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I picked up an MXR Flanger (Vintage model with LED) and just had time to crack it open and look at it. So here is the info...

Schematic: http://www.shredaholic.com/mxrflanger.html

Problem: Pedal passes CLEAN signal when on AND off

Voltages: All of the IC voltages are within a few 10ths of a volt from the readings I posted from my clone build here:
http://www.diystompboxes.com/smfforum/index.php?topic=90539.msg774002#msg774002

EXCEPT for the following:

SAD1024 Pins 5 & 6 are reading 5.1 VDC instead of 9.8 VDC.

I did not check transistor voltages as I am wondering if one side of my SAD chip is KA-PUUT!!!

Just looking for some insight and possible confirmation of my findings. Any other ideas would be great as I really do not want to have to replace the SAD  :'(

Thanks for helping!

Your only hope is a leaking C6...
try and lift it then check pin 5-6 voltage.
you might as well connect C6 lead-to-pins-5-6 at C1-C12 junction just to see if "side B" works...

BTW
clock is present, isn't it?



Otherwise...
My deepest condolences for your SAD  :icon_cry:

Quote from: Fender3D on September 07, 2011, 10:16:30 AM
you might as well connect C6 lead-to-pins-5-6 at C1-C12 junction just to see if "side B" works...

Could you explain this  ??? Maybe a little more exact on your explanation as I don't follow your thinking here...

Quote
BTW
clock is present, isn't it?

I will post that here in a few minutes. Gotta wait till lunch to fiddle with more readings. The voltages look good BUT, I will put an oscope to it  ;)

Quote
Otherwise...
My deepest condolences for your SAD  :icon_cry:

Please don't say that  :'(

Also, I am surprised that I am reading voltage at pins 5 & 6 of the SAD. I would think that if that "side" was bad, then it would be 0  ??? Do you have any ideas on that?

Thanks for the help  ;D

Found out something interesting (Maybe?)

I checked at SAD pins 3, 8, 10, and 14 and I am getting a clock signal at all of them (31KHz)

For troubleshooting, I injected a 440Hz/200mV Sine wave at the Input and probed around with my oscope to try to see what was going on. I found something odd...

When the pedal is unplugged from the wall (power removed) I get the full sine wave all the way up to Pin 5 of U4. This is regardless of the switch position (seems normal to me)

However, as soon as I plug the unit into the wall, I get the sine wave on the Input side of C16 but, it is gone after that  ???  This is also regardless of the stomp switch position.

Shouldn't I get some kind of signal after C16 when power is applied?

You should see the sinewave signal after C16, but with a DC offset of Vb, which should be around 7.5V (15V / 2).

Quote from: Fender56 on September 07, 2011, 12:23:00 PM
You should see the sinewave signal after C16, but with a DC offset of Vb, which should be around 7.5V (15V / 2).

Thanks F56.

After C16, all I see is what apprears to be a semi-noisy DC signal (about 7.5V as you say) however, there is no sign of a sine wave form  ???

I am wondering what the signal "should" look like. Being at work and looking at this on my spare time, I don't have my working clone here to compare with. I can say that before C16, the signal is a clean 440Hz sinewave. After C16 it is a semi-noisy DC flatline at a 7.5V reference level on the oscope.

Best I can describe it.  :-\

Perhaps the sinewave @ 200mV is not visible at the scale in which your scope is setup in order to see the 7.5V DC level. Put your scope in AC mode, it will be easier to validate your audio signal.

Quote from: Fender56 on September 07, 2011, 12:48:29 PM
Perhaps the sinewave @ 200mV is not visible at the scale in which your scope is setup in order to see the 7.5V DC level. Put your scope in AC mode, it will be easier to validate your audio signal.

And again... Thank you F56  ;D

Will reset to AC monitor mode and will repost with findings in a bit.

Quote from: Govmnt_Lacky on September 07, 2011, 10:21:37 AM

Quote from: Fender3D on September 07, 2011, 10:16:30 AM
you might as well connect C6 lead-to-pins-5-6 at C1-C12 junction just to see if "side B" works...

Could you explain this  ??? Maybe a little more exact on your explanation as I don't follow your thinking here...

