I want to build a DS-1!

[ElectricDruid]

Yes, I noticed that a sort of "fat mod" by Muzique.com is to increase the 1k, this pairs the bass and the treble response of the boost stage, but cut a lot of boost, too. If you mean this I could try to cut the boost of the Q2 stage, and to turn the buffer op-amp stage into a boost.
It was this what you meant, right?

Yes, exactly. Tame the Q2 stage a bit, then try a op-amp boost in front of it.

[Elijah-Baley]

I drawn this for my personal use, so maybe some parts could be seem cryptic, and I have to explain at least those areas. I'll report what the software emulator does.



1. This parts is generally left out to cut the fet switching. Bypassing it I got a little bass boost.
(From Aion Comet Project:
«With the FET switching in the original, there are two capacitors in series here, 470n and 47n. A series
calculation puts the "consolidated" value for this at 42n. However, since 42n is a pretty rare value for a
capacitor, the more common 47n can be used instead and won't be noticeably different.»)

2. One mod is add the Big Muff clipping.

3. Some mod are called Synth/Fuzz/Oscillation (now called SFO) and three start from there.

4. This is a buffer, originally, but it could be a boost. (R41, R42, C24, C25 are ipothetical.) This mod is never been documented.

5. Connecting this spots it shuld sound like a fuzz.

6. It's one of the connection of the SFO.

7. It's one of the connection of the SFO.

8. In rare schematic R40 1k resistor is missing. My emulator doesn't prove it but that resistor could give a bit of mid boost.

9. One mod add that cap.

10. It's one of the connection of the SFO.

Later I'll write some possible mods.

[Lino22]

The Q2 gain stage of DS-1 has quite some gain. Is that intentional? It almost looks like it clips right there.
Someone has asked me to make his DS-1 sound less harsh. I wonder if lowering that gain would help.

[Steben]

The Q2 gain stage of DS-1 has quite some gain. Is that intentional? It almost looks like it clips right there.
Someone has asked me to make his DS-1 sound less harsh. I wonder if lowering that gain would help.

there are two harsh-es: too much treble and too much gain.
The Q2 stage has a bit of a low cut effect. Classic AMZ mod lowers the gain while tempering the high boost at once. SO yes, this might help.
Or you could change the freq response of the tone control circuit if the gain character suits you anyway.

[Elijah-Baley]

Hello.
Here's the schematic, with some correction, though the old one contain some other thing I described in my post that you can read.



I added some other synth/fuzz/oscillation option, one of these is the tremolo effect.
I added (I don't know if somebody really tried it) the soft clipping diodes in the gain stage.

The following descriptions are based on what someone else tried, experimented or just what my emulator software said, and those have to considered tried one by one, and the response if adopted some together could influence themselves, of course. I am no still building this pedal, so I can't give you my personal opinion, anyway there are ton of opinion. Phrase between « » are taken from someone else in some forums.
I indicated the number of the part, what happens if you change it, and the range of the value.
I avoided to speak about all the package of mods.

R2: 470k - Increase it for an higher impedance.
R6: 100k - It adjusts the bias of the boost stage and increasing it seems we get slightly more treble. (150k).
R7: 470k - «Increasing the value increases gain, while decreasing it will give you a little less gain overall but will tighten up the DS-1's low-end.» In my emulator lower value cut bass, higher value boost bass and cut treble. (180k-1M).
R9: 22R - It determines the amount of the gain of the boost stage. Bigger resistor decrease the treble boost. (10R-1k).
R11: 100k - «It controls the gain in combination with the distortion knob, R13 and C8.» I found just one that change it with a 220k, my emulator doesn't show any change in the amount of gain.
R13: 4.7k - Smaller resistor to push the gain in the high frequency. Bigger resister to decrease the gain an get lower frequency (510R-10k).
R14: 2.2k - Smaller value for more treble, bigger value cut bass, but very big value cut treble and gain, too. (1.5k-10k).
R15: 2,5k - Bigger value cut treble, smaller value increase it.
R16: 6.8k - Smaller value decrease treble and increase mi, low-mid. (1k-4.7k)
R17: 6.8k - Bigger value for flat eq more volume. Take it out for maximum effect. SMaller value increase the mid scoop. (3.3k 8.2k-33k).
R21: 10k/100k. The value is often 10k, but some schematic shown 100k. I think it doesn't change so much.
R39*: 47k - Someone decrease this resistor, but in my emulator doesn't make almost difference even if you jumper it. In theory it should let pass more gain and maybe more treble.
R40*: 1k - It seems has some effect in the midrange. «This resistor is labeled as R40 and will force the op-amp to work into class-A reducing distortion».
R43: It's the pull down resistor, necessary when the pedal is true bypass. It could influence the impedance. (1M-2.2M)

