Old Space Filter WIP thrown open

[StephenGiles]

https://www.dropbox.com/s/lu5q1cvudlj8aew/Space%20Filter.jpg

I found this lurking on an old backup CD this morning, so if anyone cares to move it forward - as they say, please feel free as I seem to have no breadboards to hand at the moment.

You will recognise the EH Space Drum sweep generator, but using LM13600 which is still available at the moment. I wonder if the SSM 2164 could be made to work here?        

Very rough circuit description - borrowed from Space Drum circuit description:

IC1a amplifies the incoming guitar signal and its output is sent to the VCF, formed around IC3a/b. IC1a output is also buffered and further amplified by IC1b, the gain of which is selected by the Sensitivity control. The voltage at IC1b output should be converted by Ra into a current suitable for triggering the Sweep Generator.

The sweep generator is formed by IC2a, IC1c and their associated components. With the system at rest, no current flows through Ra into IC2a pin 1. This results in the transconductance amplifier portion of IC2a being effectively disconnected from its darlington emitter follower output stage - IC2b, hence the voltage at IC2b pin 8 follows pin 5, which is at the voltage set by the Stop Frequency pot and buffered by IC1c, When a note is plucked on the guitar, the voltage at the output of IC1b is proportional to the strength of the note played (important because this is to determine the range of the sweep), converted into a current by Ra, energising IC2a via it's pin 1, turning it into a voltage follower, forcing IC2b pin 8 to equal the IC2a pin 3 voltage, set by the Start Frequency pot. (that is what happens when the Space Drum is struck).

Soon after each note is plucked, current  into IC2a pin 1 ceases to flow however, and the voltage on IC2a pin 5 decays through the Sweep Rate CR network to the voltage set by the Stop Frequency control, at a rate set by the Sweep Rate control - should be independent of the natural decay of the note played, providing a filter sweep no jitter even at long sweep settings.

[armdnrdy]

Hey Stephen,

Thanks for posting this.

A couple of questions. Is this circuit 9 volts like the space drum?

And, I see VB on the schematic but didn't notice an origin, so I would imagine a couple of resistors to suit it's need?

Also, I see a resistor marked RA and one with a question mark. Any clues as to values?

[Kipper4]

Thanks for sharing Stephen.
I like it.
A few questions.
Yes I too am interested in Ra. I'd be tempted to put a 1k in there for a start and probably work down from there. Just guessing.
What is the function of the 100k pot at top of the design after Ic3 b?

[nocentelli]

What is the function of the 100k pot at top of the design after Ic3 b?

Resonance?

[Kipper4]

Thanks Leo.

[noisette]

Definitly resonance...

But why the gain in IC1a, since the OTA needs lots of attenuation anyway?
The fourth OTA feels so useless

On second note it´s an interesting looking variety of feedback paths.
Output a 1 Pole LP? They DO sound good with resonance...

[StephenGiles]

Just got back from seeing "Noah" - we saw the fim as Ray Winstone fans and he was his usual good self! As to the film itself, well I think the director is stark raving bonkers!

Now, the 100k pot at the top I'm pretty sure is resonance.

Yes Larry, 9v is correct with a couple of resistors giving Vb, but would there be any advantage in using a higher voltage?

Gain in IC1a is to ensure the sweep generator is energised. Would it be better to utilise IC1d which is currently unused to buffer the input, then send it's output to both the VCF and IC1b?

Ra was 20k in the Space Drum, I don't know what it would be in the LM 13600 configuration,

[Scruffie]

You could just divide down the input pre OTA and then use the spare opamp for gain recovery at the end of the circuit providing a nice output impedance at the same time.

You could use the Darlington in the spare OTA half to buffer the V.Ref... so it's a little less wasted 

[Lurco]

Is this remotely related? http://www.diystompboxes.com/smfforum/index.php?topic=37931.0

[StephenGiles]

Is this remotely related? http://www.diystompboxes.com/smfforum/index.php?topic=37931.0

Crickey, I forgot that one dragged on so long, but it died a death with no conclusion. 

I've updated the circuit description slightly in post #1. I omitted an important point in 5th paragraph.

If I get time today, I'll try to locate my breadboads and put some parts in holes.

[deadastronaut]

Cool, i,d like to hear a clip of this if you get it breaded...

[StephenGiles]

Cool, i,d like to hear a clip of this if you get it breaded...

I'm hoping that some of the technical minds here will do that as well!

[StephenGiles]

And if I might be permitted to throw in a little "Viv Stanshall" here  - if you are cross eyed - when crossing the road, look straight ahead, then straight ahead and straight ahead again!!

[StephenGiles]

https://www.dropbox.com/s/h3cgr06lz7c977r/Space%20Filter%20ver%202.png

Circuit updated to Version 2 incorporating various suggestions.

[puretube]

https://www.dropbox.com/s/h3cgr06lz7c977r/Space%20Filter%20ver%202.png

Circuit updated to Version 2 incorporating various suggestions.

Stephen, you don`t attenuate the output of IC1d anymore before going into IC3a? (e.g. with a 22k...) 

[StephenGiles]

https://www.dropbox.com/s/h3cgr06lz7c977r/Space%20Filter%20ver%202.png

Circuit updated to Version 2 incorporating various suggestions.

Stephen, you don`t attenuate the output of IC1d anymore before going into IC3a? (e.g. with a 22k...) 

Oops thanks for that - copy & paste gone wrong!!

https://www.dropbox.com/s/5ffoimb5uefgux1/Space%20Filter%20ver%203.png

[StephenGiles]

Celebrations - I just found a very dusty large breadboard on top of least played CDs stored on the top shelf in our music room, just 3 inches from the ceiling! That is why I have not been able to find them for months!

There are 2 very lonely ICs in it - LM13600 and LM324!!! Crickey, I'm sneezing for all the dust in this thing!

[StephenGiles]

Is SSM 2164 quad VCA available? Don't want to waste time if it's not.

[Lurco]

Is SSM 2164 quad VCA available? Don't want to waste time if it's not.

No - obsolete/discontinued.

But: http://www.coolaudio.com/docs/datasheet/V2164MD_DATASHEET.pdf by Behringer: http://www.coolaudio.com/index.html
available here: http://www.mammothelectronics.com/Coolaudio-V2164D-Quad-Voltage-Controlled-Amplifier-p/400-1034.htm  and  http://uk-electronic.de/onlineshop/product_info.php?products_id=1267  and  http://synthengineering.co.uk/products/coolaudio-v2164d-quad-vca 

Dual VCA: http://www.coolaudio.com/docs/datasheet/DATA_V2162%20Specs_2011-12-06.pdf  compare: http://www.thatcorp.com/THAT_Alternatives_to_SSM2164.shtml

[nocentelli]

https://www.dropbox.com/s/5ffoimb5uefgux1/Space%20Filter%20ver%203.png

Finally found a second 13700 in my dead veroboard pile, going to try this out tonight.