Please help me fix my Multivox Jazz Flanger from the 70's

[Zero]

Hello everyone!

I recently acquired a Multivox Jazz Flanger (SE-12, "Big Jam" Series) from the late 70's. I got it NOS (!) but it turned out to be defective. After I complained with the dealer (and got my money back without any hassle), he told me I could keep the defective pedal (it was the last one he had). So: I'm already quite happy 

As this effect is pretty rare, here's a picture I borrowed from Discofreq's FX Site (excellent, btw). As you can see, it uses sliders rather than rotary pots and has a built-in distortion. An no, it is not true bypass 


Let me shortly describe the defect: Everything works fine, but it doesn't flange! The level and distortion controls work (fine), but the other sliders don't do anything at all. Bypass works as well.

After I managed to get the PCB out the box (I had to unsolder both audio jacks!!), I set off to inspect the unit for the obvious: cold solder joints, broken wires, faulty switches, power supply pins an all the ICs, etc... Everything seems fine. As I said, the unit is NOS, so it is in perfect condition.. at least optically/mechanically 

** Now the BAD news: The flanger is built around the infamous SAD512D from Reticon which seems to be almost impossible to get nowadays. [I read a lot of threads on this forum about this]. Now I fear the BBD could be dead (no flanging..) but I pray it's something else.

I examined the effect with my scope last night, and the BBD is getting some kind of a clock signal on pin 1.. This signal changes its form when I play with the controls. The next thing I will try is to change all the electrolytic caps (Like R.G. Keen wrote: "Don't think, just do it..."). But I'd like to determine if the SAD512 is dead first. I read a post from Marc Hammer where he wrote he once found the clock generator to be the culprit (the SAD512 was fine). Could I be that lucky, too? 

I've also begun tracing the PCB with the aim of producing a schematic. As soon a I'm finished, I'll post it to the forum for your enjoyment. Maybe I could try (I'd need some help..) to adapt the circuit to work with R5106 BBD (which from what I've read is relatively similar to the SAD512) ?

Any hints on this one? Does anyone else have this pedal?

I don't have:
- A schematic (and believe me, I've searched...)
- Lots of experience with BBD circuits

I have:
- Decent experience in electronics and guitar effects
- A tube (!) oscilloscope (Looks like it's from WWII, but still works  )
- DMM and all the necessary tools...
- Patience and motivation to resuscitate this green monster!

Thanks in advance, and sorry for the lengthy post

Lorenz

[Mark Hammer]

Tell us what chips are in there, and perhaps we might identify something easily replaced.  In my case (good memory, incidentally!), it was a CMOS chip providing a uniphase clock pulse to the SAD512 (Note: The 512 divides the single-phase clock pulse down to provide the two complementary pulses.  One of the advantages of this is that you don't have two lower frequency clock pulses running around the board where they can bleed into other parts of the circuit.  In theory, this lowers audible clock whine.)

Yours would appear to use FET-based switching, as do so many others.  In these instances, a single FET is used to enable or lift the wet signal at a mixing stage.  If the delay signal does not make it to the mixing stage to be combined with the dry signal, then the effect is cancelled.  It CAN happen that a) the FET goes or is bad for whatever reason, so the switching circuit has not practical impact, or b) the FET is fine but the switching flip flop is bad.  There have been a variety of discrete and chip-based flip-flop circuits over the years to use with FETs.  Boss uses a discrete bipolar circuit, but DOD uses a CMOS chip and so does Danelectro.  Perhaps Multivox also used a CMOS-based circuit, and the problem lies in the replacement of easily obtainable 50-cent CMOS chips, rather than largely unobtainable $50 BBDs.  We can hope, I guess.

Either way, even if you can't post a photo, let us know what semiconductors are in there.  That includes transistors.  I imagine some trannies will be part of a filtering circuit, but at least one will be a FET.

