I have build one of these and i have problem with some distortion in reverb sound. I think this is a problem with eletrolitc capacitors, because the age of this pedal (maybe 20 years old). The ICs of this box are 2 MN3011 and some other that i cant identify yet. If someone can help me... How i can test eletrolitc capacitor? i don´t have a capacimeter (i don´t know if this word exists in english, i´m brazilian, but is about a cap meter) Thanks

if there arent a lot of them it would probably be better and easier just to go ahead and swap them out with new ones, if you have some.

Twenty year-old caps should not be failing because of age at this point.  Many pedals that are 40 years old continue to work perfectly with caps that are twice as old.  After 20 years of being on the floor and getting kicked, there is a bigger probability that the bias voltage (set by a trimpot on the board) is incorrect.  Like any BBD chip, the MN3011 needs to have the audio signal sitting on top of a DC voltage.  If the DC bias violtage is incorrect, the  BBD will produce distorted sound.  If the bias is VERY incorrect, the BBD will produce no sound.

You can adjust this voltage by ear without needing an oscilloscope.  It is best to do this with a very clean signal and listening through a very clean amplifier/speaker with good frequency response.  You can use your guitar but it would be best to have a steady signal, like a sustaining chord from a keyboard.  Moving the trimpot around until you find the perfect setting will not damage the chip or the effect.

Two MN3011 chips on the same pedal?  I think I am going to keep my eyes open for these pedals!

Quote from: Mark Hammer on April 11, 2006, 09:16:05 AM
Twenty year-old caps should not be failing because of age at this point.  Many pedals that are 40 years old continue to work perfectly with caps that are twice as old.  After 20 years of being on the floor and getting kicked, there is a bigger probability that the bias voltage (set by a trimpot on the board) is incorrect.  Like any BBD chip, the MN3011 needs to have the audio signal sitting on top of a DC voltage.  If the DC bias violtage is incorrect, the  BBD will produce distorted sound.  If the bias is VERY incorrect, the BBD will produce no sound.

You can adjust this voltage by ear without needing an oscilloscope.  It is best to do this with a very clean signal and listening through a very clean amplifier/speaker with good frequency response.  You can use your guitar but it would be best to have a steady signal, like a sustaining chord from a keyboard.  Moving the trimpot around until you find the perfect setting will not damage the chip or the effect.

Two MN3011 chips on the same pedal?  I think I am going to keep my eyes open for these pedals!

Very thanks. I will take pictures to put here. I think this is a very rare pedal. Is normal the bias voltage changed? I buy this pedal this week. maybe in the future i try to make the schematic. Someone writed that its sound is like a short delay. There are 3 controls "room size" "reverb time" and "reverb level" i think.

Quote from: danielm on April 11, 2006, 09:36:26 AMVery thanks. I will take pictures to put here. I think this is a very rare pedal. Is normal the bias voltage changed? I buy this pedal this week. maybe in the future i try to make the schematic. Someone writed that its sound is like a short delay. There are 3 controls "room size" "reverb time" and "reverb level" i think.

You are very welcome.
The MN3011 was developed to try and simulate reverberation.  It has 6 "taps" or outputs so that 6 different delays are produced at once.  It tries to sound like reverberation, but you are right.  It is more like 6 different echoes.

It is not "normal" for the bias voltage to change, but this is something that happens often enough.  Like I said, if something is on the floor and being kicked around, then sometimes fine ajustments can be moved.  The good thing is that you do not have to take anything out of the board and risk damage.  All you need is a small screwdriver and your ears.  If this is NOT the problem with your pedal, then we can try something else, but at least you will not damage it.

Be sure to mark off where the trimpot was set before you start turning it!

Could someone please provide me the DOD FX45 circuit diagram/schematic
I have two MN3011(BBD) and MN3101 (clock driver) and want to make the pedal for my own.

Your suuggestion will highly be appreciated.

Thanks in advance.

