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Euro 258 Dual Oscillator clone
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AlanP



Joined: Mar 11, 2014
Posts: 746
Location: New Zealand
Audio files: 41

PostPosted: Fri Sep 27, 2019 8:23 pm    Post subject: Euro 258 Dual Oscillator clone Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

This is a clone of Buchla's 258 Dual Oscillator, with a saw side and a square side, both having Waveshape knobs to morph the waveform into a sine.

I'm working off Verbos' annotated copy of the schematics, hence the THAT340. I'm also using polystyrene timing caps.

Hope this works. It's currently at the "I need parts" stage.
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ixtern



Joined: Jun 25, 2018
Posts: 145
Location: Poland

PostPosted: Mon Sep 30, 2019 11:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Looks very nice. Are those trimpots one-turn or multiturn? If one-turn, it may be little hard to set correct V/Oct tracking.
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AlanP



Joined: Mar 11, 2014
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PostPosted: Tue Oct 01, 2019 4:03 am    Post subject: Reply with quote  Mark this post and the followings unread

One turn, but if I do get worried about V/oct tracking, I can probably wedge some multi turns in somehow Smile

The THAT340 chips were... excitingly expensive. If I do another revision of this (don't count on it unless there are major issues), I'll lay down some pads for BC5xx transistors as well.
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ixtern



Joined: Jun 25, 2018
Posts: 145
Location: Poland

PostPosted: Tue Oct 01, 2019 5:39 am    Post subject: Reply with quote  Mark this post and the followings unread

There are still CA3096 available (although they are not very good, so I've heard).
Also dual transistors like BC847DS (npn) or DMMT5401 (pnp) in SOT cases.
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MapacheRaper



Joined: Feb 15, 2018
Posts: 166
Location: Spain

PostPosted: Tue Oct 01, 2019 7:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

So cool!

As long as you add the footprints for standard trannies, all good
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AlanP



Joined: Mar 11, 2014
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Location: New Zealand
Audio files: 41

PostPosted: Fri Oct 04, 2019 7:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Rest of the parts turned up, and soldering ensued. (The THAT340 arrays are on the back of the engine pcb.)

Firstly, the range on this VCO is insane, just nuts. It can go from serious LFO territory, to mad kHz, depending on where you set the 'INITFREQ' trimmer on the back.

Secondly, I used a couple of random Jfets I had lying around for the sine circuit. I didn't bother to test for 0.8 to 1.1 Idss, and I think I should have, as the sine I'm getting looks nothing like a sine.

Edit -- removed the J112's I had in there, replaced with some SIL sockets on the back, and tried different Jfets until I got a nice sine. 2N5457 work very nicely (well, some 2N5457... FETs of all sort have insane variance.) Something weird is going on with the CV attenuverters, there is no 'off' spot on the knob.
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ixtern



Joined: Jun 25, 2018
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Location: Poland

PostPosted: Sat Oct 05, 2019 11:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Post your V/Oct tracking results of this VCO if you may. I am just working with 4046 TH VCO. Range is also insane but tracking is rather poor.
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AlanP



Joined: Mar 11, 2014
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PostPosted: Sat Oct 05, 2019 6:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Found the problem with the CV attenuverters. There was no deadspot in the middle, and there was also some CV bleedthrough between oscillators -- a CV signal into the left channel could affect the right, and vice versa.

The fix was really simple, and the cause was really embarassing.

Forgot power to the opamp doing that job. Two wires later, no issues left!

ixtern, I don't normally worry about tracking too much, but if I get around to it, I might do some measurements.
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AlanP



Joined: Mar 11, 2014
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PostPosted: Fri Nov 01, 2019 7:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Quite pleased with how it turned out. The THAT340 boards are verified, I'll solder up the transistor pair ones in a day or two and verify those.
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Ayab



Joined: Oct 27, 2015
Posts: 180
Location: London, UK

PostPosted: Sun Nov 03, 2019 1:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Looking Good Smile

Can you confirm if the continuous waveshapes CV controllable? Looks like there is a jack under the wave shape knob.

Are you thinking of selling the boards? So tempting.... Razz
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AlanP



Joined: Mar 11, 2014
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PostPosted: Sun Nov 03, 2019 9:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yep, CV controllable. The THAT340 boards are verified, the transistor-pair ones are not.
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LFLab



Joined: Dec 17, 2009
Posts: 497
Location: Rosmalen, Netherlands

PostPosted: Tue Nov 26, 2019 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

ixtern wrote:
There are still CA3096 available (although they are not very good, so I've heard).
Also dual transistors like BC847DS (npn) or DMMT5401 (pnp) in SOT cases.


BCM847DS (NPN)
BCM857DS (PNP)

"Matched" (They are no LM394's)
The "bs" suffix parts of these are insanely small, but the "ds" are juuusst manageable to hand solder (for me at least)

Nice work Alan! Are you also going to do the intermediate circuitry to make it into a 259?
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AlanP



Joined: Mar 11, 2014
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PostPosted: Tue Nov 26, 2019 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Probably not, as the 259 really, really ramps up the complexity.
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AlanP



Joined: Mar 11, 2014
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Location: New Zealand
Audio files: 41

PostPosted: Sat Jun 27, 2020 7:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Finally got these working, after a hell of a lot of troubleshooting that turned out to be bad SMD soldering on one of the matched transistor pairs.

For the waveshaper jFETs, I used mmbf5457, although mmbfj201 would probably also work well. These are SMD versions of the now discontinued 2N5457, and J201 parts. I included an option for through-hole versions of these and, on reflection, I should have done that for the SMD transistor pairs too, or looked harder for through-hole matched transistors that are still in production.

The caps are RS brand 4n7 polystyrene caps, intended for use in telecom applications. I thought they look dead spiffy here, and lucky me they had the right lead spacing.

I need to get a bottle of cleaning alcohol. The flux remover I used doesn't seem to get everything.
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LFLab



Joined: Dec 17, 2009
Posts: 497
Location: Rosmalen, Netherlands

PostPosted: Tue Aug 11, 2020 1:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Are you using solder wire with no clean flux? Just leave it, it is not RF equipment Very Happy
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