Tycobrahe Pedalflanger questions

[Dirk_Hendrik]

I just got a Tycobrahe pedalflanger in for repair. Great challenge which will work out eventually bot leaves me with a few questions since it's the first time I have such a device on the bench. Revere engineering will probably answer all below (and must be done anyway to supply this community and the rest of the world with the schematic) but the daytime job is requiring a lot of energy lately:

The thing is powered from a single 9V battery which seems rather low to me already since the power is reduced to 7.1 volts by means of a 7905 regulator lifted with 2 diodes. All application data (BBD Dimentia (thanks as always Mark Hammer)) shows that the usual voltage for MN30xx's (3001 in this case) is 15 volts. Can anyone confirm proper operation at this low voltage?

OK.
The flanging part kinda works but is far from impressive and requires the 2 front knobs (spread and intensity) to be maxed for effect.  Is anyone able to supply a settin at which effect should clearly kick in?

The effect has 2 footswitches under the pedal. The heel position one seems to be general bypass. The other one doesn't seem to do anything. What is it supposed to do?

Thanks for reading.

And..
Has anyone ever heard op a DIL16 TL044

[Dirk_Hendrik]

Wow!! That was a lot of response!!!

Nevermind, I've spent my saturday afternoon on this baby. Over the last couple of years I reversed quite some pedals but this one really had me cornered. There's stuff going one I have never seen before in a flanger (e.g. a switched power supply for the MN3001's VBB on pin 1) About nothing is what it seems and the double sided PCB didn's make it much easier.

Here's the work so far. Anyone willing, please study and shoot questions on things unclear etc while I still have the pedal here. It has to go back to it's owner next week. I'll have to verify before that time. It may take years before another shows up here to be reversed.

Schematic:
www.dirk-hendrik.com/tycobrahe_pedalflanger.pdf

[Dirk_Hendrik]

And yet another bump. Feels good talking to myself!
Other than te fact that the PDF was a) updated and b) downloaded 86 times today I don't believe there's much interest in this rarity. shame.

[Ry]

I'm certainly interested, but working a ton of overtime lately leaves no time for building/researching pedals  .  What does it sound like?  Do you have any sound samples?

Thanks for tracing it out, I'm sure I'll get around to digging through the schematic eventually.

[Dirk_Hendrik]

What does it sound like?.. Well, like a good but not too extreme (like jet style) flange with the capability of high rate settings. Personally I'd say it's overrated due to it's rareness but nevertheless, especially at low rates, very usable.

[Eirik]

Overrated or not. It's really great that you do this job of tracing and sharing. After all it is a Tychobrahe=Mojo! 
Unfortunatly I am totally unable to help you. But hey! Thumbs up! 

[rocket]

I can't see a feedback, as you would expect in a flanger.

[Dirk_Hendrik]

Which is exactly why I still wonder about C24 which is definitely there in thet position but ruines all that could be regarded ad feedback.

[Arno van der Heijden]

Hey Barend,

Nice work! Too bad there isn't more response.

I thought Mark Hammer would've chimed in already!

[puretube]

too much dry signal (via R20) in the feedback-path through the "intensity"-pot from U2B to U2C...

[Mark Hammer]

Hey Barend,

Nice work! Too bad there isn't more response.

I thought Mark Hammer would've chimed in already!

Well I would have, if I had noticed/seen this thread before now.

What Dirk has shown as the "Intensity" control IS the feedback/regen path.  You will note the presence of the back-to-back GE diode pair.  This is a technique used to keep the input+regen signal from exceeding what the BBD can handle and is often found in one version or another in flangers lacking a compander for managing levels.  This particular regen path is not within the delay portion, as is often seen, but rather is taken from the overall dry+wet mixed output and fed back to the point before wet and dry are split up.  Opinions vary on whether this is the more desirable method for producing  regen.  Some folks like it a lot and tote it as the "secret weapon" in their design.

I was sort of perplexed by the rather high value of R20 (1M) but then I remembered that the earliest BBDs had a fair bit of passive loss to them (its mentioned in the spec sheet).  Consequently the 1M input and 330k feedback resistor for the dry path at the mixing stage (U2B) attenuates the dry signal, while the 47k input resistor with 330k feedback adds gain for the wet signal.  Whether the amount of attenuation and complementary gain make sense I leave for others to calculate, but in principle, based on what I know about the 3001, this more or less makes sense.

You will note that it uses the same envelope-controlled gate strategy to manage noise from the wet path as does the CE-1 and A/DA flanger, except that here, for whatever reasons (and I am assuming the schematic is accurate) the gating is inserted before the BBD rather than after where it has the most impact on noise.  I gather Boss and A/DA learned from Tychobrahe's error.

