Looking for a simple schematic to use mn3204/mn3102 combo

[Kevin Mitchell]

Sorry for bringing this up again guys. My recent post was about finding a flanger for these chips and I've had good success! But I'm looking around for a simple schematic whether it be a reverb/echo or a chorus I'd like to mess around with some mn3204/mn3102 combos. I'm really just looking for something I can wrap my head around to test out these chips.

I guess the Omnifex Chorus uses these chips but the only schematic available isn't readable and is a bit more than what I'm looking for. There's also a schematic on the datasheet but I find it.... daunting?

If someone could explain a bit about these BBD chips and how one could make a "barebone" circuit for a basic effect to test them I'd really appreciate it.

Here's a couple data sheets;
mn3204
mn3102

[Mark Hammer]

"Simple" is not generally a word one uses with BBD circuits, I'm afraid.

[Kevin Mitchell]

Ehh I was hopping someone around the forum knows of a simple schematic or has an idea of an effect these could be used in and possibly expanded on.

It was a shot in the dark. Most projects that use these chips are too much to wrap my head around to confidently tinker with.

Feelin' a BBD itch here 

[mth5044]

The circuit is right in the datasheet!

[Kevin Mitchell]

The circuit is right in the datasheet!

There's also a schematic on the datasheet but I find it.... daunting?

I guess this is a case where beggars can't be choosers 
I'll figure something out to fill my tinkering/breadboarding needs.

[Fender3D]

"Simple" is not generally a word one uses with BBD circuits, I'm afraid.

Mark is correct...
Any pedal brand willing to sell their stompboxes, will add 1 LPF before BBD and another LPF after the chip.
You may swap the filters' op-amp with a transistor, thus saving 1 pin (and maybe some board space...).

...but if you just wanna test 'em you only need an input buffer, a bias trimmer, and an output buffer.
You may rip the datasheet schematic out at will....

[Scruffie]

I chucked this together for Kevin, little easier to read than the datasheet schematic and using values we all have lying about... don't think i've missed anything.

[Kevin Mitchell]

Thank you very much for the schematic!

Could you or anyone explain a bit about the circuit and how it should behave?

[Scruffie]

It'll give a very lo-fi double track/slap back.

If you wanted you could put an LDR in parallel with R8 and wave your hand over it to get a chorus

You have an input buffer, pre-emphasis (formed by U1A) with some low pass filtering from the large value C3, in to the BBD, a sallen-key low pass filter set at about 1.5kHz in to the mixing opamp (signal mixed via R12 & 13) and de-emphasis.

[Kevin Mitchell]

I got around to bread boarding your schematic last night. Since I haven't been able to test the mn3204 chips this would be my first time using them.

The sound;
Through a solid state amp and a clean signal it sounded like I was playing in an auditorium with my amp on stage and myself all the way back by the front doors. It's almost like reverb but more distant less subtle sounding - "lo-fi slap back" as you've said. Messing with the bias pot dialing it to get the most of the effect also gave it the most noise.

Putting an ldr in place of the 33k resistor was way cool! I was stoked tapping the ldr with my finger lol. Feeding an LED (to LDR) a square wave (should have done sine for sure  ) gave it an oldschool chorus sound but did increase the nose and gave some popping though that shouldn't be too difficult to work out if I were to improve the circuit as well as consider PCB routing techniques (BBDs on bread board are usually noisy as far as I've read).

That schematic is good ground to start tinkering with BBDs. Thank you again!
Now I'd like to play with adjustable timing delay capabilities these chips could have - if any. Idk if 512BBDs could be good for some decent reverb or memory man type delay.

[Scruffie]

Glad it worked out for you and you know your BBDs are good now

You probably got popping just because it was a square wave (high current draw) a triangle would be more appropriate for chorus and less likely to tick.

I'm not surprised it was noisy, I purposely made the delay time long to give the most audible effect, there's not much filtering to compensate for that.

3204s aren't really ideal for a delay pedal as the delay time is too short without severely limited headroom/bandwidth, they're best suited to flangers and chorus pedals. Reverb... you could get a pseudo one going but it'd be more hassle than it's worth to get anything approaching usable reverb, you'd be better off using a Belton Reverb Brick or FV-1 for that.

[Puguglybonehead]

Sorry to be dredging up such an old thread. Scavenging through the search function and this thread was exactly what I was in search of.

