Unipolar supply to +/-5V with LTT1054. Am I doing this right?

[strungout]

Someone asked me to build them a multi-band fuzz. I suggested the QuadraFuzz (he mentioned the Iron Ether and the Four Eyes). I'm fitting it in a 1590XX box. I want it to be powered by a unipolar supply. 9V. Q's are +5V/-5V regulators. Will this work for powering the circuit?:



I just tagged regulators to the +Vo/-Vo of a circuit example from the datasheet. But it's a voltage doubler... so I would get +/-18V before the regulators?

[Keppy]

I just tagged regulators to the +Vo/-Vo of a circuit example from the datasheet. But it's a voltage doubler... so I would get +/-18V before the regulators?

That's correct. If you want +-5v as the schematic seems to indicate, you'd be better off feeding your 9v supply into the +5v regulator, and feeding the -5v regulator with the "Basic Voltage Inverter" circuit from the datasheet.

[Vivek]

Like Keppy said :

You would not want to have such a high voltage like +18 going down to +5

So you can always use your +9 and regulate that to +5

and if you could mod that circuit to get -9, you could tap -5 out of that with a regulator.



Or another option, you could mod your +/-5V schematic and make it run with +9V and zero, by having a buffered Vref in there along with some other minor mods.

[strungout]

Alright, options!

I was focusing on getting +/- 5V. But the simplest way would indeed be to convert the circuit to single supply circuit. I'll breadboard it. I'm losing 1V of headroom though, aren't I? Not sure if that'll make that big a difference. I'll try both ways and hear.

Thanks much to both of you.

[Vivek]

It might fuzz better with lower headroom !!!!

[strungout]

So, I did the single supply conversion. The only thing I had to add was a 10k resistor from Vref at the first stage non-inverting. The rest is just changing power connections.

I haven't played a lot with it, but I see how versatile it is. I couldn't find a guitar demo of  the QuadraFuzz to compare with (DId find one where it's demo'ed with some electronic music). The circuit sounds good. Very fuzzy. Max fuzz is intense.  I think I'll need to lower the gain of the low and low mids stages. They're... uh... not so pleasant. Kinda greasy. Anyone have any suggestion to start me up on it? I'll probably need to tinker with the 10k mixing resistors...

Anyway, I drew up a schematic:

[Vivek]

There are errors at your input, caused by new 10k going to Vref

Better to send 220k to Vref

And add input DC decoupling capacitor.

[Vivek]

I suggest :

[Vivek]

I sense something funny about the original schematic

I had understood that the idea to break up the guitar signal into 4 parts before fuzzing was

A) Reduce the inter-modulation byproducts

B) Greater control on the final sound


However if appears that the first stage has a max gain of 200. It will surely clip the input signals before it enters the band pass filters

Shouldn't the first stage have been squeaky clean for above idea to work  ?

We need :

Ultra Clean signal is broken up into 4 parts. Each part is fuzzed separately and then summed

not

Input signal is severely clipped, then the clipped signal is broken up into 4 parts and each part is again re-fuzzed and summed

[Vivek]

MOD SUGGESTION


right now, the circuit has fixed amount of clipping per band
and user can change mix ratio but not gain


you could try either

pots for user controlled gain per band
or internal trimmers so user can set his desired gain per band

That would make the pedal go from totally clean to very fuzzed, per band.

add another level of versatility !!

Coax pots could be nice, one level controls gain for that band, other controls mix ratio

[strungout]

EDIT: using the 220k to Vref doesn't work well. The circuit doesn't like it XD My guitar volume becomes intermittent and it'S really noisy.

Thanks for the suggestion and pointers, man.

Yeah, I forgot the 1M pull down from the input to ground and a coupling cap. Good catch.
Before, I had both the parallel 10pF cap and 220k res at the input connected to Vref. But it was gating and I was getting 8V at the output of the first opamp. I'll try only the 220k to Vref.

Your though about needing a clean signal to feed the clipping stages makes sense. I think I will lower the gain. I can't get down to sutle fuzz anyway, it stays pretty fuzzy at minimum.

As for the gain control for each section. I like it. I'll probably use trimmers. My boards always have the component side down, it'll be easy to access the trims to adjust. 4 more knobs would bring the total to 11! plus the 4 switches... I'll see if I have room.


And then, I just noticed I forgot to put the power section on my schem.

[Vivek]

EDIT: using the 220k to Vref doesn't work well. The circuit doesn't like it XD My guitar volume becomes intermittent and it'S really noisy.

