BL3208 and reverse voltage

[Dimitree]

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

[madbean]

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.

Sonically, I much prefer the BL3208 to the v3205 and you will get closer to an MN3005 with them IMO. They do have better headroom and also the decay sounds better to me. However, the max voltage you can use is 10v on the BL3208. So, you might consider using a charge pump on a 9v supply then regulating it down with a 10v regulator (yes they do exist). Also, you will need to adjust the two resistor values on the compander so that the output voltage on pin 7 of your NE571 is about 5v.

A side note: you know that hugely expensive Toneczar delay? It's 8xBL3208 running on 10v (the rest of the audio path is 15v). FYI.

[muddyfox]

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

sent from my mobile device

[Dimitree]

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

[jighead81]

I'd like a couple too if they come up for sale. I'd like to mess around with these cheaper alternatives

[madbean]

Ahh my bad, somehow I read you were using a Dirtbag in there. Sorry I did not read more carefully.

The answer is I don't know, then. In principle, I think it would. However, one question I would consider is whether or not pin7 will still put out the correct Vgg voltage. I haven't looked at the datasheet in a while but if it just uses a pair of resistors then it should. If not, you may have to use a set of resistors or a trimpot off the supply to achieve the 14/15 supply. I really don't know.

Worst case scenario is set up a test condition and check out what happens when you flip the polarity on the chip. That way you only risk burning up one.

[Dimitree]

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)

[muddyfox]

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

Thanks much!
I sense a groupbuy here... 

[Dimitree]

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)?