freestompboxes.org

Hmm. I have to disagree. I quoted PRR (which is an authority for me) hoping that I would not have to debate this subject.

Of course he is an authority. That's why I actually agreed with him, saying it's the same order of magnitude. You might want to calculate the noise of a 1M/2M/4,7M at some point.

This one was easy to check, as all that it needs is a DMM. This is the circuit:
breadboard_2.pngThe IC is actually a HCF4069UBE. R8 is there to lower the load to COD-100 comparable values. The results are these:
1. when powered with 9V the circuit eats 14.9mA with 3 inverters (the other 3 being tied to the negative rail as in COD-100) and 39.1mA with the other 3 inverters connected in parallel
2. when powered with 15V the circuit eats 28.5mA with 3 inverters and 69.2mA with the other 3 inverters connected in parallel
As expected, the circuit use maximum power when has no input signal and the inverters stay all the time at half-supply voltage.

So, my statement about the wall-wart overloading was clearly exaggerated. However, I wouldn't call this power consumption "absolutely negligible".

How could I be so wrong. By now I have given up on tube amps so I can afford playing those hungry CMOS overdrives. The amps were just too much of a strain on the electricity bill. I hope those additional 0,2W will keep me warm during cold winter times.

...audiophile lore...

See you around, buddy.

I've build a high gain distortion circuit using 12 stages that only draws 12,2 mA, (Each CD4049UBE chip has a 1k in it's powerline).
So either it's a manufacturer thing or those parallel stages draw a lot more (I'd normally assume the double) than singles ones.
If so, the higher current through the resistors would counter act the noise benefit stated . More facts please,
I love those chips but info about them seems always to get blurry when it comes to linear use.

marshmellow wrote:

Hmm. I have to disagree. I quoted PRR (which is an authority for me) hoping that I would not have to debate this subject.

Of course he is an authority. That's why I actually agreed with him, saying it's the same order of magnitude. You might want to calculate the noise of a 1M/2M/4,7M at some point.

Sorry, it seems you missed the first part of my quote. Read the first sentence of my quote again, especially the beginning:

[...] Resistor hiss-noise is a non-issue: the MOS transistor self-noise is several/many microVolts, more than a 1Meg resistance. [...]

Your posts seem to assert that the problem is the resistor thermal noise and using smaller resistances will help with inverter gain stages noise. From what I've read and tested, it seems that the problem is the 1/f noise of the MOSFETs.

deafbutpicky wrote:I've build a high gain distortion circuit using 12 stages that only draws 12,2 mA, (Each CD4049UBE chip has a 1k in it's powerline).
So either it's a manufacturer thing or those parallel stages draw a lot more (I'd normally assume the double) than singles ones.
If so, the higher current through the resistors would counter act the noise benefit stated . More facts please,
I love those chips but info about them seems always to get blurry when it comes to linear use.

Wow, 12 stages? I'd love to know more! It should sound really brutal - 12 inverters with a gain of 2.4 each will have more gain than Emma Reezafratzitz! How did you deal with the noise?

About the consumption: 1k for each 6 inverters would starve them quite a lot. I've just tried it with the 3 inverter circuit, which is still on the breadboard, and a 1k on pin 14 drops the current from 13.52mA to 2.97mA and the voltage at pin 14 from 8.67V to 5.83V. I used a 8.9V battery because I didn't want to wake my little daughter while plugging/unplugging, but I'll try it again tomorrow. I also have two other brands of inverters and I can try the 4049 as well. It seems that a 1k at 9V will limit the current to around 1mA per inverter.

This are the schematics of the inverters: I think the only current is the one passed through the two MOSFETs. The current passed through the feedback and input resistors would be really small and would not change with the number of the inverters they serve.
To me, it seems that @marshmellow treats the inverters as resistors, thus paralleling them to decrease the noise. I don't think he tried it practically, though.

1K seems to be quite big but these ICs like to be starved (they're used at 5V usually) and it helps the distorion (lower headroom).
There's thread over at diysb: https://www.diystompboxes.com/smfforum/ ... #msg914820

The schematic I refer to is: (The original links got mixed up for some reason)

Ah, too late,just read your post.
He might have mixed up driving capability with current consumption, but I haven't delved into this yet (due to missing info).