[analogguru]

Doesn´t have the SAD 512D (that´s what was talking about) a built in clock generaotor ?

analogguru

[Mark Hammer]

No.  Just the flip-flop divider.  Reticon's blurb for the chip states an advantage of the 512D as being that it requires only a "...single TTL-level clock input...".  Clock input pin is pin 1.  As noted (perhaps not as transparently as I thought) in my previous post, this not only reduces the external circuitry needed, but places the lower-frequency divided-down clock pulses inside the BBD, rather than running between an external flip-flop and the BBD, where they have the potential to do the most audio harm.  There still IS a HF clock signal running between the external clock and the BBD, but at twice the frequency, pushing it well up past the audio range in even the worst-case scenario.  The result is that the lowpass filtering intended to keep the clock at bay doesn't have to be quite so severe.  I have to say that, whatever its other shortcomings, my SAD512D-based MXR Commande series flanger sounds quite crisp and clean.

Note that the 8-pin 512D is not the same as the other 16-pin SAD512, which is essentially an SAD1024 with half the chip disabled (or at least not guaranteed as functional).

[dr]

....Zero- I have two of them; when I got them they were both not working-I got them both going by tweaking the trimmers inside and returning them to their original spots;one started working and the other had a bad trimmer that tested open....as for the SAD512, I can't help you there-I haven't found any anywhere....supposedly there are some BBD's available at a company called the Organ Service Co. in Illinois or Indiana (I'm not sure I haven't scoped them out, but my keyboard playing friend has).....................

[Zero]

Thank you for your quick replies 

It's indeed the 8-pin SAD512D that was used in this circuit--

I had already written .txt lists for this anyway:

**Other ICs (I did some google-ing to find out):
MC14011B (1x)   Quad 2-input NAND
MC14011UB (1x)   Quad 2-input NAND
MC14007UB (1x)   Dual Complementary Pair Plus Inverter
C4558 (3x)  Dual op-amp

**Trannies:
C2240 (5x)   NPN Transistor  Hfe ~ 200-700
C1815 (1x)    NPN Transistor  Hfe ~ 100


@dr: Thanks for the hint with the trim pot.. I will fiddle around with it later tonight.. So tell me: How do they sound? 
@Mark Hammer: I would be awesome if I just had to replace a couple of CMOS chips      There seem to be no FET in the circuit, so I guess the switching is done via the CMOS chips like you mentioned.

Here's a picture of the PCB:

[Mark Hammer]

Okay, that is EXTREMELY helpful.  The 4007 is very likely used for the flip-flop, the same way it is in the DOD pedals.

The pair of 4011 chips in the upper left hand corner are for the LFO and high frequency clock  These are cheap as borscht and you can probebly even buy them at, gulp, Radio Shack.  If you feel you can safely desolder them, install a pair of sockets, and then plug in replacements.  Shouldn't cost you more than a couple bucks for the whole deal.

My guess is that the horizontally-mounted trimpot near the Regen slider is for setting the maximum regeneration just prior to oscillation.  The vertically mounted one closest to the SAD512D is or setting the bias.  The one closest to the Manual control is likely for fine-tuning/setting the overall clock range or something like that.

Since the least invasive thing to do is to verify that the BBD bias is set right, start with that.  You can tweak that trimpot all over the place without harming the peal itself.  When the chip is underbiased you will hear no delay signal.  Then as you increase bias, you'll hear first a distorted delay signal, then a cleaner, clean, less clean and again distorted delay signal, before once again killing the delay signal.  Set the flanger for an obvious, but yet easy-to-hear flanger tone - manual to min, width to 75%, rate to 50-75%, regen to maybe 30% - and tweak until you think you hear a decent sound.  Important to NOT set it for too extreme a flange sound since that will make it hard to tell the difference between a distorted and a clean delay signal. 

If adjusting the bias is NOT the source of the dysfunction, then I'd suggest replacing the 4011's as suggested....unless you find the LED does not correspond to on/off switch actions.  In that instance, it may well be the 4007 that needs replacing.  Worse comes to worse, you can always buy a 4007 while you're picking up some 4011s.

Once you get the thing up and running, it *may* be that you can improve the noise performance of the device by replacing the 4558s with something a little fancier.  That's not a given, but when you consider the age of the pedal, and the era in which it was produced, those may have been the cheapest op-amps to use from what was available at the time, though not necessarily the best to use.  So, something to consider down the line.....once you get it working.

[Zero]

I tried messing around with the trimmers (especially the SAD512 bias) .. but nothing seemed to change sound-wise in any setting. 
I tried this with the control settings you suggested, Marc.