SAD1024 has 2 512 stages BBDs:
1 on the left "side" of the chip, and the other on the right "side".
left input is pin2 and outs pins 5 and 6.
right input is pin 15 and outs pins 11 and 12.

In MXR flanger stages are connected in series: signal arrives on pin 2 exits from 5-6 , goes into 15 and finally exits at 11-12
To "jump" first stage you should connect C1 (going to pin 2) to pin 15, without any influences from pins 5-6 (lifting C6).

Quote from: Govmnt_Lacky on September 07, 2011, 10:21:37 AM

Quote
BTW
clock is present, isn't it?

I will post that here in a few minutes. Gotta wait till lunch to fiddle with more readings. The voltages look good BUT, I will put an oscope to it  ;)

OK clock is there...

Quote from: Govmnt_Lacky on September 07, 2011, 10:21:37 AM

Quote
Otherwise...
My deepest condolences for your SAD  :icon_cry:

Please don't say that  :'(

Also, I am surprised that I am reading voltage at pins 5 & 6 of the SAD. I would think that if that "side" was bad, then it would be 0  ??? Do you have any ideas on that?

Thanks for the help  ;D

The outputs MOSFETs have their Ds connected to Vdd so you may have a DC voltage...

OK. I changed my monitor to AC on the oscope and things look a lot different.

I get a wobbling semi-square waveform on Pins 5 & 6 of the SAD.

I get a slightly different wobbling waveform on Pins 11 & 12 of the SAD.

Other than the clock squarewave I see on the SAD pins, can anyone tell me exactly what I should see at the following points?

SAD Pins 2, 5/6, 15, 11/12
U1 Pins 2 & 1
Output jack tip

It appears that my LFO is working and that the Width, Manual, and Speed pots are working as they seem to adjust the waveform at different points in the circuit.

I do not however, know where to look to see if the Regen is working or even what to look for.

This is all exploratory to me right now. I have the tools at my disposal but I just need to piece together what I should be seeing from some of the more experienced forumites. I am hoping to do this to help others in the future.

I appreciate any and all help that comes my way.

Hopefully, tomorrow I will be able to A/B this with my working clone but for now, I would just like to educate myself with the help of the forum   :icon_wink:

A bit more possibly useful info on this debug:

All controls set fully CCW
Oscope set for AC monitor
400Hz/200mV signal at input:

SAD Pin 2 = 400Hz/335mV Sinewave

SAD Pins 5 & 6 = 32KHz/1.5Vp-p Soft clipped Squarewave

SAD Pin 15 = 32KHz/1.2Vp-p Soft clipped Squarewave

SAD Pins 11 & 12 = 32-580KHz/540-980mV Sawtooth Waveform

This is what I saw on my Oscope. The terminology may be incorrect for pins 11/12 but that is the best way I could describe it.

I can't check for SAD, but I guess you should have:

pin2 = ~double input signal, BTW check its level not just the waveform (it will depend on freq applied)

pin 5-6 = ~signal at pin2, waveform will be "disturbed" by clock chops (you'll want your scope in sinc with the input, cause it might sinc with BBD's clock). You' re working with a sine wave, any "chop" from BBD will look like a dent on your waveform...

pin15= signal at pins 5-6, waveform as above

pin11-12 = ~signal at pin2, waveform more "distorted" by clock chops and slightly dimmed

U1 pin2&1 = ~double input signal, less signal than A1 pin2 though.

with a single sine wave regen may increase or decrease signal at A1's pin 2 [depends on freq applied and delay time (manual)]

EDIT
I'm definitely too slow on replies... your measurements weren't there while typing...

Quote from: Fender3D on September 07, 2011, 03:14:39 PM
pin 5-6 = ~signal at pin2, waveform will be "disturbed" by clock chops (you'll want your scope in sinc with the input, cause it might sinc with BBD's clock). You' re working with a sine wave, any "chop" from BBD will look like a dent on your waveform...

pin15= signal at pins 5-6, waveform as above

I don't know if I "sync'd with the BBD clock" but the signal at SAD Pins 5, 6, and 15 looked like the clock signal EXCEPT that it had a smaller P-P (1.5V instead of 15V) and the tops of the squarewaves were not flat, they looked clipped a bit.