The use of an expander seems a reasonable approach but it's new to me and I wouldn't start a fight over it.
Thrice I is a take at it and I've heard worse for it...

ggedamed wrote: Can you check R14? I don't get the role of IC1A, as it's just an unity gain inverter with a bit of filtering.

Back at my desk. And R14 is definitely 47k (yellow-violet-orange-gold). I'm putting this back together now...


And on the current consumption matter.. I do not think tube amps compare particularly well against stompboxes which are powered by single 9V battery. 15mA isn't trivial. I'd say anything under 8-10mA is.

Thanks.

On the breadboard I added the first two op amps (IC1) and the compander. I compared it with a Tripple Wreck clone and a Tight Metal clone. Definitely different animals. Much more bass, much less treble, much less distortion. To me it feels strange, like it would respond after a delay. Maybe it's just my inability to use compressors.
From the schematic, High EQ is centered around 5.2kHz and Low EQ around 40Hz. 40Hz is really low, which makes me me wonder again if it is a bass effect. It sure sounds nice on the low notes.

I don't feel like I'll test it anymore. The tone control cannot make a big difference, I tried it with an EQ pedal after it anyway.

I can confirm that @marshmellow's noise combat techniques are really effective, see this topic: CMOS inverters noise reduction.

wow, that's a LOT better
hearing is believing... thanks for testing it.

ggedamed wrote:

marshmellow wrote:I don't understand why everybody always uses the inverters with those überhigh impedances. It's not like those chips would have problems driving 10k... But then use a compander to deal with the unnecessary noise they just produced . Also, there are a couple of inverters doing nothing. Put them in parallel, cut the noise in half, and decrease the resistors even more because you have double the driving power.

Sadly, it doesn't work like this. There's a nice explanation by PRR on DIYSB from which I quote:

Resistor hiss-noise is a non-issue: the MOS transistor self-noise is several/many microVolts, more than a 1Meg resistance.

Input impedance is often an issue. If you want gain of 30 and a 10K feedback resistor, you want a 330 ohm input resistor and have a nearly 330 ohm input impedance. That's awful low. In fact a CMOS amp won't drive 300 ohms well.

(Although, at 10V-15V supply, you hardly have open-loop gain of 30 so you can't really NFB-define a gain of 30 without cascading.)

OTOH with 1Meg feedback we get 33K input resistance, managable in many audio systems. For guitar we like over 100K, and 150K is popular. If we wanted gain of 30 (in this case maybe not) then the NFB computes to 4.5Meg. There's no realistic upper limit on the NFB resistor: CMOS gate current is VERY low, and in this case there's some gate current cancellation.

So, it's not the output impedance that's causing the resistor choice, it's the input impedance.

The inherent noise level of the CMOS inverters is really high. Sadly again, to make them clip/distort nice (and they can distort really nice) you have to starve them somewhat. The Bias control in a Emma Reezafratzitz will give you a good image of that. I fantasized since quite a lot ago about a "current compressor" to feed the inverters, so they have all they can eat at low levels (so lower noise), then when the signal goes large the inverters would be starved more and more, for the nice distortion they can make. Didn't find the time to do it yet, but who knows?
Also, in linear mode, the inverters eat gobbles of power. I can imagine using all six inverters leading to the overloading the smaller 9V/150mA wall-warts.

Bottom line, I think that the designer knew what he was doing and he played well enough within the constraints.

The designer missed several tricks: reducing the resistor values around the CMOS will improve the noise figure markedly, and won't affect any impedances "seen" by the guitar - that's why there's an op-amp buffer at the input. The use of the 571 as a compander will help a lot, but if the resistor (and capacitor) values are scaled, and the compressor is configured for a bit more output, the noise can be reduced to negligible amounts. It's also fun to make the output expander track the original guitar envelope (as a switchable option) so you can get "fuzz without sustain" which sounds bizarre and is very musically useful!

I don't like the fact that the CMOS switches are not electrically isolated from the output - I'd add either another op-amp buffer or a single transistor emitter-follower stage there for protection - CMOS switches are easily killed by static.