Cheers,
Anshuman

Unless you really like the sound of 3011s, I recommend you either sell them (they can probably fetch at least $25-30 each) or find something different to build.  The 3011 was a temporary measure in the historic search to find something that sounded acceptable and wasn't as big or heavy as a spring reverb pan.  Once digital reverb chips became available, production of MN3011s pretty much disappeared because they did not live up to the state of digital reverb technology even as early as the mid-1980s.  You can easily score yourself one of the assorted Alesis or older Lexicon units with vastly superior reverb for little.  I bought a Lexicon MPX-100 and a Behringer Virtualizer Pro 1000 for $50 each and they can do a great many reverb tricks without any of the headaches that a DIY FX45 would entail.

Now, if you were interested in making a chorus using an MN3011, I think that would merit your persistence.  Chorus effects with multiple staggered delays are difficult to produce in analog form without risk of heterodyning, and the taps of the 3011 get you past that successfully.  For instance, consider making a Hollis Zombie Chorus, with stereo outputs and alternate taps mixed together at each output.

Thanks Mark for your suggestion. Could you advise any specific chorus unit using MN3011, actually I managed to get two 3011 s in very inexpensive rate $3 each  and I checked  those are good. I already designed the PCB (only some confusions) after getting some good reviews for DOD FX45, though I know that it can not replace the spring reverb with maximum delay time and real effects.
If you could advise me making chorus units with these 3011 that would be really helpful for me or you have the schematic of DOD FX45.
Next i have a plan to make the digital one for my electric guitar.

Thanks once again for your reply.

Best Regards,
Anshuman

If these are the MN3011 I am thinking of, that is an excellent price.  You're a very lucky man!

This device is likely way too complicated for a full DIY build, but it gives an idea of what is possible:  http://www.adadepot.com/adagear/gearpages/effects/ADA-STD-1.htm

Mark... I think it's about time you got on with your stripped down A/DA! I'm still holding on to mine till a repair comes along but it could be used untill then...

Regards the FX45, why not just do a Mono Version and use one of the chips (i'm assuming it uses each per channel rather than summed and split elsewhere) the MN3011 datasheet has an example circuit and PCB layout if I remember.

Thanks Mark ... I am looking into the ADA schematic.... Its having around 26 chips.

Hi Scruffie,
I had already made the ETI/Digisound reverb using single MN3011 and its it doesn't sound good at all. Its better to make a delay unit using MN3005 (4096 stages BBD) along with a NE571 (compressor/expander) which sounds really impressive.
I would like to utilize 3011 s 6 taps in stereo/dual mode and if it can be done with NE571 for making better sound effect.

Thanks and Regards,
Anshuman

If I had a MN3005 to make a Delay I would!

I heard most reverbs using this chip don't sound great... I think Mark is right about using it for Chorus rather than Reverb... It could make some kind of decent trailing or stereo delay type thing too maybe.

Quote from: anshuman2512 on September 21, 2010, 05:31:15 PM
Thanks Mark ... I am looking into the ADA schematic.... Its having around 26 chips.

Hi Scruffie,
I had already made the ETI/Digisound reverb using single MN3011 and its it doesn't sound good at all. Its better to make a delay unit using MN3005 (4096 stages BBD) along with a NE571 (compressor/expander) which sounds really impressive.
I would like to utilize 3011 s 6 taps in stereo/dual mode and if it can be done with NE571 for making better sound effect.

Thanks and Regards,
Anshuman

I have a board for that "reverb" circuit etched and partly populated.  Since the intention was to socket the 3011, I thought I'd try it out in that circuit but not "commit" it to that board.  My sense is that the circuit is not well thought out with respect to how the various taps are blended together.
In theory, a circuit like the Hollis "Zombie" chorus could be adapted to a 3011 and built on perf-board.  Using the taps would necessitate several changes/additions to the basic circuit:
- duplicating the op-amp filter stage after the BBD
- preceding each filter stage with an op-amp mixer for combining taps
- feeding the clean signal to two output mixer stages instead of just one

I have just completed etching the board, hopefully can start populating the components from tomorrow. Will update you how it is going on and of course will try to improve the performance.
Regards,
Anshuman

here you'll find the schem of the FX45!

http://www.americaspedal.net/fx45/

Thanks for the link to the schematic, Mr. Crisis.  Much obliged.