I think I may just have to wait until I can A/B the measurements with my working clone. That will for sure tell me whether the SAD has crapped out or not.

Fingers crossed!  :icon_eek:

Maybe grasping at straws here but...

Would adjusting R49 (Dist Trim) correct the lower voltage problem I am seeing on Pins 5 & 6 of the SAD?

As stated previously, On my working clone, I get 9.8V on these pins but, on this vintage unit I get 5.1V  ???

It was a bad channel in the SAD chip  :'(

Swapped out with my 1 and only spare and it works like a champ!

I guess I could use this semi-bad chip in a Electric Mistress build possibly. I have heard they work!  ;D

I'm repeating myself, but reading flanger posts here around, it seems everybody's looking for a shorter BBD to achieve  liquid/jet sound...
You have a wonderful chance:
with a minimal modding (read my previous post, it may be an M117 mod itself) you can have a ìn M117 with 512 stages BBD  :icon_exclaim:
You already have a proper working M117, why don't taste the same performance and control setup, just "higher" ?

Please try and report  :-*

Quote from: Fender3D on September 10, 2011, 10:54:35 AM
I'm repeating myself, but reading flanger posts here around, it seems everybody's looking for a shorter BBD to achieve  liquid/jet sound...
You have a wonderful chance:
with a minimal modding (read my previous post, it may be an M117 mod itself) you can have a ìn M117 with 512 stages BBD  :icon_exclaim:
You already have a proper working M117, why don't taste the same performance and control setup, just "higher" ?

Please try and report  :-*

Here is my reasoning...

I have (3) M117s. One is a Vintage working unit. NO WAY ON EARTH will I mod that one  :o

I also have 2 working clones. I could mod one of them to try the SAD with the bad channel HOWEVER, I have to weigh the risks.

1) How much chance is there for me to damage the perfectly good SAD that is in there by removing/replacing it?
2) Will the circuit survive the modding? (i.e. traces undamaged, components undamages, etc.)

This may be a job for a whole NEW etch.

-OR-

I can etch a whole new Deluxe Electric Mistress and try the chip in there as I said before. That way, if it does not work out I can try to get another SAD and have a whole new DIFFERENT effect.

Decisions... Decisions...  ???

Quote from: Fender3D on September 07, 2011, 02:02:33 PM
In MXR flanger stages are connected in series: signal arrives on pin 2 exits from 5-6 , goes into 15 and finally exits at 11-12
To "jump" first stage you should connect C1 (going to pin 2) to pin 15, without any influences from pins 5-6 (lifting C6).

If I attempt what you are saying here, would I still need to keep R1, R2, and R49 (trim) in the circuit?

Or, could they be removed and I would essentially be feeding the signal coming out of C1 straight into Pin 15?

Also, could the 2 clock inputs at Pins 3 and 8 be removed since that channel is dead?

Definitely interested in trying this  :icon_wink:

In the vintage PCB you'll simply lift C1 and C6 then connect one of those caps from C1's right pad (near R1 on PCB) to C6's highest pad (towards C1 on PCB). No tracks cutting needed.

On Madbeans' PCB http://....org/download/file.php?id=13224 (//http:///download/file.php?id=13224) you'll desold the jumper in front of IC5, take out C19 and put the jumper from the old jumper's lowest pad (near IC5's pin 16) to C19's leftiest pad (towards IC5).

I guess you shouldn't have any major issues from the remaining connections...

Whether it sounds good, you may put a switch on the working unit and owe me a beer for the mod...  :icon_mrgreen:

Quote from: Fender3D on September 10, 2011, 11:53:37 AM
In the vintage PCB you'll simply lift C1 and C6 then connect one of those caps from C1's right pad (near R1 on PCB) to C6's highest pad (towards C1 on PCB). No tracks cutting needed.

On Madbeans' PCB http://....org/download/file.php?id=13224 (//http:///download/file.php?id=13224) you'll desold the jumper in front of IC5, take out C19 and put the jumper from the old jumper's lowest pad (near IC5's pin 16) to C19's leftiest pad (towards IC5).

I guess you shouldn't have any major issues from the remaining connections...

Whether it sounds good, you may put a switch on the working unit and owe me a beer for the mod...  :icon_mrgreen:

Interesting idea  ;D One of my clones is on the madbean layout!