C1: 47nF - Bigger cap increases the low end, but hardly perceptible. (100nF).
C3: 47nF - Bigger cap increases the low end, smaller cap decrease it. (15nF-100nF).
C4: 250pF - Bigger cap to smooth the high end, smaller cap let pass more treble. (100pF, 220pF, 1nF).
C5: 68nF - Bigger cap increase bass (but it can't increase so much), smaller cap decrease it. (22nF, 100nF, 220nF 470nF, 1uF, 10uF).
C7: 100pF - Bigger cap to smooth the treble. Generically it's increased, in one case it's been removed. (220pF-470pF)
C8: 470nF - 1uF. Bigger cap pushes the gain in lower frequency. (One schematic show a 47nF, maybe a mistake, it seems too much small). (1uF-2.2uF).
C9: 470nF - Bigger cap increases the low end. But the increasing is minimal. (1uF).
C10: 10nF - Bigger cap cut treble, smaller let pass more treble. (1nF-56nF).
C11: 22nF - Bigger cap for a flat eq, smaller cap for (even) more mid scoop. (10nF-56nF).
C12: 100nF - Small cap for mid boost. Someone removes it for more treble, but my emulator says it seems mess up the tone control. (15nF-56n).
C13: 47nF - Bigger cap to increase the low end. But it seems the change is invisible. (100nF-1uF)
C25 47pF - Adding it in parallel with the diode D4 and D5 to tame a treble. But in the emulator it's almost not visible. My opinion is that cap is very small.

D4 & D5: 1N4148 - Replace both or one with two or more diodes to change texture, gain and volume. There are all the combiantion you want. Old Boss DS-1 pedal used diodes that measured about 1.0v as voltage forward. In the newer the 1N4148 diodes are not so close to that voltage forward. (All diodes!).
D8*: 1N4148. «The diode D8 is placed to protect the op-amp input».

Distortion pot 100k Linear - Higher resistance for more gain, maybe it give just more fuzziness. (250k).

Transistors: I think I'll use 2N3904 for the buffers and a 2N5088 for the booster.

IC: TL072, JRC4558, OPA2134, MC1458, LM358, NE5532, LM833, TL2262, LM385N...

*R39, R40 and D8 has been added in the circuit after the single op-amp was replaced by the dual op-amp. Maybe this parts was necessary for the DS-1 stock dual op-amp M5223AL, but maybe unnecessary with other models. Not sure about it.
«If you were to replace the amp with a more common bi-polar amp such as the TL072, you should probably remove R40.
Oh and R39? I think power-up/down could cause a damaging negative voltage on the amp input. D8 limits that, but R39 then keeps the discharge current from C5 low. Where it is, R39 won't affect the tone at all.»

[Steben]

The soft clippers won't do much on their own since the input of the opamp will be far over any small signal <<< diode treshold.
This means the diodes will conduct early on and the opamp will mainly have a signal out almost like "unity gain above diode treshold". This means you get the hard clipping without all the gain in front. So unless the boost stage has very low gain it won't feel as soft clipped but rather as though you "take away some gain" from the hard clipping.
Soft feedback clipping is a finicky thing. It needs careful design to shape your tone.
A soft clipper with a low input (think guitar), high gain and very treshold (think a couple of volts) will sound rather hard clipping.
A soft clipper with a high input (think booster out), low gain and very low treshold (think one silicon diode) will sound rather dull and muffled and almost like added noise and chances are the opamp will clip rather than the diodes add tone.
The Timmy was a good example of doubling the treshold compared to a Tube Screamer for example, making it sound a tad "tighter".

