Negativespace CVP issues.

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mousegarden
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Negativespace CVP issues.

Post by mousegarden » Sun Aug 04, 2019 4:05 am

I've got my boat and I've installed he CVP, however, I'm having big problems keeping voltages positive when using them with 200e modules, I find I can't actually use it as a true attenuator, which is why I bought it, as it's impossible to achieve full attenuation without going negative.
Any ideas about how I can work around this much appreciated.

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Post by tarandfeathers » Sun Aug 04, 2019 9:52 am

I don't see what you can do without modifications to the module. Wouldn't you be better off selling it and replacing it with a 256e or 257e if you want everything to be e-safe?
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Post by mousegarden » Wed Aug 07, 2019 12:47 pm

tarandfeathers wrote:I don't see what you can do without modifications to the module. Wouldn't you be better off selling it and replacing it with a 256e or 257e if you want everything to be e-safe?
Yes, I'm going to sell it, this has been a learning curve, lack of support on the CVP too, non existent as far as I can see.

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Post by Pailo » Wed Aug 07, 2019 7:15 pm

soldering a diode between two jacks is easy, and i do it on my
blade adapters to avoid the negative on my e modules from 1/8" to banana.

its really easy and cheap. Schottky Diodes can be used as a rectifier.
i can take a picture later but its a easy fix. Buying new Buchla modules are
expensive. Some of the e ones i have have problems too. For the money
it maybe better to save the CVP for cost sake.

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Post by mousegarden » Thu Aug 08, 2019 2:48 am

Pailo wrote:soldering a diode between two jacks is easy, and i do it on my
blade adapters to avoid the negative on my e modules from 1/8" to banana.

its really easy and cheap. Schottky Diodes can be used as a rectifier.
i can take a picture later but its a easy fix. Buying new Buchla modules are
expensive. Some of the e ones i have have problems too. For the money
it maybe better to save the CVP for cost sake.
I'd be very grateful if you could post a picture of this, I can then decide if I can do it or not. Many thanks!

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Post by Pailo » Thu Aug 08, 2019 11:19 am

Its a "passive way" to block negative voltages.
When it gets late at night I plug in the 2 modulars
I didn't want to think about Eurorack CV stuff hurting the e
modules. I believe the FM inputs are AC, just not the
banana or CV on the Buchla.

1n4733 are the zener ones I used, but someone with a better
engineering background may want to chime in to explain a bit :hmm:

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Post by Ginko » Thu Aug 08, 2019 12:51 pm

Pailo wrote:Its a "passive way" to block negative voltages.
When it gets late at night I plug in the 2 modulars
I didn't want to think about Eurorack CV stuff hurting the e
modules. I believe the FM inputs are AC, just not the
banana or CV on the Buchla.

1n4733 are the zener ones I used, but someone with a better
engineering background may want to chime in to explain a bit :hmm:

Image
What you are suggesting is fine, just be aware that a diode in series with the signal e.g.

SIG OUTPUT >> ++DIODE-- >> SIG INPUT

will cause a small voltage drop - the 'diode' drop, not the end of the world and certainly a quick fix.

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Post by mousegarden » Fri Aug 09, 2019 3:19 am

Thanks folks, I just need to correct the CV outputs on the CVP, I'm a bit confused, the Moog style CVP mixer? is that still a danger to use with audio on E series modules? Also, the CVP has two banana outputs on the attenuation channels, a blue one which is positive I think, and a grey one, which is negative...."I think" So, surely, if I just use the blue output, that should be positive only, surely? The lack of documentation, and support is TBQH, very amusing!

:confused:

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Post by Pailo » Fri Aug 09, 2019 10:03 am

Im confused. What CVP module are you using?
Who makes it? Is there a picture on modular grid?

Remember on Buchla 200e that TT jacks are AC and
Banana jacks are DC so you should not be able to hurt any
audio jack on a 200e with negative voltages, its only
the banana jacks I would worry about. Not the Audio jacks.

Grey should mean CV Input on Buchla if you go by the manual

https://buchla.com/guides/200e_Users_Guide_v1.4.pdf
PG 4 list what jack colors should represent.