I have to go through my stash of old ICs... maybe I've got some 4011s around somewhere.. Otherwise I'll buy some as soon as I can.

But I noticed something that I hadn't before: When I hit a chord strongly, the sound gets very distorted.. And the distortion gets worse when the (supposed) bypass is activated (the bicolor LED goes red). Which IMO means the bypass isn't working properly ...
Is there any way I could tap the output signal from the BBD directly? According to the datasheet this would be pins 3 or 4 (even and odd)

@dr: Does the distortion (set by the distortion slider) stay  when you bypass the unit?

[Mark Hammer]

Hmmm.  The absence of a discrete FET makes me wonder if the 4007 is being used as the switched element and not just as flip-flop.  If you get into replacing chips, start with the 4007 and take it from there.

And yes, the outputs arepins 3 and 4.  Take the output feed from the junction of the two resistors coming from those two pins.

[Zero]

I actually found about six 4011s... I knew they would come in handy someday (I've always wanted to say that  )
Couldn't find any 4007 though, so I'll pay visit to the local electronics shop as soon as I get the chance.

Thanks again, and I'll keep you posted of the progress!

[dr]

.....no, the distortion doesn't stay.....check the slider pot...

[StephenGiles]

Local electronics shop -  What a luxury!! You could also check that power is present on all the power pins of the ICs, and that the voltage on those pins is in the same region as the battery voltage.

[analogguru]

concerning the 4007:

have a look at a Pearl schematic...

analogguru

[Zero]

Thanks for the replies, guys!

concerning the 4007:

have a look at a Pearl schematic...

analogguru

Danke für den Tipp! I did some google-ing and found the schematic of the Pearl PH03 Phaser:
http://www.geocities.com/SunsetStrip/Vine/6655/images/pearl_ph03scm.jpg

I guess now I have a clearer idea of how these FETs were used for the bypass .. of course, assuming they were used in a similar manner in my flanger.
I'll try to "intercept" the wet signal before it is mixed by this 4007 switcher stage.. at least I'll know if there's anything flanging in there at all.. 

Local electronics shop -  What a luxury!! You could also check that power is present on all the power pins of the ICs, and that the voltage on those pins is in the same region as the battery voltage.

That was one of the first things I checked... But it won't harm to do it again, as I did it very quickly and I just remember the voltages being more or less ok... 
My local electronics shop is one of those old "Mom 'n Pop" shops ... They sell a lot of stuff that has sometimes been lying there for years. Just to give you an idea: from tubes down to "Learn to use Windows 3.11" books       The only problem (besides the prices ) is their literally chaotic organization inside the store.. It takes a lot of patience to find what you need if you're looking for capacitors or similar components. At least they sell ICs and trannies over the counter.

[Zero]

Ok, here's an update on what I've found/done so far:

1) I changed the 4007, after which the distortion in bypass mode seems to be gone. Still no flanging...
2) I then replaced both 4011s, which didn't seem to change anything.

3) With the help of an audio probe I was able to hear what must have been the clock. It reacted to all 4 sliders (manual, regen, depth, speed) in the way I would have expected it.. This confirms that my oscilloscope is still working 

4) I held the audio probe to the outputs of the SAD512D (pins 3 and 4) .. no sound at all 
5) The input (pin 6) has my guitar signal, but distorted in a really nasty way (the distortion slider is completely off, so it shouldn't be that) Could this be a problem?

6) I also noticed that all the ICs have ~11 V on the supply pin, except one of the 4011s and one Opamp, which read 5.8 Volts.
The SAD512D's Bias supply pin (Vbb, pin 5) reads 5.8 as well.
The datasheet says that, for optimum performance, the Bias voltage should be 1 volt below the Drain (supply) voltage. But it should still work like this, right?

Some ideas that come to my mind about what to try next:
- Change all the electrolythic capacitors. (Maybe I should have done that long ago..)
- Replace some of the trimpots .. although I do read a resistance on them.

A schematic would be so infinitely helpful ...     Do I really have to reverse-engineer this thing? I see it as some kind of a last resort... but it would be waste if the SAD is dead anyway.

So, what's your diagnosis, docs? What else could I try?

[R.G.]

