Understanding the Schulte Compact Phasing 'A'

[puretube]

in my view of the orig schemo,
your R6 (on the side of C6/C7)
of the LFO
should go to ground.
(me thinx, there`s a dot drawn...).

[majormono]

Hey guys - has anyone ever actually heared one of these in working condition? Mine was so long forgotten and out-of-order no one could remember it was even there...
It must have been put to permanent rest when the Quadraverb (oh boy) came out but I can hardly think *that* was better.
On the other hand - if it's great I have to try to fix it again (fist time I got frustrated at some point, hm) or take it to a more real tech (what a shame...).

Sorry Charlie, I don't have a X-ray camera yet, but I could ask the folks at radiology if they want to test their new CT for metal-induced artifacts  .

[moosapotamus]

in my view of the orig schemo,
your R6 (on the side of C6/C7)
of the LFO
should go to ground.
(me thinx, there`s a dot drawn...).

Makes sense. That fat line for the ground rail makes it kind of hard to tell.
So, I guess that would also move C6 & C7 over to the PSU scheme, then. Thanks!

Updated schemes...

SCP'A' Power Supply

SCP'A' LFO Section

Hey guys - has anyone ever actually heared one of these in working condition?

I'm going on reputation alone... Mike Irwin posted some interesting comments about it here some time ago, including the unique sound of the feedback around the first two filter stages. May be an opportunity to tap the feedback at other (maybe multiple) stages to get some other different character sounds. And, if it's good enough for Jürgen, I'll bet it'll be good enough for me, too.

Sorry Charlie, I don't have a X-ray camera yet, but I could ask the folks at radiology if they want to test their new CT for metal-induced artifacts  .

Let me know what they say... Actually, was referring to that back-lit shot of the PCB. I did a similar shot of the Gonkulator PCB a while back. Nice stuff.

Thanks!
~ Charlie

[puretube]

of course, you could email/PM J.Haible,
who happens to have posted here once,
but doesn`t seem to frequent the forum too much,
and ask him if he ever made up his own schemo...


heck - he lives 10 miles from here, but I never managed
to find the time to bike over there... 

[moosapotamus]

That's a good idea. I think he does frequent The Lab.

I finally finished a draft of the audio signal path and added a couple of notes to the LFO and PSU schemes. I tried to eliminate that 5-pin DIN plug for the audio input/output.

Nowadays, I guess the preferred way to do the I/O without the DIN would be to just have an unbalanced mono input (connect R30 (1k8) to ground) and have two output jacks... one with the mix from the modulation pot, and another switching output jack that would tap the clean unmodualted signal and, when plugged, switch the signal to the first output jack to have only the pure modulated signal.

But the way I've drawn it, just trying to copy the original scheme for now, I'm thinking the input would work with either a balanced or unbalanced mono signal, but not a stereo input signal. And, the output would give a clean, unmodualted signal at the ring connection and a mixed signal (via the modulation pot) at the tip connection, yes/no?.

SCP'A' Audio Signal Path

SCP'A' LFO Section

SCP'A' Power Supply

Thanks!
~ Charlie

[Nasse]

Yeah I tried to look that 6,3 mm "stereo" jack input and thought a piece of gear I bought that has spiffy jacks that allow you connect balanced or unbalanced cable/plug. Tried to google trough some mixer circuits but was not my lucky day. I think I have seen input circuit that does it, and similar output too, but where... somewhere in my messy pile of papers perhaps. But I think it is not important for cloning this sound. But if the input scheme works as left/right difference amplifier that would be funny to test and hear, in stereo

[mph]

Hello
I'm currently trying to upgrade a bit my Compact Phasing (mostly changing the electros cause it distords too easily even with a passive telecaster as input signal) and I would like to know what pot value in the expression pedal is suitable?
I haven't found any infos about that, even on the JH's clone page... could it be really a 100K lin like printed on the back panel?

I want to make a small utility box to interface easily the line in/outs and the switching/modulation stuff, using 6,35mm jacks instead of the DINs.

For the moment I have an original (but cheap) switch pedal which only changes the status of the phaser: auto/manual mode.
So I still don't understand if the pedal needs two switches, or if the "fast/slow" mode works in "auto" mode in addition to the expression pedal which could allow to sweep the rate from fast to slow..?

Also please could someone repost the redrawn schematics?

Thanks in advance.

I can post pictures of mine if you like, it's a BCxx version, and the input & output jacks have already been repaired (holes have been drilled to mount replacement jacks slightly upper than the originals).

Cheers.

[moosapotamus]

Since I built Jeurgen's version, I never bothered to go back and verify my old redrawn schematics. So there may be errors.

SCP'A' Audio Signal Path
SCP'A' LFO Section
SCP'A' Power Supply

I strongly recommend that you compare them against the original schematic to see how they might differ.
http://www.tasteundtechnik.de/bilder/compactphasing.jpg

Also, you can find schematics (and a lot more info) for Jeurgen's version here...
http://www.jhaible.de/compact_clone/compact_clone.html

I can't offer any info about the expression pedal, but hope you might find the documentation helpful.

