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Old EMF VC LFO and a Wasp VCF question
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wackelpeter



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PostPosted: Wed Aug 10, 2016 10:02 am    Post subject: Old EMF VC LFO and a Wasp VCF question Reply with quote  Mark this post and the followings unread

It's been a while since i last touched a soldering iron, but after messing around with my previous builds i decided to improve the performance of some of my builds and getting rid of unwanted side effects or smaller issues i already knew and ignored until now or those i recently discovered or that occured within last time.

In one of my boxes... the one with the smallest PSU i have the stripboard of the old EMF VC LFO. It works fine but i have some issues with it consuming maybe a little bit too much current and therefore having effect on the voltage of my PSU which drops within 0,06 Volts up and down depending on the rate of the lfo...
Current measuring directly after the PSU was 213 to 233mA within a cycle.
A while back i changed all LED's to low current ones and increased the resistors for them so much that i have lovely 1-2 mA or less at each blinking light...
but here the voltage drops seem to come from the circuit itself and not the LED as it appears even with disconnected LED.
Luckily i have no VCO's in this box but 2 VCF's where you can hear these Voltage drops when in self oscillating mode and a little bit less when filtering some sounds...

tried to solve the problem with some higher value caps at the power rails for the VC LFO (changed from 10uF to 47uF) but nothing changes...

also tried some higher caps 1000uF momentary placed directly after the power bus... same as before...

does anybody know what is the suspicious current sucker (roughly 20mA per cycle) in this circuit and how i could tweak it for some better behaviour?

Well i could change my PSU to a better one and maybe will do this some time when this currently used PSU goes into a smaller circuit/box...

The circuit documentation can be found here:
http://www.modular.fonik.de/Page37.html
It's the LFO 5A... i have build the LFO part only... but with some minor mods... have an inverted version of the square and saw waveform and an sinusoid wave output via a FET 2n3819 via this method mentioned By Tim Stinchcombe (Middlebrook & Richer JFET-based method) seen here:
http://www.timstinchcombe.co.uk/forums.html?pge=trisin

Nearly forgot my initial Wasp VCF Question...
Is this normal that the BP output is much higher as all the 3 other (HP,LP,AP) outputs? Also this circuit seems to be very sensitive to the audio input level... especially when switching between the different modes of the VCF... any suggestions how to handle this properly... i only have an attentuating pot on the input signal...

Any tips, hints and infos are welcome.

cheers Bastian

P.S. also tried if a 7812 directly at the power rails of the circuit would reduce the problem... nada... stays the same via my not so decent ears...

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JovianPyx



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PostPosted: Sat Aug 20, 2016 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

I can't help with the WASP filter, but the EFM stuff almost always had schematic errors and Tom Gamble (EFM guy) released "corrected" schematics all over the internet. He'd shut down sites (really, just stopped maintaining them) and start new ones and it was often not apparent which docs were the most recent and whether they were truly correct. Even some of the corrected docs had other different errors in them. I personally helped someone with an EFM ADSR design that had rather blatent schematic errors. Unfortunately, the only way I could troubleshoot the design would be to build it and scope it, but I'm not set up to do that kind of stuff anymore. It's possible more up to date docs can be found - but I've no idea where.
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wackelpeter



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PostPosted: Sat Aug 20, 2016 11:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for your reply. Well i'm not 100% sure if the schematics are correct, it's from Fonik's site wiht all the collected schematics of the old EFM forum.
But it worked from start the only thing it's a bit too thirsty after current...
I think i will run a simulation of this and see if i can find some way to improve it or not...

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AlanP



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PostPosted: Tue Aug 23, 2016 11:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

If it's the one with BAT85 diodes as input protection that Fonik released, I can confirm the schematic itself is correct -- I did a layout based on it.
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wackelpeter



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PostPosted: Wed Aug 24, 2016 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

AlanP wrote:
If it's the one with BAT85 diodes as input protection that Fonik released, I can confirm the schematic itself is correct -- I did a layout based on it.


took a bit to understand what you meant... you responded to the WASP VCF, correct?

If so can you detect significant changes in output volume when switching through the modes? I wasn't sure if some 1% resistors at the divider on the input of the OTA's would improve the whole thing and changed them, without any noticeable changes to my ears... One of the suspicious parts could be the 4069 IC... my brand is HCF4069UBE from SGS-Thomson...

maybe should try some other brand from another seller, as my retail seller only carrys this brand...

At least it's not the schematics for the WASP Clone that are incorrect as i have some of the schematics availbale all around (J.Haible;original schemo, Fonik's redrawn version and even Ken Stones) compared and everything looks nice and correct

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