The answer to a lot of your questions lies in getting access to an oscilloscope.

To find out if the BBD is working:
1) ensure the DC voltages being fed to the chip are correct
2) put in a test sine wave
3) verify that solid clock pulses with square edges, full supply voltage are going into the clock pin(s)
4) verify that the test sine appears at the input pin
5) look at the output pin. If there is a stairstepped approximation of the input signal there, the chip is good. If not, sorry.

It's very difficult to determine if the clock is correct without a 'scope.

[Zero]

Oh, but I do have an oscilloscope.. it's very, very old but still works.

Thanks for the tips, R.G. --
I checked the clock input, and something doesn't seem to be in order after all.. I took some pictures of what my scope is showing me:





This is about the best view I could get with my scope.. I'm not very experienced with oscilloscopes though.. and much less with scopes older than me. 
In the second picture, it's set to about 5 usec/cm. This is obviously not a square wave. Some capacitor not holding a charge? The waveform you see in the picture reacts to movements of the control pots... i.e. Rate makes it move faster and slower, etc...

The clock seems to be generated by a 4011 (quad NAND) IC, from which 2 NANDs are used as inverters (inputs tied together). There's one capacitor feeding back the signal after the first inverter... which I'm guessing sets the frequency of the clock signal together with a signal (in better words: some kind of variable resistance) coming from the Rate (et al) sliders ..

After doing some reading, I've found that this method of clock generation (NANDs + capacitor in feedback + resistance) is quite common..

I will try to get this clock working first and then move on to checking the BBD as R.G. suggested.
Any help will be much appreciated.

[leonhendrix]

....Zero- I have two of them; when I got them they were both not working-I got them both going by tweaking the trimmers inside and returning them to their original spots

I couldnt get my Colorsound Flanger to work, so I came here read that ^^ and now im 

This big bugger also uses the SAD512D, here's a schem if anyones intrested (in two parts).

[Zero]

Hi! This has turned out to be a weekend fully devoted to debugging... I'm hoping for at least some kind of success.

To find out if the BBD is working:
1) ensure the DC voltages being fed to the chip are correct
2) put in a test sine wave
3) verify that solid clock pulses with square edges, full supply voltage are going into the clock pin(s)
4) verify that the test sine appears at the input pin
5) look at the output pin. If there is a stairstepped approximation of the input signal there, the chip is good. If not, sorry.

My findings:
1) check
2) check
3) PROBLEM ... clock isn't square-edged at all (See below)
4) check
5) nothing... ouput is dead.

Before I give up on the BBD, I want to get decent clock signal driving it...
I drew out the clock circuit, which is based on an 4011:


I also drew more or less the waveforms I'm getting on my scope... It's a little far away from the square wave we're expecting
Maybe I should mention again that I can change the sweep speed depth of these triangular waveforms.

I've already tried using several other 4011's, diodes & caps (even diffeent values). No change. I actually built this part on a breadboard and fed the clock signal back into the board.
Can this circuit work as shown? The input voltage coming from the speed control is between 30 and 70 mV.

Maybe I could generate a  square clock by similar means just to test the BBD... any ideas?

[R.G.]

Well, the problem is that whether or not the SAD512 thinks that waveform is a "clock" depends on the innards of the 512. I would not be happy with it, but it's possible that a new 512's clock input will take anything above X voltage as a "1" and anything below X as a "0" and work.

Maybe.

The voltage you show, 1.2V peak to peak, is not really a good clock voltage for driving anything that's powered from 9V.

So it could well be that the clock is not good enough. I stuck the circuit into my simulator and it did oscillate, but the waveforms were not like you show, which just means that my simulator is not good enough to do it right.

If I were you, I'd do two things. First, what's that clock frequency, calculated as 1/period? And can your o'scope see that high a frequency OK? Are you using a 1:1 scope probe or a 10:1 probe? All this is just to filter out measurement error before we go hunting for ghosts. Try calibrating your probe on the scope's calibrator.

Then before I junked the 512, I'd feed it a similar frequency square wave that the scope showed as a nice square-shouldered waveform. I have this feeling that the clock is not telling the 512 to switch. At least we can't tell that yet.

Can you breadboard a simple three-inverter CMOS oscillator and feed the output of that into the clock input?