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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Fri Sep 27, 2019 8:23 pm Post subject:
Euro 258 Dual Oscillator clone |
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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
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Posted: Mon Sep 30, 2019 11:25 pm Post subject:
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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 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Tue Oct 01, 2019 4:03 am Post subject:
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One turn, but if I do get worried about V/oct tracking, I can probably wedge some multi turns in somehow
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
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Posted: Tue Oct 01, 2019 5:39 am Post subject:
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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
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Posted: Tue Oct 01, 2019 7:10 pm Post subject:
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So cool!
As long as you add the footprints for standard trannies, all good |
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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Fri Oct 04, 2019 7:00 pm Post subject:
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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 Posts: 145 Location: Poland
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Posted: Sat Oct 05, 2019 11:42 am Post subject:
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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 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Sat Oct 05, 2019 6:10 pm Post subject:
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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 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Fri Nov 01, 2019 7:22 pm Post subject:
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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
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Posted: Sun Nov 03, 2019 1:38 pm Post subject:
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Looking Good
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.... |
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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Sun Nov 03, 2019 9:16 pm Post subject:
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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
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Posted: Tue Nov 26, 2019 3:39 am Post subject:
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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 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Tue Nov 26, 2019 8:35 am Post subject:
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Probably not, as the 259 really, really ramps up the complexity. |
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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Sat Jun 27, 2020 7:20 pm Post subject:
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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
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Posted: Tue Aug 11, 2020 1:09 am Post subject:
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Are you using solder wire with no clean flux? Just leave it, it is not RF equipment |
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