Further noise reduction can be achieved by making the CMOS stage gains smaller earlier on, and larger later - take a look at the Runoffgroove "Double D" for ideas there.

Finally - there's lots of noise (and consumption) variation in CMOS ICs. I've used some older 4069UBEs that I had lying around for years, and they're practically hiss-free. The 4049UB seems to be quieter (but more current hungry) than the 4069UB - it's always worth socketing the device and seeking the quietest one you can find from a batch! The "Emma" circuit deliberately "starves" the CMOS in an effort to reduce the noise (though they claim it's to allow the player to find the bias "sweet spot")....

If you want to get exactly the same kind of distortion with two orders of magnitude less noise (and no compander needed), just build a couple of FET µ-amps and feed one into the next. Drive them with a low noise op-amp buffer (sacrilege for the "golden eared" idiots) and increase (or decrease) the number of µ-amp stages to taste! The output can be buffered with the other half of your dual low-noise op-amp, and you can use a real switch (or relay) for bypass. This is almost exactly this Christmas's pedal given to a few friends. There's two footswitches - bypass and stage select - and three LEDs to indicate the number of µ-amps in the path. Levels are pre-set internally, and the thing sounds "gritty" (1 µ-amp), "overdriven" (2 µ-amps), or "screaming" (3 µ-amps)......

You're right. You can see three posts above that, despite my initial misbelief, reduction of the resistors' values and paralleling the inverters were impressively effective, for me at least.

I cannot say anything about companding as it seems beyond my ability to use and enjoy it.

I'm with you when you say that the CMOS switches should be buffered. Given that the pedal still works, it appears that the output of the inverter is not that sensitive, though.

I'll definitely try starting with small gain and increasing it with every subsequent µ-amp stage - they sound close to inverters to me, too. Thanks for the tip.

The power consumption discussion was mainly academic. I dont' really care, I don't use batteries. I don't know why I brought it up, probably for exhaustiveness (I'm somehow OCD prone).

The Emma Reezafratzitz circuit starves the inverters for the sound, not noise. It has the least noise when is not starved, so for minimum noise they should have discarded the bias pot. I can confirm that their claim - about the Bias pot being designed to allow the player to find the "sweet spot" - is true. When the Bias pot is at 0% the effect has minimum noise, but the distortion is meh. As the pot is dialed, it passes through some kind of threshold (the passing through it can be heard) and the distortion becomes richer and nice to my ear. Unfortunately, at the same time, the noise also starts increasing. So, the Bias pot in a Emma Reezafratzitz allows me to set a trade-off between noise and sound. Where is this trade-off occuring highly depends on one's taste and habits.

ggedamed wrote: The Emma Reezafratzitz circuit starves the inverters for the sound, not noise. It has the least noise when is not starved, so for minimum noise they should have discarded the bias pot. I can confirm that their claim - about the Bias pot being designed to allow the player to find the "sweet spot" - is true. When the Bias pot is at 0% the effect has minimum noise, but the distortion is meh. As the pot is dialed, it passes through some kind of threshold (the passing through it can be heard) and the distortion becomes richer and nice to my ear. Unfortunately, at the same time, the noise also starts increasing. So, the Bias pot in a Emma Reezafratzitz allows me to set a trade-off between noise and sound. Where is this trade-off occuring highly depends on one's taste and habits.

The "Emma" I tried had a spot somewhere down the pot with minimum noise: presumably it just had a different CMOS characteristic.

I tried paralleling Inverter Stages. It adds a little more body to the signal but you loose that flat snappy single-coil-esque clipping when you play chords.

Also, scaling down the Resistor values did not lower the noise floor for me. I later found PRR's post on the subject and it seems to make sense.

stumbled into the manual (in Japanese; for whatever reason, no English one available on the Yamaha US site--I checked) :

http://download.yamaha.com/search/resul ... ch=COD-100

shows power consumption at 32mA(9V).

(also) battery life (with National/Panasonic Neo Hi-Top



carbon (I think) battery) given as "approx. 5 hours"

tone control center freqs.: (Low)120Hz, (High)5kHz