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CA3080 revived
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roglok



Joined: Aug 28, 2010
Posts: 159
Location: uptown

PostPosted: Sun Jan 19, 2014 12:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

new voodoo wrote:

But its always easier to say or imply something deleterious than attempt to see things frm another point of view...so why not imply im inventing an opinion from ignorance?


dude, what's your problem? i'm not telling you how to hear or think. i was merely surprised that you claim one device sounds better than another although the designer says they are the same.

if you can back up your claim via sound samples, scope shots or other objective criteria, i'd be interested in your findings.

if it's just a 'feeling' on your end, that's cool - just don't expect me to feel the same...
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synchroma



Joined: Oct 18, 2011
Posts: 69
Location: London

PostPosted: Sun Jan 19, 2014 4:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

roglok wrote:
dude, what's your problem? i'm not telling you how to hear or think. i was merely surprised that you claim one device sounds better than another although the designer says they are the same.


Chill roglok! This is like the filter debate (although one can definitely say there is a difference between a TB303 filter and a Moog diode ladder filter).

There probably is a difference in the electrical characteristics of the LM13700, since you have to take account of the capacitance of the linearizing diodes, and the choice of an op-amp for the buffer with the CA3080 will make a difference rather than the darlington used in the LM13700 - which does a good job but is "_different_"

(edit) hence the Wasp filter - a product of cheap necessity rather than design - uses CD4069UB logic inverters in an "off datasheet" linear mode.

This is not a matter of pride for me! I like the 3080, and it's a lot easier for me to make single-sided boards with them, which are cheaper to buy and etch. I'm also a fan of the LM13700 - I built a great VCO with it last year. But you use what you want to use and it's nice to have the choice.
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roglok



Joined: Aug 28, 2010
Posts: 159
Location: uptown

PostPosted: Sun Jan 19, 2014 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

synchroma wrote:

There probably is a difference in the electrical characteristics of the LM13700, since you have to take account of the capacitance of the linearizing diodes, and the choice of an op-amp for the buffer with the CA3080 will make a difference rather than the darlington used in the LM13700 - which does a good job but is "_different_"


i stand corrected. looking at the schematics in the datasheets it becomes apparent that there are indeed differences (not just the linearization diodes). however, the darlington buffer is not in the OTA signal path. it's an optional feature.

comparing the electrical characteristics i can't find any significant differences though... i'd really be interested in a proper comparison cyclops

Quote:
This is not a matter of pride for me! I like the 3080, and it's a lot easier for me to make single-sided boards with them, which are cheaper to buy and etch. I'm also a fan of the LM13700 - I built a great VCO with it last year. But you use what you want to use and it's nice to have the choice.


i'm not bashing the CA3080 at all. building lots of stuff on stripboard, i totally see where you are coming from - some parts are more convenient to use than others in a given project or layout... Very Happy
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synchroma



Joined: Oct 18, 2011
Posts: 69
Location: London

PostPosted: Thu Apr 03, 2014 5:21 pm    Post subject: CA3080 matching Reply with quote  Mark this post and the followings unread

I made a board design for matching characteristics of the CA3080, taken from the Elektron Formant Synthesizer manual - http://shop.textalk.se/shop/24074/art8/11805008-a50519-efms.pdf
Go to page 58 for the description...


Here are some files. All 600dpi except the schematic. Note that Top Copper is pretty useless since there's only two connections and you can make them from a piece of wire, so it's really a single-sided board. EDIT: There was a mistake on the previous version. This has been corrected now.

PS the new server is really fast! Thanks electro-music.com Smile


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Last edited by synchroma on Tue Apr 08, 2014 11:58 am; edited 2 times in total
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The Bad Producer



Joined: Mar 08, 2009
Posts: 255
Location: The Manhole

PostPosted: Sun Apr 06, 2014 2:37 am    Post subject: Reply with quote  Mark this post and the followings unread

That is really great synchroma, thanks for that!

I really love the Formant book, the graphics especially, but I've only ever found a french copy (I sort of had to learn french to read it!) and must have missed this bit...

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synchroma



Joined: Oct 18, 2011
Posts: 69
Location: London

PostPosted: Sat May 31, 2014 6:01 pm    Post subject: CA3080 improved matching circuit Reply with quote  Mark this post and the followings unread

I recently built a clone of the filter in the Roland SH-7 using my Rochester Electronics CA3080AE chips. The result was quite disappointing since the resonance only worked at high frequencies. I recognize that I probably need to use metal film resistors throughout and match all of the components. Bummer! But I only matched the CA3080s for gain (circuit above) and not for tracking.

The circuit I posted earlier is a pain to check the tracking of the OTA, so here is another circuit that makes it easier, and has a 1KHz test tone built in singing

You can fit a SPDT switch between the test tone and the CA3080 test circuit (with the other pole of the switch connected to GND) to measure Voffset with no input signal.

Calibrate each current stage by connecting an ammeter between 4PSW1 to 4 and CAL2, with a CA3080 in the circuit. Then connect a jumper wire between the central pole of the 4-pole switch and the CAL2 connection (see the board legend, below) once all currents are calibrated.

Also, adjust POT1 until the peak-to-peak voltage at CAL1 is 2Vpp.

Use arduino 4-pole stackable headers for the CA3080, so that the devices can be inserted into the circuit with plastic tweezers (they are temperature-sensitive).

I haven't made this yet, but I'm confident it's correct. Next time I get into my etching lab I'll make a board, and report back as to the results.

There are only 4 straight jumpers on the top copper side, so this is fine as a single-sided board with jumpers.

600DPI images. Legend: Bottom copper is green, top copper is pink.
BTW, the other part of the SH7 filter is an SH7 ADSR. So far I got an ASR. Still working on it...

JP5 is test point for the CA3080


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