I want to build a DS-1!

[Steben]

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.

// means parallel. You know parallel impedance?
the 200k is when the hFE (= β)  is around 55 as Antonis said.
Each transistor's gain is different, so the input impedance is as well. So it could be 400k for example.
One of the reasons opamps came to live was the reliable and predictable performance and properties.

[antonis]

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.

What Steben said above..





edit: Wrong h_FE estimation..
(thought Q1 was 2N3904..)

[Steben]

Could be 250 ish as minimum.... So Zin (base) is about 2.5Mohms.



The result is dominated by the 470k however, Zin circuit will always be << 470k.

R43//R2//R3*β = 1M // 470k // 2M5 = 1/(1/1M + 1/470k + 1/2M5) = 282k.
So we have a Zin which becomes less than 50% higher although the component (transistor) seems to have 5 times higher current gain than 2N3904.

This explains why one always has to change the dominant element, which means here the lowest impedance = R2.
Changing it to 1M will give Zin circuit of 417k. Which means doubling the component value gives 50% change in result.

I do find the input impedance chapter sometimes overrated. It can be an issue if placed straight after the guitar especially with humbuckers and high value pots.
282k input impedance for a high gain device however is more than ok if it is placed after circuits with a low output impedance anyway. Think of all circuits with buffers (Boss and Ibanez pedals).

Do not forget that high impedance parts are usually found in tube amps. Zin of tubes are galactic. In those amps the signals are huge compared to our 9V circuits. Any noise coming from high impedance resistors is in comparison to the signal low and tube amps have their own sources of noise and hum and whatever.
In 9V circuits the signals are much lower, yet the noise coming from resistors not.
It is generally speaking always preferable to use the lowest R value possible without losing too much signal. Behind buffers and opamps this can go muuuuuuch lower than 100dreds of k.

[antonis]

I presume that at DS-1 initial release times, 2 BJTs should be much cheaper than a dual op-amp..

[Steben]

I presume that at DS-1 initial release times, 2 BJTs should be much cheaper than a dual op-amp..

yes.
Yet the boost stage can't be but deliberate. It is not the most beautiful way of overdrive yet I imagine in those times fuzz and simple distortion was mainstream. The non true bypass was still alive. The wah hardly ten years old? So we see a sturdy box, buffered and with excellent electronic switching giving one hell of a distortion. Couldn't loose.

[duck_arse]

what antonis said below.

is there Collector resistance in that dia that I can't see?

[antonis]

what antonis said below.

is there Collector resistance in that dia that I can't see?

It surely is there..
If you notice my expression, I said "resistance" (physical quantity) and not "resistor" (real world item)..

A BJT Collector can be considered as a non-ideal current source (either g_m*Vbe or β*Ib)..
Any non-ideal current source has a high value internal resistance which is considered in parallel with the source (just like a voltage source is considered with its internal resistance in series..)

That resistance measures (V_A+V_CE) / I_C, where V_A is the Early voltage of particular device (usually between 50 and 150 Volts)

Just look at dashed framed model below:

[duck_arse]

is there Collector resistance in that dia that I can't see?

It surely is there..
If you notice my expression, I said "resistance" (physical quantity) and not "resistor" (real world item)..

I did, indeed, notice your use of resistance, which is why I corrected my werding before posting to read that I can't see. coffees all round.

oh, and a rockcake each.

[antonis]

coffees all round.

Not enough here, yet..
(spilled all over the keyboard..)

[PRR]

is there Collector resistance in that dia that I can't see?

On clean modern (post 1963) Silicon, the collector impedance is thousands of times higher than anything else. Megaohms. At least for resistance-coupled work.

[antonis]

That's for sure, Paul but whereas its high value can easily omitted for applications like the above buffer, there are cases (e.g. CE amp current source) where it should be taken into account..

