EHX - Micro Synth XO Version  [schematic]

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Re: Micro Synth XO Version EHX (half-schematic)

Postby Bernardduur » 11 Apr 2012, 21:30

I'm busy completing the schematic;

In the mean time, does anyone know the voltages of this beauty? My unit was abused with a 40V adapter and has blown something......

Right now the unit has +4.5V and -4.5V
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Liquids » 11 Apr 2012, 23:18

Bernardduur wrote:I'm busy completing the schematic;

In the mean time, does anyone know the voltages of this beauty? My unit was abused with a 40V adapter and has blown something......

Right now the unit has +4.5V and -4.5V

[img]
http://www.ehx.com/products/micro-synthesizer[/img]
The image suggests it runs off a 9v positive voltage adaptor.
Unless you see a charrge pump chip in there, I'd assume you'll see voltages (at op amps) as referenced to the ground supply of 9v, and maybe a 'center rail' 4.5v generated by an r-c network into an op amp, or a 5v voltage regulator.

I'd just go ahead and replace every cap, op amp, and semiconductor. You might waste more time in trying to find the few voltage-sensitive components that survived unharmed than doing a clean sweep.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Liquids » 11 Apr 2012, 23:26

Actually, let me amend that...it looks like, from the 'half drawn' schematic, that the adaptor's V+ goes through a diode, and the adaptors ground is isolated via a ferrite bead...from there, ground becomes V-, and an op amp buffered voltage divider becomes ground....so from the points that would suggest 'ground' on the board, you will get +/-4.5 volts, yep.

That said, while some semiconductors might freak out at 40v, like caps, (or +/- 20v, as it were via reference points) that's only slightly beyond many components max...and for example, a cap between 40v and 'true' ground would need to be 50v rated, but if all the caps were referenced to 'ground' as created by the op amp....they only say 20v across them...
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Bernardduur » 11 Apr 2012, 23:33

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Re: Micro Synth XO Version EHX (half-schematic)

Postby Bernardduur » 12 Apr 2012, 11:29

PSU.JPG


Error in the former schematic

The unit is fixed now....... turned out to be full wave rectifier + buffer (U3) that was broken.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Liquids » 12 Apr 2012, 13:32

Bernardduur wrote:
PSU.JPG


Error in the former schematic

The unit is fixed now....... turned out to be full wave rectifier + buffer (U3) that was broken.

Nice!!!

Now trace that sucker for all the lazy 9v 'make me a layout' members so this can be put to rest :twisted:
....and a complete for the rest of of us who simply want to see the implementation/simplification/variation at 9v beyond the change in value for current-limiting resistors on the OTA controls, and the way they adapted the CA3094 circuits with LM13x00 OTAs, since apparently my adaptation didn't put it to rest. :roll:
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Bernardduur » 12 Apr 2012, 13:51

Preamp.JPG

Note; this is work in progress........

First part; I've used the original EHX schematic I had laying around to cue this schematic. Filter section is in the second part I'll upload when it is traced!

Values in red are the bass versions; in black the guitar version. One extra adaptation for bass will be on the other schematic.
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Re: Micro Synth XO Version EHX (half-schematic)  [schematic]

Postby Bernardduur » 12 Apr 2012, 21:03

Full schematic; quite close to the bigger versions but also different.......

Enjoy!
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Re: Micro Synth XO Version EHX (half-schematic)

Postby lufox15 » 15 Apr 2012, 18:29

OK Bernardduur, you're a amazing!!! :applause: :applause: :applause: .

That's awesome!!, now we can start doing a PCB.
Just one thing, the collectors of the filter stage don't go to Vc+? I don't remember if I saw well that part.

One more time, Thanks!!! for complete the schematic.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Bernardduur » 15 Apr 2012, 19:18

lufox15 wrote:OK Bernardduur, you're a amazing!!! :applause: :applause: :applause: .

That's awesome!!, now we can start doing a PCB.
Just one thing, the collectors of the filter stage don't go to Vc+? I don't remember if I saw well that part.

One more time, Thanks!!! for complete the schematic.


Yep; the LM13700's Vcc+ is connected to the collectors of the transistors that are already onboard..........
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Re: Micro Synth XO Version EHX (half-schematic)

Postby lufox15 » 15 Apr 2012, 19:25

Oh yeah, I didn't remember that the IC already, I've just seen the datasheet.

Well, I can't wait to confirm the schematic and start the PCB.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Nocentelli » 15 Apr 2012, 19:35

lufox15 wrote:OK Bernardduur, you're a amazing!!! :applause: :applause: :applause: .

That's awesome!!, now we can start doing a PCB.


+1, excellent work Mr D'ur

I will have one of those pcbs in a heartbeat: I sold my big bix microsynth about 6 years ago (D'oh!) and have been trying to get that sound ever since.
mmolteratx wrote:absolutely zero commercial use allowed. If I find anyone selling these, I'll fly to your house and kick you in the nads. And you may or may not find yourself in trouble.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby lufox15 » 05 May 2012, 19:04

I can't get the LM13700 in my country so I bought some ones in eBay and they'll arrive here around 2 week later. I'll confirm the schematic by that time.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Liquids » 06 May 2012, 01:32

Futurlec sells dual OTAs. The LM13700 or LM13600 should both work well/the same.

In the states, many distributors sell them as NJM13700 or NJM13600. "Coolaudio" also makes a 13700.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby lufox15 » 06 May 2012, 03:41

LM13600 are the same? I thought that have a different voltage drop o something
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Re: Micro Synth XO Version EHX (half-schematic)

Postby uncleboko » 06 May 2012, 11:47

Any difference between the two is neither here nor there, there has been plenty of unnecessary lost sleep over this in the past.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby uncleboko » 06 May 2012, 11:53

uncleboko wrote:Any difference between the two is neither here nor there, there has been plenty of unnecessary lost sleep over this in the past.


From Wikipedia:

The LM13700 series consists of two current controlled operational transconductance amplifiers (OTA) each having differential inputs and a push-pull output. The LM13700 is like a standard op-amp: both have a pair of differential inputs and a single output, but an OTA is voltage in and current out rather than voltage in and voltage out; and OTAs are programmable via the IABC pin. Linearizing diodes at the input reduce distortion and allow increased input levels. The darlington output buffers provided are specifically designed to complement the wide dynamic range of the OTA. This chip is very useful in audio electronics especially in analog synthesizer circuits like voltage controlled oscillators, voltage controlled filters, and voltage controlled amplifiers. The darlington output buffers on the LM13700 are different from those on the LM13600 in that their bias currents (and hence their output DC levels) are independent of IABC pin. This usually results in performance superior to that of the LM13600 in audio applications.
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Re: Micro Synth XO Version EHX (half-schematic)

Postby Liquids » 06 May 2012, 13:31

Exactly.

That said, that difference for our purposes is typically negligable.

The two have almost all the same datasheet example circuits...

If you're really concerned, but LM13600s are all you can get and you think the internal darlingtons are inferior, use discrete darlingtons (better yet, op amps) in place of the internal darlingtons. :D
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Re: Micro Synth XO Version EHX (half-schematic)

Postby uncleboko » 06 May 2012, 15:53

You certainly won't hear any difference because the sound will be swathed in distortion will it not!
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Re: Micro Synth XO Version EHX (half-schematic)

Postby lufox15 » 23 May 2012, 07:31

Thanks for the information :thumbsup

For the diodes? It's correct to use 1N4148? like in the big version?

I'll start this week to test the circuit and I think I'll make a pcb for the next week.
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