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Post by tarandfeathers » Fri Aug 09, 2019 11:41 am

I am assuming it is a 4U build of the CVP DIY boards done by forum user negativspace, which are now sold under the name Manhattan Analogue. As far as I can remember these were a layout based on something else and were sort of supposed to mimic the function of a 256, without mixing but with the option of slew. I don't remember them being anything to do with a Moog design? Presumably a 4U panel was done as a group buy or built by an individual. If any support is expected it should probably be from whoever built/sold you the module, which I don't think was negativspace/Manhattan Analogue.

If it is in fact the same CVP project the schematics are available so I don't know what further support would be expected for a DIY project that is apparently working as intended.

Edit: the original thread about these boards - viewtopic.php?p=463573

If it has inverted and non inverted outputs it looks like these are done with an extra CGS PCB, I guess both outputs are capable of going positive and negative, depending on the polarity of the input.

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Post by Pailo » Fri Aug 09, 2019 2:15 pm

I would not use this for voltage going to a buchla without that
diode between the 1/8' jack and the banana. That module is wild west
style cause it was designed by one dude modded by another etc...
that's cool and all but.... the 200e did not have negative voltages in mind.

Plus the Minus on the panel indicated negative voltage, and after
reading negative space said you can put the voltage wherever.

That is very different from say a 257, because the 257 inverts the voltage.
It never puts the voltage into a negative place.

So if you are looking for a 4u processor
building the 257r is cost effective and
will not harm your 200e stuff. That CVP is
made with eurorack or dot com in mind....
Surprises me people made buchla versions
but they could have put a diode on the
output to make sure of that.

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Post by cygmu » Fri Aug 09, 2019 2:44 pm

Pailo wrote: That is very different from say a 257, because the 257 inverts the voltage.
It never puts the voltage into a negative place.

So if you are looking for a 4u processor
building the 257r is cost effective and
will not harm your 200e stuff.
The 257r definitely puts out negative voltages when used in inverting mode.

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Post by Pailo » Fri Aug 09, 2019 4:29 pm

Yea I just went and scoped everything and you are right cygmu...
Damn I guess I could have hurt my e modules.

Never mind the 257r...

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Post by cygmu » Fri Aug 09, 2019 4:53 pm

It's a bit odd, because Don Buchla himself wrote:
Signal, control voltage and pulse levels are another aspect of compatibility. Once again, our last revision was in 1970 — all 200 modules, including 200e versions, have followed suit. My conclusion is that the 200e series modules maintain their intended compatibility with their predecessors
in his response to the Sound On Sound review of the 200e in 2006.

https://www.soundonsound.com/people/cro ... la-replies

"Intended compatibility" and "turning the knob too far to the left will destroy your module" are not very consistent.

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Post by Pailo » Fri Aug 09, 2019 8:58 pm

My 254v also puts out negative voltage.
Now I’m hella confused....

Wild West I tell ya. Glad we are all talking about it.
I use a rigol and it’s no lie. 254v and 257r are putting out negative voltages.
Guess I’ve been lucky not to hurt anything.

Lesson learned today and thank you all for the help.
Gonna keep the scope on and learn a lot more.
Still not gonna feed 200e negative voltage
But with offset I understand why......

Here is that pic of my blade.

Image

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Post by mousegarden » Mon Aug 12, 2019 4:15 am

Hi, here is my module...

Image

As you can see, there are blue and purple CV output jacks, I'm wondering, does the blue only output a pos voltage? and the purple just neg. or does pos/neg come out of both?

:hmm:

I'm selling it anyway, it's just too risky, and information about it is so varied.

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Post by tarandfeathers » Mon Aug 12, 2019 5:46 am

According to this post:

viewtopic.php?p=962656#962656

From the thread I linked above, that is one of the RSFC panels designed for the negativspace PCBs, and if built as intended the two outputs are simply multiples, the black jacks are inputs and the grey jacks are a buffered copy of that input. The different colours are purely aesthetic and the grey jack is not in keeping with the standard Buchla colours.

The CVP boards were designed for Euro systems but it seems lots of people made different front panels for them. If you are not capable or do not have the equipment to test whether the outputs are identical you would need to contact the builder of the module for clarification.
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Post by mousegarden » Tue Aug 13, 2019 4:54 am

tarandfeathers wrote:According to this post:

viewtopic.php?p=962656#962656

From the thread I linked above, that is one of the RSFC panels designed for the negativspace PCBs, and if built as intended the two outputs are simply multiples, the black jacks are inputs and the grey jacks are a buffered copy of that input. The different colours are purely aesthetic and the grey jack is not in keeping with the standard Buchla colours.

