BBDs biasing doubts

[Fender3D]

why R25 is inside the opamp loop and not before R39?

because L. Dang made a mistake... 

[Dimitree]

really? so I should put it outside the loop, like any standard opamp configuration..

I am reversing the polarity in the whole circuit, from -15V to +15V.
I have a doubt about R15, a resistor that is tied to ground on the original schematic (on the filter after the compressor).
Should I leave it to ground or should I tie it to +15V? (I've seen it tied to +15V in other "reversed" memory man schematics). What's the difference?

[Fender3D]

GND in the above schematic will be +V if you reverse polarity...
You can (and should) leave the jacks section as it is (with GND to... Ground)

But, really, I don't understand why bothering reversing electros and swapping a regulator for the same result...


What's the difference?

[Dimitree]

I'm reversing the polarity for two reasons:
1) I'm not sure that I can use BL3208 with 0V on V+ and -9V on V- (and I don't want to ruin some of my chips just to try=
2) +15V would be easier (less parts) to get starting from the standard +9V that I use on other pedals

it is really not a problem for me to reverse the polarity on the schematics..
my only doubts are:
1) R15, I can't understand the purpose of this part since I can't see it in any filter topology that I've seen (of course I may be wrong), so I don't know if this should be reversed too (putting it to +V) or it should remain to ground.
2) as we have seen previously, that 100K trimmer on every BBDs, togheter with a 6.8K resistor, should give the correct 14/15 of voltage needed for VGG. But this is only true when using a negative voltage.
When using a positive voltage on the trimmer, VGG become more or less 900mV. Can I simply use a 10K trimmer instead of 100K trimmer and 140K resistor instead of 6.8K? that would give me 8.4V
would it make the biasing harder/impossible?

[armdnrdy]

I'm reversing the polarity for two reasons:
1) I'm not sure that I can use BL3208 with 0V on V+ and -9V on V- (and I don't want to ruin some of my chips just to try=

Dimitree....

You can reverse the polarity on most ICs. They just want the GND or -V pin to be more negative than the VCC or +V pin.

Read the first part of this thread...you'll see a MN32XX series BBD fed with negative voltage on the ground pin:

http://www.diystompboxes.com/smfforum/index.php?topic=105116.0

[Dimitree]

thanks Larry, yep that was my intention initially, but then someone told me not to do because I couldn't be sure that BL3208 could like that.. so I reversed everything.
the work is mostly done by now, I don't want to reverse it again, so I just need to make clear the two points I marked in the previous post to finish it and stop thinking about it.

[armdnrdy]

Let's address the VGG voltage...

The factory configuration powered by -15 volts.
The MN30XX series requires VDD +1 for VGG.
VDD is -15 volts. +1 of -15 volts is -14 volts. The Memory Man voltage divider design gives you -14 volts.

You want to power the circuit with 9 volts.
The MN32XX series requires 14/15 VDD for VGG.
The stock Memory Man Divider of 6.8K on the top, and 100K (Bias Adj trimmer) to ground gives you 8.42 volts (14/15 VDD)

You don't have to change a thing! If the original circuit's BBD were the MN30XX series fed with positive voltage...then you would have had to switch the VGG resistors.

R15 is providing bias to U2A so...I would imagine that it should go to +9 volts.

If you are planning to include the "overload indicator"....you will need to take a look at that circuit and make changes as well.

[Dimitree]

perfect!
now my really last question about it (I hope..)
since I need not to overload the BL3208 with clock signals >9V, can I simply reduce the 2 clock output of 4047 IC by using two resistors on each output as a voltage divider?

[armdnrdy]

perfect!
now my really last question about it (I hope..)
since I need not to overload the BL3208 with clock signals >9V, can I simply reduce the 2 clock output of 4047 IC by using two resistors on each output as a voltage divider?

Re-read Page 1 of the thread for info and suggestions on the clock.

[Dimitree]

those days I tried to simulate the modulation circuit (LFO + clock) using LTspice and also using other sim tools, but with no luck (can't get the 4047 to work in simulations). My aim was trying to understand if LFO output frequency/voltage was changing when I change the power voltage. I know that they change in the LFO, but I don't know how the 4047 would react. Unfortunately I don't have a real life oscilloscope so I can't just breadboard and test it.
So I guess I will try to use a voltage divider on the 4047 output to lower its output voltage to less than 9V, and keep powering the modulation circuit using 15V.

[armdnrdy]

You can breadboard the 4047 VCO circuit and check the voltage with your meter. Does you meter have frequency function?
If so, you can take the frequency reading.

If it doesn't....you may want to purchase a meter that does if you are working on circuits such as this.
Frequency measurements are a must to properly calibrate many flanger and delay circuits.

[Dimitree]

I don't have such meter but yes, I will do my best to get one soon.
one thing I didn't understand on the simulation is the role of the 1N4001 diode near the 4047 inputs. what's there for?

[Dimitree]

also, do I want to check the frequency differences (between 9V and 15V supplies) when the LFO depth is 0%?
if > than 0%, the triangle LFO would change the clock continuously, making it impossible to understand if there are differences, unless the meter can tell you min and max frequencies measured. Am I wrong?

[armdnrdy]

The LFO depth you can check with a meter. Depth = amplitude = voltage.

It's not only the depth that you need to be concerned with. The rate will change with a lower voltage as well.

I'm a little lost...without reading through this whole thread...I didn't think that you were converting the whole circuit over to 9 volts.

I don't think that you have to lower the LFO voltage.

You need to breadboard the clock circuit to check the output voltage of the clock lines...that way you will be able to tell if the clock voltage will work with the MN32XX series.

Armed with that information...you will have a better handle on what needs to be changed.