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Messages - TFZ

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1
Open Discussion / Re: what are you guys listening to at the moment?
« on: November 07, 2020, 11:03:44 AM »

2
Open Discussion / Re: Suitable JFets for phases?
« on: November 01, 2020, 08:42:17 AM »
If you want to match SMD JFETs, consider buying this. The adapter can be bought without pcb too, but then you need to make one yourself, or solder wires to the pins, since they are not in the standard 0.1 format.

3
Bias network can be removed, add filter capacitor for negative rail, use negative supply on opamps, reference JFET input and opamps to ground, connect JFET source to negative supply.

4
Open Discussion / Re: Surface mount soldering. I don't like it.
« on: October 12, 2020, 03:37:04 PM »
I actually quite like SMT soldering. I'm faster and it feels like a simpler process. But I have been doing it for all my electronic life.

One story from a tube old-timer comes to my mind: he told about when noval tubes were introduced. People of that time, used to octals and even larger, complained about this miniature stuff, who would want to deal with something that tiny!  ;)

5
General Questions / Re: MOSFET reverse polarity protection
« on: October 09, 2020, 01:07:06 PM »
Yes, drain and source are wrong in the schematic. Protection diode: never used one. BS250 has +-25VGS, the MOSFET I use has +-20V. So far no problems...

6
Open Discussion / Re: You ever get that one guy...
« on: October 08, 2020, 11:39:35 AM »
A friend of mine who sells repaired vintage amps regularly always makes a video of him playing and demonstrating that everything works perfectly. Maybe for the true specialists one could include where to put which cable...

7
Open Discussion / Re: Favorite pedal brand
« on: October 03, 2020, 10:40:39 AM »
To me there is a difference between pedals for playing live, and pedals for messing around at home or recording. I would never take any Lovetone on a stage, too much nuance is wasted there anyway. They are just fun toys to play with by myself or for a recording situation. That is where I want all the possibilities they can offer.

8
You just need to add one transistor. This avoids the problem of having to accomodate the resistor for both the zener current and your circuit. Make the resistor 1-2k, the capacitor is for filtering the zener diode noise, 100n will do. For the transistor use any standard high-beta type, BC550C or similar. If you want to have 3V, you need to add one VBE drop to the zener diode, so use a 3,6V or 3,9V. Or add a silicon or schottky diode in series, depending on where you want to land exactly.

The other advantage of this circuit is it is more stable and less load-dependent.

9
Open Discussion / Re: Mouser Xicon Resistors New MOQ of 200
« on: September 26, 2020, 03:40:55 AM »
I don't understand. I see more than ten different 2,7k resistors with 0,5W or 0,6W available in singles.

If it really was Mouser's intention to get rid of single part sales, I think they would start with 0201 SMD parts...

10
Open Discussion / Re: Favorite pedal brand
« on: September 25, 2020, 02:19:54 AM »
I have a couple of old Boss and EHX pedals, plus some more modern crap, other than that everything I have and use is DIY. Boss to me is the pedal archetype, the compact boxes, the consistent look in all the different colours, I really like them. The vintage EHX stuff I have in comparison oozes cheap to me, I'm not really too fond of them. The mechanics, the look, the thin sheet metal boxes, I've just never really been a fan.

The only pedals I would ever see myself buying if they were available is Lovetone. The creativity and plethora of sounds out of analog pedals they achieved is unrivalled to me. Plus again, nice consistent boxes in pretty colours. Seems to be something I value  :D.

From the stuff I actually play, I couldn't really make out a favourite brand. It is a fairly mixed affair with all sorts of stuff including DIY circuits, no brand really standing out. Closest to my heart really are the Lovetones I've built, even though I don't use them all that often.

11
General Questions / Re: Op amp substitution
« on: September 24, 2020, 11:07:05 AM »
Ok then let's agree to disagree on the current draw. Regarding the input impedance: erm... no that's wrong. The value in the datasheet is the input impedance running the opamp open loop, which means no feedback applied. So that is not the input impedance of any practical circuit. Once the loop is closed, which of course is the case in pretty much all applications, the input impedance is a lot higher than that. It is not possible to blankly state the input impedance in the datasheet, because it depends on the circuit the opamp is put in.

It is roughly the open loop gain times the applied gain times the open loop input impedance. So for the NE5532, that would be 100,000 x 300,000kOhm x gain. As you can see, its input impedance is far from "very low". Other opamps will produce similar numbers, even ones that are older and worse. That's why we can always safely assume that the input impedance of a non-inverting amplifier stage is the same as the bias resistor (in parallel to maybe other stuff).

12
Open Discussion / Re: 3D printed drill guides?
« on: September 24, 2020, 09:44:21 AM »
I think I saw somebody do exactly that in one of the build threads. But if you have a printer, designing that would be a matter of minutes in Fusion 360 or Freecad.

Not sure how Github factors into all of this. If you have found a design on there just download it. As long as you don't want to contribute to a project you don't need to concern yourself with all the version control stuff and command line headaches  ;D.

13
General Questions / Re: Op amp substitution
« on: September 24, 2020, 09:40:23 AM »
> I refer to the 1Hz bandwidth at 1kHz that rating is taken at which isn't very realistic in practice.
I still don't understand. That number is a way to compare different opamps, and gives you the information you need to calculate the actual noise in your circuit.

> The NE5532 has its own quirks, very low input impedance
You've stated that before, and when I asked you to explain how you came to that conclusion you didn't answer unfortunately. Please do  ;).

> not to mention massive current draw
For the dual the supply current is 16mA, I certainly wouldn't call that massive. A PT2399 is about the same, a Spin FV-1 takes 55mA. Some people drive their bypass LEDs harder than that ;D, a bypass relay takes way more current as well. I really don't think there is any problem with that.

> There's no one size fits all if you get to the nitty gritty which is why there's so many op amps to chose from
Well yes of course. Engineering is the art of finding a workable compromise from conflicting requirements, same goes for choosing an opamp. But it's usually not too hard to find a solution that doesn't suck.

14
General Questions / Re: Op amp substitution
« on: September 24, 2020, 05:45:08 AM »
That's not just "test conditions". Overall noise is the result of voltage and current noise. Depending on the impedances involved, one or the other will dominate. Hence there will be circuits where the 4558 can be quieter of course.

The fact of the matter is, many guitar pedals are terribly designed in that regard. High impedance environments with old bipolar opamps put in haphazardly. Many EHX circuits come to mind. And the result of that is people jumping to simple conclusions without any understanding and getting wrong impressions about parts, but the problem is they are only used improperly.

Suffice it to say, the 4558 isn't a good part by today's standards, far from it. For the same price you can get a NE5532, which beats it in every way. But we're building guitar pedals here, so at least for distortion the ear might have to decide what you put in. Still, many circuits can be adapted to lower impedances in order to reduce noise, without changing the tone.

15
General Questions / Re: Power problems
« on: September 21, 2020, 06:32:51 PM »
You need to switch to DC voltage. The wave in the display means you're measuring AC voltage. Look at the labels at the switch positions, there are two functions for each position. My guess would be you change the function with the orange button.

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