I may have to investigate the switch idea too. I wonder if this can be done, without any potential damage, to a circuit with a FULLY functional SAD chip  :icon_idea:

Switching the BBD between 512-stage and 1024-stage whenever you want. I am thinking it would need trim adjustments between changes though  :icon_frown:

There should be a slight increase of the wet signal 'cause the lower loss trough BBD... but I guess it wouldn't matter so much...
Bias is the same for both 512 stages, so no trimming...
A switch won't be harmful, even when shorted to ground (case/box)...

Come on, you're this close...  :icon_twisted:









DO IT

Quote from: Fender3D on September 10, 2011, 12:44:06 PM
There should be a slight increase of the wet signal 'cause the lower loss trough BBD...

I suppose a happy medium could be found without level trimming when switching between stages  ;D

Quote
Come on, you're this close...  :icon_twisted:


DO IT

Easy to say if it was 25+ years ago when SAD chips were somewhat plentiful and CHEAP! :icon_lol:

Another roadblock is that my madbean version is already boxed up TIGHT with no room for switches. I gotta figure something out with that:
1) A good switching diagram to switch out the jumper and cap
2) Someplace to squeeze in a switch  :icon_eek:

I think I have some DPDT miniature slide switches BUT, at first glance, I think this will require something with more than 2 poles.

IIRC, you need to connect some pins of the unused 1/2 of the SAD to ground or power. Don't remember which goes where. Check out the datasheet.
BTW; 25+ years ago SAD1024's were plentiful; but at approx. $12-15 US in 1980's dollars; they hardly qualified as cheap...

Quote from: oldschoolanalog on September 10, 2011, 01:22:11 PM
IIRC, you need to connect some pins of the unused 1/2 of the SAD to ground or power.

Good Call  ;D

According to datasheet, ALL unused OUTPUTS should be connected to Vdd (Input power). Or, they should essentially be connected to Pin 7 of the SAD.

This complicates things a bit!  :-\

The way I look at it AND taking into account Dave's contribution....

This will take no less than a 3PDT switch with a few more off-board wires  :icon_eek:

Fortunately, madbean's board provides a jumper/access point to Pins 5 & 6 of the SAD so that can be run to a switch lug to go between normal and Vdd.

It is do-able for sure...... I just don't see it ALL happening in a 125B

1590BB is a definite possibility though  ;D

EDIT: NEVERMIND... Apparently ALL of the unused pins need to be tied to either Vdd or Ground. That is 5 pins in total. Too many for reasonable mechanical switching  :'(

Man, I would be totally willing to try this, since I have a couple of half-functioning SADs, but I would have to do a new etch, repopulate, etc. which would take some time, plus I only have the shredaholic layout to work with.  Is there anywhere I can find the MadBean layout?  The link above didn't work for me. So Greg, if you're willing to wait a bit (probably not! ;D), I'm willing to guinea pig it for ya...

You have no unused pins on SAD, they're just NOT WORKING...
leaving all other parts ON the board, they will act as usual but with no signal.

@jdub
the link will work substituting 3 dots with the name of the other site...  :icon_wink:

Oooooh, gotcha  :o

Quote from: jdub on September 10, 2011, 01:56:15 PM
So Greg, if you're willing to wait a bit (probably not! ;D), I'm willing to guinea pig it for ya...

I am more than happy to wait  ;D

I already have 3 that are up and running so I can hold my breath for a while.  :icon_eek:

Let us know what you come up with.

Just remember also that the "changes" that fender3D recommended on the madbean board ASSUMES that your SAD chip has OUTPUT A broken (No output from Pins 5 & 6). If your chip had output B broken, then you will have to find another work-around.

Good Luck  ;D

Just checked in Madbean's PCB you will have to lift R32 or R33 (it's the same) too.  :icon_redface:

If you lift C6 (stock PCB) / C19 (MB PCB) and just 3 wires it's a simple 1 pole bypass, and no other lifting

(http://www.wizardinside.it/foto/schemi/117mod.jpg)

Aw crud- wasn't thinking. Both of my half-SADs have bad B-sides- the one you and I corresponded about, Greg, plus I have an SAD512, which is a 1024 with, of course, a non-functioning B-side  :-\.  Well, since both sides are pretty much the same, I might be able to jury-rig something (like a psuedo-daughterboard, just to see if ot works); otherwise, it's gonna entail modification of a layout, which is more time consuming. Sorry about that.  Lemme see what I can do.