[zbt]

This Dirt Sky One not learning from his Dirt Vader which supposed to be stayin alive
maybe due to the influence of Oddy One Knob Be to use the buffer

TA7504M which I think is the 741 family from Toshiba has a slew rate of around 0.5 V/us
for this I have feeling that for hard clipping is better using low slew rate like Dirty RAT does LM308 0.3 V/us
make not so square

for  TA7136AP I dont know what slew rate value is, but one think I notice it has greater THD compare to 741
perhaps Q2 is to push harmonic

compare with this table for your preference

741       0.5 V/us      THD=0.06%
TA7504M   0.5 V/us
TA7136AP  VNI=0.8uV rms THD=0.1%
BA728N    0.7 V/us
M5223AL   0.6 V/us
NJM2904L  0.5 V/us     
NJM3404   1.2 V/us
JRC4580   5.0 V/us SMD  Noooooooooooooo........

[FSFX]

The slew rate itself is not all you should be considering.
If like in the RAT you are driving the op amp into clipping then its behaviour as the output level approaches the supply rails is probably more important as regards the resultant sound.
Some op amps clip gracefully when the output approaches the supply rails whilst others exhibit unwanted characteristics like 'foldback' or phase inversion of the waveform.
You probably need to get a scope and test the various op amps rather than rely on specifications on datasheets.

[antonis]

Some op amps clip gracefully when the output approaches the supply rails whilst others exhibit unwanted characteristics like 'foldback' or phase inversion of the waveform.

Do I smell a circuitous TL072 admonition..??

[anotherjim]

I tell you, the original MIJ DS-1 was a real goto pedal. You could do R. Fripp cello-style lines with ease as well as hammer-on only legato or pick any possible harmonics. The ones they made after are just like any other ton-of-gain + clipping box that just seems to choke your playing unless the amp is loud enough for natural feedback assistance.

Anyway, I never noticed the original had that BJT preamp stage.  I'm suspecting it is probably of high importance and a 741 might do for the opamp. I think it's no wonder the mods hoping to backdate the dual opamp versions don't really work.

[Steben]

Some op amps clip gracefully when the output approaches the supply rails whilst others exhibit unwanted characteristics like 'foldback' or phase inversion of the waveform.

Do I smell a circuitous TL072 admonition..??

or a positive wink to some rail to rail opamps that seem to be made for clipping.
What about the TLC2262? Afaik the sansamp uses them and not the TL0xx series, which is seen in some kits/clones....

[zbt]

Noooooooooooooo........

I though no fat not good, the Low Fat 351 and Tender Loin 081 which 13V/us
would be bad but some folks like also

in case of DOD Preamp 250
4558 1V/us mod to 1458 0.5V/us only 0.5 different
this probably my thinking could be about slew rate

the most dangling for RAT which OP07 same slew rate with 308

https://www.electrosmash.com/boss-ds1-analysis

M5223AL (3K pull up resistor) and NJM2904L (Rp<Rl//Rf pull down resistor)
are noisy probably because crossover distortion
which replace with better chip 4580

is it bias of original ?
feeling like Tube Screamer JRC4558
or Original Colonel Sanders KFC
or People resist to change
people are awesome

in case Roland Jet Phaser the distortion part is using LM324
well if we change LM324 with TL074 would it be better?
or it will loosing it signature

my preference will choose 741 family instead 324 family

the odd of OCD with TL082, people like it or because of that mosfet clipping

The klon TL072 is weird to using more voltage to make slewrate to max 13V/us
would not chip with slewrate 13V/us at 9V enough if it is slewrate

Thinking about my klon is like RAT(LM308) 0.3V/us + BULL(LM318) 50V/us,
just using 9V supply.



Q2 form asymmetric clipping, unlike Range Master which change Peak Voltage
or like pair Led + Diode, it seem it make change duty cycle.
another trick to make asymmetric

Range Master + MXR D+ or DOD 250
Q2 + DOD 250





cant find NJM3404 but I think would be better find old chip like TA7136 pre amplifier
many like Sanyo, Panasonic, NEC