CD4049UBE Hot Harmonics Weirdness

[Nick C.]

I`d be afraid of even more weirdness, building according to that schematic. (including switchpop)

Both circuits are now surprisingly very quiet and controlled even when driven by another overdrive pedal. My channel switch is on a toggle not stomp, so pop isn't an issue. Due to volume and tone variations, separate tone and vol pots would be needed, so not really 2 channel, more 2 mode.

In the end the Hot Harmonics mode is not terribly different than than TSF maxed out, just more compressed and saturated. I'm really liking the sound coming out of the 4049, I'll have to play around with a lower gain circuit in the future. The TSF should be a much more popular effect. I imagin calling it a Fuzz or Llama didn't help

[snap]

no cap at no rail?

[Mark Hammer]

I've noted it before but I'll mention it again: a number of solid-state Laney amps use invertors as their overdrive element.  Here's an example of one:

[Nick C.]

no cap at no rail?

Hastily drawn using LTSpice, yea I've got a 100uF // to D1.

I've noted it before but I'll mention it again: a number of solid-state Laney amps use invertors as their overdrive element.  Here's an example of one:

Interesting, and they drive them with an opamp. I wonder if Anderton was the first to OD a CMOS with a guitar or maybe someone else had a happy accident. 

[snap]

You don`t know how lucky you are! One high gainer with open input while the other one is engaged. Maybe it works because the inverters are intermodulating their supplyvoltages in R4?

[Mark Hammer]

Actually, you know, the 4 invertor stages that encompass the driver before the first half of the Drive Gain dual-ganged pot, and the two stages prior to the Drive Volume control, might make for an interesting overdrive on its own, minus the switching FETs.

If we could only read the component values.

[snap]

Download/save to HD the elekrotanya image following their instructions. Click it and see the .pdf (64kb) clearly.

[Mark Hammer]

So here is the Laney overdrive circuit, extracted from one of their amps.  Note that it uses a CD4069UBE invertor as its core, not a 4049.  I have no idea how readily the circuit can be adapted to a 4049.

Does it absolutely need +/-15V?  No.  Does it absolutely need the op-amp stage at the input?  Maybe.  It has a gain of around 5x, and the first invertor stage doesn't seem to have much gain, so while one could just feedC8 directly from the input,  I suspect a greater range of tones is available with the inclusion of the op-amp stage.  The diagram says TL072, but you could pretty much use any single op-amp.

I have to confess, I just don't get R17/R18/C12.  Why have a parallel pathway through a cap if the two input resistances are identical?  Something doesn't make sense here.

I have a mountain of projects to get to, so I won't attempt building it...unless somebody else does and proclaims "Where has this BEEN all my life?!"

[Keppy]

I have to confess, I just don't get R17/R18/C12.  Why have a parallel pathway through a cap if the two input resistances are identical?  Something doesn't make sense here.

The input resistances are not identical. Frequencies that pass through the cap will pass through the resistors in parallel, meaning an input resistance of 23.5k instead of 47k and thus twice as much gain in that stage at those frequencies. R16/C12 is really a modified Tube Screamer filter, with the same corner frequency of ~720Hz but with a high shelf instead of a high pass response.

[anotherjim]

R17/R18/C12 and R28/C21 pre-emphasis boost followed by R26/C16 and R25/C17 de-emphasis cut? A noise reduction technique? Inverter amps can be quite noisy -  all those series resistors etc.

[Mark Hammer]

I have to confess, I just don't get R17/R18/C12.  Why have a parallel pathway through a cap if the two input resistances are identical?  Something doesn't make sense here.

The input resistances are not identical. Frequencies that pass through the cap will pass through the resistors in parallel, meaning an input resistance of 23.5k instead of 47k and thus twice as much gain in that stage at those frequencies. R16/C12 is really a modified Tube Screamer filter, with the same corner frequency of ~720Hz but with a high shelf instead of a high pass response.

Okay, that makes more sense, now.  I guess I have to just imagine that R17/R16 is a 23.5k resistance for lower freqs, and a 47k resistance for higher ones.  I'm just used to seeing different-value resistors in such networks, used for purposes of boosting high end.  Using it to boost low-end instead, is somewhat counter-intuitive.  But it makes sense, now.  Thanks.

[anotherjim]

Beg to differ.
C12 halves Rin for high frequencies by adding a parallel resistor - it is a treble boost.
C21 does the same  - differently - it bypasses a series resistor, but I don't know why they did it different in these 2 cases.

[Keppy]

I have to confess, I just don't get R17/R18/C12.  Why have a parallel pathway through a cap if the two input resistances are identical?  Something doesn't make sense here.

The input resistances are not identical. Frequencies that pass through the cap will pass through the resistors in parallel, meaning an input resistance of 23.5k instead of 47k and thus twice as much gain in that stage at those frequencies. R16/C12 is really a modified Tube Screamer filter, with the same corner frequency of ~720Hz but with a high shelf instead of a high pass response.

Okay, that makes more sense, now.  I guess I have to just imagine that R17/R16 is a 23.5k resistance for lower freqs, and a 47k resistance for higher ones.  I'm just used to seeing different-value resistors in such networks, used for purposes of boosting high end.  Using it to boost low-end instead, is somewhat counter-intuitive.  But it makes sense, now.  Thanks.

Glad to help.

C12 halves Rin for high frequencies by adding a parallel resistor - it is a treble boost.
C21 does the same  - differently - it bypasses a series resistor, but I don't know why they did it different in these 2 cases.

I thought that was weird too. The corner frequency and the effect on gain are the same. Why do the same thing in a different way? Maybe it made the layout easier.

[anotherjim]

Thought I'd better check the freq's.
2 poles Hf boost aimed about 720Hz
1 pole Hf cut aimed about 2.25kHz
1 pole Hf cut over 33Khz!
Looks like a mid boost to me.
Ok, nix what I said about noise reduction!

[teemuk]

Here's more inverter ingeniousity:


One inverter stage in the preamp for waveshaping, quad of inverters driving spring reverb in push pull, and yet another inverter as voltage amp / driver stage of the power amp! A power amp that clips softly like a MOSFET inverter. Nice. I also like how floating power supply and DC servos are implemented to it. You don't see power amp designs like this everyday.

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I wish I could relocate schematics of Lab Series L3 and L6 amps. These, if I remember right, used the MOSFETs within the IC both in "conventional" push-pull arrangement, or as discrete MOSFET gain stages alone. Also, if I remember right, these amps had active tone controls that were implemented to feedback loop stages of inverters/MOSFETs.

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Then there are, of course, these Fender amps:



...But yeah, it's just another overdriven inverter stage. I do like the "outside-the-box" design of the Sunn amp. 

[anotherjim]

Fender approach is interesting though. All 3 inverters in a CD4007 used in parallel. Lower power supply volts reduces shoot-through current (gives moderate increase in open-loop gain too). Series resistance too (R34-35). Deliberate power sag tactics?
The Sunn reverb driver is similar to a plan I had to drive a small audio transformer - going with the thought that a valve amp sim should include a transformer stage.