Quote from: Fender3D on September 10, 2011, 02:57:24 PM
Just checked in Madbean's PCB you will have to lift R32 or R33 (it's the same) too.  :icon_redface:

If you lift C6 (stock PCB) / C19 (MB PCB) and just 3 wires it's a simple 1 pole bypass, and no other lifting

(http://www.wizardinside.it/foto/schemi/117mod.jpg)

I follow you Fender however, I am worried about this operation with a fully functioning SAD.

If you lift C6, that leave the OUTPUT on Pins 5 & 6 going to GND (via R10 and R11) and that is where the datasheet warning comes into play.

Will the GOOD chip react well if those outputs ARE NOT tied to Vdd when in the 512-stages position?

-AND- will it affect the operation of the outputs of the working channels on the 1/2 BAD chip?

Quote from: jdub on September 10, 2011, 02:59:55 PM
...plus I have an SAD512, which is a 1024 with, of course, a non-functioning B-side  :-\. 

???

I thought the 512s were 8 pin DIPs. SAD512s don't have 2 sides.

Let's put it this way:
what if you were using a SAD in a stereo device with 1 section per channel (L/R), then shut off R channel?

SAD were used as delay line in older scopes to record waveforms... I recall an older Elektor project doing just this (it was "doable" it had 2 different separated clocks without heterodyning on the same device) and the claim "The sections may be used independently" must allow this operating setup  :icon_exclaim:

You're not "not using" those pins, you simply don't use the signal available there...
You will connect CMOS pins to Vcc or GND just to avoid autooscillations or signal bleeding, it won't broke anything not connecting unused pins (unless you touch them after sliding your feet over acrylic or wool  :icon_mrgreen: ), anyway they're connected somewhere actually..

@ jdub:
SAD512D were 8 pins, SAD512 were 16

QuoteI thought the 512s were 8 pin DIPs. SAD512s don't have 2 sides.

Yeah, as F3D said, the SAD512Ds were the the 8 pin DIPs and are damn near impossible to find these days.  The SAD512 (no D) is a 512-stage BBD which, according to the datasheet, is identical to one half of a 1024, in a 16-pin package.  Datsheet also mentions that "in some instances" 1024s with a bad B-side may be used to make 512s.  I'm betting that there were a lot of those instances  ;)

Dudes:
http://www.experimentalistsanonymous.com/diy/Datasheets/SAD512-1024.pdf
http://www.experimentalistsanonymous.com/diy/Datasheets/SAD512D.pdf
Okay? ;)

Consider me knowledgified!!  8)

Can anyone think of a good way to determine FOR SURE which side of a suspected SAD is broken? With a sig gen, oscope, etc?

Sorry I said jdub, but I meant Govmnt_Lacky  :icon_redface:

Quote from: jdub on September 10, 2011, 03:43:02 PM
Yeah, as F3D said, the SAD512Ds were the the 8 pin DIPs and are damn near impossible to find these days.  The SAD512 (no D) is a 512-stage BBD which, according to the datasheet, is identical to one half of a 1024, in a 16-pin package.  Datsheet also mentions that "in some instances" 1024s with a bad B-side may be used to make 512s.  I'm betting that there were a lot of those instances  ;)

Or maybe they were trying to mod an M117  :icon_mrgreen:

lol  :D

Does anyone else find it odd that it is always the same 4 or 5 people that talk about Flangers or modulation effects?

Fender3D, oldschoolanalog, jdub, Tomas, myself......

I wonder how many pages this post would be like if it was a Fuzz or a TS derivitive...  :icon_eek:

MODULATION ADDICTS UNITE!!!  :icon_lol:

Quote from: Fender3D on September 10, 2011, 03:32:45 PM
SAD were used as delay line in older scopes to record waveforms... I recall an older Elektor project doing just this (it was "doable" it had 2 different separated clocks without heterodyning on the same device) and the claim "The sections may be used independently" must allow this operating setup  :icon_exclaim:

This statement hit me like a ton of bricks!!  :o

We have a crap ton of broken/unused oscopes at my work that are just sitting and collecting dust! A lot of Tektronix models and some others. I wonder if some disassembly is in order??  :icon_cool:

Sadly I guess they might have been used in cheap scopes (Elektor's project was translated Videoscope in italian. it was a scope out of a TV)...