Cheers,
~ Charlie

[mph]

Thank you very much Charlie.

This very helpful 

[mph]

Hi

I've finished the interface box for the Compact Phasing.
So it has two spst switches and a pair of jacks for the modulation DIN, and 3 jacks for the line in & outs DIN.
Everything works like a charm but I have not managed to find a good place to link the 4th pin of the 6 pin DIN connector (as you can see on my schematic I left it unconnected):



If pin 4 is connected to pin 6 or pin 3 it reduces a bit the depth of the LFO, but that's not better with or without this connection. Any idea?

On my original on/manual switch the pins 3&4 are linked together and pins 1&2 too; but this pedal only uses one switch and does not allow for fast/slow or expression pedal connection.

Note that you'll need a 7 wire cable because there is the ground on the seventh wire (the other cable to connect the line in/out DIN plug can be a standard 5 pin midi cable).

The expression pedal trick is ok with a simple volume pedal VPJunior from Ernie Ball (which has a 250K log pot, but I had to change the setting of the internal curve switch to make it usable with the CP1).

Thanks again for your help!

[automa]

Sorry for the zombie thread resuscitation but I thought it makes sense to post questions within it to avoid people pointing me to this.

I have a Schulte Compact Phasing A which was modified a while ago to compensate for the fact that the original pedal was missing. It had a 100k B poti added as per backpanel schematic to simulate the expression pedal and a switch which strangely enough was closing a contact between pin 5 of the switch DIN socket and a ground somewhere else on the PCB (not pin 6 as stated in the diagram on the back of the unit). It was working but I always found irritating that i have to pick a corner freq with the pot and there's no thing like a default freq as I would image it has if operated with no expression pedal. Also despite sounding good I always thought it's not working properly.
It seems like with the old mod I could only dial up limited settings compared to what I heard from youtube demos.

I want to restore the unit to it's original state (and build a switch/expression breakout box - i like the schematic above and will test it tonite) and have started doing so but I am having problems understanding the schematic and the unit (good starting point uh?).

My questions:
Does anyone have the original switch to find out following things:
- which pins are being shorted upon switching
- how many switch positions are possible on the original switch (i guess only 2 on/off but I am wondering how to switch on/off and slow/fast with just that)
- is there any resistors in the DIN plug of the switch to simulate the expression pedal across pins 1,2 and 3
what I don't understand here: if I remove the poti and switch mod from the circuit the unit is non functional.
- I re-attached the dip switch to bridge pin 5 and 6 but like that the unit is also not working 100%, only giving a very faint sound
on the other hand the switch now toggles the speed as opposes to the on/off it used to do.

How confusing. I would really appreciate any help here.

[automa]

Update: I made some progress by bridging pins 1 and + 3 and 4 as stated by the previous poster but I am still trying to understand the diode connecting 3 with 2 and what that is continuing to pin 1. There was no sign of that on the PCB so I am guessing that is intended to happen in the original footswitch. What I found on the PCB was two points intended for soldering a jumper between connect pins 1 and 2. I tried the diode between 3 and 2 but that just turned off the phasing. It's a part of the schematic that is really unclear. I will try some more when I get the chance to. So far I have been able to replace the old on/off switch from the mod with a 3 way on/on/on switch which allows me to switch between manual and auto (LFO) and fast/slow. In my version of the schematic (a reasonable quality PDF fom the original manual) it's a bit easier to see that the switching happens between pin 5 and 6 (fast slow) and 5 to ground to switch the LFO off (if 6 is connected to 5 it then also goes to ground). It sounds pretty cool already but I have a suspicion that this is not the final answer. When I was trying contacts I had one combination that whenever I was touching a pin of the DIN switch for a very brief moment I would get superdeep sweeps that made the unit almost sound Uni-Vibe-ish. Honestly it was late at night and I didn't make notes so I will have to get more systematic to find out what causes that effect. But if someone can help me decypher that part of the schematic it would be greatly appreciated. I will translate the original manual from german to english in a near future and post a link to it, as it has some very useful infos about the concept of the controls and it's use and some good setting presets recommended by the manufacturer. Anyway as it is now it already sounds great and it finally usable but I suspect there's more to find out about the original footswitch. Also mine has a pretty lenient feedback control as in the manual it states that any feedback over 7 begins self-oscillation and mine does that past 9. Maybe someone has tinkered with the 50k trimmer labeld f min which I guess controls the feedback.



Little side note: the unit was given to me for free as the previous owner (a Tangerine Dream keyboarder from their 80s era) didn't want it anymore. So it's actually a true Krautrock Phaser in the literal meaning. And it's orange which seems to be the rarer kind.

[tubegeek]

Little side note: the unit was given to me for free as the previous owner (a Tangerine Dream keyboarder from their 80s era) didn't want it anymore. So it's actually a true Krautrock Phaser in the literal meaning. And it's orange which seems to be the rarer kind.

Unfortunately I don't have anything to add except: 1) it's Tangerine, not orange, of course, and 2) Cool!

