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thank you, everything is clear! 

I also spotted another pair of differences, on the Expander section, what is the advantage in using C17 and C18, instead of a single cap (the original uses a single 4.7uF cap)? Same for the Compressor section (added C8, 2.2uF).

just upping this post, in case you forgot :-)

thank you really much, that would be awesome and really interesting!

hi everyone,
for fun and as a learning tool, I was comparing the schematic of the Skoolie with the Total Recall / Tourbus, as I find interesting to learn how to convert a design from positive ground to negative ground.
I noticed some differences and I'd like to know why these were needed (if they were needed for the positive to negative conversion of just to improve the design)

1) there is a missing resistor (68K) between pin 5 and 6 of the NE570, and the other two resistors (R9/R10) have a lower value (47K instead of 68K). Also, on the second half of the NE570, the two resistors R17/R18 have higher value compared to the others schematic.



2) those two capacitors were added on the circuit before the BBDs



3) for the second BBD, the pin 8 is tied to the VG point of the first BBD (and so, dependant on the BIAS1 trimpot). On the other schematics, the pin 8 is tied to the voltage set by the BIAS2 trimpot (pin 5 of IC10).



4) on the Skoolie the voltage feeding the opamps is the VC point right after the 7815 regulator, and the voltage for the LFO/BBD is taken after a 22R resistor. On the other schematic, it is the opposite, the LFO/BBD is taken right after the regulator, and the audio path is supplied by the "isolated" voltage.



many thanks and sorry for the dumb question! :-)

up please

could you post a link to the schematic? I couldn't find it in the archives...
anyhow, just from the top of my head I think to remember that the v3205 are run on lower voltages than the MN3005. that could be the reason for the different R11/12 values, but I'm basically just guessing.

of course, here it is:
http://www.madbeanpedals.com/projects/Dirtbag/DirtBagDeluxe.pdf

1) Converted from -15V to +15V

that was my guess, but I can't explain why..I mean, out of curiosity, why many other parts in the circuit are tied to ground just like on the original DMM(-15V), while ONLY this part is "inverted" (without considering opamp supply pins and cap polarity, of course)?
for example, the close parts C11 and R14, and many other, they just are tied to ground like on the original..
Why R17 need to be to V+?
if you tied it to ground, what's the difference?

2) The Compander needs biasing to half supply at its output, this changes with supply, those resistors set the bias.

ok so if I understand correctly it is not because of the BBDs used after the compader..
I need to check carefully the datasheet to understand how to calculate those resistors in different situations..

hi everyone, 

I have some question regarding two parts in the DirtBag delay:
1) why R17 is not tied to ground like on the deluxe memory man? what's the difference?
2) R11/R12 should be lowered from 68K to 47K when using V3205. Is this needed because the circuit is powered with 9V instead of 15V (and so inherent to the compander supply), or only for the headroom of V3205? more specifically, when using another BBD (not V3205) but still using 9V supply, should that resistors be lowered too?

thank you!!

Hello
so I decided to slightly redesign my 2 layers PCB to accept 3208 BBDs. So I reversed the voltages on the power pins of BBDs, opamps, clock and compander.
But now I have some doubts:
1) where should I connect the 100K resistor (Clock cancellation if I'm not wrong) on every BBD output? to ground or to +V?
2) can I power the whole circuit with +15V and supply +9V only to BBDs?
3) if yes, is ok to power with +15V the clock/modulation circuit AND the opamp between the 2 BBDs (the one that restore gain between stages)?

ok so I will get one and I will try with reverse voltage

in the meanwhile I will re-design another pcb to accept a positive voltage, so, like on the dirtybag, I can be sure that I can put there 3205-3208 series BBD.
I guess since dirtybag delay uses positive voltage for MN3005, there would be no differences in comparison with -15V.
Why do you think Electro Harmonix used -15V and not 15V?

also, I noticed two things, on the dirtybag, that I don't understand:
- why R17 goes to VB (while on the original DMM it goes to ground)
- why C10 goes to ground (in the original it goes to -15V)
Of course the polarity for the opamps and BBDs is reversed, but why also the polarity of those 2 parts (and not for C28 for example, that should be the counterpart of C10 if I'm not wrong)

You can use BL3208 in place of MN3005 (if you use 2x for every one MN3005). You do not need to use reverse polarity to power it, but you need to set the BBD jumpers on the board to match the v3205 instead of the MN3005. This flips the power and ground between pins 1 and 5. The Dirtbag runs on negative ground no matter what BBD you are using...the needed change is in the jumpers.

thank you for the support!
but actually I designed a SMD version of the DMM, that only uses -15V, so I'm not working on the Dirtbag pcb
That's why I asked if I could power BL3208 in reverse, since the voltages in my pcb are -15V.
Do you think that if I put -9V to the GND pin of the BBD and 0V to the +V pin it would work?
If not, I think I should stay with 4xMN3008 instead of 4xBL3208 (or redesign the pcb to work with +15V)

Needless to say, I will be needing one of those smd boards should you offer them for sale. :-)

I won't offer them for sale, but I will happily share the design files (that you can use to manufacture the board) here if they work as intended

Hi everyone, my name is Dimitri
I've seen that many people here build a deluxe memory man clone using either MN3005 or more common BBDs.
To do some practice, I designed a SMD pcb for a deluxe memory man, using the original schematic (the one with 4x MN3008). Now I'd like to know if I can use it using BL3208 so I have some questions:

- how does the BL3208 compares to MN3008 in terms of sound? I know the headroom differences..but I've read bad things about the V3205 so I'd like to know if with BL3208 is the same story.
- the dirtybag delay uses MN3005 with positive voltage instead of negative. Can I do the opposite with BL3208? I mean, can I power it using -9V and reversing the power pins?
- if I can't power BL3208 with -9V, can I power the rest of the circuit with -15V (like the original DMM) but the BBDs with +9V? would that create problems?

thank you everyone
Dimitri