Boy, no wonder this thing didn't sell!

You will note that all the taps are mixed in equal proportion, using identical-value mixing resistors, and that all taps pass through the same filtering.  When was the last time that multiple reflection in a reverberant room all had the exact same amplitude and frequency content?

So, a noble gesture on DOD's part, but I think there was insufficient thinking put into the characteristics of actual reverb, and the circuit design reflects that.  The ETI circuit, while not perfect, is a little better in that it mixes the later "reflections" (taps) at a lower level than the early reflections (shorter taps).  Ideally, if one was going to aim for a realistic BBD-based reverb, you'd want to filter each tap, or perhaps groups of 2 to keep it simpler, separately, and then mix them together, with a little more treble taken from the later reflections/taps.  The ETI circuit mixes the taps directly, and then filters them all together.

Thank you very much Gila for providing the link.

Mark, I appreciate your idea, if we can divide 6 taps in 3 groups (2 taps each) separately and then can mix the three outputs after filter that would be much better, BBD delay time decreases when the high frequency(treble) is increased.
The Gallien Krueger reverb circuit looks good with combination of one MN3007.

Actually, after giving it some thought, there is probably a relatively simple way to do what I suggested.  A little bulky, but simple.

The schematic for the FX45 shows that a resistor array in a SIP provides a single 100k mixing resistor for each of the taps on the MN3011.  Lets say that the mixing resistance for the first two taps is left at 100k, but the next two taps use 1 20k mixing resistance, and the next 2 use 150k.  There ARE other resistances, and by no means are these suggested values the ideal ones.  This is just an example using standard resistor values.  Within those limitations, this would provide the suggested amplitude difference between earlier and later reflections.

But what about the differential filtering, you say?  Glad you're paying attention.   Those mixing resistances do not have to be a single resistor.  Each path could be split up into two resistors in series, with a cap to ground from their junction.  The sum of their resistances would provide the different amplitude for each tap, and the combination of the first resistor in each series pair and the cap to ground, would provide ultra-simple single-pole lowpass filtering.  So, the basic existing structure of mix-then-apply-a-single-master-lowpass-filter would remain intact; we'd just be adding a little more filtering and tweaking the mix along the way.

Let's assume that taps 1 and 2 (pins 9 and 8, at 396 and 662 stages) are left as is, with a 100k mixing resistor.  Taps 3 and 4 (pins 7 and 6 at 1194 and 1726 stages) would each run through a 68k then 51k fixed resistor, in that order, with a 1800pf cap to ground from their junction.  That's a 119k resistance in total, with a rolloff starting around 1300hz.  Taps 5 and 6 (pins 5 and 4 at 2790 and 3328 stages) pass through a 68k then 82k fixed resistor, with a 3300pf cap to ground from their junction.  That's 150k series resistance and a rolloff around 700hz.

Again, I'm not professing this would be perfect, but it is a step closer towards the ideal, providing differential mixing and progressively less treble content at longest delay times.  It should prove to be a little more realistic and provide gentler decay when recirculation is used.

Helo, my unit of this pedal are broken, I used some poor power suply and I really apreciate if someone can help me where to start to find what is the problem.
The unit works, but with no effect - the led turn on and off, but with no effect.

Thinks I discovered. After find some cold connections, I followed the signal. There is reverbered signal (its a lot of robotic, but there is), at the input 5 of the U2, but there are no reverb signal at output of this opamp. I think this is because the non reverbered input of the opamp it's very loud, but the reverbered signal is very low. This is correct, or maybe the opamp is the problem. I think the level of the 2 inputs (clean and reverb) must be the same at the opamp input.
The transistor Q1 and Q2 are amplifying the reverb signal, but is very low than the clean signal coming from the U1 opamp.

http://www.americaspedal.net/fx45/fx45schem.jpg