The pedal was never a huge commercial success.  My guess is that it was because a flanger is not the sort of pedal you want to use in footswept mode all the time.  A wah you can go back and forth and back and forth.  A volume pedal you can gradually sweep up and leave there.  A flanger you have to think about a lot to use in footsweep mode.  Frankly, as useful as such a device can be, I think players who knew what to do with it were in very short supply back then.

[puretube]

I knew, that Mark would chime in, after puretube did...   

glad you agreed with me, Mark (the "intensity" pot being the feedback...);

but: take a look at the values of R28/29/30 + R22 versus R21 (across U2B):
that makes aprrox unity gain for the wet signal.

while the 1M R20 versus R21 (330k) amounts to ~1/3rd dry signal
in the output-mix,
plus the amount of dry being fed back / clipped by D1/2
and re-circulated through the BBD and directly through R20 again...

OK: too much "wet" in the feedback loop for me,
but interestingly enough reminding of some of the Small Stone "mixings" in earlier issues...

[Mark Hammer]

I knew, that Mark would chime in, after puretube did...   

glad you agreed with me, Mark (the "intensity" pot being the feedback...);

but: take a look at the values of R28/29/30 + R22 versus R21 (across U2B):
that makes aprrox unity gain for the wet signal.

while the 1M R20 versus R21 (330k) amounts to ~1/3rd dry signal
in the output-mix,
plus the amount of dry being fed back / clipped by D1/2
and re-circulated through the BBD and directly through R20 again...

OK: too much "wet" in the feedback loop for me,
but interestingly enough reminding of some of the Small Stone "mixings" in earlier issues...

Well, the signal-limiting diodes ARE Ge, as opposed to the more typical Si diodes found in other flangers using diode soft-limiters.  Perhaps the intent is to introduce more harmonic content to the regen path by "saturating" the diodes?

Of course, as much as I appreciate Dirk's diligence at tracing out the circuit, there IS also the matter of orange or red or brown stripes, or blue and green ones, that have become difficult to tell apart from each other over the course of 35 years.  So, without questioning your honest attempt to replicate the circuit, are the values in question truly what you believe them to be?

[puretube]

never (blindly, as R.G. sez) trust a schemo on the web...

but: I can imagine Tyco attempted to save 1 opamp by combining the "wet+dry" and the "feedback send" circuitry...

IMHO the "Ge" vs. "Si" fact doesn`t weigh too much concerning "sound",
but just tries to keep the "wanted" wet feedback as well as the "neccessary" dry feedback
low enough as not to cause too much so-called: "oscillation"...

[Mark Hammer]

never (blindly, as R.G. sez) trust a schemo on the web...

but: I can imagine Tyco attempted to save 1 opamp by combining the "wet+dry" and the "feedback send" circuitry...

IMHO the "Ge" vs. "Si" fact doesn`t weigh too much concerning "sound",
but just tries to keep the "wanted" wet feedback as well as the "neccessary" dry feedback
low enough as not to cause too much so-called: "oscillation"...

Agree on all points.  But, since you find the feedback signal a little too hot, maybe the use of a deliberately hot regen signal and a low forward-voltage Ge diode-limiter was intentional FOR sonic reasons.  I'm not saying it is, just that maybe there was a method to their madness that doesn't seem "proper" at first glance.

Of course, that it may have been deliberate doesn't necessarily mean it was smart.  After all, if the schem is correct, the gating scheme allows the clock noise to reach the mixing stage unfettered, while the 2N5460 kills the input signal going to the BBD.


As for the choice of feedback tap-point, I think Mike Irwin told me in conversation some time back that he actually preferred the sound of regen taken from AFTER the mixing point.  There are a whole bunch of choices that can be made with respect to regen in a flanger, particularly when companding is involved.  I've never knowingly heard a Tychobrahe, so I can't comment, and in any event I'm open to any feedback method if it suits the context.  It may be the case that one type of feedback path sounds better for cyclically/LFO swept flanging, while another sounds better-adapted to manual or foot-operated flanging, largely because of how each method manages to create emphasis with respect to the musical phrasing structure.  I'm a guitar player so I think in terms of LFOs and narrow bandwidth, while Mike is a synth guy and thinks in terms of voltage control and synchrony to notes or very long sweeps across harmonically/spectrally rich sources.  Sometimes you need a flathead screwdriver, and sometimes you need a Philips.

[FredCDobbs]

See:  http://wc6w.50webs.com/wc6wvint/index.html?fr413.html

[notchboy]

A Tycobrahe analog delay?  That's got to be uber-unobtainium, like the A/DA Delay System 2000.

[tommy.genes]

Heh, I like that Tycobrahe Decision Maker. Kinda like the MXR Paperweight.

-- T. G. --