Quote from: Fender3D on September 10, 2011, 06:13:41 PM
Sadly I guess they might have been used in cheap scopes (Elektor's project was translated Videoscope in italian. it was a scope out of a TV)...

Won't know until I try... right?  ;D

OK, so I think I understand how to do the 512-stage mod with a bad-B-side SAD, but I wanna check before I try it.  If I understand correctly, all one is really doing is eliminating the input signal from (in F3D's suggestion) the A-side of the SAD; going from the stock schematic, this entails taking the signal that would normally go into pin 2 via C1 (from junction C1/C12) and rerouting it to enter pin 15 via C6 then taking your output from pins 11/12.  Thus, eliminating input signal from the first half of the SAD.  If I want to do an analogous move with the B-side, it seems all I gotta do is take the output from pins 5/6 and jump that straight to R48 trim, right?  That bypasses the B-side;  my question is whether or not I need to bypass R10.  I assume yes, since in the A-side mod we have nothing between pins 11/12 and R48.  Am I correct in this assumption?  Thanks!

Mod for a bad B side is somewhat trickier since you must disconnect pin 11 and 12.
You should remove R48 and connect it instead of R10 and R11, then connect R48's wiper to C7.
Just 1 more wire (if there's no room on PCB)

Quote from: Govmnt_Lacky on September 10, 2011, 04:22:53 PM

Quote from: Fender3D on September 10, 2011, 03:32:45 PM
SAD were used as delay line in older scopes to record waveforms... I recall an older Elektor project doing just this (it was "doable" it had 2 different separated clocks without heterodyning on the same device) and the claim "The sections may be used independently" must allow this operating setup  :icon_exclaim:

We have a crap ton of broken/unused oscopes at my work that are just sitting and collecting dust! A lot of Tektronix models and some others. I wonder if some disassembly is in order??  :icon_cool:

After a few hours of digging...... the scopes came up EMPTY on usable ANYTHING!  :'(

QuoteMod for a bad B side is somewhat trickier since you must disconnect pin 11 and 12.

What if I just use a socket with pins 11 & 12 lifted, and run a jumper from 5/6 to the 11/12 trace (that goes to R48)? 

Greg, sorry to hear that the 'scopes didn't pan out... :-\

Paging Kaiser Soze please... :icon_lol:

Are YOU dancing to the Radio? Well, what RU waiting for???

Just call me "Verbal" Kint  :D

Had a chance last night to try the 512 mod...and it works well!  On the Shredaholic board, I just lifted the end of R10 that connects to pins 5/6 and installed a wire at that pad; then I lifted the pin of R48 that normally connects to pins 11/12 and connected the other end of the wire to that.  I didn't have time to fiddle with C21 & optimally dial in, just a quick adjustment of R48 and R49, so to my ears wasn't quite as intense as before (due to less stages?) but it's close.  Proper calibration might improve this.

Since I'm by no means an expert on flangers, I'm puzzled as to why this works.  Are the full 1024 stages unnecessary?  Why use them, then- better chip availability (SAD1024 vs SAD512(D))?  Because they are there?  To be honest, I've never been quite clear on parallel vs series mode in SAD-using flangers, either.
I understand why my bad SAD won't work in a stock M117 (because the signal is being routed through the bad side in a series config, which the mod bypasses), but why does that same chip work in my Electric Mistress (parallel)? Is it because the signal is split in the chip, and the box will still function with only one side passing through?

Anyway, Federico, consider your mod verified.  Kudos and thanks to you! If by some strange quirk of fate we ever meet, I shall buy you several beers.  ;D

@jdub

Good on ya' for the effort  :icon_wink:

Concerning your question about why it will work in the EM with one bad channel.... Does the Balance trimmer need to be cranked to one side to get the effect? With the balance trimmer fully CW or CCW, this would essentially only let one channel through.

