Author Topic: MAGNUS MODULUS - PROJECT - Another PT2399 Echo Modulator/Chorus/Tremolo/Boost  (Read 79428 times)

Thomeeque

Btw. is there C13 neccessary? Doesn't it suppress modulation for slower VCO LFO speeds?
« Last Edit: November 30, 2008, 05:46:50 PM by Thomeeque »
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ForcedFire

Btw. is there C13 neccessary? Doesn't it suppress modulation for slower VCO speeds?

C13 is required as a DC block. You could probably increase it to 100uF, if that makes you feel better...

R9 and the time pot set the nominal DC voltage to the VCO inside the PT2399. If you don't have C13 this nominal DC value will be affected by the LFO. By using a coupling capacitor the LFO voltage is just superimposed on top of the DC point set by R9 and the time pot.

Without R10 and C13 the voltage would be pretty high at pin 6. It's not a good idea to apply voltages higher than the breakdown voltage of the CMOS process, you would blow the internal diodes in the chips transistors. The way I have it arranged with R9 and R10, it forms a voltage divider so that even if the LFO was swinging full scale at 9V pk-pk, the largest AC voltage it could apply is 1.914V pk-pk. When the time pot is maxed at 50k, there will be a large enough voltage drop before pin 6 that it won't damage the chip. When the pot is turned to 0 ohms, R9 and the internal resistor set the voltage very low so that the maximum possible LFO voltage will never cause the swing at pin 6 to approach VDD of the PT2399.

EDIT: After re-reading this I sound pretty sure of myself. I just made this up off the top of my head, it makes sense now but feel free to put me in my place  :icon_biggrin: Take what I say with a grain of salt I guess... :icon_wink: I don't really know what's inside the chip and how much voltage it can handle, mine works great though.
« Last Edit: November 30, 2008, 06:00:11 PM by ForcedFire »

mnordbye

Checked out the sound sample... Wicked sick!  :D

EDIT: And by the way, thanks for accidentaly naming it after me! hehe

Magnus Nordbye
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Thomeeque

R9 and the time pot set the nominal DC voltage to the VCO inside the PT2399. If you don't have C13 this nominal DC value will be affected by the LFO..

 So, wouldn't it modulate delay time as well?

Without R10 and C13 the voltage would be pretty high at pin 6..

 Yep, definitely - no doubts about R10 ;)
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ForcedFire

R9 and the time pot set the nominal DC voltage to the VCO inside the PT2399. If you don't have C13 this nominal DC value will be affected by the LFO..

 So, wouldn't it modulate delay time as well?



That's the whole point?

Thomeeque

R9 and the time pot set the nominal DC voltage to the VCO inside the PT2399. If you don't have C13 this nominal DC value will be affected by the LFO..

 So, wouldn't it modulate delay time as well?



That's the whole point?

So, wouldn't it modulate delay time without C13 (by modulating nominal DC value) as well? That's my point ;)
Do you have a technical question? Please don't send private messages, use the FORUM!

ForcedFire

Checked out the sound sample... Wicked sick!  :D

EDIT: And by the way, thanks for accidentaly naming it after me! hehe

Magnus Nordbye

Actually I didn't name it, another user, Culturejam, suggested it. My cousin has a son named Magnus so it was pretty fitting. But you can just assume it was named after you... :icon_razz:

andrew_k

Sounds excellent, thank you for your detailed documentation!


Please put me down for a PCB when they're available  :)

ForcedFire

R9 and the time pot set the nominal DC voltage to the VCO inside the PT2399. If you don't have C13 this nominal DC value will be affected by the LFO..

 So, wouldn't it modulate delay time as well?



That's the whole point?

So, wouldn't it modulate delay time without C13 (by modulating nominal DC value) as well? That's my point ;)

Yeah but not the way I wanted it to  :icon_biggrin:

The LFO swings around an analog ground (DC value) set by the 'Spacing' pot. Without C13 the DC value from the 'time' pot would be directly affected by the DC point from the LFO. C13 just decouples the two. It might work if you want to try it, I just wanted to keep those two 'systems' seperate. There are some other things you can omit, on the layout there's space for some capacitors from the power rails to ground that are in the Echo Base and Ping Pong, I didn't use them in my build but I put them in the layout if it makes people happy  :icon_smile:.

slacker

The Echo Base has that exact issue, the delay time increases as you increase the modulation depth because of the DC offset added to the bias voltage of the modulation transistor . Personally it never bothered me because apart from at the more chorus like speeds you can just tweak the delay time know back a bit.
Someone, I can't remember who, raised it in the Echo Base thread and solved it by decoupling the LFO like you have. I've been meaning to try it, the only problem I can see with it is that in theory in distorts the waveform from the LFO, but I don't know if it will make any audible difference.
« Last Edit: December 01, 2008, 05:28:28 PM by slacker »