[VintageGear]

Totally bumping an ancient thread here, but guess what I acquired... a broken Schulte Compact Phasing 'A', including footswitch. Although, the footswitch looks home made, it is just a switch in a plastic enclosure. Currently it's not working, so I can't verify what the switch would do. I will report and take some pictures once it is up and running again.
The voltages are off; +16V is there, but the -16V rail reads somewhere around +3v. My best guess would be that its the 830CE voltage regulator, but the ones I found were for sale in USA for $7 each (ex shipping). I am hesitant to put those in, as an electrolytic capacitor exploded just now (temporarily replaced all the orange ones to ensure these weren't leaking and causing the problem). Gonna put them back in for originality later on!
I just purchased a couple of 7815 for 1 $ off eBay.
What do you guys think; drop-in replacements (minding the pin-out)

[ElectricDruid]

I think you'd do ok with 7815 as a replacement. The inclusion of the "optional" diode suggests to me that the regulation of the originals might have been a bit hopeless, so the extra diode lets you shift the voltage up or down by 0.6V to get it closer to whatever the other regulator was doing. I haven't checked the 830CE data sheet though, so that's speculation.

I'd definitely replace power supply electrolytics *if it's not too difficult to do so*. Anything original will be old and dry by now and probably a long way out of spec. That said, if the board or tracks are fragile and it's still working, don't mess with it - it's not worth risking more damage.

I love the note on the schematic about "selected" 741's too. Wow. Those were the days.

HTH,
Tom

[VintageGear]

Update: Placed a 7815 in, but no cigar, meaning that the obsolete 830ce was probably not broken (yeah).
Did leave me wondering though; why isn't it powering up. After switching over the bridge rectifiers (+16 was fine, -16 wasn't, and figured it might be due to a borderline rectifier). It suddenly worked again: LED came on. So I figure it was a bad solder joint although I did resolder it beforehand. Oh well.
Sound passes through, although it is not phasing. Using my audioprobe I lose the signal at the output of IC2. I don't see any voltage fluctuations either, so probably a bad LFO.
Tomorrow's another day.

Oh. And don't place your hand over the exposed leads around the 230v transformer. That tickle woke me up. 

[VintageGear]

Summarizing the results I found: 1) Cracked solderjoints all around. 2) IC2 was defective. 3) One light bulb was burned out so the other one didn't work either 4) Switch was faulty and badly connected inside. 5) Dried up capacitors. 6) Pots were scratchy.
And ensure the footswitch is plugged in, else it won't start oscillating.

Hope this helps someone. I am off playing some krautrock!!! 

[ElectricDruid]

So pretty scrambled all over then?! But also nothing that unusual - just multiple faults on an old pedal.

Well done for getting it sorted. Not easy on these ancient items, especially when you're trying to debug half a dozen things at once! 

T.

PS: Watch those mains voltages. You only get nine lives, and sometimes you don't even get those. I think I'm on about six, but I'm not pushing my luck any longer...

[t_tangent]

I realise this is an old thread, but I thought the following info might be useful. I was recently repairing my Schulte Compact Phasing A which after a reflow of some cold solder joints is now working properly once more.

When I bought the unit some years back it only came with a small 6 pin DIN plug with pin 1 & 2 and pin 3 & 4 shorted together. So while I had the unit on the worktop I wanted to build a Control pedal for it similar to the one made by Coopersonics for SoundGas in UK, which has LFO Run/Stop footswitch, LFO Fast/Slow footswitch, LFO Speed pot and Manual (Center Frequency Offset) pot.

After reading this very useful thread along with a few other forum posts on the web I was able to build a similar control pedal, so thanks for the helpful posts. Referring to the last few posts by mph and by automa, I also stuggled to understand where to connect pin 4. On the back of the CPA there is a diagram which shows connecting pin 1 & 3 to each end of an A100K pot and the wiper connects to pin 2. But when I tried this I notice the full range of the phasing sweep seems to be reduced even when the Phasing/Amplitude pot on the CPA is at or close to 10. After some experimenting I found that if pin 1 & 2 are shorted and then pin 3 is connected to one end of a pot & pin 4 to the wiper, this acts as the Manual Center Frequency Offset pot. This works perfectly at every setting.

So for example if you want a full phase slow sweep, set CPA as follows

Osc Period 3
Phasing/Amplitude 8-10

then on the Control pedal set the Manual Offset pot to 0 (which in effect shorts pin 3 & 4)

Then if you want to reduce the depth of the LFO sweep, on CPA turn Phasing/Amplitude pot down to 2. This will also lower the frequency of the phasing, so if you want to target a specific frequency bandwidth, on the Control pedal turn up the Manual Offset and adjust to suit.

Unfortunately by the time I had figured this out I had already drilled the holes for the pots on the top of the Control pedal, so I just added a B25K pot to connect pin 1 to one end and pin 2 to the wiper, and just keep that fully down so those pins are effectively shorted just like on the other 6 pin DIN that came with the CPA, so please just ignore that pot.

All other pots and switches seem to work as expected, so thought I would share my findings here in case its of help to anyone else wanting to build their own control pedal box.

I have attached a simple diagram rather than a schematic, unless anyone wants that. Also please feel free to correct any errors and I am open to any improvements.