I know that the DS-1 is well treaded ground, but I wanted to share my experiences trying to mod one. My goals were to increase output volume without greatly reducing overall distortion, and to increase the low pass filtering of the tone circuit to reduce the shrillness of the tone.

So, I decreased R13 to 1.5K and increased C8 to 1uF to increase the max gain of the op amp stage; I changed the clipping diodes to 2 red LEDs in anti-parallel with 1 red LED and 1 1N4148; I changed C11 to 0.033uF and R15 to 18K to lower the knee and attenuate the high pass filtering leg of the tone control; and I changed C12 to 0.22uF to lower the knee of the low pass filtering leg of the tone control.

I achieved my objectives, however, the pedal now oscillates at high level and gain settings. You play through the pedal and your signal modulates a "chirping" sound that changes frequency and intensity depending on the gain and level settings. Now, I happen to use the pedal at low gain settings as a gain boost for my amps, so it doesn't affect my usage at all, but I find it irritating that the pedal is not fully functional.  I would like to use it flat out into a clean amp from time to time.

I suppose the layout of the pcb isn't set up for that much gain, and somehow the increased level from using higher clipping is feeding back around the circuit. If I have the gain at max, and keep the level below 1 o'clock, it won't oscillate.

These problems have led me to attempt building a DS-1 from scratch, including my modifications, using my own pcb design. I'm not some sort of layout genius; I'm an amateur electronic hobbyist and am certainly not smarter than any Boss engineers, but I wanted to give it a try. I'm also changing the op amp gain stage to inverting, in the hope that any parasitic capacitance won't cause positive feedback. I haven't received the pcbs from manufacturing yet, so I can't yet report any successes or failures.

If anyone has any insights into what can be done to alleviate the oscillation, please let me know. I'm open to any critiques of what I'm trying to do. Also, please forgive me for not posting a schematic of the DS-1 with this post. I'm a little worried about accidentally posting a copyrighted schematic and running afoul of the forum rules. Thanks, everyone!

https://www.electrosmash.com/images/tech/ds1/boss-ds1-distortion-schematic-parts.jpg

My advice would be to not mess with the gain.

After all, you didn't want more gain, so why increase it? It doesn't "compensate" for the increased clipping level because the op-amp will clip anyway, so beyond a certain point, all you're doing is adding gain and compressing the signal more.
Since Boss already pushed it fairly far, I'd leave that bit alone.
Sure, change the diodes to get a bit more level out of the far end. You won't lose any distortion by so doing because you're already getting op-amp distortion by that point. It maybe changes the balance between op-amp and diode clipping at bit, but that's all. Then tweak the tone control to remove the shrillness.

HTH

Quote from: PRR on April 03, 2025, 03:50:51 PMhttps://www.electrosmash.com/images/tech/ds1/boss-ds1-distortion-schematic-parts.jpg

Thank you, PRR. I should've just included that link.

Quote from: FleshOnGear on April 03, 2025, 03:17:21 PMI'm also changing the op amp gain stage to inverting,

It should be helpful to post a schematic of your particular modification..  

Quote from: FleshOnGear on April 03, 2025, 03:17:21 PMIf anyone has any insights into what can be done to alleviate the oscillation, please let me know.

Turn R13 back to its original value and make C8 330nF to retain low-end of your taste..
(you might need to raise C7 value, also..)

Quote from: antonis on Yesterday at 05:25:37 AM

Quote from: FleshOnGear on April 03, 2025, 03:17:21 PMI'm also changing the op amp gain stage to inverting,

It should be helpful to post a schematic of your particular modification..  

Quote from: FleshOnGear on April 03, 2025, 03:17:21 PMIf anyone has any insights into what can be done to alleviate the oscillation, please let me know.

Turn R13 back to its original value and make C8 330nF to retain low-end of your taste..
(you might need to raise C7 value, also..)

My schematic is on my computer at home, and I'm traveling at the moment. I will post the schematic when I am able.

I'm getting the impression that most of you feel the increased gain is not possible without oscillating. Oddly, the first version of my mods included the change to R13 and C8, but it did not oscillate. At first I had just 2 red LEDs in anti-parallel for clipping, and it worked great. When I increased the clipping threshold even more, and increased R15 to adjust the treble, then it started oscillating.

Quote from: FleshOnGear on Yesterday at 11:59:38 AMWhen I increased the clipping threshold even more, and increased R15 to adjust the treble, then it started oscillating.

Did you make both mods simultaneously..??

Quote from: antonis on Yesterday at 01:44:55 PM

Quote from: FleshOnGear on Yesterday at 11:59:38 AMWhen I increased the clipping threshold even more, and increased R15 to adjust the treble, then it started oscillating.

Did you make both mods simultaneously..??

Yes, those two changes were made at the same time. Like I said, the change that set the op amp gain higher had already been made and had worked without issue previously.

To me it's more important to have the output level than the gain, so I'll probably dial back the gain on the actual DS-1. Regarding the DS-1 "inspired" pedal that I'm going to build from scratch, my hope is that I'll be able to keep the higher level and the higher gain without issues.

