Zombie mod with MN3207 not working

[bioroids]

Hi there, I'm trying to make this thing work. I'm using RG's layout and modified it to accomodate the MN3207 (inverting GND and +9v pins as well as pin 4 to +9v and referencing the output to GND (pins 8 and 7)).

But the sound never gets out the BBD, I audio probed it but i get no output. I have no way to tell if the clocking is working, it should, but how to test for that?

Any help is really welcome, anything.

Regards

Miguel

[Mark Hammer]

My guess is that the bias is inappropriate.  Remember that the bias voltage is something that the audio AC rides on top of, which means it will be closer to supply voltage than ground (the reason why the Zombie uses unequal resistors for deriving the Vref).  If you switch what serves as supply and what serves as ground for the chip, you still need to alter what the bias voltage is, in relation to the supply voltage.

I'm not sure if the correct bias voltage for an MN3207 is simply the mirror image of that for an MN3007, but just for the hell of it, swap R12/R13 to move the bias voltage to the other side of the midpoint, and see if that does the trick.

If it doesn't you may have to consider using a separate trimpot to directly feed a bias voltage to pin 3 in the traditional manner.  Just as well anyways.  That way you can use equal value resistors for R12/R13 and get rid of the ticking in the LFO.

[george]

Hi there, I'm trying to make this thing work. I'm using RG's layout and modified it to accomodate the MN3207 (inverting GND and +9v pins as well as pin 4 to +9v and referencing the output to GND (pins 8 and 7)).

But the sound never gets out the BBD, I audio probed it but i get no output. I have no way to tell if the clocking is working, it should, but how to test for that?

Any help is really welcome, anything.

Regards

Miguel

what sort of opamps are you using? you need something JFET based (TL062 or TL072) (thanks to Mike Irwin for this in a previous post on the old forum)

[bioroids]

Thanks for all your answers.

Yes, I've read that thread and I'm using TL072.

I didnt know the R12 to R13 ratio was important, i just used 2 equal resistors. Im gonna stick to the exact values now, inverted as Mark points.

Tomorrow I'll have news.

Thanks again

Miguel

[puretube]

NOTE:
the solution to even maybe all the "Zombie"-issues
(in this case and in past other ones),
maybe the fact,
that the 3xxx series of BBDs don`t only need a Bias
at their input-pin,
BUT also a dedicated "Vgg", which in the case of the 3007 should be
1V LESS negative at pin 4 than at pin 5 ("Vdd").

Just saw the zombie-schemo, which has these both pins tied together
to ground.

In case of the 3207/8, the "Vgg" ought to be 14/15th of "Vdd".

Not obeying this data-sheet-fact, can of course flip the "usually working"
bias-situation. and unbalance the whole brigade...




//www.puretube.com

[puretube]

...the MN3101/2/5 clocking chips provide this "Vgg" by built-in
stabilized voltage-divider directly routing to the appropiate pin
of the 3XXX ...

Thank You, Mark H., for the comprehensive BBD-mania files.....





//www.puretube.com

[bioroids]

Hi everyone.

I'm using now 15k for R12 and 10K for R13 (the inverse of the schematic) but still I get no output at the BBD. The DC at pin 3 and 7/8 of the BBD is 3,80v, wich I believe correct because the power supply is a little less of 9v.
Is the IC so picky about the exact bias voltage?

I tested all the connections and seem to be correct, the values are all correct, so I'm kinda at a dead end.

The only thing left would be the Vgg and Vdd thing, as Puretube points. In fact I dont even know what Vgg and Vdd means, I've just heard of Vcc and GND.

So im gonna make a voltage divider to get the 14/15 relationship and feed that to pin 4 instead of conecting it to pin 5 and see what happens.

Thanks a lot everyone for your help

Miguel

[Mark Hammer]

As terrific a design as John Hollis provided, and as magnanamous a gesture as RG Keen provided in contributing and posting a layout, there remain several ongoing problems with the Zombie:

1) The design functions optimally (and sometimes *only*) with one particular dual op-amp, which not everyone has ready access to. Even when they do have access, they don't all know about it or why it is so important. There needs to be more choice of op-amp

2) Part of what compels the use of one specific op-amp chip is tha manner in which the bias voltage is created.  This shortcut not only constrains use of op-amps but also results in an audible ticking which requires tacking on extra components to eliminate.  The current method of BBD bias has got to go

3) Not everyone has access to MN3007's (which are only available as NOS or as overpriced NTE replacements), though Beiling apparently has resurrected the MN3207 and some people have ready access to those.  The board has to be more adaptable to both BBD chips

Although I couldn't do it (and it certainly isn't out of laziness), there needs to be a board redraft with a modded design that provides for:

a) a *true* Vref at mid-voltage (4.5vdc) for op-amp and LFO purposes

b) a means of converting the board for 3207 or 3007 with a few extra pads and jumpers

c) a more conventional trimpot bias adjust that feeds pin 3 of the BBD directly, rather than requiring the op-amp to "play along"

There is a redraft of the board at Munky's site which goes part of the way, but not ALL the way.  Some brave soul has to take it all the way.  Once that's done, it needs to replace the posting at GEOFEX.  Hopefully, that will mean that fewer people will have to ask questions about troubleshooting their Zombie, and more will find a quick, direct route to chorus pleasure.

It's funny how "convenience" sucks you in, isn't it?  Hollis used a Vref other than 4.5v as a "convenience" and RG's layout also provided a "convenience" to people here.  Sometimes "convenient" isn't.

[puretube]

the BBDs consist of a sample- and a hold-FET in series, with a capacitor within (simply stated); this configuration repeated hundreds of times in series;

every second sample-FET "triggers" at even clock-pulses,
every first sample-FET on the uneven pulses,
i.e.: their gates are switched between
Vdd (Vdrain)and ground (Vss or Vsource or Vsubstrate).

