Looking for EHX mini-Synth schematic, NOT micro-synth

[igor12]

anybody where I might find one?  I'm talking about the membrane keyboard thing.  The filter section sounds really cool.  I would like to cop that for something.

[Scruffie]

I think I have a copy... it's not very clear though.

PM me your e-mail address, i'll get it to you as soon as I can unless someone else steps in first.

[nexekho]

Ha!  Just looked it up on YouTube very cute!

[deadastronaut]

^ yeah that is pretty cool.....

[artifus]

reminds me of a sinclair zx81

[nexekho]

If you send him that schematic can send me a copy too please?  I'm just interested to see some of the filters/etc.  Thanks.

[nexekho]

http://www.synthfool.com/docs/Other_Misc/EH400minisynth/
Never mind, found one.

[Scruffie]

http://www.synthfool.com/docs/Other_Misc/EH400minisynth/
Never mind, found one.

Nice! Same one I have but with the manual etc.

[Earthscum]

@nexekho: Good find! I've been looking for that as well. It is what Eddie VanHalen used in Sunday Afternoon in the Park. I learned it on the bass a long time ago, and thought it would be neat to see if I could shoot for something that actually sounds similar. I couldn't find much more than discussion about what modules it contained.

http://www.youtube.com/watch?v=ptbkH5p3s6o

I was kinda bummed at first to see that it is the OTA filter, but then I realized I'm just going to have to make another "mode" on my DOD Wah, since it's already OTA based. Looks, actually, like I could extract a couple different modes from it. Right now I have a choice between sweeping bandpass or 2-pole lowpass (SPDT difference between the two. Just depends where you take the output from). The schem is definitely a chore to read.

[igor12]

Thanks so much everybody.  This sight rocks.  Ya know it sounds to me like VH slowed the track down a bit which makes the sweeps even growlier.

[Earthscum]

Ya know it sounds to me like VH slowed the track down a bit which makes the sweeps even growlier.

Yeah... it's a really bad-ass sound that they got with it, IMO. I wish I could get my hands on one to play with for an afternoon... it makes all the difference in understanding a circuit. I'm glad you had asked about it. I just think about it intermittently, and never find anything in searches.

[StephenGiles]

You will observe another variant in the Start/Stop Freq envelope generator - 1 transistor this time!!

So with an appropriate trigger and VCF you could have a half decent autowah in one of your little boxes

[SteveG]

Off topic, but...

Oh no, two Stephen Giles's on one board!

In case of confusion, I'm the one who doesn't know what he's talking about. Sorry for any collateral embarrassment caused!

Steve (Giles)

[Earthscum]

Whoa... Seeing Double!!!  

lol.. can't say I've ever ran into my own namesake before.

Anybody familiar with these mini synths know if the filter section is similar to any others that we might find schems for online? That's the roughest part of the entire schem. Ironically, that's the section, IMHO, that's also the most important to the sound.

Traced it out. OTA, single or parallel double. Single is .01uF cap, the parallel filter uses a .0033uF. The switch on the output switches between single OTA output through parallel 10k's, or each OTA mixing through a 10k. Should be able to come up with a pretty simple equivalent using 13(x)00 OTA.

[StephenGiles]

Off topic, but...

Oh no, two Stephen Giles's on one board!

In case of confusion, I'm the one who doesn't know what he's talking about. Sorry for any collateral embarrassment caused!

Steve (Giles)

Please to meet you!! Which part of the country does your family come from? I have traced mine back to my Great Great Grandfather in Cricklade, Wiltshire - but I don't expect he had a soldering iron!!

[igor12]

How do you think rolling your own CA3094 from CA3080 (cheaper) and a darlington pair would work?  Is the darlington pair somehow matched (maybe termally as well as electrically) in the die to the CA3094 thereby created some kind of mojo?

[Earthscum]

The LM13700 and 13600, from what I've read, are basically a pair of the 3080's with linearizing diodes and darlington output buffers on die. From what I can tell, you would just run the (.01 or .0033) cap to ground from the junction of the OTA output and the buffer input, just like in all the other OTA based filters. All on a guess,  though.

[Scruffie]

The LM13700 and 13600, from what I've read, are basically a pair of the 3080's with linearizing diodes and darlington output buffers on die. From what I can tell, you would just run the (.01 or .0033) cap to ground from the junction of the OTA output and the buffer input, just like in all the other OTA based filters. All on a guess,  though.

To replace a CA3094? I think from my research they're a pain to replace, a 13700 wont always (sometimes it will) work properly and the same for the CA3080 & Darlington.

I'd probaly go for the CA3080 & Darlington though.

[StephenGiles]

There are still CA3094s at Smallbear, which in spite of the price (less than the cost of a gallon of petrol in the UK!) would save a lot of hassle.

[Scruffie]

There are still CA3094s at Smallbear, which in spite of the price (less than the cost of a gallon of petrol in the UK!) would save a lot of hassle.

They're pretty rare now... I think the spares Steve stocks should reallyyy be saved for repairs.

With a bit of work a 13700 will work in its place, it just might not be a drop in job.