[antonis]

R21: 10k/100k. The value is often 10k, but some schematic shown 100k. I think it doesn't change so much.

It strongly depends on R23 value (serving for load)..
T3 Emitter is biased at about 3.7V and can't go lower than 1.75V due to R21/R23 voltage dividing effect (50% for particular values)..

High value Emitter resistor (for voltage follower, like T3) contributes positively for current consumption but negatively both for load drive capability and output impedance (0.026/I_C^Q)

P.S.
Make R23 10k, set Level pot FCW and observe the "extra" negative clipping via Tina-TI oscilloscope..

[Elijah-Baley]

The soft clippers won't do much on their own since the input of the opamp will be far over any small signal <<< diode treshold.
This means the diodes will conduct early on and the opamp will mainly have a signal out almost like "unity gain above diode treshold". This means you get the hard clipping without all the gain in front. So unless the boost stage has very low gain it won't feel as soft clipped but rather as though you "take away some gain" from the hard clipping.
Soft feedback clipping is a finicky thing. It needs careful design to shape your tone.
A soft clipper with a low input (think guitar), high gain and very treshold (think a couple of volts) will sound rather hard clipping.
A soft clipper with a high input (think booster out), low gain and very low treshold (think one silicon diode) will sound rather dull and muffled and almost like added noise and chances are the opamp will clip rather than the diodes add tone.
The Timmy was a good example of doubling the treshold compared to a Tube Screamer for example, making it sound a tad "tighter".

The soft clipping it's an idea I found that come form the Boss HM-2, but has you said, that could cut signal more useful for the hard clipping.
I think it's a bit the same thing for the muff clipping, it isn't? That idea come from the Aion project (Comet).

R21: 10k/100k. The value is often 10k, but some schematic shown 100k. I think it doesn't change so much.

It strongly depends on R23 value (serving for load)..
T3 Emitter is biased at about 3.7V and can't go lower than 1.75V due to R21/R23 voltage dividing effect (50% for particular values)..

High value Emitter resistor (for voltage follower, like T3) contributes positively for current consumption but negatively both for load drive capability and output impedance (0.026/I_C^Q)

P.S.
Make R23 10k, set Level pot FCW and observe the "extra" negative clipping via Tina-TI oscilloscope..

I think I don't care it too much and I'll use a 100k as R23, but I'll try some experiment with Tina-TI oscilloscope.

[antonis]

I think I don't care it too much and I'll use a 100k as R23

The "problem" isn't R23 value but R21 one..

As far as you really don't care, I can't see any (obvious or hidden) reason for anyone else to deal with it..
(walk in peace with an output buffer of 37μA working current, hence an output impedance of 675R..)

[m4268588]

This is probably erroneous.

I couldn't find gut shot with R21 is 100k.

[Elijah-Baley]

I think I don't care it too much and I'll use a 100k as R23

The "problem" isn't R23 value but R21 one..

As far as you really don't care, I can't see any (obvious or hidden) reason for anyone else to deal with it..
(walk in peace with an output buffer of 37μA working current, hence an output impedance of 675R..)

Is that was sarcastic?
I didn't say we can't discuss about it, just I think I'm going to trust with the original Boss schematic because I saw this is not a thing that other guys used to change in this circuit. I just find some discrepancy in the schematics with R21: 100k/10k. More precisely, in the schematic with the single op-amp R21 is 100k, in the dual op-amp R21 is 10k.
Probably I'll use 10k, in my schematic there's a mistake: R21 should be a 10k.

[antonis]

Is that was sarcastic?

Definately not..!! 

I was just trying to explain you the reason for output buffer Emitter resistor to be of low value..
(like below..)

[Elijah-Baley]

Thanks, antonis.

I have in my archive that schematic, too, but I thought that 1k to the emitter in the last stage was a mistake (or is it a mod?).
Maybe it's bit hard to hear the effect of the output impedance in the pedal because I assume it depends from the amp, or other pedal after it, or something else. So I don't know if I'll test that resistor. The veroboard layout I'm drawing has already a lot of socket pins: I want to try a lot of parts!

