume loss with an A100k volume pot. See, resistor R6 (numbering as in the breadboard drawing you posted) + the tone pot's total resistance form a voltage divider with the volume pot. That means that even with the Volume at 100%, you have (according to the voltage divider equation: https://en.wikipedia.org/wiki/Voltage_divider): Vout = Vin*100k/(10k+50k+100k) = 62.5% remaining when the volume knob is fully open, or 37.5% loss. So you loose more than a third. You can change any of those components if you like but that will have different trade-offs. I would suggest using an A250k volume pot, which will give you (all other components remaining the same) 80.6% remaining, in other words only 20% loss instead of 37.5%. That should probably be OK. If you additionally reduce the tone pot to C25k, you get 87.7% coming through. This will also have the effect of curing your tone control sweep problem. If you do not have a C25k, you can instead reduce the tone cap (the one connected to the 2nd pin of the tone pot) to about half the current value. The smaller the cap and the smaller the pot value, the less highs are cut off when the pot is fully CCW. The cap is a good place for some experimentation until you like the result.

Lastly, you can also reduce R6 but that will not have a massive influence on the volume but will change the clipping characteristics of the diodes (not much but audible). You can also change the diodes for a higher clipping threshold. For example, changing D1 to a red LED will give you a much higher volume but less distortion and a more "crunchy" sound. I strongly encourage experimenting with different clipping diodes, it's a lot of fun and can give you surprisingly different sounds. Search for "clipping diodes" on this forum, there is a lot of interesting info on that.

Some caveats: changing the ratio of R6 to the tone pot (10/50 in the example above) will change the total range of the tone pot because R6 and the tone cap define the "minimum high cut", which is the brightest setting possible. R6+Tone Pot (60k) and the tone cap define the "maximum high cut", aka the most muffled setting. Keep that in mind when changing any of those components.
I would not go higher than 250k (or maybe 300k if you happen to have that) for the volume pot because that may cause problems if the device coming after the distortion box has low input impedance. Not normally a massive issue but it can cause problems that are difficult to diagnose because they are unexpected. The professional solution to all those volume loss problems would be to add a buffer between tone and volume pot. But that makes a few other changes necessary so it may be best to try to solve the issues by adjusting the pot values first.

Hope that helps,
Andy

[DJPsychic]

1) In a gain pot configuration like the DOD250, you want to use a reverse logarithmic taper gain pot for an appropriate sweep. These are usually labelled "C" taper, so C500k is what you want. You can try C250k or C1M as well if you happen to have one of those but not the C500k. The B500k you have is linear taper, which does not work very well in this configuration. If you have a normal logarithmic taper A500k (or A250k or A1M) you can try those as well but you have to wire them "backwards" (pin 1 and 3 switched) and they will work backwards (CW for less gain, CCW for more gain). The "feel" will be the same as with C taper only backwards. Since it is often more difficult to get C pots, using As backwards can be useful for testing while waiting for delivery of the "right" pot.

I only have a C1k, so I will try some Log values there

2 and 3) What value are you using for the tone pot? C50k? In that case you will get quite some volume loss with an A100k volume pot. See, resistor R6 (numbering as in the breadboard drawing you posted) + the tone pot's total resistance form a voltage divider with the volume pot. That means that even with the Volume at 100%, you have (according to the voltage divider equation: https://en.wikipedia.org/wiki/Voltage_divider): Vout = Vin*100k/(10k+50k+100k) = 62.5% remaining when the volume knob is fully open, or 37.5% loss. So you loose more than a third. You can change any of those components if you like but that will have different trade-offs. I would suggest using an A250k volume pot, which will give you (all other components remaining the same) 80.6% remaining, in other words only 20% loss instead of 37.5%. That should probably be OK. If you additionally reduce the tone pot to C25k, you get 87.7% coming through. This will also have the effect of curing your tone control sweep problem. If you do not have a C25k, you can instead reduce the tone cap (the one connected to the 2nd pin of the tone pot) to about half the current value. The smaller the cap and the smaller the pot value, the less highs are cut off when the pot is fully CCW. The cap is a good place for some experimentation until you like the result.

I'm using A100k for Tone. I have a bit larger cap than the 3.3nf you suggested there. I will play with the those values.

Lastly, you can also reduce R6 but that will not have a massive influence on the volume but will change the clipping characteristics of the diodes (not much but audible). You can also change the diodes for a higher clipping threshold. For example, changing D1 to a red LED will give you a much higher volume but less distortion and a more "crunchy" sound. I strongly encourage experimenting with different clipping diodes, it's a lot of fun and can give you surprisingly different sounds. Search for "clipping diodes" on this forum, there is a lot of interesting info on that.

I reduced R6 to 2.7k and Volume maxed is about the same as Bypass signal.

I may be approaching this all wrong.

My end goal is to Recreate a Ross Distortion "type" pedal, dial in the components to "improve" design, and add tone knob. I really love the classic sound of the Ross.

The MXR + and DOD seemed close enough so that's why I started there. And there was an easy to follow breadboard layout. I'm still trying to learn how to breadboard from schematic.

Again, thank you for your detailed response. You and @Antonis (and the entire forum)have been a huge help in this journey!

[Fancy Lime]

Ah, I see. 100k for the tone knob is definitely too large. Do you have a 20k to 50k log pot?

Andy

[DJPsychic]

Ah, I see. 100k for the tone knob is definitely too large. Do you have a 20k to 50k log pot?

Andy

I do not. I'll have to add to the next shopping list.

Would the A100k be effecting volume?

[Fancy Lime]

Ah, I see. 100k for the tone knob is definitely too large. Do you have a 20k to 50k log pot?

Andy

I do not. I'll have to add to the next shopping list.

Would the A100k be effecting volume?

Yes it would. Have a look at the Wikipedia article on the Voltage Divider and apply that to all the resistors that come after the output of the opamp. With R6 = 2.7k, Tone = 100k and Vol = 100k, that works out to Vout = Vin * 100k/202.7k. That means you loose a little over 50% of the volume in that voltage divider even with the Vol knob at max. You want to make the tone pot much smaller than the vol pot to minimize this loss. If the Vol pot is five times as big as the Tone pot, the loss is small enough not to matter.

Andy