49er debug, pls help

[awitee]

high i built the 49er pedal using this http://gaussmarkov.net/wordpress/circuits/forty-niner/
the pedal is working fine with the boost disengage, but whenever i engage it, there seems to be a fast rate of tremolo type effect
i can still hear the sound for a split second, and on that split second i can hear the boost pot and the freq switch working, because there's a change when i adjust it
i measure the voltages and the Vb that goes to pin 6 of the 8 pin ic (1458) seems to go from 2v to 6v then 2v and so on
it measure 7v on the right leg of r14 and then becomes the fluctuating voltage on the left leg
before engaging boost, all the pins of the ic measures 3.9v except pin 8 and 4
im assuming that the problem is on the fluctuating voltage on pin 6 of the ic because based on the schematic, that is what the switch is connecting to the Vb
any ideas or suggestions will be very much appreciated, thank you
based on the layout i put a jumper from R2 to the hole with the number 2 on it that i connected to the middle lug on a on none on toggle switch, the right most lug of the switch i connected to the hole with the 1 that connects to r7

[awitee]

anyone?

[Mark Hammer]

As based on the original Anderton Tube Sound Fuzz, the 49-er (not affiliated with the football team! ) decouples the power supplied to the op-amp and invertor chip.  I just noticed that gaussmarkov has them ganged.  That is, the power from the battery should go directly to the op-amp V+ pin, with a separate path from the battery to the 4049 chip, via a 100R resistor with its own decoupling cap (47uf-100uf).  I don't know if this is the source of your difficulty, but it is something you should probably correct; i.e., the current limiting is for the invertor chip, NOT for the op-amp too.  Perhaps it has something to do with the fluctuating bias voltage at Vb.

Fix that first, and let's see what happens.

[awitee]

hmmm so i need to supply a full 9v to the +v pin of the opamp instead of the one after the 100ohm resistor?
do i just use a wire and directly connect it to the 9v?

[Mark Hammer]

Note that while the op-amp needs and makes use of a +4.5v Vref, the 4049 chip does not.  So, what you should do is:
a) insert a wire link instead of the 100R resistor in the existing PCB layout
b) cut the existing trace between the +9V source and the 4049
c) run a 100R resistor from the +9v source to the 4049 power pin
d) run a 47uf-100uf cap from the power pin on the 4049 to ground

This will provide separate - or at least minimally interacting - power lines to the op-amp and 4049 chip.

[awitee]

hmm ok ill try dat later
what i did for now is i just lifted the v+ pin of the 1458 from the socket then attached a wire to it from the 9v
it still does the tremolo effect hehe

[Mark Hammer]

Okay,think I found it.  The SPST bypass toggle for the booster is supposed to tie to ground, not Vref, as you can see here: http://www.muzique.com/schem/ca-eq.gif

Hope that fixes it.  I like the sound of it on its own, but the extra nudge at certain resonant frequencies gives it a nice twist.

[awitee]

whoa, im gonna try it ryt now!

[awitee]

okay so what i did was directly connect the v+ pin of the ic to 9v and also connect the switch to ground instead of vref
the tremolo has stopped, i think the boost is functioning well, ive only tried it on the podxt and speakers, havent tried it on a real amp
the boost function boosts certain frequencies depending on the dpdt ryt? whenever i engage the boost, it sorta sounds more fuzzier
the boost is sorta subtle, boost knob does not really have a wide range
but im glad it works! thx a lot for the help! if you guys have any mods that would make this circuit better pls post here
overall satisfied, i just have to test it on a bigger amp

[gaussmarkov]

Okay,think I found it.  The SPST bypass toggle for the booster is supposed to tie to ground, not Vref, as you can see here: http://www.muzique.com/schem/ca-eq.gif

Hope that fixes it.  I like the sound of it on its own, but the extra nudge at certain resonant frequencies gives it a nice twist.

hmm.  i wonder if Vref isn't correct?  there's a note on Jack's schem mentioning that his version is for a dual power supply.  the forty-niner has an artificial ground at Vref=4.5V.

thanks for pointing out this thread, Mark.  i have revised the power supply for the gaussmarkov forty-niner project.  i made this change also.  but now i am thinking we should go back to your original connection to Vref.

cheers, paul

[Mark Hammer]

Aw crap.  You're right.  I forgot that Jack's re-drawing was for a bi-polar supply.  My own drawing here - http://hammer.ampage.org/files/FortyNiner-1.zip - has the switch going to Vref, and I'll bet when I check my scan of the Anderton article athome tonight it will also show Vref as the connection.

So, as far as the low-frequency motorboating taking place, I am now officially stumped.

[gaussmarkov]

i see a problem with gaussmarkov layout as it currently sits on the site:  the negative lead of c16 is not grounded.  in fact, what seems to have happened is some ground fill that also grounds R1, C3, R15 and C16 is missing.  so all of those need a connection to ground.

this is a user error, but easy to do with eagle.  i'll download the files here at work and make a correction for the current files.

apologies, paul

[gaussmarkov]

ok.  the images on gaussmarkov.net are corrected.  here's the new layout image:



what was missing, IIRC, was part of the ground trace along the bottom between C3 to C15.  the part the connected C3 ground and R15 ground was there.  but not the part from R15 ground onto C16 ground and the part from C16 ground to C15 ground.

this is still for the old power supply arrangement.  i have a reworked eagle file at home that will have to wait until tomorrow.

awitee, pls let us know if those ground connections are missing in your build.

cheers, gm

[awitee]

the ground trace is present in the transfer file of the layout
hmm so i should change the switch back to vref? darn i thought it was working already hahaha, once i change it back, the tremolo type returns

[gigimarga]

I've built a Forty-Niner tonight (thx Mark Hammer - it sounds very well!) and i had the same problem: a strong ticking.
After modding it as Mark wrote above, the ticking stopped, but when i engage Anderton's booster the sound becomes farty and decays very fast, with scratches...

[awitee]

yup, never resolved that, thats why i just built a hot tubes with an lpb2 in front so i can use the box and ics from the 49er hehe

[gigimarga]

i've built an ehx hot tubes too, but it has too much hiss for my taste

[awitee]

yeh, at stock it sorta hates the neck pickup and its noisy, but after about 20 mods (well actually only around 8 full of trial and error cap values) i finally got a sound that suited me

[gigimarga]

glad to hear that...you're a lucky man

[deafbutpicky]

Hi there,

I know this thread is somewhat dead, but after my 49er bugged me two whole afternoons
I found a way to make the booster work, enough reason to zombify...

I put a 100n cap between the 10k on pin6  and the switch and connected the switch to ground.

The cap was totally guess work but hey, it's running.
Thanks Mark for this really cool pedal.

edit:
I changed the cap to 320n, now the corner frequency is around 49 Hz