What classic effect circuits react well to dying batteries?

[zenpeace69]

I know alot of fuzzes really get their mojo working when the battery is dying, but are there any other kinds of effects that respond well?  Any particular classic pedals?

thanks

[Eb7+9]

... as far as I know the MXR Dynacomp is the only well-known classic effect that responds well to dropping supply voltage ... used to be a Country Producer's secret, way back ...

//www.lynx.net/~jc/pedals.html

... somebody told me Dunlop came up with a variable bias version of the re-issue Dyna ... I never checked ...

jc

[bwanasonic]

I have convinced myself at various times that my DOD 201 phasor sounds best with an *aged* carbon 9v. But I usually just run it with a PS.  Not a big enough difference to fiddle around with IMO.  I always run my Fuzz Face and Rangemaster with Carbon batts.  My Fulltone Supa-Trem likes carbon 9v, but  I always use a PS with that as well. Ideally I'd love a PS that allowed the full spectrum from weak Carbon batt, to +18v for each effect. Sounds like the Voodoo PS2. One of these days...

Kerry M

[Bluesgeetar]

Duane Allman swore by a almost dead battery in his Fuzz Face, Billy Gibbons seems to like a low battery in the Bixonic Expandora.  Skynryd doing the same thing Allman did.  Those are the only ones I know of.  I imagine there are many more.  Recording sessions can last awhile so I imagine that at the end of the day Page, Hendrix, Clapton or whoever where playing through a low battery when laying down tracks.  If they didn't like what they where hearing I guess they just popped in a new fresh one.  
I'm really digging the little battery sim thang I was talking about from the hellish thread from earlier.  It is working great and was so damn easy to get set up. :twisted:

[Jay Doyle]

I'm really digging the little battery sim thang I was talking about from the hellish thread from earlier.  It is working great and was so damn easy to get set up.

Then,

A - Why don't you post it or at least describe the circuit?

and

B - Why did you ask for help in the first place?

It was only hellish because you were rude to the people who tried to help you.

If this degenerates, I apologize, but I don't like being called an a$$hole by someone who I helped. (The thread was closed and Bluesgeetar's posts were deleted before I could respond)

[zenpeace69]

thanks for the responses

I knew that fuzz circuits and even overdrives could benefit from lower voltage, but I had no idea that people used them on compressors.  That's exactly the tidbit I was looking for.

[nightingale]

3 knob tonebender too..

[Tim Escobedo]

There are lots of circuits that will work at lower voltages. Lots more that will just get crappier at lower voltages. There are a couple that may have some mojo with a saggy high impedance power source. Which is kinda different than just a lowered power supply.

[bwanasonic]

There are lots of circuits that will work at lower voltages. Lots more that will just get crappier at lower voltages. There are a couple that may have some mojo with a saggy high impedance power source. Which is kinda different than just a lowered power supply.

If it were easier and practical to provide the *mojo-inducing* exact voltage and impedance from a single supply to all my pedals under gig conditions, I would probably obsess about this more, but until I get my own crew of techs to keep me in a steady supply of properly aged carbon batteries on a gig, I'll stick with a power supply for everything but my Fuzz Face and Rangemaster.

Kerrry M

[Eb7+9]

thanks for the responses

I knew that fuzz circuits and even overdrives could benefit from lower voltage, but I had no idea that people used them on compressors.  That's exactly the tidbit I was looking for.

glad to hear about those other pedals, the toneBenderMkIII eh ?! ...

.. btw,  about loss-of FI in compressors - I took out my little Orange Squeezer to check it out (original but stuck into box with footswitch and tripots replaced by external pots), and aside from slight distortion during heavy transients I found the pedal to be quite good FI wise - quite a bit better than the MXR ...

It's a circuit I haven't really studied, but I wondered if that slight distortion would be elliminated by going to 18volts supply instead of 9 ... going the other way with this one ... or am I looking at device swaps

anybody try this 18v thing on the OS ???

(RIP Dan)

[Eric H]

.. btw,  about loss-of FI in compressors -

FI  :?:

-Eric

[Bluesgeetar]

FI= Friendly Interface

:mrgreen:

[bwanasonic]

.. btw,  about loss-of FI in compressors -

FI  :?:

You know - as in fee FI fo fum!

Maybe not.

HIgh FIdelity vs. LOw FIdelity...

Kerry M

PS. I think the so-called *distortion* in the OS has been discussed by M. Hammer before. I don't think it's a headroom issue.  It's here somewhere...

[Eric H]

Glad to see I wasn't the only one.

F'ing Inscrutable

[R.G.]

... somebody told me Dunlop came up with a variable bias version of the re-issue Dyna ...

What the devil would they bias?? There's not much there to bias.

... as far as I know the MXR Dynacomp is the only well-known classic effect that responds well to dropping supply voltage

You haven't hear about Eric Johnson's ramblings on battery brand and age on his Fuzz Faces???

A - Why don't you post it or at least describe the circuit?

See "Pedalboard Power Supply" at GEO for the first instance I know of of a circuit like this. It's an LM317 voltage regulator adjustable from 7-10Vdc and a resistor in series with the output. Six months *after* I put that up on GEO, someone else applied for and later received a patent on that specific setup. 8-)

I believe I pointed the guy to it then as well.

