Messages

IC12/Q2 is your envelope detecty business, IC11 is acting like a resistor dividing the signal around the J-FET buffer.

Does the 'chirping' sound a little like a fuzzy octave up?

Envelope ripple can sometimes sound like distortion, I've not tried the circuit so don't know how it responds.

I got some cool ehx stuff from you guys in the oven right now, bout to be serving up some "brownies" soon!

Sent from my moto z4 using Tapatalk

Brownies!?



You pretty much hit the nail on the head with your description, I've always found the EHX stuff to be the most inspiring in its palettes. I get the BOSS/Ibanez/MXR stuff... but it can be a bit... utilitarian.

Mu-tron, A/DA and to a lesser extent, DOD are brands that trod a similar path.

 

I'll take you at your word on it, I'm not fussed enough to go digging as given the option I'd pick the FET input op amp for any high impedance jobs if I wanted low noise. But even if it's not the input impedance, I distinctly remember under certain conditions an NE5532 isn't suitable... high bias current?

It's an extremely specific parameter, not a real world one, hence, test condition. A handy quick reference, but there's more comprehensive noise specs elsewhere.

Yeah a PT2399 might be the same, but that's an entire digital delay circuit including a dual op amp on a chip, not an audio op amp... If your design used 4 duals you'd be at 60mA, I'd call that high for an guitar pedal audio path... if you had a charge pump in your circuit you could easily run in to issues, in a high current circuit that might push you over the 100mA of a lot of standard 9V taps.

The 5532 has about 2-300k impedance at its non-inverting pin IIRC, read the datasheet.

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.

I refer to the 1Hz bandwidth at 1kHz that rating is taken at which isn't very realistic in practice.

The NE5532 has its own quirks, very low input impedance and not to mention massive current draw. 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. But rule of thumb, TL072 quiet, 4558 less so but usually fine, NE5532 very quiet but not suitable for all applications.

Voltages at the pins should be the same and they're pin-compatible as Willybomb mentioned.  The TL072 might be a touch noisier, but is better at driving capacitive loads than the 4558 and has a higher input impedance, so a substitution should be fine.

TL072 noisier than a 4558? 

For voltage noise, yep, according to the TI datasheets for both, typical voltage noise @ 1 kHz for a TL072 is 18 nV/square root Hz, while RC4558 is about half of that at 8 nV/square root Hz.

Ah, for that one spec under test conditions perhaps, but its input current noise is much smaller and in practice, I think most would agree the TL072 is the quieter chip for pedal use.

Your Vgg voltage is way off. It should read under 1v yet yours is 8v.

Almost as if someone had relabelled a MN3102...

You can test that by checking the resistance between Vgg and Power & Ground out of socket. If it be a 3101, the resistance to ground will be smallest, be it a 3102, the other way round.

Can you link to the schematic please.

Voltages at the pins should be the same and they're pin-compatible as Willybomb mentioned.  The TL072 might be a touch noisier, but is better at driving capacitive loads than the 4558 and has a higher input impedance, so a substitution should be fine.

TL072 noisier than a 4558? 

It's your meter, it has an internal resistance of 1M, hence the exactly halve voltage.

Your voltages look reasonable but getting reputable supplier chips is the only way to be certain.

Just because some people had luck with a specific bias voltage, doesn't mean that will always work out to be the case, why not try audio probing the BBD output pins and adjusting it?

Ohhh, I was looking at the wrong one... So it does have a series protection diode.

Well, my advice either way is the same, try replacing the regulator.

Okay... the schematic I'm looking at only goes up to C32, you're going to have to link to what version you're using.

Are you using a regulator in it?

The Total Recall supply isn't AC, don't worry.

You'd know if it was AC, it tends to make things... crispy.

It's very likely just one of the electro's in the power section, the parallel protection diodes aren't as fool proof as series. You nuked it with DC (if it was AC, I'd tell you to bin it and start over) but of the wrong polarity (also those supplies are unloaded so can be higher voltage than stated) so whatever the electro next in line to the protection diode, replace it and then the next etc.