The CVP boards were designed for Euro systems but it seems lots of people made different front panels for them. If you are not capable or do not have the equipment to test whether the outputs are identical you would need to contact the builder of the module for clarification.
Yeeeees! Trouble is, I don't know who built it?

:hmm:

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Post by tIB » Tue Aug 13, 2019 5:18 am

I thought I'd covered all this via PM, apologies if not-

I commissioned it.
Negativespace built it to the specs I asked for at the time.
The lower most out is most likely negative (or the main out inverted) - check it using the feedback on the module or with a meter.
The audio out on the mixer is most likely attenuverting - see above.
It can be made 'safe' using the fox above.
I used it (without knowing of any negative voltage issues) for a couple of years at least without killing my 200e system.

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Post by Pailo » Tue Aug 13, 2019 11:26 am

yea I have been in the Buchla world for almost 4 years and
haven't hurt anything with the 254v and 257r.

they have both been used with 261e, 285e and 266e with no issues.

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Post by monokinetic » Tue Aug 13, 2019 2:15 pm

FWIW I built one using Negativspace's boards and an RSFC panel from the run back in the day. I hooked up the bottom output of each channel to the inverted out on the PCB. So sticking a 0 to +10V 281 envelope CV out in comes out as a 0 to -10V copy. It has it's uses (modulating an oscillating 291j for example!). I don't run any 200e stuff so haven't needed to worry about negative CVs in my clone system.... Personally I've always found it a pretty useful module, apart from the lag which I always thought was pretty subtle.

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Post by Drillionaire » Tue Aug 13, 2019 3:12 pm

The circuit described above with the diode between the 3.5mm and banana will indeed work, but you are going to get a diode drop across it, reducing your voltage by around .7v for a regular diode, and around .2v for a schottky diode.

If you build it the way the blade adapters are done, i.e., with the schottky diode anode to ground, and the cathode to the tip connection on the 3.5mm jack/banana jack, it will shunt all negative voltages to ground, save for a diode drop, about -.2v, which is typically within the safe absolute maximums for single-supply devices.

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Post by mousegarden » Wed Aug 14, 2019 2:40 am

tIB wrote:I thought I'd covered all this via PM, apologies if not-

I commissioned it.
Negativespace built it to the specs I asked for at the time.
The lower most out is most likely negative (or the main out inverted) - check it using the feedback on the module or with a meter.
The audio out on the mixer is most likely attenuverting - see above.
It can be made 'safe' using the fox above.
I used it (without knowing of any negative voltage issues) for a couple of years at least without killing my 200e system.
Yes, thanks tIB, I'm just not very up on all this.
I did check the outputs of each channel, they seemed to be just duplicates, the blue and purple, not inverted.
I would be using the mixer for audio, straight into my main mixer, mixing my Easel and the new boat. I don't think there's any danger in this.
One thing bothers me, it's impossible to achieve full attenuation, which is why I bought it, I tried feeding the output into another channel to attenuate it even more, but the more you attenuate the more negative voltage you get, until the light goes completely green.

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Post by tIB » Wed Aug 14, 2019 10:17 am

If you mod it with that diode though you will be able to get full attention. I'm by no means an expert but I'd take a hack at it for price of post, parts and a pint or two!

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Post by batchas » Wed Aug 14, 2019 2:54 pm

I saw a FS post by Adam and didn't even know the studio-h modules so after a very long time not visiting this part of the forum, I'm checking some posts quickly.
And I see yours.
First, you say "the more you attenuate the more negative voltage you get, until the light goes completely green". I don't understand this. What kind of signal are you trying to attenuate exactly?
The more you attenuate should be going CCW, meaning in the negative direction, meaning the LED goes red...

Anyway, an easy workaround for the full attenuation you want to achieve: when you turn the LEVEL pot for attenuation and you reach the minimum setting you can get at 12 o'clock (before your signal goes negative), you could turn at the same time a bit the LAG pot CW (like if it was for instance on 9 o'clock), then the signal will go to 0. Full attenuation.
It will impact the shape of your incoming signal, but as it full attenuated, it doesn't matter anyway as the level is 0.
You just need to put LAG back to zero (full CCW) when you turn the LEVEL up again.

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