All of the hold-FET`s gates are connected together at the Vgg-pin, which,
according to data-sheet should be the ominous 14/15th of Vdd (battery-voltage or B+ supply).

In case of 9V, you`re lucky: Vgg is about a diode-drop (roughly 0.6V) down from Vdd.

When these conditions are met, I don`t find the MN3207 overly
picky concerning the INPUT-BIAS.
(it`ll just affect the headroom and/or distortion).

It seems to me that s.o. has started to tie Vgg to Vdd in "his" circuit,
which happened to be balanced out in some strange kind of way by
the input-bias circuit such, that it worked, in this special case.
But as soon as a little s.th. in this input-circuit is altered, strange
things start to happen.

When I keep the data-sheet standards, and un-couple the BBD`s
input circuit capacitively from the preceding stage,
supplying the input-bias the "traditional way" like s.o. stated
(M. Hammer?),
the delay doesn`t care, if it`s driven by a TL064, 74/84, an
LM324 or a 12AX7 (yes, the tube...).

The Zombie`s achievement is simplicity - no doubt -
"as is", using exactly the original parts/circuit,
but it could be
"improved" by just a small amount of extra parts,
making it more universal ("foolproof" for "cloners"),
which would just be half a dollar more at most
(and a little bit more PCB real estate, ok...)




//www.puretube.com

[puretube]

Good Morning Mark, from Germany to Canada....

[bioroids]

Wow, thats very informative really.

Now I'm going to make this work, hopefully, with all your help.

When finished, I might be able to provide a schematic and pcb layout adapting this to the MN3207. I dont have any problems sharing it with anyone wich may be interested, as long as the author of the original circuit (Hollis) and PCB (RG) dont mind.

Good luck everyone

Miguel

[puretube]

here`s wishing you the most of success!

(I wonder if it will start a new thread of "whose circuit" or "whose PCB"
is it.... or:  "is it OK to call it Zombie any longer?" ).....

[Mark Hammer]

Well, Zombie's ARE the "undead" aren't they?  :wink:

Good morning from Canada, where the weather cannot make up its mind if it wishes to rain or snow.

[bioroids]

Well, this is getting too abstract  

Well, I'm running it now with a separate vref for the 14/15 and still not working.

Is there a way to test for the clock frequency? it should be around 20Khz right?

Brain damaged good bye!

Thanks a lot

Miguel

[puretube]

sorry that it hasn`t worked out yet - do you have a scope?

[bioroids]

I wish I had a scope, I have to depend on my computer simulated analizer, but I'm restringed to audio frequency signals

Anyway, I finally got it WORKING! yes

I had to do the right thing, capacitor isolate BBD input and feed a separate bias via a trimpot. Also the same for the Vdd (or was it Vgg) to get the 14/15 voltage.

Now i got chorus, sounds pretty nice. With 8.94 volts at the battery, the signal needs like 4,35v bias, pretty close to half the supply. Once I got it I tried conecting pin 4 to pin 5 and still works, thought it seems a less pronounced effect? I'll have to check this out again.

I want to thank everyone here, in special Mark and Puretube, this forum is really a great place.

Now I think i got something wrong on the LFO, as it delivers like a 9 hz modulation, too quick for a chorus? Or that is how its supposed to be?

Also I got to tame the bias a little better as with too hot signals it makes some amount of pretty bad distortion. It seems the headroom is not high enough.

Thanks again everyone.

Miguel

[puretube]

congrats!
(I`m glad you succeeded to get s.th. heard, otherwise I`d breadboarded
the Zombie over the weekend and started scoping............)

the max input signal voltage is said to be 0.35V (rms) for 2.5% distortion.

with an input-bias trimpot, you can find the "sweet spot", where the (hot) signal distorts the least. You can do this by ear; it`d be nice if you had a signal generator or other source of sinewave for constant variable level (start with 100mV), so you`d hear by turning the pot, that the signal clips on the upper signal half in one direction of the trimpot, and clipping on the lower half at a certain point in the other direction of the pot.
Both clippings sound the same, but you`ll find out that the middle between the 2 clipping-settings is your sweet spot.
Now turn up the input volume (say 250mV) till clipping starts again, and redo the procedure. And one more time with 500mV.
Probably you`ll find out, that the higher possible distortion-free level will be obtainable with pin 4/5 not connected together.

[puretube]

concerning the 9Hz: are you sure the res. (R17) at the wiper of the speed-pot is 4.7MOhm (4700kOhm) ?

[puretube]

there may be another source of distortion:

is the BBD output (pins 7/8) still at 1/2 Ub ?
Hence the input-bias of the output-opamp?

if not, this output filter opamp might assymetrically clip the signal;

which would ask for again capacitively discouple it from the BBD,
and give it a Ub/2 bias for itself. (yes, a scope would be great, again).

BTW: the MN3207 doesn`t seem to care, if the output-working-resistor (R6) is tied to Ub or ground (acc. to data-sheets).

[bioroids]

Hi!

Im gonna go thru this procedure to find the "sweet spot". I also believe he headroom will be bigger with pin 4 and 5 each to their respective voltage.

I'm still counting with the computer as signal generator, i'll just have to check that the signal voltages are accurate, but I need a fresh battery for my multimeter for that!

I imagine there is a chance that the output opamp may be responsible for some clipping. I'll check that out too.

Thanks for all your help, I wish I could help other people like you help me
( my english is a little limited, any synonyms for the word "help"?)

Hopefully I'll post a few sound samples when finished.

Thanks

Miguel

PS: yes, i'm using a 4M7 resistor, but I'll double check that