Can you put a little bit more detail into the differences in the effect between the 512 and 1024 stages? Are the controls still as interactive on the 512 setting as on the 1024?

How much trimmer adjustment was needed (if any) to get good flanging with the 512 mod?

So many questions....  ;D

jdub 1 , Govmnt_Lacky ? ???

:icon_mrgreen:

You welcome  :icon_cool:
Now you just have a little more...  :icon_evil:

I guess the "lesser intensity" deserves some consideration...
Less stages means you have less delay time @ the same clock, less delay time means higher comb filtering.
Intensity should be dictated by Dmax/Dmin ratio, and this should be, more or less, the same.
Nevertheless an higher comb filtering may look like a lesser intensity... but I'm sure you can achieve a better jet sound.

You should check the higher filtering won't play outside guitar frequencies range... lowering clock is the easy way, lowering clock at the same Dmax/Dmin ratio will be the hard way tinkering with caps...  :icon_neutral:
Of course, lowering clock too much will arise clock noise/whining, preventing you to get the stock delay time

About EM, with parallel-multiplex you double the waveform's samples: even samples are managed by one BBD, odds by the other.
If you loose one block, you always have a waveform following the input signal, just not perfect, but a little distortion may be unnoticeable yet the flanging effect might cover it...

@Greg-
Lemme get back to you with more details...I didn't have much time to fiddle with it last night.  First impression was that controls were still interactive, good range of sounds, but a bit less "in your face" (which I guess is just anopther way of saying "less intense"  :-[).  For example, max speed seemed a little slower and boosting regen seemed a little noisy (but my build isn't boxed yet, so take with a grain of salt). As soon as I get a chance (hopefully tonight), I'll play around with Federico's suggestions and see if I can improve it a bit, maybe get a couple clips.

@Federico
Thanks again, dude!   8)

Re: Series vs. parallel. It's all about effective sampling & clock cancellation. Read that Reticon SAD1024 datasheet I linked to in an earlier post carefully.
Want more intense? Play around w/the feedback loop. If you can't get it to self oscillate then you haven't reached max intensity. Get it to the point where it self oscillates, then back off a bit.
Also, proper BBD bias is very important when it comes to getting the best overall sound/intensity.
BTW, in theory anyway... If you are going to halve the stages used (1024 to 512); you will need to also halve the clock min/max to keep the min & max delay times the same. If the sweep just keeps going up, up, up; you are going to run out of useful sonic information for the flanger to process. W/a clean guitar there really isn't all that much going on up there. However if you run the axe through a nice Foxx Tone Machine OR a synth, watch that baby come alive in the upper part of the sweep. You are still limited by the units LP filtering and the inherent (very) limited bandwidth of the speakers used w/guitar amps.
Food for thought...
Dancing yet? ;D

Dig it.  Like I said, I was just trying to see if the thing would work; I didn't have time to focus on it too deeply.  I'll work on it tonight, hopefully...

I actually read through the SAD datasheet a number of times a couple years ago when I first built an EM, cuz I was attempting to use 2 SAD512s wired in parallel to replace 1 1024, which I didn't have at the time (it did work, BTW).  But when I read it then I didn't really understand it, being new to BBDs and electronics in general; I was more interested in quick n dirty info for a specific result...I'll have to read it again as I'll probably get more out of it now...Thanks Dave

An SAD1024 used in parallel-multiplex is essentially the same as a 512-stage BBD in terms of delay time, but with double the system sample rate (because alternating samples from each section are combined at the output); it might be said that parallel-multiplex offers double resolution analog sampling for a given sampling rate.   Using only one half of an SAD1024 in such a configuration would effectively reduce it to a regular single 512-stage device at the nominal system sampling rate.  Finally, removing one half of an SAD1024 in a serial configuration would reduce the delay time by half and therefore shift the range of the flanger up one octave (as mentioned above). 

Dave and Federico, taking to heart your reminders about half the stages/halve the clock, last night I changed my C21 to a 56pF, adjusted the trim to get ~18kH - ~580kH, tweaked bias and distortion trims got it sounding pretty good.  Nice rich sound, full range of controls, maybe still a tad noisy.  Will play with it more when I get a chance...Thanks again.  You guys rule  8)