I knew that fuzz circuits and even overdrives could benefit from lower voltage, but I had no idea that people used them on compressors. That's exactly the tidbit I was looking for.

It is impossible to generalize that. Each circuit acts how it acts under lower or higher voltages. This may sound good or bad to your personal ear, but there is no general behavior.

If it were easier and practical to provide the *mojo-inducing* exact voltage and impedance from a single supply to all my pedals under gig conditions, I would probably obsess about this more,

It's not that hard. You use the LM317 variable voltage regulator in the TO-92 package to set exactly the voltage you like and then stick a resistor after it for the impedance. See the article on the "Pedalboard Power Supply" at GEO for how to do this. You can either have one power supply with a customized voltage/impedance per pedal by putting the regulators inside the power supply box, or by putting one regulator/resistor inside each effect box and feeding all the boxes +12, which the regulator turns into whatever the pedal needs.

It's a circuit I haven't really studied, but I wondered if that slight distortion would be elliminated by going to 18volts supply instead of 9

Won't help. The distortion is from the envelope rectifier/JFET combo.

By the way, the reason you can simply turn up the power supply voltage on the OS and note run its biasing absolutely nuts is that the bias point for the gain change JFET is dead fixed by the use of the second JFET as a constant current source to set the bias for the second one.

[Eb7+9]

What the devil would they bias?? There's not much there to bias.

... try the whole circuit, which is OTA based - very different response to supply drop than op-amp based ...

[R.G.]

... try the whole circuit, which is OTA based - very different response to supply drop than op-amp based ...

... um... yeah, I know it's OTA based. I've drawn out and posted the schematic a couple of times on GEO for both the Ross and Dyna, as well as doing PCB layouts for both and writing a "Technology of the Dynacomp". I've kinda been there.

You see, the thing with an OTA circuit is that the gain of the OTA is proportional to the *bias current*, which is fed in through the Iabc pin, which is what the gain changing circuit varies all over the map every time the loudness of a note changes. It's almost impossible to speak of the "bias" of something that's waved around so much.

If you were talking about
(a) the DC return point for the output pin (6) of the OTA, that's completely immaterial to the operation of the OTA, being fed by two high compliance current sources inside the OTA. It will happily DC return to any DC voltage within the power supply range with no change of AC characteristics except for running out of power supply volts.
(b) the trimmer pot or DC bias point for the + and - inputs, these are also almost completely independent of the power supply. The emitter biasing of the input differential pair is current source and hence power supply and bias insensitive, as is the drive from the differential pair to the two high-side current sources driven by the input differential pair. The diff pair also does not care where in the power supply it's biased, and so is unaware of the DC bias level. It is very sensitive to the *difference* in voltage between the two bases, but that is not a power supply voltage question.

So, like I said, there's substantially nothing there to bias. There's probably something I'm missing - please describe to me in some detail how changing the DC power supply changes the operation of the whole OTA based circuit. Is there perhaps a new natural law here that I'm missing?

[mattv]

See "Pedalboard Power Supply" at GEO for the first instance I know of of a circuit like this. It's an LM317 voltage regulator adjustable from 7-10Vdc and a resistor in series with the output. Six months *after* I put that up on GEO, someone else applied for and later received a patent on that specific setup. 8-)

I believe I pointed the guy to it then as well.

I think the originator of this thread is wanting to sell a voltage regulating device as well. I hope he doesn't get trouble from the patent holder.  :wink:  :roll:

[Eb7+9]

... the thing with an OTA circuit is that the gain of the OTA is proportional to the *bias current*, which is fed in through the Iabc pin, which is what the gain changing circuit varies all over the map every time the loudness of a note changes. It's almost impossible to speak of the "bias" of something that's waved around so much.

... actually the bias of the OTA is regulated by the mirrored FET reference and doesn't fall linearly with supply voltage, and also the transconductance of the low offset CA3080A is linear over six decades of bias current and with a fixed +/-50mV linear input range ... if it had degeneration resistors in the diff-pair input then the linear range would modulate with bias but not with this OTA ... so the OTA and it's bias circuit are to, a first order, somewhat insensitive to that drop ...

... what does vary significantly with supply drop however is the dynamic Slewing of the detector circuit, specifically by lowering supply voltage you're dropping the bias of the second FET stage with the ground connected source and who'se drain is feeding the large 10uF cap - it is biased with less current for one (less current to share) and it's channel resistance is higher also (slower RC constants) ... increasing the attack/release times a bit ... the gain of the first stage also drops a bit too - so there's less drive in the front-end of the detector circuit also ... two spots are affected by the supply drop, both in the detector circuit ...

... the lack of top-end FI can be used for taking some of the painful sting of a Tele - especially when plugged into a Solid State amp ... not sure but it seems that by removing or reducing either (i) the 0.01uF cap in parallel with the 16k resistor (as part of the voltage divider network before the OTA) it would restore some of those lost highs, or (ii) the 0.001uF across the 150k OTA loads resistor which is shunting highs to ground through the grounded 1uF cap next to it ... I'd look at the 0.001uF cap first ...