[antonis]

I have in my archive that schematic, too, but I thought that 1k to the emitter in the last stage was a mistake (or is it a mod?).

Can't say for sure but a 10k Emitter resistor should be upwards marginally OK..
(same value resistor is implemented to Q1 input buffer which drives Q2 CE amp ridiculously low input impedance..)

P.S.
After all, IN-OUT buffers should (or not..??) let "main" circuit character be unaltered..

[Elijah-Baley]

The input impedance declared of the original DS-1 is not so high, but still fine: "just" 470k 'cause R2. Indications I read around say: "R2: 470k - Increase it for an higher impedance".
In the true bypass schematic the thing could be a bit difference, we need (probably) a pull down resistor 1M-2.2M (R43 in my schematic) that should pair with R2 and change the impedance. And I'm thinking about it right now, maybe this lowers the 470k impedance. To adjust the impedance around the original Boss I should use as R2 an 1M ressistor (or 820k), if the pull down resistor is 1M.

Considering I will not build this pedal soon, we could go deep in some discussion. Indeed, now I'm wondering what determines the input impedance in the DS-1 schematic, not in the original, but in the true bypass version, my schematic above. I'm calculating R2 and R43 in parallel, but does R1 1k make some difference? To calculate the input impedance is important the transistor? (by the way, a trick to raise up the impedance could be to replace the BJT transistor with a jfet).

[Steben]

Indications I read around say: "R2: 470k - Increase it for an higher impedance".

But why? 

[antonis]

Considering I will not build this pedal soon, we could go deep in some discussion. Indeed, now I'm wondering what determines the input impedance in the DS-1 schematic, not in the original, but in the true bypass version, my schematic above. I'm calculating R2 and R43 in parallel, but does R1 1k make some difference? To calculate the input impedance is important the transistor?

Actually, it's important the transistor DC current gain at particular working condition..

T1 input impedance is considered the equivalent resistance of R43 // { R1 + X_C1 + [ R2 // ( β*re + (β+1)*R3) // β*rc ], where re = 26mV / Collector current and rc = Early voltage / Collector current..

By neglecting series low values and shunt high values, we simplify it to R43//R2//R3*β..
For a minimun h_FE of 55 for 2N3904 at 370μA quiescent current, we get about 200k input impedance..
By making R2 1M, total input impedance is raised only 30% (from 200K to 260K) while voltage drop across it, due to Base current, is overdoubled resulting into even lower Emitter voltage hence lower next stage driving capability for signal negative waveform..
(R3 forms a voltage divider with T2 input impedance precluding T1 Emitter from going all the way down to zero volts..)

As for input HPF corner frequency, it's set by 1 / 2π*C1*(R3 + R2//R3*β)

[Steben]

It's quite random but I remember modding a DS-1 once by
- taming Q2's gain and filtering as AMZ mod suggests
- raising the opamp stage's gain
- modding the freq response of the opamp stage
- swpped for clipping LED's

This resulted in a cleaner low gain setting and more marshall-esque distortion.
The Q2 mod makes the stage more linear with a slight hint of even order harmonics while the actual hard clipping is done after that. Stock, the Q2 stage adds (on the edge of fuzz) clipping as well which makes the DS-1 an aggressive beast but less "amp like".

On another I swapped the stage for a jFET stage by omitting the feedback 470k R and changed some R values. Can't recall it sounded better than the BJT solution.

[m4268588]

Thanks, antonis.

I have in my archive that schematic, too, but I thought that 1k to the emitter in the last stage was a mistake (or is it a mod?).
Maybe it's bit hard to hear the effect of the output impedance in the pedal because I assume it depends from the amp, or other pedal after it, or something else. So I don't know if I'll test that resistor. The veroboard layout I'm drawing has already a lot of socket pins: I want to try a lot of parts!

Don't worry too much, but if the emitter resistor is large, it will clip when the load impedance(=Rl) is small.
0.22*R21/(4.5-0.6) = R21‖Rl
(Assume 440mv P-P)

[Elijah-Baley]

Thank you, but I'm kind of lost.

Antonis, please, can you translate in number this formula? R43//R2//R3*β..
200k impedance seems lower than I thought, and I can't understand why.