Scruffie, the schematic that you posted is no longer showing up in full rez. Do you still have a copy of this around? If so, a re-post would be greatly appreciated. I was looking to start breadboarding some BBD stuff myself. I have some MN3209s, 3102s (untested) and 3207s around and am on the hunt for some 3204s.

[box]

Thank you very much for the schematic!

Could you or anyone explain a bit about the circuit and how it should behave?

Vintage as reference:
https://www.muzines.co.uk/articles/amdek-chorus-kit/4433

[anotherjim]

I think of the BBD, its bias voltages and clock as a self-contained subsystem. The pre and post filters depend on the slowest clock speed unless exclusively for guitar when we know we won't have much going on over 5kHz.
Normally, the pre-filter does provide the DC bias for the input of the BBD, but there's no reason it couldn't be supplied via a resistor after a coupling cap just as we do with a non-inverting opamp +input.

I do think that if you wanted to work with that combo a lot, or at least breadboard a lot, making some daughterboards for the standard bbd/clock pair and multiple-feedback/sallen-key filters might be handy. the filters in particular are a mess on a breadboard with too many places for bad contact & disturbance to mislead and frustrate - if one cap wasn't connecting properly, you may not notice except it's letting more highs through and perhaps making things worse than they should be.

And BBD's are one noisy party. Don't forget as delay time increases the clock is slowing down and Mr Nyquist wants the filter cut-off frequency lower to suit.

[Kevin Mitchell]

Sorry to be dredging up such an old thread. Scavenging through the search function and this thread was exactly what I was in search of.

Scruffie, the schematic that you posted is no longer showing up in full rez. Do you still have a copy of this around? If so, a re-post would be greatly appreciated. I was looking to start breadboarding some BBD stuff myself. I have some MN3209s, 3102s (untested) and 3207s around and am on the hunt for some 3204s.

That schematic is actually at full res. You'll have to make due - the values are still readable.

Here's a more simple schematic but not for audio. It just shows if the BBD has any life in it (able to pass signal). Pin compatible for MN/V3204, MN3206, MN/V3207, BL3208 (8DIP package) & MN3209. The diode at the output is an LED and there's a switch (or just use a jumper) to change the input's state.


PS - don't buy MN3204 bbds online. They'll more than likely be fake and/or relabeled MN3207.

[Mark Hammer]

The Boss HF-2 "Hi-Band" Flanger is essentially a BF-2.  Indeed, comparing schematics, it appears to be absolutely identical to a BF-2, but uses an MN3204 instead of a 3207, for half the number of stages, hence half the delay time (nothing about the clock is different).  I realize the request was for a "simple" schematic, but this circuit is tried and true.  The main thing "wrong" with the BF-2 was that it crapped out around 1msec delay, making it less dramatic-sounding.  Pushing beyond/below 1msec improves it as a flanger.  I would imagine that dropping the value of the C30 clock cap from 47pf to something just a little lower (e.g., 39pf) would make it even more capable of dramatic-sounding sweeps.  Not quite an A/DA flanger, but much better than a BF-2.  Just seems a shame to "waste" an MN3204 on a chorus.

Here's a board layout for a BF-2.  I assume parts layout can be easily found.

[Kevin Mitchell]

The sad truth is that anyone looking to buy MN3204 to repair a BF-2 will more-or-less convert it to a HF-2 without knowing due to the relabeling scam. And most folks wouldn't be able to tell since they'll pass a delayed signal.

I'm hoping cool audio lifts their no sale stance on their V3204 product. More true to the original ADA flangers will flood the market for sure. Certainly not a bad thing!

[Puguglybonehead]

That schematic is actually at full res. You'll have to make due - the values are still readable.

Here's a more simple schematic but not for audio. It just shows if the BBD has any life in it (able to pass signal). Pin compatible for MN/V3204, MN3206, MN/V3207, BL3208 (8DIP package) & MN3209. The diode at the output is an LED and there's a switch (or just use a jumper) to change the input's state.


PS - don't buy MN3204 bbds online. They'll more than likely be fake and/or relabeled MN3207.

I can make out most of it holding a magnifying glass up to the screen. It's more useable than the one that comes with the datasheet. (hard to find op-amps on those)
I've found a couple of component sellers (non-Ebay, not in China) that look promising. If the 3204s turn out to be 3207s they'll still be useful.

[Kevin Mitchell]

Here ya go