Could you please post voltages on the important pins of the IC.

and your latest schematics

Thanks.

[strungout]

EDIT 2: I rebuilt two of the sections on another board and now everything works fine. I also powered it on 12V, which I like better. Crunchier. There's still noise, but, it's pretty high gain, so...

EDIT: I noticed the level know see to work in pairs... both need to be turned up for the other to work. If one is turned down there's no sound... wth.

Alright, here's my voltages:

I used 6 TL072 cause I didn't have the 3 TL074 yet. When I turn my guitar volume all the way down, I can hear the circuit's oscillating. Even after I sub'ed the 470k (IC1A) with a 120k. It's on my BB so there's wires going everywhere and the fuzz is high gain...

The voltages look ok to me...

IC1
4.71
4.71
4.58
0
4.70
4.69
5.83
9.15

IC2
4.95
4.82
4.74
0
4.56
4.56
4.56
9.15

IC3
4.56
4.56
4.56
0
4.56
4.57
4.72

IC4
4.54
4.57
4.56
0
4.56
4.57
4.55

IC5
4.57
4.57
4.56
0
4.56
4.57
4.47

IC6
4.57
4.56
4.56
0
4.56
4.56
4.56

And my current Schematic:



And a stripped version of the PAiA one:

[Vivek]

A) Great to know that the idea of input 220K going to Vref is working fine.

B) You could try "Coring Diodes" as a cheap and primitive noise gate for high gain pedals

C) if the idea was that distortion is only created after the frequency bands are separated, then the first IC cannot have a gain of more than 3 !!!

Something is not right with the original design. According to me, the first stage has tooooooooooo much gain.

Even 120K is too high for that gain determination resistor.

You could try to reduce the gain of first stage to below 3. That just might solve your noise problems too, while sticking to the original concept of "Distortion created only after frequency bands have been separated"


Hope that helps.

[duck_arse]

you seem to have a bad voltage at pin 7 [un-numbered, only guessing] of IC1, it can't be higher than the inputs. and you show all the splitter level pots going to ground, but not AC coupled to the output mixer. when any of those pots are at zero, they will mess the DC around IC1B. I think.

[Vivek]

Great catch, Duck !

Needs one cap more !

[strungout]

Vivek: Thanks. The 'coring' diodes worked really well, they cause a substantial noise drop. I tried a few Ge and Si, and settled on 1N914s. Most noise reduction and it only causes a barely-noticeable gating. I added them in between the output cap and level pot of each section. Can I get away with using just one before ICB or...? I have the room.

It help to drop the Gain below 3. I used a 43k, with the stock 2k2, but I need to check if I didn't screw with the frenquency corner in any meaningful way.

At max gain, it is noisy, but it's only the last small part of the rotation of the pot. It sorta jumps in. Below that, it's pretty silent.


Stephen: new voltages for IC1:

1-4.60
2-4.60
3-4.47
4-0
5-4.61
6-4.61
7-4.72
8-9.22

Pin 7 's voltage dropped, but it's still higher than the inputs.

I had the level pots both at Ground and Vref, and it didn't seem to make much of a change. It sound at least. They are connected to ground right now.

I put in a 4.7uF cap (Like the others. To color match). I hadn't put one because none of the three QF schematic I've seen have one 

[Vivek]

The patent for coring diodes:

https://patents.google.com/patent/US4571511A/en


Yes you should try having only one set of coring diodes

Unless you discover which band creates much more noise than the other bands, in which case you could fine tune the coring diodes on that leg

Already the high Opamp has 470pf in the loop, you could experiment with increasing it to cut noise but still have sufficient treble.


Maybe a similar cap on final Opamp could tame more noise / highs.


Wrong bias on ICB will make if fuzz

But if we feed it with a fuzz, it's harder to understand that ICB is fuzzing too

[Vivek]

It's good to have a 0.1uF in parallel with the bigger Vref cap.

[strungout]

Vivek:

So I did the one set of coring diodes, right before the 4.7uF cap I just added to the inverting input of IC1B. It sounds more quiet with each section having it's own set, I think. I tried a set only in the 2nd section. Noise.
All the sections have their own particular noise, but the hiss on the High section is a bit annoying. Low Mid is ok. Low is ok.

The real culprit is the High Mid section. Noisiest and loudest. I sub'ed the feedback loop cap up to 1nF, but while this last value does reduces the noise, it reduces the upper frequencies... Which is where the noise is. Heh.

I added a cap to the last stage's fb loop, but it didn't sound like it had an effect on the noise. Did that with IC1B too.