ForcedFire

It just makes more sense to me to use a coupling capacitor. I want the voltage at the VCO port to be some value set by one control, then add a signal to it to vary it around that value. It makes sense to keep them independent. I don't have an oscilloscope to look at the LFO waveform as it's hitting pin 6. All I have are my ears and it sounds good to me. Like I said in the intro to the project, it's a highly modifiable circuit, you can build it however you want.  :icon_biggrin:

runmikeyrun

I would buy a kit version of that in a second!
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Instagram: @torcheffects

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ForcedFire

Maybe one of the kit companies will pick something like this up. I'm not really set up to organize that so it won't be happening anytime soon from me. I am organizing the sale of the PCB's though, the prototype of the sale model should be available tomorrow or the next day.

John Lyons




-Magnus Modulus-
PCBs For Sale




$20 US
$22 worldwide
Shipping included


Paypal: basicaudiowv AT yahoo.com




Basic Audio Pedals
www.basicaudio.net/

ForcedFire




-Magnus Modulus-
PCBs For Sale




$20 US
$22 worldwide
Shipping included


Paypal: basicaudiowv AT yahoo.com





You're the man John.  :icon_smile:

niopren

Great Job.. thanks

i work on the list part, but i need help whit some values

RESIST   
R1   10K
R2   10K
R3   15K
R4   1K
R5   10K
R6   10K
R7   1M
R8   47K
R9   1K
R10   4,7K
R11   47K
R12   100K
R13   1M
R14   10K
R15   10K
R16   1M
R17   1M
R18   1M
R19   100K
R20   1K
R21   12K
R22   10K
R23   240K-220K
R24   10K
R25   4,7K
R26   
R27
   
R28   240K-220K
R29   
R30   100 OHMS
R31   240K-220K
R32   470K


CAPS.
C1   0,1UF       104
C2   0,1UF      104
C3   0,1UF      104
C4   0,1UF      104
C5   0,0022UF      222
C6   0,0022UF      222
C7   47UF   ELECT   
C8   47UF   ELECT   
C9         
C10   0,022UF      223
C11   0,047UF      473
C12   1UF      
C13   4,7UF   ELECT   
C14         
C15   100UF   ELECT   
C16   47UF   ELECT   
C17   470PF      471
C18   0,015UF      153
C19   1UF      
C20   0,22UF      224
C21   0,1UF      104
C22   N/A      
C23   1UF      
C24   1UF      
C25   100UF   ELECT   
C26   100UF   ELECT   
C27   0,01UF      103
C28   100UF   ELECT   

ForcedFire

Nice, Niopren, I haven't checked all the values in your list but I can say there is no R29, this is a problem with the numbering in the software I used. R25, R26 and R27 can be anything from like 2k to 10k, I used ultra bright LED's with 10k resistors and they're still very bright.

C22 is optional, I didn't use it, you can try caps from like 1pF-100pF to roll of some high frequency from the input if you need it.
C9 and C14 are also optional, I didn't use them either, some people might want to add them for extra power filtering but I don't see the point. You could try 0.001 uF to 0.1 uF here.

So you have R25 listed as 4.7k, you can just use that for R26 and R27 and forget about all those capacitors, just leave them empty.

If you look at the picture of the PCB from my build you will see that these capacitor spaces are empty.
« Last Edit: December 02, 2008, 04:42:47 PM by ForcedFire »

niopren

Nice, Niopren, I haven't checked all the values in your list but I can say there is no R29, this is a problem with the numbering in the software I used. R25, R26 and R27 can be anything from like 2k to 10k, I used ultra bright LED's with 10k resistors and they're still very bright.

C22 is optional, I didn't use it, you can try caps from like 1pF-100pF to roll of some high frequency from the input if you need it.
C9 and C14 are also optional, I didn't use them either, some people might want to add them for extra power filtering but I don't see the point. You could try 0.001 uF to 0.1 uF here.

So you have R25 listed as 4.7k, you can just use that for R26 and R27 and forget about all those capacitors, just leave them empty.

If you look at the picture of the PCB from my build you will see that these capacitor spaces are empty.

thank you.




here┤s the complete list and resume.




resume



cheers

ForcedFire

I just swapped the LFO op-amp for TL022CP, TL072(CW?), and JRC4558D and they all work. To my ears the 5532 sounds better and that's what I designed the pedal on. I didn't find the modulation as intense with the TL series op-amps. If you want the exact sound from the Youtube demo, use NE5532.  :icon_biggrin: Or you could tweak the coupling network so it works for you.

The other buffer op-amp can be any dual op-amp.

frequencycentral

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