DIY bassballs debug help: rectifier section

[mrslunk]

So i built a DIY bassballs from the schematic below, omitting the fuzz section (eventually i'll modifiy it to have a sidechain in too)
but the filters aren't moving..

I've triple-checked my wiring and traced the signal with multimeter and scope;
i've got clean signal right up until the rectifier opamp stage
Voltages at that opamp (IC1b on schematic)
V+(pin 5) = GND
V-(pin 6) = sig + 7VDC
Vout(pin 7) = ~8V and no AC component at all

I was using a TL072 initially, till i had a good look at the circuit and realised the opamp would be going below the -ve rail
I replaced it with a RC4558, which is not supposed to latchup, however it's still not working
Running some simulations, the circuit should theoretically work..
The original circuit used a LM1458, however i don't have any on hand right now...

Can anyone give me a pointer at where to start looking?
Am i barking up the wrong tree by ordering a LM1458 for this? If not, why should a LM1458 work and not a RC4558?

Thanks for your help.



edit: fixed image

[jonfoote]

the choice of IC's in the bassballs are important, lots of lovely info here...

http://topopiccione.atspace.com/PJ08EHBassBalls.html

also somewhere on this site someone has posted voltages for the IC's, have a search

[oldrocker]

I just went through this when I recently built mine.  Yes you need a 1458 to get the filters to sweep.  I was able to get a 358 to work too but it acts a little different but it works.  No a 4558 will not work.  A great pedal.

[PRR]

Try this boost-recty stage, no special parts:

Changes marked in purple.

[mrslunk]

thanks all, i will order some 1458's and 358's and toss them in.
so why does the 1458 work and not and TL072 or 4558?

PPR: thanks, i may try that in the future, but at the moment, the circuit is all perfed up, and i don't have the room in my layout to stick and ic and 2 more trannys in

thanks again all

[PRR]

> why does the 1458 work and not and TL072 or 4558?

You gave the clue:

> the opamp {input} would be going below the -ve rail

That's "not legal".

What happens? We do not know.

In most op-amps, nothing "bad" happens. (The TL072 does get wacky.)

However this plan -uses- some "good" accident in the "not legal" zone.

And what happens there will be different for every topology.

There's NO way this was designed (or simulated). Someone was messing-around on the breadboad, did something "wrong", and found a useful side-effect. It apparently turns out to depend on THAT chip, and (unlike most op-amp circuits), it matters.

> don't have the room in my layout

Suit yourself. It looks a nice circuit, and it is a shame it depends on an obscure old chip. Maybe others will try this alternate boost/rect idea.

Note that it does not need another IC. And for testing you could just lift one end of C3, R6, and C5, hay-wire two transistors and two resistors in the air, with ground and 9V leads.

[tam]

Maybe others will try this alternate boost/rect idea.

I have just tried it - for fixing an original pedal without the 1458 and it works like a charm

Thanks PRR.

[PRR]

> it works

Thanks for the report.

[Mark Hammer]

I'm impressed with the usefulness of the suggested sub (kudos to PRR).

However, if one is aiming for the stock sound of the Bassballs, the "fuzz" sound of the unit is derived from the way that the 1458 breaks up.  Personally, I'm not that fond of it, but distortion is always a matter of personal taste, so while the fix may yield a decent rectifier, it may or may not yield a distorted tone that is acceptable to all fans of the Bassballs.  There is also the matter of the level of the "fuzz" and clean signals being fed to the filters.  They are not equal.  I don't know how this fix impacts on that.

Just so you know.  The easiest thing is just to be patient, and wait for the 1458 to arrive.