Quote from: FleshOnGear on Yesterday at 02:49:42 PMYes, those two changes were made at the same time.

Could you plz repeat them once at a time..??

Quote from: FleshOnGear on Yesterday at 02:49:42 PMmy hope is that I'll be able to keep the higher level and the higher gain without issues.

You could keep the higher gain with low clipping threshold (provided no oscillation) and replace output buffer with a low gain CE amp, couldn't you..??

Quote from: antonis on Yesterday at 03:21:58 PM

Quote from: FleshOnGear on Yesterday at 02:49:42 PMmy hope is that I'll be able to keep the higher level and the higher gain without issues.

You could keep the higher gain with low clipping threshold (provided no oscillation) and replace output buffer with a low gain CE amp, couldn't you..??

Yeah, that was my thought too.

I think you need to think about the relationship between the gain and the cipping threshold. If the clipping is lower, you don't *need* so much gain to generate more distortion. The higher you raise the clipping threshold, the more gain you need to get an *equal* amount of distortion. In many ways, to boost the output level, the best way is to add just a little bit of gain on the output (and really, x2 to x5 should be more than enough with a 1.2Vpp signal coming from the diodes). That amount of extra gain shouldn't cause you oscillation problems, especially as it is so late in the circuit. It's certainly a much safer option than boosting the op-amp gain where you won't hear it because it's clipped by both the op-amp and the clipping diodes after as well.

This whole process is called "gain staging" and is a big part of the design process for distortion pedals. Welcome onboard!

Quote from: FleshOnGear on Yesterday at 11:59:38 AM....you feel the increased gain is not possible without oscillating.

Of course it is possible. Layout. Layout! Shielding! Layout!!

Quote from: PRR on Yesterday at 06:40:19 PM

Quote from: FleshOnGear on Yesterday at 11:59:38 AM....you feel the increased gain is not possible without oscillating.

Of course it is possible. Layout. Layout! Shielding! Layout!!

+1 yeah, that too! 

Quote from: ElectricDruid on Yesterday at 06:11:10 PMThis whole process is called "gain staging" and is a big part of the design process for distortion pedals. Welcome onboard!

How much more bad to the bone could you become, Tom..?? 

Quote from: ElectricDruid on Yesterday at 06:11:10 PM

Quote from: antonis on Yesterday at 03:21:58 PM

Quote from: FleshOnGear on Yesterday at 02:49:42 PMmy hope is that I'll be able to keep the higher level and the higher gain without issues.

You could keep the higher gain with low clipping threshold (provided no oscillation) and replace output buffer with a low gain CE amp, couldn't you..??

Yeah, that was my thought too.

I think you need to think about the relationship between the gain and the cipping threshold. If the clipping is lower, you don't *need* so much gain to generate more distortion. The higher you raise the clipping threshold, the more gain you need to get an *equal* amount of distortion. In many ways, to boost the output level, the best way is to add just a little bit of gain on the output (and really, x2 to x5 should be more than enough with a 1.2Vpp signal coming from the diodes). That amount of extra gain shouldn't cause you oscillation problems, especially as it is so late in the circuit. It's certainly a much safer option than boosting the op-amp gain where you won't hear it because it's clipped by both the op-amp and the clipping diodes after as well.

This whole process is called "gain staging" and is a big part of the design process for distortion pedals. Welcome onboard!

Yeah, I thought about that on the original DS-1, but the final buffer works on the distorted signal and the bypass signal. When I designed the copy, I forgot all about trying a common emitter stage. If my layout and design don't work out, I will probably go back to the drawing board any put in a CE stage on the end.

I feel like it should be possible to get it to work as is, because I've only increased the gain by about 3x. The initial transistor stage has gain of about 100, I think, then the op amp gain stage only has a gain of about 22 stock, and only about 68 with the mod. This seems like it should be manageable. I tried to be careful about running output traces clear of input traces and such, but I'm no layout genius. The pcbs will arrive in a week, then I'll find out how I did.

Quote from: FleshOnGear on Today at 02:21:49 PMI feel like it should be possible to get it to work as is, because I've only increased the gain by about 3x. The initial transistor stage has gain of about 100, I think, then the op amp gain stage only has a gain of about 22 stock, and only about 68 with the mod. This seems like it should be manageable.

Another way of saying that would be that the maximmum gain goes from 2200 to 6800. That makes it sound much worse!  Of course, in decibel terms, it's still only a small increase, so you might well be right that it can be made to work perfectly well.

QuoteI tried to be careful about running output traces clear of input traces and such, but I'm no layout genius. The pcbs will arrive in a week, then I'll find out how I did.

Good luck!

Quote from: FleshOnGear on Today at 02:21:49 PMThe initial transistor stage has gain of about 100, I think,

Marginally about 50, I think..

Q2's open-loop gain is considerably lower than "very high" so closed-loop gain can't be considered simply R7(470k) / Q1's r_e..

Precise calculation can be perfomed via A_OL / (1 + β*A_OL), where A_OL= R8/(R9+0.025/Ic2) and β= (0.025/Ic1) / R7