... jc

[R.G.]

... actually the bias of the OTA... [yada, yada, yada] ... so the OTA and it's bias circuit are to, a first order, somewhat insensitive to that drop ...

OK, good we got that one down correctly. The OTA circuit isn't sensitive to the bias waving around, except as it should be by changing gain when the Iabc changes, in spite of your earlier note claiming that

... try the whole circuit, which is OTA based - very different response to supply drop than op-amp based ...

... which I interpreted as you saying that the OTA circuit made a difference with a varying voltage. I'm glad to know that I did, indeed understand the circuit correctly and that no new physical laws were involved.

But then you say:

... what does vary significantly with supply drop however is the dynamic Slewing of the detector circuit, specifically by lowering supply voltage you're dropping the bias of the second FET stage with the ground connected source and who'se drain is feeding the large 10uF cap - it is biased with less current for one (less current to share) and it's channel resistance is higher also (slower RC constants) ... increasing the attack/release times a bit ... the gain of the first stage also drops a bit too - so there's less drive in the front-end of the detector circuit also ... two spots are affected by the supply drop, both in the detector circuit ...

Huh?? FET?? Those detectors are both bipolars, not FETs. And their *bases* are biased to ground by 1M resistors, then clamped to ground by the diodes and input DC blocking capacitors to act like voltage doubling peak detectors. There is no bias there - the bases tie to ground.

Interestingly enough, bipolars don't *have* channel resistances, not like FETs of any stripe do, so could you possibly elaborate a little for me about how changes in the bias that the detectors don't have can make the nonexistant channel resistances affect any RC constant? I just don't see that. Maybe you can explain it to me.

By the way, the way that detector works is that the two *bipolar* transistors with their emitters grounded and collectors tied to the 10uF cap are fed from out-of-phase signals from the collector and emitter of the transistor whose base connects to the output of the OTA.  The two out of phase signals are half wave rectified by pushing current into the bases of the detector transistors; the diodes and pulldown 1M resistors clamp the negative going end of the signal to ground, giving an effective gain of two to the detection, but softening the attack as the clamp diodes ramp the coupling caps to their clamping voltage. (See Halliday and Resnick, "Clipping and Clamping Circuits" in "Pulse and Digital Waveforms" for a more complete explanation). The collectors pull a pulse of charge out of that 10uF cap. The cap charges to +V through that 150K resistors (which, by the by, sets the release time constant), when there is no signal. The signal pulses, being out of phase, effectively full wave rectify in the detector, the 10uF cap smooths that, and the last transistor acts as an emitter follower to drive the buffered 10uF cap voltage into the Iabc pin through the variable resistance sustain pot.

The **only** effect of lowered V+ on that circuit is that the gain of the OTA can't get as high since there is less voltage available to drive its gain up. There isn't any bias effect there.

Ah (I can hear you say) but the ... (FET?? no, bipolar) NPN with its base connected to the OTA, that one is biased! Right??

Yes, it is. And you may wonder why the designer chose to bias its base and the output of the OTA output to a funny non-centered voltage with the 56K/27K Vr generator. The secret is (a) as I mentioned before, the OTA cares not a whit where its output is biased in voltage; it's a current output, with the full power supply voltage for compliance but (b) the NPN bipolar phase splitter/output transistor does care. For it to be an effective phase splitter, it needs its emitter and collector sitting at 1/4 and 3/4 of the B+ power supply for the widest undistorted swing on its two outputs. And that is what that off-center Vr does, at least for voltages around 9V.

What lowering the power supply voltage does on this circuit is make it distort earlier, since its biggest undistorted output is limited by that NPN phase splitter to at best half the power supply, and in practice significantly less. If you had said that there was some slight distortion introduced, that is perhaps a plausible reason for producers liking the change in tone.

By the by, the gain/bandwidth of the OTA *is* affected by the bias current; alas, that's not a lowered power supply voltage effect either, as it swings all over the map with each note, too.

not sure but it seems that by removing or reducing either (i) the 0.01uF cap in parallel with the 16k resistor (as part of the voltage divider network before the OTA) it would restore some of those lost highs, or (ii) the 0.001uF across the 150k OTA loads resistor which is shunting highs to ground through the grounded 1uF cap next to it ... I'd look at the 0.001uF cap first ...

Let me help you.

The neat thing about electronics is that you can calculate rolloffs. Whenever there's a resistor in parallel with a capacitor, the capacitor rolls off any frequencies above F = 1/(2*pi*R*C) at a rate of -6db per octave (for voltage ratios). So we can see something immediately - the RC product of 0.01uF and 15K is the same as the product of 150K and 0.001uF, so they have exactly the same rolloff. One of them rolls off the input, one of them the output. But at what frequency?

Oops, I already said it! F= 1/(2*pi*R*C) = 1062 Hz, which we'll just call a kHz (if I got the decimal point right in my head). So this thing already rolls off starting at 1K.  If you wanted to roll it off even more, change one or both caps to start the rolloff earlier in frequency.



As you guessed, the 0.001uF at the 150K OTA load is indeed the treble rolloff for the signal path.