New OTA Phaser Design - “Causality 4”

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frequencycentral
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Post by frequencycentral »

Here's the latest design out of the frequencycentral fun factory. Designed to be an easy build, so no FET matching or hard to source parts - just build and phase! It's a four stage OTA based phaser with two fixed stages and two swept stages.

Here's some soundclips:

Dirty: http://dl.dropbox.com/u/967492/Causalit ... Phaser.mp3 Signal Path:

My below average guitar fumblings >>> Squier Tele Custom (bridge humbucker) >>> Big Muff Violet Rams Head (clone) >>> Causality 4 (on the breadboard) >>> Harley Benton GA5 (VJ clone) >>> Shure SM58 >>> Wavelab.

Clean: http://dl.dropbox.com/u/967492/Causality%20Clean.mp3 Signal Path:

My below average guitar fumblings >>> Squier Tele Custom (bridge humbucker) >>> Magnus Modulus (a bit of chorus and delay) >>> Causality 4 (on the breadboard) >>> Harley Benton GA5 (VJ clone) >>> Shure SM58 >>> Wavelab.

The soundclips above are of the prototype on the breadboard. There have been a few slight tweaks since then, now the phasing is a little 'wetter', I'll do some more soundclips when I get time. BTW, I used a 1M speed pot in my build, in place of the 470k specified on the schematic, even slower phasing now available.

The layout is verified, and tweaked to the max:

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rocklander
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Post by rocklander »

yowzers! that's on my list now.. :applause:
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Post by himister »

Damn good job Rick! :applause: Cheers for this one! :thumbsup

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Post by elrengofa »

Excelete work!, Beautiful pedal!
separate question: Is there any way to replace the lm13700 with a TL084? What is the difference between them?

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Post by lolbou »

elrengofa wrote:replace the lm13700 with a TL084? What is the difference between them?
Check datasheets : the first is a transconductance opamp, the second is a classic opamp... These can't be exchanged...
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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Post by elrengofa »

thanks, do some research and understood the differences hehe.

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Post by rocklander »

hmm.. so now my turn.. is the lm13600 compatible then?
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Post by frequencycentral »

rocklander wrote:hmm.. so now my turn.. is the lm13600 compatible then?
Both LM13600 and NE5517 have identical pinouts to LM13700. I can't vouch for either being 100% compatible in this circuit but I would make the asumption that they should be. If you wanna send me some samples of either I'll be able to confirm that. 8)

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Post by rocklander »

:lol: postage from NZ is more than the chips are worth .. I'll bang one of these out in a couple of weeks and let ya know ;-)
thanks so much for the circuit.. it's something I've been keen on for a long time... phaser with regen, speed AND depth and I prefer the sound of OTA phasers... good man yourself!
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Post by frequencycentral »

frequencycentral wrote:If you wanna send me some samples of either I'll be able to confirm that. 8)
rocklander wrote::lol: postage from NZ is more than the chips are worth ..
I know - only joking. I am curious though. I may have to get some of each to try.

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Post by elrengofa »

frequencycentral wrote:
rocklander wrote:hmm.. so now my turn.. is the lm13600 compatible then?
Both LM13600 and NE5517 have identical pinouts to LM13700. I can't vouch for either being 100% compatible in this circuit but I would make the asumption that they should be. If you wanna send me some samples of either I'll be able to confirm that. 8)

so i can replace lm13600 whit ne5517 ? them are too much cheaper than lm13600/13700

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Post by frequencycentral »

elrengofa wrote:
frequencycentral wrote:
rocklander wrote:hmm.. so now my turn.. is the lm13600 compatible then?
Both LM13600 and NE5517 have identical pinouts to LM13700. I can't vouch for either being 100% compatible in this circuit but I would make the asumption that they should be. If you wanna send me some samples of either I'll be able to confirm that. 8)

so i can replace lm13600 whit ne5517 ? them are too much cheaper than lm13600/13700
Like I said, I can't vouch for LM13600 or NE5517 being 100% compatible with LM13700 in this circuit but I would make the asumption that they should be. If you wanna send me some samples of either I'll be able to confirm that. :lol:

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Post by borislavgajic »

really nice sound, and precise build......... :applause:

how about tube version Rick?

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Post by SPeter »

Sounds great!
Thanks!
:applause:
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:D

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Post by rocklander »

just finished testing one.. replaced the following:
lm13700 ->lm13600
ne5532->tl072
tl084->lm324

it works, but is a lil dirty sounding, so will wait till I get the correct parts to see if that cleans it up (also only had a 100KB so used that for the depth).

it's more subtle than the ross phaser, but I'm guessing that's cos it's 2 stages versus the 2 stages in the ross? how hard would it be to add 2 more stages (daughter board?)? is that what gives it the depth, or am I looking at it wrong?

again, thanks for this Rick.. wasn't till this time that I noted the graphics... 100 extra internet points for trekiness ;-) :thumbsup
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Post by frequencycentral »

The LM324 may be the source of your 'dirty', as it's a single rail opamp and biases differently to TL084. I'll try subbing one into mine and see what happens.

Part of the subtlety in this design is probably down to the LFO I used, I'm planning to experiment with using a different LFO, the dual opamp LFO Boss used in their PH-2. I think it should broaden the sweep some. For perf builds it should just be a case of reconfiguring the existing LFO to the PH-2 spec.

Adding extra OTA stages would be easy, just tack then in between the two existing OTA stages. The existing Tonepad Ropez extra stages board would be ideal.

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Post by elrengofa »

I put the NE5517AN instead of lm13600 and it worked, many hanks: D

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Post by rocklander »

frequencycentral wrote:The LM324 may be the source of your 'dirty', as it's a single rail opamp and biases differently to TL084. I'll try subbing one into mine and see what happens.
ah, that's good news then.. it'll be a while till the parts arrive (long shipping times to here heh) but will chuck the tl084 in when it arrives thanks :D
frequencycentral wrote:Adding extra OTA stages would be easy, just tack then in between the two existing OTA stages. The existing Tonepad Ropez extra stages board would be ideal.
hmm.. 'easy' is a relative term heh.. I'm just a solder jockey, and don't really know what I'm doing.. I tried to figure it out (in a graphical sense) by basically copying and pasting your stages there. I started between R23 and r29 and finished at pin 9of the LM13700.
I then went to paste links so that pin 9 of the lm13700 went to the 'start of the extra stages (between the 'new' r23 and r29) but got pretty lost cos then lug3 of the regen pot would end up at the start of the new stages.. should I have 'disconnected' the regen connection to pin9(lm13700) and just extend it out to the end of the 2nd lot (4th stage)? sorry.. I'm really such a n00b :oops:
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Post by rocklander »

this is kinda how I meant, but I'm sure I've guffed it... any suggestions as to how/where/what I should change?


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Post by frequencycentral »

How about this, "Causality 6". No reason why not to have the regen going back through the extra stages too.

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Last edited by frequencycentral on 20 Dec 2009, 21:02, edited 1 time in total.

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